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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!

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.

The End of Physics?

For 45 years I have followed the great pageant of ideas in theoretical physics. From high school through retirement, although my career and expertise is in astronomy and astrophysics, my passion has always been in following the glorious ideas that have swirled around in theoretical physics. I watched as the quark theory of the 1960s gave way to Grand Unification Theory in the 1970s, and then to string theory and inflationary cosmology in the 1980s. I was thrilled by how these ideas could be applied to understanding the earliest moments in the Big Bang and perhaps let me catch at least a mathematical glimpse of how the universe, time and space came to be literally out of Nothing; explanations not forthcoming from within Einstein’s theory of general relativity.

Even as recently as 2012 this story continued to captivate me even as I grappled with what might be the premature end of my life at the hands of non-Hodgkins Lymphoma diagnosed in 2008. And still I read the journal articles, watching as new ideas emerged, built upon the theoretical successes of the 1990s and beyond. But then a strange thing happened.

In the 1980s, the US embarked on the construction in Texas of the Superconducting Super Collider, but that project was scrapped and de-funded by Congress after ¼ of it had been built. Attention then turned to the European Large Hadron Collider project, which after 10 years finally achieved its first collisions in 2009. The energy of this accelerator has steadily been increased to 13 TeV, and now records some 600 million collisions per second, which generates 30 petabytes of data per year. Among these collisions were expected to be the traces of ‘new physics’, and physicists were not dissappointed. In 2012 the elusive Higgs Boson was detected some 50 years after it was predicted to exist. It was a major discovery that signaled we were definitely on the right track in verifying the Standard Model. But since then, following many more years of searching among the debris of trillions of collisions, all we continue to see are the successful predictions of the Standard Model confirmed again and again with only a few caveats.

Typically, physicists push experiments to ever-higher degrees of accuracy to uncover where our current theoretical model predictions are becoming thread-bare, revealing signs of new phenomena or particles, hence the term ‘new physics’. Theoreticians then use this anomalous data to extend known ideas into a larger arena, and always select new ideas that are the simplest-possible extensions of the older ideas. But sometimes you have to incorporate entirely new ideas. This happened when Einstein developed relativity, which was a ‘beautiful’ extension of the older and simpler Newtonian Physics. Ultimately it is the data that leads the way, and if not available, we get to argue over whose theory is more mathematically beautiful or elegant.

Today we have one such elegant contender for extending the Standard Model that involves a new symmetry in Nature called supersymmetry. Discovered mathematically in the mid-1970s, it showed how the particles in the Standard Model that account for matter (quarks, electrons) are related to the force-carrying particles (e.g. photons, gluons), but also offered an integrated role for gravity as a new kind of force-particle. The hitch was that to make the mathematics work so that it did not answer ‘infinity’ every time you did a calculation, you had to add a whole new family of super-heavy particles to the list of elementary particles. Many versions of ‘Minimally Supersymmetric Standard Models’ or MSSM’s were possible, but most agreed that starting at a mass of about 1000 times that of a proton (1 TeV), you would start to see the smallest of these particles as ‘low-hanging fruit’, like the tip of an upside-down pyramid.

For the last seven years of LHC operation, using a variety of techniques and sophisticated detectors, absolutely no sign of supersymmetry has yet to be found. In April, 2017 at the Moriond Conference, physicists with the ATLAS Experiment at CERN presented their first results examining the combined 2015 – 2016 LHC data. This new dataset was almost three times larger than what was available at the last major particle physics conference held in 2016. Searches for the supersymmetric partners to quarks and gluons (called squarks and gluinos) turned up nothing below a mass of 2 TeV. There was no evidence for exotic supersymmetric matter at masses below 6 TeV, and no heavy partner to the W-boson was found below 5 TeV.

Perhaps the worst result for me as an astronomer is for dark matter. The MSSM model, the simplest extension of the Standard Model with supersymmetry, predicted the existence of several very low mass particles called neutralinos. When added to cosmological models, neutralinos seem to account for the existence of dark matter, which occupies 27% of the gravitating stuff in the universe and controls the movement of ordinary matter as it forms galaxies and stars. MSSM gives astronomers a tidy way to explain dark matter and closes the book on what it is likely to be. Unfortunately the LHC has found no evidence for light-weight neutralinos at their expected MSSM mass ranges. (see for example https://arxiv.org/abs/1608.00872 or https://arxiv.org/abs/1605.04608)

Of course the searches will continue as the LHC remains our best tool for exploring these energies well into the 2030s. But if past is prologue, the news isn’t very promising. Typically the greatest discoveries of any new technology are made within the first decade of operation. The LHC is well on its way to ending its first decade with ‘only’ the Higgs boson as a prize. It was fully intended that the LHC would have given us hard evidence by now for literally dozens of new super-heavy particles, and a definitive candidate for dark matter to clean up the cosmological inventory.

So this is my reason for feeling sad. If the Higgs boson is a guide, it may take us several more decades and a whole new and expensive LHC replacement to find something significant to affirm our current ‘beautiful’ ideas about the physical nature of the universe. Supersymmetry may still play a role in this but it will be hard to attract a new generation of young physicists to its search if Nature continues to withhold so much as a hint we are on the right theoretical track.

If supersymmetry falls string theory, which hinges on supersymmetry, may also have to be put aside or re-thought. Nature seems to favor simple theories over complex ones so are the current string theories with supersymmetry really the simplest ones?

Thousands of physicists have toiled over these ideas since the 1970s. In the past, such a herculean effort usually won-out with Nature rewarding the tedious intellectual work, and some vestiges of the effort being salvaged for the new theory. I find it hard to believe that will not again be the case this time, but as I prepare for retirement I am realizing that I may not be around to see this final vindication.

So what should I make of my 45-year intellectual obsession to keep up with this research? Given what I know today would I have done things differently? Would I have taught fewer classes on this subject, or written fewer articles for popular science magazines?

Absolutely not!

I have thoroughly enjoyed the thrill of the new ideas about matter, space, time and dimension. The Multiverse idea offered me a new way of experiencing my place in ‘reality’. I could never have invented these amazing ideas on my own, which have entertained me for most of my professional life. Even today’s Nature seems to have handed us something new: Gravity waves have been detected after a 60-year search; detailed studies of the cosmic ‘fireball’ radiation are giving us hints to the earliest moments in the Big Bang; and of course we have discovered THOUSANDS of new planets.

Living in this new world seems almost as intellectually stimulating, and now offer me more immediate returns on my investment in the years remaining.

Eclipse!!!

In nine weeks, on August 17, 2017, residents of the continental United States will be treated to a total solar eclipse as they enjoy their noon-time repast. If you are standing along the line of totality, which stretches from Oregon’s Pacific coast to South Carolina’s Atlantic surf, and if you have a good telescope, you may even be treated to a view such as the one below photographed by Luc Viatour ( www.Lucnix.be) during the August 1999 total solar eclipse over France!

In this blog, I am going to mention some of the work I am doing to help the public enjoy this once-in-a-lifetime event through my various projects at NASA. NASA, as part of its informal education programs, has adopted this event as a major national PR effort to focus its many assets on the ground and in space. In early-2016, my group at the NASA Goddard Spaceflight Center called the Heliophysics Education Consortium (HEC) was asked to lead the charge organize this event. Led by Dr. Alex Young, the HEC team has created the Official Eclipse website, and I have had the great pleasure and honor to have written many of its resources. So, think of this Blog as an introduction to the What, Where, When and How of this eclipse, and a personal tour by me for how you can enjoy this rare and magnificent event!

First, you probably have a lot of questions about solar eclipses, so I wrote a FAQ Page that covers most of the common ones. I also wrote an essay about the many Eclipse Misconceptions that people have had about solar eclipses. Some are quite bizarre, but seem to be passed on from generation to generation despite our deep scientific understanding of them!

Take a look at the picture at the top of this blog. During most total eclipses of the sun, you are guaranteed to see the brilliant solar corona. With a telescope or a good telephoto lens, you may even glimpse the reddish hue of the solar chromosphere following along the darkened limb of the moon. Here and there, you may even see a solar prominence also glowing in reddish light. These features are hard to see because they are rather small and with the naked eye you just don’t have the natural magnification to see them well.

I will be writing a number of  essays that discuss particular aspects of the sun and post them at the Eclipse SCIENCE page. Topics will include the corona, prominences, chromosphere and the dramatic helmet streamers  so far as astronomers understand them today. It’s all about solar magnetism and how this interacts with the 100,000 degree plasma in the solar atmosphere. The corona, itself, has a temperature of several million degrees! It is about a million times fainter than the disk of the sun, which is why you only get to see it during an eclipse. But astronomers can use instruments called coronagraphs to artificially eclipse the sun, and allow us to study coronal features at our leisure.

There are many things you can do while waiting for the eclipse to start, and a few non-invasive things you can do while the eclipse is in progress. I have tried to collect these ideas into two areas called Citizen Explorers and Citizen Scientists depending on how serious you want to be in exploring eclipses. If you have a mathematical mind, I have even created a dozen or so curious Math Challenges that help you look at many different aspects of the event.

Just about everyone is going to want to use their smartphones to photograph the eclipse, so in my article on Smartphone Photography I try to outline some of the things you can do, what kinds of technology you need like inexpensive telephoto lenses, and what to expect. Below is a photo taken by a smartphone with no other technology from Longyearbyen, Svalbard in 2015. Your camera phone will give you a brilliant, over-exposed corona but don’t expect detailed resolution because your lens is simply not good enough to show details like those in the photo above. If you use an inexpensive smartphone telephoto with 15x or higher, you need a camera tripod too. Also, be careful that you do not use the telephoto on the sun while the brilliant photosphere is visible to avoid camera damage. (Credit: Stan Honda/AFP/Getty Images)

Some people may be interested in uploading their images, and in my essay on Geotagging I describe two ways that you can upload your selfies so that others can enjoy your efforts. The first is to use GOOGLE Maps but you can only upload your photo to  preexisting ‘tagged’ locations in GOOGLE Maps (nearby businesses, monuments, parks, etc). This is unlike the discontinued Panoramio/GOOGLE Earth feature where you could upload your picture to any geographic location on the planet. The second way is to send your pictures to a NASA site that is collecting them.

For a rare event like this, you might also want to create a time capsule of your experience. I have suggested that you write a letter to yourself about who you are today, and what you think the future holds for you. On April 8, 2024 there will be another total solar eclipse across the continental United States and you might set that date as the time when you next read your letter being at that time 7 years older!

People have observed total solar eclipses for centuries, and in my Eclipse History area I have a number of essays that describe earlier observations in the United States. There is even an archive of newspaper articles since the early 1800s in which you can read  first-hand accounts. Some music has also been written and performed with solar eclipses in mind! In my Music Page I list many of these pieces both in classical and pop music over the years. Who can forget Carly Simon’s ‘…You flew your Lear Jet to Nova Scotia to see the total eclipse of the sun’ about the March 7, 1970 eclipse!

One thing I find interesting is that since the 1500s there have been over a dozen eclipse paths that have crossed the one for August 21, 2017. I created several resources that describe these ‘magical’ crossing points and what history was going on in North America during these dates. I also created a set of math problems where you can calculate the latitude and longitude for these crossing points  if you are in-to math!

Where should you go to see this eclipse? In one essay I discussed how  there are dozens of airline flights on that day from which passengers may be able to see the total solar eclipse out their windows if the Captain gets you to the right place and time along the route. For folks on the ground, you can check out NASA’s Path of Totality maps and see if your travels on that day take you anywhere close. For the rest of us, no matter where you are in North America, you will at least see a partial solar eclipse where a small ‘bite’ is taken out of the solar disk. With a pair of welder’s goggles or solar viewing glasses, you can look up anytime around noon and see the eclipse in progress.

Created with GIMP

NASA plans to collect stunning images from some of its available spacecraft, so on this page I collected information about which spacecraft will participate. After the eclipse, you will see in the News Media many of these images as they are produced during the days after the event.

Myself, I will be joining the NASA Eclipse Team in Carbondale, Illinois for a huge public celebration of the total solar eclipse. This will be televised through numerous NASA feeds all along the path of the eclipse so you can view it on your smartphone or laptop screen wherever you are. I will be involved with this telecast between 11:45 and 1:45 CDT as a panelist on several of the program segments. When I return from this event, or perhaps even during it, I will upload a follow-up blog about what it was like from ‘Ground Zero’. I have never experienced a total solar eclipse before, so I am prepared to be stunned and amazed!

Stay tuned!

Exoplanets Galore!

The year was 2001 – The first of the new millennium. It was also the year astronomers reached a historic milestone: They had catalogued more planets orbiting distant stars than the eight we knew about in our own solar system!

The first of these was discovered in 1988: A Jupiter-sized world orbiting the star Gamma Cephi A at a distance of 45 light years from our sun. Since then, well over 3,600 ‘exo’planets have been discovered using many different detection methods both on the ground and in space. We are truly living in a very different age than we experienced only a few short decades ago. We no longer have to speculate whether other planetary systems exist across the universe. We now have the technology and a growing catalog of examples to prove our solar system is not alone in the universe!

One of these detection methods is the Transit Method. As a planet passes in front of its star as viewed from Earth, the brightness of the star dims by an amount equal to the ratio of the planet’s circular area to the star’s circular area. For example, a Jupiter-sized planet has a diameter of 143,000 km while a sun-like star has a diameter of 1.4 million km, so the ratio of their areas is 1/100. As this exoplanet transits the disk of its star as viewed from Earth, the brightness of the star will dim by 1%. By measuring the time between successive transit ‘dips’ you can deduce the orbit period of the planet. From the orbit period and the mass of the star you also obtain the distance between the star and the planet. Once you have this information, you can estimate the surface temperature of the planet and its average density (rocky planet or gas giant). In the example below, the orbit period is 4.887 days and from the amount of dimming ( 0.7%) the ratio of their areas is 1/142, and planet’s diameter is 1/12 the diameter of its star.

To take advantage of the transit method on a large scale, NASA launched the Kepler Observatory in 2009. Using a super-sensitive digital camera, it took a picture of the same star field in the constellation Cygnus every minute and captured brightness information for over 150,000 stars similar to our sun. Over the course of its survey, now in its eighth year, it has discovered 4,496 exoplanet candidates of which 2,335 have been verified by independent study. These statistics now show that virtually all stars in the sky have at least one planet in orbit around them, and about 1 in 20 have Earth-sized worlds!

What was entirely unexpected was the diversity of exoplanet types, and orbits about their parent stars. Our solar system offered as templates the small rocky Earth-sized worlds of the inner solar system, the two gas giants (Jupiter and Saturn) and the two ice giants (Uranus and Neptune), but among the thousands of worlds discovered so far, a vaster array of possibilities have been found.

There are super-Earths over three times as large as our world apparently fully covered by deep oceans (Kepler 22b). There are hot-Jupiters that orbit their stars in a matter of hours, and swelter at temperatures of thousands of degrees (51 Pegasi b). Some planets have ‘water cycles’ in which silicate rock evaporates from their surfaces, condenses in clouds, and then rains droplets of lava back to the surface (COROT-7b, Alpha Centauri Bb, Kepler 10b). The cloud-shrouded super-Earth GJ 1214b is so hot that its clouds could be made of zinc sulfide and potassium chloride! One exoplanet is so close to its star that it is literally evaporating before our eyes, leaving a huge comet-like tail of gas in its orbital wake (HD 221458b).

The thousands of exoplanets detected by the transit method are especially intriguing. From Earth, as the exoplanet passes in front of its star, some of the starlight passes through the exoplanet’s atmosphere. Various gases in the atmosphere absorb selected wavelengths of this light and leave their unique fingerprints behind for distant astronomers using spectroscopes to study. So far among the dozen or so worlds examined, atmospheres rich in water vapor, carbon dioxide, methane, sulfur and other common molecules have already been found. This figure shows the spectrum of the exoplanet Wasp-19b and signs of methane (CH4) and hydrogen cyanide (HCN) – a lethal mixture for humans to breathe! Future ground and space-based observatories will be able to detect the molecules in thousands of exoplanet atmospheres, but this is no idle scientific pursuit. Living systems on a planetary scale sculpt their atmospheres by creating free molecular oxygen, so if we ever detect an exoplanet atmosphere rich in oxygen, it will be a major discovery of life in the cosmos beyond our own Earth.

Another aspect of the search for Earth-like worlds is to find exoplanets about as large as Earth that orbit their stars in what is called the Habitable Zone (HZ). In this range of orbital distances from the exoplanet’s star, the surface temperatures would allow liquid water to exist. In our solar system, this zone is located between the orbits of Venus and Mars, and Earth is smack in the middle of it. Currently, the various surveys have identified 13 exoplanets that are not only Earth-sized but are within their star’s HZ. The closest of these is GJ 273b at a distance of 12 light years! But there are complicating factors to finding an exact twin to our Earth upon which we might also hope to discover a living biosphere.

If a planet in the HZ has too much carbon dioxide – a potent greenhouse gas – its temperature would be more Venus-like and it would be a desert world or worse. If the exoplanet had significant traces of common gases such as hydrogen cyanide or methane, it would be unbreathable for humans though some extremophile bacteria on Earth thrive in such environments.

Another thing to think about is that an Earth-like world could be in orbit around a Jupiter-sized exoplanet in its star’s HZ. Even though we do not directly see the Earth-sized world there could be several of them as satellite worlds of larger exoplanets. The Jupiter-sized exoplanet WASP-12b appears to have an ‘exomoon’ with several times the mass of Earth. We know of hundreds of Jupiter-sized exoplanets orbiting in the habitable zones of their stars. We can no longer discount the possibility that their exomoons may be Earth-like though currently undetectable.

So far we have had to detect and study exoplanets indirectly from transit and spectroscopic data, but in a growing number of cases we can actually directly see these worlds as they spin around their stars. In 2008, the bright star Fomalhaut was observed by the Hubble Space Telescope and revealed a small planet among the debris of its dense disk of gas and dust. In another instance, the young star HR 8799 was observed by the Keck Observatory in Hawaii and revealed four massive planets (HR8799 b, c, d and e) in orbit. This is only the beginning of direct-imaging studies as we enter a new era of exoplanet studies.

What will the future bring? The spectacular success of the NASA Kepler mission is just the beginning of new missions to come that will discover thousands of new exoplanets. The NASA, Transiting Exoplanet Survey Satellite (TESS) will be launched in 2018 and will perform a Kepler-like survey of the 500,000 brightest stars in the sky. This survey will double the number of known exoplanets and include hundreds of additional Earth-sized candidates. At the same time, the Webb Space Telescope will be launched and among its many research programs will be ones to study the atmospheres of known exoplanets and Earth-sized candidates.

Check back here on June 18 for my next blog!

Synthia

We can micro-miniaturize electronics by making their components smaller and smaller, but what about living organisms? Humans consist of over 20,000 genes coded into a billion-nucleotide molecule called DNA. That’s a lot of information for a complex organism like humans, but when it comes to genome size, a rare Japanese flower, called Paris japonica, is the current heavyweight champ, with 50 times more DNA than humans. But what is the smallest number of genes and nucleotides needed to create a living system?

Researchers call this the Minimal Genome, and it is what you get when you take a simple organism and strip away all of the non-essential and duplicative genes, leaving a bare minimum behind to spawn a healthy living system. To find one of these organisms in Nature, one would think that you have to search far and wide to find it among the millions of organisms on Earth. Luckily, a prime candidate was found much closer to ‘home’!

Following an intense multi-decade search, the current champion organism with the fewest naturally-occurring genes is a rather dangerous pest called Mycoplasma genitalium (M. genitalium). MG is a sexually-transmitted disease  that doctors have known about since the 1980’s and more than 1 in 100 adults have it. It causes urethritis and pelvic inflammatory disease among other symptoms. It is also a bacterium with only 482 genes among 582,970 nucleotides.

By 2008 the researchers had artificially synthesized the complete 482-gene, circular chromosome of M. genitalium, however, M. genitalium is a slow-growing bacterium so by 2010 the research switched to another simple organism called M. mycoides with a faster reproduction cycle. They were able to synthesize the 1-million nucleotide DNA of this bacterium and transplant it into the body of yet another bacterium called M. capricolum, which had been scrubbed of all its DNA. The new genome quickly took over the cell and was dubbed Synthia, but it behaved exactly as M. mycoides even though it was entirely synthetic. It had been created from a computer record of its sequential gene compliment and a set of chemicals, so it truly was the first lifeform whose parents were a computer and a set of chemical pumps!

Syn 3.0 – (Credit: Mark Ellisman/National Center for Imaging and Microscopy Research)

Following a tedious process of trial-and-error where over 100 different analogues with different minimal DNA sets were created, most non-viable, the creation of a new synthetic bacterium, Syn. 3.0, was announced by Nobel laureate Ham Smith, microbiologist Clyde Hutchison, and genomics pioneer Craig Venter at Harvard University in the journal Science on March 25, 2016.

Although Syn 3.0 only had 473 genes, amazingly, the function of 149 of these remains unknown. Some create proteins that stick out from the bacterium’s cell wall but their functions are unknown. Other genes seem to be involved in creating proteins that shuttle molecules in and out of the bacterium’s cell wall, but the nature of these molecules and their role in the cell’s metabolism is unknown. The artificial genome was also reorganized using a computer algorithm to place similar genes near each other – like de-fragging a hard drive, but this did not have any obvious effect on the bacterium.

In at least one case, a ‘watermark’ sequence was inserted into the genome of an earlier synthetic bacterium called M. laboratorium. The 4 watermarks are coded messages in the form of DNA base pairs, of 1246, 1081, 1109 and 1222 nucleotides respectively, which give the names of the researchers, and quotes from James Joyce, Robert Oppenheimer, and an especially relevant one by Richard Feynman: ‘What I cannot build I cannot understand’.

Is M. Genitalium really the smallest organism? Probably not, but it depends on how you define such minimal organisms. Since its genome was sequenced in 1999, we now know of five additional bacteria with even smaller genome sizes. The smallest of these is Candidatus Hodgkinia cicadicola Dsem with only 169 genes, however like the others this organism’s genome is supplemented by the host cell’s genome so it acts more like an organelle than a free-standing organism.
 M. genitalium is classified as an intracellular parasite and cannot exist by itself in the biosphere. It requires a host system such as the human urinary tract to provide the environment to sustain it. For truly free-standing organisms that can actually live by themselves and reproduce, the smallest of these is currently thought to be Pelagibacter ubique, which was found in 2002. It makes up 25% of all bacterial plankton cells in the ocean. It also undergoes regular seasonal cycles in abundance – in summer reaching ~50% of the cells in the temperate ocean surface waters. Thus it plays a major role in the Earth’s carbon cycle! Its genome was sequenced in 2005 and consists of 1,308,759 nucleotides forming 1,389 genes. Its genome has been streamlined by evolution so that it requires the least amount of nitrogen to reproduce (a scarce resource in the bacterium’s ocean environment). The base pairs C and G are nitrogen-rich, with a total of 11 nitrogen atoms between them. A and T are nitrogen-poor and have only 7 nitrogen atoms between them. All other environmental factors being equal, instead of 50% of the genome containing A and T, a whopping 70% does. Somehow, this bacterium has found a way to find alternative ways to create genes that are essential for life by avoiding the ‘expensive’ alternatives. Over billions of years it optimized itself to the current low-nitrogen compliment.

Why is all of this important? Why is synthetic genomics such an important research area? Because it is a direct way to identify how hundreds of genes work together to create viable living systems: their skeletons, metabolisms and reproductive strategies. For astrobiologists, it is a glimpse of what alien life might look like when it is pared down to its absolute essentials but still behaves as an independent system rather than a viral symbiont requiring a pre-existing host. Also, once we know what a basic viable bacterium host looks like, genetically, we can systematically add to this genome other factors of interest to us. We can explore what the process of epigenetics looks like as various environmental factors are added to switch on and off genes. Above all, it is the inevitable questions to come about the essential mechanism of life that will be the most exciting to watch develop!

Check back here on  Tuesday, June 6 for the next essay!

The Proton’s Spin

Protons are the work horses of chemistry. Their numbers determine which element you are talking about, and their positive charge determines how many electrons will form a cloud around them to facilitate all manner of chemical reactions.

For decades we thought that protons were absolutely fundamental particles along with neutrons and electrons, but then came the quantum revolution of the 1920s and the escalating quest to understand what their actual physical properties were. Through experimentation, we found that protons all had exactly the same mass to many decimal places. They all had exactly +1.0000 unit of charge, also to many decimal places. But they also possessed an entirely new physical quantity found only in atomic-scale physics. This quantity was called ‘spin’ but had nothing to do with the motion of a top about its axis, although paradoxically it could nonetheless be interpreted in that way.

Quantum spin, unlike the continuous spinning of a top, comes only in integer units like 0, 1, 2, etc, or in half-integer units like ½, 3/2, 5/2 etc. Physicists soon discovered that fundamental particles like photons ( the carriers of light energy) only had a quantum spin of exactly 1.0, while protons, neutrons, neutrinos and electrons had exactly ½ unit of spin. The former kinds of particles were called bosons while the latter were given the name fermions. Composite particles made up from these elementary bosons and fermions could have other spin values, but only what arises from adding, in the proper way, the elementary spins of their constituents.

By the 1960s, experiments had begun to show that protons were not actually fundamental particles at all, nor were neutrons for that matter. Theoretical models that built-up protons and neutrons and many other known particles called mesons and baryons soon led to the idea of the quark. For protons and neutrons, you needed three quarks, while for the mesons you only needed two of which one would be a quark and the other an anti-quark. The mathematics were impressive and elegant, and this system of quarks soon became the favored model for all particles that interacted through the strong nuclear force, itself produced by the exchanges of particles called gluons. Also in this scheme, quarks would be spin-1/2 fermions and the gluons would be spin-1 bosons much like the photons which carry light energy.

All seemed to be going great by the 1970s and 1980s. The quark model flourished, and many new subtle phenomena were uncovered through the application of what became the Standard Model of physics. But there was a fly in the ointment.

At first the explanation for how a proton could have a spin of ½ while at the same time being composed of three quarks, each also spin-1/2 particles, was pretty well settled. Because a proton consisted of two identical ‘up’ quarks and one ‘down’ quark, it was entirely reasonable that the two up quarks would have equal and opposite spin canceling each other out, leaving behind the down quark to carry the protons ½ unit of spin. Similarly for the neutron, its two down quarks combined to have a net-zero spin leaving the single up quark to carry the ½ unit of spin for the neutron.

The Proton Spin Crisis

All seemed to be well until experiments in 1987 at the European Muon Collaboration actually used carefully prepared beams of particles called muons to probe the interior of protons and double-check the way the quark spins were oriented with the protons spin. What they found was startling. Not more than 25% of the proton’s spin was generated by the quarks at all. The remaining 75% of what defines the spin of a proton had to come from some other source!

When you look at the mass of a proton compared to the masses of the three constituent quarks you discover something very fascinating. The masses of the quarks only account for about 1% of the mass of the entire proton. Instead, thanks to Einstein’s E=mc2, it is the stress energy of the gluon fields inside the proton that contribute the missing 99%. The mass that you read on the bathroom scale is only 1% contributed by the mass of your elementary quarks in grams, but 99% by the invisible energy(mass) of the gluon fields that occupy nuclear space!

Now for proton spin, the only other things rattling around inside the intense fields in the interior of a proton were the gluons holding the quarks together, and an ephemeral sea of quark-antiquark pairs that momentarily appeared and disappeared in the vacuum of space found there. This sea of vacuum or ‘virtual’ particles is absolutely required by modern quantum physics, and although we can never detect their comings and goings by any direct observation, we can detect their influence on nearby elementary particles.

In 2014, experiments at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven, New York collided polarized protons together and physicists think they have found a large part of the remainder of the protons spin. Perhaps 40% to 50% seems to be contributed by the gluons themselves. This still leave about 25% in some other source. Meanwhile, other experiments by MIT physicists determined that any anti-quarks produced inside a proton among the virtual quark sea contribute very little to the over-all spin of the proton.

The bottom line today seems to be what this table shows:

Quark spin……………………….………..25%
Gluon spin…………………………………40-50%
Orbital angular momentum……..25% to 35%

When the experimental constraints are added up, we still do not have a precise measure of how the various proton constituents add up to give the universally constant spin of 1/2 to a proton that is observed for all protons to many decimal places.

Who would have thought that such an important number as ‘1/2’ arises from combining a number of messy phenomena that themselves seem imprecise!

Check back here on Tuesday, May 30 for my next topic!

The First Billion Years

When we think about the Big Bang we tend only to look at the first few instants when we think all of the mysterious and exciting action occurred. But actually, the first BILLION years are the real stars of this story!

My books ‘Eternity:A Users Guide’ and ‘Cosmic History I and II’ provide a more thorough, and ‘twitterized’, timeline of the universe from the Big Bang to the literal end of time if you are interested in the whole story as we know it today. You can also look at a massive computer simulation developed by Harvard and MIT cosmologists in 2014.

What we understand today is not merely based on theoretical expectations. Thanks to specific observations during the last decade, we have actually discovered distant objects that help us probe critical moments during this span of time.

Infancy

By the end of the first 10 minutes after the Big Bang, the universe was filled with a cooling plasma of hydrogen and helium nuclei and electrons – too hot to come together to form neutral atoms at seething temperatures over 100 million Celsius. The traces that we do see of the fireball light from the Big Bang are called the cosmic background radiation, and astronomers have been studying it since the 1960s. Today, the temperature is 2.726 kelvins, but at one part in 100,000 there are irregularities in its temperature across the entire sky detected by the COBE, WMAP and Planck satellites and shown below. These irregularities are the gravitational fingerprints of vast clusters of galaxies that formed in the infant universe after several more billion years.

By 379,000 years, matter had cooled down to the point where electrons could bond with atomic nuclei to form neutral atoms of hydrogen and helium. For the first time in cosmic history, matter could go its own way and no longer be affected by the fireball radiation, which used to blast these assembled atoms apart faster than they could form. If you were living at this time, it would look like you were standing inside the surface of a vast dull-red star steadily fading to black as the universe continued to expand, and the gas steadily cooled over the millennia. No matter where you stood in the universe at this time, all you would see around you is  this dull-red glow across the sky.

6 million years – By this time, the cosmic gas has cooled to the point that its temperature was only 500 kelvins (440 F). At these temperatures, it no longer emits any  visible light. The universe is now fully in what astronomers call The Cosmic Dark Ages. If you were there and looking around, you would see nothing but an inky blackness no matter where you looked! With infrared eyes, however, you would see the cosmos filled by a glow spanning the entire sky.

20 million years – The hydrogen-helium gas that exists all across the universe is starting to feel the gravity effects of dark matter, which has started to form large clumps and vast spiders-web-like networks spanning the entire cosmos, with a mass of several trillion times the mass of our sun. As the cold, primordial gas falls into these gravity wells, it forms what will later become the halos of modern-day galaxies. All of this hidden under a cloak of complete darkness because there was as yet no physical objects in existence to light things up. Only detailed supercomputer simulations can reveal what occurred during this time.

The First Stars

100 million years – Once the universe got cold enough, large gas clouds stopped being controlled by their internal pressure, and gravity started to take the upper hand. First the vast collections of matter destined to become the haloes of galaxies formed. Then, or at about the same time, the first generation of stars appeared in the universe. These Population III stars made from nearly transparent hydrogen and helium gas were so massive, they lived for only a few million years before detonating as supernova. As the universe becomes polluted with heavier elements from billions of supernovae, collapsing clouds become more opaque to their own radiation, and so the collapse process stops when much less matter has formed into the infant stars. Instead of only producing massive Population III stars with 100 times our sun’s mass, numerous stars with masses of 50, 20 and 5 times our sun’s form with increasing frequency. Even smaller stars like our own sun begin to appear by the trillions. Most of this activity is occurring in what will eventually become the halo stars in modern galaxies like the Milky Way. The vast networks of dark matter became illuminated from within as stars and galaxies began to form.

200 million years – The oldest known star in our Milky Way called SM0313 formed about this time. This star contains almost no iron — less than one ten millionth of the iron found in our own Sun. It is located 6000 light years from Earth. Another star called the Methusela Star is located about 190 light years from Earth and was formed about the same time as SM0313.

The First Quasars and Black Holes

300 million years The most distant known ‘quasar’ is called APM 8279+5255, and contains traces of the element iron. This means that at about this time after the Big Bang, some objects are powered by  enormous black holes that steadily consume a surrounding disk of gas and dust. For APM 8279+5255, the mass of this black hole is about 20 billion times more massive than the Sun. Astronomers do not know how a black hole this massive could gave formed so soon after the Big Bang. A dimple division shows that a 20 billion solar mass black hole forming in 300 million years would require a growth rate higher than 60 solar masses a year!

The First Galaxies

400 million years – The cold primordial matter becomes clumpy under the action of its own gravity. These clumps have masses of perhaps a few billion times our sun or less, and over time this material starts to collapse locally into even smaller clouds that become mini-galaxies where intense episodes of star formation activity are playing out.

This image shows the position of the most distant galaxy discovered so far with the Hubble Space Telescope. The remote galaxy GN-z11 shown in the inset is actually ablaze with bright young blue stars. They look red in this image because the wavelengths of light have been stretched by the expansion of the universe to longer, redder wavelengths. Like the images of so many other young galaxies, we cannot see individual stars, but their irregular shapes show that the stars they contain are spread out in irregular clumps within their host galaxy, possibly because they are from separate, merging clouds whose collisions have triggered the star-forming activity we see.

Although it is hard work, astronomers can detect the faint reddish traces of dozens of other infant galaxies such as MACS0647-JD, UDFj-39546284 and EGSY-2008532660. These are all  small dwarf galaxies over 100 times less massive than our Milky Way. They are all undergoing intense star forming activity between 400 and 600 million years after the Big Bang.

The Gamma-Ray Burst Era begins about 630 million years after the Big Bang. Gamma-ray bursts are caused by very massive stars, perhaps 50 to 100 times our own sun’s mass, that explode as hypernovae and form a single black hole, so we know that these kinds of stars were already forming and dying by this time. Today from ‘across the universe’ we see these events occur about once each day!

800 million years – The quasar ULAS J1120+0641 is another young case of a supermassive black hole that has formed, and by this time is eating its surrounding gas and stars at a prodigious rate. The mass of this black hole is about 2 billion times the mass of our sun, and like others is probably the result of frequent galaxy mergers and rapid eating of surrounding matter.

Also at around this time we encounter the Himiko Lyman Alpha Blob; one of the most massive objects ever discovered in the early universe.  It is 55,000 light-years across, which is half of the diameter of the Milky Way. Objects like Himiko are probably powered by an embedded galaxy that is producing young massive stars at a phenomenal rate of 500 solar masses per year or more.

Again the most brilliant objects we can see from a time about 900 million years after the big bang includes galaxies like SDSS J0100+2802 with a luminosity 420 trillion times that of our own Sun. It is powered by a supermassive black hole  12 billion times the mass of our sun.

The Re-Ionization Era

960 million years – By this time, massive stars in what astronomers call ‘Population III’ are being born by the billions across the entire universe. These massive stars emit almost all of their light in the ultraviolet part of the visible spectrum. There are now so many intense sources of ultraviolet radiation in the universe that all of the remaining hydrogen gas becomes ionized. Astronomers call this the Reionization Era. Within a few hundred million years, only dwarf galaxy-sized blobs of gas still remain and are being quickly evaporated. We can still see the ghosts of these clouds in the light from very distant galaxies. The galaxy SSA22-HCM1 is the brightest of the objects called ‘Lyman-alpha emitters’. It may be producing new stars at a rate of 40 solar masses per year and enormous amounts of ultraviolet light. The galaxy HDF 4-473.0 also spotted at this age is only 7,000 light years across. It has an estimated star formation rate of 13 solar masses per year.

1 billion years First by twos and threes, then by dozens and hundreds, clusters of galaxies begin to form as the gravity of matter pulls the clumps of galaxy-forming matter together. This clustering is speeded up by the additional gravity provided by dark matter. In a universe without dark matter, the number of clusters of galaxies would be dramatically smaller.

Clusters of Galaxies Form

Proto-galaxy cluster AZTEC-3 consists of 5 smaller galaxy-like clumps of matter, each forming stars at a prodigious rate. We now begin to see how some of the small clumps in this cluster are falling together and interacting, eventually to become a larger galaxy-sized system. This process of cluster formation is now beginning in earnest as more and more of these ancient clumps fall together under a widening umbrella of gravity. Astronomers are discovering more objects like AzTEC-3, which is the most distant known progenitor to modern elliptical galaxies. By 2.2 billion years after the Big Bang, it appears that half of all the massive elliptical galaxies we see around us today have already formed by this time.

Thanks to the birth and violent deaths of generations of massive Population III stars, the universe is now flooded with heavy elements such as iron, oxygen, carbon and nitrogen: The building blocks for life. But also elements like silicon, iron and uranium which help to build rocky planets and heat their interiors. The light from the quasar J033829.31+002156.3 can be studied in detail and shows that by this time, element-building through supernova explosions of Population III stars has produced lots of carbon, nitrogen and silicon. The earliest planets and life forms based upon these elements now have a chance to appear in the universe. Amazingly, we have already spotted such an ancient world!

Earliest Planets Form

At 1 billion years after the Big Bang, the oldest known planet PSR B1620-26 b has already formed. Located in the globular cluster Messier-4, about 12,400 light-years from Earth, it bears the unofficial nicknames “Methuselah” and “The Genesis Planet” because of its extreme age. The planet is in orbit around the two very old stars: A dense white dwarf and a neutron star. The planet has a mass of 2.5 times that of Jupiter, and orbits at a distance a little greater than the distance between Uranus and our own Sun. Each orbit of the planet takes about 100 years.

Wonders to Come!

Although the Hubble Space Telescope strains at its capabilities to see objects at this early stage in cosmic history, the launch of NASA’s Webb Space Telescope will uncover not dozens but thousands of these young pre-galactic objects with its optimized design. Within the next decade, we will have a virtually complete understanding of what happened during and after the Cosmic Dark Ages when the earliest possible sources of light could have formed, and one can only marvel at what new discoveries will turn up.

What an amazing time in which to be alive!

Check back here on Wednesday, May 24 for my next topic!

Our Unstable Universe

Something weird is going on in the universe that is causing astronomers and physicists to lose a bit of sleep at night. You have probably heard about the discovery of dark energy and the accelerating expansion of the universe. This is a sign that something is afoot that may not have a pleasant outcome for our universe or the life in it.

Big Bang Cosmology V 1.0

The basic idea is that our universe has been steadily expanding in scale since 14 billion years ago when it flashed into existence in an inconceivably dense and hot explosion. Today we can look around us and see this expansion as the constantly- increasing distances between galaxies embedded in space. Astronomers measure this change in terms of a single number called the Hubble Constant which has a value of about 70 km/sec per megaparsecs. For every million parsecs of separation between galaxies, a distance of 3.24 million light years, you will see distant galaxies speeding away from each other at 70 km/sec . This conventional Big Bang theory has been the main-stay of cosmology for decades and it has helped explain everything from the formation of galaxies to the abundance of hydrogen and helium in the universe.

Big Bang Cosmology V 2.0

Beginning in the 1980’s, physicists such as Alan Guth and Andre Linde added some new physics to the Big Bang based on cutting-edge ideas in theoretical physics. For a decade, physicists had been working on ways to unify the three forces in nature: electromagnetism, and the strong and weak nuclear forces. This led to the idea that just as the Higgs Field was needed to make the electromagnetic and weak forces look different rather than behave as nearly identical ‘electroweak’ forces, the strong force needed its own ‘scalar field’ field to break its symmetry with the electroweak force.

When Guth and Linde added this field to the equations of Big Bang cosmology they made a dramatic discovery. As the universe expanded and cooled, for a brief time this new scalar field made the transition between a state where it allowed the electroweak and strong forces to look identical, and a state where this symmetry was broken representing the current state of affairs. This period of time extended from about 10(-37) second to 10(-35) seconds; a mere instant in cosmic time, but the impact of this event was spectacular. Instead of the universe expanding at a steady rate in time as it does now, the separations between particles increased exponentially in time in a process called Inflation. Physicists now had a proper name for this scalar field: The Inflaton Field.

Observational cosmology has been able to verify since the 1990s that the universe did, indeed, pass through such an inflationary era at about the calculated time. The expansion of space at a rate many trillions of times faster than the speed of light insured that we live in a universe that looks as ours does, especially in terms of the uniformity of the cosmic ‘fireball’ temperature. It’s 2.7 kelvins no matter where you look, which would have been impossible had the Inflationary Era not existed.

Physicists consider the vacuum of space to be more than ‘nothing’. Quantum mechanically, it is filled by a patina of particles that invisibly come and go, and by fields that can give it a net energy. The presence of the Inflaton Field gave our universe a range of possible vacuum energies depending on how the field interacted with itself. As with other things in nature, objects in a high-energy state will evolve to occupy a lower-energy state. Physicists call the higher-energy state the False Vacuum and the lower-energy state the True Vacuum, and there is a specific way that our universe would have made this change. Before Inflation, our universe was in a high-energy, False Vacuum state governed by the Inflaton Field. As the universe continued to expand and cool, a lower-energy state for this field was revealed in the physics, but the particles and fields in our universe could not instantaneously go into that lower-energy state. As time went on, the difference in energy between the initial False Vacuum and the True Vacuum continued to increase. Like bubbles in a soda, small parts of the universe began to make this transition so that we now had a vast area of the universe in a False Vacuum in which bubbles of space in the True Vacuum began to appear. But there was another important process going on as well.

When you examine how this transition from False to True Vacuum occurred in Einstein’s equations that described Big Bang cosmology, a universe in which the False Vacuum existed was an exponentially expanding space, while the space inside the True Vacuum bubbles was only expanding at a simple, constant rate defined by Hubble’s Constant. So at the time of inflation, we have to think of the universe as a patina of True Vacuum bubbles embedded in an exponentially-expanding space still caught in the False Vacuum. What this means for us today is that we are living inside one of these True Vacuum bubbles where everything looks about the same and uniform, but out there beyond our visible universe horizon some 14 billion light years away, we eventually enter that exponentially-expanding False Vacuum universe. Our own little bubble may actually be billions of times bigger than what we can see around us. It also means that we will never be able to see what these other distant bubbles look like because they are expanding away from us at many times the speed of light.

Big Bang Cosmology 3.0

You may have heard of Dark Energy and what astronomers have detected as the accelerating expansion of the universe. By looking at distant supernova, we can detect that since 6 billion years after the Big Bang, our universe has not been expanding at a steady rate at all. The separations between galaxies has been increasing at an exponential rate. This is caused by Dark Energy, which is present in every cubic meter of space .The more space there is as the universe expands, the more Dark Energy and the faster the universe expands. What this means is that we are living in a False Vacuum state today in which a new Inflaton Field is causing space to dilate exponentially. It doesn’t seem too uncomfortable for us right now, but the longer this state persists, the greater is the probability our corner of the universe will see a ‘bubble’ of the new True Vacuum appear. Inside this bubble there will be slightly different physics such as the mass of the electron or the quark may be different. We don’t know when our corner of the universe will switch over to its True Vacuum state. It could be tomorrow or 100 billion years from now. But there is one thing we do know about this progressive, accelerated expansion.

Eventually, distant galaxies will be receding from our Milky Way at faster that the speed of light as they are helplessly carried along by a monstrously-dilating space. This also means they will become permanently invisible for the rest of eternity as their light signals never keep pace with the exponentially-increasing space between them. Meanwhile, our Milky Way will become the only cosmic collection of matter we will ever be able to see from then on. It is predicted that this situation will occur about 100 billion years from now when the Andromeda Galaxy will pass beyond this distant horizon.

As for what the new physics will be in the future True Vacuum state is anyone’s guess. If the difference in energy between the False and True vacuum is only a small fraction of the mass of a neutrino (a few electron-Volts) we may hardly know that it happened and life will continue. But if it is comparable to the mass of the electron (512,000 eV), we are in for some devastating and fatal surprises best not contemplated.

Check back here on  Tuesday, May 16  for my next topic!

Boltzmann Brains

Back in the 1800’s, Ludwig Boltzmann (1844-1906) developed the idea of entropy and thermodynamics, which have been the main-stay of chemistry and physics ever since. Long before atoms were identified, Boltzmann had used them in designing his theory of statistical mechanics, which related entropy to the number of possible statistical states these particles could occupy. His famous formula

S = k log W

is even inscribed on his tombstone! His frustrations with the anti-atomists who hated his crowning achievement ‘statistical mechanics’ led him in profound despair to commit suicide in 1906.

If you flip a coin 4 times, it is unlikely that all 4 flips will result in all-heads or all-tails. It is far more likely that you will get a mixture of heads and tails. This is a result of their being a total of 2^4 = 16 possible outcomes or ‘states’ for this system, and the state with all heads or all tails occur only 1/16 of the time. Most of the states you will produce have a mixture of heads and tails (14/16). Now replace the coin flips by the movement of a set of particles in three dimensions.

Boltzmann’s statistical mechanics related the number of possible states for N particles moving in 3-dimensional space, to the entropy of the system. It is more difficult to calculate the number of states than for the coin flip example above, but it can be done using his mathematics, and the result is the ‘W’ in his equation S = k Log W. The bottom line is that, the more states available to a collection of particles (for example atoms of a gas), the higher is the entropy given by . How does a gas access more states? One way is for you to turn up its temperature so that the particles are moving faster. This means that as you increase the temperature of a gas, its entropy increases in a measurable way.

Cosmologically, as our universe expands and cools, its entropy is actually increasing steadily because more and more space is available for the particles to occupy even as they are moving more slowly as the temperature declines. The Big Bang event itself, even at its unimaginably high temperature was actually a state of very low entropy because even though [particles were moving near the speed of light, there was so little space for matter to occupy!

For random particles in a gas colliding like billiard balls, with no other organizing forces acting on them, (called the kinetic theory of gases), we can imagine a collection of 100 red particles clustered in one corner of a box, and 1000 other blue particles located elsewhere in the box. If we were to stumble on a box of 1100 particles that looked like this we would immediately say ‘how odd’ because we sense that as the particles jostled around the 100 red particles would quickly get uniformly spread out inside the box. This is an expression of their being far more available states where the red balls are uniformly mixed, than states where they are clustered together. This is also a statement that the clustered red balls is a lower-entropy version of the system, and the uniformly-mixed version is a higher form of entropy. So we would expect that the system evolves from lower to higher entropy as the red particles diffuse through the box: Called the Second Law of Thermodynamics.

Boltzmann Brains.

The problem is that given enough time, even very rare states can have a non-zero probability of happening. With enough time and enough jostling, we could randomly find the red balls once again clustered together. It may take billions of years but there is nothing that stands in the way of this happening from statistical principles. Now let’s suppose that instead of just a collection of red balls, we have a large enough system of particles that some rare states resemble any physical object you can imagine: a bacterium, a cell phone, a car…even a human brain!

A human brain is a collection of particles organized in a specific way to function and to store memories. In a sufficiently large and old universe, there is no obvious reason why such a brain could not just randomly assemble itself like the 100 red particles in the above box. It would be sentient, have memories and even senses. None of its memories would be of actual events it experienced but simply artificial reconstructions created by just the right neural pathways randomly assembled. It would remember an entire lifetime to date without having actually lived or occupied any of the events in space and time.

When you calculate the probability for such a brain to evolve naturally in a low-entropy universe like ours rather than just randomly assembling itself you run into a problem. According to Boltzmann’s cosmology, our vast low-entropy and seemingly highly organized universe is embedded in a much larger universe where the entropy is much higher. It is far less likely that our organized universe exists in such a low entropy state conducive to organic evolution than a universe where a sentient brain simply assembles itself from random collisions. In any universe destined to last for eternity, it will rapidly be populated by incorporeal brains rather than actual sentient creatures! This is the Paradox of the Boltzmann Brain.

Even though Creationists like to invoke the Second Law to deny evolution as a process of random collisions, the consequence of this random idea about structure in the universe says that we are actually all Boltzmann Brains not assembled by evolution at all. It is, however, of no comfort to those who believe in God because God was not involved in randomly assembling these brains, complete with their own memories!

So how do we avoid filling our universe with the abomination of these incorporeal Boltzman Brains?

The Paradox Resolved

First of all, we do not live in Boltzmann’s universe. Instead of an eternally static system existing in a finite space, direct observations show that we live in an expanding universe of declining density and steadily increasing entropy.

Secondly, it isn’t just random collisions that dictate the assembly of matter (a common idea used by Creationists to dismantle evolution) but a collection of specific underlying forces and fundamental particles that do not come together randomly but in a process that is microscopically determined by specific laws and patterns. The creation of certain simple structures leads through chemical processes to the inexorable creation of others. We have long-range forces like gravity and electromagnetism that non-randomly organize matter over many different scales in space and time.

Third, we do not live in a universe dominated by random statistical processes, but one in which we find regularity in composition and physical law spanning scales from the microscopic to the cosmic, all the way out to the edges of the visible universe. When two particles combine, they can stick together through chemical forces and grow in numbers from either electromagnetic or gravitational forces attracting other particles to the growing cluster, called a nucleation site.

Fourth, quantum processes and gravitational processes dictate that all existing particles will eventually decay or be consumed in black holes, which will evaporate to destroy all but the most elementary particles such as electrons, neutrinos and photons; none of which can be assembled into brains and neurons.

The result is that Boltzmann Brains could not exist in our universe, and will not exist even in the eternal future as the cosmos becomes more rarefied and reaches its final and absolute thermodynamic equilibrium.

The accelerated expansion of the universe now in progress will also insure that eventually all complex collections of matter are shattered into individual fundamental particles each adrift in its own expanding and utterly empty universe!

Have a nice day!

Check back here on Tuesday, May 9 for my next topic!