Paul Steinhardt, one of the original cosmic-inflation theorists and the man who coined the term "quintessence" has a new theory of cosmology which is described at http://arxiv.org/abs/astro-ph/020447. The abstract reads,

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The Cyclic Model is a radical, new cosmological scenario which proposes that the Universe undergoes an endless sequence of epochs which begin with a `big bang' and end in a `big crunch.' When the Universe bounces from contraction to re-expansion, the temperature and density remain finite. The model does not include a period of rapid inflation, yet it reproduces all of the successful predictions of standard big bang and inflationary cosmology. We point out numerous novel elements that have not been used previously which may open the door to further alternative cosmologies. Although the model is motivated by M-theory, branes and extra-dimensions, here we show that the scenario can be described almost entirely in terms of conventional 4d field theory and 4d cosmology. The theory does not actually have a "big crunch" in the traditional sense; rather, after a long period of expansion so that there is less than one particle in each visible segment of the universe, a hidden dimension contracts and suddenly the universe is full of light and energy, and it starts expanding again. There is no inflation as in the regular model, instead the long period of expansion from the previous cycle is what is responsible for the remarkable uniformity that is observed. The interesting aspect from this list's perspective is how to regard infinite-time cosmologies. Does it make sense to imagine a universe which has had an infinite past? How could we simulate that on a computer, if there were no starting point? I think Steinhardt's model also allows for a spatially infinite, flat universe as well. So we have infinities in all directions, temporal as well as spatial. We could avoid the problem by postulating that every cycle in Steinhardt's model is identical, giving the effect of a single universe, but I don't think there is any reason in the theory to suppose that would happen. Rather, each crunch is slightly different, and these small perturbations carry over into unique initial conditions for the next big bang. How could we go about modelling a universe like this? Can we rule out Steinhardt's cosmology on fundamental principles? Are infinite-time universes of zero measure compared to ones with a fixed beginning? It would be interesting if the everything-exists model could be used to constrain cosmological theorizing in this way. Hal Finney