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As another dude with a doctorate in Physics, I have to disagree with you (at least somewhat). > From this point of view as our ability to connect experiment wi

by kitchi 1y ago

As another dude with a doctorate in Physics, I have to disagree with you (at least somewhat). > From this point of view as our ability to connect experiment with outcome has increased our ability to actually say what it is we are even talking about outside of the purely instrumental has decreased since the 19th Century. Back then we though we knew that there were atoms or electrons or whatever. Light waves or photons. Now, I would argue very strenuously, we genuinely have no understanding at all of what those things are outside of a set of purely instrumental definitions which leave a lot to be desired. I disagree with this entirely. The existence of QFT, and our knowledge of the inconsistency between say GR and the quantum realm does not negate the idea of photons and electrons as real, measurable quantities. The fact that we have GR does not negate the fact that we still use Newtonian gravity in regimes where it is sufficiently accurate. All the new knowledge we have learned still is (and absolutely must be) consistent with our old knowledge that has been proven correct in the regimes that they were proven correct. This is effectively what Asimov is saying (as I understand anyway) - the knowledge that the Earth is a sphere does not invalidate the assumption that the Earth is flat approximately and locally. I would also argue that the only things we can "know" are what you call the instrumental definitions. We only know what we measure. The rest is interpretation, and self-consistent understanding. String theory can tell me that we have several dimensions etc but until we have a way to measure and check it remains a conceptual framework to make predictions, rather than a description of how things really are. GR is much closer to a description. It told us about the precession of mercury, it told us to account for time dilation so we can use GPS satellites. It also predicted black holes, which were conceptually consistent but it's only been in the last ~ 5 years that we have the closest thing yet to experimental verification with the Event Horizon Telescope and gravitational wave measurements. If another theory comes along and explains all of GR with a different explanation for black holes, we will need still more accurate measurements to discriminate between the two theories. Knowledge is only as accurate as we can measure.

glenstein 1y ago
I agree much more with your approach. The way I've heard it best described is these notions of electrons and photons etc will still be retained as a special case of whatever theory supersedes them, which is critical, because that's at the heart of the "relativity of wrong" argument. Some take the prospect of a future revision of theories to mean our present state of knowledge is no different than any prior failed theory, which I think is an urgently, catastrophically wrong, catastrophically confused way to regard the history of scientific knowledge.
nathan_compton 1y ago
I don't think you get my point because I don't think of anything you are saying as having anything to do with what I was saying. If you have a purely instrumentalist view of reality, where, as I said, your so-called knowledge is actually just a model of an unknown thing which you employ to predict the measurements you read out against a ruler or on a meter or something, then yes, we've made progress exactly of the kind you describe. But I was trying to make a point about epistemology and ontology. Physics has actually been pretty catastrophic for ontology. I don't think its wrong to say that from the point of view of physics we simply do not know what anything actually is. > I would also argue that the only things we can "know" are what you call the instrumental definitions. We only know what we measure. The rest is interpretation, and self-consistent understanding. Yes. But this is a fairly radical position historically and philosophically. Most people would say that there is more to existence than measurement and I while I share your instrumentalist sympathies, like most physicists, I don't see the philosophical case that we can have a consistent worldview if we denounce all knowledge not related to measurement as a total non-starter. Think about what instrumentalism really means. When you utter the sentence the earth is an oblate spheroid, you are actually making an incredibly complicated set of statements about the outcomes of experiments. If we take the instrumentalist view the measurement doesn't actually tell us the earth is an oblate spheroid - it just tells us that if we make a series of measurements then they come out in such a way as to be concordant with a model of the earth as an oblate spheroid. Are you really prepared to give up the idea that the earth is a thing you can know about? I actually rather think physics strongly encourages us to adopt the instrumentalist view, primarily because it seems so clear that physics has a local character. In GR there simply is no state of affairs whatever about what is happening "right now" except at the point in spacetime where you make a measurement. Really think about what that means. If we are standing at the north pole and make a measurement of some kind, how can it pertain to the earth as a distributed object in space when we know GR says there is no state of affairs pertaining to that object at the moment of the measurement? GR tells us all about what the outcome of various measurements will be, but it also calls into question what precisely those measurements might mean. The instrumentalist is committed to the idea that the only thing we can talk about is the results of measurements. What the measurements operate on is just not something we can know. I think that's weird. Physicists often conflate their mathematical models with reality and that lets them think an instrumentalist view is sufficient: the measurements coming out such and such a way is taken as evidence that the universe is filled with objects consistent with the model. But that association is non-trivial in modern physics.
tycho-newman 1y ago
QM is so platonic though. Reality consists, ultimately, of forms that can only be described mathematically. It just happens that the math returns (what we see) as a probability distribution/wave function. I’ve never quite understood what a quantum theory of gravity would be though. QM involves the observer but gravity engages spacetime - the place where you are observing things. A quantum field theory of gravity seems like a contradiction in terms to me. Unless quantum gravity is really about the Big Bang?
- nathan_compton 1y ago
  The observer/observed thing is present in every part of physics and isn't really about observers but about where we choose to draw the line between one physical system and another (with the other usually containing ourselves). Think of it this way: classically or quantum mechanically, when we pick out a physical system to talk about we are isolating the terms for that system in the universal lagrangian and assuming that in the time of interest that the terms for our physical system couple weakly to the rest of the universe (which happens to contain us). In principal nothing really weird is going on here and in classical mechanics the idea is totally trivial as far as it goes. On short time scales with appropriately sized actions the deviation from the isolated system and the real system (which is weakly coupled to the world) can be demonstrated to be small as long as the coupling is small. In quantum mechanics two things complicate this situation. The first is that quantum mechanical systems sort of defy separation into distinct subsets except in special situations. Classically there is a strong sense in which we can point to two different parts of a system and call them separate, but quantum mechanically we really only know how to time evolve _the whole system_ and from a mathematical point of view its the actual object of interest. This is what we are getting at when we talk about entanglement: the two spin 1/2 particles flying away from one another in Bell style experiments are not separate things in the QM description: there is just one wave function. But in practice I don't think there is any real reason we can't quantize gravity. I'm not an expert but loop quantum gravity seems like a reasonable approach and its very straightforward and its base: just find an acceptable description of geometry and then apply the ordinary quantum mechanical tricks we use to quantize it. Also, you don't observe things in spacetime. Observations are always purely local. You just infer the existence of spacetime from local observations which are conveniently organized by putting them on a curved 4d Lorentzian signature manifold.

by kitchi 1y ago

glenstein 1y ago

I agree much more with your approach. The way I've heard it best described is these notions of electrons and photons etc will still be retained as a special case of whatever theory supersedes them, which is critical, because that's at the heart of the "relativity of wrong" argument. Some take the prospect of a future revision of theories to mean our present state of knowledge is no different than any prior failed theory, which I think is an urgently, catastrophically wrong, catastrophically confused way to regard the history of scientific knowledge.

nathan_compton 1y ago

I don't think you get my point because I don't think of anything you are saying as having anything to do with what I was saying. If you have a purely instrumentalist view of reality, where, as I said, your so-called knowledge is actually just a model of an unknown thing which you employ to predict the measurements you read out against a ruler or on a meter or something, then yes, we've made progress exactly of the kind you describe. But I was trying to make a point about epistemology and ontology. Physics has actually been pretty catastrophic for ontology. I don't think its wrong to say that from the point of view of physics we simply do not know what anything actually is. > I would also argue that the only things we can "know" are what you call the instrumental definitions. We only know what we measure. The rest is interpretation, and self-consistent understanding. Yes. But this is a fairly radical position historically and philosophically. Most people would say that there is more to existence than measurement and I while I share your instrumentalist sympathies, like most physicists, I don't see the philosophical case that we can have a consistent worldview if we denounce all knowledge not related to measurement as a total non-starter. Think about what instrumentalism really means. When you utter the sentence the earth is an oblate spheroid, you are actually making an incredibly complicated set of statements about the outcomes of experiments. If we take the instrumentalist view the measurement doesn't actually tell us the earth is an oblate spheroid - it just tells us that if we make a series of measurements then they come out in such a way as to be concordant with a model of the earth as an oblate spheroid. Are you really prepared to give up the idea that the earth is a thing you can know about? I actually rather think physics strongly encourages us to adopt the instrumentalist view, primarily because it seems so clear that physics has a local character. In GR there simply is no state of affairs whatever about what is happening "right now" except at the point in spacetime where you make a measurement. Really think about what that means. If we are standing at the north pole and make a measurement of some kind, how can it pertain to the earth as a distributed object in space when we know GR says there is no state of affairs pertaining to that object at the moment of the measurement? GR tells us all about what the outcome of various measurements will be, but it also calls into question what precisely those measurements might mean. The instrumentalist is committed to the idea that the only thing we can talk about is the results of measurements. What the measurements operate on is just not something we can know. I think that's weird. Physicists often conflate their mathematical models with reality and that lets them think an instrumentalist view is sufficient: the measurements coming out such and such a way is taken as evidence that the universe is filled with objects consistent with the model. But that association is non-trivial in modern physics.

tycho-newman 1y ago

QM is so platonic though. Reality consists, ultimately, of forms that can only be described mathematically. It just happens that the math returns (what we see) as a probability distribution/wave function. I’ve never quite understood what a quantum theory of gravity would be though. QM involves the observer but gravity engages spacetime - the place where you are observing things. A quantum field theory of gravity seems like a contradiction in terms to me. Unless quantum gravity is really about the Big Bang?

nathan_compton 1y ago
The observer/observed thing is present in every part of physics and isn't really about observers but about where we choose to draw the line between one physical system and another (with the other usually containing ourselves). Think of it this way: classically or quantum mechanically, when we pick out a physical system to talk about we are isolating the terms for that system in the universal lagrangian and assuming that in the time of interest that the terms for our physical system couple weakly to the rest of the universe (which happens to contain us). In principal nothing really weird is going on here and in classical mechanics the idea is totally trivial as far as it goes. On short time scales with appropriately sized actions the deviation from the isolated system and the real system (which is weakly coupled to the world) can be demonstrated to be small as long as the coupling is small. In quantum mechanics two things complicate this situation. The first is that quantum mechanical systems sort of defy separation into distinct subsets except in special situations. Classically there is a strong sense in which we can point to two different parts of a system and call them separate, but quantum mechanically we really only know how to time evolve _the whole system_ and from a mathematical point of view its the actual object of interest. This is what we are getting at when we talk about entanglement: the two spin 1/2 particles flying away from one another in Bell style experiments are not separate things in the QM description: there is just one wave function. But in practice I don't think there is any real reason we can't quantize gravity. I'm not an expert but loop quantum gravity seems like a reasonable approach and its very straightforward and its base: just find an acceptable description of geometry and then apply the ordinary quantum mechanical tricks we use to quantize it. Also, you don't observe things in spacetime. Observations are always purely local. You just infer the existence of spacetime from local observations which are conveniently organized by putting them on a curved 4d Lorentzian signature manifold.