How Will The Universe End?

How Will the Universe End?

While it may seem as if the universe will go on forever, it more-than-likely has an expiration date. Luckily, you won’t have to worry about it, and neither will your grandkids. Estimates on when the end of all things will actually occur range from 100 trillion to just 2.8 billion years away. In either case, it’s an unbelievably long time. But when we consider that the universe is about 14 billion years old right now, we can see that – if the closest estimates prove true – it may currently be toward the tail end of its lifespan. But when everything does grind to a halt, how will it do so? And what will it look like?

As with many of the universe’s most momentous questions, we don’t really know for sure. But there are plenty of theories. And the five most prominent ideas (in ascending order of likelihood) are cosmic uncertainty, the false vacuum collapse theory, the Big Crunch, the Big Rip, and the Big Freeze.

First off, the supposedly least likely theory – cosmic uncertainty. Cosmic uncertainty hinges on our current understanding of the properties of dark energy – the mysterious and unseen form of energy responsible for the current expansion and acceleration of space. While scientists agree that dark energy is making space bigger, there are little-to-no theories on its nature, composition, or practical workings. Because it’s so mysterious, experts are unsure how, or if, it will play a role in the continued existence of the universe – especially as it’s believed that today’s dark energy is different from what was around at the early stages of creation. So, the cosmic uncertainty theory proposes that, because we don’t know the true nature of dark energy, we don’t know how it will react in the future. Maybe it will dramatically change its nature once again, inflicting untold catastrophes on the known universe. However, as dark energy doesn’t seem to show signs of change based on the little we do know about it, this seems unlikely. And regardless, there’s no way of predicting the damage that it could suddenly decide to deliver.

The second and slightly more accepted theory is the false vacuum collapse theory, also known as vacuum decay. This one certainly brings an efficient end, if nothing else. It rests on something called the Higgs field, which stretches through space, determining if we’re in a true or false vacuum. Should these vacuums ever infiltrate each other – by some sort of seemingly random, high-energy event – even one stray particle could cause a small bubble of true vacuum within a false one, which would expand at the speed of light to engulf and kill the entire universe.

What’s a little frightening is that this theory shows some promise, as the Higgs boson particle seems to indicate that we are currently living in a false vacuum universe. So, technically, it could all end at literally any second, but it is very unlikely. Various other studies appear to simply disprove the theory. And even if it could happen, the life cycle for a false vacuum universe is far longer than the 14-billion-years ours has so far afforded us. So, the potentially unimaginable disaster isn’t due for a long, long time.

Theory number three sounds like a breakfast cereal, but it’s quite a bit more complex; The Big Crunch. Often explained as a reverse Big Bang, it too builds on how dark energy has expanded the universe. However, advocates for this theory believe the growth will one day slow and stop. If and when this happens, gravity beats dark energy to become the dominant force in the universe and everything begins to collapse in on itself – retracting into the mother of all meeting points, the singularity. Along the way, there’d be huge collisions of stars, planets and all forms of matter, as they merge into black holes, which merge into themselves, until everything has returned to a single, immeasurably dense point – as in, before the Big Bang.

And, as if that wasn’t all cool enough already, Big Bounce theorists have suggested that we could then see a new Big Bang, wherein all the forms of matter collapsed into the singularity are burped back out, ready to begin a new cycle of creation. All of that said, however, as it’s not believed that the relationship between dark energy and gravity will ever change, the Big Crunch and Bounce hypotheses are still shrouded in severe scepticism. It’s just not that likely.

On the other hand, the accelerating expansion could result in another form of universe extinction – the Big Rip. As its title suggests, this idea is the polar opposite of the Big Crunch, arguing that dark energy will ultimately rip apart the fabric of spacetime itself. According to the theory, dark energy will eventually cause everything to expand at such a dangerous rate that galaxies, stars, planets, black holes, atoms, subatomic particles, and every other comprehensible thing would be completely torn apart. Think of it like breaking off a piece of sticky toffee or chewy candy. Your hands are dark energy, and the candy is spacetime. Eventually, the force of your hands will overcome the force of gravity keeping the candy together, so it splits apart. Dark energy is strong stuff and may in fact be strong enough to first splinter and then disintegrate all we’ve ever known.

While this may sound like a solid – if scary – possibility, the limitless expansion of the universe will most likely result in another more realistic outcome – the Big Freeze. According to this final theory, the universe will one day grow so large – and all matter will be spread so thin – that temperatures will reach absolute zero and the universe as we know it would cease to function. While the stars wouldn’t disappear especially quickly – and so the 100 trillion-year mark from earlier could theoretically be reached - the supply of gas necessary for star formation would be spread too far apart to properly coalesce into anything.

Eventually, even the existing stars would run out of energy, resulting in their destruction, too. So, with old stars stripped of energy and new stars failing to form, the universe will grow steadily darker and colder – with even the black holes eventually disappearing, and space transforming into a dark, freezing, empty, and energy-less void. And without energy, nothing can exist. Of all the theories, there’s a general belief that this is the most likely outcome for our universe.

But it is still just a theory, and we still don’t know how, when or why the universe will conclude. It could be that dark energy deviates, and destroys all before it. Perhaps we’ll all eventually be incinerated by a massive bubble of true vacuum. The universe could one day shrink back into itself, and while it’s at it, even reproduce another cosmos creation that’ll live for billions of years more. Failing that, spacetime itself may be stretched to the point of tearing and total ruin, or the universe’s energy supply could simply run out, triggering endless darkness. But, apart from all of the above, the future’s bright – and the universe isn’t going anywhere today, tomorrow or for a few million more years yet!