• Question: If they are real, could we travel to parallel universes?

    Asked by Logan F on 10 Sep 2021.
    • Photo: Giles Strong

      Giles Strong answered on 10 Sep 2021:

      As I mention in my answer to the other question on parallel universes (/hydrogen21-zone/question/is-there-a-parallel-universe/), there are many theories which describe how parallel universes could exist. The answer to your question therefore heavily depends on which theory is being considered.

      Taking the “Many Worlds” interpretation, where parallel universes are created due to the outcome of a random process: assuming we had a way to repeat the random process (e.g. going back in time and retrying), then potentially we could “travel” to the other universe in which the opposite outcome occurred. I would argue, though, that “travel” is only meaningful if we retain memories of the previous universe/timelines, otherwise the outcome is not different to just accepting the original result and having our clones exist in the other universe. There would also have to be a mechanism which prevents our clones from retrying the random process in order to “travel” to our universe.

      Other theories, like in cosmology, predict that sometimes parallel universes “collide” with each other and influence what happens in the other universes (e.g. cause Big Bangs). Depending on how loosely one defines “travel” this could be one potential mechanism.

      This question is kind of special to me, since one of my motivations to become a scientist was the “His Dark Materials” book trilogy, which deals with travelling between parallel universes. So part of me would like to think that it is possible. However, let’s assume that we can travel between universes: there could be an infinite number of parallel universes, so there would be an infinite number of people travelling in and out of our universe, but where are they? And what would be the consequences?

    • Photo: Andrew Hone

      Andrew Hone answered on 13 Sep 2021:

      It’s a very interesting question. As Giles says in his answer, it depends what theory/interpretation you are working with. The many-worlds theory of quantum mechanics is quite well-known, where the universe splits into different copies according to different possible outcomes of random events, but it is not clear if there are any experiments that can tell the difference between this version of reality and other interpretations of quantum theory (the “Copenhagen interpretation”) which say that only one outcome happens, but it is only fixed when a measurement is made.

      In inflationary cosmology, there are models of “baby universes” that involve different pockets of the cosmos, that behave like separate universes, but they all expand so rapidly away from each other by inflation that it would be impossible to travel or send a signal between them (because the speed of light is an upper limit on all communication), unless there could be some sort of wormhole connecting a point in one to a point in another; and it might be hard to survive travel through one of those!

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