I’m not sure what you mean by ‘anthropic per se’. Everett (MW) explains apparent quantum indeterminism anthropically, via indexical ignorance; our knowledge of the system as a whole is complete, but we don’t know where we in the system are at this moment. De Broglie (HV) explains apparent quantum indeterminism via factual ignorance; our knowledge of the system’s physical makeup is incomplete, and that alone creates the appearance of randomness. Von Neumann (OC) explains apparent quantum indeterminism realistically; the world just is indeterministic.
The SE’s dynamics lead to decoherence, which makes MWI have branching. It’s all just noticing the structure that’s already in the system.
This is either a very implausible answer, or an answer to a different question than the one I asked. Historically, the Born Probabilities are derived directly from experimental data, not from the theorized dynamics. The difficulty of extracting the one from the other, of turning this into a single unified and predictive theory, just is the ‘Measurement’ Problem. Bohm is taking two distinct models and reifying mechanisms for each to produce an all-encompassing theory; maybe that’s useless or premature, but it’s clearly not a non sequitur, because the evidence for a genuine wave/particle dichotomy just is the evidence that makes scientists allow probabilistic digressions from the Schrödinger equation.
MW is not a finished theory until we see how it actually unifies the two, though I agree there are at least interesting and suggestive first steps in that direction. BM’s costs are obvious and clear and formalized, which is its main virtue. Our ability to compare those costs to other theories’ is limited so long as it’s the only finished product under evaluation, because it’s easy to look simple when you choose to only try to explain some of the data.
I see what you mean now about anthropism. Yes, ignorance is subjective. Incidentally, this is how it used to be back before quantum ever came up.
This is either a very implausible answer, or an answer to a different question than the one I asked. Historically, the Born Probabilities are derived directly from experimental data, not from the theorized dynamics
Historically, Born was way before Everett and even longer before decoherence, so that’s not exactly a shocker. Even in Born’s time it was understood that subspaces had only one way of adding up to 1 in a way that respects probability identities—I’d bet dollars to donuts that that was how he got the rule in the first place, rather than doing a freaking curve fit to experimental data. What was missing at the time was any way to figure out what the wavefunction was, between doing its wavefunctiony thing and collapse.
Decoherence explains what collapse is made of. With it around, accepting the claim ‘The Schrödinger Equation is the only rule of dynamics; collapse is illusory and subjective’, which is basically all there is to MWI, requires much less bullet-biting than before it was introduced. There is still some, but those bullets are much chewier for me than any alternate rules of dynamics.
(incidentally, IIRC, Shminux, you hold the above quote but not MWI, which I find utterly baffling—if you want to explain the difference or correct me on your position, go ahead)
maybe that’s useless or premature, but it’s clearly not a non sequitur
Decoherence explains what collapse is made of. With it around, accepting the claim ‘The Schrödinger Equation is the only rule of dynamics; collapse is illusory and subjective’, which is basically all there is to MWI
Well, you still need a host of ideas about how to actually interpret a diagonal density matrix. Because you don’t have Born probabilities as a postulate, you have this structure but no method for connecting it back to lab-measured values.
While it seems straightforward, its because many-world’s advocates are doing slight of hand. They use probabilities to build a theory (because lab experiments appear to be only describable probabilistically), and later they kick away that ladder but they want to keep all the structure that comes with it (density matrices,etc).
I know of many good expositions that start with the probabilities and use that to develop the form of the Schroedinger equation from Galilean relativity and cluster decomposition (Ballentine, parts of Weinberg).
I don’t know any good expositions that go the other way. There are reasons that Deutsch, Wallace,etc have spent so much time trying to develop Born probabilities in a many world’s context- because its an important problem.
Hold on a moment. What ladder is being kicked away here?
We’ve got observed probabilities. They’re the experimental results, the basis of the theory. The theory then explains this in terms of indexical ignorance (thanks, RobbBB). I don’t see a kicked ladder. Not every observed phenomenon needs a special law of nature to make it so.
Instead of specially postulating the Born Probabilities, elevating them to the status of a law of nature, we use it to label parts of the universe in much the same way as we notice, say, hydrogen or iron atoms - ‘oh, look, there’s that thing again’. In this case, it’s the way that sometimes, components of the wavefunction propagate such that different segments won’t be interfering with each other coherently (or in any sane basis, at all).
Also, about density matrices—what’s the problem? We’re still allowed to not know things and have subjective probabilities, even in MWI. Nothing in it suggests otherwise.
I’m not sure what you mean by ‘anthropic per se’. Everett (MW) explains apparent quantum indeterminism anthropically, via indexical ignorance; our knowledge of the system as a whole is complete, but we don’t know where we in the system are at this moment. De Broglie (HV) explains apparent quantum indeterminism via factual ignorance; our knowledge of the system’s physical makeup is incomplete, and that alone creates the appearance of randomness. Von Neumann (OC) explains apparent quantum indeterminism realistically; the world just is indeterministic.
This is either a very implausible answer, or an answer to a different question than the one I asked. Historically, the Born Probabilities are derived directly from experimental data, not from the theorized dynamics. The difficulty of extracting the one from the other, of turning this into a single unified and predictive theory, just is the ‘Measurement’ Problem. Bohm is taking two distinct models and reifying mechanisms for each to produce an all-encompassing theory; maybe that’s useless or premature, but it’s clearly not a non sequitur, because the evidence for a genuine wave/particle dichotomy just is the evidence that makes scientists allow probabilistic digressions from the Schrödinger equation.
MW is not a finished theory until we see how it actually unifies the two, though I agree there are at least interesting and suggestive first steps in that direction. BM’s costs are obvious and clear and formalized, which is its main virtue. Our ability to compare those costs to other theories’ is limited so long as it’s the only finished product under evaluation, because it’s easy to look simple when you choose to only try to explain some of the data.
I see what you mean now about anthropism. Yes, ignorance is subjective. Incidentally, this is how it used to be back before quantum ever came up.
Historically, Born was way before Everett and even longer before decoherence, so that’s not exactly a shocker. Even in Born’s time it was understood that subspaces had only one way of adding up to 1 in a way that respects probability identities—I’d bet dollars to donuts that that was how he got the rule in the first place, rather than doing a freaking curve fit to experimental data. What was missing at the time was any way to figure out what the wavefunction was, between doing its wavefunctiony thing and collapse.
Decoherence explains what collapse is made of. With it around, accepting the claim ‘The Schrödinger Equation is the only rule of dynamics; collapse is illusory and subjective’, which is basically all there is to MWI, requires much less bullet-biting than before it was introduced. There is still some, but those bullets are much chewier for me than any alternate rules of dynamics.
(incidentally, IIRC, Shminux, you hold the above quote but not MWI, which I find utterly baffling—if you want to explain the difference or correct me on your position, go ahead)
Good thing I never said it was.
Well, you still need a host of ideas about how to actually interpret a diagonal density matrix. Because you don’t have Born probabilities as a postulate, you have this structure but no method for connecting it back to lab-measured values.
While it seems straightforward, its because many-world’s advocates are doing slight of hand. They use probabilities to build a theory (because lab experiments appear to be only describable probabilistically), and later they kick away that ladder but they want to keep all the structure that comes with it (density matrices,etc).
I know of many good expositions that start with the probabilities and use that to develop the form of the Schroedinger equation from Galilean relativity and cluster decomposition (Ballentine, parts of Weinberg).
I don’t know any good expositions that go the other way. There are reasons that Deutsch, Wallace,etc have spent so much time trying to develop Born probabilities in a many world’s context- because its an important problem.
Hold on a moment. What ladder is being kicked away here?
We’ve got observed probabilities. They’re the experimental results, the basis of the theory. The theory then explains this in terms of indexical ignorance (thanks, RobbBB). I don’t see a kicked ladder. Not every observed phenomenon needs a special law of nature to make it so.
Instead of specially postulating the Born Probabilities, elevating them to the status of a law of nature, we use it to label parts of the universe in much the same way as we notice, say, hydrogen or iron atoms - ‘oh, look, there’s that thing again’. In this case, it’s the way that sometimes, components of the wavefunction propagate such that different segments won’t be interfering with each other coherently (or in any sane basis, at all).
Also, about density matrices—what’s the problem? We’re still allowed to not know things and have subjective probabilities, even in MWI. Nothing in it suggests otherwise.