I can think of three different theories that predict a kind of multiverse.
The wave form theory described in this thread.
One where new bubble universes are being produced in an eternally inflating mother universe at an almost infinite rate.
One where in an infinite universe things keep repeating; so if you eventually travel in one direction you will find an infinite number of identical analogues to Earth.
My science knowledge is limited to watching interesting youtube videos. I’ve never seen a video where someone claims all three to be true simultaneously. If so, that’s a ton of matter!
Is there any known reason they couldn’t all be true? Are any mutually exclusive? 1 and 2 seems to be at odds, since they are two completely separate mechanisms for universe creation, which seems strange. 3 seems to be ok, since it would apply within the universes already created by either 1 or 2.
Perhaps it helps to think of things in terms of the difference between conservation of energy (which is the more general notion than mass) in the Copenhagen versus the many worlds-picture. Suppose you have a system in superposition of two energy states. Say that, upon measurement, you have probability 1/4 to obtain energy E1, and 3/4 to obtain energy E2. On Copenhagen, with any measurement, you will have a collapse to one of the two, and repeating the experiment many times, you will obtain an average energy of 1/4*E1 + 3/4*E2.
On the many worlds picture, what happens is that you’ll entangle with the state of the system, that is, there’ll be one ‘you’ that observes E1, and ‘another you’ that observes E2. So now, there’s two yous—and as you have a certain amount of energy (say, Ey) associated to yourself, doesn’t that mean we’ve violated conservation of energy?
But that’s not the case: before you made your observation, the energy was Ey + 1/4*E1 + 3/4*E2; afterwards, you’ll see E1 in 1/4 of the branches, and E2 in the remaining 3/4—so, the average energy of the whole shebang must be 1/4*(Ey + E1) + 3/4*(Ey + E2), which is the same as before. Thus, (average) energy (and thereby mass) is conserved in the splitting process.
One should point out that this view isn’t well accepted in the community. The reason is that the result of the computation in the case of Shor’s algorithm isn’t in the properties of any given element of the superposition in the final state, but in the total state—so in a sense, it’s exactly to that degree that the computation hasn’t branched off into parallel ‘realities’ or the like that you can extract some useful information about the system. Once you do have ‘many worlds’ in the mix, that just means that your quantum state has decohered, and you can’t extract any information about the result anymore.
What quantum computation does show is that the state of a quantum system is an exponentially big thing, but that doesn’t tell you anything about whether, at the point of measurement, that exponential amount of ‘branches’ snip off into their own worlds, or reduce by collapse to some specific, single one: on both stories, as long as you’ve manipulated your state carefully enough beforehand, you may profit from this amount of complexity to carry out useful computation.
The Many Worlds interpretation is consistent with anything that’s consistent with quantum mechanics, just like any other interpretation. I don’t think that it’s philosophically meaningful to say whether Many Worlds is “true” or not.
Of your list, models 2 and 3 are (probably) not consistent with each other, because the bubble-universes produced in an eternal-inflation mother universe are (probably) finite in size.
Oh, and also add to your list of scientifically-plausible multiverses that there might be other three-dimensional spaces separated from each other across some other dimension (or dimensions). Depending on the model, such other spaces might be very, very close to ours, or very far away, and might not be able to interact at all through any means we know of (but might be able to through means we don’t know of), or might be able to interact with each other gravitationally. These are usually referred to as “braneworld models”, with the separate parallel universes being “branes”.
You are far more expert in these matters than I. So I’m not making any assertions here, and any I do inadvertently make should be viewed as questions, not answers.
Can we say what you suggest with the degree of confidence you assert? Clearly today we don’t know enough to say the MW interpretation is any more or less “true” than other interpretations. I buy that completely.
But if indeed out understanding of QtM is as yet incomplete, and even more so our understanding of the ToE is definitely incomplete, then as we discover the now-unknown whatevers that we’ll someday discover, that info may well enable us to declare some current interpretations to be provably wrong or provably “right enough” as best we know then, not now
All of the interpretations of quantum mechanics that any physicist uses are known with mathematical certainty to be precisely consistent with all of the others. Now, it might well be (in fact, it’s known for sure, in sufficiently-extreme conditions) that our understanding of the physics itself of quantum mechanics is incomplete, and it might be that some day we’ll come to a more complete understanding, and in that more complete understanding, there might be new mental frameworks for quantum mechanics that do make different predictions from all of the current interpretations, and experiment might show those different predictions to be correct. But in that case, we’d be throwing out all of the current interpretations (though some of the new interpretations might closely resemble the ones we’re throwing out).
Well, with a slight caveat. Basically, any interpretation of a theory must have the same empirical consequences, otherwise, it’s not an interpretation but a rival theory. In the context of quantum mechanics, however, one sometimes encounters talk about ‘objective collapse interpretations’, which add a nonlinearity to the usual quantum dynamics that leads to a stochastic collapse of the state with a high likelihood once a certain threshold is reached. These models generally will predict some empirically different behavior from ‘vanilla’ quantum mechanics, and thus, strictly should be considered alternative theories. They go under the label of ‘interpretation’ mostly for the historical reason that they originated in an attempt to resolve the measurement problem of QM.
Neither. The measurement problem, in quantum mechanics, broadly refers to the question of how measurements always yield a definite value, even if the system is not in a state that assigns a definite value to the measured quantity (i.e. a superposition).
