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I recently read the book by Max Tegmark, The mathematical Universe, where he expounds upon the multiverse and how if ANYTHING can happen, will happen, because of all the ways things can be arranged.

I came away confused because he also talked about fine tuning of the universe.

But if one believes in the multiverse, then there shouldn't be a need for fine tuning because if some thing can happen, it will. Meaning, there's a universe where the the orbit of the electron is X, and then there's a universe the orbit is X.1, and X.2, etc etc etc...

So eventually there will be a universe where the constants are set to what they are in ours, because if anything can happen, it will.

I am not a physicist, obviously, or scientist. Only a curious mind in need of clarification.

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    $\begingroup$ multiverse theory or an infinite number of universes does not imply that anything that can happen will happen. similar to the statement I have an infinite set of integers does not imply that this set contains even numbers $\endgroup$ Feb 17 at 21:03
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    $\begingroup$ Hi and welcome to physics SE! Could you please clarify what you mean by fine tuning and why it would be needed without a multiverse? Thanks! $\endgroup$
    – Jonas
    Feb 17 at 21:05
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    $\begingroup$ "The" multiverse does not refer to one specific idea. In fact, Tegmark describes four distinct "levels" of multiverses, so you may want to clarify which conception of a multiverse you're talking about. $\endgroup$
    – Sandejo
    Feb 17 at 21:31
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Sort of. I'll stress that this is not firm, well-understood physics, a lot of it is speculative. But the logic goes something like this:

  • String theory has a vast number of possible solutions (more technical term is "vacua") - as many as $10^{500}$. For comparison the number of atoms in the observable universe is of the order $10^{80}$.
  • It seems possible that all of these vacua correspond to their own universe. All the universes have their own laws of physics at low energies (at high energies they are all governed by string theory). Together, all these $10^{500}$ universes are called the "multiverse".
  • Some of these universes will not work for life as we know it, but then we simply won't exist in those universes. We can only exist in universes which have viable laws of physics at low energies. Naturally we are going to observe that the physical constants have the values necessary for life ("fine tuning").

The third bullet point is also known as the "anthropic principle", and it is something that makes many people uncomfortable on an intuitive level. The multiverse gives it a bit more credibility because it provides a mechanism to produce the necessary universe.

In other words, some (and only some) of the $10^{500}$ universes are going to have laws of physics conducive for life, and we are necessarily going to live in one of them. We then observe that the laws of physics are conducive for life, i.e. we observe fine tuning. So yes, the multiverse sort of obviates the need for fine tuning.

If you don't find this line of reasoning convincing, you're not alone, but it's the gist of the argument.

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