There is a dense feeling which suggests that nothing is permanent in this world. This logic, if true, should hold good for the universe as well. We’d like to think that the Universe will continue forever, but chances are, at some point it will cease to be. Today we share an article by Richard Edwards, a science enthusiast and the deputy editor of SFX. Here’s how current thinking suggests the end may come to pass.
The Universe is becoming less and less structured. That’s a result of the second law of thermodynamics, which states that the disorder (or ‘entropy’, in a physicist’s language) of any closed system will always increase. The so-called heat death of the Universe may be the endgame of this process, and would happen when entropy reaches a maximum and the temperature of the entire cosmos becomes uniform.
If that happened, ordered structures such as planets, stars and galaxies would no longer exist. Just as a sandcastle eventually collapses into particles of sand, they would have disintegrated into a sparse gas of photons, electrons and neutrinos. With all matter in the Universe at a single temperature, there would be no temperature gradients to drive the reactions that make the Universe an active, dynamic place, leaving behind a dead expanse where nothing interacts.
But there’s no reason to panic just yet – we’re looking at somewhere in the region of 10100 (10 billion, billion, billion, billion, billion, billion, billion, billion, billion, billion, billion) years before this particular fate is likely to come our universe’s way.
The Big Rip
Two of the biggest mysteries facing cosmologists are dark matter and dark energy. Our models of the Universe suggest dark matter exists, but we can’t see it, and even if it’s out there, we have no idea how it might interact with normal matter. Meanwhile, observations tell us the Universe is growing at an ever-increasing rate, but this is counter-intuitive – you’d expect the gravitational attraction between galaxies to keep this growth in check, or even pull them back together. Astronomers believe dark energy is driving this expansion.
As the galaxies move further apart, the gravitational force between them decreases. If this continued, the force exerted by dark energy would gradually overwhelm the force of gravity. Galaxies would fall apart, planets would leave the orbits of their stars and the planets themselves would disintegrate. The process would continue until the Big Rip, when the ‘fundamental forces’ that hold the Universe together would become obsolete and reactions would become impossible. The Universe would be dead.
The Big Crunch
We know so little about dark energy and how it behaves that the destiny of the Universe may actually go in the opposite direction to the Big Rip. If it turned out, for example, that the forces causing galaxies to move apart are weaker than gravity, then gravity would be dominant.
Eventually, gravitational attraction would win out, galaxies would stop moving apart and gradually the Universe would start to shrink. All of the matter in the cosmos would clump together in increasingly large masses, until everything collided in a cataclysmic Big Crunch, bringing the whole thing to an apocalyptic end.
While our observations that the Universe is expanding seem to make a Big Crunch unlikely, it’s not beyond the realms of possibility. The rate of expansion has not been uniform throughout the Universe’s history – it could just take a shift in the equilibrium between dark energy and gravity to bring everything tumbling back together.
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The Big Bounce
The Big Bounce takes the Big Crunch theory one step further, suggesting that the end of one universe could trigger the creation of another. As all the matter in the old universe is compressed into a smaller volume, some scientists believe that the effects of quantum mechanics would start to kick in, repelling the particles that were previously being pulled together by gravity.
This, they say, would create a rebound effect that would send all of that matter whizzing out again, creating a new universe in an all-new Big Bang. Supporters of the theory like the elegance and simplicity of a cyclical model, where one universe replaces another, which replaces another, and so on. Also, it’s a neat way of explaining what triggered the Big Bang, particularly for those sceptical about the premise of an entire universe being spawned by an infinitely small singularity.
However, we have no evidence that the end of one universe could start another this way – and the physics of particles during the high-energy conditions surrounding the Big Bang are notoriously difficult to model.
The eternal inflation model is consistent with the Big Bang theory and, as the name suggests, theorises that the Universe will keep expanding forever. There are a couple of ways this could work. The ‘standard inflation’ version allows for the expansion of one single universe (the one we experience), which is more or less uniform throughout.
The ‘bubble universe’ version, meanwhile, implies an expanding multiverse made up of many different universes of normal space. Our own universe would be one of these. These would be entirely separate and unable to interact with one another; they could even feature different laws of physics. Within the multiverse, the individual universes could live and die a heat death, while the larger multiverse continued – the small universes would be finite entities within an infinite structure.
Other versions of the eternal inflation model abandon the Big Bang theory entirely and imply that the Universe has no beginning and no end at all.
Apart from these five possibilities, there could be many more ways that could make the universe cease to exist. The future generation will have to battle with many more challenges and make an attempt to seek more answers to the mysteries of the universe.
- Science Uncovered (July 2014)