The Cosmos, or the universe, if one prefers the latter term is quite a mystery. The grim yet inevitable end of our vast universe is one of the most discussed subjects. Let’s talk about reasons why they’re ‘inevitable’ and why we shouldn’t be worried about them for at least for a few billion years.

1. Heat Death (or The Big Freeze)

Some believe that the universe would end in ice, some say fire. Thermodynamics, one of the oldest pillars of physics refutes both these statements with its assertion, that the end would be characterized by tepidity and sluggishness, in more scientific terms, equilibrium. This theory is based on the second law of thermodynamics, which dictates that large systems evolve toward equilibrium over time. A balanced, calm state where no reactions are favorable; There isn’t any energy to gain or lose.

Wonder what this would look like? Galaxies will no longer be visible to each other and the formation of new stars would cease. Eventually, atomic particles will decay into subatomic particles, and those subatomic particles will move so far away from each other that interaction will not be an option. This would result in what physicists refer to as ‘Heat Death’ or ‘Big Freeze’. Note that ‘Big Freeze’ does not have anything to do with temperature, and everything to do with entropy.

2. Theory of eternal inflation (Time isn’t gonna last forever)

This is my favorite theory to talk about, probably because it sounds quite hilarious. At least at first read, or listen, or any mode of communication. Let me put it out there, the gist of this hypothesis is that time can’t last forever. Published in a paper, in 2010, ‘Present treatments of eternal inflation regulate infinities by imposing a geometric cutoff. We point out that some matter systems reach the cutoff in a finite time duration.

This implies a nonzero probability for a novel type of catastrophe. According to the most successful measure proposals, our galaxy is likely to encounter the cutoff within the next 5 billion years’, In layman terms, this means that the cutoffs we use, while giving us nice and probably correct predictions in regards to the cosmos, leave an imprint which suggests that the cutoff, i.e the end of time, has a non-zero probability.

In other words, if you use a cutoff to compute probabilities in eternal inflation, the cutoff itself”—and therefore the end of time—becomes an event that can happen. The study also adds that we’d come across the cutoff in 5 BILLION YEARS! That’s not a lot of time, the universe has been around for 14 billion years, 5 billion is approximately when the sun is going to go all red giant on us. Well, one can say that it is poetic, everything dies at once.

3. Big Crunch

Quite like many other scenarios of a similar nature, the ‘Big Crunch’ revolves around Einstein’s Theory of General Relativity. Primarily, if the beginning of the universe was described by the Big Bang, Big Crunch tries to illustrate the end, as a result of that beginning.

The principal idea is that the expansion of our universe, which was a consequence of the Big Bang would not continue forever. Eventually, the expansion would cease and the cosmos would collapse into itself, pulling everything along until it turns into the biggest black hole ever. Well, we all know how everything is squeezed when in that hole. Hence the name Big Crunch.

For scientists to predict with certainty the possibility of a Big Crunch, they will have to determine certain properties of the Universe. One of them is its density. It is believed that if the density is larger than a certain value, known as the critical density, an eventual collapse is highly possible.

4. Big Rip

After our discussion on the Big Crunch, let’s talk about an event which is the polar opposite, yet as catastrophic as the above scenario. The Big Rip, which says that the acceleration of the expansion of our universe isn’t stopping, it isn’t even slowing down, and this is explained by something called “Dark energy” (Coincidentally, the main reason for the Big Crunch was that dark energy was getting weaker and wouldn’t sustain the expansion, in this case, it’s getting stronger).

Scientists say that this has led to the expansion getting faster, and if one looks at the most distant objects, they’re actually moving away from us and the acceleration is increasing the acceleration of expansion. That’s the ‘Big Rip’ – if dark energy gets stronger and stronger over time, it will eventually overcome any forces of attraction, and everything, from galaxies, planets and atomic particles to space-time itself, will eventually be torn apart before vanishing from view.

There’s no need for immediate alarm, however: the extreme sequence of events is predicted for around 22 billion years from now.

5. Vacuum Decay

While the other scenarios wouldn’t occur for billions of years, giving us some breathing space, vacuum decay has no qualms as such, it could happen anytime, and as such, humanity would never see it coming. It’s based on the nature of something called the Higgs field, which permeates our universe and varies in strength based on its potential.

To understand vacuum decay, you need to consider the Higgs field potential. Think of it as a track on which a ball is rolling. The higher it is on the track; the more energy the ball has. The Higgs potential determines whether the Universe is in one of two states: a true vacuum, or a false vacuum. A true vacuum is the stable, lowest-energy state, like sitting still on a valley floor. A false vacuum is like being nestled in a divot in the valley wall – a little push could easily send you tumbling. A universe in a false vacuum state is called “metastable” because it’s not actively decaying (rolling), but it’s not exactly stable either.

If an event with enough energy occurs in the universe at any time, it could set the ball rolling. So as not to forget, such an event does not need prodding at all (Quite alarming, that): Quantum particles have the ability to “tunnel” through a barrier, whether from one side of a wall to another or from one vacuum state to another, so random quantum fluctuations could do this too.

A true vacuum has different constants of nature than a false vacuum. Constants of nature are things like the charge of the electron or the mass of the particles or even the strength of gravity sometimes. So if you take the molecules that you’re made of and put them into a true vacuum state, those molecules don’t hold together anymore. This would mean total destruction, and to think that all this might come to pass just because a particle darted off to a place it shouldn’t have.

I hope that these grim visions of the future of our universe don’t keep you up at night, but if they do, take heart in the fact that you most likely wouldn’t see these come to pass in your lifetime, unless someone figures out a way to prolong life, which is another matter altogether.

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