This article is about the notion of multiverse in physics. For other notions of multiverse, see multiverse. In physics, the term “multiverse” refers to certain picture of cosmology. The intended meaning tends to differ between authors and/or remain vague (see below) but broadly what goes with it is the idea that, just as the configuration of matter and energy changes from place to place within our observable universe, clearly, it could be that beyond the observable universe (for immediate or not so immediate notions of “beyond”) eventually even the laws of physics might change from place to place, possibly altogether, but at least as concerns the values of coupling constants or even field-content. The idea remains hypothetical, naturally, and might ultimately be empty as an idea about physics as opposed to philosophy, but it is arguably in historical continuation with a sequence of famously confirmed insights about cosmology, which led from an archaic picture of a cosmos centered all around the world directly experienced by humans (the continent a disk inside an ocean hung in the center of the heavenly spheres), via the Copernican revolution, then the confirmation of distant galaxies etc., to the realization that the observable universe is immense and varied and our physical place and whereabouts inside it just a random result of chance, subject only to the tautological condition that it allows us to be here at all – known as the “anthropic principle” in these discussions. Accordingly, one motivation for the idea of the multiverse is as an explanation for apparent ‘fine-tuning’ in the “constants of nature”, in particular concerning the presence of complex life. The thought here is that were the constants/laws of nature to be ever so slightly different from what they are, then the universe would not have been to able to evolve to support complex, intelligent life forms (see SEP: Fine-tuning). But an account which proposes that a vast number of universes exist...