Scientists theorize that the entire universe began with something called the ‘Big Bang’ – what may be described, in layman’s terms, as a vast explosion of matter and energy from a single point in space that gave birth to atoms, molecules and the universe as we know it. What caused the Big Bang, or how exactly it happened and when, is a matter of ongoing scientific debate. What is for sure, though, is all that begins must one day come to an end. The universe, vast and immeasurable though it might be, is no exception to this rule of ultimate demise of all matter. The only question that remains now that we know how the universe began, is how will it one day come to an end? Well, there are three widely accepted theories among the scientific community regarding what might cause the end of the universe in the distant future.
- The Big Rip
The universe is constantly expanding equally in all directions. What is stranger, however, is that not only is it constantly expanding, but the rate of expansion is constantly accelerating as well. This means that everything in the universe is moving farther and farther away from everything else at an ever-increasing pace. It is a fascinating thought. We do not know what force causes this constant and accelerating expansion or even how this force works – hence we call it ‘Dark Energy’.
A section of cosmologists believe that the rate of expansion of the universe will continue to accelerate indefinitely. What this means is that all galaxies will move farther and farther away from each other. Not only that, but the space within a single galaxy will also continue to expand at a growing pace.
At present, the force of gravity holds the galaxies together, but once the rate of the expansion of the universe outpaces the force of gravity, this will mean that constellations and planetary systems within a galaxy will move apart at a rate faster than gravity can hold them together. As a result, galaxies will be ripped apart; their unity disintegrating as all the parts that make up the whole is thrown helter-skelter by an ever-expanding cosmos. Later, smaller bodies such as stars and planets and even black holes will begin to be ripped apart, as their gravitational cores would not be strong enough to hold them together. Once the speed of the expansion grows even faster, it will start affecting the very atoms and molecules themselves. The atoms would simply disband into their particulate matter. Molecules would no longer exist. Once the speed of the expansion crosses the speed of light, no particle in the universe will ever be able to interact with any other particle, leading to an eternity of a vast and ever expanding cosmos full of individual particles that can never ever touch another particle. And thus, the universe would end; a dark and lonely place.
- The Big Crunch
Yet another group of cosmologists believe that the universe would end in a way completely the opposite of the Big Rip. This is based on the assumption that there is only a limited amount of ‘dark energy’ in the universe and that given enough time, this energy will sooner or later run out. When this happens, the expansion of the universe would slow down, and eventually, reverse. In the absence of ‘dark energy’, gravitational forces shall rule the universe and the universe would start contracting, as matter would be pulled together by gravity. As the universe contracted and the concentration of matter increased, so would the temperatures. Thousands of years before the Big Crunch, background radiation of the universe would be hotter than the surface of the hottest star at the current time. All matter would start banging into each other and contracting due to the constant gravitational pull. Planets would be ripped out of their orbits. Eventually, the contraction would give rise to the formation of numerous gigantic black holes that would swallow up everything around them. Minutes before the Big Crunch, all the black holes would merge into one monumental, ultra-large black hole that would swallow up every particle in the universe, and eventually even itself. As the entire cosmos collapses in on itself in the form of a giant black hole, so shall end the universe as we know it.
- The Big Freeze
This may be called the most mundane and unexciting of the three scenarios, and yet, the most likely. There is a school of thought in the scientific community that believes that the universe will neither be ripped apart by dark energy not be crunched to nothingness by gravity – rather, it will just…burn out. This is called entropy, and all physical systems evolve towards a condition of maximum possible entropy.
This school of thought believes that the universe would continue to expand, consequently taking cosmic bodies farther and farther away from each other. Eventually, the gas clouds that give rise to stars would exhaust all their energy. The existing stars would burn for a while and then die out one by one. The universe would become a cold, dark and lonely place, populated only by black holes, until even they disintegrate over a course of billions of years into nothingness. As no new photon particles would be formed, the universe would descend into total, frigid and lifeless darkness – thus having reached maximum entropy. The disintegration of the universe would therefore be complete. It would die not with a bang, but with a whimper.
We do not know how and when the universe would be destroyed, or even how it would happen. But while scientists are working hard trying to figure that out, make sure your life is awesome enough that the universe is glad to have existed just to have made you happen!