What is outside the universe?
A colleague asked me this question on Friday. Good to see college leaders take the time to ponder the important questions.
The stock answer is nothing – or rather, there is no outside, simply because the technical meaning of the word ‘universe’ is all of matter, energy, space and time. So ‘outside the universe’ is a bit of an oxymoron – like asking what is north of the north pole, or what happened before the beginning of the universe.
It’s an important question and at the root of many misconceptions in cosmology. Consider for example the expansion of the universe. There is very strong evidence that our universe is expanding (see post on Hubble graph). However, this expansion is not really like the expanding balloon so beloved of science writers, because the universe is not expanding into space in the manner of a balloon inflating in a room. Instead it is space itself that is expanding (really spacetime). This is also why the theory of cosmic inflation can posit an exponential expansion of the universe (many times faster than the speed of light) in the first fraction of a second, without contradicting relativity (which forbids travel faster than the speed of light in space).
That said, the question has got more complicated recently. If inflation is right, it seems we have to accept the possibility that a great many universes may have been spawned in the first fractions of an instant – the multiverse. Hence might one ask about ‘outside a particular universe’? I think this is essentially the same question, except it is now ‘what is outside the mulitverse?’. A question which has the same answer, which is nothing .Or better, there is no outside. We think. So far.
Artist’s impression of the mulitverse