Ethan Siegel has an excellent post up contemplating the various models of the timeline of the universe.
It’s only human to ask the most fundamental of all questions: where did all this come from? And we like to think we know the answer; it all came from the beginning.
But if you think about it for a little while, that simplistic answer — an answer that at first glance, might appear to be a tautology — presumes something very important about our Universe: that it had a beginning!
For a long time, scientifically, it didn’t appear that we knew whether that was true or not. The Universe could have had a beginning, before which nothing existed (or, at the very least, nothing as we understand it to be), or it could have existed eternally, like an infinite line extending in both directions, or it could have been cyclic like the circumference of a circle, repeating over and over again infinitely.
One thing I’ve noticed about this is that, at least in the last century or so, theoretical physics seems to have had a strong prejudice for the infinite universe.
It was Einstein’s preferred model, so much so that he introduced the cosmological constant to avoid dealing with the otherwise mathematical need to explain either an expanding or contracting universe. He later referred to that move as his greatest blunder. (Even though it ultimately proved prescient with dark energy, but for the wrong reasons.)
Once it became apparent that we were in an expanding universe, Fred Hoyle introduced the steady state theory to explain away any possibility of a beginning. His theory remained a respectful alternative to the big bang until the discovery of the cosmic microwave background, a prediction unique to the big bang. But Hoyle never accepted defeat, holding on to steady state until the end.
Shortly after a need for cosmic inflation was realized, eternal inflation became a popular assumption. Even if eternal inflation ultimately ends up not being accurate, and our universe appears to have a beginning, there will be the various multiverses theories to make the whole works timeless and eternal again.
Whenever theoretical physics has little or no observational information, it seems to default to reality being timeless and eternal. To a large extent, I can understand this, since timeless infinity is mathematically simpler than a finite or circular timeline.
But since observational data is generally assessed within the framework of theoretical assumptions, it seems like this should make the physics community a bit uneasy, a bit on guard that this preference could blind them for a while to contrary empirical evidence or even mathematical implications. I see posts like this one from Siegel as a good sign that there are physicists resisting this temptation, but I it seems like I read a lot more from others assuming infinity.