The current, seemingly comprehensive theory of the origin and evolution of our universe is called inflationary, big bang cosmology. This theory explains how our universe emerged from a singularity of high temperature and density and expanded and cooled. As it did so, space dilated at a faster-than-light pace and cooled so that the familiar elementary particles and forces could produce the cosmic background radiation and a variety of complex particles as the universe expanded. By about three minutes after the Big Bang, the ratio of hydrogen to helium had been cosmologically established, and so had the amount of cosmic background photons and neutrinos. In addition, during the rapid ‘inflation’ period, irregularities in the cosmic density of matter were established as well as a background of gravitational radiation.

The spectacular results of the WMAP satellite , along with the results from COBE and a number of other high-precision studies of the cosmic background radiation have now established that the universe is 13.7 billion years old, and that its space geometry is exactly ‘flat’. Also, according to the most recent WMAP ‘pie graph’ above, the amount of the gravitating matter in ordinary stars and gas is only 4.6%. The rest of the gravitating ‘mass’ of the observable universe is in the form of Dark Matter (24%), with an additional contribution of Dark Energy (71.4%). It is this Dark Energy that is causing our universe to expand at an accelerated pace, which has been observationally detected using distant supernovae.

There have been over the years several potential rivals to Big Bang cosmology, but with the exception of Steady State theory, none have attracted more than a handful of interested supporters. The reason is that they failed to predict, or offer explanations for, some basic observations that are widely agreed upon to be key tests of any cosmological theory, even by the rivals to Big Bang theory!

DeSitter Cosmology ca 1917 – The universe is presumed to be entirely empty of matter, but expands exponentially in time because of the presence of a non-zero cosmological constant. This refutes nearly every observational fact now available, including the actual rate of expansion which follows a linear, Hubble law, not an exponential expansion law with time. Also, the density of matter in the universe is not zero because we are here, and so are a lot of other stars and galaxies!

Einstein Static Cosmology ca 1917-The universe does not expand, and is static in time. The cosmological constant is precisely tuned to balance the attractive tendency of matter. Like DeSitter cosmology, it also fails to agree with modern observations, because the universe is expanding linearly with time. It is also unstable to the slightest perturbation in the value of this constant.

Lemaitre Cosmology ca 1924 – The universe started with a ‘big bang’ with no cosmological constant. The initial state was a giant radioactive atom containing all the matter in the universe near absolute zero. This theory agrees with the observed expansion, but fails to explain the existence of the cosmic background radiation and the universal abundances of hydrogen, helium and deuterium because it requires the decay of a single massive ‘super atom’ at the instant of the Big Bang.

Steady State Cosmology ca 1950 – Developed by Fred Hoyle and Thomas Gold, it proposes that the universe has been expanding for eternity and that new galaxies are created, atom by atom, in intergalactic space ‘out of empty space’. This theory had its heyday in the 1950’s and 1960’s, but was never able to explain convincingly where the cosmic background radiation came from, why it is so isotropic, and why its temperature is fixed at 2.7 K. It also provided no clues as to why there ought to be a universal abundance ratio for hydrogen, helium and deuterium.

Cold Big Bang Cosmology ca 1965 – Developed by David Layzer at Harvard, it proposes that the Big Bang occurred, but that the initial state was at absolute zero and consisted of a pure solid of hydrogen. This fragmented into galaxy-sized clouds as the universe expanded. It provided no explanation for where the cosmic background field came from and why it is isotropic and at a temperature of 2.7 K.

Hagedorn Cosmology ca 1968 – Physicist Robert Hagedorn proposed that all of the details of big bang theory are probably true, except that the early history of the universe had a limiting temperature of about 1 trillion degrees because the structure of matter has an infinite ladder of ‘fundamental particles’ out of which electrons, protons and neutrons are constructed. This has been refuted with the discovery that quarks exist which place any limiting temperature for the early history of the universe at temperatures well above 1000 trillion degrees.

Brans-Dicke Cosmology ca 1955 – Einstein’s equation for gravity in general relativity is modified to include a ‘scalar’ field. This field causes the value of the constant of gravity to change slowly over billions of years. This also leads to a modification of the early history of the universe. Experimental searches for a change in the constant of gravity show that it has not changed to within experimental error during the last 2 – 3 billion years. It would cause the evolution of the Earth-Moon system to be significantly altered, and the evolution of the Sun to be severly modified. Neither of these effects have been observed.

Old Inflationary, Big Bang Cosmology ca 1980 – Developed as a ‘toy’ model by Alan Guth in 1980. The Inflationary era which ended 10^-34 seconds after the Big Bang caused the nucleation of innumerable ‘bubbles’ of true vacuum which merged together to form a patina of matter and radiation in a very lumpy configuration. The cosmic background radiation, however, shows that the universe is very smooth to 1 part in at least 10,000 since about 300,000 years after the Big Bang. There is no evidence for such a turbulent and lumpy transition era.

Oscillatory Big Bang Cosmology ca 1930 – This a a possible modification to Big Bang cosmology that differs only in that the current expansion will be replaced by a collapse phase and then an expansion phase etc etc. There is no evidence that there was ever a prior expansion-collapse phase. The universe also does not seem to have enough matter to make it a ‘closed’ universe destined to recollapse in the future; an important requirement for any future oscillation cycle.

Big Bang Cosmology with added Neutrino Families ca 1970 – Big Bang cosmology is largely correct, except that to solve the ‘missing’ or ‘dark’ matter problem, new families of neutrinos have to be added to the universe. This would change the cosmological abundance ratios of helium and deuterium relative to hydrogen so that the current observed values no longer are possible. There is also no experimental evidence that more than 3 types of neutrinos exist; and these are already consistent with the measured cosmological abundances.

Chronometric Cosmology ca 1970 – Developed by I. Segal at MIT, it proposes that space-time has a different mathematical structure than the one that forms the basis for Big Bang cosmology. So far as we can tell, the major disagreement is in the rate of the expansion of the universe which comes out as a quadratic law between distance and expansion speed, rather than the linear Hubble Law. This proposal seems to be inconsistent with what has been observed for distant galaxies during the last 3-4 decades. There may be other disagreements with Big Bang cosmology, but Chronometric cosmology has not been explored deep enough to make testable predictions in these other areas.

Alfven Cosmology ca 1960 – Developed by physicist Hans Alfven, it proposes that the universe contains equal parts of matter and anti-matter. No explanation is made for many of the other observational facts in cosmology. If there were equal parts of matter and anti-matter, there ought to be regions in the universe where these were in contact to produce X-rays or gamma rays due to the annihilation process. No such large-scale background has ever been detected that can be attributed to proton or electron annihilation.

Plasma Cosmology ca 1970 – The matter in the universe, on the largest scales, is not neutral, but has a very weak net charge which is virtually undetectable. This causes electromagnetic forces to dominate over gravitational forces in the universe so that all of the phenomena we observe are not the products of gravitation alone. This is an intriguing theory, but other then denying their importance, it cannot easily explain the origin of the cosmic background radiation, its isotropy and temperature, and the abundances of helium and deuterium.

The basic observations that are agreed to me cosmological tests for any theory are:

1…. The universe is expanding. – This is a large-scale observation which spans the entire observable universe so it must be ‘cosmological’

2…. There exists a cosmic background radiation field detectable at microwave frequencies. – Why doesn’t it occur at other frequencies and only seen in the microwave region, covering every direction of the sky?

3…. The cosmic microwave background field is measurably isotropic to better than a few parts in 100,000 after compensation is made for the relativistic Doppler effect caused by Earth/Sun/Milky Way motion. – This is a large-scale property of this phenomenon that has nothning to do with the Milky Way or other galaxies so it must be a cosmological feature.

4…. The cosmic microwave background radiation field is precisely that of a black body. – Many other kinds of radiation are known, but NONE have exactly a black body spectrum. Only the cosmic background radiation is a perfect black body to the limits of our ability to measure its spectrum.

5…. The cosmic microwave background radiation field has a temperature of 2.7 K. – Why 2.7 K? Why not 5.019723 K. Only Big Bang cosmology predicts a relic radiation at a temperature near 3 degrees and not some other value.

6…. There does exist a universal abundance ratio of helium to hydrogen consistent with the current expansion rate and cosmic background temperature. – Whether we look at the compsition of stars, planets or even gas clouds in distant galaxies, we always seem to come upon a ‘universal’ constant ratio of helium to hydrogen and deuterium to hydrogen. There must be an explanation for this that has nothing to do with just our solar system or Milky Way.

7…. The cosmological abundance of deuterium relative to hydrogen and helium is consistent with the levels expected given the current expansion rate and density. – If the universe expanded faster, then there would be less time for heavier elements such as helium and deuterium to form.

8…. There are only three families of neutrinos. – Although we have not confirmed this to be true in the vicinity of distant galaxies, we do see the same kinds of elements and physics occurring out there, especially supernovae whose physics depend very sensitively upon the numbers of distinct types of neutrinos, and the constancy of the underlying ‘weak interaction’ physics.

9…. The night sky is not as bright as the surface of the Sun. – A simple but profound observation which can only be resolved by the correct distribution of stars in the universe, their ages, and the expansion of the universe.

10… The cosmic background radiation field is slightly lumpy at a level of one part in 100,000 to 1,000,000. – Why is this? And why by this amount?

11… There are no objects that have ages indisputably greater than the expansion age of the universe. – Our universe nearby does not seem to have very old stars older than 20 billion years even though their properties should be easily recognizable and a simple extension of the physics and evolution of the oldest stars we do see.

12… There are about 10,000,000,000 photons in the cosmic background radiation field for every proton and neutron of matter. – This is an important ‘thermodynamic’ number which tells us how the universe has evolved up to the present time. Why is its entropy so huge?

13… The degree of galaxy clustering observed is consistent with an expanding universe with a finite age less than 20 billion years. – A direct observation which again tells us that gravity has not had a long time to act to build up large complex structures in today’s universe.

14… There are no elements heavier than lithium which have a universal abundance ratio. – What process created these heavier elements?

15… The universe was once opaque to its own radiation. – This must follow from the black body shape of the cosmic background radiation.

16… The universe is now dominated exclusively by matter and not a mixture of matter and anti-matter. – Only a few contenders to Big Bang cosmology make any attempt at explaining this direct observation.

So there you have it. This is not a game of billiards where the cue ball (data) is carefully lined up so that Big Bang theory comes out looking inevitable. Any of these other theories have been repeatedly invited to take their best shot too, and the results are always the same. The proponents have to intervene to even get their theories to pony up a simple prediction for any of these cosmological data.

The biggest prediction of Big Bang cosmology lies in its very foundations. It is based on the inerrancy of general relativity and how this theory accounts for gravity under extreme conditions. Its basic predictions have been tested many times, and new exotic phenomena such as the Lenze-Thirring effect and gravity waves have also been predicted and confirmed by the theory. It seems to be a flawless explanation for how grfavity workd, but if it is accurate, then we need lots of Dark Matter and Dark Energy in the universe in addition to the 5% of stars and gas that we can see. That is the big problem.

Dark matter is found not only on the cosmic scale but in regions as small as galaxies. In fact it was discovered in galaxies long before WMAP made its first studies. Our own Milky Way seems to have six times more gravitating stuff orbiting its center than in all the luminous matter and gas clouds we can detect. In fact, any large systems of matter we have studied have this Dark MAtter problem. Some physicists have interpreted this as an actual breakdown in General Relativity itself, but their proponents cannot find an extension or replacement for general relativity that makes Dark Matter go away. Meanwhile, physicists have not detected any of the particle candidates for Dark matter at the Large Hadron Collider or other labs around the world.

So Dark Matter can be added to Big Bang cosmology, but we don’t yet know what kind of physical material it is, or whether there might be something subtly wrong with General Relativity itself.