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Sean Carroll, the author, is a huge proponent and believer [1][1.1] in Many-Worlds Interpretation (MWI) interpretation of QM. MWI's basic idea is that the wavef

• acqq 7y ago
  In the article, there is a statement: "Empirically minded physicists have realized that the phenomenon of measurement can be directly probed by sufficiently subtle experiments." Then please write about these probes, and not just the rant that "nobody understands." The public doesn't have to worry (and we don't have to read) about the "interpretations" until there is a specific proposition of how to do such probe an the experiment can be constructed and performed. He writes "students who demonstrate an interest in the topic are gently but firmly — maybe not so gently — steered away, sometimes with an admonishment to “Shut up and calculate!”." My answer to this article would be, to theoretical physicists: "shut up and construct an experiment that can be performed." As long as there's no practical difference (in the sense that any experiment that can be imagined can demonstrate it) there's just no physics there. So yes... "shut up and calculate."
  • zxcb1 7y ago
    It's either that or "shut up and meditate"
• platz 7y ago
  I don't believe any of the possible interpretations of QM have a clear path to being proven, so are they pseudoscience as well? If Hawking Radiation can never be observed till the heat death of the universe, is that pseudoscience, or just really hard to test? At this regime, all of physics is very hard to design an experiment for on ranges we have access to.
  • nwallin 7y ago
    > I don't believe any of the possible interpretations of QM have a clear path to being proven, so are they pseudoscience as well? The characterization is a little bit harsh, but yes. The Copenhagen interpretation is non-falsifiable, (relative to MWI) so while I don't know what it is, I know it isn't science. There's a reason most reputable scientific journals don't accept papers dealing with interpretations of quantum mechanics. There's no "there" there. Hawking radiation is interesting because a proof of lack of Hawking radiation is a proof of the falsehood of quantum mechanics. Which is really interesting; any time you can falsify something like quantum mechanics every physicist should be paying attention. Also, if certain models of string theory are correct, particle accelerators like the LHC should be able to produce micro black holes, which will then evaporate in detectable ways. So Hawking radiation is of observational interest as of 2010 as a possible way to provide evidence to support string theory. (spoiler alert: we didn't find any)
    • NotSammyHagar 7y ago
      It feels like you are way too quick to kick things out that aren't on a path to being proven. String theory forever has had the problem that it didn't make experimentally verifiable conclusions. A quick web search finds recent articles discussing apparently discussing this. Aren't people still working on string theory? Or why is mwi impossible to verify.
      • mrpara 7y ago
        The difference is, string theorists are trying. Everyone knows that it is a major problem that we cannot currently design experiments to falsify ST or other quantum gravity theories, and everyone is working towards it in the hope that one day we may. When it comes to interpretations of QM, there is not only nothing on the horizon, people don't even speak in these terms. No one is insisting on falsifiablity, and indeed every new interpretation seems completely hell-bent on just providing a "story" around the equations in a way that does not - and fundamentally cannot - make any predictions that contradict basic QM. I can count on one hand the number of interpretations I can think of that make experimentally testable assertions, and for those I have plenty of respect[1]. But the majority of interpretations and their proponents seem to deliberately stay within the comfort zone of non-falsifiablity, writing paper after paper whose actual impact on either physics or philosophy can be summed up with "yeah well, that's just like, your opinion, man". I did my MSC in physics under a professor who is a well-known proponent of MWI (though my master's thesis was not directly related to the subject). Two years of working side by side with him proved to me that the detractors of work on interpretations are, by and large, correct in their assertions about the proponents of them. [1] There is this one theory whose name I cannot remember, where each particle in the universe gets their wavefunction multiplied by a delta function or very thin gaussian at random intervals, and whose sudden localization also causes a sort of chain reaction and localizes all particles it is entangled with. This theory is interesting because it helps set a (statistical) limit between microscopic and macroscopic interactions; basically, when you go past a certain number of entangled particles, everything will be well-localized virtually all of the time, but for small numbers of particles we'll see quantum phenomena. Unfortunately I recall this theory having too many holes, and perhaps it has already been falsified, but the point is that at least it made an effort to address inherent problems in QM (namely, wavefunction collapse) in a way that physicists actually should; by making testable claims.
• blackholesRhot 7y ago
  Completely agree.
• djmips 7y ago
  "he's just unhappy that most physicists don't share his view about QM" - Can you prove that? Are you just unhappy that Carroll doesn't share your view about QM?
• paulddraper 7y ago
  IMO, I have heard no explanation that is more consistent and coherent than this. --- Consider the famous Schroedinger's Cat. The decayed particle has two states: decayed and not decayed. The cat has two states: dead and alive. The researcher that opens the box has two states: sad and happy. The waveform does not collaprse. The particle, the cat, and the researcher each have a uncollapsed waveform; i.e. are in both states. However, these waveforms are not independent; they are entangled. The decayed particle is coincident with the dead cat and the unhappy researcher. And the undecayed particle with the alive cat and the happy researcher. All states "exist" simultaneously, but not independently. This bifurcation in the wave function magnitudes is a "split" in the universe: every future waveform interaction will be in the context of decayed particle/dead cat/unhappy researcher and undecayed particle/alive cat/happy researcher. "Many worlds" sounds nonsensical, but it is really just a colloquial expression for waveform entanglement. --- Now this does present a philosophical question on how consciousness functions in light of the split waveforms. I maintain that science -- quantum mechanics or otherwise -- has no explanation or even language to express "consciousness". It's like asking science an ethics question. And this inability applies to all science, not just quantum mechanics.
  • RyanAF7 7y ago
    Schroedinger's Cat is the most cited and incorrectly applied outcome in all of science. There is no state, there are no changes, there is no other world. Once again, the modalities overtake concepts. Analogeous to pi. Just because the maths game of ratios creates irrationality doesn't mean we can't draw circles. It's all one. No other number, no other outcome. Maths are just puzzles.
  • millstone 7y ago
    Many Worlds is not "a colloquial expression for wavefunction entanglement." Entangled states are part of the mathematics of QM, not a feature of an individual interpretation. MWI distinguishes itself by omitting (as you say) any notion of "collapse" from its axioms. This is appealing for simplicity but the problem is how it connects to experimental results: 1. How does the Born rule arise? If the universe split into two but the measure of cat-dead is 1/pi, why do I find myself in the cat-alive universe more often? 2. More generally, how does randomness arise? MWI contains only deterministic axioms, so how can it explain the experimental observation that measurements of similarly prepared states result in different values?
• au64 7y ago
  Motl is a zealot for his own interpretation and thinks everyone else is an idiot crackpot, including his colleagues. Carroll does not mention his preference for many-worlds in the article because that's not what it's about. The fact that he has a preferred interpretation is not relevant to the point that physicists should pay closer attention to the lack of consensus on the interpretation of qm.
• pdonis 7y ago
  > when Carroll talks about 'physicists not understanding QM', he's just unhappy that most physicists don't share his view about QM I don't see that in this particular article (which is not to say it isn't there in other articles Carroll has written). In this article, he is simply pointing out that QM is the only physical theory we have ever had that does not have a single generally accepted interpretation. Not believing the MWI is fine (I'm not a fan of it myself), but that just means you have to find some other interpretation that works, and nobody has done that; every interpretation of QM has issues that nobody has figured out how to resolve.
• sandworm101 7y ago
  >> Each time there's a decoherence, there's a universe split. Or, the universe was split before and that quantum uncertainty is really us perceiving those already-existing other universes. The collapsed wave is really just us measuring the only particle, the one in our universe, capable of stronger interactions. Under that interpretation the rest of the electron shell is a cloud of other electrons existing across universes but unable to interact strongly in ours, literal ghost particles.
  • jhanschoo 7y ago
    Every claim you are making requires justification why it explains reality better than the model you are arguing against. Without that this reply paints you as a crank.
    • sandworm101 7y ago
      I, and more than a few others, find the ongoing existence of multiple universes easier to swallow than the concept of new universes being created whenever a wave function collapses. The pre-existence of an infinity is of greater likelihood than the continuing creation of multiple infinities as time moves forward. This is testable, if not practical atm. If something like an electron exists in ghost forms across multiple universes then they may be linked in those other universes more strongly than ours, a concept that may offer explanations for a variety of quantum behaviors. Proof of this would be the observation of a reliable link between particles not linked in our universe.
• ErotemeObelus 7y ago
  > Sean Carroll, the author, is a huge proponent and believer Don't use that word. "Believer" is for cultists, flat-earthers and UFO worshippers.
• yoaviram 7y ago
  A thought experiment called Quantum Suicide [1] is an interesting read in this context. [1] https://thoughtexperiments.net/quantum-suicide/ https://thoughtexperiments.net/quantum-suicide/
  • akvadrako 7y ago
    All these people saying many worlds and Copenhagen have identical predictions are totally ignoring this. If many worlds implies quantum immortality and Copenhagen doesn't, that's a clearly detectable physical difference.
    • kgwgk 7y ago
      Detectable how precisely?
      • akvadrako 7y ago
        By not dieing.
        • kgwgk 7y ago
          So if you do it and you don't die would you say that you proved something? If someone does it and doesn't die would you think that did prove anything? If one thousand people do it and one of them is still alive after 10 coin flips does that prove anything? What is the detectable physical difference? How do you carry on an experiment to detect that physical difference? What is the protocol to determine that the physical difference has been detected? Please let me know how should we do to not totally ignore this.
          • akvadrako 7y ago
            QI predicts you’ll still be alive in 1M years with 100% probability. Not-QI puts that probability lower. So if you are still alive in 1M years that’s evidence of QI. Basic Bayesian reasoning.
• nabla9 7y ago
  > So when Carroll talks about 'physicists not understanding QM', he's just unhappy that most physicists don't share his view about QM and he's been known for trying to shame physicists for not sharing his view too. This is incorrect and bad faith representation of Carrol's position. While Carrol is proponent of MWI, he is calling more research on foundations of quantum theory in general. If you follow his podcast it's clear what his position is. Some of these so called interpretations are "legitimately distinct physical theories, with potentially new experimental consequences". In this article he specially mentions Ghirardi–Rimini–Weber theory. https://en.wikipedia.org/wiki/Ghirardi%E2%80%93Rimini%E2%80%93Weber_theory https://en.wikipedia.org/wiki/Ghirardi%E2%80%93Rimini%E2%80%...
  • deleted 7y ago
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• blablabla123 7y ago
  > 'physicists not understanding QM' This is quite a popular claim among the Physics community. It goes even further saying: those who understand it don't understand it. ;-) Emphasizing how counter-intuitive the concepts are and also the fact the even Standard QM (with 1 or 2 particles) is still a research topic. Even Einstein didn't believe in QM as it stands now.
• ThePhysicist 7y ago
  I agree that deciding between MWI and other interpretations seems impossible, so it's not a problem that's considered important in physics, more of a good topic for a dinner conversation among physicists. Our understanding of quantum measurements is much better now than it was at the advent of quantum mechanics, and it's understood that there's no such thing as an "abrupt" collapse of a wave function during measurement, it's instead a continous process involving entanglement and decoherence between two quantum systems (the system being measured and the measurement system). This understanding allows us to explain any measurement process using only "plain" quantum mechanics, i.e. unitary evolution of two coupled systems described by a Hamiltonian. If we just look at the Hamiltonian of the measured system it will seem that it shows wave function collapse because its evolution is non-unitary, but the evolution of the entire system is still unitary. From this angle I personally find any further invokation of a wave-function collapse mechanism unnecessary, and I think it overcomplicates quantum mechanics without giving us any benefits, so we might as well do away with it. Unfortunately, most courses on quantum mechanics still introduce the students to wave-function collapse when explaining measurement outcomes, which might be the reason that so many physicists have a bad understanding of the measurement process. Of course wave-function collapse is still a good shortctut for describing strong quantum measurements, I think it should be introduced as an approximation of a continuous measurement though.
  • atq2119 7y ago
    Contra your first paragraph, isn't your second paragraph ultimately saying that MWI has won over Copenhagen as the more useful theory?
    • ThePhysicist 7y ago
      I'd say wave-function collapse is a good approximation for many strong quantum measurements, but isn't able to describe many experiments that involve weak quantum measurements or quantum feedback. As I said it might be good to start teaching quantum measurements using the entanglement+decoherence mechanism first and then introduce wave-function collapse as an approximation.
• jhanschoo 7y ago
  The article strikes me as crackpottery, but this statement > A lot of physicists also don't see any value in MW's interpretation since it offers no predictive value is not entirely correct either. This is the probably best "explain like I am an undergraduate not in Physics" article on Everett's proposal. https://plato.stanford.edu/entries/qm-everett/ https://plato.stanford.edu/entries/qm-everett/ To further summarize the value of Everett's proposal: In the standard von Neumann-Dirac collapse formulation of QM, a collapse happens when we measure it. But what a measurement event looks like and conditions when it occurs are not described by the theory at all. This is one reason why QM cannot completely describe the universe, or approximate it. Note that even if we can describe what a collapse is, this+QM still fails to model parts of the world, only approximating it. But one can try to propose a formulation of QM that agrees with the collapse formulation, that does not have that collapse, so that it is closed in the sense that for each system of observers observing a quantum system collapsing, that system can be modeled as quantum system itself. That is Everett's proposal. From the linked article, > Everett’s solution to the problem was to drop the collapse postulate from the standard formulation of quantum mechanics then deduce the empirical predictions of the standard collapse theory as the subjective experiences of observers who were themselves modeled as physical systems in the theory. The result was his relative-state interpretation of pure wave mechanics.
  • kgwgk 7y ago
    The “no predictive power” is beyond what is predicted by standard QM, because the MWI is supposed to recover the same predictions. And it’s not clear how does it so, because if standard QM has an issue with “what a measurement event looks like and conditions when it occurs” then exactly the same problem remains in the MWI if the same predictions have to be recovered. Even though there is no collapse in the MWI it looks like there is a collapse, even though you don’t have to specify when the collapse happens you have to specify when does it look like a collapse does happen.
    • jhanschoo 7y ago
      > even though you don’t have to specify when the collapse happens you have to specify when does it look like a collapse does happen. In MWI there is no collapse event, because there are no observers in the traditional sense that may collapse the system. In MWI we resign and just say that observers are subject to QM, and when a "measurement" is made, what happens is that observers and the observed system get entangled so that certain combinations of properties of the observer-observed system are not possible. This entanglement of two projections of a composite system can be described in the language of QM. > what is predicted by standard QM, because the MWI is supposed to recover the same predictions. MWI recovers the same predictions. Where in standard QM if one says an observer observes that a system may collapse 40% in state a and 60% in state b, MWI says that in systems (of the observer and the observed) where the observer makes the observation in the same exact manner, the observer will record state a with the system in state a 40% and the observer will record state b with the system in state b 60%, and there are no states where the observer observes something and the subsystem is in the other state. Of course, you can simply model the entire system of observer and observed in standard QM and recover the same relative predictions without invoking the absolute observation of an observer. In MWI we do away with the conceit that there is an absolute observation of an absolute, but ill-defined observer.
• wheels 7y ago
  > A lot of physicists also don't see any value in MW's interpretation since it offers no predictive value David Deutsch (in many ways, the father of quantum computing) initially imagined quantum computing as a way to test MWI: if a problem could be solved that required more gates than there are particles in the universe, then it would (so the argument goes) prove that the problem was being solved in the multiverse.
  • kgwgk 7y ago
    Paraphrasing the title of the submission, “David Deutsch doesn’t understand Quantum Mechanics” (if what you said is true).
• im3w1l 7y ago
  > Each time there's a decoherence, there's a universe split. The universe is constantly splitting. Not just when there is decoherence. Or more accurately. Every possible state of the universe has a probability amplitude right now. And those probability amplitudes are constantly evolving, diffusing into each other, interfereing with each other. Every such state with a probability amplitude is a world of the many worlds.
• JaimeThompson 7y ago
  >Each time there's a decoherence, there's a universe split. Where does the energy come from to create the other universes?