(April 27, 2022 at 3:55 pm)JairCrawford Wrote: So, what I’m wondering is… Is it possible that there was no Big Bang and that the universe simply always existed?
We seem to have a lot of evidence of the universe expanding. We also have evidence of cosmic background radiation from when the universe was hot. But do we have evidence that these things started from a singularity? Is that part of all of it truly known fact? How can this even happen since in order for such an event to happen it would have to be “outside” time, because it would be before the expansion of the space time fabric?
We don't know how to model a singularity - it is by definition a breakdown of space and time. Whether there was one or not is an open question. However, it is clear that the universe was at one point very tiny (as you have said, expansion, background radiation, smoothness of spacetime, galactic evolution as we look back in time).
There are a number of proposals as to how the universe started. One is the Hartle-Hawking no-boundary proposal, that says that the beginning of the universe involved space without time. Only when space expanded did time start to form.
Another is that there was a quantum tunneling event that started the universe, followed by a rapid inflationary stage.
Both these are compatible with the idea that the total energy of the universe is zero. That is, you can get something from nothing, because the universe is nothing.
