There are several significant features of our universe that seem to be firmly established by observation:
The first two features seem to show that the universe can't be in equilibrium. The last two are what one would expect of a universe in equilibrium (although there is a tendency for the heavy elements, which have to be produced in supernovae explosions with the big bang model, to be more common close to us than farther away). The middle one, the red-shift, can fit either. Not surprisingly, theories of the structure of the universe have generally fallen into two groups, ones based on equilibrium, and others on the opposite. (I note that such alternate cosmological models need not affect our current understanding of quantum mechanics or of general relativity, both of which are far more securely established than any cosmology.)
For almost my entire life time, high-energy physicists and astronomers have embraced a 'big bang' model of our universe: that it began as a single quantum, which 'exploded' some 1010 years ago. It is inherently not in equilibrium in this model, for it is still expanding at 2x10-18/s. Distant stars are redder than close ones because they are physically moving away from us (the Doppler shift, if the universe is in equilibrium), or equivalently, that their light is being stretched by space-time expansion (the non-equilibrium view). Stars are mostly hydrogen because that is what would be created during the big bang (the first three minutes or so) according to current high-energy physics, if you choose the right energy density. The universe should keep on expanding forever because at that density it has only 3% of the mass required for it to re-contract with a 'big crunch'. The background radiation is the space-time-expanded glow of the big bang...
There are competing models of the universe - 'steady state' models. In these views, the universe is eternal - a desirable philosophy for many (although that has nothing to do with science). Distant objects are red because light quanta gradually lose energy through postulated non-scattering interactions with the universe as they traverse it (tired light), or via an equivalent cosmological function. Such lost energy would be turned into mass - a rate equivalent to only one hydrogen atom per cubic kilometre per year could produce a steady physical expansion thus a Doppler red shift similar to that we see. It is not, however, understood how a steady state universe could be gravitationally stable. (A 'cosmological constant' is a fudge factor, not an explanation. Besides, Einstein's version of it doesn't work.) Stars are in galaxies because gravitation is always attractive, therefore unstable, and will merge together into black holes once they dissipate their angular momentum relative to each other. Where does the radiation necessary for matter creation and space expansion come from once everything is sucked into black holes? Besides, the success of the quantum origin of the universe at predicting the distribution of elements long ago disheartened most supporters of steady state. About the only supporters of the pure steady-state universe left are those who propose that gravitational flatness is a necessary condition for existence of any universe. (Of course, they may just be right in that - measured densities keep inching towards that required for flatness.)
However, the real power of the big bang model was that it united the two sciences that depended on big money - astronomy and high-energy physics. Ever-larger particle accelerators, which pack more and more energy into a point, were not just self-generating data (more in, so more out), they were exploring 'the beginning of everything'. So were ever more powerful telescopes - seeing fainter meant seeing farther which in turn meant seeing nearer 'the beginning'. And so, astronomy and high-energy physics closed ranks - anyone who didn't support the standard model was out, from either field. The guiding principle of both fields became 'being right' rather than 'getting things right', in short, the 'big science' syndrome.
In this atmosphere, it is not surprising that there are other potentially productive models of our universe that have escaped serious scrutiny. One possibility, promoted by Lee Smolin and a few others, is that our universe is dissipative - that it might be viewed as the inside of a black hole. Mass 'falls into' our universe from 'outside', to spiral in its turn into other black holes, thus matter is 'flowing through' our universe.
One must choose words carefully here - outside our universe and inside a black hole are not science, because they aren't observable. Most descriptions of black holes are grossly unscientific. Any concept that is self-consistent is a valid subject of mathematics, but any scientifically-defensible theory must be based upon what we can observe, for example objects decelerating to zero movement and absolute zero temperature as they approach an event horizon. The properties of a scientific event horizon must be physical - near-infinite density in a thin shell and near-zero entropy, among others. The only thing science can hope to accomplish is to show consistency between equations modelling a black hole event horizon, the appearance to us of the limits of our universe, and what we see in between.
The rate of 'expansion' of the universe could vary with time with a dissipative model, since its mass would decrease with time by Hawking radiation and increase with matter falling into it, the latter exceeding the former unless the temperature 'outside' the universe is lower than the equivalent temperature of the universe as a black hole. These are being modelled by 'dark energy' within the big bang model. There is still a creation event - the initial creation of the black hole event horizon - but probably without the singularity implicit in the traditional big bang. (Quantum gravity theory might avoid the singularity in the big bang model; the question doesn't arise in equilibrium models.) In fact, most of the mass of our universe might already be in internal black holes. Current observations indicate that most of the mass of our universe has not yet been detected except by its gravitational effects within spiral galaxies.
It is conceivable in fact that all the mass of our universe is black holes. The current assumption is that a black hole small enough that its effective temperature is greater than that of the background radiation (about the mass of our moon at present) will evaporate at an accelerating rate, finally vanishing in a puff of radiation. But, everything else in our universe is quantized - why not black holes? If the ground state of a black hole is a Higgs, then all of the mass in our universe derives from them. Not to mention that the Higgs is a possible candidate for dark matter.
Some objects in our universe combine the red-shift of extreme distance with the brightness of much closer objects. And, light variations from some are observed that makes it appear that they are of stellar dimensions, hence their name: quasars - Quasi-Stellar objects. They seem too compact to be the source of sufficient energy to match the big bang model (although they might be black holes with a very large amount of matter falling into them). And, while they are fairly evenly distributed around us angularly, all have large red-shifts - none are 'close to us'. One astronomer, Halton Arp, began to suspect, first on statistical grounds, that quasars were associated with other objects with much smaller red shifts - an apparent impossibility in the standard model. When his statistics were attacked (not entirely without reason), he switched to looking methodically for cases where 'impossible' visible links between such objects seemed to exist, and started finding them. He then was in essence blackballed from North American observatories, and had to seek refuge in Germany.
Fortunately, science is self-correcting (just slow at it, sometimes): new images from the Hubble Space Telescope are demonstrating that Arp's suspicions were justified in one respect - there is much more gravitational lensing than was expected a few years ago. The gravitational field of middle-distance objects can magnify the apparent brightness of far objects, and make far objects visible in several places around nearer objects. (Don't be surprised if Arp's 'connecting filaments' turn out to be artifacts of gravitational lensing, not real connections.) Hubble images are also showing that the current model of quasars needs considerable revision. Still, given Arp's experience, not to mention the peer-approval grant system, it is hardly surprising that few young astronomers feel like entertaining such possibilities as that quasars are where 'outside' energy appears in our universe to keep it going, that some red shift might be quantized, that the properties of a shell of Bose-Einstein condensate or similar quantum construct might be consistent with the appearance of the limits of our universe including those quasars ...
In fact, there are a lot of significant problems with the big bang model, more than most people realize. There have had to be major adjustments made to it over the years to keep it consistent with new observations, adjustments of an arbitrariness and magnitude that normally make scientists suspicious of a theory. (Theories are supposed to predict things not yet observed, not just be an arbitrary fit to existing observations.) An 'inflationary period', whose existence is unsupported by evidence other than the phenomenon for which it was invented, is proposed to permit the observed large scale uniformities of the universe. At the same time, cosmic strings and similar concepts (also unsupported by other evidence) are proposed to 'explain' its observed lumpiness. (They are now going to have to 'explain' fully formed stable-looking galaxies at red shifts over 5 - and the Hubble keeps observing farther ones.) The distribution of hydrogen, deuterium and helium are in agreement with the big bang, if you choose the right starting density, but where are all the other things predicted by it: a large cosmological constant in particular? And, with that starting density, how do galaxies get heavy enough to do all that gravitational lensing? Yet, those who look for alternatives to the big bang model are the ones being derided as irrational and unscientific ...
We should all be better off with the humble view of one of the most brilliant scientists of all time, Isaac Newton:
"I do not know what I may appear to the world, but to myself I seem to have been only like a boy playing on the seashore, and diverting myself in now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me."
John Sankey (1990)
other notes on physics