Physicist John A Wheeler proposed the "Principle of mutability" which said that it could be the case that the universe would eventually shrink in a "Big Crunch" and the be re-born in another Big Bang. He proposed that the laws of physics (even the considered most fundamental ones) would change and therefore, between cycles, we could have completely different universes.

I find this approach very interesting and I was wondering if any physicists have further developed this model? Specifically, I was wondering if there are any physicists that have proposed that there are multiple co-existing universes, which their most "fundamental" laws (not only effective laws) would change due to Wheeler's principle of mutability. Are there any?


1 Answer 1


The cosmological multiverse does what you ask. There are several kinds of cosmological multiverse, the most common being eternal inflation, but first we do not think our universe will end in a Big Crunch:

If the cosmological constant were actually zero, the critical density would also mark the dividing line between eventual recollapse of the universe to a Big Crunch, or unlimited expansion. For the Lambda-CDM model with a positive cosmological constant (as observed), the universe is predicted to expand forever regardless of whether the total density is slightly above or below the critical density; though other outcomes are possible in extended models where the dark energy is not constant but actually time-dependent. https://en.wikipedia.org/wiki/Lambda-CDM_model

But that doesn't mean other pocket/bubble universes (n.b. parallel is usually restricted to talking about the Many Worlds interpretation of QM, not for cosmological universes) within the multiverse can't have a Big Crunch, among many other possibilities. Whether or not there is a multiverse is of course unknown, and there are many types of multiverses and how they are formed. There are many reasons to ponder their existence. [1] Apparent "fine tuning" of many physical constants [2] No way to calculate many of them except empirically (no underlying theory to predict them).


Lambda (Λ), commonly known as the cosmological constant, describes the ratio of the density of dark energy to the critical energy density of the universe...If the cosmological constant were not extremely small, stars and other astronomical structures would not be able to form. https://en.wikipedia.org/wiki/Fine-tuned_universe


N and ε govern the fundamental interactions of physics. The other constants (D excepted) govern the size, age, and expansion of the universe. These five constants must be estimated empirically. https://en.wikipedia.org/wiki/Dimensionless_physical_constant#Fine_structure_constant

So without any deeper mechanism behind these constants being what they are (and suitable for life), we either got lucky, or some aspect of the anthropic principle had an effect and we are just one of many (bubble) universes with varying fundamental constants. The most common type of multiverse is the inflationary multiverse. Some patches of this spacetime have negative cosmological constants and thus "Big Crunches", some rip apart before any structure can form, and some are like ours where there is balance between gravity and dark energy/CC allowing structure to form.

  • $\begingroup$ I appreciate your answer, but the cosmological inflationary universe would not be able to do what I asked for, since only low-energy (effective) laws of physics could be different between universes. Wheeler talked about the most fundamental laws of nature being different (not only effective laws) @JKusin $\endgroup$ Jun 18, 2020 at 0:08

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