It’s been a while, but I’ve occasionally mentioned on the blog that Cecil B. Demille’s The Ten Commandments (the 1950s color version) is one of my favorite movies. And this has remained true even as I’ve come to see it as straight fantasy.
An interesting fact from when I first saw it as a very young boy. I initially thought Yul Brenner’s Ramses was two different characters. This was because there were several scenes with him outside in armor, and other scenes of him inside in more comfortable attire. To my five year old self, it looked like two different guys. Until the scene after Ramses’ son has just died, when he decides to go after the Israelites. Inside-Ramses calls for his armor, and in the process transforms onscreen into outside-Ramses, making me realize they were one and the same.
Over the years, I’ve encountered many other entities which initially looked like separate things, but turned out to just be the same thing seen from different perspectives or in different contexts. Time and time again, I’ve learned to be on the lookout for underlying patterns that might indicate I’m looking at different aspects of the same thing. (I think this is why I have little trouble conceptualizing consciousness as functionality.)
Which is why found this video from Matt O’Dowd interesting. He explores a proposition that David Deutsch has often expressed, that the pilot-wave interpretation of quantum mechanics is just a special case of the many-worlds interpretation.
O’Dowd, around the thirteen minute mark, does note one seemingly structural difference between the two, the guiding equation of pilot-wave, which tells the particle where to go. It’s not needed under many-worlds because under it, a version of the particle goes everywhere the wave function is non-zero. As he notes, many-worlds is pilot-wave minus any one version of the particle being the one true real one.
I don’t know much about the guiding equation. I do wonder if, under many-worlds, it could be seen an expression of the relationship between particles in one particular world. Or if there’s simply no room for it in that theory.
I think one reason Deutsch emphasizes the similarities between the two theories, and the one difference, is it seems to answer a common question for the idea of pure wave mechanics: waves of what? According to Deutsch, it’s waves of the different versions of the particle. This leads him to hold a particle first ontology, which seems like a minority view among Everettians (many-worlders).
Although ultimately this may just be “a six of one, half a dozen of the other” type thing. Are waves, waves of particle versions? Or are particles just fragments of waves? Under any degree of wave function realism, the answer could just be “yes”.
Unless of course I’m missing something?
SelfAwarePatterns 
I’m not qualified to comment on pilot wave theory, and I’m yet to be convinced by many worlds, but the way I understand wave-particle duality is by thinking of the wave as the fundamental object, and regarding the particle as a transient point-like event that we interpret as a physical object, but which is simply the signature of a quantum event. We only ever “see” a particle when it interacts with another particle in some way. Does a particle go through two slits? The wave goes through both, and the detection of the wave occurs as a point-like interaction.
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My credence in many-worlds varies by mood, although probably in a range centered around 50%. But all the other realist options seem much lower.
I see value in the way you’re thinking about it. A lot of people try to minimize the wave ontology, insisting that the particle is what we actually “observe” and the wave is just a mathematical contrivance. Of course, in truth we never observe either, only infer them from their effects. After a lot of vacillation, I’ve reached the point where I think both are real, and struggle to see a fact of the matter on which is more fundamental. I might think differently later.
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Um … FWIW … ditto.
*
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I’m extremely sympathetic to One Ramses style hypotheses. But in this case I don’t think it can work, because pilot wavers are flat-out committed to spooky action at a distance, while Everettians are not. Spooky action at a distance meaning the (not-all-that-spooky) idea of influences faster than light.
Pilot wave theory’s two real particles in an EPR experiment have separate locations, yet are governed by a wavefunction with only one t variable. So, as David Bohm acknowledged, this model violates the light-speed limit. An Everettian however, can say that particles (and physicists) are emergent patterns in wavefunctions, along the lines that Steve Morris commented upon. When Alice and Bob make their respective EPR measurements, they create particles out of wavefunctions. Moreover, each of them, in a crucial case, creates multiple particles* corresponding to multiple measurement outcomes, and each physicist decoheres into multiple physicists* with the corresponding beliefs “I got spin up” and “I got spin down”. When they communicate their data, eventually concluding that Bell’s Inequality was violated, all this communication happens at sub-light speeds. When physicist/lab-apparatus pairs decohere into separate “spin up” and “spin down” components, this decoherence happens at light speed or less, too.
*Asterisks: particles, on a natural reading, have particular measurable properties. Physicists, on a natural reading, have thoughts and experiences that generally cohere with each other, e.g. they do not simultaneously believe “I got spin up” and “I got spin down” regarding trial #n.
So I think Everettians can deny that *causality* connects faster-than-light volumes of spacetime. (And this separates them from Bohmians.) On the other hand, Everettians might not be able to claim *separability* for spacetime regions outside of light-cones. I haven’t read or understood enough about that.
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I agree that Everettians can claim local dynamics. Explaining how this works has always been tricky, particularly for the gradual split description, where spacetime diagrams are typically required. Deutsch’s description of preexisting worlds (corresponding to positions on the relevant dimensions in Hilbert space) have always seemed like the easiest lift, but that highlights the particle ontology.
As you note, Bohmians have to explicitly reject locality. What I’m not clear on is if they were simply to accept that there is no one true particle, that it’s on an equal footing with the rest of the wave, whether their need for non-local dynamics disappears without further effort. In other words, does the guiding equation still work within a subset of Everett? Given the problems it introduces for reconciling with QFT, I tend to think the answer is no, which does seem to put more distance between the views.
The separability issue is disputed. Most Everettians accept that they can’t claim it. But Deutsch and Alyssa Ney claim they can. But I think it involves accepting full wave function realism, which even many Everettians seem reluctant to buy.
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I like your inside and outside Ramses anecdote. I remember reading something by Asimov about particle-wave duality. He said it’s like asking if a cone is a circle or a triangle. It’s kind of both. If you insist on using two-dimensional shapes to describe a three dimensional object, then a cone is a circle and a triangle, depending on how you look at it.
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Thanks. That analogy sounds interesting. I can’t remember if I’ve ever read anything from Asimov on quantum theory. And a quick search shows his science books are starting to become hard to find, which is a shame. It’s interesting that it’s the reverse from the late 1970s when I first started reading him. Back then you had to go to used bookstores to find most of his sci-fi stuff, but his science stuff was everywhere.
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That is unfortunate. Whenever I’ve read one of his science books, there are always some specific details that are out of date, but the general ideas are still valid, and Asimov explained things so clearly. It’s a shame more people can’t read his stuff today.
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I like his videos. Although he can come across as a bit pedantic. Maybe it’s the PhD level subjects…
“Maybe there’ more to learn…” Masters of the Universe with incomplete knowledge and understanding. Keep it going, just remember, in the end there’s only death and beer, not in that order.
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Shame I’m not much of a beer drinker then. But there are also cookies, which helps.
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Hi, random internet person here, found your post after googling on this topic after watching Matt’s video myself. I’m a layperson so I could have this all wrong, but here is a comment I just posted on the video:
“Wait, wait, wait. This assumes that in pilot-wave theory, interactions between particles are mediated always and only by the pilot wave, not by the (shudder) corpuscle. It makes much more sense to me that pilot waves would mostly interact with their own corpuscle, not with other pilot waves, and it would be the corpuscle that interacts with other particles. Basically, interaction that would be described as wave function collapse in Copenhagen would be mediated by corpuscles, any other interactions (we’re reaching the extent of my knowledge here) would be mediated by the pilot wave. Wouldn’t this give much cleaner results, and explain why every measurement (ie every interaction) updates the wave function at the location of the particle?
To the point above, the detector electrons wouldn’t be in a superposition in Copenhagen. The excitation of the electron is a measurement, no?, and so it would collapse the wave function. So in pilot-wave theory, this would mean it was a corpuscule-mediated reaction, no empty superpositions to be seen.
I suppose it’s possible to say that there is a pilot-wave theory that’s MWI-like (all interactions are mediated by never-ending pilotwaves) and a pilot-wave theory that is Copenhagen-like (intereactions that are described by Copenhagen as collapse are mediated by corpuscules, other interactions are mediated by pilot waves).”
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Hi fellow random internet person!
Interesting idea. The first issue that comes to mind, at least for me, is what does it imply for entangled particles, which are described by a single wave function? Do the waves of those corpuscles now interact? If so, what leads them to interact where normally they wouldn’t? I guess you could say the guiding equation (definitely don’t know what I’m talking about here) propagates some kind of change nonlocally?
Overall, the issues with pilot-wave just seem to pile up the more we consider it. Which is probably why few physicists see it as promising.
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