The question of where a model is expected to generalize and where it isn’t is the entire problem. You are taking expectations about generalization as basic; I argue that these expectations are based on considerations of parsimony and symmetry. The order isn’t reversed here; parsimony/symmetry give rise to intuitions about whether a model will generalize.
The argument that no collapse happens at intermediate scales between very small and the entire universe is a symmetry-based argument, just as the argument that things beyond the cosmological horizon still exist is a symmetry-based argument.
The argument that no collapse happens at intermediate scales between very small and the entire universe is a symmetry-based argument, just as the argument that things beyond the cosmological horizon still exist is a symmetry-based argument.
Yes, I agree. But to discover and effectively apply symmetry one generally has to have a workable model first. For example, the invariance of the speed of light followed from the Maxwell equations, and was confirmed experimentally, and was incorporated in the math of the Lorentz transformations, yet without a good theory those appeared ugly, not symmetric. It took a new theory to reveal the hidden symmetry. And to eventually write the Maxwell equations in half a line, []A=J and divA=0, down from the original 20. Same with the cosmological horizon: it does not appear symmetric and one needs to understand some amount of general relativity to see the symmetry. Or believe those who say that there is one. The “no collapse at the intermediate scales” is a good hypothesis, but quite possible wrong, because gravity is likely to cause decoherence in some way, as Penrose pointed out.
I agree with most of the things you are saying here. I am not sure I agree about the cosmological horizon; it seems like you could derive this from special relativity, but in any case this is a minor point. I don’t know enough physics to confirm the thing you said about gravity and collapse.
In any case it seems you are currently saying “no collapse at intermediate scales is a good hypothesis and maybe wrong for this specific reason” whereas initially you were saying “interpretations [of quantum mechanics] by definition make no difference” and “I don’t know what untestable musings can say about the nature of reality”, and these statements seem to be in tension (as the question of whether collapse happens at intermediate scales depends on what are currently called “interpretations of quantum mechanics”, and is currently untestable); do you still agree with your original statements?
Yes, you could derive the horizon stuff from special relativity, but to construct an asymptotically de Sitter spacetime you need general relativity. Anyway, that wasn’t the original issue. “no collapse at intermediate scales is a good hypothesis and maybe wrong for this specific reason” is one possibility, the likelihood of which is currently hard to evaluate, as it extrapolates quantum mechanics far beyond the domain where it had been tested (Zeilinger’s bucky ball double slit experiments). The nature of the apparent collapse is a huge open problem, with decoherence and Zurek’s quantum Darwinism giving some hints at why certain states survive and others don’t, and pretending that MWI somehow dissolves the issue, the way Eliezer tells the tale, is a bit of a delusion. Anyway, MWI does not make any predictions, since it simply tells you that the feeling of being in a single world is an illusion, without going into the details of how to resolve the Wigner’s friend and similar paradoxes. See Scott Aaronson’s lecture 12 on the topic for more discussion.
The question of where a model is expected to generalize and where it isn’t is the entire problem. You are taking expectations about generalization as basic; I argue that these expectations are based on considerations of parsimony and symmetry. The order isn’t reversed here; parsimony/symmetry give rise to intuitions about whether a model will generalize.
The argument that no collapse happens at intermediate scales between very small and the entire universe is a symmetry-based argument, just as the argument that things beyond the cosmological horizon still exist is a symmetry-based argument.
Yes, I agree. But to discover and effectively apply symmetry one generally has to have a workable model first. For example, the invariance of the speed of light followed from the Maxwell equations, and was confirmed experimentally, and was incorporated in the math of the Lorentz transformations, yet without a good theory those appeared ugly, not symmetric. It took a new theory to reveal the hidden symmetry. And to eventually write the Maxwell equations in half a line, []A=J and divA=0, down from the original 20. Same with the cosmological horizon: it does not appear symmetric and one needs to understand some amount of general relativity to see the symmetry. Or believe those who say that there is one. The “no collapse at the intermediate scales” is a good hypothesis, but quite possible wrong, because gravity is likely to cause decoherence in some way, as Penrose pointed out.
I agree with most of the things you are saying here. I am not sure I agree about the cosmological horizon; it seems like you could derive this from special relativity, but in any case this is a minor point. I don’t know enough physics to confirm the thing you said about gravity and collapse.
In any case it seems you are currently saying “no collapse at intermediate scales is a good hypothesis and maybe wrong for this specific reason” whereas initially you were saying “interpretations [of quantum mechanics] by definition make no difference” and “I don’t know what untestable musings can say about the nature of reality”, and these statements seem to be in tension (as the question of whether collapse happens at intermediate scales depends on what are currently called “interpretations of quantum mechanics”, and is currently untestable); do you still agree with your original statements?
Yes, you could derive the horizon stuff from special relativity, but to construct an asymptotically de Sitter spacetime you need general relativity. Anyway, that wasn’t the original issue. “no collapse at intermediate scales is a good hypothesis and maybe wrong for this specific reason” is one possibility, the likelihood of which is currently hard to evaluate, as it extrapolates quantum mechanics far beyond the domain where it had been tested (Zeilinger’s bucky ball double slit experiments). The nature of the apparent collapse is a huge open problem, with decoherence and Zurek’s quantum Darwinism giving some hints at why certain states survive and others don’t, and pretending that MWI somehow dissolves the issue, the way Eliezer tells the tale, is a bit of a delusion. Anyway, MWI does not make any predictions, since it simply tells you that the feeling of being in a single world is an illusion, without going into the details of how to resolve the Wigner’s friend and similar paradoxes. See Scott Aaronson’s lecture 12 on the topic for more discussion.