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Oblivion: the death of the universe

The theories behind the inevitable end of the universe

By Patrick Regan

Source: © ESA/Herschel/PACS/MESS Key Programme Supernova Remnant Team; NASA, ESA and Allison Loll/Jeff Hester (Arizona State University)
A Crab Nebula

There will come a time when nothing will remain of what we call our universe. Every star will fade and all matter will decay into radiation. The cosmos will be stagnant and dark. Chaos will rule.

In general, the universe tends towards chaos (or disorder), but what does this mean? We know from our own experiences that the longer we leave something, the more likely it is to fall apart. Take a student’s bedroom for example. It may be tidy at the start of term, butas the year progresses: plates will pile up on the desk, sheets won’t have been washed and the piles of clothes on the floor will make the colour of the carpet a distant memory. This is because it takes energy to maintain order - energy which a student may not have.

Note that in physics when we say order, we are simply referring to how tightly particles are

arranged. Intuitively, we know that a brick is more ordered than a pile of dust. Ice is more

ordered than steam because its atoms are closer together. A universe that is filled with

complex structures such as galaxies and stars is more ordered than one that only contains

distributed particles of energy. When particles are more spread out, they are less ordered.

Now, think of the universe as a cosmic bedroom. Currently, we can consider it to be ordered

because it has billions of galaxies with stars and planets inside them. But as time goes on,

everything becomes less ordered. Eventually the stars will explode and die and after many

generations, the gas clouds in deep space used to form suns will have run out of fuel and no

new stars will be formed. Galaxies will collide, merge into one and eventually be sucked

into the supermassive black holes at their centres. Even these black holes will lose energy

and evaporate over trillions of years. Once this has happened there will be no matter left in

the universe, it will have all decayed into energy.

At this point, the universe will continue to become more disordered as each particle of

energy moves as far away from its neighbour as possible. In an ever-expanding universe,

these particles will eventually become infinitely far apart. When this happens, time as we 

know it will cease because the universe will have reached its final state and remain this way: cold and unchanging for eternity.

However, the end of the universe need not necessarily be so bleak. There is another theory known as ‘the big crunch’. This theory takes a more symmetric view of the life cycle of the cosmos. It proposes that the expansion of the universe will one day slow down and change direction, contracting inwards. All matter would get closer and closer together, eventually reaching a single, infinitely dense point. This would lead to another big bang and the creation of a new universe. It’s theorised that this has already happened and that we are merely one iteration of a never-ending cycle.

No one knows for sure what the fate of the universe is. However, if the inevitable end of everything is still troubling you, take solace in the fact that the cosmos might not die but be born anew and even that won’t be happening for a very long time.

From Issue 16

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