By Samaira Kalia
The universe is everything. The expanding space holds all the stars and planets, all the matter and energy, including you. It even holds time itself. But eventually, there must be an end to time. Long after people go extinct, there will be an end to the universe. But how will it end, and what would be the last thing to ever actually happen?
Most of the examples that will come up later in this article will include the expansion of the universe. So to understand why that happens, we need to understand how that happens.. Every day, the universe expands due to the existence of dark energy. Dark energy can be described as an “anti-gravity” force that provides negative pressure, fills up the universe, and stretches the fabric of spacetime. Scientists are unsure what exactly dark energy is; it’s mostly used as the word to describe the mysterious substance that causes the universe to expand rapidly.
So now that we know how the universe is growing, how will the universe end its life?
Scientists have many theories for how the universe ends. One of them includes the Big Crunch. Another way to think of this is like the opposite of the Big Bang. One day, the universe will stop growing. Slowly, it’ll start to shrink. As the universe grows smaller, it also gets hotter, trapping all the heat and everything else in a smaller area. Finally, all that existed in the universe collapses into a small point, where the universe began. And what happens after the Big Crunch? Maybe there will be another Big Bang, and a new universe will be born. And maybe the cycle repeats over and over again, making several universes other than our own. But this is probably not what will happen at all. Instead of slowing down, currently, the universe is expanding faster than before, instead of slowing down.
Another theory is the Big Freeze. A slightly less exciting one compared to the Big Crunch, the Big Freeze states that the universe will continue to expand, but as it expands, it becomes colder and colder. The universe will eventually become too cold for any life to stay alive. The stellar remnants of stars and galaxies will fall apart, and all remaining matter will be locked up inside black holes, introducing the “Black Hole Era”, where the black holes will be the only normal matter left in the universe. After an incredibly long time that we can’t even show with numbers, the black holes will also die, leaving a large empty gap with no light; nothing.
The third way the universe might end is known as the Big Rip. In that scenario, if dark energy keeps accelerating the expansion of the universe, in simple terms; the universe would be torn apart. There is a chance that if the universe keeps accelerating its expansion, it will expand so fast that it will tear the universe apart, breaking up every atom, until nothing remains. Thankfully, most physicists don’t believe that this will happen. It’s unclear how this process of ripping can affect some specific parts of the universe. For example, it’s impossible to tear apart quarks; the small subatomic particles that make up the protons, electrons, and neutrons in an atom. When you attempt to tear them apart, you’d need so much energy, new quarks would form from that. So ripping apart quarks would lead to some more interesting reactions. Also, this energy that tears apart the universe doesn’t behave according to normal physics. This phantom energy would need some sort of negative kinetic energy. But since kinetic energy can only be zero or a positive number, it’s not possible. Negative kinetic energy usually doesn’t happen in the universe; otherwise we’d have balls rolling uphill naturally.
So which one of these scenarios is correct?
The answer is…
We don’t know.
All of this will happen trillions of years into the future, long after the Earth is destroyed. So there’s still so much time between now and the end of the universe, and there’s still so much to discover. We still don’t know what’s the mysterious dark energy that’s making the universe grow. Maybe we’ll learn a new and more solid theory after discovering dark energy. Or maybe the true answer is none of these theories. Scientists are pretty sure that after a very long time, as the universe grows, the galaxies and stars and planets will all spread out and be farther away than before. We won’t be able to see any galaxies or stars in our night sky. Any remaining humans on Earth or other planets will hear stories about stars, and many will not believe they exist. So there’s still a long way to go before the end of time itself.