8 ms·

Y'know, I'm a physicist, specializing in quantumy stuff, and I suspect that some form of many-worlds is probably true. But I don't really like the preachy "Man

by hugh 18y ago

Y'know, I'm a physicist, specializing in quantumy stuff, and I suspect that some form of many-worlds is probably true. But I don't really like the preachy "Many Worlds is just the way it is, and anyone who thinks otherwise is a fool" tone of this series of articles. They're actually pretty well written (I'd rate them above David Deutsch's Fabric of Reality, frinstance -- though I don't consider that very high praise), but I recommend taking them with a grain of salt. Example: We have embarrassed our Earth long enough by failing to see the obvious. So for the honor of my Earth, I write as if the existence of many-worlds were an established fact, because it is. The only question now is how long it will take for the people of this world to update. --- Sheesh, that kind of thing just doesn't belong in any scientific debate. The domain name bothers me as well. Is it supposed to imply that anybody who doesn't agree with everything written in overcomingbias has simply done a poor job in overcoming their biases?

DaniFong 18y ago
I don't really like them either. They're written well enough for one to basically follow along the sentences, and the tone is such that it seems they're really understanding something I'm not. But I looked pretty deeply into these questions. I read the original papers of Einstein Podolsky and Rosen, of Bohr, of Born. I read much of John Bell's original work, and I'm pretty sure that there are results being assumed here (and elsewhere) that haven't really been proven, or were even originally stated. For example, it's commonly asserted that Bell's theorem rules out any deterministic quantum mechanical description of reality with local hidden variables. But this was, to my knowledge, never shown explicitly by Bell -- he simply ruled out a particular class of local hidden variable theories. There exist theories, consistent with experiment, which are local and deterministic: for what it's worth, a toy example is just a classical computer simulating everything in our universe we've yet seen. We don't know where the Born probabilities come from, but we also don't really understand the implications of many body entanglement. We don't even have a consistent definition of entanglement for three or more particles. We don't know, we haven't been able to calculate, but I have reason to suspect, that measurement consistent with Born probabilities could be entirely explained by the deterministic axioms already part of Quantum Mechanics. We haven't really gone as far as we could go with them. And already people are treating Many-Worlds as axiomatic. I don't really buy it.
- icky 18y ago
  > for what it's worth, a toy example is just a classical computer simulating everything in our universe we've yet seen. I suddenly feel the need for much, much more RAM...
- yummyfajitas 18y ago
  >for what it's worth, a toy example is just a classical computer simulating everything in our universe we've yet seen. I think the state of the classical computer qualifies as a nonlocal hidden variable. To use the language of formal logic, the classical computer is a model for quantum theory, i.e. (classical computer) |- QM. Within the QM theory, the computer qualifies as a non-local hidden variable, even though within the classical theory the computer is embedded in, it is local. Another toy example is Bohmian mechanics on configuration space: the theory is just a local PDE + local particle. But that's non-local in physical space. >We don't even have a consistent definition of entanglement for three or more particles. We don't know, we haven't been able to calculate, but I have reason to suspect, that measurement consistent with Born probabilities could be entirely explained by the deterministic axioms already part of Quantum Mechanics. Decoherence makes sense on the macroscale (1000+ particles), although it's true that 40 particles is iffy. Different classical states (i.e., experimental apparatus has light on vs light off) are separated by a distance sqrt(number of particles) in configuration space, and don't interact. As for explaining measurement with Born probabilities, that's reasonable. My co-conspirators and I currently have a physical, macroscale model where we show this to be true (no citation yet, but I'd be happy to explain more via email). But you still need some ontology. All deterministic QM can show is that the probabilities work out correctly; i.e., the born probability of (measurement 1 says spin up, measurement 2 says spin down) = 0. You still need a way to actually pick a configuration based on that probability distribution. The universe as we (you, me, even pg) know it is a point in configuration space, not a wavefunction. I'm happy with both MW and Bohm for that purpose.
  - DaniFong 18y ago
    I concede that by this definition of locality, a simulator doesn't quite count. But it is a physical model both consistent with our quantum experiments and special relativity, and it's local in something. And if it's local physics in something we're talking about, why is it 3-space that we're treating as the real embedding. > Decoherence makes sense on the macroscale (1000+ particles), although it's true that 40 particles is iffy. Different classical states (i.e., experimental apparatus has light on vs light off) are separated by a distance sqrt(number of particles) in configuration space, and don't interact. > As for explaining measurement with Born probabilities, that's reasonable. My co-conspirators and I currently have a physical, macroscale model where we show this to be true (no citation yet, but I'd be happy to explain more via email). But you still need some ontology. Please do. I looked for a while at decoherence and others, and the mechanism behind the processes kept fading from view. It's was like thermodynamics, where we can say something about the equilibrium states eventually reached, but we're having a hard time explaining the processes by which it reaches one state or another, and by those processes, the reasoning in other parts of physics break down. Like microscopic <-> macroscopic reversibility. But the people in nonequilbrium statistical mechanics have made a lot of progress in reconciling microscopic reversibility and macroscopic apparent irreversibility. Is such a thing possible for quantum measurement, or more generally, the quantum classical transition, as well? Might there be a reversible description -- Schrodinger's all the way down, so to speak? Finally, I'm not so sure that MW, decoherence, Bohmian mechanics, etc. are truly equivalent. In other words, I expect that one might start getting different answers. And there's reason to believe that they're incomplete descriptions. If you take one measurement, you'll notice it takes time. And the microphysics of QM says that it's time evolution should be unitary. So, halfway done, if we stop the clock, when we're doing a measurement, what do we find? Or rather, what would our laws tell us we'd find? The more popular interpretation seem to tell me 'don't ask this question.' But it seems there's something important hidden here.
extantproject 18y ago
"The Fabric of Reality" is horrible; there's way too much hand-waving going on in that book.
deleted 18y ago
[deleted]
mnemonicsloth 18y ago
Is it supposed to imply that anybody who doesn't agree ... has simply done a poor job in overcoming their biases? No. "Bias" is a term of art among statisticians and social scientists who study human decision-making. It's my understanding that Overcomingbias started out as a collaboration between Robin Hanson ("futurist" economist at George Mason) and Eliezer Yudkowsky (the just-plain futurist who wrote the quantum sequence at OB). Eliezer's got a pretty good introductory paper, which deserves to be read strictly on the merits of its opening paragraph: http://www.singinst.org/Biases.pdf http://www.singinst.org/Biases.pdf
eyudkowsky 18y ago
Re: Domain name: That's bias as in "cognitive bias" not "racial bias". OK, so you're a physicist, and you know that, when the dust settles and the true theory whatever-it-may-be is found, it's going to have multiple worlds in it, rather than violating relativity. At what point, in your opinion, should physicists go ahead and announce this fact to the public as the official verdict of Science? Make no mistake, quantum gibberish has trickle-down negative effects on the rest of the planet - people watching "What the Bleep Do We Know?" and losing hope in Reason. It may not hurt them any less than disbelief in natural selection, on average. At what point should physicists get together and say: "Oops! Werner Heisenberg was wrong about the special role of consciousness. We now know this for sure. Everyone stop reading 'The Secret'."? It's easy to say "Don't be too emphatic about that truth there" when you're a physicist and you can see the arguments clear as sunlight. If we were all evolutionary biologists we wouldn't need emphatic defenses of evolution, either.
- pfedor 18y ago
  OK, so you're a physicist, and you know that, when the dust settles and the true theory whatever-it-may-be is found, it's going to have multiple worlds in it, rather than violating relativity. I'm not a physicist, but I had studied physics for five years and I from what I have seen most physicists certainly wouldn't agree with you that the many-worlds interpretation is "the official verdict of Science." For the most part, physicists don't really care, because the all the results that can be tested experimentally remain the same no matter whether you talk about many worlds, about the wave function collapse or about something else entirely. This said, the majority of physicists who care at all choose to think in terms of the Copenhagen interpretation, which, as much as you may not like it, is simple and lets you get straight to the point. Which by the way does not imply that they think relativity is violated or that consciousness has any special status. If you want to consider relativity then the regular quantum mechanics is probably not the right framework anyway, since it is non-relativistic. What you want is the quantum field theory.

by hugh 18y ago

DaniFong 18y ago

I don't really like them either. They're written well enough for one to basically follow along the sentences, and the tone is such that it seems they're really understanding something I'm not. But I looked pretty deeply into these questions. I read the original papers of Einstein Podolsky and Rosen, of Bohr, of Born. I read much of John Bell's original work, and I'm pretty sure that there are results being assumed here (and elsewhere) that haven't really been proven, or were even originally stated. For example, it's commonly asserted that Bell's theorem rules out any deterministic quantum mechanical description of reality with local hidden variables. But this was, to my knowledge, never shown explicitly by Bell -- he simply ruled out a particular class of local hidden variable theories. There exist theories, consistent with experiment, which are local and deterministic: for what it's worth, a toy example is just a classical computer simulating everything in our universe we've yet seen. We don't know where the Born probabilities come from, but we also don't really understand the implications of many body entanglement. We don't even have a consistent definition of entanglement for three or more particles. We don't know, we haven't been able to calculate, but I have reason to suspect, that measurement consistent with Born probabilities could be entirely explained by the deterministic axioms already part of Quantum Mechanics. We haven't really gone as far as we could go with them. And already people are treating Many-Worlds as axiomatic. I don't really buy it.

icky 18y ago
> for what it's worth, a toy example is just a classical computer simulating everything in our universe we've yet seen. I suddenly feel the need for much, much more RAM...
yummyfajitas 18y ago
>for what it's worth, a toy example is just a classical computer simulating everything in our universe we've yet seen. I think the state of the classical computer qualifies as a nonlocal hidden variable. To use the language of formal logic, the classical computer is a model for quantum theory, i.e. (classical computer) |- QM. Within the QM theory, the computer qualifies as a non-local hidden variable, even though within the classical theory the computer is embedded in, it is local. Another toy example is Bohmian mechanics on configuration space: the theory is just a local PDE + local particle. But that's non-local in physical space. >We don't even have a consistent definition of entanglement for three or more particles. We don't know, we haven't been able to calculate, but I have reason to suspect, that measurement consistent with Born probabilities could be entirely explained by the deterministic axioms already part of Quantum Mechanics. Decoherence makes sense on the macroscale (1000+ particles), although it's true that 40 particles is iffy. Different classical states (i.e., experimental apparatus has light on vs light off) are separated by a distance sqrt(number of particles) in configuration space, and don't interact. As for explaining measurement with Born probabilities, that's reasonable. My co-conspirators and I currently have a physical, macroscale model where we show this to be true (no citation yet, but I'd be happy to explain more via email). But you still need some ontology. All deterministic QM can show is that the probabilities work out correctly; i.e., the born probability of (measurement 1 says spin up, measurement 2 says spin down) = 0. You still need a way to actually pick a configuration based on that probability distribution. The universe as we (you, me, even pg) know it is a point in configuration space, not a wavefunction. I'm happy with both MW and Bohm for that purpose.
- DaniFong 18y ago
  I concede that by this definition of locality, a simulator doesn't quite count. But it is a physical model both consistent with our quantum experiments and special relativity, and it's local in something. And if it's local physics in something we're talking about, why is it 3-space that we're treating as the real embedding. > Decoherence makes sense on the macroscale (1000+ particles), although it's true that 40 particles is iffy. Different classical states (i.e., experimental apparatus has light on vs light off) are separated by a distance sqrt(number of particles) in configuration space, and don't interact. > As for explaining measurement with Born probabilities, that's reasonable. My co-conspirators and I currently have a physical, macroscale model where we show this to be true (no citation yet, but I'd be happy to explain more via email). But you still need some ontology. Please do. I looked for a while at decoherence and others, and the mechanism behind the processes kept fading from view. It's was like thermodynamics, where we can say something about the equilibrium states eventually reached, but we're having a hard time explaining the processes by which it reaches one state or another, and by those processes, the reasoning in other parts of physics break down. Like microscopic <-> macroscopic reversibility. But the people in nonequilbrium statistical mechanics have made a lot of progress in reconciling microscopic reversibility and macroscopic apparent irreversibility. Is such a thing possible for quantum measurement, or more generally, the quantum classical transition, as well? Might there be a reversible description -- Schrodinger's all the way down, so to speak? Finally, I'm not so sure that MW, decoherence, Bohmian mechanics, etc. are truly equivalent. In other words, I expect that one might start getting different answers. And there's reason to believe that they're incomplete descriptions. If you take one measurement, you'll notice it takes time. And the microphysics of QM says that it's time evolution should be unitary. So, halfway done, if we stop the clock, when we're doing a measurement, what do we find? Or rather, what would our laws tell us we'd find? The more popular interpretation seem to tell me 'don't ask this question.' But it seems there's something important hidden here.

extantproject 18y ago

"The Fabric of Reality" is horrible; there's way too much hand-waving going on in that book.

deleted 18y ago

[deleted]

mnemonicsloth 18y ago

Is it supposed to imply that anybody who doesn't agree ... has simply done a poor job in overcoming their biases? No. "Bias" is a term of art among statisticians and social scientists who study human decision-making. It's my understanding that Overcomingbias started out as a collaboration between Robin Hanson ("futurist" economist at George Mason) and Eliezer Yudkowsky (the just-plain futurist who wrote the quantum sequence at OB). Eliezer's got a pretty good introductory paper, which deserves to be read strictly on the merits of its opening paragraph: http://www.singinst.org/Biases.pdf http://www.singinst.org/Biases.pdf

eyudkowsky 18y ago

Re: Domain name: That's bias as in "cognitive bias" not "racial bias". OK, so you're a physicist, and you know that, when the dust settles and the true theory whatever-it-may-be is found, it's going to have multiple worlds in it, rather than violating relativity. At what point, in your opinion, should physicists go ahead and announce this fact to the public as the official verdict of Science? Make no mistake, quantum gibberish has trickle-down negative effects on the rest of the planet - people watching "What the Bleep Do We Know?" and losing hope in Reason. It may not hurt them any less than disbelief in natural selection, on average. At what point should physicists get together and say: "Oops! Werner Heisenberg was wrong about the special role of consciousness. We now know this for sure. Everyone stop reading 'The Secret'."? It's easy to say "Don't be too emphatic about that truth there" when you're a physicist and you can see the arguments clear as sunlight. If we were all evolutionary biologists we wouldn't need emphatic defenses of evolution, either.

pfedor 18y ago
OK, so you're a physicist, and you know that, when the dust settles and the true theory whatever-it-may-be is found, it's going to have multiple worlds in it, rather than violating relativity. I'm not a physicist, but I had studied physics for five years and I from what I have seen most physicists certainly wouldn't agree with you that the many-worlds interpretation is "the official verdict of Science." For the most part, physicists don't really care, because the all the results that can be tested experimentally remain the same no matter whether you talk about many worlds, about the wave function collapse or about something else entirely. This said, the majority of physicists who care at all choose to think in terms of the Copenhagen interpretation, which, as much as you may not like it, is simple and lets you get straight to the point. Which by the way does not imply that they think relativity is violated or that consciousness has any special status. If you want to consider relativity then the regular quantum mechanics is probably not the right framework anyway, since it is non-relativistic. What you want is the quantum field theory.