The Many Worlds Of The Multiverse

The idea of a multiverse is a staple of sci-fi, being used as a plot device in everything from Star Trek to Doctor Who. It is also a fun thought to entertain yourself with - what if you had got into the university you wanted? What would have happened if you had plucked up the courage to ask that girl out? What if the Matrix sequels had never been made? However, the probability of the existence of the multiverse is more likely than people realise. While technically unprovable, and therefore not proven 'science', the universe as we currently understand it points to it being there, though forever out of our reach. First, a lesson in terminology. When most consider the universe, they refer to everything that exists in all of reality, so a multiverse, being in reality, would itself fall under the umbrella of 'the universe'. However, when physicists refer to the universe, they tend to be referring to the observable universe, which has a radius of around 13.8 billion light years around Earth1, due to the speed of light. The universe however is expanding much faster than the speed of light, and so we can reliably deduce that there are more galaxies and stars and planets beyond the limit we are able to see - as far as we know, the universe is likely to continue forever in every direction, as the density of galaxies does not diminish with distance away from us2. This is where the 'multiverse' idea comes into this. Imagine if you were standing on a planet 27.6 billion light years from Earth, twice the radius of the observable universe. The universe around you would be completely different, though still obeying the same physical laws as us. In essence, they are in a parallel universe, where almost everything is different, and we will never be able to reach them. Taking this idea further, if the universe is infinite in every direction, and there are only finite possibilities for matter to come together, eventually things will start repeating. It may be a perfectly identical star, 10 billion light years apart, or a perfectly identical planet, 32 billion light years apart. But like infinite monkeys with infinite typewriters, eventually you are going to come across a planet that is identical to Earth, down to the last atom. In fact, somewhere unimaginably far away, there are infinite identical 'yous' reading an identical article, and reading this exact same sentence. Even further away, there is an identical observable universe, with a copy of every star, planet and galaxy that we can see from Earth. Some cosmologists have even put a number on how far away this identical universe is - around 10^10^118 metres away, or 10 followed by one billion trillion trillion trillion trillion trillion trillion trillion trillion trillion zeroes.3 Needless to say, an unimaginably large distance. I feel I need to reiterate that none of this has been empirically proven. By definition, it can't be. However, while we're discussing sci-fi tropes, if humanity somehow invents an instantaneous teleporter to anywhere in reality, we can hope to one day meet our parallel selves, and introduce them to the horrors of the Matrix sequels.

References: 1. Planck collaboration (2013). "Planck 2013 results. XVI. Cosmological parameters". 2. Anon (n.d). "Brief Answers to Cosmic Questions". http://www.cfa.harvard.edu/seuforum/faq.htm 3. Max Tegmark (2003). "Parallel Universes". In "Science and Ultimate Reality: from Quantum to Cosmos", honoring John Wheeler`s 90th birthday. J. D. Barrow, P.C.W. Davies, & C.L. Harper eds. Cambridge University Press (2003).