this is my first question here so I hope I'm following the guidelines correctly. I recently found a relatively obscure physicist/philosopher who asserts that the concept of Many Worlds is tautologically true (Note: he specifies a concept of a Classical Many Worlds, which as far as I can tell is basically like modal realism). He has a series of articles talking about it, but I think the most bare-bones argument is most well-summed up by this article: https://www.science20.com/alpha_meme/modest_agnostics_expect_multiverse_and_hold_many_worlds_true-85038 and specifically this excerpt:

"A fundamental description aims to take account of the whole of totality, of all that is possible. If you refused Many Worlds in such a description, you will do the following ridiculous thing:

You would assume that in the very foundation of totality, the very most fundamental laws of nature, the absolute rock bottom core of physics in its most profound and general symmetries, there is something inside there that ensures that you, yes you personally with name and address, wear that silly color shirt today!"

I know that there's a similar genre of argument for the Multiverse involving the idea of fine-tuning, specifically the fine-tuning of the constants of the universe potentially implying that there are other universes out there with different constants or even different laws of physics. However, I believe the current stopping point of that debate is that we can't know for certain right now since for all we know, the constants are fundamental to a theory of reality or something.

However, this article asserts that even if the laws of our universe are fundamental, the initial conditions that led to the universe being the way that it is today is not, and therefore all initial conditions (i.e., initial conditions that lead to you wearing a different colored shirt) must be fundamental to reality, which argues in favor of Many Worlds.

I'm not a student of philosophy, I just read around, but as far as a quick Google search tells I haven't really seen this argument before. However, this scientist is by no means a well-established philosopher, so I'm curious to know whether or not there are other philosophers/philosophies out there that make this kind of argument, so that I could read more into it. Thanks!

  • Not an area I’ve explored much, but if this notion was tautological, that would mean he has a logical proof akin to a mathematical theorem. . . and nobody would dispute it except for not grasping the formulas. So, this seems suspect.
    – Hokon
    Sep 8, 2023 at 6:23
  • 1
    David Lewis's modal realism for logic is short to prove such tautology of many world in the sense of many worlds obeying different fundamental possibly contingent (simple) physical laws. On possible way is to invoke principle of indifference of Bayesian priors of defeasible inductive logic of science and apply to initial conditions within a properly scaled possible range... Sep 8, 2023 at 7:05
  • He seems to be equivocating on what a world is, or possibly he doesn't really get the difference between a possible world and an alternate world. Sep 8, 2023 at 11:03
  • If no new knowledge and contingent decision can be added to a totality which is nothing but totality of total possibilities, such is a form of necessitarinism. Also per David Lewis's famous principal principle a correct physical chance theory up to time t has to mirror degree of belief probability up to same time t without inadmissible evidence, therefore every possibility has to be grasped in thought completely and since the said objective chance theory is correct thus modal realism is tautological, nothing is merely actually actualized... Sep 13, 2023 at 6:01
  • @DoubleKnot if I'm understanding your last comment correctly, David Lewis also argues that modal realism is tautological?
    – user
    Sep 19, 2023 at 7:40

2 Answers 2


The idea of a multiverse is just a lame attempt to support the idea of a deterministic universe. The problem with determinism as a worldview is that it doesn't answer the big question:

Why exactly this is happening instead of something else?

In a deterministic universe every event is completely determined by the initial conditions, but determinism does not tell us how the initial conditions were determined. As determinism denies both possible methods for setting up the initial conditions (deliberate choice and random chance), determinists had to come up with an idea of infinite number of universa each with different initial conditions.

Therefore everything possible is happening in at least one of them. No need to choose or draw out of infinite possibilities, let's have everything. Exactly this is happening in this universe, everything else is happening in others.

The excerpt merely assumes that this Universe is deterministic and the colour of a shirt was determined by the initial conditions. Therefore, to maintain the idea of a deterministic universe, the author must assume other universa to cover all other possibilities.

I can see no tautology here, only assumptions to patch the holes in other assumptions.


The article that you cite does not constitute a proof. It is a weak argument, and badly written. It does make a useful distinction between many worlds and the multiverse. Using the principle of parsimony, I assume that there is only one universe. Multiple universes are as useless as metaphysics. I recommend The Philosophy of Quantum Physics by Friebe, Kuhlmann et al.

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    Badly written indeed. I understood every one of his words, but none of his sentences. Dec 5, 2023 at 22:35

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