I think it is time to take physics seriously. — tom
The Level III Multiverse (Tegmark) gets a lot of stick, despite the fact that it adds zero complexity to our conception of Reality according to known physics. — tom
It is a Tegmark designation, and I'm not sure how much the video gets into it. Type (or level) 1: Places that are too distant to causally interact with here, ever. There is a duplicate Earth out there if you go far enough. Type 2 is other bubbles in eternal inflation theory. Those bubbles all have the same QM, but different dimensions, light speed, and other physical constants. There is a duplicate Earth there as well. Type 3 is Everett multi-worlds, essentially parallel-here. Type 4 is other structures altogether, and it is hard to argue that they're not separate universes, but ours exists no more than those others.For those of us who prefer not to sit through a video, and who have only a nodding acquaintance with the topic, can you please remind us what a level 3 multiverse is? — fishfry
They're not separate universes (especially types 1 and 3), just separate worlds in this universe. For type 1, the distant Earth is a true duplicate. The space is infinite, but the possible states in a finite space (say that of Earth) are not, so each state much eventually be duplicated given enough distance.How does the second sentence follow from the first? Do the universes share the same history? Why should they do that? — fishfry
Models say otherwise. For the distance to be finite, there would need to be an edge where there is stuff only on one side, and not uniform as we see it. This is true of a subjective model (one with a frame and a 'current event'), but not of any objective view. Other-worlds is necessarily a description from the outside.That would not seem to follow, since no distance is infinite. — Janus
For type 1, the distant Earth is a true duplicate. The space is infinite, but the possible states in a finite space (say that of Earth) are not, so each state much eventually be duplicated given enough distance. — noAxioms
Indeed, it doesn't require infinite space. It (a type 1 world, not a duplicate) does at least require an expanding universe, else eventually light would have time to cross the distance. The dup-Earth requires space big enough to form duplicates of something, which could in theory be close enough to be visible from here once light had time to make the trip. That is more probable than what you show below where it by chance just never happens.First, why is the space infinite? Your premise is that the universe is finite but sufficiently large that there are regions inaccessible to each other due to light not having had enough time to get from one place to the other. That doesn't require an infinite universe. — fishfry
Not guaranteed, no. A coin may flip tails forever. It's just a probability after enough distance.Secondly, even if the universe is finite AND the possible states in a given region of space are finite, you STILL are not guaranteed a duplicate earth. Say there are two states, and infinitely many universes:
0, 1, 1, 1, 1, 1, 1, ...
Not sure I follow this. If there is a duplicate, there would seem to be an infinite number of them. There is simply a probability as to how far away (measured in non-linear units) the nearest one is. There are infinite type-1 worlds given infinite universe size. In fact, each point in space is centered on such a world, so you are in a different one than I am. Light can in theory reach (immortal) you from your slightly-left-shifted world but never reach me in mine. That means that by the time the light gets to you, the expansion of the universe separates us so far that we're forever isolated from each other.Again thought, you're betraying your original premise. You started with TWO regions of the universe that are causally and informationally isolated from one another. That's two, not infinitely many.
Models say otherwise. For the distance to be finite, there would need to be an edge where there is stuff only on one side, and not uniform as we see it. This is true of a subjective model (one with a frame and a 'current event'), but not of any objective view. Other-worlds is necessarily a description from the outside. — noAxioms
For those of us who prefer not to sit through a video and who have only a nodding acquaintance with the topic, can you please remind us what a level 3 multiverse is? — fishfry
On the contrary, it seems that in the past few years it's becoming time to stop taking physics seriously. Theories that can not be experimentally verified or refuted are not science. — fishfry
They're not separate universes (especially types 1 and 3), just separate worlds in this universe. For type 1, the distant Earth is a true duplicate. The space is infinite, but the possible states in a finite space (say that of Earth) are not, so each state much eventually be duplicated given enough distance. — noAxioms
Indeed, it doesn't require infinite space. It (a type 1 world, not a duplicate) does at least require an expanding universe, else eventually light would have time to cross the distance. The dup-Earth requires space big enough to form duplicates of something, which could in theory be close enough to be visible from here once light had time to make the trip. That is more probable than what you show below where it by chance just never happens. — noAxioms
I think you misunderstood; the point is that there is no actual infinite distance. Even if you traveled away from Earth, for example, forever you would never reach an infinite distance from earth. — Janus
True, but I don't understand how this is relevant to what noAxiom was saying. — SophistiCat
Indeed, it doesn't require infinite space. It (a type 1 world, not a duplicate) does at least require an expanding universe, else eventually light would have time to cross the distance. The dup-Earth requires space big enough to form duplicates of something, which could in theory be close enough to be visible from here once light had time to make the trip. — noAxioms
Edit: I think that mathematically, a coin cannot come up tails forever. There cannot not be a dup Earth given infinite space. The probability of of that is 0.000... which is zero. — noAxioms
Not sure I follow this. If there is a duplicate, there would seem to be an infinite number of them. — noAxioms
a probability as to how far away (measured in non-linear units) the nearest one is. There are infinite type-1 worlds given infinite universe size. — noAxioms
In fact, each point in space is centered on such a world, so you are in a different one than I am. Light can in theory reach (immortal) you — noAxioms
Good point.A 3-manifold, e.g. a 3-sphere, is finite with no edge. — tom
Isn't just a curvature measurement enough? If flat enough, there are places sufficiently separated to never interact. Yes, expansion is required for that, but not infinite space.It is psychologically interesting that people generally accept the existence of the Type 1 multiverse, when there is absolutely no evidence for it. I'm not sure if evidence for it is even possible? — tom
I didn't watch it either — tom
I have no idea what you mean by "the last few years", — tom
If so, the dup-Earth bit kinda falls apart, eh?Which is good, because contemporary physics holds that the universe is finite. — fishfry
No, disagree with this. A finite sequence has a nonzero probability. An infinite one is not a specific one, and has probability zero and does not happen.In infinite probability spaces, probability zero events may still happen. Suppose you flip infinitely many coins and they come up in any sequence whatsoever: hthhthththththhthttthhthththt... say. A completely random sequence. What's the probability? Well, the prob that flip 1 is h is 1/2. The prob that flip 2 is t is 1/2. Etc. The prob of the first n flips being exactly what they are is 1/2^n, and that goes to zero as n goes to infinity. Every particular sequence has probability zero. Do you follow that point? — fishfry
If so, the dup-Earth bit kinda falls apart, eh? — noAxioms
No, disagree with this. A finite sequence has a nonzero probability. An infinite one is not a specific one, and has probability zero and does not happen.
Every particular sequence has half the probability of the flip sequence of one-less flip. That is not zero. Some probability-zero sequence is not a particular sequence and thus does not in fact occur. — noAxioms
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