more about the Big bang.

this is the graphic Craig used for this article


On his most recent Q/A William Lane Craig deals with the Question about is the standard model (Big Bang singularity) still the prevailing model. Here's what he says:

Question from reader:

I recently was told by some physicists whom I had the chance to interview for a paper that the standard big bang model of the universe does not include a singularity anymore. That may have been the case twenty five years ago, they said, but nowadays physicists say that the big bang extends only back to Planck time. Can you PLEASE clarify the confusion I’m having on this?
God bless,
Glenn

Dr. Craig responds:

I’m just in the process of wrapping up an article on the kalam cosmological argument co-authored with James Sinclair for a forthcoming volume with Blackwell entitled Companion to Natural Theology. Jim is writing the section on the empirical evidence of astrophysical cosmology for the beginning of the universe. He does a marvelous job of summarizing the current state of the field, a preview of which I’ll give you here.
First, though, in answer to your question, the standard Big Bang model includes an initial singularity. The model cannot lose that feature and remain the same model. So there’s no question of the standard model’s not including a singularity anymore. Rather what the physicists you interviewed meant is that the standard model is no longer the prevailing view today. Their claim is that while the standard model was the accepted view 25 years ago, that is no longer the case today.

Now in one sense that’s true. The standard Big Bang model needs to be modified in various ways. For example, the model is based on Einstein’s General Theory of Relativity. But Einstein’s theory breaks down when space is shrunk down to sub-atomic proportions. We’ll need to introduce quantum physics at that point, and no one is sure how this is to be done. That’s what your physicists meant when they said that the Big Bang extends back only as far as the Planck time. (That, by the way, is no new realization; everyone always knew that General Relativity breaks down by that point.) Moreover, the expansion of the universe is probably not constant, as in the standard model. It’s probably accelerating and may have had a brief moment of super-rapid, or inflationary, expansion in the past.

But none of these adjustments need affect the fundamental prediction of the standard model of the absolute beginning of the universe.
Indeed, Jim’s survey of contemporary cosmology reinforces just how robust the standard model’s prediction of an absolute beginning continues to be. He considers three broad research programs being currently pursued based on possible exceptions to the Hawking-Penrose singularity theorems, which support the standard model’s prediction of an initial cosmological singularity. These are (1) Closed Timelike Curves, (2) Violation of the Strong Energy Condition (Eternal Inflation), and (3) Falsity of General Relativity (Quantum Gravity). The first of these postulates an exotic spacetime which features circular time in the past and so is not taken very seriously by the vast majority of cosmologists. The real work has been on the other two alternatives.
With respect to the alternative of Eternal Inflation, it was suggested by some theorists during the 1980s that perhaps the inflationary expansion of the universe was not confined to a brief period early in the history of the universe but is eternal in the past, each inflating region being the product of a prior inflating region. Although such models were hotly debated, something of a watershed appears to have been reached in 2003, when three leading cosmologists, Arvin Borde, Alan Guth, and Alexander Vilenkin, were able to prove that any universe which has, on average, been expanding throughout its history cannot be infinite in the past but must have a past space-time boundary.
What makes their proof so powerful is that it holds regardless of the physical description of the universe prior to the Planck time. Because we can’t yet provide a physical description of the very early universe, this brief moment has been fertile ground for speculations. (One scientist has compared it to the regions on ancient maps labeled “Here there be dragons!”—it can be filled with all sorts of fantasies.) But the Borde-Guth-Vilenkin theorem is independent of any physical description of that moment. Their theorem implies that even if our universe is just a tiny part of a so-called “multiverse” composed of many universes, the multiverse must have an absolute beginning.

For whatever its worth.