Time was born with the universe that, since the Big Bang, is expanding. Is it possible that, at some point, it starts to contract?
Or Graur , University of Portsmouth
Time arose when the universe did, and how the universe ends (if it ever ends) will also determine whether time might end.
We believe that the universe arose compressed into an infinitesimally small space, and for some reason that we have yet to understand, immediately began to expand, getting larger and larger. This idea or model of the beginning of the universe is called the Big Bang .
In 1998 science discovered that the universe was expanding faster and faster, but we still don’t know why.
It must have something to do with the energy that exists in the vacuum of space. It could be a new type of energy field or something that responds to completely unknown physical laws. To symbolize this gap in knowledge we call this new phenomenon “ dark energy ”.
Although we are still working to determine the nature of that energy, we are already in a position to envision different ways in which the universe could come to an end.
If dark energy weren’t too powerful, that would mean it would take an infinite amount of time for the universe to expand to infinite size. Infinite means that it has no end, so in this case time would never end.
But if that energy were too intense, it could cause the universe to expand so fast that everything in it would be obliterated (including atoms , the tiny building blocks that make up everything in existence). In this scenario, known as the Big Rip , the universe would not expand forever.
Instead, it would expand so fast that it would reach infinite size at a given moment in time. And that exact moment, when the universe was infinitely large and all matter had been torn apart, would be the last. The universe would cease to exist, and time would die with it.
But there is another way the universe could go, the Big Crunch . In this scenario, the universe would at some point stop expanding and start contracting again.
The universe would get smaller and smaller, galaxies would collide with each other, and all the matter in the universe would cram together. And when the universe had shrunk into an infinitesimally small space, time would disappear.
The Big Bounce
Some physicists believe that the Big Crunch would not mean the end of the world, but simply mark the midpoint of its existence. According to this theory, the universe would start out infinitely large and then contract for a long time until it was reduced to the smallest possible size. But when this happened, instead of disappearing, a Big Bang would occur and the universe would begin to expand.
According to the Big Bounce hypothesis , there would be an infinite amount of time before the universe contracted to occupy the smallest possible space, and, similarly, there would be an immense amount of time when it later began to expand. In this way, time would have neither beginning nor end.
In some Big Bounce models the universe only bounces once, but in others there are an infinite number of bounces; the universe would constantly expand and contract, like an accordion that never stops playing.
All these theories show us possible scenarios, but not necessarily certain ones. First of all, we would have to determine what dark energy is, and more importantly, we have to be aware that there are no guarantees that any of the current theories about how the universe works are correct.
A day will come, perhaps in a few weeks or perhaps in a hundred years, when someone (and why not you?) will come up with a better theory than the current ones that explains how the universe works. Perhaps then we will know if time can be extinguished, and perhaps then the new theory will also propose a radically different concept of time… Or eliminate it altogether.
Or Graur , Senior Lecturer in Astrophysics, University of Portsmouth
This article was originally published on The Conversation . Read the original .