Oct 24 2014

The Many Interacting Worlds Hypothesis

Howard Wiseman, a theoretical quantum physicist at Griffith University in Brisbane, Australia, and his colleagues have come up with an entirely new theory to explain the weird behavior of particles at the quantum level. The idea is that quantum effects result from classical universes interacting with each other.

Classical physics is essentially the physics of Newton and describes the macroscopic world. In classical physics particles have a definitive location and momentum. At the scale of fundamental particles, however, the world behaves very differently.

At this so-called quantum level, particles move in waves but then interact as particles. They have only a probabilistic location and cannot be nailed down specifically. There is a minimum amount of uncertainty when trying to measure any linked properties, such as location and momentum. Even more bizarre is quantum entanglement in which particles have linked properties, even when separated across the universe.

The bottom line is that we do not really know why the quantum world behaves as it does. We have experimental data, such as the double-slit experiments, that show consistent results. When light beams shine through two close narrow slits they interfere with each other as if they are moving like waves, even when the beams are so faint that only one photon will be passing through the silts at a time. One photon can apparently cause a wave interference with itself. But when those same photons strike a film plate or detector, they behave like a particle.

The experimental results are fairly clear. What is not clear is how to interpret those results. Quantum mechanics defies all of our evolved intuitions. It seems to reflect an aspect of reality that is completely foreign to us. Our experiments, while important, are not directly accessing the deepest level of reality. We are just probing in ways that we know how to probe and then trying to infer from the results something about reality that goes beyond our current concepts.

Perhaps the most popular interpretation of quantum experiments is the Copenhagen interpretation. This hypothesis states that fundamental particles exist as waves of probability, but when they are forced to interact with their environment the probability waves collapse into a specific value, more like a classic particle. This is a consistent interpretation, but it’s just that – an interpretation.

We cannot conclude that this is likely to be the correct interpretation because we don’t know what all the alternatives are. We don’t know enough about the fundamental nature of reality to have any confidence that we have a complete set of hypotheses.

This new “many interacting worlds” hypothesis is a good example of the fact that physicists can still come up with entirely new interpretations of quantum observations that are no more bizarre than the Copenhagen interpretation. In this hypothesis there are many universes that coexist along with our own, but they are (at least as far as we can say) completely isolated and inaccessible from our own universe. This “many worlds hypothesis” is not new to quantum physics, and has been offered as an interpretation alternative to Copenhagen. In the many worlds view, each collapse of a probability wave actually splits off a separate universe – there is a separate universe in which each quantum possibility becomes reality.

This new twist assumes that universes are classical all the way down. However, these classical universes can bump into each other and interact with each other. They speculate that this interaction might be able to explain some of the quantum experimental observations. For example, two universes bumping into each other might cause one to surge forward while the other bounces back. This behavior could explain the observation of quantum tunneling, where quantum particle will tunnel through a barrier.

It’s actually a little generous to call this a hypothesis. It’s more of a wild speculation, but you have to start somewhere. The next challenge will be to work out some of the math and physics, and to see if this notion could explain other quantum phenomena, like entanglement. Then the real challenge comes – designing an experiment that could distinguish the many interacting worlds hypothesis from the Copenhagen interpretation. It’s possible that the two interpretations will make slightly different predictions about experimental measurements.

Conclusion

It is very uncertain if the many interacting worlds interpretation will turn out to be of any use to theoretical physics and it’s unlikely to transform our understanding of quantum mechanics. It might, but it’s a long shot.

The bigger lesson here, in my opinion, is that it is premature, to say the least, to use any specific interpretation of quantum mechanics as a justification for otherwise fantastical claims.  I find it interesting that most people doing so, for example justifying claims of ESP or astrology, generally don’t really understand quantum theory or the current interpretations, none of which allow for superluminal remote information transfer.

My sense is that we are still a long way away from a meaningful understanding of what our observations of quantum phenomena actually mean in terms of the fundamental nature of reality. There still room for theoretical physicists to say, “hey, what if this completely different interpretation is true.’

27 responses so far

27 Responses to “The Many Interacting Worlds Hypothesis”

  1. Kieselguhr Kidon 24 Oct 2014 at 12:02 pm

    Yeah, I was intrigued by the article too, although I don’t see a good experimental test any time soon.

    That said, I don’t think it’s “this as an alternative to Copenhagen” — when I was taught it I think nobody anywhere thought, or thinks, Copenhagen is a “real” description. There’s quite a number of other models out there, but Copenhagen doesn’t have much credibility in p-chem circles — maybe never did — and I think a paper a couple years ago by Barrett, Pusey and Rudolph showed that the statistical interpretation doesn’t hold up.

  2. hardnoseon 24 Oct 2014 at 1:29 pm

    I prefer the “nobody knows” hypothesis.

  3. sonicon 24 Oct 2014 at 1:35 pm

    Kieselguhr Kid-
    I was under the impression Pusey et. al. has been thoroughly debunked.
    http://motls.blogspot.com/2011/11/nature-hypes-anti-qm-crackpot-paper-by.html

    Using this new idea, they can’t explain entanglement (as of yet).
    Seems a bit early to be hyping the thing.

    “It’s more of a wild speculation…” (Novella)

    It seems there are a number of attempts to get an ‘objective’ interpretation of QM.
    This latest effort is symptomatic of the difficulties.
    It seems trying to interpret the wave function as an actual physical object leads to all sorts of difficulties.

    String theory to the rescue?

  4. Ori Vandewalleon 24 Oct 2014 at 3:59 pm

    My understanding is that most physicists who deal in the quantum subscribe to the “Shut up and calculate!” interpretation.

  5. YtterbiJumon 24 Oct 2014 at 4:21 pm

    “Quantum effects result from classical universes interacting with each other” sounds exactly like David Deutsch’s description of the many-worlds interpretation in his book The Fabric of Reality.

  6. Insomniacon 24 Oct 2014 at 5:48 pm

    I’m having a hard time grasping what on Earth these Universes’ interactions could mean. Can we really use these common words as “bumping” and “surging forward” as if there were a kind of mechanical reality to it ? I imagine these are analogies.

    For the time being, as I’ve heard several times about the Many Worlds hypothesis, or other Multiverse ideas, I stick with the Copenhagen interpretation. It almost seems natural to me now to think of tiny objects as both particles and waves.

  7. Yiannison 24 Oct 2014 at 11:09 pm

    Once one starts discussing interpretations of QM, one steps in a very thorny area, and it is even possible to summon Beetlejuice this way.

    Readers of this blog may be interested in my completely biased and personal endorsement of Peter Woit’s blog (Not Even Wrong) concerning interpretation issues of QFT and QM. Briefly, the word ‘interpretation’ is splendidly chosen, because that is what those statements are: they are not scientific theories, they have no predictive power and they cannot be verified by experiments. ‘

    If an experiment can verify or falsify a statement about QM, it is not an interpretation: it is an extension or elaboration of QM. Peter Woit’s positions may be viewed as extremely skeptical for some (as a researcher in a mathematical field with connections to string theory, I stand to lose in terms of funding), but they can serve as an excellent wake up call to a drowsy but necessary morning of experiment.

    I have no specific comments on the particular interpretation reported in the article, I can only say with certainty that if the authors are serious about their claims, then firstly, they have chosen the wrong words and secondly, Prof Novella’s question about devising an experiment to test the claims should have been completely addressed in the paper; this is not done. The ‘put to the test’ section indicates that clearly: there is no mathematical test that can verify a scientific theory. Period. Only experiment can do that. As a mathematician, it pains me and my grant proposals, but honesty is paramount.

    Tl;dr: as a mathematically consistent framework which interprets the quantum mechanical formalism, sure, it is a possibly viable proposition. It involves some interpretation of QM at its basis and the authors need to work out the equations to see if entanglement is accurately reflected in the framework. As an extension of the scientific theory of QM? Where is the experimental basis? The only thing we are given is this:

    “If the many-interacting-worlds approach is true, it will probably predict small differences from quantum theory, Wiseman says. “We haven’t yet worked out what these deviations would be, but I think they would be very different from the sort of deviations that people are currently looking for.””

    Inspecting the paper proper, there are no false claims there but only one significant sentence in the paragraph: “We haven’t yet worked out what these deviations would be.” I have to emphasize that this is meant in the mathematical meaning of the sentence: “We haven’t yet determined whether measurable deviations exist in the first place and therefore a fortiori have not worked out what they would be if they exist.”

  8. Charonon 25 Oct 2014 at 12:02 am

    I wouldn’t call Copenhagen a “consistent interpretation”. The measurement process is bizarre, doesn’t preserve things that should be preserved, arbitrarily divides the world into “classical” and “quantum”… it’s what we teach students. It’s fine. It’s not the actual right answer, but it’s fine.

    For most people, “shut up and calculate” is all they need. I don’t care if an electron is a point particle, a wave, a vibration in a quantum field, a string or whatever, as long as I can calculate how it scatters light.

    For those who really care about the fundamental stuff, it does matter. Sean Carroll has a favorite interpretation: http://www.preposterousuniverse.com/blog/2014/06/30/why-the-many-worlds-formulation-of-quantum-mechanics-is-probably-correct/

  9. BillyJoe7on 25 Oct 2014 at 12:29 am

    Insomniac,

    “For the time being, as I’ve heard several times about the Many Worlds hypothesis, or other Multiverse ideas, I stick with the Copenhagen interpretation. It almost seems natural to me now to think of tiny objects as both particles and waves”

    I think you might have your worlds mixed up. The “Many Worlds” belongs to quantum physics, but the “Multiverse” belongs to cosmology. And you can’t really call them “objects” if you want to claim that they are both particles and waves. Also, they are not “particles and waves”, they are entities that exhibit both particle and wave like behaviour (waves while travelling, and particles while interacting).

    Finally, why do you want an “interpretation” of quantum physics?

    Almost all these interpretations are attempts to explain difficult concepts in terms of our everyday experience. But there’s no reason to think that this is a reasonable thing to do in expectation of success. How would you go about explaining time dilation and space contraction in terms of our everyday experiences?

    And what about everyday experiences themselves?
    How do you explain gravity? What is it that actually attracts one mass to another mass. Well, we have curved space. But what is curved space in terms of our everyday experiences. It seems to me we make interpretations in order to make it easier to think about these concepts. Which is fine if it actually works. But, perhaps it should not come as such a surprise that this doesn’t always work.

    Certainly you’re going to be hard up finding an interpretation for entanglement in terms of our everyday experience.

  10. Nitpickingon 25 Oct 2014 at 2:59 pm

    The whole “how to interpret QM” argument seems silly to me. If your model gives the same result as Copenhagen, it’s … the same as Copenhagen. If not, it disagrees with experimental evidence and can be disregarded.

    Show me a model that makes different predictions than Copenhagen and yet doesn’t disagree with experiment.

    [waits]

  11. bobzeon 25 Oct 2014 at 4:51 pm

    Long time reader first time poster here. This is interesting, but I didn’t think it was new. Back when Michael Crichton used to write great sci-fi he wrote a book called Time line. Interestingly in the book the physicists explained the double slit experiment results as photons in other universes closely related to ours as the cause for the results. I’ve always assumed he didn’t come up with that on his own.

    I’ve often wondered if “dark matter” and the gravitational effects we see from it could be explained by other universes in a multiverse interacting with our own as well? I’ve never really researched it much and only have an amateurs understanding of advanced physics as I’m a physician by trade. Anyway interesting article Steve.

  12. BillyJoe7on 25 Oct 2014 at 6:03 pm

    Nitpicking,

    Just to pick a nit, if you think that the whole idea of interpreting quantum physics is silly, then why are you backing Copenhagen?

    I think interpretations of QM are interesting and often help you to understand or remember concepts, but I don’t think they are the be all and end all. Entanglement is a fact of life. If the many worlds interpretation is correct, then the entangled particles always had the values that they are revealed to have when one of them interacts – no need for “instantaneous action at a distance”. If not then we have to accept “instantaneous action at a distance”. We used to think gravity acted instantaneously. But it turns out that, if the Sun suddenly disappeared, it would take another eight minutes before the Earth flew off at a tangent. That seems weird – it seems weird that the reaction would not be instantaneous. But somehow it’s the instantaneous behaviour of entangled particles that seems weird.

    If their interpretations of QM help physicists to get some understanding of what’s going on and, if this improved understanding helps them to move the field forward, then great. If not, well that’s just the way it is, no big deal, they’ll just slog through. And it doesn’t lend weight to any wild unscientific speculations such as telepathy for which there is no evidence in the first place

  13. Adam Bjerreon 25 Oct 2014 at 7:46 pm

    Steven,

    I understand your worry of premature interpretation of quantum mechanics to justify fantastical claims. (e.g. ESP or astrology).

    If I understand you correctly here and elsewhere you primarily want to look to the physicists for an interpretation/explanation of “the fundamental nature of reality”. That is the tradition of viewing the formalization as primary in relation to the reality that is formalized. It sounds to me like you are extremely close to a modern version of Platonic idealism (the idea that behind the world that we can sense there is an ideal world and that the world we can sense is only an incomplete or distorted version of the ideal world).

    Einstein said that “it is the theory that describes what we can observe.” I think that we have to remember that mathemathical accounts are extremely useful tools, but they are just tools. I think we have to be careful if we primarily want to rely on a mathematical capability of describing “the fundamental nature of reality”. We might end up concluding that the world essentially is mathemathical. It is not. We do not need another divine entity that is mathematics instead of a supernatural being in the sky.

    I consider myself a scholar of science and nature and I think the idea of anything supernatural is a denying of what is. A soon as we enter the field of biology the mathemathical models are suffering. We are here dealing with both chance and necessity. Evolution implies that human thinking is also a process and a product of nature. Charles S. Peirce wrote in 1891:
    “Thus it is that our minds having been formed under the influence of phenomena governed by the laws of mechanics, certain conceptions entering into those laws become implanted in our minds, so that we readily guess at what the laws are. Without such a natural prompting, having to search blindfold for a law which would suit the phenomena, our chance of finding it would be as one to infinity.”

    Human logic is a fundamental aspect of nature, but that doesn’t mean that all phenomena of nature can fit into logical thinking.
    I suggest we look to biology, life and evolution for an interpretation/understanding of “the fundamental nature of reality”.

    Thank you for your relentless work in the name of reason.

  14. Nitpickingon 25 Oct 2014 at 9:19 pm

    Just to pick a nit, if you think that the whole idea of interpreting quantum physics is silly, then why are you backing Copenhagen?

    Because Steve mentioned it first, is all. Feel free to substitute, e.g. many-worlds if you like.

  15. Insomniacon 26 Oct 2014 at 4:30 am

    BillyJoe7,

    Thanks for your comment.

    In fact, there are plenty of ideas surrounding the concept of Multiverse, of which the many worlds hypothesis is one. Indeed, the term Multiverse just refers to the fact that there could be more than one Universe.

    The Multiverse, although the term may originally have been coined in this context, does not exclusively relates to the idea that multiple Universes are being born in black holes, with slight differences in fundamental constants from its parent Universe. It’s just a general concept suggesting there might be multiple Universes.

    I agree with your nuanced phrasing about the wave-particle duality. Saying they are both particles and waves is not, however, too far from it. Anyway, I would say they are primarily waves which evolution is predictable and, when interacting with the macroscopic world, reduce to a particle involving probabilistic aspects. You would say instead that these objects usually behave like waves, and then behave like particles when the measurement happens.

    I’m not looking for interpretations in terms of every day experiences. I recognize the mathematical properties of these objects, and I call a wave what is mathematically characterized as a wave, that’s it. About entanglement, one has to acknoledge the non-local feature of QM and recognized entangled particles as one single object. I’m not looking for every day explanations here, and indeed, you’re going to have a hard time trying to do so.

  16. grabulaon 26 Oct 2014 at 8:35 pm

    “Saying they are both particles and waves is not”

    I’ve always been under the impression that it’s more appropriate to say they can behave like a particle and a wave and not necessarily that they ARE both things?

  17. Giovaneloon 01 Nov 2014 at 4:33 pm

    Steve Novella:

    “Quantum mechanics defies all of our evolved intuitions. It seems to reflect an aspect of reality that is completely foreign to us. Our experiments, while important, are not directly accessing the deepest level of reality.”

    This is the main problem with all anti-QM “theories”: from the fact that QM defies our primitive, Newtonian, evolved intuitions about the world, we derive the conclusion that “the deepest level of reality” must be somehow Newtonian and adjusted to our evolved notions. And, consequently, that QM which does cater to our primitive Newtonian intuitions must be either wrong or “incomplete”.

    However, that’s just another form of anthropomorphism, like creationism, intelligent design and similar things; just the newest version of the old (and clearly wrong) Einstein’s adage “God does not play dice”. Niels Bohr’s response was as good today as it was then: “Einstein, don’t tell God what to do”. Or, as we would express it today: “don’t tell the Universe what to do”. Anthropomorphism won’t die so easily.

    Richard Feynmann’s adage seems to me much deeper and much more truthful than Einstein’s “deep”, “philosophical” musings about “reality”: “Shut up and calculate”.

  18. Giovaneloon 01 Nov 2014 at 4:41 pm

    a very good review here

    http://motls.blogspot.ca/2014/10/many-interacting-worlds-approach-is.html

  19. BillyJoe7on 01 Nov 2014 at 5:42 pm

    Giovanelo,

    “from the fact that QM defies our primitive, Newtonian, evolved intuitions about the world, we derive the conclusion that “the deepest level of reality” must be somehow Newtonian and adjusted to our evolved notions. And, consequently, that QM which does [not] cater to our primitive Newtonian intuitions must be either wrong or incomplete”

    I can’t believe we agree.
    Of course, I’m not saying it is necessarily the case that the deepest level of reality is NOT
    intuitive/newtonian/anthropomorphic but, rather, that it is not necessarily the case that it IS.
    And, moreover, that there is NO REASON to think that that will turn out to be the case.
    After all, how intuitive are time dilation, space contraction, curved space, and gravitational waves?
    There is already a lot of accepted counterintuitive stuff out there so why should QM be any different?

  20. Giovaneloon 03 Nov 2014 at 9:59 pm

    It gets better and better. A new group now uses string theory to “validate” QM, instead the other way around.
    http://phys.org/news/2014-11-field-theory-foundation-quantum-mechanics.html

    and unavoidably, the same “we need something deeper” talking point:

    “Clearly the rules are correct, but they beg for an explanation of their origins in some physical phenomena that are even deeper”

  21. BillyJoe7on 04 Nov 2014 at 1:03 am

    Giovanelo,

    There is nothing wrong with what they are doing. They are trying to see if M theory could provide common ground to quantum mechanics and relativity. Not everything is like your three decade long, three hundred leaf toilet roll.

  22. Giovaneloon 04 Nov 2014 at 1:40 pm

    Billy Joe,
    M-theory DOES provide a common ground for QM and relativity. Moreover, it UNIFIES them. That’s the essence of the theory. But, it does not provide a “realistic foundation” for QM. Those are two different things. M theory has been around for 20 years or so; if the only thing they are claiming is that M theory provides a common ground for QM and relativity, what’s the point of advertizing that trivial claim as a big discovery?

  23. BillyJoe7on 04 Nov 2014 at 3:49 pm

    Giovanelo,

    M-theory is an attempt to unify general relativity and quantum field theory.
    It will be news to physicists that this has already been achieved.
    Perhaps they should read your book.

  24. jsterritton 04 Nov 2014 at 9:50 pm

    It is my understanding that string theory and M theory both “predict gravity.” I don’t see M theory as an attempt to unify GR and QM, but as a theory that necessarily arrives at conclusions about gravity that make it a candidate for a possible better understanding of gravity — at the Planck scale — than GR (our best understanding so far) or the standard model (no understanding at all) provide. Obviously, M theory is more concerned with gravity than its predecessor theories. One of the reasons M theory is perceived to be failing is that gravitational waves (and gravitons) have not been detected. Or SUSY particles at the LHC. Still, this seems like a shortcoming of the theory’s ability to predict, not a fatal flaw. I have never understood this theory to be at odds with QM or GR. Rather, in trying to create a robust framework for unifying QCD with QED, compelling ideas about gravity pop out — something we can hardly ignore. M theory is “on the rocks” — with reason — but I don’t quite get the “turf war.” No one will argue that QM isn’t the best understanding we have for how the world works, but bristling at string theory’s attempts to dig deeper makes no sense.

  25. jsterritton 04 Nov 2014 at 9:50 pm

    It is my understanding that string theory and M theory both “predict gravity.” I don’t see M theory as an attempt to unify GR and QM, but as a theory that necessarily arrives at conclusions about gravity that make it a candidate for a possible better understanding of gravity — at the Planck scale — than GR (our best understanding so far) or the standard model (no understanding at all) provide. Obviously, M theory is more concerned with gravity than its predecessor theories. One of the reasons M theory is perceived to be failing is that gravitational waves (and gravitons) have not been detected. Or SUSY particles at the LHC. Still, this seems like a shortcoming of the theory’s ability to predict, not a fatal flaw. I have never understood this theory to be at odds with QM or GR. Rather, in trying to create a robust framework for unifying QCD with QED, compelling ideas about gravity pop out — something we can hardly ignore. M theory is “on the rocks” — with reason — but I don’t quite get the “turf war.” No one will argue that QM isn’t the best understanding we have for how the world works, but bristling at string theory’s attempts to dig deeper makes no sense.

  26. Giovaneloon 05 Nov 2014 at 7:49 pm

    Billy Joe, your infantile expressions of animosity don’t change anything. The M-theory provides a unification of QM and relativity, and does not try “to see if the M-theory provides a common ground between QM and relativity”, as you claimed. Of course, the M-theory has not been YET established experimentally, but we are talking here about theoretical, not experimental advances. The point is that the M-theory PRESUPPOSES that QM is right, not the other way around, so your initial claim that those guys, who claim that it is the other way around, are just doing straightforward M theory, is, how shall I put it – wrong.

  27. Also65on 10 Nov 2014 at 6:18 am

    Think about two intersecting fields that vary (expanding and contracting) periodically. Their mutual interaction comes from their periodical variation. In their intersection, they create four new fields that are the subatomic particles of the central and shared atomic nucleus. If the two intersecting fields are universes, they will be two interacting parallel universes.

    http://curvaturasvariantes.com/2014/10/09/animacion-de-modelo-atomico/

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