Prof. Harvey Brown: The evolution of Bell's thinking about the Bell theorem

Рет қаралды 10,834

CUPS - Cambridge University Physics Society

Күн бұрын

Slides: drive.google.com/file/d/1lqOr...
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Abstract
The 1964 Bell nonlocality theorem did much to expand the foundations of quantum mechanics from philosophy seminars into mainstream physics. In this talk I will concentrate on how the theorem was conceived, and how later variations of the theorem led Bell to a wider notion of nonlocality, and a change in the significance of the theorem. I will also discuss whether Bell thought nonlocality is consistent or otherwise with special relativity, and address the wider question as to whether the Bell theorem, in any of its variants, shows that quantum mechanics is necessarily nonlocal, as is often claimed. (The talk will be for non-experts, but based on my paper with Christopher Timpson: "Bell on Bell's theorem: The changing face of nonlocality", in Quantum Nonlocality and Reality, Mary Bell and Shan Gao (eds.), Cambridge University Press, 2016, pp. 91-123. arxiv.org/abs/1501.03521)
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Speaker Information
Harvey Brown is a Professor of Philosophy of Physics at Oxford University, and a fellow of the British Academy. He studied physics at the University of Cantebury in New Zealand, and then pursued graduate studies in philosophy at Chelsea College in London. Prior to moving to Oxford he taught at the University of Sao Paulo in Brazil. Professor Brown has written on varied topics in the philosophy of physics, including 4 books on on topics including the philosophy of quantum field theory and on spacetime. His present research interests include the foundations of quantum mechanics, relativity theory and thermal physics, the philosophy of space and time, and the role of symmetry principles in physics.
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Пікірлер: 31

@davidhand9721 25 күн бұрын

An excellent, excellant presentation on the whole. Thanks for bringing in Everett at the end there, it's a very important clarification. I don't say "many worlds" anymore, but all the same.

@ricomajestic Ай бұрын

Great talk!

@davidhand9721 25 күн бұрын

Thank you for stating Einstein's problem with QM in its full detail. Far too often I hear "spooky action at a distance" is synonymous with entanglement. I've always felt that wavefunction collapse alone was intolerable to relativity.

@TheWyrdSmythe 3 жыл бұрын

Excellent talk!

@dimitrispapadimitriou5622 Жыл бұрын

In the Many Worlds version of the Everett interpretation there's still the issue of the ( global or local?) splitting of the "semi-classical worlds". So, the "spooky action" is actually there, too: it's just "transformed" to the non local splitting of the spacetime geometries.. As usual, we can't have our cake and eat it too..

@schmetterling4477 Жыл бұрын

Everett was an idiot who couldn't even get the second sentence of his thesis right.

@davidhand9721 25 күн бұрын

No, the Everett interpretation is entirely local. When things "split", there is nothing new being created. There's only one wavefunction, just an ever-increasing number of ways to look at it coherently. If you really need to hear the whole Alice and Bob story, I can tap it out for you, but I hope you can see that everything is fine just knowing that Alice and Bob don't have to agree until they meet to talk about the result, so each outcome is local. There's no reason to think that a measurement causes some physical event everywhere in the universe at once.

@dimitrispapadimitriou5622 25 күн бұрын

@@davidhand9721 Many worlds is non local in the same sense that the other interpretations are. And the emergence of the -irreducible - probabilities at the "macroscopic level" is another issue for the various versions of Everettian interpretations.

@davidhand9721 23 күн бұрын

@@dimitrispapadimitriou5622 I'm only talking about the legit Everett interpretation, formed entirely by dropping the Born rule and replacing the Schrodinger equation with its Lorentz invariant counterparts. I have no doubt that there are a multitude of pop science and pseudoscience portrayals of the interpretation that have conceptual issues related to locality and a lot of other things, but those are irrelevant for serious discussion. The "split" is something that happens to observers locally, not the creation of a whole new universe.

@5ty717 11 ай бұрын

Very good. Thank you for shining the light on JSB’s thoughts. btw…. G is “felt” perturbed at c (not instantly) … if the sun disappears at one instant we see it for 8 minutes longer here and similarly our orbit continues around the coordinates of the ex sun for that 8 minutes. Lol.

@das_it_mane 11 ай бұрын

I believe he mentioned it was that under Newton but under Einstein, gravity propagates at C

@LisaBlooper 2 ай бұрын

@@das_it_mane Not right. And E fully knew that. The premise "if the sun disappears on one instant" implies there is some global time in which an 'instant' plots. There is no global time. We must talk about events only in context of how they relate to other events. The sun IS THERE if we see it, and orbit it. Not "we orbit an EX sun". We may speak of the sun vanishing only by saying "it vanished simultaneous with this door closing". The event (vanishing sun) is not something separate to the event "suddenly not receiving light" or "suddenly not orbiting".

@yacc1706 Жыл бұрын

47:42 entanglement => perfect correlations, + "locality" => pre-defined => incompleteness; + =?=> determinism??? 1:00:18

@edoardodeo 4 жыл бұрын

Why is there no mention of loopholes in Bell's theorem and the recent work of Larsson and Hanson?

@leckansibanda1927 3 жыл бұрын

It's the most troubling and depressing situation in Physics since thee Solvay conference. Millions of people have been lied to. Even the EPR Paper was twisted to give the illusion that Eintein's with Quantum Physics was about determinism. John Bell Himself said Bohmian physics wasn't disproved by His theorem. He just proved that a certain class of hidden variable theories cannot exist or be complete in their modeling of quantum phenomena. Check out Tim Maudlin - What Bell Did. Sheldon Goldstein - John Bell and the Foundations of Quantum Mechanics

@itsanki 3 жыл бұрын

@@leckansibanda1927 It means young folks like me have big opportunity.

@lepidoptera9337 2 жыл бұрын

@@leckansibanda1927 In other words... you are not smart enough to understand quantum mechanics but want to appear smarter than you are. ;-)

@schmetterling4477 Жыл бұрын

There are no loopholes in Bell's theorem. The only problem with it is that it's not science but religion. It talks about non-existing things.

@oldoddjobs Ай бұрын

Physics can't be dead if it's still attracting the usual cranky hyperbole

@davidhand9721 25 күн бұрын

I really still don't understand what use there is for non-deterministic hidden variables. A probabilistic theory is not causal, period; there is not enough information in the system to predict its future state. That's the whole thing. You might as well just not have any hidden variables.

@philipoakley5498 Жыл бұрын

Still doesn't explain how the photons decided how to reach the particular slit they each decided to go through... Pretty pictures of the path afterwards ;-)

@yacc1706 Жыл бұрын

Caution! 8:08 Bohm theory and Schroedinger equation applies to massive particles, not to photons! The pilot wave passes through the two slits and the particle is guided through one of those

@azjaguardesign 4 ай бұрын

The wave function is merely the recipe for “spinning up” a manifestation given time ;where time is a singularity when confined mathematically and therefore subject to the infinite spiraling down of the rabbit hole of a #Mandelbrot-set’s ever approaching infinity. 😊 2:45

@lepidoptera9337 2 жыл бұрын

It boggles the mind that the professor doesn't seem to understand that the wave function (with exception of a few corner cases of constant pure states) doesn't give any information about the individual quantum system. It only give information about an ensemble of that quantum system.

@yacc1706 Жыл бұрын

45:04 dont use these words. 46:04 they are loaded

@rl7012 5 ай бұрын

Write the words then, not just the time stamps. These time stamp comments only are so annoying

@markjager8544 Жыл бұрын

Audio too poor to watch

@bustercam199 11 ай бұрын

People have made too big of a deal about Bell's theorem. It's only relevant in a limited defined context and does not have the broad applicability that Copenhagenists want it to have.