• Shawn
    12.1k
    I had a phase of liking the MWI in terms of a mathematical universe. By, which I mean the branching of a collapse of a wavefunction can transpire without violating any conservation of energy laws.

    However, if one assumes in physics, as do many physicists, that the world is not mathematical, then doesn't it mean that conservation of energy laws would become violated for every branching of wavefunction collapses?
  • fishfry
    2.6k
    However, if one assumes in physics, as do many physicists, that the world is not mathematical, then doesn't it mean that conservation of energy laws would become violated for every branching of wavefunction collapses?Shawn

    Sean Carroll explains this by saying that the energy splits too. Each world takes with it half the energy of the parent world, so that conservation of energy is preserved. Of course that means that if the total energy of the universe is finite, at some point there's not enough energy to split into any more worlds. I'd like to ask Sean Carroll that. I'm sure he's thought about it.
  • Shawn
    12.1k
    Sean Carroll explains this by saying that the energy splits too. Each world takes with it half the energy of the parent world, so that conservation of energy is preserved.fishfry

    This confronts a pretty pernicious issue as to what or which kind of wavefunction collapses cause this to occur along with the extent of the parent universe splitting to what localized or even global effect(s)?
  • fishfry
    2.6k
    This confronts a pretty pernicious issue as to what or which kind of wavefunction collapses cause this to occur along with the extent of the parent universe splitting to what localized or even global effect(s)?Shawn

    I'm already in way over my head and know nothing of this other than a couple of Sean Carroll videos on Youtube. My understanding is that MWI avoids wavefunction collapse. The wavefunction doesn't collapse; rather, everything happens. The cat is awake and asleep, as Carroll says. No reason to kill a cat. He mentions that Schrödinger's daughter said, "My father just didn't like cats."
  • Shawn
    12.1k
    My understanding is that MWI avoids wavefunction collapse. The wavefunction doesn't collapse; rather, everything happens.fishfry

    But, there are certain thermodynamic laws that govern probability distributions even for observers.

    If you might mean that entropy is limited in certain branches where less entropy progresses summum bonum, then that might be an interesting way these branches evolve. Yet, there's no grand observer, observing this so it doesn't seem to make sense in general.

    So, if branching occurs, then it happens with regard to theoretical constants along with conservation of energy and thermodynamic laws, and then you still end up with the base universe just with branching occurring to maintain the least amount of entropy arising, hence some sort of tautology.

    What baffles me is how these worlds occur when a QM observation that is made on a probability distribution that has a local effect such as statistical distributions for low entropic and high ordered states. In other words does a minute variation in a probability distribution cause a branching or how large does the magnitude of the effect is required to be to cause branching?
  • Wayfarer
    16.3k
    I'm sure he's thought about it.fishfry

    Informed comment.
  • Shawn
    12.1k


    From the article:

    This scrutiny forced the question that Everett’s thesis had somewhat skated over. If all the possible outcomes of a quantum measurement have a real existence, where are they, and why do we see (or think we see) only one? This is where the many worlds come in. DeWitt argued that the alternative outcomes of the measurement must exist in a parallel reality: another world. You measure the path of an electron, and in this world it seems to go this way, but in another world it went that way.

    That requires a parallel, identical apparatus for the electron to traverse. More, it requires a parallel you to observe it — for only through the act of measurement does the superposition of states seem to “collapse.” Once begun, this process of duplication seems to have no end: you have to erect an entire parallel universe around that one electron, identical in all respects except where the electron went. You avoid the complication of wave function collapse, but at the expense of making another universe. The theory doesn’t exactly predict the other universe in the way that scientific theories usually make predictions. It’s just a deduction from the hypothesis that the other electron path is real too.
    Philip Ball

    This kind of hap hazardous growth of the entire universe would be in only some mathematical abstraction, no? Otherwise some physicist with an axe to grind would claim something about Occam's Razor.
  • Shawn
    12.1k
    Earlier I wrote that the wavefunction collapses, what I should have said is that measurements technically cause another world forming.
  • Wayfarer
    16.3k
    This kind of hap hazardous growth of the entire universe would be in only some mathematical abstraction, no? Otherwise some physicist with an axe to grind would claim something about Occam's Razor.Shawn

    You know that Everett was drinking when he first had his brainwave, while busy thinking up “ridiculous things about the implications of quantum mechanics” ? That at first his thesis was totally ignored until another physicist, Bryce DeWitt, popularised it years later? That he met with Neils Bohr, who refused to even consider the 'many worlds' idea? That Everett left academic research, disillusioned, and became a highly-paid analyst for the Defense Department designing ICBM re-entry paths during the Cold War? That he might have been a character in Dr Strangelove? That he died an alcoholic age 51, with instructions that his ashes be put out in the household waste? See The Many Worlds of Hugh Everett, Scientific American. Note also the telling remark at the end of the first edition of his thesis:

    Once we have granted that any physical theory is essentially only a model for the world of experience we must renounce all hope of finding anything like the correct theory ... simply because the totality of experience is never accessible to us. — Hugh Everett

    You have to ask whether the whole thing is kind of a joke.
  • Shawn
    12.1k


    I found Max Tegmark interesting in his mathematical universe and multiverse theory. Then again, it seems remarkable for physicists to think it true that MW's exist when you can simply ask them where do the measurements end and where do they begin. To make the entire universe less intelligible by stating a mathematical notion of determinism with no clear adherence to why I experience this time evolution rather than the other where I won the lottery or Russian roulette game is odd.
  • Shawn
    12.1k


    I actually posted the following question to stackexchange:

    How do time evolutions occur in the Many Worlds Interpretation?

    For example, if I assume that I played the lottery today and will probably not win it tomorrow, then what governs the time evolution of the other world where I won the lottery rather than the one where I didn't win it?
  • Marchesk
    4.6k
    Sabine Hossenfelder is of the opinion that the popularity of MWI and other multiverse ideas are due to the majority of physicists being Platonists. They think math is real, and not just some system of thought we invented that can work as a shorthand for scientific theories.
  • Philosophim
    1.2k
    Multiverse theory is the same as unicorn theory. No one has found a unicorn yet, and no one has found a different universe yet. As such, they are just postulates of imagination, no more.
  • Wayfarer
    16.3k
    Sabine Hossenfelder is of the opinion that the popularity of MWI and other multiverse ideas are due to the majority of physicists being Platonists.Marchesk

    Well, I'm extremely sympathetic to Platonism in mathematics, but i see no reason whatever to beleive that justifies the 'many worlds' intepretation. Like I asked in another thread - what problem does it solve? If the many worlds intepretation is the solution, what is the problem?

    I think, and it's not only my opinion, that the problem it solves is the so-called collapse of the wave function. That, prior to being measured, 'the object' doesn't actually exist anywhere. All you have is a distribution of probabilities, but it's not as if the electron is hiding in a thicket, awaiting discovery. It's not anywhere, it doesn't actually exist, in an unequivocal way. So this introduces the whole problem of why does observing it cause it to exist? Avoiding that problem is the rationale.

    Another solution is given in this paper, which draws on Heisenberg's philosophy of physics.

    At its root, the new idea holds that the common conception of “reality” is too limited. By expanding the definition of reality, the quantum’s mysteries disappear. In particular, “real” should not be restricted to “actual” objects or events in spacetime. Reality ought also be assigned to certain possibilities, or “potential” realities, that have not yet become “actual.” These potential realities do not exist in spacetime, but nevertheless are “ontological” — that is, real components of existence.

    “This new ontological picture requires that we expand our concept of ‘what is real’ to include an extraspatiotemporal domain of quantum possibility,” write Ruth Kastner, Stuart Kauffman and Michael Epperson.

    Hear ye the imminent cries of 'woo-woo'? This is because, in modern thinking, there's no room for any 'degrees of reality' - something either exists, or it doesn't. Whereas what this is saying is that

    Observations of a “pure” quantum state, containing many possibilities, turns one of those possibilities [described by the wave function] into an actual one. And the new actual event constrains the list of future possibilities, without any need for physical causation. “We simply allow that actual events can instantaneously and acausally affect what is next possible … which, in turn, influences what can next become actual, and so on,” Kastner and colleagues write.

    Measurement, they say, is simply a real physical process that transforms quantum potentia into elements of res extensa — actual, real stuff in the ordinary sense. Space and time, or spacetime, is something that “emerges from a quantum substratum,” as actual stuff crystalizes out “of a more fluid domain of possibles.” Spacetime, therefore, is not all there is to reality.

    So, the wave function actually transcends space and time. I put that view on Physics Forum where it was dismissed as 'gobledygook' by one of the residents, but I find the same view in a textbook I'm currently reading, Nature Loves to Hide, by Shimon Malin (a physicist, not a pop science writer.)
  • Marchesk
    4.6k
    Like I asked in another thread - what problem does it solve? If the many worlds intepretation is the solution, what is the problem?Wayfarer

    From listening to several of Sean Carol's podcasts, it seems he and other physicists of his persuasion take the wavefunction as being descriptive of reality, and it's simpler to go that route than try and come up with some means for there being a wavefunction collapse. You take the math at face value.

    But then you can go really overboard with that and end up with Tegmark's multiverse where all mathematical forms exist.
  • prothero
    401
    it seems a high price to pay to preserve determinism.
  • fishfry
    2.6k
    Multiverse theory is the same as unicorn theoryPhilosophim

    Could well be. But for purposes of this discussion, please note that multiverse theory and the many-worlds interpretation are two entirely different speculative theories.
  • T Clark
    9.8k
    However, if one assumes in physics, as do many physicists, that the world is not mathematical, then doesn't it mean that conservation of energy laws would become violated for every branching of wavefunction collapses?Shawn

    Seems to me that if we buy the many worlds interpretation, violation of the conservation of energy and matter is the least of our problems.
  • Philosophim
    1.2k
    Could well be. But for purposes of this discussion, please note that multiverse theory and the many-worlds interpretation are two entirely different speculative theories.fishfry

    Mind explaining how? As far as the specifics go, my understanding of many worlds interpretation is that all quantum states exist in some type of branching world or universe. This is just a multiverse theory. All multiverse theories fail at their core, because they are pure speculation without evidence.

    Put a horn on a horse, and that sounds plausible. Spin the idea that measurement of quantum objects prevents us from knowing another aspect about that quantum object, and say that all possible quantum entities could exist, and it sounds plausible. But at the end of the day, its all speculation if you can't prove one shred of evidence that such a thing can actually exist.

    I understand you might be interested in the higher levels of MWI speculations, but at the end of the day its like speculating whether a unicorn is able to magically heal wounds, or cast spells so it can fly. Its all moot until you can prove a unicorn exists.
  • fishfry
    2.6k
    Mind explaining how?Philosophim

    MWI is as you explain it, branching due to QM, as an alternative to wave function collapse.

    The multiverse theory says that the universe consists of "bubble universes" that branch off and are causally independent of each other. Entirely different theory. Nothing to do with quantum branching. It's a cosmological theory.

    https://en.wikipedia.org/wiki/Multiverse
  • BrianW
    999
    There's a big difference between 'conceptual' and 'actual'. Multiple worlds, parallel universes, time travel, teleportation, etc, etc, are still just conceptual renderings. Also, a big part of our understanding of quantum phenomena (mechanics) is conceptual. Whatever the actual phenomena/activities are and however they take place, there's bound to be a big difference.

    How do we compare our technology today with whatever ideas (concepts - if any) of them that existed 200, 500, 1000, 2000 years ago?

    A 'purely' mathematical dimension/perspective mostly refers to the conceptual. Actual phenomena can be worked out even without adequate mathematical knowledge provided there's adequate experiential knowledge.
  • Michael
    11.8k
    Sean Carroll explains this by saying that the energy splits too. Each world takes with it half the energy of the parent world, so that conservation of energy is preserved. Of course that means that if the total energy of the universe is finite, at some point there's not enough energy to split into any more worlds. I'd like to ask Sean Carroll that. I'm sure he's thought about it.fishfry

    Could be that there's actually zero energy in the universe.
  • fishfry
    2.6k
    Could be that there's actually zero energy in the universe.Michael

    Way above my pay grade. If Sean Carroll didn't make a video about it, I have no idea :-)
  • Philosophim
    1.2k
    The multiverse theory says that the universe consists of "bubble universes" that branch off and are causally independent of each other. Entirely different theory. Nothing to do with quantum branching. It's a cosmological theory.

    https://en.wikipedia.org/wiki/Multiverse
    fishfry

    If you read the wiki article you linked, you'll see that MWI is a level 3 classification scheme of multiverse theory. I was correct then.

    You seem to have side stepped the larger issue I made however. In the end, MWI is a unicorn theory. Do you have an answer for this?
  • Wayfarer
    16.3k
    MWI is a level 3 classification scheme of multiverse theory....Philosophim

    ...according to Max Tegmark's classificatory scheme, which is shared by practically nobody.

    MWI is a unicorn theoryPhilosophim

    I think it's all nonsense on stilts, but who am I?
  • Philosophim
    1.2k

    MWI is a level 3 classification scheme of multiverse theory....
    — Philosophim

    ...according to Max Tegmark's classificatory scheme, which is shared by practically nobody.

    I was replying to fishfry's link. He linked me that, so I assume he found that to be a valid source. If you would like to enter the conversation, feel free. If Max Tegmark's scheme is wrong, who's scheme is right?

    MWI is a unicorn theory
    — Philosophim

    I think it's all nonsense on stilts, but who am I?
    Wayfarer

    So one in agreement with unicorn theory then! But I want to give fishfry a chance to refute it.
  • Wayfarer
    16.3k
    Sure, sorry if I butted in, but Fishfry is right to point out that what is generally referred to as the multiverse, is a different conception from the many-worlds interpretation of quantum mechanics. Tegmark lives on his own planet, as far as i can discern, so has limited relevance to the debate.

    My personal view, which of course I don’t have any credentials to support. Is that a lot of this kind of theorisation is sign of a kind of decadence. It provides this kind of unlimited conceptual elbow space which can be used to rationalise all kinds of mathematical conjecture, but which will be forever outside any kind of validation even in principle. So It has all the worst features of metaphysics, which scientific types routinely vilify, without even the association with an ethical code which traditional metaphysics at least has. I think science ought to be practiced without any reference to this kind of speculative foam, which I think would provide a kind of bracing austerity, and some needed humility.

    Check out this article.
  • fishfry
    2.6k
    If you read the wiki article you linked, you'll see that MWI is a level 3 classification scheme of multiverse theory. I was correct then.Philosophim

    They seem to be using multiverse in a more general way, so in that sense you're right. My understanding of multiverse is as in eternal inflation, which is not a QM theory. I'd agree that there's a considerable confusion between the multiverse and the MWI.

    You seem to have side stepped the larger issue I made however.Philosophim

    I didn't sidestep it, I didn't address it at all.

    In the end, MWI is a unicorn theory. Do you have an answer for this?Philosophim

    I have no answer for that. Multiverses as in bubble universes are plausible, in the sense that there are parts of the universe that are causally unreachable from the observable universe. We can't know what's out there. MWI I don't find very plausible, but I don't know enough QM to have an informed opinion.
  • Metaphysician Undercover
    10.4k
    All multiverse theories fail at their core, because they are pure speculation without evidence.Philosophim

    That's what I see as the principal issue. Evidence is derived from "our" universe, and we generally do not allow conflicting evidence as this is contradictory. If there are multiple universes with conflicting evidence, then we need some principles whereby we could distinguish our universe from others, allowing that conflicting evidence could be acceptable. This is not simply a matter of distinguishing one possible world from others, but what distinguishes our world from all the other possible worlds. At present, there are no principles which would allow us to distinguish one universe from the rest, as "our" universe, except that it's the one we have evidence of.

    This is the age-old old ontological question, which is yet to be answered, what distinguishes our world from the many logically possible worlds, as the real world. The simple answer is "evidence", But the many different ways in which evidence may be interpreted produces ambiguity in that distinction. If the ambiguity leads us to believe that every logically possible world is just as real as every other, then we lose the standard by which our world is distinguished from other logically possible worlds, as the real world.. In other words, evidence no longer helps us.
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