Section of Wikipedia article on the possibility of universes with space & time dimensions other than 3 and 1 respectively.

If one of these other universes exist, could we in principle quantum tunnel to it?

I'm thinking in particular of how string theory predicts $10^{500}$ universes, and how we could, in principle, quantum tunnel to a universe that is in a lower-energy state. However, I do not know if these $10^{500}$ universes necessarily have the same dimensionality as the one we live in.


1 Answer 1


One conception of “other universes”, coming from the theory of eternal inflation, is that they all exist within a mother multiverse with some fixed number of dimensions such as 10 or 11. The child universes would have different numbers of macroscopic and microscopic dimensions, depending on how dimensional “compactification” occurred in them, but they would all have the same 10 or 11 total dimensions.

So I see no reason why quantum tunneling between universes would be impossible in principle. It would just be absurdly unlikely, in the same way that the probability of your car tunneling through a hill is absurdly unlikely.

  • $\begingroup$ Are you confident in this answer? I'm reading a paper by Andrei Linde (iopscience.iop.org/article/10.1088/1361-6633/aa50e4/meta) and there's this paragraph: "If the fundamental theory of all interactions has many different vacuum states, or allows different types of compactification, the laws of the low-energy physics and even the dimensionality of space in each of these mini-universes may be different." If your answer is correct, how is this apparent tension explained? $\endgroup$
    – Allure
    Sep 30, 2019 at 4:48
  • $\begingroup$ @Allure I don’t see any tension. What did I write that you think is in conflict with Linde? I had Linde’s inflationary theories in mind when I wrote my answer. $\endgroup$
    – G. Smith
    Oct 1, 2019 at 4:42
  • $\begingroup$ Well, Linde says "... even the dimensionality of space in each of these mini-universes may be different". You on the other hand wrote "... they would all have the same 10 or 11 total dimensions". That seems at odds to me - Linde is saying that we can have N=100 vacuum states for example, but your answer permits only N=10 or 11. $\endgroup$
    – Allure
    Oct 1, 2019 at 4:51
  • $\begingroup$ He’s talking about the apparent dimensionality after compactification... the number of macroscopic dimensions. $\endgroup$
    – G. Smith
    Oct 1, 2019 at 4:59

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