As you can see, we think we have a fairly good understanding of our universe’s past. However, its future is much less clear. Right now, the universe is still expanding outward in all directions and, as it is with any expanding universe, it must meet with one of three possible conclusions.
First, the pull of gravity produced by all the matter in the universe will be great enough to reverse this expansion, eventually collapsing the universe back into itself in an event those infinitely creative physicists out there have dubbed the Big Crunch. Many people like this idea because it seems to fit in well with the continual cycles of death and rebirth that we observe so many other places in nature.
However, it may also be possible that the rate of expansion of the universe will exceed its gravitational pull. In this case, the universe will eventually break free of its own pull and will continue to expand for all eternity. Some people may find this a significantly more disturbing scenario, perhaps because the idea of something existing forever is simply hard to deal with.
There is a third but rather unlikely possibility that would also deny the universe an end. Here, the pull of gravity from all the matter in the universe would just equal its rate of expansion. This would mean that the speed at which our universe is expanding would continue to drop and drop yet it would never quite reach zero so it could never reverse. In effect, the universe would enter a nearly perfect stand-still.
However, for this scenario to occur, the balance between expansion speed and gravitational pull would need to be absolutely perfect. Just think, there are an infinite number of possible combinations for expansion speed and gravitational strength that would lead to the universe collapsing on itself. Likewise, the number of combinations that would cause the universe to expand forever is also infinite. Yet there is just one combination that would allow for the third case. In fact, the chances of it occurring are so infinitely tiny that we probably would have neglected to mention it at all if it weren’t for one curious fact: our universe’s expansion rate and gravitational pull seem to be so closely balanced that scientists still aren’t sure if it will eventually collapse on itself or expand forever. With this bit of information, the possibility that gravity will eventually slow our universe down to a virtual and eternal stand still suddenly becomes much more plausible. Granted, its chances are still very small but, for right now, we just don’t know for certain.
