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How will the Universe end? Three likely possibilities from Astrophysics & Cosmology


Universe – all that there is, was and will be… This sounds like a bit too philosophical take on defining the term, but in a way, it’s correct even scientifically. It is the potential playground of all those particles, stars, nebulas and planets that will come to existence at a later time. It had been the background of the things that were, in the past. And it’s inevitably true that it is the support of the existence of everything there is!

Ok, enough with philosophy. Now, let’s get down to Natural Philosophy, the golden realm of what we popularly call Physics!

So, as you all know, the most commonly accepted theory about the beginning of the universe is the Big Bang Theory (not the sitcom, bazinga!). This theory was initially brought to the table by the work of George Lemaitre, who had solved Einstein’s Relativistic Field Equations and come to the conclusion that the universe, everything we see there is, must have a beginning. Initially, he wasn’t taken that seriously – even Einstein himself is known to have remarked “Your mathematics is correct, but your physics is abominable!”. That must have been a great downer for Lemaitre, but that was hardly the end of the story. Soon after, a number of other scientists picked up the idea, and after Edwin Hubble laid down his ground-shaking observational conclusion that there are thousands of other galaxies in the universe (and like Galaxy S5, they may all be life-companions!), as well as the fact that these galaxies were moving apart from each other at mind-blowing speeds, even Einstein himself had to change his previous decision. It was then accepted that the universe must have had a beginning.

If you’ve followed my other article on the Steady State Theory, then you’re aware of the clash between Hoyle’s boys with the proponents of the Big Bang Theory. But as we all know, thanks to the discovery of the CMB (Cosmic Microwave Background) that pretty much established the existence of an afterglow of the Big Bang, as well as the discovery of the Quasars and such stuff, gradually the Steady State Theory had to take a back seat, before finally leaving the theatre (and kickin‘ the bucket too, eh?).

This lot is pretty much figured out. However, questions do remain. And of the countless questions still poking us at present, perhaps one of the most interesting ones is how will this drama end, once and for all, and if at all. This is what I intend to write about, in this brief article of mine.

The first scenario – Big Crunch

So, what we have as the first scenario is the famous (or infamous?!) Big Crunch theory, which is a result of the Oscillating Universe model. In the model, it is agreed upon that the universe began as a result of the Big Bang, a celestial event that triggered the birth of the cosmos. And since the time of the Big Bang, virtually the universe is expanding, with everything moving apart from everything else. Gravity gradually took the charge, as the outward thrust somewhat slowed down, and this lead to the formation of stars, galaxies, planets and other celestial things that constitute the observable universe.

Similarly, in the Big Crunch model, the ultimate globule that will be formed will be extremely dense and hot, quite similar to its cousin that created the universe in the first place. And it will also be extremely small, smaller even than an atom (previously, Lemaitre described his primordial atom to be a few thousand kilometers in diameter, but recent calculations have shown that even that is too great a size to consider). And similar to the singularity that dwelled during the birth of the cosmos (upto 10 powered -43 seconds from the moment of the Big Bang, i.e the birth of time), a new singularity will emerge, which will cause all the fundamental forces of nature (gravity, strong and weak nuclear forces and the electromagnetic force) to fuse together, giving rise to one unknown (yet) superforce.Whenever a star is formed, the force of gravity pulls the nebular cloud together, and creates a very heavy and increasingly dense mass. And naturally, with the rise in density, the temperature of the mass continues to increase. This first kick-stars nuclear fusion, that acts as the power source of the star.However, since the force of gravity continues to pull everything towards everything else, there will come a time when the outward thrust of the universe will reduce to 0, before finally turning negative. Physically speaking, the expansion of the universe will cease, and an opposite process of contraction will begin. This is the opposite of the Big Bang. Finally, everything will get smashed together, overwhelmed by the force of gravity.

And the bright side is that, from that seed, a new universe will gradually emerge, through the occurrence of another Big Bang. This is why the entire model is popularly known as the oscillating model. Like a pendulum oscillates between two extremes, the universe similarly oscillates between the creation (Big Bang) and the destruction (Big Crunch).

This all sounds pretty optimistic, and it does fit nicely into the somewhat forced reinterpretation of the Hindu cosmology, but that’s not the only thing to it. New kids have arrived in the town, and some of them are tougher than this guy, our poor, little Big Crunch model here, at least they’re equipped better, thanks to some of the recent experimental and observational findings.

Big Chill – Chillax, ’cause time’s runnin‘ out!

Ok, so what exactly is the second possibility? Before plunging into the depths, take a deep breath, because we’ll have to encounter two new terms before we do so. These are Dark Matter and Dark Energy respectively. What are they? No one seems to know for sure, at least as of now. But one thing is quite clear, there’s an eternal battle going on between the two opposing forces. On one hand, Dark Matter, popularly compared to a glue that has kept the structure of the universe together, is trying to pull everything together, and there, right on the other hand, Dark Energy is trying to pull everything apart.

During the late 20th century, it was found out that even the mass of the supermassive Black Holes at the centres of galaxies like ours isn’t enough to keep the structure of the galaxy as it is, after accounting for the total mass of all the stars, planets, nebulas etc of the galaxies. So, there must have been something else that could account for that hidden mass of the galaxies, that compensated for the additional gravitational force required to prevent the constituents of the galaxy from flying away. These matter were then named Dark Matter – not because there’s anything Voodooish about them, the classical ideas of physics simply don’t work for them. This dark matter accounts for the gravity of the universe as a whole, that tries to counterbalance the force of outward expansion of space itself.
Now, as per the Big Chill model, the Dark Matter in the universe might actually be strong enough to slow down the process of expansion, thereby reducing the outward (more precisely, away from each other) acceleration of the galaxies altogether. But even then, calculations tend to show that the dark matter might not be strong enough to reverse the process. What we’d have, as a result, is a universe that continues to expand indefinitely, but much more slowly.
The consequence? It’s often called a very sad and anticlimactic end to the whole drama that we called The Universe. Finally, all matter – stars, planets, moons, molecules and even atoms according to some suggestions – will get so far apart from each other, that nothing further will happen to the universe, or in the universe. As the nuclear fuel of the stars will finally give in to the stranglehold of time, the universe will go on becoming a far lonelier, darker and colder place, with nothing more to add to the show. Thus, in a way, that would be The End for the universe as a whole.

R.I.P, dear Universe – The Big Rip scenario

In yet another, and by far the most frightening, model which we popularly call the Big Rip, a much more severe consequence may be waiting for the universe. In addition to the Dark Matter that we’ve already discussed (very briefly), there’s additionally the Dark Energy, which is a mysterious force that has become, in the words of some, the dominant property of space itself. Dark Energy is mysterious, and what we know is that, it’s pulling everything away from everything else. In both the Big Rip and Big Chill models, the force of the Dark Energy is shown to be stronger than that of the Dark Matter. The only difference is, in the Big Chill scenario, the Dark Matter is strong enough to slow down the expansion of the universe sufficiently. However, in the Big Rip scenario, it isn’t.
What happens then? Since the Dark Energy is shown to be far stronger than Dark Matter, the expansion of the universe – the expansion of space itself! – isn’t going to slow down at all! Instead, the universe will accelerate in its rate of expansion. And finally, when you puff too much air into a balloon, it bursts. Similarly, the universe will tear itself to shreds, thanks to the inevitable and extreme level of expansion. In the National Geographic documentary The Death of the Universe, a similar analogy has been used. Also, as shown in the documentary (which you can find on YouTube), the Big Rip will cause the very fabric of spacetime to crack, causing everything to disappear into blackness or nothingness. Existence itself, in a way, will cease to remain as space gives in to the fatal and deadly consequence of its own dominant property.
But how do we exactly know that Dark Energy does indeed exist? Well, the answer is simple – the latest observational data show that the galaxies are showing no sign of slowing down in their process of flying away from each other. Einstein, in his pursuit of building the framework for a stable, static and overall unchanging, eternal universe, had introduced the concept of Labmda Force or Antigravity, to counterbalance gravity. Later, after Hubble’s findings were brought to the table, he called that the worst mistake in his scientific career. However, in the words of another famous scientist, what Einstein had thrown away had now re-entered the house through the window. The only catch is that, this hypothetical antigravity now is far stronger, strong enough to overwhelm gravity itself.
Should I start packing my bags now?
Nah, there’s enough time before any of the above events happen, if they happen at all! And to be honest, as Epicurus said about death itself not being an event that will happen to you, the end of the universe is, in a way, the end of existence itself. Thus, there won’t be anyone left to cry over the corpse of the universe after it all ends, unless you manage to sneak into another universe, if they exist after all!
NOTE: Also hosted on my blog.

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