Why We Think There's a Multiverse, Not Just Our Universe

An anonymous reader writes "It's generally accepted that the Universe's history is best described by the Big Bang model, with General Relativity and Quantum Field Theory as the physical laws governing the underlying framework. It's also accepted that the Universe probably started off with an early period of cosmic inflation prior to that. Well, if you accept those things — as in, the standard picture of the Universe — then a multiverse is an inevitable consequence of the physics of the early Universe, and this article explains why that's the case."

Comments

Not the quantum mechanical multiverse

[JoshuaZ]

Note that this isn't talking about the quantum mechanical multiverse where whenever a decoherence occurs you get branching of different copies. This is talking about a more concrete notion of multiverse where the early inflation spreads out so much that there are lots of little regions of observable space time which cannot observe each other.

Re:Not the quantum mechanical multiverse

[JoshuaZ]

From TFA:

Now, the story I’ve told you is a conservative one. In this version of the story, the fundamental constants are the same in all the different regions of the multiverse, and the other Universes have the same laws of physics—with the same quantum vacuum and all—as our own. But most of what you hear about the multiverse these days are from people who have speculated much farther than that.

They don't discuss any of the ideas about differing constants although others have done so.

Misleading summary

[SoftwareArtist]

It's generally accepted that the Universe's history is best described by the Big Bang model, with General Relativity and Quantum Field Theory as the physical laws governing the underlying framework.

No no no. It's generally accepted that each one of these theories taken individually is the best currently known description within its particular domain. It is not generally accepted that you can just throw them together and get an accurate description of the fundamental nature of the universe! In fact, we know you can't do that because general relativity and quantum field theory are deeply incompatible with each other. People have been working for half a century to find a single consistent theory that can reproduce the predictions of both. They've made a lot of progress, but we're still a long way from having any confidence about what the true fundamental theory is.

The picture of eternal inflation described in this article is plausible based on what we know. But it's still very speculative. That's true of any discussion of cosmology. Our current knowledge is just way too limited to have any confidence about it.