Question: Heyo! What do you think on the potential prospect of parallel universes? And if so, what about the paradoxes that could occur within the theory, for example, a parallel universe in which parallel universes don't exist? Been a joy hearing back from you all. Thanks.

Ian Stephenson answered on 19 Jun 2014:

Parallel universes is a pretty theoretical concept that’s used to explain some of the results that come from theoretical physics. They’re essentially something that comes out of the maths. The maths is generally pretty reliable, but in practical terms it probably doesn’t make a lot of difference.

One of the big points of parallel universes is that they AVOID paradoxes. Whenever you do something which would cause a paradox, you get to say it happened in a parallel universe, rather than this one. For example if I go back and kill my grandparents, then in a parallel universe thats OK because in they were killed in the other universe, so I can still be born in this one! However that’s more about movie plots than real science. In real science the paradoxes are much more boring, like if a sub-atomic particle is spinning one way or the other.

However they would all arise from a common set of rules. Some things in Physics would be common to all universes. Some things have to be the same – not every universe can exists. And even if parameters can change (for example G the universal strength of gravity [not g the strength of gravity on earth]),there would still at least BE a constant G.