Our universe is but one in an unimaginably massive ocean of universes called the multiverse.

If that concept isn’t enough to get your head around, physics describes different kinds of multiverse. The easiest one to comprehend is called the cosmological multiverse. The idea here is that the universe expanded at a mind-boggling speed in the fraction of a second after the big bang. During this period of inflation, there were quantum fluctuations which caused separate bubble universes to pop into existence and themselves start inflating and blowing bubbles. Russian physicist Andrei Linde came up with this concept, which suggests an infinity of universes no longer in any causal connection with one another – so free to develop in different ways.

Cosmic space is big – perhaps infinitely so. Travel far enough and some theories suggest you’d meet your cosmic twin – a copy of you living in a copy of our world, but in a different part of the multiverse. String theory, which is a notoriously theoretical explanation of reality, predicts a frankly meaninglessly large number of universes, maybe 10 to the 500 or more, all with slightly different physical parameters.

And then there’s the quantum multiverse. Physicist Hugh Everett came up with this idea, which is predicted by his “many worlds” interpretation of quantum physics. Everett’s theory is that quantum effects cause the universe to constantly split. It could mean that decisions we make in this universe have implications for other versions of ourselves living in parallel worlds.

However, we recommend restricting your concerns to entities in the current plane of existence. Rowan Hooper..