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Was ultraviolet catastrophe really an experimental inconsistency? It seems to best understood as a theoretical inconsistency: The theory predicts a diverging (i

Was ultraviolet catastrophe really an experimental inconsistency? It seems to best understood as a theoretical inconsistency: The theory predicts a diverging (infinite) value, which we know would be wrong regardless of what the experimental evidence is. It's a mathematical problem, not an empirical one. You also give the example of "the measured invariance of the speed of light in different rest frames," but Einstein claims SR was motivated by the invariance of Maxwell's equations (a theoretical consideration), not e.g. Michelson–Morley. So it sure seems that investigating theoretical inconsistencies has motivated a lot of good work. I agree that, practically speaking, studying the black hole information paradox might not be so productive. Maybe there are special features of the problem that make it difficult to investigate productively through theoretical considerations alone. But this is not how I read Hossenfelder. Taking her blog post literally, she seems to be against theoretical investigations of any phenomenon (any inconsistency, etc.) where experimental tests aren't forthcoming. I think this is ridiculous. Maybe she doesn't actually believe this, but then she needs to make an argument specifically about the black hole information paradox and why this particular problem is unproductive, not launch a broadside on non-empirical reasoning more generally.

tsimionescu 4y ago
> Was ultraviolet catastrophe really an experimental inconsistency? It seems to best understood as a theoretical inconsistency: The theory predicts a diverging (infinite) value, which we know would be wrong regardless of what the experimental evidence is. Well, that theory also predicts that the universe can't exist for very long, which is a pretty big experimental inconsistency. > You also give the example of "the measured invariance of the speed of light in different rest frames," but Einstein claims SR was motivated by the invariance of Maxwell's equations (a theoretical consideration), not e.g. Michelson–Morley. Well, Maxwell's equations were relatively well experimentally verified by other experiments, so there were good reasons to at least tentatively accept their prediction of a constant speed of light* in any rest frame as a given. Even if the Michaelson-Morley experiment was not big on his mind, it was still relatively clear that this type of experiment could be performed with technology already available at the time, as the speed of light had been measured with pretty good precision already for a few decades. So, SR was not some highly speculative theory based only on extrapolating other theories, as solutions that only address BHILP but not other problems of QM/GR are currently. * or at least of electro-magnetic radiation, not sure when it became accepted light was EM radiation relative to the SR paper
- spekcular 4y ago
  > Well, that theory also predicts that the universe can't exist for very long, which is a pretty big experimental inconsistency. Sure, but I don't need to appeal to this fact to know there's a problem that must be solved. The infinities are enough. > Well, Maxwell's equations were relatively well experimentally verified by other experiments, so there were good reasons to at least tentatively accept their prediction of a constant speed of light* in any rest frame as a given. Even if the Michaelson-Morley experiment was not big on his mind, it was still relatively clear that this type of experiment could be performed with technology already available at the time, as the speed of light had been measured with pretty good precision already for a few decades. But again, even if MM couldn't have been performed, Einstein still would have had good theoretical reasons (consistency with Maxwell's equations) to posit SR. And indeed, this was the path the discovery seems to have actually taken. > So, SR was not some highly speculative theory based only on extrapolating other theories, as solutions that only address BHILP but not other problems of QM/GR are currently. Sure, but this is a difference in degree, not in kind. You accept that theoretical arguments for new phenomena that are not directly testable (at present) are acceptable if they're convincing enough. The question about BHILP under this view (which I agree with) is then about how convincing the theoretical arguments are. Hossenfelder, taken literally, suggests that no theoretical arguments will ever good enough in the absence of empirical evidence.
  - tsimionescu 4y ago
    > Sure, but I don't need to appeal to this fact to know there's a problem that must be solved. The infinities are enough. By that logic, you shouldn't believe in black holes / GR at all, right? In practice, we can always replace infinities with some arbitrarily large numbers that don't grow all the way to infinity because of yet-unknown physics (probably quantum gravity, in the case of black holes). > But again, even if MM couldn't have been performed, Einstein still would have had good theoretical reasons (consistency with Maxwell's equations) to posit SR. And indeed, this was the path the discovery seems to have actually taken. I don't think this would have been promising if the MM experiment seemed a hundred years away, and in general I don't think SR would have been as compelling in that case. I suspect we would have still had arguments about an aether if experiments on the speed of light in different inertial frames had remained beyond reach. > Sure, but this is a difference in degree, not in kind. You accept that theoretical arguments for new phenomena that are not directly testable (at present) are acceptable if they're convincing enough. The question about BHILP under this view (which I agree with) is then about how convincing the theoretical arguments are. Sure, it's a difference in degree in the end. The plausibility of having an experiment "soon" is the degree here. I don't think that Hossenfelder would argue that if an experiment is only possible 2 years from now, or maybe even 20 years from now, you shouldn't work on some theoretical subject. But, when that time horizon stretches well beyond your lifetime and the lifetime of your students, it's perhaps time to reconsider. I also know for sure she doesn't have a problem with doing theoretical research where you don't yet know how something would be testable, as long as you plan to define an experiment as well. She explains this in some detail when discussing her own work on superdeterminism - where she plans to first define a concrete model, and then come up with experiments which could invalidate that particular model - instead of giving up a priori because "there's no known way to test such a theory".

tsimionescu 4y ago

> Was ultraviolet catastrophe really an experimental inconsistency? It seems to best understood as a theoretical inconsistency: The theory predicts a diverging (infinite) value, which we know would be wrong regardless of what the experimental evidence is. Well, that theory also predicts that the universe can't exist for very long, which is a pretty big experimental inconsistency. > You also give the example of "the measured invariance of the speed of light in different rest frames," but Einstein claims SR was motivated by the invariance of Maxwell's equations (a theoretical consideration), not e.g. Michelson–Morley. Well, Maxwell's equations were relatively well experimentally verified by other experiments, so there were good reasons to at least tentatively accept their prediction of a constant speed of light* in any rest frame as a given. Even if the Michaelson-Morley experiment was not big on his mind, it was still relatively clear that this type of experiment could be performed with technology already available at the time, as the speed of light had been measured with pretty good precision already for a few decades. So, SR was not some highly speculative theory based only on extrapolating other theories, as solutions that only address BHILP but not other problems of QM/GR are currently. * or at least of electro-magnetic radiation, not sure when it became accepted light was EM radiation relative to the SR paper

spekcular 4y ago
> Well, that theory also predicts that the universe can't exist for very long, which is a pretty big experimental inconsistency. Sure, but I don't need to appeal to this fact to know there's a problem that must be solved. The infinities are enough. > Well, Maxwell's equations were relatively well experimentally verified by other experiments, so there were good reasons to at least tentatively accept their prediction of a constant speed of light* in any rest frame as a given. Even if the Michaelson-Morley experiment was not big on his mind, it was still relatively clear that this type of experiment could be performed with technology already available at the time, as the speed of light had been measured with pretty good precision already for a few decades. But again, even if MM couldn't have been performed, Einstein still would have had good theoretical reasons (consistency with Maxwell's equations) to posit SR. And indeed, this was the path the discovery seems to have actually taken. > So, SR was not some highly speculative theory based only on extrapolating other theories, as solutions that only address BHILP but not other problems of QM/GR are currently. Sure, but this is a difference in degree, not in kind. You accept that theoretical arguments for new phenomena that are not directly testable (at present) are acceptable if they're convincing enough. The question about BHILP under this view (which I agree with) is then about how convincing the theoretical arguments are. Hossenfelder, taken literally, suggests that no theoretical arguments will ever good enough in the absence of empirical evidence.
- tsimionescu 4y ago
  > Sure, but I don't need to appeal to this fact to know there's a problem that must be solved. The infinities are enough. By that logic, you shouldn't believe in black holes / GR at all, right? In practice, we can always replace infinities with some arbitrarily large numbers that don't grow all the way to infinity because of yet-unknown physics (probably quantum gravity, in the case of black holes). > But again, even if MM couldn't have been performed, Einstein still would have had good theoretical reasons (consistency with Maxwell's equations) to posit SR. And indeed, this was the path the discovery seems to have actually taken. I don't think this would have been promising if the MM experiment seemed a hundred years away, and in general I don't think SR would have been as compelling in that case. I suspect we would have still had arguments about an aether if experiments on the speed of light in different inertial frames had remained beyond reach. > Sure, but this is a difference in degree, not in kind. You accept that theoretical arguments for new phenomena that are not directly testable (at present) are acceptable if they're convincing enough. The question about BHILP under this view (which I agree with) is then about how convincing the theoretical arguments are. Sure, it's a difference in degree in the end. The plausibility of having an experiment "soon" is the degree here. I don't think that Hossenfelder would argue that if an experiment is only possible 2 years from now, or maybe even 20 years from now, you shouldn't work on some theoretical subject. But, when that time horizon stretches well beyond your lifetime and the lifetime of your students, it's perhaps time to reconsider. I also know for sure she doesn't have a problem with doing theoretical research where you don't yet know how something would be testable, as long as you plan to define an experiment as well. She explains this in some detail when discussing her own work on superdeterminism - where she plans to first define a concrete model, and then come up with experiments which could invalidate that particular model - instead of giving up a priori because "there's no known way to test such a theory".