Multiverse—Too Much or Not Enough?

Abstract

The aim of this essay is to look at the idea of the multiverse—not so much from the standpoint of physics or cosmology, but rather from a philosophical perspective. The modern story of the multiverse began with Leibniz. Although he treated “other worlds” as mere possibilities, they played an important role in his logic. In a somewhat similar manner, the practice of cosmology presupposes a consideration of an infinite number of universes, each being represented by a solution to Einstein’s equations. This approach prepared the way to the consideration of “other universes” which actually exist, first as an auxiliary concept in discussing the so-called anthropic principle, and then as real universes, the existence of which were supposed to solve some cosmological conundrums. From the point of view of the philosophy of science, the question is: Could the explanatory power of a multiverse ideology compensate for the relaxation of empirical control over so many directly unobservable entities? It is no surprise that appealing to a possibly infinite number of “other universes” in order to explain some regularities in our world would seem “too much” for a self-disciplined philosopher. With no strict empirical control at our disposal, it is logic that must be our guide. Also, what if logic changes from one world to another in the multiverse? Such a possibility is suggested by the category theory. From this point of view, our present concepts of the multiverse are certainly “not enough”. Should this be read as a warning that the learned imagination can lead us too far into the realms of mere possibilities?

Anthropic Selection of Physical Constants, Quantum Entanglement, and the Multiverse Falsifiability

“…As for the level III it is perhaps also possible to study the entanglement within the branching of the total wave function of the universe and its decoherence within individual branches. However, the level IV (and perhaps "level V" [79]) does not seem to be testable, though one would attempt to formulate an idea of some "signals" of different mathematics or even logics (what?) in the multiverse, but they seem to be much behind the reach of "observable quantities" in the regular sense of physics though still can perhaps be falsifiable in the sense of Popper.…”

“…An interesting and perhaps even further going idea which perhaps rises the level IV onto the "level V" is due to Heller [79] who considers the universes with different logic (reasoning comes from the category theory) rather than just different mathematics.…”

The String Theory Landscape

“…A particularly important example is the distribution of values of the effective potential at the minima, in other words the cosmological constant (or c.c.). This is an important input into the arguments for the multiverse from cosmology and especially for the anthropic solution to the cosmological constant problem, for which we refer to [6,7] and the article [8] in this issue. This argument requires the existence of a large number of vacua such that the a priori probability that we will observe a given vacuum is roughly uniform in the cosmological constant at small values.…”

“…See also the article [8] in this issue. 6 Our point was not to claim that the multiverse is a simulation, in fact we explicitly postulate that no local observer can tell that the multiverse is being simulated.…”

Post-Editorial of “The Multiverse” Special Volume

“…The area of philosophy and history of physics is where the debate about how to define the category of the multiverse and the need (or not) to endow it with physical meaning exists [3]. In several papers we cover the ideas that philosophy of science provide to falsify multiverse theories and describe the scientific progress.…”