Monthly Archives: July 2017

Astronomy, Brain Research, Physics

Thinking Visually

Look at the two images  for a few minutes and let your mind wander.

What impressions do you get from the patterns of light and dark? If I were to tell you that the one at the top is a dark nebula in the constellation Orion, and the one on the bottom is a nebula in the Pleiades star cluster, would that completely define for you what you are experiencing…or is there something more going on?

Chances are that, in the top image you are seeing what looks like the silhouette of the head and shoulders of some human-like figure being lit from behind by a light. You can’t quite put your finger on it, but the image seems vaguely mysterious and perhaps even a bit frightening the more you stare at it.

The image on the bottom evokes something completely different. Perhaps you are connecting the translucence and delicacy with some image of a shroud or silken cloak floating in a breeze. The image seems almost ghost-like in some respects…spiritual

“But of course this is rather silly” you might say. “These are interstellar clouds, light-years across and all we are doing is letting our imaginations wander which is not a very scientific thing to do if you want to understand the universe.” This rational response then tempts you to reach for your mouse and click to some other page on the web.

What has happened in that split second is that a battle has been fought between one part of your brain and another. The right side of your brain enjoys looking at things and musing over the patterns that it finds there. Alas, it cannot speak because the language centers of the brain live in the left cerebral hemisphere, and it is here that rules of logic and other ‘scientific’ reasoning tools exist. The left side of your brain is vocal, and talking to you right now. It gets rather upset when it is presented with vague patterns because it can’t understand them and stamp them with a definite emotion the way the right hemisphere can. So it argues you into walking away from this challenge of understanding patterns.

If you can suspend this indignation for a moment or two, you will actually find yourself thinking about space in a way that more nearly resembles how a scientist does, though even some scientists don’t spend much time thinking about space. This indifference has begun to change during the last 20 years, and we are now in the midst of a quiet revolution.

There are three child-like qualities that make for a successful scientist:

Curiosity. This is something that many people seem to outgrow as they get older, or if they maintain it as adults, it is not at the same undiluted strength that it was when they were a child.

Imagination. This is something that also wanes with age but becomes an asset to those that can hang on to even a small vestige of it. It is what ‘Thinking out of the box’ is all about.

Novelty. As a child, everything is new. As an adult we become hopelessly jaded about irrelevant experiences like yet another sunset, yet another meteor shower, yet another eclipse. In some ways we develop an aversion for new experiences preferring the familiarity of the things we have already experienced.

If you wish to understand what space is all about, and explore the patterns hidden in the darker regions of nature, you will have to re-acquaint yourself with that child within you. You will need to pull all the stops out and allow yourself to ‘play’ with nature and the many clues that scientists have uncovered about it. You will need to do more than read books by physicists and astronomers. They speak the language of the left-brain . They can help you to see the logical development of our understanding of space and the Void, but they can not help you internalize this knowledge so that it actually means something to you. For that, you have to engage your right-brain faculties, and this requires that you see the patterns behind the words that physicists and astronomers use. To do that, you will need to think in terms of pictures and other types of images. You will need to bring something to the table to help you make sense of space in a way that you have not been able to before. You will need to expand your internal library of visual imagery to help you find analogues to what physicists and astronomers are trying to describe in words and equations. These visual analogues can be found in many common shapes and patterns, some seen under unusual and evocative circumstances. Here are some evocative images that seem to suggest how space might be put together compliments of  a diatom, the painters Miro and Mondrian, dew on a spider web, and atoms in a tungsten needle tip!

Spider web covered with dew drops

Remember, the right brain uses ALL sensory inputs to search for patterns and to understand them. It even uses imaginary information, dreams, and other free-forms to decode what it is experiencing.  

My book ‘Exploring Quantum Space’ is a guidebook that will give you some of the mental tools you will need to make sense of one of the greatest, and most subtle, discoveries in human history. Space, itself, is far from being ‘nothing’ or merely a container for matter to rattle around within. It is a landscape of hidden patterns and activity that shapes our universe and our destiny. You cannot understand it, or sense the awe and mystery of its existence, by simply reading words and following a logical exposition of ‘ifs and thens’. You also have to experience it through evocative imagery and imagination. Space is such a different medium from anything we have ever had to confront, intellectually, that we need to employ a different strategy if we wish to understand it in a personal way. Once we do this, we will be reconnected with that sense of awe we feel each time we look at the night sky.

My next blog about Nothing introduces some of the other ideas and techniques that scientists use to think about the impossible!

 

Astronomy, Brain Research, Physics

Thinking about Nothing

Looking back at the millennia of model building and deduction that has occurred, not a century has gone by when the prevailing opinion hasn’t been that a perfectly empty vacuum is impossible.

Aristotle’s Aether blends seamlessly into the 19th century Ether. In this century, overlapping quantum waves and virtual particles have finally taken root as the New Ether, though it is now infinitely more ephemeral than anything Aristotle or Maxwell could have imagined. We have also seen how the Atomist School of ancient Greece reached its final vindication in the hands of 19th century scientists such as Boltzman. By the 20th century, the Atomist’s paradigm has even been extended to include not just the graininess of matter, but the possible quantum graininess of the vacuum and space itself. In the virtual particles that animate matter, we finally glimpse the world which Heinrich Hertz warned us about nearly a century ago when he said that we would eventually have to reach some accommodation with “invisible confederates” existing alongside what we can see, to make our whole model of reality more logically self-consistent.

Even by the start of the 21st Century, we have reached this accommodation only by shrugging our shoulders and honestly admitting that there are things going on in the world that seem to defy human intuition. What impresses me most about the evolution of our vision of the vacuum is that the imagery we find so potent today is actually in some sense thousands of years old.

It is difficult to imagine that humans would be drawn to the same understanding of physics and astronomy that we now enjoy if our brains had been wired only slightly differently. Without sight and mobility we could not form the slightest notion of 3-D space and geometry. This is what Kant spoke about, what Henri Poincare described at great length without the benefit of 20th century neuroscience, and what Jacob Bronowski described in his book The Origins of Knowledge and Imagination with the benefit of such knowledge. But the object of science is more than just making sense of our senses. It must also guide us towards a deeper understanding of the physical world. This understanding must be self-consistent, and independent of whether we are sensorially or neurologically handicapped. Mathematics as the premier language of physical model building, seems uniquely suited to providing us with an understanding of the physical world. Mathematics lets us see the world in a way that all of the other human languages do not.

If our mathematical understanding of nature is a product of mental activity, and this activity can be physically affected by the hard-wiring of our brain, how do we arrive at a coherent model of the physical world? Can we see in this process any explanation for why certain ideas in physics appear to be so historically tenacious?

It is commonly believed that in order for mathematics and the underlying logic to exist, at the very least a conscious language must be pre-existent to support it. This is the point of view expressed by Benjamin Whorf. But the thoughtful reflections by individuals such as Einstein, Feynman and Penrose point in a very different direction. Einstein once wrote a note to Jaques Hadamard prompted by Hadamard’s investigation of creative thinking,

“…The words of language, as they are written or spoken, do not seem to play any role in my mechanism of thought. The psychical entities which seem to serve as elements of thought are certain signs ( symbols ) and more or less clear images which can be voluntarily reproduced and combined…The above mentioned elements are, in my case, of visual and some muscular type…”

Roger Penrose echoes some of this same description in his book, The Emperor’s New Mind,

“…Almost all my mathematical thinking is done visually and in terms of non-verbal concepts, although the thoughts are quite often accompanied by inane and almost useless verbal commentary such as ‘that thing goes with that thing and that thing goes with that thing’..”

Freeman Dyson, one of the architects of modern QED had this to say about how Feynman did his calculations,

“…Dick was using his own private quantum mechanics that nobody else could understand. They were getting the same answers whenever they calculated the same problem…The reason Dick’s physics was so hard for ordinary people to grasp was that he did not use equations…Dick just wrote down the solutions out of his head without ever writing down the equations. He had a physical picture of the way things happen, and the pictures gave him the solutions directly with a minimum of calculation…It was no wonder that people who had spent their lives solving equations were baffled by him. Their minds were analytical; his was pictorial…”

In many instances, the conversion of abstract thinking into conventional language is seen as a laborious, almost painful process. Often words are inadequate to encompass the subtleties of the non-verbal, abstract ideas and their interrelationships. According to Penrose,

“I had noticed, on occasion, that if I have been concentrating hard for a while on mathematics and someone would engage me suddenly in conversation, then I would find myself almost unable to speak for several seconds”

In fact, abstract thinking is often argued to be a right-hemisphere function. Visual or pattern-related thinking and artistic talents are frequently coupled to this hemisphere, and since the language centers are in the left-hemisphere, with such a disconnect between language and abstract thinking, there is little wonder that theoreticians and artists find themselves tongue-tied in explaining their ideas, or are inclined to report that their work is non-verbal.

So the creation of sophisticated physical theories may involve a primarily non-verbal and visual-symbolic thinking processes, often manipulating patterns and only later, with some effort of will, translating this into spoken language or fleshing out the required mathematical details. Could this be why scientists, and artists for that matter have such difficulty in explaining what they are thinking to the rest of the population? Could this be why ancient philosophers managed to land upon archetypes for their Creation legends that seem familiar to us in the 20th century? The symbols that are used appear disembodied, and no amount of word play can capture all of the nuances and motivations that went into a particular interpretive archetypes, and make them seem compelling to the non-mathematician or non-artist. Feynman once wrote about the frustrating process of explaining to the public what goes on in nature,

“…Different people get different reputations for their skill at explaining to the layman in layman’s language these difficult and abstruse subjects. The layman then searches for book after book in the hope that he will avoid the complexities which ultimately set in, even with the best expositor of this type. He finds as he reads a generally increasing confusion, one complicated statement after another,… all apparently disconnected from one another. It becomes obscure, and he hopes that maybe in some other book there is some explanation…but I do not think it is possible, because mathematics is NOT just another language. Mathematics is a language plus reasoning…if you do not appreciate the mathematics, you cannot see, among the great variety of facts, that logic permits you to go from one to the other…”

If this is the mental frame used by some physicists to comprehend physics, it is little wonder that a great chasm exists between the lay person and the physicist in explaining what is going on. The task that even a physicist such as Freeman Dyson had in translating Feynman’s diagrammatic techniques into mathematical symbology, seems even more challenging knowing that Feynman may have had a whole other perspective on visualization via his apparent color-symbol synthesia. The equations below are the current best mathematical expression for the Standard Model in physics, which describes all known particles and fields excepting gravity.

Another feature of thinking that separates scientists and artists from everyone else seems to be the plasticity of the thinking process itself. Scientists flit from one idea to another until they arrive at a model that best explains the available data, although scientists can also get rooted to particular perspectives that are difficult to forget after decades of inculcation. The general adult population prefers a more stable collection of ideas and ‘laws’ which it can refer to over a lifetime.

Where does this all leave us?

The vacuum has been promoted to perhaps the most important clue to our own existence. The difficulty is that we lack a proper Rosetta Stone to translate the various symbolisms we use to describe it. The clues that we do have are scattered among a variety of enigmatic subjects which strain at our best intellectual resources to understand how they are linked together. Could it be that we are lacking an even more potent symbolic metaphor, and an internal non-verbal language, to give it life? Where would such a thing come from?

Spider web covered with dew drops

If we take our clue from how ideas in physics have emerged in the past, the elements of the new way of thinking may be hidden in some unexpected corner of nature. We may find an analogy or a metaphor in our mundane world which, when mixed with mathematical insight, may take us even closer to understanding gravity, spacetime and vacuum. It is no accident that string theory owes much of its success because it asks us to think about quantum fields as ordinary strings operating in an exotic mathematical setting. It is exciting to think that the essential form of the Theory of Everything could be this close to us, perhaps even lurking in a pattern we see, and overlook, in our everyday lives.

Much of this symbolic process may be performed sub-consciously, and only the form of dreams, insights or hunches seem to bring them into consciousness when the circumstances are appropriate. It is, evidently, the non-verbal and unconscious right hemisphere which experiences these ideas. Is there a limit to this process of symbolic thinking? At least a dozen times this century, physicists have had to throw up their hands over what to make of certain features of the world: the collapse of the wave function; quantum indeterminacy; particle/wave dualism; cosmogenesis. Some of these may eventually find their explanation at the next level of model building. Others such as the meaning of quantum indeterminacy and particle/wave dualism, seem to be here to stay.

In working with these contradictions, the human mind prefers the avenue of denial, you can almost hear your inner voice saying “Aw come on, quantum mechanics just can’t be that weird!” or a state of anxiety as the two hemispheres try to fabricate conflicting world models. Little wonder that we have particle/wave duality, the seeming schism between matter and energy, and a whole host of other ‘polar’ ideas in physics, as two separate minds try to resolve the universe into one model or another with the left one preferring time ordered patterns, and the right one, spatial patterns.

It is hard to believe that our brains can control what we experience of the objective world, but we need only realize that the brain actually blindsides us in a variety of subtle ways, from seeing a wider sensory world. The object of science, however, is to discern the shapes of objective laws in a way that gets to the universal elements of nature that are not coupled to a particular kind of brain circuitry. It doesn’t matter if all scientists have anasognosia and see the world differently in some consistent way, what counts is that they must still live by the laws of motion dictated by gravity and quantum mechanics.

Nils Bohr believed atoms are not real in the same sense as trees. The quantum world really does represent a different kind of reality than our apparently naive understanding of macroscopic reality implies. This being the case, we must first ask to what extent fields and the denizens of the quantum vacuum can be represented by any analogy drawn from the macroworld? We already know that the single most important distinguishing characteristic of atomic particles is their spin; far more so than mass or charge. Yet unlike mass and charge, quantum mechanical spin has ABSOLUTELY no analog in the macroscopic world. Moreover, fundamental particles cannot be thought of as tiny spheres of charged matter located at specific points in space. They have no surface, and participate in an infernal wave-like dance of probability, at least when they are not being observed. Yet despite this warning, we feel comfortable that we understand something about what reality is at this scale, in the face of these irreconcilable differences between one set of mental images and what experiments tell us over and over again. What is the true nature of the vacuum? How did the universe begin? I suspect we will not know the answer to these questions in your lifetime or mine, perhaps for the same reason that it took 3000 years for geometers to ‘discover’ non-Euclidean geometry.

At the present time we are faced with what may amount to only a single proof of the parallel-line postulate, unable to see our way through to another way of looking at the proof. There is also the very real worry that some areas of nature may require modalities of symbolic thinking beyond the archetypes that our brains are capable of providing as a consequence of their neural hard-wiring. Today, we have quantum field theory and its tantalizing paradoxes, much as the ancient geometers had their parallel-line postulate. We, like they, scratch the same figures in the sand over and over again, hoping to see the glimmerings of a new world view appearing in the shifting sands. At a precision of one part in a trillion, our quantum theories work too well, and seem to provide few clues to the new direction we must turn to see beyond them.

The primary arbiters we have at our disposal to decide between various interpretive schemes, experimental data, are not themselves in unending supply as the abrupt cancellation of the U.S. Superconducting Super Collider program in 1989 showed. It was replaced by the CERN Large Hadron Collider shown above, but even the LHC may not be large enough to access the new physics we need to explore to further our theories and understanding.

Whatever answers we need seem to be hidden, not in the low- energy world accessible to our technology, but at vastly higher energies well beyond any technology we are likely to afford in the next few centuries. It is easy to provide a jet plane with an energy of 100 billion billion billion volts — its energy of motion at a speed of a few hundred miles per hour, but it is beyond understanding how to supply a single proton or electron with the same energy. On the other hand, our internal symbolic thinking seems to lead us to similar interpretative schemes, and unconscious dualities which may only be a reflection of our own neural architecture, which we all share, and which has remained essentially unchanged for millennia. We visualize the vacuum in the same way as the Ancients did because we are still starting from the same limited collection of internal imagery. At least for some general problems, we seem to have hit a glass ceiling for which our current style of theory building seems to lead us to a bipolar and contradictory world populated by various dualities: matter/energy, space/time, wave/particle. When we finally do break through to a new kind of reality in our experiments, would we be able to recognize this event? Will our brains filter out this new world and show us only the ghostly shadows of contradictory archetypes cast upon the cave wall?

We have seen that many schemes have been offered for describing the essential difference between matter and empty space; many have failed. Theoreticians since Einstein have speculated about the geometric features of spacetime, and the structure of electrons and matter for decades. The growing opinion now seems to be that, ultimately, only the properties of space such as its geometry or dimensionality can play a fundamental role in defining what matter really is. In a word, matter may be just another form of space. If the essence of matter is to be found in the geometric properties of ’empty’ space, our current understanding of space will not be sufficient to describe all of matter’s possible aspects.

Astronomy, Physics

Misconceiving the Big Bang

The Big Bang was NOT a Fireworks Display!

Written by Sten Odenwald
Copyright (C) 1997. Published in the Washington Post Horizon education supplement on May 14, 1997.

The Big Bang wasn’t really big. Nor was it really a bang. In fact, the event that created the universe and everything in it was a very different kind of phenomenon than most people–or, at least, most nonphysicists–imagine.
Even the name “Big Bang” originally was a put-down cooked up by a scientist who didn’t like the concept when it was first put forth. He favored the idea that the universe had always existed in a much more dignified and fundamentally unchanging, steady state.

But the name stuck, and with it has come the completely wrong impression that the event was like an explosion and that the universe is expanding today because the objects in it are being flung apart like fragments of a detonated bomb.

Virtually every basic aspect of this intuitive image for the Big Bang (we ARE stuck with the name) is incorrect. To understand why, you need to understand Albert Einstein’s general theory of relativity. Or, at least, you need to have a sense of it. That may sound daunting, but general relativity is the most revolutionary scientific advance of the 20th century, and we all ought to acquire some feeling for it before the century ends.

After all, it’s been 82 years since Einstein put forth his theory. It’s been tested in scores of experiments and has always passed with flying colors and is now firmly established as our premier guide to understanding how gravity operates. Moreover, it is part of the foundation of Big Bang cosmology. And it is because of general relativity that we know the Big Bang was (and is, for the event is still going on) nothing like an explosion.

Albert Einstein developed general relativity in order to make his famous theory of special relativity include the effects of gravity. It is a better way than Sir Isaac Newton’s of understanding how gravity works. Like a hungry amoeba, general relativity ( or just GR for short) had absorbed both Einstein’s newly-minted special relativity and Newton’s physics, giving us the means to replicate ALL of the predictions from these two great theories, while extending them into unfamiliar realms of experience. One of these realms was the Black Hole. The other was the shape and evolution of the universe itself.

Big Bang cosmology says that the universe came into existence between 10 to 20 billion years ago, and that from a hot dense state has been expanding and cooling ever since, remains unassailable. Yet, Big Bang cosmology is vulnerable. It is based on GR being accurate over an enormous range of scales in time and space. Just how good is general relativity? So far, GR has made the following specific predictions:

1…The entire orbit of Mercury rotates because of the curved geometry of space near the sun. The amount of ‘perihelion shift’ each century was well known at the time Einstein provided a complete explanation for it in 1915.

2…Light at every frequency can be bent in exactly the same way by gravity. This was confirmed in the 1919 Solar Eclipse for optical light using stars near the Sun’s limb, and in 1969-1975 using radio emissions from star-like quasars also seen near the limb of the Sun. The deflection of the light was exactly as predicted by GR.

3…Clocks run slower in strong gravitational fields. This was confirmed by Robert Pound and George Rebka at Harvard University in 1959, and by Robert Vessot in the 1960’s and 70’s using high-precession hydrogen maser clocks flown on jet planes and on satellites.

4…Gravitational mass and inertial mass are identical. Most recently in 1971, Vladimir Braginsky at Moskow University confirmed GRs prediction of this to within 1 part in a trillion of the exact equality required by GR.

5…Black holes exist. Although these objects have been suspected to exist since they were first introduced to astronomers in the early 1970’s, it is only in 1992 that a critical acceptance threshold was crossed in the astronomical community. It was then that Hubble Space Telescope observations revealed monstrous, billion-sun black holes in the cores of nearby galaxies such as Messier 87, Messier 33 and NGC 4261.

6…Gravity has its own form of radiation which can carry energy. Russel Hulse and Joseph Taylor in 1975 discovered two pulsars orbiting each other, and through careful monitoring of their precise pulses during the next 20 years, confirmed that the system is loosing energy at a rate within 1 percent of the prediction by GR based on the emission of gravitational radiation.

7…A new force exists called ‘gravito-magnetism’. Just as electric and magnetic fields are linked together, according to GR, a spinning body produces a magnetism-like force called gravitomagnetism. GR predicts that rotating bodies not only bend space and time, but also make empty space spin. A NASA satellite called Gravity Probe B will be launched in the next few years to see whether this effect exists. This is a killer. If it is not found, GR is mortally wounded despite its long string of other successes.

8…Space can stretch during the expansion of the universe. This was confirmed by Edwin Hubble’s detection of the recession of the galaxies ca 1929. More recently in 1993, Astronomer Kenneth Kellerman confirmed that the angular sizes of distant radio sources shrink to a minimum then increase at greater distances exactly as expected for a dilating space. This is not predicted by any other cosmological model that does not also include the dilation of space as a real, physical phenomenon.

We have now boxed ourselves into a corner. If we accept the successes of GR, we are forced to see the world and the cosmos through its eyes, and its eyes alone, since it is the theory which satisfies all known tests to date.

So, how should we think about the Big Bang? Our mental ‘fireworks’ image of the Big Bang contains these basic elements: 1) A pre-existing sky or space into which the fragments from the explosion are injected; 2) A pre-existing time we can use to mark when the explosion happened; 3) Individual projectiles moving through space from a common center; 4) A definite moment when the explosion occurred; and 5) Something that started the Big Bang.

All of these elements to our visualization of the Big Bang are completely false according to GR!

Preexisting Space?

There wasn’t any!

The mathematics of GR state specifically and unambiguously that 3-dimensional space was created at the Big Bang itself, at ‘Time Zero’, along with everything else. It was a ‘singular’ event in which the separations between all particles everywhere, vanished. This is just another way of saying that our familiar 3-dimensional space vanished. Theorists studying various prototypes for the Theory of Everything have only modified this statement somewhat. During its earliest moments, the universe may have existed in a nearly incomprehensible state which may have had more than 4 dimensions, or perhaps none at all. Many of these theories of the earliest moments hypothesize a ‘mother space-time’ that begat our own universe, but you cannot at the same time place your minds eye both inside this Mother Spacetime to watch the Big Bang happen, and inside our universe to see the matter flying around. This is exactly what the fireworks display model demands that you do.

Preexisting Time?

There wasn’t any of this either!

Again, GR’s mathematics treats both space and time together as one object called ‘space-time’ which is indivisible. At Time Zero plus a moment, you had a well defined quantity called time. At Time Zero minus a moment, this same quantity changed its character in the mathematics and became ‘imaginary’. This is a mathematical warning flag that something dreadfully unexpected has happened to time as we know it. In a famous quote by Einstein, “…time and space are modes by which we think and not conditions in which we live”. Steven Hawking has looked at the mathematics of this state using the fledgling physics of Quantum Gravity Theory, and confirms that at the Big Bang, time was murdered in the most thorough way imaginable. It may have been converted into just another ‘timeless’ dimension of space…or so the mathematics seems to suggest.

Individual objects moving out from a common center?

Nope!

GR says specifically that space is not a passive stage upon which matter plays out its dance, but is a member of the cast. When you treat both galaxies and space-time together, you get a very different answer for what happens than if you treat them separately, which is what we instinctively always do. Curved space distorts the paths of particles, sometimes in very dramatic ways. If you stepped into a space ship and tried to travel to the edge of the universe and look beyond, it would be impossible. Not only could you not reach a supposed “edge” of the universe no matter how long or how fast you traveled, in a closed universe, you would eventually find yourself arriving where you departed. The curvature of space would bring you right back, in something like the way the curvature of Earth would bring you home if you flew west and never changed course. In other words, the universe has no edge in space. There is nothing beyond the farthest star.

As a mental anchor, many have used the expanding balloon as an analogy to the expanding universe. As seen from any one spot on the balloon’s surface, all other spots rush away from it as the balloon is inflated. There is no one center to the expansion ON THE SURFACE of the balloon that is singled out as the center of the Big Bang. This is very different than the fireworks display which does have a dramatic, common center to the expanding cloud of cinders. The balloon analogy, however, is not perfect, because as we watch the balloon, our vantage point is still within a preexisting larger arena which GR says never existed for the real universe.

The center of the Big Bang was not a point in space, but a point in time! It is a center, not in the fabric of the balloon, but outside it along the 4th dimension…time. We cannot see this point anywhere we look inside the space of our universe out towards the distant galaxies. You can’t see time afterall! We can only see it as we look back in time at the ancient images we get from the most distant objects we can observe. We see a greatly changed, early history of the universe in these images but no unique center to them in space.

It is at this point that common sense must give up its seat on the bus, and yield to the insights provided by GR. And it is at precisely this point that so many non-physicists refuse to be so courteous. And who can blame them? But there’s more to come.

Projectiles moving through space?

Sorry!

GR again has something very troubling to say about this. For millions of years we have learned from experience on the savanas of the African continent and elsewhere, that we can move through space. As we drive down the highway, we have absolutely no doubts what is happening as we traverse the distance between landmarks along the roadside. This knowledge is so primal that we are incapable of mustering much doubt about it. But science is not about confirming our prejudices. It’s about revealing how things actually are.

What if I told you that you could decrease the distance from your house and the Washington Monument by ‘standing still’ and just letting space contract the distance away? GR predicts exactly this new phenomenon, and the universe seems to be the only arena we know today in which it naturally occurs. Like spots glued to the surface of the balloon at eternally fixed latitude and longitude points, the galaxies remain where they are while space dilates between them with the passage of time. There is no reason at all we should find this kind of motion intuitive.

If space is stretching like this, where do the brand new millions of cubic light years come from, from one moment to the next? The answer in GR is that they have always been there. To see how this could happen, I like to think of the shape of our universe as a “Cosmic Watermellon”. The fact that this is only the shape for a ‘closed’ finite universe is only a technicality. Finite watermellons are also cheaper to buy than infinite ones.

GR predicts the entire past, present and future of the universe all at once, and predicts its entire 4-dimensional shape. As we slice the 4-dimensional, Cosmic Watermellon at one end of the cosmic time line, we see 3-dimensional space and its contents soon after the Big Bang. At the other end of the Cosmic Watermellon in the far future, we see the collapse of space and matter just before the Big Crunch. But in between, our slices show the shape of space (closed, spherical volumes) and the locations of galaxies ( at fixed locations) as space dilates from one extreme to the other.

As a particular slice through an ordinary watermellon, we see that its meat has always been present in the complete watermellon. The meat is present as a continuous medium, and we never ask where the meat in a particular slice came from. Cosmologically, GR ask us to please think of 3-dimensional space in the same way. Space, like the meat of the watermellon, has always existed in the complete shape of the universe in 4-dimensions. But it is only in 4-dimensions that the full shape of the universe is revealed. It is a mystery why our consciousness insists on experiencing the universe one moment at a time, and that is why we end up with the paradox of where space comes from. There really is no paradox at all.

Space is not ‘nothing’ according to Einstein, it is merely another name for the gravitational field of the universe. Einstein once said, “Space-time does not claim existence on its own but only as a structural quality of the [gravitational] field”. If you could experimentally turn-off gravity with a switch, space-time would vanish. This is the ultimate demolition experiment known to physics for which an environmental impact statement would most certainly have to be filed.

The gravitational field at one instant is wedded to itself in the next instant by the incessant quantum churnings of the myriad of individual particles that like bees in a swarm, make up the gravitational field itself. In this frothing tumult, the gravitational field is knit together, quantum by quantum, from perhaps even more elemental building blocks, and it is perhaps here that we will find the ultimate origin for the expansion of the universe and the magical stretching of space. We hope the much anticipated Theory of Everything will have more to say about this, but to actually test this theory may require technologies and human resources that we can only dimly dream of.

Was there a definite moment to the Big Bang?

GR is perfectly happy to forecast that our universe emerged from an infinite density, zero-space ‘Singularity’ at Time Zero, but physicists now feel very strongly that this instant was smeared out by any number of quantum mechanical effects, so that we can never speak of a time before about 10^-43 seconds after the Big Bang. Just as Gertrude Stein once remarked about my hometown, Oakland, California that “There is no ‘There’ there”, at 10^-43 seconds, nature may tell us that before the Big Bang, “There was no ‘When’ there” either. The moment dissolves away into some weird quantum fog, and as Steven Hawking speculates, time may actually become bent into a new dimension of space and no longer even definable in this state. Ordinary GR is unable to describe this condition and only some future theory combing GR and quantum mechanics will be able to tell us more. We hope.

Something started the Big Bang!

At last we come to the most difficult issue in modern cosmology. In the fireworks display, we can trace the events leading up to the explosion all the way back to the chemists that created the gunpowder and wrapped the explosives. GR, however, can tell us nothing about the equivalent stages leading up to the Big Bang, and in fact, among its strongest statements is the one that says that time itself may not have existed. How, then, do we speak or think about a condition, or process, that started the whole shebang if we are not even allowed to frame the event as “This happened first…then this…then kerpowie!”? This remains the essential mystery of the Big Bang which seems to doggedly transcend every mathematical description we can create to describe it.

All of the logical frameworks we know about are based on chains of events or states. All of our experiences of such chains in the physical world have been ordered in time. Even when the mathematics and the theory tell us ‘What happened before the Big Bang to start it?’ is not a logical or legitimate question, we insist on viewing this as a proper question to ask of nature, and we expect a firm answer. But like so many other things we have learned this century about the physical world, our gut instincts about which questions ought to have definite answers is often flawed when we explore the extreme limits to our physical world.

I wrote this essay before seeing the new IMAX file at the Air and Space Museum ‘Cosmic Journey”, by far one of the nicest and most heroic movies of its kind I had ever seen. But of course it showed the Big Bang as a fireworks display. No matter. It doesn’t take a rocket scientist to accept the fact that the Big Bang was a spectacular moment in history. What is amazing is that the daring audacity of humans may have demystified some of it, and revealed a universe far stranger than any could have imagined.

Still, we are haunted by our hunches and intuitions gathered over millenia, and under circumstances far removed from the greater physical world we are now exploring. No wonder it all seems so alien and maddeningly complex.

Astronomy, Physics

Before the Big Bang

Beyond the Big Bang

Written by Sten Odenwald Copyright (C) 1987, Kalmbach Publishing. Reprinted by permission

Sometime between 15 and 20 billion years ago the universe came into existence. Since the dawn of human awareness, we have grappled with the hows and whys of this event and out of this effort have sprung many ideas. An ancient Egyptian legend describes how the universe was created by Osiris Khepera out of a dark, boundless ocean called Nu and that Osiris Khepera created himself out of this ocean by uttering his own name. Human inventiveness has not stood still in the 5000 years since these ideas were popular. The modern theory of the Big Bang states that our universe evolved from an earlier phase billions of times hotter than the core of our sun and trillions of times denser than the nucleus of an atom. To describe in detail such extreme physical conditions, we must first have a firm understanding of the nature of matter and of the fundamental forces. At the high temperatures likely to have attended the Big Bang, all familiar forms of matter were reduced to their fundamental constituents. The forces of gravity and electromagnetism together with the strong and weak nuclear forces, were the essential means through which the fundamental particles of matter interacted.
The feedback between cosmology and particle physics is nowhere more clearly seen than in the study of the early history of the universe. In October, 1985 the giant accelerator at Fermilab acheived for the first time, the collision of protons and anti-protons at energies of 1.6 trillion electron volts, about 1600 times the rest mass of the proton. This was a unique event because for one split second, on a tiny planet in an undistinguished galaxy, a small window onto the Creation Event was opened for the first time in at least 15 billion years.

THE LIMITS OF CERTAINTY

The persuit by physicists of a single, all encompassing theory capable of describing the four natural forces has, as a by-product, resulted in some surprising glimpses of the Creation Event. Although such a theory remains perhaps several decades from completion, it is generally recognized that such a theory will describe physical conditions so extreme it is quite possible that we may never be able to explore them first- hand, even with the particle accelerators that are being designed today. For example, the Superconducting Supercollider to be built by the early 1990’s will cost 6 billion dollars and it will allow physicists to collide particles at energies of 40 trillion electron volts ( 40,000 GeV) matching the conditions prevailing 10 seconds after the Big Bang. The expected windfall from such an accelerator is enormous and will help to answer many nagging questions now plaguing the theoretical community, but can we afford to invest perhaps vastly larger sums of money to build machines capable of probing the quantum gravity world at 10 GeV? At these energies, the full unification of the natural forces is expected to become directly observable. How curious it is that definite answers to questions such as, ‘What was Creation like?’ and ‘Do electrons and quarks have internal structure?’ are so inextricably intertwined. Our ability to find answers to these two questions, among others, does not seem to be hampered by some metaphysical prohibition, but by the resources our civilization can afford to devote to finding the answers. Fortunatly, the situation is not quite so bleak, for you see, the ‘machine’ has already been ‘built’ and every possible experiment we can ever imagine has already been performed!

WHAT WE THINK WE KNOW

We are living inside the biggest particle accelerator ever created – the universe. Ten billion years before the sun was born, Nature’s experiment in high-energy physics was conducted and the experimental data can now be examined by studying the properties and contents of the universe itself. The collection of fundamental facts that characterize our universe is peculiar in that it derives from a variety of sources. A partial list of these ‘meta-facts’ looks like this:

1) We are here, therefore, some regions of the universe are hospitible to the creation of complex molecules and living, rational organisms.

2) Our Universe has 4 big dimensions and all are increasing in size as the universe expands in time and space.

3) There are 4 dissimilar forces acting in Nature.

4) Only matter dominates; no anti-matter galaxies exist and this matter is built out of 6 quarks and 6 types of leptons.

The task confronting the physicist and the astronomer is to create, hopefully, a single theory consistent with these metafacts that can then be used to derive the secondary characteristics of our universe such as the 2.7 K background radiation, the primordial element abundances, and galaxy formation. The interplay between the study of the macrocosm and the microcosm has now become so intense that astronomers have helped physicists set limits to the number of lepton families — No more than 4 are allowed otherwise the predicted cosmological abundance of helium would seriously disagree with what is observed. Physicists, on the other hand, use the astronomical upper limits to the current value of the cosmological constant to constrain their unification theories.

An extention to the standard Big Bang model called the Inflationary Universe (see The Decay of the False Vacuum) was created by MIT physicist Alan Guth in 1981. This theory combined Grand Unification Theory with cosmology and, if correct, allows astronomers to trace the history of the universe all the way back to 10 seconds after the Big Bang when the strong, weak and electromagnetic forces were unified into a single ‘electro-nuclear’ force. During the 4 years since the Inflationary Universe model was proposed, other theoretical developments have emerged that may help us probe events occurring at an even earlier stage, perhaps even beyond the Creation Event itself. Ten years ago, theoreticians discovered a new class of theories called Supersymmetric Grand Unified Theories ( SUSY GUTs). These theories, of which there are several competing types, have shown great promise in providing physicists with a unified framework for describing not just the electro-nuclear force but also gravity, in addition to the particles they act on (see The Planck Era: March 1984). Unfortunately, as SUSY GUTs were studied more carefully, it was soon discovered that even the most promising candidates for THE Unified Field Theory suffered from certain fundamantal deficiencies. For instance:

1) There were not enough basic fields predicted to accomodate the known particles.

2) Left and right-hand symmetry was mandated so that the weak force, which breaks this symmetry, had to be put in ‘by hand’.

3) Anomalies exist which include the violation of energy conservation and charge.

4) The Cosmological Constant is 10 times larger than present upper limits suggest.

In recent years, considerable effort has gone into extending and modifying the postulates of SUSY GUTs in order to avoid these problems. One avenue has been to question the legitimacy of a very basic premise of the field theories developed heretofore. The most active line of theoretical research in the last 25 years has involved the study of what are called ‘point symmetry groups’. For example, a hexagon rotated by 60 degrees about a point at its center is indistinguishable from one rotated by 120, 180, 240, 300 and 360 degrees. These 6 rotation operations form a mathematical group so that adding or subtracting any two operations always result in a rotation operation that is already a member of the group ( 180 = 120 + 60 etc). The Grand Unification Theories of the electro-nuclear interaction are based on point symmetry groups named SU(3), SU(2) and U(1) which represent analogous ‘rotations’ in a more complex mathematical space. In the context of ponderable matter, point symmetry groups are also the mathematical statement of what we believe to be the structure of the fundamental particles of matter, namely, that particles are point-like having no physical size at all. But what if this isn’t so? The best that experimental physics has to offer is that the electron which is one of a family of 6 known Leptons, behaves like a point particle at scales down to 10 cm, but that’s still an enormous distance compared to the gravitational Planck scale of 10 cm where complete unification with gravity is expected to occur.

By assuming that fundamental particles have internal structure, Michael Green at Queen Mary College and John Schwartz at Caltech made a remarkable series of discoveries which were anounced in the journal NATURE in April 1985. They proposed that, if a point particle were replaced by a vibrating ‘string’ moving through a 10-dimensional spacetime, many of the problems plaguing SUSY GUTs seemed to vanish miraculously. What’s more, of all the possible kinds of ‘Superstring’ theories, there were only two ( called SO(32) and E8 x E8′) that were: 1) Consistent with both the principles of relativity and quantum mechanics,2) Allowed for the asymmetry between left and right-handed processes and, 3) Were free of anomalies. Both versions were also found to have enough room in them for 496 different types of fields; enough to accomodate all of the known fundamental particles and then some! Superstring theories also have very few adjustable parameters and from them, certain quantum gravity calculations can be performed that give finite answers instead of infinite ones. In spite of their theoretical successes, Superstring theories suffer from the difficulty that the lightest Superstring particles will be completely massless while the next more massive generation will have masses of 10 GeV. It is not even clear how these supermassive string particles are related to the known particles which are virtually massless by comparison (a proton has a mass of 1 GeV!). It is also not known if the 496 different particles will cover the entire mass range between 0 and 10 GeV. It is possible that they may group themselves into two families with masses clustered around these two extreems. In the later instance, experimental physicists may literally run out of new particles to discover until accelerators powerful enough to create supermassive particles can be built.

An attractive feature of the SO(32) model, which represents particles as open-ended strings, is that gravity has to be included from the start in order to make the theory internally consistent and capable of yielding finite predictions. It is also a theory that reduces to ordinary point field theories at energies below 10 GeV. The complimentary theory, E8 x E8′, is the only other superstring theory that seems to work as well as SO(32) and treats particles as though they were closed strings without bare endpoints. This model is believed to show the greatest promise for describing real physical particles. It also includes gravity, but unlike SO(32), E8 x E8′ does seem to reduce at low energy, to the symmetry groups associated with the strong, weak and electromagnetic interactions, namely, SU(3), SU(2) and U(1).

If E8 x E8′ is destined to be the ‘ultimate, unified field theory’, there are some additional surprises in store for us. Each group, E8 and E8′, can be reduced mathematically to the products of the groups that represent the strong, weak and electromagnetic forces; SU(3) x SU(2) x U(1). If the E8 group corresponds to the known particles what does E8′ represent? In terms of its mathematical properties, symmetry considerations alone seem to require that the E8′ group should be a mirror image of E8. If E8 contains the groups SU(3), SU(2) and U(1) then E8′ contains SU(3)’, SU(2)’ and U(1)’. The primed fields in E8′ would have the same properties as those we ascribe to the strong, weak and electromagnetic forces. The E8′ particle fields may correspond to a completly different kind of matter, whose properties are as different from matter and anti-matter as ordinary matter is from anti-matter! ‘Shadow Matter’ as it has been called by Edward Kolb, David Seckel and Michael Turner at Fermilab, may actually co-exist with our own – possibly accounting for the missing mass necessary to close the universe. Shadow matter is only detectable by its gravitational influence and is totally invisible because the shadow world electromagnetic force (shadow light) does not interact with any of the particles in the normal world.

BEYOND SPACE AND TIME

The quest for a mathematical description of the physical world uniting the apparent differences between the known particles and forces, has led physicists to the remarkable conclusion that the universe inhabits not just the 4 dimensions of space and time, but a much larger arena whose dimensionality may be enormous (see Does Space Have More Than 3 Dimensions?). Both the Superstring theories and SUSY GUTs agree that our physical world has to have more than the 4 dimensions we are accustomed to thinking about. A remarkable feature of Superstring theory is that of all the possible dimensionalities for spacetime, only in 10-dimensions ( 9 space dimensions and 1 time dimension) will the theory lead to a computationally finite and internally consistent model for the physical world that includes the weak interaction from the outset, and where all of the troublesome anomalies cancil exactly. In such a 10-dimensional world, it is envisioned that 6 dimensions are now wrapped-up or ‘compactified’ into miniscule spheres that accompany the 4 coordinates of every point in spacetime. What would a description of the early universe look like from this new viewpoint? The 6 internal dimensions are believed to have a size of order 10 cm.

As we follow the history of the universe back in time, the 3 large dimensions of space rapidly shrink until eventually they become only 10 cm in extent. This happened during the Planck Era at a time, 10 seconds after the Creation Event. The appearance of the universe under these conditions is almost unimaginable. Today as we look out at the most distant quasar, we see them at distances of billions of lightyears. During the Planck Era, the matter comprising these distant systems was only 10 cm away from the material that makes-up your own body!

What was so special about this era that only 4 of the 10 dimensions were singled-out to grow to their enormous present size?. Why not 3 ( 2 space + 1 time) or 5 ( 4 space + 1 time)? Physicists have not as yet been able to develope an explanation for this fundamental mystery of our plenum, on the other hand, it may just be that had the dimensional breakdown of spacetime been other than ‘4 + 6’, the physical laws we are the products of, would have been totally inhospitable to life as we know it.

As we relentlessly follow the history of the universe to even earlier times, the universe seems to enter a progressively more and more symmetric state. The universe at 10 seconds after the Big Bang may have been populated by supermassive particles with masses of 10^15 GeV or about 10^-13 grams each. These particles ultimatly decayed into the familiar quarks and leptons once the universe had grown colder as it expanded. In addition, there may only have been a single kind of ‘superforce’ acting on these particles; a force whose character contained all of the individual attributes we now associate with gravity, electromagnetism and the strong and weak nuclear forces. Since the particles carrying the ‘superforce’ had masses similar to those of the supermassive particles co-existing then, the distinction between the force-carriers and the particles they act on probably broke-down completely and the world became fully supersymmetric.

To go beyond the Planck Era may require a radical alteration in our conventional way of thinking about time and space. Only glimpses of the appropriate way to think about this multidimensional landscape can be found in the equations and theories of modern-day physics. Beyond the Planck Era, all 10 dimensions (and perhaps others) become co-equal at least in terms of their physical size. The supermassive Superstring particles begin to take-on more of the characteristics of fluctuations in the geometry of spacetime than as distinguishable, ingredients in the primordial, cosmological ‘soup’. There was no single, unique geometry for spacetime but, instead, an ever-changing quantum interplay between spacetimes with an unlimited range in geometry. Like sound waves that combine with one another to produce interference and reinforcement, the spacetime that emerged from the Planck Era is thought to be the result of the superposition of an infin ite number of alternate spacetime geometries which, when added together, produced the spacetime that we are now a part of.

Was there light? Since the majority of the photons were probably not created in large numbers until at least the beginning of the Inflationary Epoc, 10^-36 seconds after the Big Bang, it is not unthinkable that during its earliest moments, the universe was born out of darkness rather than in a blinding flash of light. All that existed in this darkness before the advent of light, was an empty space out of which our 10-dimensional spacetime would later emerge. Of course, under these conditions it is unclear just how we should continue to think about time itself.

In terms of the theories available today, it may well be that the particular dimension we call Time had a definite zero point so that we can not even speak logically about what happened before time existed. The concept of ‘before’ is based on the presumption of time ordering. A traveler standing on the north pole can never move to a position on the earth that is 1 mile north of north! Nevertheless, out of ingrained habit, we speak of the time before the genesis of the universe when time didn’t exist and ask, “What happened before the Big Bang?”. The list of physicists investigating this ‘state’ has grown enormously over the last 15 years. The number of physicists, worldwide, that publish research on this topic is only slightly more than 200 out of a world population of 5 billion!

QUANTUM COSMOLOGY

In the early 1970’s Y. Zel’dovitch and A. Starobinski of the USSR along with Edward Tryon at Hunter College proposed that the universe emerged from a fluctuation in the vacuum. This vacuum fluctuation ‘ran away’ with itself, creating all the known particles out of empty space at the ‘instant’ of no-time. To understand what this means requires the application of a fundamental fact of relativistic quantum physics discovered during the latter half of the 1920’s. Vacuum fluctuations are a direct consequence of Heisenberg’s Uncertainty Principle which limits how well we can simultaneously know a particle’s momentum and location (or its total energy and lifetime). What we call empty space or the physical vacuum is a Newtonian fiction like absolute space and time. Rather than a barren stage on which matter plays-out its role, empty space is known to be filled with ‘virtual particles’ that spontaneously appear and disappear beyond the ability of any physical measurement to detect directly. From these ghost particles, a variety of very subtle phenomena can be predicted with amazing accuracy. Depending on the total rest mass energy of the virtual particles created in the vacuum fluctuation, they may live for a specific lifetime before Heisenberg’s Uncertainty Principle demands that they vanish back into the nothingness of the vacuum state. In such a quantum world, less massive virtual particles can live longer than more massive ones. Edward Tyron proposed that the universe is just a particularly long-lived vacuum fluctuation differing only in magnitude from those which occur imperceptably all around us. The reason the universe is so long lived in spite of its enormous mass is that the positive energy latent in all the matter in the universe is offset by the negative potential energy of the gravitational field of the universe. The total energy of the universe is, therefore, exactly zero and its maximum lifetime as a ‘quantum fluctuation’ could be enormous and even infinite! According to Tryon, “The Universe is simply one of those things which happens from time to time.”

This proposal by Tryon was regarded with some scepticism and even amusement by astronomers, and was not persued much further. This was a fate that had also befallen the work on 5-dimensional general relativity by Theodore Kaluza and Oskar Klein during the 1920’s which was only resurrected in the late 1970’s as a potent remedy for the ills plaguing supersymmetry theory.

In 1978, R. Brout, P. Englert, E. Gunzig and P. Spindel at the University of Brussels, proposed that the fluctuation that led to the creation of our universe started out in an empty, flat, 4-dimensional spacetime. The fluctuation in space began weakly, creating perhaps a single matter- antimatter pair of supermassive particles with masses of 10^19 GeV. The existence of this ‘first pair’ stimulated the creation from the vacuum of more particle-antiparticle pairs which stimulated the production of still others and so on. Space became highly curved and exploded, disgorging all of the superparticles which later decayed into the familiar leptons, quarks and photons.

Heinz Pagels and David Atkatz at Rockefeller University in 1981 proposed that the triggering agent behind the Creation Event was a tunneling phenomenon of the vacuum from a higher-energy state to a lower energy state. Unlike the Brout-Englert-Gunzig-Spindel model which started from a flat spacetime, Pagels and Atkatz took the complimentary approach that the original nothingness from which the universe emerged was a spatially closed, compact empty space, in other words, it had a geometry like the 2-D surface of a sphere. but the dimensionality of its surface was much higher than 2. Again this space contained no matter what-so-ever. The characteristics (as yet unknown) of the tunneling process determined, perhaps in a random way, how the dimensionality of spacetime would ‘crystallize’ into the 6+4 combination that represents the plenum of our universe.

Alex Vilenkin at Tufts University proposed in 1983 that our spacetime was created out of a ‘nothingness’ so complete that even its dimensionality was undefined. In 1984, Steven Hawkings at Cambridge and James Hartle at UCSB came to a similar conclusion through a series of quantum mechanical calculations. They described the geometric state of the universe in terms of a wavefunction which specified the probability for spacetime to have one of an infinite number of possible geometries. A major problem with the ordinary Big Bang theory was that the universe emerged from a state where space and time vanished and the density of the universe became infinite; a state called the Singularity. Hawkings and Hartle were able to show that this Big Bang singularity represented a specific kind of geometry which would become smeared-out in spacetime due to quantum indeterminacy. The universe seemed to emerge from a non-singular state of ‘nothingness’ similar to the undefined state proposed by Vilenkin. The physicist Frank Wilczyk expresses this remarkable situation the best by saying that, ” The reason that there is Something rather than Nothing is that Nothing is unstable.”

PERFECT SYMMETRY

Theories like those of SUSY GUTS and Superstrings seem to suggest that just a few moments after Creation, the laws of physics and the content of the world were in a highly symmetric state; one superforce and perhaps one kind of superparticle. The only thing breaking the perfect symmetry of this era was the definite direction and character of the dimension called Time. Before Creation, the primordial symmetry may have been so perfect that, as Vilenkin proposed, the dimensionality of space was itself undefined. To describe this state is a daunting challenge in semantics and mathematics because the mathematical act of specifying its dimensionality would have implied the selection of one possibility from all others and thereby breaking the perfect symmetry of this state. There were, presumably, no particles of matter or even photons of light then, because these particles were born from the vacuum fluctuations in the fabric of spacetime that attended the creation of the universe. In such a world, nothing happens because all ‘happenings’ take place within the reference frame of time and space. The presence of a single particle in this nothingness would have instantaneously broken the perfect symmetry of this era because there would then have been a favored point in space different from all others; the point occupied by the particle. This nothingness didn’t evolve either, because evolution is a time-ordered process. The introduction of time as a favored coordinate would have broken the symmetry too. It would seem that the ‘Trans-Creation’ state is beyond conventional description because any words we may choose to describe it are inherently laced with the conceptual baggage of time and space. Heinz Pagels reflects on this ‘earliest’ stage by saying, “The nothingness ‘before’ the creation of the universe is the most complete void we can imagine. No space, time or matter existed. It is a world without place, without duration or eternity…”

A perusal of the scientific literature during the last 20 years suggests that we may be rapidly approaching a major crossroad in physics. One road seems to be leading to a single unification theory that is so unique among all others that it is the only one consistent with all the major laws we know about. It is internally consistent; satisfies the principles of relativity and quantum mechanics and requires no outside information to describe the particles and forces it contains . A prototype of this may be superstring theory with its single adjustable parameter, namely, the string tension. The other road is much more bleak. It may also turn out that we will create several theoretical systems that seem to explain everything but have within them hard to detect flaws. These flaws may stand as barracades to further logical inquiry; to be uncovered only through experiments that may be beyond our technological reach. It is possible that we are seeing the beginning of this latter process even now, with the multiplicity of theories whose significant deviations only occur at energies near 10^19 GeV.

I find it very hard to resist the analogy between our current situation and that of the Grecian geometers. For 2000 years the basic postulates of Eulidean geometry and the consequences of this logical system, remained fixed. It became a closed book with only a few people in the world struggling to find exceptions to it such as refutations of the parallel line postulate. Finally during the 19th century, non-euclidean geometry was discovered and a renaissance in geometry occurred. Are physicists on the verge of a similar great age, finding themselves hamstrung by not being able to devise new ways of thinking about old problems? Egyptian cosmology was based on motifs that the people of that age could see in the world around them; water, sky, land, biological reproduction. Today we still use motifs that we find in Nature in order to explain the origin of the universe; the geometry of space, virtual particles and vacuum fluctuations. We can probably expect that in the centuries to follow, our descendents will find still other motifs and from them, fashion cosmologies that will satisfy the demands of that future age with, possibly, much greater accuracy and efficiency than ours do today. Perhaps, too, in those future ages, scientists will marvel at the ingenuity of modern physicists and astronomers, and how in the space of only 300 years, we had managed to create our own quaint theory as the Egyptians had before us.

In the meantime, physicists and astronomers do the best they can to fashion a cosmology that will satisfy the intellectual needs of our age. Today, as we contemplate the origin of the universe we find ourselves looking out over a dark, empty void not unlike the one that our Egyptian predecessors might have imagined. This void is a state of exquisite perfection and symmetry that seems to defy description in any linguistic terms we can imagine. Through our theories we launch mathematical voyages of exploration, and watch the void as it trembles with the quantum possibilities of universes unimaginable.

Astronomy, Physics

Decay of the False Vacuum

The Decay of the False Vacuum

Written by Sten Odenwald. Copyright (C) 1983 Kalmbach Publishing. Reprinted by permission

In the recently developed theory by Steven Weinberg and Abdus Salam, that unifies the electromagnetic and weak forces, the vacuum is not empty. This peculiar situation comes about because of the existence of a new type of field, called the Higgs field. The Higgs field has an important physical consequence since its interaction with the W, W and Z particles (the carriers of the weak force) causes them to gain mass at energies below 100 billion electron volts (100 Gev). Above this energy they are quite massless just like the photon and it is this characteristic that makes the weak and electromagnetic forces so similar at high energy.

On a somewhat more abstract level, consider Figures 1 and 2 representing the average energy of the vacuum state. If the universe were based on the vacuum state in Figure 1, it is predicted that the symmetry between the electromagnetic and weak interactions would be quite obvious. The particles mediating the forces would all be massless and behave in the same way. The corresponding forces would be indistinguishable. This would be the situation if the universe had an average temperature of 1 trillion degrees so that the existing particles collided at energies of 100 Gev. In Figure 2, representing the vacuum state energy for collision energies below 100 Gev, the vacuum state now contains the Higgs field and the symmetry between the forces is suddenly lost or ‘broken’. Although at low energy the way in which the forces behave is asymmetric, the fundamental laws governing the electromagnetic and weak interactions remain inherently symmetric. This is a very remarkable and profound prediction since it implies that certain symmetries in Nature can be hidden from us but are there nonetheless.

During the last 10 years physicists have developed even more powerful theories that attempt to unify not only the electromagnetic and weak forces but the strong nuclear force as well. These are called the Grand Unification Theories (GUTs) and the simplist one known was developed by Howard Georgi, Helen Quinn,and Steven Weinberg and is called SU(5), (pronounced ‘ess you five’). This theory predicts that the nuclear and ‘electroweak’ forces will eventually have the same strength but only when particles collide at energies above 1 thousand trillion GeV corresponding to the unimaginable temperature of 10 thousand trillion trillion degrees! SU(5) requires exactly 24 particles to mediate forces of which the 8 massless gluons of the nuclear force, the 3 massless intermediate vector bosons of the weak force and the single massless photon of the electromagnetic force are 12. The remaining 12 represent a totally new class of particles called Leptoquark bosons that have the remarkable property that they can transform quarks into electrons. SU(5) therefore predicts the existence of a ‘hyperweak’ interaction; a new fifth force in the universe! Currently, this force is 10 thousand trillion trillion times weaker than the weak force but is nevertheless 100 million times stronger than gravity. What would this new force do? Since protons are constructed from 3 quarks and since quarks can now decay into electrons, through the Hyperweak interaction, SU(5) predicts that protons are no longer the stable particles we have always imagined them to be. Crude calculations suggest that they may have half-lives between 10^29 to 10^33 years. An immediate consequence of this is that even if the universe were destined to expand for all eternity, after ‘only’ 10^32 years or so, all of the matter present would catastrophically decay into electrons, neutrinos and photons. The Era of Matter, with its living organisms, stars and galaxies, would be swept away forever, having represented but a fleeting episode in the history of the universe. In addition to proton decay, SU(5) predicts that at the energy characteristic of the GUT transition, we will see the affects of a new family of particles called supermassive Higgs bosons whose masses are expected to be approximately 1 thousand trillion GeV! These particles interact with the 12 Leptoquarks and make them massive just as the Higgs bosons at 100 GeV made the W, W and Z particles heavy. Armed with this knowledge, let’s explore some of the remarkable cosmological consequences of these exciting theories.

The GUT Era

To see how these theories relate to the history of the universe, imagine if you can a time when the average temperature of the universe was not the frigid 3 K that it is today but an incredable 10 thousand trillion trillion degrees (10^15 GeV). The ‘Standard Model’ of the Big Bang, tells us this happened about 10^-37 seconds after Creation. The protons and neutrons that we are familiar with today hadn’t yet formed since their constituent quarks interacted much too weakly to permit them to bind together into ‘packages’ like neutrons and protons. The remaining constituents of matter, electrons, muons and tau leptons, were also massless and traveled about at essentially light-speed; They were literally a new form of radiation, much like light is today! The 12 supermassive Leptoquarks as well as the supermassivs Higgs bosons existed side-by-side with their anti-particles. Every particle-anti particle pair that was annihilated was balanced by the resurrection of a new pair somewhere else in the universe. During this period, the particles that mediated the strong, weak and electromagnetic forces were completely massless so that these forces were no longer distinguishable. An inhabitant of that age would not have had to theorize about the existence of a symmetry between the strong, weak and electromagnetic interactions, this symmetry would have been directly observable and furthermore, fewer types of particles would exist for the inhabitants to keep track of. The universe would actually have beed much simpler then!

As the universe continued to expand, the temperature continued to plummet. It has been suggested by Demetres Nanopoulis and Steven Weinberg in 1979 that one of the supermassive Higgs particles may have decayed in such a way that slightly more matter was produced than anti-matter. The remaining evenly matched pairs of particles and anti-particles then annihilated to produce the radiation that we now see as the ‘cosmic fireball’.

Exactly what happened to the universe as it underwent the transitions at 10^15 and 100 GeV when the forces of Nature suddenly became distinguishable is still under investigation, but certain tantalizing descriptions have recently been offered by various groups of theoriticians working on this problem. According to studies by Alan Guth, Steven Weinberg and Frank Wilczyk between 1979 and 1981, when the GUT transition occured, it occured in a way not unlike the formation of vapor bubbles in a pot of boiling water. In this analogy, the interior of the bubbles represent the vacuum state in the new phase, where the forces are distinguishable, embedded in the old symmetric phase where the nuclear, weak and electromagnetic forces are indistinguishable. Inside these bubbles, the vacuum energy is of the type illustrated by Figure 2 while outside it is represented by Figure 1. Since we are living within the new phase with its four distinguishable forces, this has been called the ‘true’ vacuum state. In the false vacuum state, the forces remain indistinguishable which is certainly not the situation that we find ourselves in today!

Cosmic Inflation

An exciting prediction of Guth’s model is that the universe may have gone through at least one period in its history when the expansion was far more rapid than predicted by the ‘standard’ Big Bang model. The reason for this is that the vacuum itself also contributes to the energy content of the universe just as matter and radiation do however, the contribution is in the opposite sense. Although gravity is an attractive force, the vacuum of space produces a force that is repulsive. As Figures 1 and 2 show, the minimum energy state of the false vacuum at ‘A’ before the GUT transition is at a higher energy than in the true vacuum state in ‘B’ after the transition. This energy difference is what contributes to the vacuum energy. During the GUT transition period, the positive pressure due to the vacuum energy would have been enormously greater than the restraining pressure produced by the gravitational influence of matter and radiation. The universe would have inflated at a tremendous rate, the inflation driven by the pressure of the vacuum! In this picture of the universe, Einstein’s cosmological constant takes on a whole new meaning since it now represents a definite physical concept ; It is simply a measure of the energy difference between the true and false vacuum states (‘B’ and ‘A’ in Figures 1 and 2.) at a particular time in the history of the universe. It also tells us that, just as in de Sitter’s model, a universe where the vacuum contributes in this way must expand exponentially in time and not linearly as predicted by the Big Bang model. Guth’s scenario for the expansion of the universe is generally called the ‘inflationary universe’ due to the rapidity of the expansion and represents a phase that will end only after the true vacuum has supplanted the false vacuum of the old, symmetric phase.

A major problem with Guth’s original model was that the inflationary phase would have lasted for a very long time because the false vacuum state is such a stable one. The universe becomes trapped in the cul-de-sac of the false vacuum state and the exponential expansion never ceases. This would be somewhat analogous to water refusing to freeze even though its temperature has dropped well below 0 Centigrade. Recent modifications to the original ‘inflationary universe’ model have resulted in what is now called the ‘new’ inflationary universe model. In this model, the universe does manage to escape from the false vacuum state and evolves in a short time to the familiar true vacuum state.

We don’t really know how exactly long the inflationary phase may have lasted but the time required for the universe to double its size may have been only 10^-34 seconds. Conceivably, this inflationary period could have continued for as ‘long’ as 10^-24 seconds during which time the universe would have undergone 10 billion doublings of its size! This is a number that is truely beyond comprehension. As a comparison, only 120 doublings are required to inflate a hydrogen atom to the size of the entire visible universe! According to the inflationary model, the bubbles of the true vacuum phase expanded at the speed of light. Many of these had to collide when the universe was very young in order that the visible universe appear so uniform today. A single bubble would not have grown large enough to encompass our entire visible universe at this time; A radius of some 15-20 billion light years. On the other hand, the new inflationary model states that even the bubbles expanded in size exponentially just as their separations did. The bubbles themselves grew to enormous sizes much greater than the size of our observable universe. According to Albrecht and Steinhardt of the University of Pennsylvania, each bubble may now be 10^3000 cm in size. We should not be too concerned about these bubbles expanding at many times the speed of light since their boundaries do not represent a physical entity. There are no electrons or quarks riding some expandind shock wave. Instead, it is the non-material vacuum of space that is expanding. The expansion velocity of the bubbles is not limited by any physical speed limit like the velocity of light.

GUMs in GUTs

A potential problem for cosmologies that have phase transitions during the GUT Era is that a curious zoo of objects could be spawned if frequent bubble mergers occured as required by Guth’s inflationary model. First of all, each bubble of the true vacuum phase contains its own Higgs field having a unique orientation in space. It seems likely that no two bubbles will have their Higgs fields oriented in quite the same way so that when bubbles merge, knots will form. According to Gerhard t’Hooft and Alexander Polyakov, these knots in the Higgs field are the magnetic monopoles originally proposed 40 years ago by Paul Dirac and there ought to be about as many of these as there were bubble mergers during the transition period. Upper limits to their abundance can be set by requiring that they do not contribute to ‘closing’ the universe which means that for particles of their predicted mass (about 10^16 GeV), they must be 1 trillion trillion times less abundant than the photons in the 3 K cosmic background. Calculations based on the old inflationary model suggest that the these GUMs (Grand Unification Monopoles) may easily have been as much as 100 trillion times more abundant than the upper limit! Such a universe would definitly be ‘closed’ and moreover would have run through its entire history between expansion and recollapse within a few thousand years. The new inflationary universe model solves this ‘GUM’ overproduction problem since we are living within only one of these bubbles, now almost infinitly larger than our visible universe. Since bubble collisions are no longer required to homogenize the matter and radiation in the universe, very few, if any, monopoles would exist within our visible universe.

Horizons

A prolonged period of inflation would have had an important influence on the cosmic fireball radiation. One long-standing problem in modern cosmology has been that all directions in the sky have the same temperature to an astonishing 1 part in 10,000. When we consider that regions separated by only a few degrees in the sky have only recently been in communication with one another, it is hard to understand how regions farther apart than this could be so similar in temperature. The radiation from one of these regions, traveling at the velocity of light, has not yet made it across the intervening distance to the other, even though the radiation may have started on its way since the universe first came into existence. This ‘communication gap’ would prevent these regions from ironing-out their temperature differences.

With the standard, Big Bang model, as we look back to earlier epochs from the present time, the separations between particles decrease more slowly than their horizons are shrinking. Neighboring regions of space at the present time, become disconnected so temperature differences are free to develope. Eventually, as we look back to very ancient times, the horizons are so small that every particle existing then literally fills the entire volume of its own, observable universe. Imagine a universe where you occupy all of the available space! Prior to the development of the inflationary models, cosmologists were forced to imagine an incredably well-ordered initial state where each of these disconnected domains (some 10^86 in number) had nearly identical properties such as temperature. Any departure from this situation at that time would have grown to sizable temperature differences in widely separated parts of the sky at the present time. Unfortunately, some agency would have to set-up these finely-tuned initial conditions by violating causality. The contradiction is that no force may operate by transmitting its influence faster than the speed of light. In the inflationary models, this contradiction is eliminated because the separation between widely scattered points in space becomes almost infinitly small compared to the size of the horizons as we look back to the epoc of inflation. Since these points are now within each others light horizons, any temperature difference would have been eliminated immediatly since hotter regions would now be in radiative contact with colder ones. With this exponentially-growing, de Sitter phase in the universe’s early history we now have a means for resolving the horizon problem.

Instant Flat Space

Because of the exponential growth of the universe during the GUT Era, its size may well be essentially infinite for all ‘practical’ purposes . Estimates by Albrecht and Steinhardt suggest that each bubble region may have grown to a size of 10^3000 cm by the end of the inflationary period. Consequently, the new inflationary model predicts that the content of the universe must be almost exactly the ‘critical mass’ since the sizes of each of these bubble regions are almost infinite in extent. The universe is, for all conceivable observations, exactly Euclidean (infinite and flat in geometry) and destined to expand for all eternity to come. Since we have only detected at most 10 percent of the critical mass in the form of luminous matter, this suggests that 10 times as much matter exists in our universe than is currently detectable. Of course, if the universe is essentially infinite this raises the ghastly spectre of the eventual annihilation of all organic and inorganic matter some 10^32 years from now because of proton decay.

In spite of its many apparent successes, even the new inflationary universe model is not without its problems. Although it does seem to provide explainations for several cosmological enigmas, it does not provide a convincing way to create galaxies. Those fluctuations in the density of matter that do survive the inflationary period are so dense that they eventually collapse into galaxy-sized blackholes! Neither the precise way in which the transition to ordinary Hubbel expansion occurs nor the duration of the inflationary period are well determined.

If the inflationary cosmologies can be made to answer each of these issues satisfactorily we may have, as J. Richard Gott III has suggested, a most remarkable model of the universe where an almost infinite number of ‘bubble universes’ each having nearly infinite size, coexist in the same 4-dimensional spacetime; all of these bubble universes having been brought into existence at the same instant of creation. This is less troublesome than one might suspect since, if our universe is actually infinite as the available data suggests, so too was it infinite even at its moment of birth! It is even conceivable that the universe is ‘percolating’ with new bubble universes continually coming into existence. Our entire visible universe, out to the most distant quasar, would be but one infinitessimal patch within one of these bubble regions. Do these other universes have galaxies, stars, planets and living creatures statistically similar to those in our universe? We may never know. These other universes, born of the same paroxicism of Creation as our own, are forever beyond our scrutiny but obviously not our imaginations!

Beyond The Beginning…

Finally, what of the period before Grand Unification? We may surmise that at higher temperatures than the GUT Era, even the supermassive Higgs and Leptoquark bosons become massless and at long last we arrive at a time when the gravitational interaction is united with the weak, electromagnetic and strong forces. Yet, our quest for an understanding of the origins of the universe remains incomplete since gravity has yet to be brought into unity with the remaining forces on a theoretical basis. This last step promises to be not only the most difficult one to take on the long road to unification but also appears to hold the greatest promise for shedding light on some of the most profound mysteries of the physical world. Even now, a handful of theorists around the world are hard at work on a theory called Supergravity which unites the force carriers (photons, gluons, gravitons and the weak interaction bosons) with the particles that they act on (quarks, electrons etc). Supergravity theory also predicts the existence of new particles called photinos and gravitinos. There is even some speculation that the photinos may fill the entire universe and account for the unseen ‘missing’ matter that is necessary to give the universe the critical mass required to make it exactly Euclidean. The gravitinos, on the other hand, prevent calculations involving the exchange of gravitons from giving infinite answers for problems where the answers are known to be perfectly finite. Hitherto, these calculations did not include the affects of the gravitinos.

Perhaps during the next decade, more of the details of the last stage of Unification will be hammered out at which time the entire story of the birth of our universe can be told. This is, indeed, an exciting time to be living through in human history. Will future generations forever envy us our good fortune, to have witnessed in our lifetimes the unfolding of the first comprehensive theory of Existence?

Astronomy, Physics

What is Space? Part I

Does Space Have More Than 3 Dimensions?
Written by Sten Odenwald
Copyright (C) 1984 Kalmbach Publishing. Reprinted by permission

The intuitive notion that the universe has three dimensions seems to be an irrefutable fact. After all, we can only move up or down, left or right, in or out. But are these three dimensions all we need to describe nature? What if there aree, more dimensions ? Would they necessarily affect us? And if they didn’t, how could we possibly know about them? Some physicists and mathematicians investigating the beginning of the universe think they have some of the answers to these questions. The universe, they argue, has far more than three, four, or five dimensions. They believe it has eleven! But let’s step back a moment. How do we know that our universe consists of only three spatial dimensions? Let’s take a look at some “proofs.”

On a 2-dimensional piece of paper you can draw an infinite number of polygons.  But when you try this same trick in 3-dimensions you run up against a problem.There are five and only five regular polyhedra. A regular polyhedron is defined as a solid figure whose faces are identical polygons – triangles, squares, and pentagons – and which is constructed so that only two faces meet at each edge. If you were to move from one face to another, you would cross over only one edge. Shortcuts through the inside of the polyhedron that could get you from one face to another are forbidden. Long ago, the mathematician Leonhard Euler demonstrated an important relation between the number of faces (F), edges (E), and corners (C) for every regular polyhedron: C – E + F = 2. For example, a cube has 6 faces, 12 edges, and 8 corners while a dodecahedron has 12 faces, 30 edges, and 20 corners. Run these numbers through Euler’s equation and the resulting answer is always two, the same as with the remaining three polyhedra. Only five solids satisfy this relationship – no more, no less.

Not content to restrict themselves to only three dimensions, mathematicians have generalized Euler’s relationship to higher dimensional spaces and, as you might expect, they’ve come up with some interesting results. In a world with four spatial dimensions, for example, we can construct only six regular solids. One of them – the “hypercube” – is a solid figure in 4-D space bounded by eight cubes, just as a cube is bounded by six square faces. What happens if we add yet another dimension to space? Even the most ambitious geometer living in a 5-D world would only be able to assemble thee regular solids. This means that two of the regular solids we know of – the icosahedron and the dodecahedron – have no partners in a 5-D universe.
For those of you who successfully mastered visualizing a hypercube, try imagining what an “ultracube” looks like. It’s the five- dimensional analog of the cube, but this time it is bounded by one hypercube on each of its 10 faces! In the end, if our familiar world were not three-dimensional, geometers would not have found only five regular polyhedra after 2,500 years of searching. They would have found six (with four spatial dimension,) or perhaps only three (if we lived in a 5-D universe). Instead, we know of only five regular solids. And this suggests that we live in a universe with, at most, three spatial dimensions.

All right, let’s suppose our universe actually consists of four spatial dimensions. What happens? Since relativity tells us that we must also consider time as a dimension, we now have a space-time consisting of five dimensions. A consequence of 5-D space-time is that gravity has freedom to act in ways we may not want it to.

To the best available measurements, gravity follows an inverse square law; that is, the gravitational attraction between two objects rapidly diminishes with increasing distance. For example, if we double the distance between two objects, the force of gravity between them becomes 1/4 as strong; if we triple the distance, the force becomes 1/9 as strong, and so on. A five- dimensional theory of gravity introduces additional mathematical terms to specify how gravity behaves. These terms can have a variety of values, including zero. If they were zero, however, this would be the same as saying that gravity requires only three space dimensions and one time dimension to “give it life.” The fact that the Voyager space- craft could cross billions of miles of space over several years and arrive vithin a few seconds of their predicted times is a beautiful demonstration that we do not need extra-spatial dimensions to describe motions in the Sun’s gravitational field.

From the above geometric and physical arguments, we can conclude (not surprisingly) that space is three-dimensional – on scales ranging from that of everyday objects to at least that of the solar system. If this were not the case, then geometers would have found more than five regular polyhedra and gravity would function very differently than it does – Voyager would not have arrived on time. Okay, so we’ve determined that our physical laws require no more than the three spatial dimensions to describe how the universe works. Or do they? Is there perhaps some other arena in the physical world where multidimensional space would be an asset rather than a liability?

Since the 1920s, physicists have tried numerous approaches to unifying the principal natural interactions: gravity, electromagnetism, and the strong and weak forces in atomic nuclei. Unfortunately, physicists soon realized that general relativity in a four-dimensional space-time does not have enough mathematical “handles” on which to hang the frameworks for the other three forces. Between 1921 and 1927, Theodor Kaluza and Oskar Klein developed the first promising theory combining gravity and electromagnetism. They did this by extending general relativity to five dimensions. For most of us, general relativity is mysterious enough in ordinary four-dimensional space-time. What wonders could lie in store for us with this extended universe?

General relativity in five dimensions gave theoreticians five additional quantities to manipulate beyond the 10 needed to adequately define the gravitational field. Kaluza and Klein noticed that four of the five extra quantities could be identified with the four components needed to define the electromagnetic field. In fact, to the delight of Kaluza and Klein, these four quantities obeyed the same types of equations as those derived by Maxwell in the late 1800s for electromagnetic radiationl Although this was a promising start, the approach never really caught on and was soon buried by the onrush of theoretical work on the quantum theory of electromagnetic force. It was not until work on supergravity theory began in 1975 that Kaluza and Klein’s method drew renewed interest. Its time had finally come.

What do theoreticians hope to gain by stretching general relativity beyond the normal four dimensions of space-time? Perhaps by studying general relativity in a higher-dimensional formulation, we can explain some of the constants needed to describe the natural forces. For instance, why is the proton 1836 times more massive than the electron? Why are there only six types of quarks and leptons? Why are neutrinos massless? Maybe such a theory can give us new rules for calculating the masses of fundamental particles and the ways in which they affect one another. These higher-dimensional relativity theories may also tell us something about the numbers and properties of a mysterious new family of particles – the Higgs bosons – whose existence is predicted by various cosmic unification schemes. (See “The Decay of the False Vacuum,” ASTRONOMY, November 1983.)

These expectations are not just the pipedreams of physicists – they actually seem to develop as natural consequences of certain types of theories studied over the last few years. In 1979, John Taylor at Kings College in London found that some higher- dimensional formalisms can give predictions for the maximum mass of the Higgs bosons (around 76 times that of the proton.) As they now stand, unification theories can do no more than predict the existence of these particles – they cannot provide specific details about their physical characteristics. But theoreticians may be able to pin down some of these details by using extended theories of general relativity. Experimentally, we know of six leptons: the electron, the muon, the tauon, and their three associated neutrinos. The most remarkable prediction of these extended relativity schemes, however, holds that the number of leptons able to exist in a universe is related to the number of dimensions of space-time. In a 6-D space-time, for example, only one lepton – presumably the electron – can exist. In a 10-D space-time, four leptons can exist – still not enough to accommodate the six we observe. In a 12-D space- time, we can account for all six known leptons – but we also acquire two additional leptons that have not yet been detected. Clearly, we would gain much on a fundamental level if we could increase the number of dimensions in our theories just a little bit.

How many additional dimensions do we need to consider in order to account for the elementary particles and forces that we know of today? Apparently we require at least one additional spatial dimension for every distinct “charge” that characterizes how each force couples to matter. For the electromagnetic force, we need two electric charges: positive and negative. For the strong force that binds quarks together to form, among other things, protons and neutrons, we need three “color” charges – red, blue, and green. Finally, we need two “weak” charges to account for the weak nuclear force. if we add a spatial dimension for each of these charges, we end up with a total of seven extra dimensions. The properly extended theory of general relativity we seek is one with an 11 -dimensional space-time, at the very least. Think of it – space alone must have at least 10 dimensions to accomodate all the fields known today.

Of course, these additional dimensions don’t have to be anything like those we already know about. In the context of modern unified field theory, these extra dimensions are, in a sense, internal to the particles themselves – a “private secret,” shared only by particles and the fields that act on them! These dimensions are not physically observable in the same sense as the three spatial dimensions we experience; they’stand in relation to the normal three dimensions of space much like space stands in relation to time.

With today’s veritable renaissance in finding unity among the forces and particles that compose the cosmos, some by methods other than those we have discussed, these new approaches lead us to remarkably similar conclusions. It appears that a four-dimensional space-time is simply not complex enough for physics to operate as it does.

We know that particles called bosons mediate the natural forces. We also know that particles called fermions are affected by these forces. Members of the fermion family go by the familiar names of electron, muon, neutrino, and quark; bosons are the less well known graviton, photon, gluon, and intermediate vector bosons. Grand unification theories developed since 1975 now show these particles to be “flavors” of a more abstract family of superparticies – just as the muon is another type of electron. This is an expression of a new kind of cosmic symmetry – dubbed supersymmetry, because it is all-encompassing. Not only does it include the force-carrying bosons, but it also includes the particles on which these forces act. There also exists a corresponding force to help nature maintain supersymmetry during the various interactions. It’s called supergravity. Supersymmetry theory introduces two new types of fundamental particles – gravitinos and photinos. The gravitino has the remarkable property of mathematically moderating the strength, of various kinds of interactions involving the exchange of gravitons. The photino, cousin of the photon, may help account for the “missing mass” in the universe.

Supersymmetry theory is actually a complex of eight different theories, stacked atop one another like the rungs of a ladder. The higher the rung, the larger is its complement of allowed fermion and boson particle states. The “roomiest” theory of all seems to be SO(8), (pronounced ess-oh-eight), which can hold 99 different kinds of bosons and 64 different kinds of fermions. But SO(8) outdoes its subordinate, SO(7), by only one extra dimension and one additional particle state. Since SO(8) is identical to SO(7) in all its essential features, we’ll discuss SO(7) instead. However, we know of far more than the 162 types of particles that SO(7) can accommodate, and many of the predicted types have never been observed (like the massless gravitino). SO(7) requires seven internal dimensions in addition to the four we recognize – time and the three “every day” spatial dimensions. If SO(7) at all mirrors reality, then our universe must have at least 11 dimensions! Unfortunately, it has been demonstrated by W. Nahm at the European Center for Nuclear Research in Geneva, Switzerland that supersymmetry theories for space-times with more than 11 dimensions are theoretically impossible. SO(7) evidently has the largest number of spatial dimensions possible, but it still doesn’t have enough room to accommodate all known types of particles.

It is unclear where these various avenues of research lead. Perhaps nowhere. There is certainly ample historical precedent for ideas that were later abandoned because they turned out to be conceptual dead-ends. Yet what if they turn out to be correct at some level? Did our universe begin its life as some kind of 11-dimensional “object” which then crystallized into our four- dimensional cosmos?

Although these internal dimensions may not have much to do with the real world at the present time, this may not always have been the case. E. Cremmer and J. Scherk of I’Ecole Normale Superieure in Paris have shown that just as the universe went through phase transitions in its early history when the forces of nature became distinguishable, the universe may also have gone through a phase transition when mensionality changed. Presumably matter has something like four external dimensions (the ones we encounter every day) and something like seven internal dimensions. Fortunately for us, these seven extra dimensions don’t reach out into the larger 4-D realm where we live. If they did, a simple walk through the park might become a veritable obstacle course, littered with wormholes in space and who knows what else!

Alan Chocos and Steven Detweiler of Yale University have considered the evolution of a universe that starts out being five- dimensional. They discovered that while the universe eventually does evolve to a state where three of the four spatial dimensions expand to become our world at large, the extra fourth spatial dimension shrinks to a size of 10^-31 centimeter by the present time. The fifth dimension to the universe has all but vanished and is 20 powers of 10 – 100 billion billion times – smaller than the size of a proton. Although the universe appears four- dimensional in space-time, this perception is accidental due to our large size compared to the scale of the other dimensions. Most of us think of a dimension as extending all the way to infinity, but this isn’t the full story. For example, if our universe is really destined to re-collapse in the distant future, the three- dimensional space we know today is actually limited itself – it will eventually possess a maximum, finite size. It just so happens that the physical size of human beings forces us to view these three spatial dimensions as infinitely large.

It is not too hard to reconcile ourselves to the notion that the fifth (or sixth, or eleventh) dimension could be smaller than an atomic nucleus – indeed, we can probably be thankful that this is the case.

Astronomy, Physics

The Cosmological Redshift

Galaxy Redshifts Reconsidered

Written by Sten Odenwald 
Copyright (C) 1993 Sky Publishing Corporation. Reprinted by permission. See February 1993 issue

Since its discovery nearly 65 years ago, the cosmological redshift has endured as one of the most persuasive ‘proofs’ that our universe is expanding. The steps leading to its discovery are well known. Soon after Christian Doppler discovered that motion produces frequency shifts in 1842, astronomers began an aggressive spectroscopic program to measure the velocities of stars and planets using their Doppler shifts. This continued through the first few decades of the 20th century ‘culminating’ in the work by Vesto Slipher, Edwin Hubble and Milton Humason on the so-called spiral nebulae — distinctly non- stellar objects that also seemed to display star-like Doppler shifts. So long as velocities of only a few hundred kilometers per second were measured, no one questioned that the frequency shifts for the spiral nebulae indicated relative motion just as they had for stars and planets.
But, during the 1920’s and 30’s spiral nebulae with Doppler shifts of over 34,000 kilometers per second were discovered. In a letter by Hubble to the Dutch cosmologist Willem De Sitter in 1931, he stated his concerns about these velocities by saying “… we use the term ‘apparent velocities’ in order to emphasize the empirical feature of the correlation. The interpretation, we feel, should be left to you and the very few others who are competent to discuss the matter with authority.” Dispite this cautionary note, the fact of the matter was that the redshifts measured for the distant galaxies LOOKED like Doppler shifts. The terms ‘recession velocity’ and ‘expansion velocity’ were quickly brought into service by astronomers at the telescope, and by popularizers, to describe the physical basis for the redshift.

As astronomers explored the universe to greater depths, galaxies and quasars appeared to be rushing away at faster and faster speeds. It seems to be a completely natural consequence of the outrushing of matter from the big bang. Like a sparkling display of fireworks on a warm summer evening, we imagine ourselves standing on one of those galactic ‘cinders’, watching the others rush past us into the dark void of infinite space. Upon closer examination, however, this intuitively-compelling and seductive mental image is both inadequate and misleading.

The Mysteries of Relativity

Big bang cosmology is based on Einstein’s general theory of relativity. It is a theory transcending both Newton’s mechanics and Einstein’s special theory of relativity, introducing us to concepts that do not exist within the older theories. Nor are these concepts easily comprehensible by our common sense which has been honed by organic evolution to see the world only through a narrow set of glasses.

For example, special relativity is based on the difficult-to-fathom postulate that the speed of light is absolutely constant when measured in reference frames moving at a constant speed. From this emerges the concept of ‘spacetime’ which then becomes the arena for all phenomena involving time dilation, length contraction and the Twin Paradox. Beyond special relativity lies the incomparably more alien landscape of general relativity. Gravitational fields now become geometric curvatures of spacetime. This has no analog in special relativity based as it is on a perfectly flat spacetime that remains aloof from any influence on it by matter or energy.

Just as the constancy of the speed of light led to the Twin Paradox, the curvature of spacetime leads to its own menageri of peculiar phenomena. One of these involves the slowing-down of clocks in the presence of a strong gravitational field. Related to this is the “gravitational redshift” which occurs when the frequency of light sent from the surface of a body is shifted to lower frequencies during the journey to the observer. This redshift is not related to the famous Doppler shift since the observer is not in motion relative to the body emitting the light signal!

A second phenomenon predicted by general relativity that also has no analog in special relativity is the cosmological redshift. Simply stated, the cosmological redshift occurs because the curvature of spacetime was smaller in the past when the universe was younger than it is now. Light waves become stretched en route between the time they were emitted long ago, and the time they are detected by us today.

The Doppler shift and cosmology

It is tempting to refer to cosmological redshifts as Doppler shifts. This choice of interpretation has in the years since Hubble’s work led to an unfortunate misunderstanding of big bang cosmology, obscurring one of its most mysterious beauties. As noted with a hint of frustration by cosmologists such as Steven Weinberg and Jaylant Narlikar and John Wheeler, “The frequency of light is also affected by the gravitational field of the universe, and it is neither useful nor strictly correct to interpret the frequency shifts of light…in terms of the special relativistic Doppler effect.”.

By refering to cosmological redshifts as Doppler shifts, we are insisting that our Newtonian intuition about motion still applies without significant change to the cosmological arena. A result of this thinking is that quasars now being detected at redshifts of Z = 4.0 would have to be interpreted as traveling a speeds of more than V = Z x c or 4 times the speed of light. This is, of course, quite absurd, because we all know that no physical object may travel faster than the speed of light.

To avoid such apparently nonsensical speeds, many popularizers use the special relativistic Doppler formula to show that quasars are really not moving faster than light. The argument being that for large velocities, special relativity replaces Newtonian physics as the correct framework for interpreting the world. By using a special relativistic velocity addition formula the quasar we just discussed has a velocity of 92 percent the speed of light. Although we now have a feeling that Reason has returned to our description of the universe, in fact, we have only replaced one incomplete explanation for another. The calculation of the quasar’s speed now presupposes that special relativity ( a theory of flat spacetime) is applicable even at cosmological scales where general relativity predicts that spacetime curvature becomes important. This is equivalent to a surveyor making a map of the state of California, and not allowing for the curvature of the earth!

The adoption of the special relativistic Doppler formula by many educators has led to a peculiar ‘hybrid’ cosmology which attempts to describe big bang cosmology using general relativity, but which is still firmly mired in the ruberik of special relativity. For instance, under the entry ‘redshift’ in the Cambridge Encyclopedia of Astronomy it is explicitly acknowledged that the redshift is not a Doppler shift, but less than two paragraphs later, the special relativistic Doppler formula is introduced to show how quasars are moving slower than the speed of light! It is also common for popularizers of cosmology to describe how ‘space itself stretches’ yet continue to describe the expansion of the universe as motion governed by the restrictions of special relativity. What’s going on here?

General relativity to the rescue

By adopting general relativity as the proper guide, such contradictions are eliminated. General relativity leads us to several powerful conclusions about our cosmos: 1) special relativity is inapplicable for describing the larger universe; 2) the concepts of distance and motion are not absolutely defined and 3) Preexisting spacetime is undefined. Each of these conclusions are as counter-intuitive as the Twin Paradox or as the particle/wave dualism of quantum mechanics. As Nobel Physicist John Wheeler once put it “If you are not completely confused by quantum mechanics, you do not understand it” The same may be said for general relativity.

The first conclusion means that we cannot trust even the insights hard won from special relativity to accurately represent the ‘big picture’ of the universe. General relativity must replace special relativity in cosmology because it denies a special role to observers moving at constant velocity, extending special relativity into the arena of accelerated observers. It also denies a special significance to special relativity’s flat spacetime by relegating it to only a microscopic domain within a larger geometric possibility. Just as Newtonian physics gave way to special relativity for describing high speed motion, so too does special relativity give way to general relativity. This means that the special relativistic Doppler formula should not, in fact cannot, be used to quantify the velocity of distant quasars. We have no choice in this matter if we want to maintain the logical integrity of both theories.

Distance and motion

The second conclusion is particularly upsetting because if we cannot define what we mean by distance, how then can we discuss in meaningful terms the ‘motion’ of distant quasars, or a Hubble Law interpreted as a distance versus velocity relation? In a small region of spacetime, we can certainly define motion as we always have because space has a static, flat geometry. When a body moves from point x to point y in a time interval, T, we say it is moving with a speed of S = (x – y)/T. There are also specific experimental ways of measuring x, y and T to form the quotent S by using clocks and rulers. The crucil feature behind these measurements is that nothing happens to the geometry of space during the experiment to change the results of the measuring process.

In the cosmological setting which we believe is accurately described by general relativity, we have none of these luxuries! Astronomers cannot wait millions of years to measure quasar proper motions. They cannot, like Highway Patrol officers, bounce radar beams off distant galaxies to establish their relative distances or speeds. Unlike all other forms of motion that have been previously observed, cosmological ‘motion’ cannot be directly observed. It can only be INFERRED from observations of the cosmological redshift, which general relativity then TELLS US means that the universe is expanding.

In big bang cosmology, galaxies are located at fixed positions in space. They may perform small dances about these positions in accordance with special relativity and local gravitational fields, but the real ‘motion’ is in the literal expansion of space between them! This is not a form of movement that any human has ever experienced. It is, therefore, not surprising that our intuition reels at its implication and seeks other less radical interpretations for it including special relativity. But even the exotic language and conundrums of special relativity cannot help us. Instead we are forced to interrogate the mathematics of general relativity itself for whatever landmarks it can provide. In doing so, we are left, however, with a riddle as profound as that of the Twin Paradox, and equally challenging to explain.

Two galaxies permanently located at positions (x1 , y1 , z1 ) and ( x2 , y2 , z2 ) at one time find themselves one billion light years apart. Then a few billion years later while located at the same coordinates, they find themselves 3 billion light years apart. The galaxies have not ‘moved’, nevertheless, their separations have increased. In fact, when the universe was only one year old, the separations between these galaxies were increasing at 300 times the speed of light! Space can expand faster than the speed of light in general relativity because space does not represent matter or energy. The displacements that arise from its dilation produce an entirely new kind of motion for which even our special relativistically-trained intuitions remain profoundly silent. Like that gentleman from Main once said “You can’t get there [to general relativity] from here [special relativity]”. To the extent that general relativity has been tested and found correct, we have no choice but to accept its consequences at face value.

Space, time and matter

The last conclusion drawn from general relativistic cosmology is that, unlike special relativity, it is not physically meaningful to speak of spacetime existing independently of matter and energy. In big bang cosmology, both space and time came into existence along side matter and energy at ‘time zero’. If our universe contains more than a critical density of matter and energy, its spacetime is forever finite and bounded, in a shape analogous to a sphere. Beyond this boundary, space and time simply do not exist. In fact, general relativity allows the Conservation of Energy to be suspended so that matter and energy may be created quite literally from the nothingness of curved spacetime. General relativity provides a means for ‘jump-starting’ Creation!

Big bang cosmology is both a profoundly beautiful, and disturbing, model for our universe, its shape and its destiny. It contains many surprises which have yet to be completely worked-out. But one feature of the evolving universe seems absolutly clear, the big bang was not some grand fireworks display, but an event of a completely different order. It resembled more an expanding soap bubble film upon which galactic dust motes are carried along for the ride. This film represents the totality of all the space and matter in our universe, and it expands into a mysterious primordial void which is itself empty of space, dimension, time or matter.

In the future it is hoped that a death knell will finally have sounded for the last vestage of the older thinking. With the Doppler interpretation of the cosmological redshift at last reconsidered, and rejected, we will finally be able to embrace the essential beauty and mystery of cosmic expansion as it was originally envisioned by its discoverers.

Astronomy, Physics

Einstein’s Fudge

Einstein’s Cosmic Fudge Factor

Written by Sten Odenwald
Copyright (C) 1991. Sky Publishing Corporation. Reprinted by permission. See April, 1991 issue

Black holes…quarks…dark matter. It seems like the cosmos gets a little stranger every year. Until recently, the astronomical universe known to humans was populated by planets, stars, galaxies, and scattered nebulae of dust and gas. Now, theoretists tell us it may also be inhabited by objects such as superstrings, dark matter and massive neutrinos — objects that have yet to be discovered if they exist at all!
As bizarre as these new constituents may sound, you don’t have to be a rocket scientist to appreciate the most mysterious ingredient of them all. It is the inky blackness of space itself that commands our attention as we look at the night sky; not the sparse points of light that signal the presence of widely scattered matter.

During the last few decades, physicists and astronomers have begun to recognize that the notion of empty space presents greater subtleties than had ever before been considered. Space is not merely a passive vessel to be filled by matter and radiation, but is a dynamic, physical entity in its own right.

One chapter in the story of our new conception of space begins with a famous theoretical mistake made nearly 75 years ago that now seems to have taken on a life of its own.

In 1917, Albert Einstein tried to use his newly developed theory of general relativity to describe the shape and evolution of the universe. The prevailing idea at the time was that the universe was static and unchanging. Einstein had fully expected general relativity to support this view, but, surprisingly, it did not. The inexorable force of gravity pulling on every speck of matter demanded that the universe collapse under its own weight.

His remedy for this dilemma was to add a new ‘antigravity’ term to his original equations. It enabled his mathematical universe to appear as permanent and invariable as the real one. This term, usually written as an uppercase Greek lambda, is called the ‘cosmological constant’. It has exactly the same value everywhere in the universe, delicately chosen to offset the tendency toward gravitational collapse at every point in space.

A simple thought experiment may help illustrate the nature of Lambda. Take a cubic meter of space and remove all matter and radiation from it. Most of us would agree that this is a perfect vacuum. But, like a ghost in the night, the cosmological constant would still be there. So, empty space is not really empty at all — Lambda gives it a peculiar ‘latent energy’. In other words, even Nothing is Something!

Einstein’s fudged solution remained unchallenged until 1922 when the Russian mathematician Alexander Friedmann began producing compelling cosmological models based on Einstein’s equations but without the extra quantity. Soon thereafter, theorists closely examining Einstein’s model discovered that, like a pencil balanced on its point, it was unstable to collapse or expansion. Later the same decade, Mount Wilson astronomer Edwin P. Hubble found direct observational evidence that the universe is not static, but expanding.

All this ment that the motivation for introducing the cosmological constant seemed contrived. Admitting his blunder, Einstein retracted Lambda in 1932. At first this seemed to end the debate about its existence. Yet decades later, despite the great physicist’s disavowal, Lambda keeps turning up in cosmologists’ discussions about the origin, evolution, and fate of the universe.

THEORY MEETS OBSERVATION

Friedmann’s standard ‘Big Bang’ model without a cosmological constant predicts that the age of the universe, t0, and its expansion rate (represented by the Hubble parameter, H0) are related by the equation t0 = 2/3H0. Some astronomers favor a value of H0 near 50 kilometers per second per megaparsec (one megaparsec equals 3.26 million light years). But the weight of the observational evidence seems to be tipping the balance towards a value near 100. In the Friedmann model, this implies that the cosmos can be no more than 7 billion years old. Yet some of our galaxy’s globular clusters have ages estimated by independent methods of between 12 and 18 billion years!

In what’s called the Einstein-DeSitter cosmology, the Lambda term helps to resolve this discrepancy. Now a large value for the Hubble parameter can be attributed in part to “cosmic repulsion”. This changes the relationship between t0 and H0, so that for a given size, the universe is older than predicted by the Friedmann model.

In one formulation of Einstein’s equation, Lambda is expressed in units of matter density. This means we can ask how the cosmological constant, if it exists at all, compares with the density of the universe in the forms of stars and galaxies.

So far, a careful look at the available astronomical data has produced only upper limits to the magnitude of Lambda. These vary over a considerable range – from about 10 percent of ordinary matter density to several times that density.

The cosmological constant can also leave its mark on the properties of gravitational lenses and faint galaxies. One of the remarkable features of Einstein’s theory of general relativity is its prediction that space and time become deformed or ‘warped’ in the vicinity of a massive body such as a planet, star or even a galaxy. Light rays passing through such regions of warped “space-time” have their paths altered. In the cosmological arena, nearby galaxies can deflect and distort the images of more distant galaxies behind them. Sometimes, the images of these distant galaxies can appear as multiple images surrounding the nearby ‘lensing’ galaxy.

At Kyoto University M. Fukugita and his coworkers predicted that more faint galaxies and gravitational lenses will be detected than in a Friedmann universe if Lambda is more than a few times the matter density. Edwin Turner, an astrophysicist at Princeton University also reviewed the existing, scant, data on gravitational lenses and found that they were as numerous as expected for Lambda less that a few times the matter density. By the best astronomical reconning, Lambda is probably not larger than the observed average matter density of the universe. For that matter, no convincing evidence is available to suggest that Lambda is not exactly equal to zero. So why not just dismiss it as an unnecessary complication? Because the cosmological constant is no longer, strictly, a construct of theoretical cosmology.

NOTHING AND EVERYTHING

To understand how our universe came into existence, and how its various ingredients have evolved, we must delve deeply into the fundamental constituents of matter and the forces that dictate how it will interact. This means that the questions we will have to ask will have more to do with physics than astronomy. Soon after the big bang, the universe was at such a high temperature and density that only the details of matter’s composition (quarks, electrons etc) and how they interact via the four fundamental forces of nature were important. They represented the most complex collections of matter in existence, long before atoms, planets, stars and galaxies had arrived on the scene.

For two decades now, physicists have been attempting to unify the forces and particles that make up our world – to find a common mathematical description that encompasses them all. Some think that such a Theory of Everything is just within reach. It would account not only for the known forms of matter, but also for the fundamental interactions among them: gravity, electromagnetism, and the strong and weak nuclear forces.

These unification theories are known by a variety of names: grand unification theory, supersymmetry theory and superstring theory. Their basic claim is that Nature operates according to a small set of simple rules called symmetries.

The concept of symmetry is at least as old as the civilization of ancient Greece, whos art and archetecture are masterworks of simplicity and balance. Geometers have known for a long time that a simple cube can be rotated 90 degrees without changing its outward appearance. In two dimensions, equalateral triangles look the same when they are rotated by 120 degrees. These are examples of the geometric concept of Rotation Symmetry.

There are parallels to geometric symmetry in the way that various physical phenomena and qualities of matter express themselves as well. For example, the well-known principle of the Conservation of Energy is a consequence of the fact that when some collections of matter and energy are examined at different times, they each have precisely the same total energy, just as a cube looks the same when it is rotated in space by a prescribed amount. Symmetry under a ‘shift in time’ is as closely related to the Conservation of Energy as is the symmetry of a cube when rotated by 90 degrees.

Among other things, symmetries of Nature dictate the strengths and ranges of the natural forces and the properties of the particles they act upon. Although Nature’s symmetries are hidden in today’s cold world, they reveal themselves at very high temperatures and can be studied in modern particle accelerators.

The real goal in unification theory is actually two-fold: not only to uncover and describe the underlying symmetries of the world, but to find physical mechanisms for ‘breaking’ them at low energy. After all, we live in a complex world filled with a diversity of particles and forces, not a bland world with one kind of force and one kind of particle!

Theoreticians working on this problem are often forced to add terms to their equations that represent entirely new fields in Nature. The concept of a field was invented by mathematicians to express how a particular quantity may vary from point to point in space. Physicists since the 18th century have adopted this idea to describe quantitatively how forces such as gravity and magnetism change at different distances from a body.

The interactions of these fields with quarks, electrons and other particles cause symmetries to break down. These fields are usually very different than those we already know about. The much sought after Higgs boson field, for example, was introduced by Sheldon Glashow, Abdus Salam and Steven Weinberg in their unified theory of the electromagnetic and weak nuclear forces.

Prior to their work, the weak force causing certain particles to decay, and the electromagnetic force responsible for the attraction between charged particles and the motion of compass needles, were both considered to be distinct forces in nature. By combining their mathematical descriptions into a common language, they showed that this distinction was not fundamental to the forces at all! A new field in nature called the Higgs field makes these two forces act differently at low temperature. But at temperatures above 1000 trillion degrees, the weak and electromagnetic forces become virtually identical in the way that they affect matter. The corresponding particles called the Higgs Boson not only cause the symmetry between the electromagnetic and weak forces to be broken at low temperature, but they are also responsible for confiring the property of mass on particles such as the electrons and the quarks!

There is, however a price that must be paid for introducing new fields into the mathematical machinery. Not only do they break symmetries, but they can also give the vacuum state an enormous latent energy that, curiously, behaves just like Lambda in cosmological models.

The embarrassment of having to resurrect the obsolete quantity Lambda is compounded when unification theories are used to predict its value. Instead of being at best a vanishingly minor ingredient to the universe, the predicted values are in some instances 10 to the power of 120 times greater than even the most generous astronomical upper limits!

It is an unpleasant fact of life for physicists that the best candidates for the Theory of Everything always have to be fine-tuned to get rid of their undesirable cosmological consequences. Without proper adjustment, these candidates may give correct predictions in the microscopic world of particle physics, but predict a universe which on its largest scales looks very different from the one we inhabit.

Like a messenger from the depths of time, the smallness – or absence – of the cosmological constant today is telling us something important about how to craft a correct Theory of Everything. It is a signpost of the way Nature’s symmetries are broken at low energy, and a nagging reminder that our understanding of the physical world is still incomplete in some fundamental way.

A LIKELY STORY

Most physicists expect the Theory of Everything will describe gravity the same way we now describe matter and the strong, weak and electromagnetic forces – in the language of quantum mechanics. Gravity is, after all, just another force in Nature. So far this has proven elusive, due in part to the sheer complexity of the equations of general relativity. Scientists since Einstein have described gravity ( as well as space and time) in purely geometric terms. Thus we speak of gravity as the “curvature of space-time”.

To acheive complete unification, the dialects of quantum matter and geometric space have to be combined into a single language. Matter appears to be rather precisely described in terms of the language of quantum mechanics. Quarks and electrons exchange force-carrying particles such as photons and gluons and thereby feel the electromagnetic and strong nuclear forces. But, gravity is described by Einstein’s theory of general relativity as a purely geometric phenomenon. These geometric ideas of curvature and the dimensionality of space have nothing to do with quantum mechanics.

To unify these two great foundations of physics, a common language must be found. This new language will take some getting used to. In it, the distinction between matter and space dissolves away and is lost completely; matter becomes a geometric phenomenon, and at the same time, space becomes an exotic form of matter.

Beginning with work on a quantum theory of gravity by John Wheeler and Bryce DeWitt in the 1960’s, and continuing with the so-called superstring theory of John Schwartz and Michael Green in the 1980’s, a primitive version of such a ‘quantum-geometric’ language is emerging. Not surprisingly, it borrows many ideas from ordinary quantum mechanics.

A basic concept in quantum mechanics is that every system of elementary particles is defined by a mathematical quantity called a wave function. This function can be used, for example, to predict the probability of finding an electron at a particular place and time within an atom. Rather than a single quantity, the wave function is actually a sum over an infinite number of factors or ‘states’, each representing a possible measurement outcome. Only one of these states can be observed at a time.

By direct analogy, in quantum gravitation, the geometry of space-time, whether flat or curved, is only one of an infinite variety of geometric shapes for space-time, and therefore the universe. All of these possibilities are described as separate states in the wave function for the universe.

But what determines the probability that the universe will have the particular geometry we now observe out of the infinitude of others? In quantum mechanics, the likelihood that an electron is located somewhere within an atom is determined by the external electric field acting on it. That field is usually provided by the protons in the atomic nucleus. Could there be some mysterious field ‘outside’ our universe that determines its probability?

According to Cambridge University theorist Stephen Hawking, this is the wrong way to look at the problem. Unlike the electron acted upon by protons, our universe is completely self-contained. It requires no outside conditions or fields to help define its probability. The likelihood that our universe looks the way it does depends only on the strengths of the fields within it.

Among these internal fields, there may even be ones that we haven’t yet discovered. Could the cosmological constant be the fingerprint in our universe of a new ‘hidden’ field in Nature? This new field could affect the likelihood of our universe just as a kettle of soup may contain unknown ingredients although we can still precisely determine the kettle’s mass.

A series of mathematical considerations led Hawking to deduce that the weaker the hidden field becomes, the smaller will be the value we observe for the cosmological constant, and surprisingly, the more likely will be the current geometry of the universe.

This, in turn, implies that if Lambda were big enough to measure by astronomers in the first place, our universe would be an improbable one. Philosophically, this may not trouble those who see our cosmos as absolutely unique, but in a world seemingly ruled by probability, a counter view is also possible. There may, in fact, exist an infinite number of universes, but only a minority of them have the correct blend of physical laws and physical conditions resembling our life-nurturing one.

Hawking continued his line of speculation by suggesting that, if at the so-called Planck scale of 10 to the power of -33 centimeters the cosmos could be thought of as an effervescent landscape, or “space-time foam”, then perhaps a natural mechanism could exist for eliminating the cosmological constant for good.

One of the curiosities of combining the speed of light and Newton’s constant of gravitation from general relativity, with Planck’s constant from quantum mechanics, is that they can be made to define unique values for length, time and energy. Physicists believe that at these Planck scales represented by 10 to the power of -33 centimeters and 10 to the power of -43 seconds, general relativity and quantum mechanics blend together to become a single, comprehensive theory of the physical world: The Theory Of Everything. The energy associated with this unification, 10 to the power of 19 billion electron volts, is almost unimaginably big by the standards of modern technology.

The universe itself, soon after the Big Bang, must also have passed through such scales of space, time and energy during its first instants of existence. Cosmologists refer to this period as the Planck Era. It marks the earliest times that physicists are able to explore the universe’s physical state without having a complete Theory of Everything to guide them.

WORMHOLES

Harvard University physicist Sidney Coleman has recently pursued this thought to a possible conclusion. Instead of some mysterious new field in Nature, maybe the Lambda term appears in our theories because we are using the wrong starting model for the geometry of space at the Planck scale.

Previous thinking on the structure of space-time had assumed that it behaved in some sense like a smooth rubber sheet. Under the action of matter and energy, space-time could be deformed into a variety of shapes, each a possible geometric state for the universe. Nearly all candidates for the Theory of Everything’s embed their fields and symmetries in such a smooth geometrical arena.

But what if space-time were far more complicated? One possibility is that ‘wormholes’ exist, filling space-time with a network of tunnels. The fabric of space-time may have more in common with a piece of Swiss cheese than with a smooth rubber sheet.

According to Coleman, the addition of wormholes to space-time means that, like the ripples from many stones tossed into a pond, one geometric state for the universe could interfere with another. The most likely states ( or the biggest ripples) would win out. The mathematics suggest that quantum wormhole interference at the Planck scale makes universes with cosmological constants other than zero exceedingly unlikely.

How big would wormholes have to be to have such dramatic repurcussions? Surprisingly, the calculations suggest that small is beautiful. Wormholes the size of dogs and planets would be very rare. Universes containing even a few of them would exist with a vanishingly low probability. But wormholes smaller than 10 to the power of -33 centimeters could be everywhere. A volume the size of a sugar cube might be teeming with uncounted trillions of them flashing in and out of existence!

Coleman proposes that the action of these previously ignored mini- wormholes upon the geometric fabric of the universe that forces Lambda to be almost exactly zero. Like quantum ‘Pac Men’, they gobble up all the latent energy of space-time that would otherwise have appeared to us in the form of a measureable cosmological constant!

The addition of wormholes to the description of space-time admits the possibility that our universe did not spring into being aloof and independent, but was influenced by how other space-times had already evolved – ghostly mathematical universes with which we can never communicate directly.

The most likely of these universes had Lambda near zero, and it is these states that beat out all other contenders. In a bizarre form of quantum democracy, our universe may have been forced to follow the majority, evolving into the high probability state we now observe, without a detectable cosmological constant.

EPILOG

Wormholes? Wave functions? Hidden fields? The answer to the cosmological constant’s smallness, or absence, seems to recede into the farthest reaches of abstract thinking, faster than most of us can catch up.

As ingenious as these new ideas may seem, the final pages in this unusual story have probably not been written, especially since we can’t put any of these ideas to a direct test. It is a tribute to Einstein’s genius that even his ‘biggest blunder’ made near the beginning of this century still plagues physicists and astronomers as we prepare to enter the 21st century. Who would ever have thought that something that may not even exist would lead to such enormous problems!

Astronomy, Physics

The Planck Era

The Planck Era

Written by Sten Odenwald. Copyright (C) 1984 Kalmbach Publishing. Reprinted by permission

The Big Bang theory says that the entire universe was created in a tremendous explosion about 20 billion years ago. The enormity of this event is hard to grasp and it seems natural to ask ourselves ‘What was it like then?’ and ‘What happened before the Big Bang?’. To try to answer these queries, lets take a brief journey backwards in time.
We first see the formation of our own sun about 15 billion years after the Big Bang and then by 5 billion years, the formation of the first galaxies. By 700,000 years, the universe is awash with the fireball radiation that keeps all matter at a temperature of 4,000 degrees. Because of this, darkness is completely absent since every point in the sky glows with the brilliance of the sun. No stars, planets or even dust grains exist, just a hot dense plasma of electrons, protons and helium nuclei. By 3 minutes, we see helium form from the fusion of hydrogen atoms while the universe seeths at a temperature of nearly 1 billion degrees. The average density of matter is that of lead. By 1 second, the Lepton Era ends and the ratio of neutrons to protons has become fixed at 1 neutron for every 5 protons. The temperature is now 5 billion degrees everywhere. At about .0001 second, we watch as the Quark Era ends and the temperature of the fireball radiation rises to an incredable 1 trillion degrees. Quarks, for the first time, can combine in groups of two and three to become neutrons, protons and other types of heavy particles. The universe is now packed with matter as densly as the nucleus of an atom. A mountain like Mt. Everest could be squeezed into a volume no greater than the size of a golf ball!

By 1 billionth of a second, the temperature is 1 thousand trillion degrees and we see the electromagnetic and weak forces merge into one force. The density of the universe has increased to the point where the entire earth could be contained in a thimble. Quarks and anti-quarks are no longer confined inside of particles like neutrons and protons but are now part of a superheated plasma of unbound particles. As the remaining history of the universe unfolds, a long period seems to pass when nothing really new happens. Then, at a time 10(-35) second after the Big Bang, a spectac ular change in the size of the universe occurs. This is the GUT Era when the strong nuclear force becomes distinguishable from the weak and electromagnetic forces. The temperature is an incredable 10 thousand trillion trillion degrees and the density of matter has sored to nearly 10(75) gm/cm3. This number is so enormous that even our analogies are almost beyond comprehension. At these densities, the entire Milky Way galaxy could easily be stuffed into a volume no larger than a single hydrogen atom! Electrons and quarks together with their anti-particles, were the major constituents of matter and very massive particles called Leptoquark Bosons caused the quarks to decay into electrons and vice versa. If we now move forward in time we would witness the vacuum of space undergoing a ‘phase transition’ from a higher energy state to a lower energy state. This is analogous to a ball rolling down the side of a mountain and coming to rest in the lowest valley. As the universe ‘rolls down hill’ it begins a brief but stupendous period of expansion. The universe swells to billions of times its former size in almost no time at all.

In addition to this, a slight excess of matter over anti-matter appears becaus of the decay of massive particles called X Higgs Bosons. As we continue to watch the universe age, the remaining pairs of particles and anti-particles find themselves and vanish in a tremendous burst of annihilation. From this paroxysm, the bulk of the fireball radiation that we now observe is born.

The GUT Era is the last stop in our fanciful journey through time. If we had asked what it was like before the GUT Era, we would immediately have entered a vast no mans land where few indisputable facts would serve to gui de us. What does seem clear is that gravity is destined to grow in importance, eventually becoming the dominant force acting between parti cles, even at the microscopic level.

G R A V I T Y

According to theories developed since the 1930’s, what we call a ‘force’ is actually a collective phenomenon caused by the exchange of innumerable, force-carrying particles called gauge bosons. The electromagnetic force, which causes like charges to attract and dissimilar ones to repel, is transmitted by gauge bosons called photons, the strong force that binds nucleii together is transmitted by gluons and the weak force which causes particles to decay is transmitted by the, recently discovered, W and Z Intermediate Vector Bosons. In an analogous way, physicists believe that gravity is transmitted by particles called Gravitons. If gravity really does have such a quantum property, its effects should appear once quarks and electrons can be forced to within 10(-33) centimeter of one another, a distance called the Planck length. To acheive these conditions, quarks and electrons will have to be collided at energies of 10(19) GeV. An accelerator patterned after the 2-mile, Stanford Linear Accelerator would have to be 1 light-year in length to push particles to these incredable energies! Fortunatly, what humans find impossible to do, Nature with its infinite resources finds less difficult. Before the universe was 10(-43) second old, matter routinely experienced collisions at these energies. This period is what we call the Planck Era.

THROUGH A LOOKING GLASS, DARKLEY

Since our technology will not allow us to physically reproduce the conditions during these ancient times, we must use our mathematical theories of how matter behaves to mentally explore what the universe was like then. We know that the appearence of the universe before 10(-43) second can only be adequatly described by modifying the Big Bang theory because this theory is, in turn, based on the General Theory of Relativity. General Relativity tells us how gravity operates on the macroscopic scale of planets, stars and galaxies. At the Planck scale, we need to extend General Relativity so that it includes not only the macroscopic properties of gravity but also is microscopic characteristics as well. The theory of ‘Quantum Gravity’ is still far from completion but physicists tend to agree that, at the very least, Quantum Gravity must combine the conceptual elements of the two great theories of modern physics: General Relativity and Quantum Mechanics.

In the language of General Relativity, gravity is a consequence of the deformati on of space caused by the presence of matter and energy. Gravity is just another name for the amount of curvature in the geometry of 3-dimensional space. In Quantum Gravity theory, gravity is produced by massless gravitons so that gravitons now represent individual packages of curved space that travel through space at the speed of light.

The appearence and dissappearence of innumerable gravitons gives the geometry of space a very lumpy and dynamic appearance. John Wheeler at Princeton University thinks of this as a foamy, sub-structure to space where the geometry of space twists and contorts so that far flung regions of space may suddenly find themselves connected by ‘wormholes’ which constantly appear and dissappear within 10(-43) seconds. Even as you are reading this article, this frenetic activity is occurring in the hyper-microscopic domain, 100 billion billion times smaller than the nucleus of an atom. For a comparison, the size of the sun and the size of a single atom stand in about this same proportion. Although Quantum Gravity effects are completely undetectable today at the atomic and nuclear scale, during the Planck Era, macroscopic and microscopic worlds merged and the Quantum Gravity of the microcosm suddenly became the Quantum Cosmology of the macrocosm!

QUANTUM COSMOLOGY

As we approach the end of the Planck Era, the random appearance and dissappearance of innumerable gravitons will eventually force us to give up the concept of a specific geometry to 3-dimensional space. Instead, the geometry at a given moment will have to be thought of as an average over all 3-dimensional space geometries that are possible. Once again, the reason for this is that particles are squeezed so closely together that we can now see individual gravitons moving around in the space between them causing space to become curved. We can no longer get away with saying that the space between two quarks, for example, is flat. This is what we mean when we say that the gravitational force between them is insignificant when compared to the other three forces of Nature.

To make matters much worse, not only will Quantum Gravity not allow us to calculate the exact 3-dimensional geometry to space but, at the Planck scale, it will not allow us to simultaneously determine its exact geometry and precise rate of change in time. What this means is that we may never be able to calculate with any certainty exactly what the history of the universe was like before 10-43 second. Today, the large-scale geometry of space is one of three possible types: flat and infinite, negatively curved and infinite or positively curved and finite. During the Planck Era, the ‘large-scale’ geometry was contorted by wormholes and and infinite number of possibilities were possible. To probe the history of the universe then would be like trying to trace your ancestral roots if every human being on earth had a possibility of being one of your parents. Now try to trace your family tree back a few generations! The farther back in time you go, the greater are the number of possible ancestors you could have had. An entirely new conception of what we mea n by ‘a history for the universe’ will have to be developed. Even the concepts of space and time will have to be completely re-evaluated in the face of the qua ntum fluctuations of spacetime at the Planck Era!

THE BIRTH OF THE UNIVERSE

The picture that seems to emerge from using our sketchy outline of what Quantum Gravity theory might look like is that as we approach the Planck Era, gravitons are exchanged between quarks and electrons with increasingly higher energy and in greater number. By the time we reach the end of the Planck Era at 10(-43) second, gravitons will begin to carry as much energy as the other force carriers (Gluons, IVBs and Photons). At still earlier times, a period of complet e symmetry and unification between all the natural forces will ensue. Only one super-unified force exists here (gravity) and only one kind of particle dominates the activity of this age(Gravitons).

During the early 70’s, the Russian physicists Ya. Zel’dovitch and A. Starobinski of the USSR Academy of Science proposed that the rapidly changing geometry of space during the Planck Era may actually have created all the matter, anti-matter and radiation that existed soon after Creation. In their picture of Creation, the rapidly changing geometry of space created particles and anti-particles with masses of 10(19) GeV. This production of matter and anti-matter removed energy from the enormous fluctuations occuring in the geometry of space and eventually succeeded in damping them out altogether by the end of the Planck Era. They also found that the rate of particle creation increased as more and more particles were created.

Several recent studies by Physicists Edward Tryon of Hunter College, R. Brout, F. Englert and E. Gunzig of the University of Brussels and david Atkatz and Heinz Pagels of the Rockefeller University have shed additional light on what Creation may have been like. Imagine if you can, nothing at all! This is the primordial vacuum of space. There is complete darkness here, no light yet exists. The number of dimensions to space was probably not the normal 3 that we are so accustomed to but may have been as high as 11 according to Supergravity theory! In this infinite emptiness, random fluctuations occurred that ever so slightly changed the energy of the vacuum at various points in space. Eventually, one of these fluctuations attained a critical energy and began to grow. As it grew, very massive particles called leptoquarks and anti-leptoquarks were created, causing the expansion to accelerate. This is much like a ball rolling down a hill that moves slowly at first and then gains momentum. The expansion of the proto-universe, in turn, caused still more leptoquarks to be created. This furious cycle continued until, at long last, the leptoquarks decayed into quarks, leptons (electrons, muons etc) and their anti-particles and the universe emerged from the Planck Era. Particle creation stopped once the fluctuations in the geometry of space subsided.

So, we are left with the remarkable possibility that, in the beginning, there ex isted quite literally, nothing at all and from it emerged nearly all of the matter and radiation that we now see. This process has been described by the physicist Frank Wilczyk at the University of California, Santa Barbara by saying, ” The reason that there is something instead of nothing is that nothing is unstable”. A ball sitting on the summit of a steep hill needs but the slightest tap to set it in motion. A random fluctuation in space was apparently all that was required to unleash the incredable latent energy of the vacuum, thus creating matter and energy and an expanding universe from ‘nothing at all’.

The universe did not spring into being instantaneously but was created a little bit at a time in a ‘bootstrap’ process. Once a few particles were created by quantum fluctuations of the empty vacuum, it became easier for a few more to appear and so, in a rapidly escalating process, the universe gushed forth from nothingness.

How long did this take? The primordial vacuum could have existed for an eternity before the particular fluctuation that gave rise to our universe happened. Physicist Edward Tryon expresses this best by saying that ” Our universe is simply one of those things that happens from time to time”.

The principles of Quantum Gravity may ultimatly force us to reconsider questions like ‘What happened before the Big Bang?’ because they imply the existence of something (time) that may not have any meaning at all. These questions may be as empty of meaning as an explorer on the north pole asking, ‘Which way is North?’. Only the complete theory of Quantum Gravity may tell us how to ask the right questions!

Astronomy, Physics

What is Space? Part II

Space-Time: The Final Frontier

Written by Sten Odenwald. Copyright (C) 1995 Sky Publishing Corporation. See February 1996 issue.
THE NIGHT SKY, when you think about it, is one of the strangest sights imaginable. The pinpoint stars that catch your eye are all but swallowed up by the black nothingness of space – an entity billions of light-years deep with which we here on Earth have no direct ex- perience.
What is empty space, really? At first the question seems silly. There’s nothing to it! But look again in light of what modern physics knows and suspects, and the nature of space emerges as one of the most important “sleeper” issues growing for the last 50 years. “Nature abhors a vacuum,” proclaimed Aristotle more than 2,300 years ago. Today physicists are discovering that this is true in ways the ancient Greeks could never have imagined.

True, the cosmos consists overwhelmingly of vacuum. Yet vacuum itself is proving not to be empty at all. It is much more complex than most people would guess. “But surely,” you might ask, “if you take a container and remove everything from inside it – every atom, every photon – there will be nothing left?” Not by a long shot. Since the 1920s physicists have recognized that on a microscopic scale, the vacuum itself is alive with activity. Moreover, this network of activity may extend right down to include the very structure of space-time itself. The fine structure of the vacuum may ultimately hold the keys to some of the deepest questions facing physics – from why elementary particles have the properties they do, to the cause of the Big Bang and the likelihood of other universes outside our own.

THINGS THAT GO BUMP IN THE DARK

The state of the art in physics – our deepest current understanding of the world – is embodied in the so-called Standard Model, in which all matter and forces are accounted for by an astonishingly few types of particles (see Sky & Telescope – December 1987, page 582). Six quarks and six leptons make up all possible forms of matter. In practice just two of the quarks (the up and down) and one lepton (the electron) account for everything in the world except for a few whiffs of exotica known only to high-energy physicists. The 12 particles of matter (and their 12 corresponding particles of antimatter, or antiparticles) are acted upon by “messenger particles” that carry all the known forces. The photon mediates the electromagnetic force, including all the familiar chemical and structural forces around us on Earth. The members of the gluon family carry the strong force that binds neutrons and protons together in atomic nuclei. The W’, W-, and Zo mediate the weak nuclear force, and the as-yet-undiscovered graviton is believed to carry the force of gravity.

Every possible event involving the 12 matter particles can be completely explained as an exchange of messenger particles. During some of these events, for example when electrons accelerate in a radio-transmitter antenna, messenger particles (in this case photons) materialize and travel through space. At other times, however, the messengers remain almost entirely hidden within the interacting system. When the messengers exist in this hidden form, they are called “virtual particles.” Virtual particles may seem ghostly and unreal by everyday standards. But real they are. Moreover, they are not limited to their role of mediating interactions. Virtual particles can also pop in and out of empty space all by themselves.

Quantum mechanics, the rulebook of the Standard Model, states as a bedrock principle that you need a certain length of time to measure a particle’s energy or mass to a given degree of accuracy. The shorter the observation time, the more uncertain the measurement. If the time is very brief, the uncertainty becomes larger than the particie’s entire mass, and you cannot say whether or not the particle is there at all. The lighter the particle, the longer its uncertainty time. In the case of an electron-positron pair, the uncertainty time scale is about 10^-21″ seconds.

On time scales shorter than this, virtual electrons and positrons can, and do, pop in and out of nothingness like peas in a shell game. It’s as if, just because you can’t say a particle doesn’t exist when you look very briefly, then in a sense it does. This is not mere theorizing. In 1958 a tabletop experiment demonstrated the “Casimir effect,” measuring the force caused by virtual particles appearing and vanishing in total vacuum through the attraction they caused between two parallel metal plates. If the vacuum were truly empty the plates should not have attracted, but the incessant dance of virtual particles in the space between them produces a detectable effect.

Every particle – matter as well as messenger – seems to display a virtual form, each seething in greater or lesser abundances in what physicists call the “physical vacuum.” When it comes to affecting the ordinary world, moreover, virtual particles may do much more than just mediate forces. Some, in fact, may cause matter to have the property we call mass. The electron is the simplest of matter particles. Our knowledge of the physical world rests upon a solid understanding of its properties. Yet despite its abundance in the circuitry around us, the electron harbors an enigma. The fact that it has mass cannot be explained in the Standard Model, at least the parts of it that have been experimentally verified. More than 30 years ago particle physicist Peter Higgs suggested that the existence of mass has to do with a new ingredient of nature that is now called the Higgs field, which provides a new type of messenger particle that interacts with the electron to make it “weigh.”

The Higgs field has yet to be discovered, but many physicists expect it to exist everywhere in the physical vacuum, ensuring through its interactions with electrons and other particles that they will display mass. Even now, particle accelerators at CERN in Switzerland and at Fermilab near Chicago are straining at their maximum capabilities to cause just one “Higgs boson,” the presumed messenger particle for this field, to break loose from the vacuum and leave a detectable trace. Success would provide a triumphant completion of the Standard Model.

So to answer our question about whether a container of empty space is truly empty, the best anyone can do is remove the normal, physical particles that nature allows us to see and manipulate. The virtual particles can never be evicted. And in addition there may exist the ever-present Higgs field.

QUANTUM GRAVITY

For most of this century, physicists have struggled to bring gravity into the scheme of forces that are mediated by virtual messenger particles. To put this another way, the theory of general relativity, which shows the force of gravity to be a curvature of space-time, needs to be integrated with quantum mechanics, which shows forces to be virtual particle exchanges. Working on the assumption that such a marriage is possible, physicists named gravity’s messenger particle the graviton. But general relativity requires that gravitons be more than just quanta of gravity. In essence, gravitons define the structure of space-time itself.

The reconciliation of quantum mechanics and general relativity may lead us to dramatically new notions of the nature of space and time. Some theorists have suggested that points in space-time become defined only when a particle (such as a graviton or photon) interacts with other particles. In this view, what they are doing between interactions is a nonphysical question, since only an interaction defines a measurable time and place. Gravitational forces (and thus gravitons) exert an influence at distances much larger than the subatomic realm, as anyone who has fallen down a flight of stairs can attest. But only at an extremely small scale – the Planck length of 10^-33 centimeters – does the quantum nature of gravity become important.

Suppose you could magically look through a microscope that magnified an atomic nucleus to be some 10 light-years across. Under this magnification the smallest gravitons – that is, the most energetic and massive ones – would be about a millimeter in size. Here we might see a strange world in which space-time itself was defined by gravitons intersecting and looping around each other. In a similar vein, Roger Penrose has suggested that the gravitational field and space-time are built up from still more primitive mathematical entities called twistors, and that “ultimately the [space-time] concept may possibly be eliminated from the basis of physical theory altogether.” In essence, space and time become factored out as less- than-fundamental parts of the physical world.

In such a view, only the interactions between twistors, or perhaps gravitons, define when and where space-time is and is not. Are there gaps in the physical vacuum, voids of true and absolute nothing where space and time themselves do not exist?

Another viewpoint on the structure of space-time is offered by “superstring theory.” String theories posit that the fundamental objects of nature are one-dimensional lines rather than points; the “elementary” particles we measure are only oscillations of these strings. Superstring theory only seems to work, however, if space-time has not just four dimensions (three of space and one of time), but 10 dimensions. This hardly seems like the world we live in. To hide the extra six dimensions, mathematicians roll them up into conceptual corners that go by such cryptic names as “Calabi-Yau manifolds” and “orbifold space.” A recent textbook on the subject concludes on a wistful note that “if the string idea is correct, we may never catch more than a glimpse of the full ex- tent of reality.”

More recently, theorists Carlo Rovelli (University of Pittsburgh) and Lee Smolin (Pennsylvania State University) completed their analysis of a quantum gravity model developed by Abhay Ashtekar at Syracuse University in 1985. Unlike string theory, Ashtekar’s work applies only to gravity. However, it posits that at the Planck scale, space-time dissolves into a network of “loops” that are held together by knots. Somewhat like a chain-mail coat used by knights of yore, space-time resembles a fabric fashioned in four dimensions from these tiny one-dimensional loops and knots of energy.

Is this the way the world really is on its most fundamental level, or have mathematicians become detached from reality? Superstring theory has enticed physicists for over a decade now because it hints at a super unification of all four fundamental forces of nature. But it remains frustratingly hard to plant anchors down from these cloud castles into the real world of observation and experiment. The famous remark that superstring theory is “a piece of 21st- century physics that accidentally fell into the 20th century” captures both the excitement and frustration of workers stuck with 20th-century tools.

Surprisingly, string theory, Ashtekar’s loopy space-time, and twistors are not entirely independent ways of looking at space-time. In 1986 theorists discovered that superstrings have some things in common with twistors. A deep connection had been uncovered between two very different, independent theories. Like two teams of tunnelers starting on opposite sides of a mountain, they had met at the middle – a sign, perhaps, that they are dealing with a single real mountain, not separate ones in their own imaginations. And in 1995 Rovelli and Smolin also found that their graviton loops are very closely related to both the twistors and superstrings, though not identical in all respects.

THE COSMIC CONNECTION

Space-time could be strange in other ways too. Theorist John A. Wheeler (In- stitute for Advanced Study) has long advocated that at the Planck scale, space-time has a complex shape that changes from instant to instant. Wheeler called his picture “space-time foam” – a sea of quantum black holes and worm holes appearing and vanishing on a time scale of about 10^-43″ seconds. This is the Planck time, the time it takes light to cross the Planck length. Shorter than that, time, like space, presumably cannot exist – or, at least, our everyday notions of them cease to be valid.

Wheeler’s idea of space-time foam is a natural extrapolation from the idea of virtual particles. According to quantum mechanics, the higher the energy and mass of a particle, the smaller it must appear. A virtual particle as small as 10^-33″ cm, lasting only 10^-43 second, has so great a mass (10^-5 gram) in such a tiny volume that its own surface gravity would give it an escape velocity greater than the speed of light. In other words, it is a tiny black hole. But a black hole is not an ordinary object sitting in space- time like a particle; it is a structure of distorted, convoluted space-time itself. Although the consequences of such phe- nomena are not understood, it is rea- sonable to assume that these virtual par- ticles dramatically distort all space-time at the Planck scale.

If we take this reasoning at face value, and consider the decades-old experiments proving that the virtual particle phenomenon in a vacuum is real, it is hard to believe that space-time is smooth at or below the Planck scale. Space must be broken up and quantized. The only question is how. Wheeler’s original idea of space-time foam is especially potent because according to recent proposals by Sidney Coleman (Harvard) and Stephen Hawking (Cambridge University), its worm holes not only connect different points very close together within our space-time, but connect our space-time to other universes that, as far as we are concerned, exist only as ghostly probabilities. These connections to other universes cause the so-called cosmological constant – an annoying intrusion into the equations of cosmology ever since Einstein (see Sky & Telescope- April 1991, page 362) – to neatly vanish within our own universe.

Space-time foam has also been implicated as the spawning ground for baby universes. In several theories explaining the cause of the Big Bang and what came before, big bangs can bud off from a previously existing space-time, break away completely while still microscopic, and inflate with matter to become new universes of their own, completely disconnected (“disjoint”) from their space- time of origin. This process, proposed by Alan Guth (MIT) and others, gives a handle on what many expect to be another key issue of 21st-century physics: was our Big Bang unique? Or was it just a routine spinoff of natural processes happening all the time in some larger, outside realm? (see Sky & Telescope- September 1988, page 253).

Yet there are problems. The amount of latent energy in the quantum fluctuations of space-time foam is staggering: 10^105 ergs per cubic centimeter. This amounts to 10 billion billion times the mass of all the galaxies in the observ- able universe – packed into every cubic centimeter! Fortunately, Mother Nature seems to have devised some means of exactly canceling out this phenomenon to an accuracy of about 120 decimal places. The problem is that we haven’t a clue how.

It’s unnerving to think that in the 16 inches separating this page from your eyes, new big bangs are perhaps being spawned out and away from our quiet space-time every instant. By comparison, it seems positively dull that the photons by which you see this page might be playing a hop-scotch game to avoid gaps where space-time doesn’t exist.

REALITY CHECK

Some physicists have begun to throw cold water on these fantastic ideas. For instance, in 1993 Matt Visser (Washington University) studied the mathematical properties of quantum worm holes and discovered that, once they are formed, they become stable: they can’t foam at all. Kazuo Ghoroku (Fukuoka Institute of Technology, Japan) also found that quantum worm holes become stable even when their interactions with other fields are considered. What Wheeler called space-time foam may be something else entirely.

Among the unresolved problems facing theorists is the nature of time, which has been recognized as inextricably bound up with space ever since Einstein posited a constant speed for light. In general relativity, it isn’t always obvious how to define what we mean by time, especially at the Planck scale where time seems to lose its conventional meaning. Central to any quantum theory is the concept of measurement, but what does this imply for physics at the Planck scale, which sets an ultimate limit to the possibility of measurement? How any of these ideas about space- time can be tested is currently unknown. Some physicists believe this makes these ideas not real scientific inquiry at all. And it’s worth remembering that mathematics can sometimes introduce concepts that are only a means to an end and have no independent reality.

In the abstract world of mathematical symbolism, it isn’t always clear what is real and what’s not. For example, when we do long division on paper to divide 54,162 by 2 to get 27,081, we generate the intermediate numbers 14, 16, and 2, which we then just throw away. Are virtual particles, compact 6-dimensional manifolds, and twistors simply nonphysical means to an end – mere artifacts of how we humans do our mathematics? Particle physicists often have to deal with “ghost fields” that are simply the temporary scaffolding used for calculations, and that vanish when the calculations are complete. Nonphysical devices such as negative probability and faster- than-light tachyon particles are grudgingly tolerated so long as they disappear before the final answers. Even in super- string theory, recent work suggests that it may be possible to build consistent models entirely within ordinary four-dimensional space-time, without recourse to higher dimensions.

ANGEL FOOD CAKE

So, how should we think of the great, dark void that we gaze into at night? All clues point to space-time being a kind of layer cake of busy phenomena on the submicroscopic scale. The topmost layer contains the quarks and electrons comprising ordinary matter, scattered here and there like raisins in the frosting. These raisins can be plucked away to make a region of space appear empty. The frosting itself consists of virtual particles, primarily those carrying the electromagnetic, weak, and strong forces, filling the vacuum with incessant activity that can never be switched off. Their quantum comings and goings may completely fill space-time so that no points are ever really missing. This layer of the cake of “empty space” seems pretty well established by laboratory experiment.

Beneath this layer we have the domain of the putative Higgs field. No matter where the electron and quark “raisins” go, in this view, there is always a piece of the Higgs field nearby to affect them and give them mass. Below the Higgs layer there may exist other layers, representing fields we have yet to discover. But eventually we arrive at the lowest stratum, that of the gravitational field. There is more of this field wherever mass is present in the layers above it, but there is no place where it is entirely absent. This layer recalls the Babylonian Great Turtle that carried the universe on its back. Without it, all the other layers above would vanish into nothingness.

We know that space-time is quite smooth down to at least the scale of the electron, 10^-20 cm – 10 million times smaller than an atomic nucleus. This is the size limit set for any internal component of the electron, based on careful comparisons between experiment and the predictions of quantum electrodynamics. But near the Planck horizon of 10^-33 cm, space-time must change its structure drastically. It may be a world in which conventional notions of dimensionality, time, and space need to be redefined and possibly eliminated altogether.

The conceit of our universe’s uniqueness may disappear, with big bangs becoming viewed as run-of-the-mill events in some much larger outside realm, and with physical constants being attributed to causes in space-times forever beyond human experience.

There is much that’s spooky about the physical vacuum. This spookiness may be rooted more in the way our brains work than in some objective aspect of nature. Einstein stressed, “Space and time are not conditions in which we live, but modes in which we think.” Our understanding of space remains in its infancy. With Aristotle smiling at us down the centuries, we now see the vacuum as much more than a vacancy. It will take many decades, if not centuries, before a complete understanding of it is fashioned. In the meantime, enjoy the nighttime view!

FURTHER READING

Davies, Paul. The New Physics. Cambridge: Cambridge University Press, 1989.

Mallove, Eugene. “The Self-Reproducing Universe.” Sky & Telescope, September 1988, page 253.

Matthews, Robert. “Nothing Like a Vacuum.” New Scientist, February 25, 1995, page 30.

Pagels, Heinz. “Perfect Symmetry.” New York: Simon & Schuster, 1985.