One day the universe is going to end, probably. How that is going to happen we don’t really know. There are three main theories. Don’t worry these aren’t set to happen in your lifetime, nor your grandkids, or their grandkids. Just in case you find this article really depressing.
Before 1998 we assumed that the universe was expanding at a steady rate and it would eventually start coming back to a central point. A bit like throwing a ball up in the air. But it turns out that the universe is actually accelerating in its expansion. Scientists believe this is because of something called dark energy. Some guy named Einstein came up with this idea but dismissed it as being rubbish. It’s now widely held that it is real. It’s also really important with our view of the universe.
The Big Rip
Measurements have shown that all the galaxies are moving away from one another. Through some weird quirk that we can’t explain the space between galaxies expands equally for all of them. Fortunately, at the moment, individual galaxies create enough gravity in order to keep their stars within their “pull”.
In the big rip theory, the speed of expansion becomes so fast that it is no longer countered by the gravitational pull of individual galaxies. Astral bodies would break down into the particles that made them, these particles would continue to accelerate to beyond the speed of light, at that speed they would never be able to interact with other particles. This means the universe would be empty space filled with rapid particles and nothing else. Bit bleak isn’t it?
The big freeze/heat death
In this, the most likely scenario, matter stays held together but the universe is brought to an end by the laws of entropy. Entropy is a tricky concept but if you think about it as a layered drink, eventually all the layers mix together. This applies to the universe as well. Stars have a life cycle, even black holes have a life cycle, albeit a very lengthy one. Eventually, all of this will be converted into radiation. The universe will continue expanding until there is nothing but radiation.
However, there is a slight ray of light in this scenario as some scientists believe in something called quantum tunnelling, in this scenario we may have another big bang that kicks off the cycle again
The big crunch/big bounce
For a long time, this was one of the most prevalent theories. If there is less dark energy then scientists think there is in the universe then gravity will be the prevalent force in the universe. What this means is that the expansion will eventually decelerate. When that happens gravity will play its part and everything in the universe will begin accelerating back towards one central point.
As this happens the universe will become increasingly denser and heat up. As everything comes together black holes will merge and matter will be drawn towards them all of these will link up to form one giant black hole which will swallow the entire contents of the universe including itself. Then from that, there will, at least in theory, be another big bang and expansion will start all over again. In this theory, the universe is a constant cycle of expansion and retraction which means technically it never ends. Of the three theories, this is probably the one that is the least depressing. However, by the time any of those scenarios become an issue that effects humanity, humanity would have almost certainly been wiped out. With the way things are going, probably through our own stupidity!