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The problem with this line of thinking comes from the way the problem is posed. The reality is worse for both GR and QM. QM is not a theory about small particl

The problem with this line of thinking comes from the way the problem is posed. The reality is worse for both GR and QM. QM is not a theory about small particles: it is a theory that describes the evolution of any object whatsoever. It just happens to be completely wrong for large objects. And even if we accepted that there is some objective cutoff points between "small objects" and "large objects" (the "objective collapse" interpretation), it would still be wrong, because it predicts effects like gravitational lensing don't exist. Conversely, GR is also a theory about any size of object; and it is also completely wrong when tested on small objects, as it predicts effects like the self-interference of particles don't exist. And again, even if some kind of objective boundary existed between the domains of GR and QM existed, that would need to be incorporated into the maths of both of them, and questions about behaviors close to that margin would arise.

cthalupa 3y ago
>because it predicts effects like gravitational lensing don't exist. But we use gravitational lensing, and the amount of lensing is predicted by GR? I don't understanding this statement. Is there some additional affect around lensing we should see if quantum gravity is a thing?
- simiones 3y ago
  No no; I'm saying that if you apply QM as it exists today to describe the motion of light beams around the sun, you will not get any effect similar to gravitational lensing. Since gravitational lensing is a real effect that we have clearly seen, it means that QM as it exists today is just wrong (in its predictions about how light moves around the sun). GR does of course predict gravitational lensing. However, if you used the formulae of GR to compute the motion of photons passing through a double-slit experiment, the solution would show two different bright spots, corresponding to the two slits; in reality, we see an interference pattern. So GR is also wrong. By definition, a (correct) theory of quantum gravity would predict both gravitational lensing and the way photons behave in a dobule-slit experiment (otherwise, we would say that either the theory is wrong, or it is not a theory of quantum gravity). However, no such theory exists today, at least none that doesn't contradict other observations.
  - raattgift 3y ago
    There are already experiments (and simulations) which show Raychaudhuri focusing and Einstein lensing in purely-quantum analog gravity (see e.g. <https://scitechdaily.com/bridging-quantum-theory-and-relativity-curved-spacetime-in-a-quantum-simulator/ https://scitechdaily.com/bridging-quantum-theory-and-relativ...> for something moderately accessible that allows for attaching a causal cone at each point in a relevant analog spacetime), so > no; I'm saying that if you apply QM as it exists today to describe the motion of light beams around the sun, you will not get any effect similar to gravitational lensing falls down because we can describe such an effect purely quantum mechanically. Also, I think you should be put to proof with respect to a claim against quantum perturbative or canonical methods in the solar-mass lensing regime in which perturbation theory works great for classical GR, taking into account all sorts of beyond-leading-order (classical) effects like noncircularity, backreaction, helicity, you name it. The sun is a fixed enough background that it's a linearized gravity problem. What exactly in "QM as it exists today" breaks (or is broken by) this? > ... if you used the formulae of GR to compute the motion of photons passing through a double-slit experiment ... GR is also wrong. How exactly does taking the fully Lorentz-invariant QED or Standard Model to local Lorentz-invariance (with the radius of curvature significantly larger than the laboratory experiment) break the picture? We are nowhere near needing to consult Birrell & Davies. What do you think needs doing here if "you used the formulae of GR", beyond solving the EFEs and the geodesic equations for the whole (region of) spacetime, and then wondering what geodesic any given photon will couple to? What do you think the scale of the correction from Minkowskian geodesics will be? And how much of that do you impute to the apparatus?
runarberg 3y ago
I see. So me and my parent are both wrong. The problem isn’t about a lack of bridge, or inconsistencies/incompleteness, it is about a lack of well defined scopes for each theory. In a sibling post I talk about how this is not a problem in psychology, and ask what the difference is. This answers that question kind of well, the difference is that in psychology/sociology the scopes are well defined. We know what a population is and apply sociology to it, and we know what an individual human being is, and apply psychology to it. With quantum mechanics and general relativity the scope is supposed to be the cosmos, but both theories fail on some places in the cosmos. So either the theories are wrong, or the scopes are wrong. I’m leaning towards the latter.
- simiones 3y ago
  The problem is that scale is completely smooth. IF there were some strict scale at which each theory applies, as I said, you'd then have problems for phenomena that straddle that scope. You can always add an extra electron or atom to a clump, so you'd have objects oscillating between obeying one set of equations vs the other, which seems very very very hard to actually believe. A similar problem actually exists in psychology vs sociology, though it seems you choose to ignore it. When you want to study the behavior of two human beings (say, a married childless couple), do you apply sociology or psychology? How about a married couple with children? An extended family? Also, psychology has to explain how an individual human behaves inside of a population, and sociology has to explain how the behavior of groups emerges out of the individual psychologies of their constituents. If they don't do this, then either one or both theories must be wrong. To take an extreme silly example, if psychology predicted that no person would never choose to kill themselves for the sake of another; but sociology predicted groups of people regularly have members sacrificing themselves for the group - then one of the theories must be wrong, you can't just say "we apply one theory when talking to a man and another when talking about the group".
- digging 3y ago
  > So either the theories are wrong, or the scopes are wrong. I’m leaning towards the latter. Well, no. That's not really possible here. The scopes can't be adjusted. The theories are wrong. They both must explain all physical phenomena, but neither does, therefore a more accurate theory exists which we have not found yet. I just don't know if there's much value in trying to make an analogy to psychology here. Currently it seems to be getting in the way of understanding.

cthalupa 3y ago

>because it predicts effects like gravitational lensing don't exist. But we use gravitational lensing, and the amount of lensing is predicted by GR? I don't understanding this statement. Is there some additional affect around lensing we should see if quantum gravity is a thing?

simiones 3y ago
No no; I'm saying that if you apply QM as it exists today to describe the motion of light beams around the sun, you will not get any effect similar to gravitational lensing. Since gravitational lensing is a real effect that we have clearly seen, it means that QM as it exists today is just wrong (in its predictions about how light moves around the sun). GR does of course predict gravitational lensing. However, if you used the formulae of GR to compute the motion of photons passing through a double-slit experiment, the solution would show two different bright spots, corresponding to the two slits; in reality, we see an interference pattern. So GR is also wrong. By definition, a (correct) theory of quantum gravity would predict both gravitational lensing and the way photons behave in a dobule-slit experiment (otherwise, we would say that either the theory is wrong, or it is not a theory of quantum gravity). However, no such theory exists today, at least none that doesn't contradict other observations.
- raattgift 3y ago
  There are already experiments (and simulations) which show Raychaudhuri focusing and Einstein lensing in purely-quantum analog gravity (see e.g. <https://scitechdaily.com/bridging-quantum-theory-and-relativity-curved-spacetime-in-a-quantum-simulator/ https://scitechdaily.com/bridging-quantum-theory-and-relativ...> for something moderately accessible that allows for attaching a causal cone at each point in a relevant analog spacetime), so > no; I'm saying that if you apply QM as it exists today to describe the motion of light beams around the sun, you will not get any effect similar to gravitational lensing falls down because we can describe such an effect purely quantum mechanically. Also, I think you should be put to proof with respect to a claim against quantum perturbative or canonical methods in the solar-mass lensing regime in which perturbation theory works great for classical GR, taking into account all sorts of beyond-leading-order (classical) effects like noncircularity, backreaction, helicity, you name it. The sun is a fixed enough background that it's a linearized gravity problem. What exactly in "QM as it exists today" breaks (or is broken by) this? > ... if you used the formulae of GR to compute the motion of photons passing through a double-slit experiment ... GR is also wrong. How exactly does taking the fully Lorentz-invariant QED or Standard Model to local Lorentz-invariance (with the radius of curvature significantly larger than the laboratory experiment) break the picture? We are nowhere near needing to consult Birrell & Davies. What do you think needs doing here if "you used the formulae of GR", beyond solving the EFEs and the geodesic equations for the whole (region of) spacetime, and then wondering what geodesic any given photon will couple to? What do you think the scale of the correction from Minkowskian geodesics will be? And how much of that do you impute to the apparatus?

runarberg 3y ago

I see. So me and my parent are both wrong. The problem isn’t about a lack of bridge, or inconsistencies/incompleteness, it is about a lack of well defined scopes for each theory. In a sibling post I talk about how this is not a problem in psychology, and ask what the difference is. This answers that question kind of well, the difference is that in psychology/sociology the scopes are well defined. We know what a population is and apply sociology to it, and we know what an individual human being is, and apply psychology to it. With quantum mechanics and general relativity the scope is supposed to be the cosmos, but both theories fail on some places in the cosmos. So either the theories are wrong, or the scopes are wrong. I’m leaning towards the latter.

simiones 3y ago
The problem is that scale is completely smooth. IF there were some strict scale at which each theory applies, as I said, you'd then have problems for phenomena that straddle that scope. You can always add an extra electron or atom to a clump, so you'd have objects oscillating between obeying one set of equations vs the other, which seems very very very hard to actually believe. A similar problem actually exists in psychology vs sociology, though it seems you choose to ignore it. When you want to study the behavior of two human beings (say, a married childless couple), do you apply sociology or psychology? How about a married couple with children? An extended family? Also, psychology has to explain how an individual human behaves inside of a population, and sociology has to explain how the behavior of groups emerges out of the individual psychologies of their constituents. If they don't do this, then either one or both theories must be wrong. To take an extreme silly example, if psychology predicted that no person would never choose to kill themselves for the sake of another; but sociology predicted groups of people regularly have members sacrificing themselves for the group - then one of the theories must be wrong, you can't just say "we apply one theory when talking to a man and another when talking about the group".
digging 3y ago
> So either the theories are wrong, or the scopes are wrong. I’m leaning towards the latter. Well, no. That's not really possible here. The scopes can't be adjusted. The theories are wrong. They both must explain all physical phenomena, but neither does, therefore a more accurate theory exists which we have not found yet. I just don't know if there's much value in trying to make an analogy to psychology here. Currently it seems to be getting in the way of understanding.