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.

Re:You mean

[Altrag]

Uhhh no. There's no serious cosmologist in the world who thinks we know even close to everything about the universe yet. The 14b year timescale works just fine as "the furthest we can see" because its well the furthest we can see. Nobody in their right mind claims that there's nothing beyond our ability to see.

And no the photons don't get "old" -- they get too far away. If your max speed is 100mph and I'm 150 miles away, there's no way you'll ever get to me in one hour. Same thing goes for photons. They have a maximum speed so if we see one, we know with absolute certainty that it can't have traveled more than a certain distance or it simply wouldn't be here yet. Short of discovering wormholes or other such objects that could somehow let light break c.

Though that's not quite right either. We actually can see a type of "edge" of the universe which is closer than the theoretical maximum range of a photon. Its the point in time when the CMB was hot enough that it was opaque to photons. Its essentially like looking at a wall of fog and not being able to see much more than an inch through it (though of course for different physical reasons!) If they ever manage to detect gravity waves to any great extent, its theorized that they could be used to gather information beyond the CMB wall (though gravitons would have their own version of the CMB wall at some point even further in the past.)

So yes, they do say "yep, that is as far as we can see" but there is definitely no "it must be the edge of everything!" conclusion drawn from that. There's all sorts of theories around regarding what was before / outside of the big bang. Trouble is, they're all unprovable because yeah.. its beyond what we can see or could ever see (again, barring the discovery of some way to break c.)

Even with gravity telescopes its pretty likely that we're just going to find a more detailed version of what we already know. Not guaranteed of course (there may be monsters out behind the CMB wall after all) but pretty likely -- still leaving the main "what came before time existed" question fundamentally unanswerable.

Greeks had that

[satuon]

The ancient Greeks had this system - it's called Sortition, or drawing of lots - http://en.wikipedia.org/wiki/Sortition

The idea was that they didn't even vote, they just picked citizens at random for various committees, similar to how a jury is chosen.