The Scientific Revolution of the 17th century which helped us come up a new model of the Universe has given us clear and deep insight on how the Universe began.
From what we know, all the matter in the Universe were together at a point of ultra-high density, then it expanded – giving everything we know in the universe: planets, stars, galaxies, etc. – its present day distribution. This cosmic expansion event, believed to have happened around 13.8 billion years ago, is the first preliminary evidence that the universe featured a cataclysmic explosion, which has come to known as the Big Bang.
According to the Big Bang theory, that cataclysmic explosion resulting from a small agglomeration of extraordinarily high density, is believed to have marked the origin of the Universe. We know about the universe’s past, and also the present – that most of the galaxies are receding from us, which suggests it is expanding at an accelerated rate. But what about the future? How will the universe end?
Albert Einstein’s theory of general relativity postulates that matter and energy can curve, or wrap space and time. This association between matter, energy, space and time spreads across the entire universe, and has inspired theoretical physicists to conjure up the theory on the ultimate fate of the universe. According to them, the fate of the universe depends on three things: the exact shape of the universe, the amount of Dark Energy it carries, and changes in its rate of expansion.
Based on those three things, cosmologists have provided three possible answers suggesting how the universe end would turn out to be. They are: the Big Freeze, the Big Rip and the Big Crunch.
To understand these scenarios, let us imagine two galaxies held together by the attractive force of gravity. Meanwhile, the repulsive force expanding the universe are dragging them apart. Now imagine this battle between these two opposing forces happening on multitude of galaxies. The after-effect of these battles determines how the universe end could come to be.
The Big Freeze:
The Big Freeze scenario is when the repulsive force expanding the universe is strong enough to pull the galaxies apart to the point the attractive force of gravity can hardly be in effect. When this happens, the universe would still keep getting bigger but it wouldn’t accelerate like it used to.
Oodles of galaxies which was once bound together by gravitational attraction would drift away from each other. Every objects within them such as stars and planetary systems would float away from each other before galaxies crumbled into lonely objects meandering serenely in the vast expanse of space.
The light emitted from them would be redshifted into longer wavelengths. The energy and gas radiated from them would be too sparse to create new stars. The universe would turn dark and cold, and finally approach a frozen state known as the Big Freeze.
The Big Rip:
The Big Rip is one of the models that accounts for the ultimate fate of the universe. When this happens, the repulsive force accelerating the unceasing expansion of the universe eventually overcomes the gravitational attraction, tearing apart galaxies and solar systems.
Even the electromagnetic, weak and strong nuclear forces which bind atoms and nuclei together are not left out. Atoms, and subatomic particles are destroyed. The matter and space-time itself are also eventually torn apart.
The Big Crunch
The Big Crunch is another cosmological scenario concerning the end of the universe. It is when gravitational force holding the galaxies wins out, slowing down the rate of expansion of the universe and bringing it to a halt. After that, it reverses it. At such juncture, galaxies would hurl towards each other, and their gravitational pull would get so strong that they would merge.
Stars too would converge and as space contracted temperature would rise everywhere all at once. The entire mass of the universe would be compressed in such a tiny space including the atoms and sub-atomic particles. And what’s all that’s left is immensely dense, hot, compact universe – the state lot like the one preceding the Big Bang.
Another theory says that this tiny incredibly dense and high-temperature state could explode in another Big Bang, causing reformation of the universe. And that the universe could have gone through this cycle of expansion and contraction over and over again, repeating its entire history. The theory describing such a scenario is called the Big Bounce.
So how many bounces could have already happened? A hundred times? A thousand times? Or perhaps millions? We don’t know for sure. And there’s no way to tell how many might happen in the future. In fact, each bounce would erase any record of the universe’s previous history.
Which of those scenario are we heading to? Like noted above, the answer depends on the shape of the universe, the amount of dark energy in existence and its expansion rate. Several scientific observations suggests that of the three possible scenarios, the Big Freeze is the most probable. But don’t just let their observations send shudder down your spine because we have got unimaginable amount of years before it sets in.