Re: What would most likely happen?

Hi Jon,

I've heard arguments both ways about your first question. The general consensus seems to be that time will continue to flow "forward." By that, I mean that if the universe is closed and begins to collapse, we will still perceive time as going forwards during the collapse.

This boils down to the question of what determines the "arrow of time," or our sense of which way time flows "forward." This is generally related to the direction in which entropy increases. You can think of entropy roughly as "disorder." Higher entropy means greater disorder. It also means a more probable arrangement of things. For example, a pile of marble dust has more entropy than Michaelangelo's statue of David. This is because there's very few ways to arrange the molecules in the marble so as to get the statue, while there's a huge number of ways to arrange the atoms to get a pile of marble dust. On average, the entropy of the universe is increasing with time, and we believe that it would continue to do so after the universe began to collapse.

As to your second question, we can't describe what would happen in the final instant of a collapsing universe, for the same reason that we can't describe the first instant of the universe after the Big Bang. If the universe were to start collapsing, both its density and temperature would increase. At the very last moment of the collapse, the density and temperature become so large that we cannot describe the behavior of the universe with any of our current theories. One possiblity (purely a conjecture) is that the energy density would be so large that it would somehow reverse the collapse. Instead of completely collapsing in on itself, the universe would then "bounce" in another big bang.