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If you find a system that doesn't satisfy the Schrödinger equation, you have falsified quantum mechanics. The point is that many worlds isn't falsifiable indepe

If you find a system that doesn't satisfy the Schrödinger equation, you have falsified quantum mechanics. The point is that many worlds isn't falsifiable independently of any other interpretation. It's "just" an interpretation. And it's a very bad interpretation IMO as it fails to provide a convincing interpretation of the probabilities QM produces, which are the main predictive content of the theory. If you believe every outcome happens then one thing happening with higher probability than another loses meaning. The decision theory argument put forward by some many worlds proponents fails to solve this as it just provides a calculation you can do that produces the Born probabilities. It doesn't provide a convincing interpretation of them. Edit: Also the claim many worlds is somehow more parsimonious in its assumptions than Copenhagen is highly dubious. It assumes an infinite multiverse that is splitting into infinite variants in every infinitesimal instant, in possibly the grossest violation of conservation of momentum and energy (and therefore the corresponding symmetries) that could be imagined.

sebzim4500 2y ago
The evolution a system undergoes when you measure it in the Copenhagen interpretation does not follow the schrodinger equation, that's his point.
- lmm 2y ago
  > The evolution a system undergoes when you measure it in the Copenhagen interpretation does not follow the schrodinger equation Do you have experimental evidence for that claim? The "cat in a box experiment in a box" thought experiment suggests that it does.
  - nyssos 2y ago
    They're talking about what the Copenhagen interpretation predicts, not what actually happens. It's a mathematical question, not an experimental one. Solutions to the Schrodinger equation all take the form `Psi(t) = U(t)Psi(0)` for some unitary operator `U`. "Collapse" applies a projection operator, which is nonunitary.
lmm 2y ago
> If you believe every outcome happens then one thing happening with higher probability than another loses meaning. The decision theory argument put forward by some many worlds proponents fails to solve this as it just provides a calculation you can do that produces the Born probabilities. It doesn't provide a convincing interpretation of them. What further interpretation is needed? To the extent that we have a number we can measure, we have a calculation that can predict it. More interpretation would be nice, but fundamentally every interpretation of QM has this problem, it's not a unique problem with MWI. > It assumes an infinite multiverse that is splitting into infinite variants in every infinitesimal instant, in possibly the grossest violation of conservation of momentum and energy (and therefore the corresponding symmetries) that could be imagined. It assumes continuous unitary evolution that preserves momentum and energy in exactly the way you'd expect, exactly the way we already assume they work. Accepting that you can reasonably make calculations about infinitesimal changes is literally the foundation of physics, it's how Newton was able to make a theory of gravity (and people were just as unhappy about it then).
mr_mitm 2y ago
Of course it would falsify quantum mechanics, because MWI is nothing but the most austere version of QM. But people always speak of Copenhagen as if it was the standard interpretation of QM and everything else must be measurable different from it. In another world, MWI would have been the first consensus interpretation, and people postulating unfalsifiable wave collapses would be the weirdos. Also, MWI doesn't assume infinite worlds, it predicts them. It's a consequence, not a postulate.
- superposeur 2y ago
  Labels are important and I think progress on Everett QM (or, maybe “unitary QM”?) has been held back by the label “Many Worlds Interpretation”. “Worlds” is inaccurate since there is still only one world (the ordinary, uncontroversial, tensor product Hilbert space of textbook qm). It the stuff in the world that enters into superposition, among which stuff are the atoms making up “observers”. Similarly “completion” would be a better word than “interpretation”.
- cfgauss2718 2y ago
  The multiverse may be a consequence of Everett’s theory, but the reality shattering nature of that consequence warrants scrutiny of the theory. Consider one of Xeno’s paradoxes. One may postulate that to go from A to B that first one passes through a midpoint C, and by naively applying induction (I.e. without knowing under what circumstances am infinite sum converges to a finite value), one concludes that a consequence is motion itself cannot exist. However, the absurdity of this consequence should mot lead us to doubt the existence of motion, but quite the opposite, it hints to us that the either the postulate is false, or otherwise we are missing some essential knowledge that allows to determine the correct consequences of that postulate.
- omnicognate 2y ago
  The Copenhagen interpretation is the most obvious thing to compare it to, but personally I'm more interested in de Broglie-Bohm (pilot wave), which might have eclipsed it in the 20th century if people had paid attention when Grete Hermann pointed out Jon von Neumann's mistake. "The most austere version of QM" is marketing bullshit and not widely accepted (or particularly meaningful). Many worlds does postulate its many worlds rather than predict them as it provides no way their existence can ever be tested for. Equating Schrodinger's equation with many worlds is both intellectual dishonesty and begging the question. Any interpretation of conventional quantum mechanics involves Schrodinger's equation. Penrose's ideas (referenced by Sean Carroll in quotes others have posted on this thread) involve violations of Schrodinger's equation because they are actual new theories that differ from standard quantum mechanics. In other words, Penrose is doing actual physics rather than blowing smoke up people's arses. This fact doesn't convey some falsifiability on many-worlds, which is just one of several interpretations of QM that all make the same predictions.
pdonis 2y ago
> If you find a system that doesn't satisfy the Schrödinger equation, you have falsified quantum mechanics. No, you haven't. Standard "shut up and calculate" QM does not say time evolution always happens according to the Schrodinger equation. It only says that happens when a measurement is not being made.
- mitthrowaway2 2y ago
  However it's very unclear how some photons bouncing around between atoms constitutes a "time evolution of the system", and other photons bouncing around between atoms constitutes a "measurement of the system". Usually this involves introducing some fictional object called a "detector", but in the world we live in, every detector is itself just built out of atoms which evolve in accordance with Schrodinger's equation.
  - whimsicalism 2y ago
    what you are saying is so obviously true to me, i have trouble understanding what people even think is happening with measurement otherwise. i remain dumbfounded that copenhagen is still the preferred interpretation
    - pdonis 2y ago
      > i remain dumbfounded that copenhagen is still the preferred interpretation So you're an MWI proponent, then? If it's "obviously true" to you that everything, including measuring devices and ourselves, always evolves in time exactly according to the Schrodinger equation, no exceptions, then the MWI is your only option as an interpretation. The fact that many people do not think the MWI is a viable interpretation is why interpretations like Copenhagen, which do not rest on the belief that the Schrodinger equation has to be literally true, everywhere, all the time, continue to exist.
      - whimsicalism 2y ago
        I view most people who profess a belief in the Copenhagen interpretation to be expressing a belief in what the role of science is: to predict experiments. Give me an experiment and using the math of QM, I can predict the result of that experiment and everything else is just metaphysics. I can understand that perspective. But once you start trying to really tease apart the potentially metaphysical question of "what's actually happening?" (a question many people believe is just not within the realm of falsifiability/science), traditional collapse theories have a bunch of trouble setting up clear lines of what macroscopic is, how collapse actually occurs, etc. that do not seem to have easy resolutions, especially as we can create bigger and bigger quantum systems.

sebzim4500 2y ago

The evolution a system undergoes when you measure it in the Copenhagen interpretation does not follow the schrodinger equation, that's his point.

lmm 2y ago
> The evolution a system undergoes when you measure it in the Copenhagen interpretation does not follow the schrodinger equation Do you have experimental evidence for that claim? The "cat in a box experiment in a box" thought experiment suggests that it does.
- nyssos 2y ago
  They're talking about what the Copenhagen interpretation predicts, not what actually happens. It's a mathematical question, not an experimental one. Solutions to the Schrodinger equation all take the form `Psi(t) = U(t)Psi(0)` for some unitary operator `U`. "Collapse" applies a projection operator, which is nonunitary.

lmm 2y ago

> If you believe every outcome happens then one thing happening with higher probability than another loses meaning. The decision theory argument put forward by some many worlds proponents fails to solve this as it just provides a calculation you can do that produces the Born probabilities. It doesn't provide a convincing interpretation of them. What further interpretation is needed? To the extent that we have a number we can measure, we have a calculation that can predict it. More interpretation would be nice, but fundamentally every interpretation of QM has this problem, it's not a unique problem with MWI. > It assumes an infinite multiverse that is splitting into infinite variants in every infinitesimal instant, in possibly the grossest violation of conservation of momentum and energy (and therefore the corresponding symmetries) that could be imagined. It assumes continuous unitary evolution that preserves momentum and energy in exactly the way you'd expect, exactly the way we already assume they work. Accepting that you can reasonably make calculations about infinitesimal changes is literally the foundation of physics, it's how Newton was able to make a theory of gravity (and people were just as unhappy about it then).

mr_mitm 2y ago

Of course it would falsify quantum mechanics, because MWI is nothing but the most austere version of QM. But people always speak of Copenhagen as if it was the standard interpretation of QM and everything else must be measurable different from it. In another world, MWI would have been the first consensus interpretation, and people postulating unfalsifiable wave collapses would be the weirdos. Also, MWI doesn't assume infinite worlds, it predicts them. It's a consequence, not a postulate.

superposeur 2y ago
Labels are important and I think progress on Everett QM (or, maybe “unitary QM”?) has been held back by the label “Many Worlds Interpretation”. “Worlds” is inaccurate since there is still only one world (the ordinary, uncontroversial, tensor product Hilbert space of textbook qm). It the stuff in the world that enters into superposition, among which stuff are the atoms making up “observers”. Similarly “completion” would be a better word than “interpretation”.
cfgauss2718 2y ago
The multiverse may be a consequence of Everett’s theory, but the reality shattering nature of that consequence warrants scrutiny of the theory. Consider one of Xeno’s paradoxes. One may postulate that to go from A to B that first one passes through a midpoint C, and by naively applying induction (I.e. without knowing under what circumstances am infinite sum converges to a finite value), one concludes that a consequence is motion itself cannot exist. However, the absurdity of this consequence should mot lead us to doubt the existence of motion, but quite the opposite, it hints to us that the either the postulate is false, or otherwise we are missing some essential knowledge that allows to determine the correct consequences of that postulate.
omnicognate 2y ago
The Copenhagen interpretation is the most obvious thing to compare it to, but personally I'm more interested in de Broglie-Bohm (pilot wave), which might have eclipsed it in the 20th century if people had paid attention when Grete Hermann pointed out Jon von Neumann's mistake. "The most austere version of QM" is marketing bullshit and not widely accepted (or particularly meaningful). Many worlds does postulate its many worlds rather than predict them as it provides no way their existence can ever be tested for. Equating Schrodinger's equation with many worlds is both intellectual dishonesty and begging the question. Any interpretation of conventional quantum mechanics involves Schrodinger's equation. Penrose's ideas (referenced by Sean Carroll in quotes others have posted on this thread) involve violations of Schrodinger's equation because they are actual new theories that differ from standard quantum mechanics. In other words, Penrose is doing actual physics rather than blowing smoke up people's arses. This fact doesn't convey some falsifiability on many-worlds, which is just one of several interpretations of QM that all make the same predictions.

pdonis 2y ago

> If you find a system that doesn't satisfy the Schrödinger equation, you have falsified quantum mechanics. No, you haven't. Standard "shut up and calculate" QM does not say time evolution always happens according to the Schrodinger equation. It only says that happens when a measurement is not being made.

mitthrowaway2 2y ago
However it's very unclear how some photons bouncing around between atoms constitutes a "time evolution of the system", and other photons bouncing around between atoms constitutes a "measurement of the system". Usually this involves introducing some fictional object called a "detector", but in the world we live in, every detector is itself just built out of atoms which evolve in accordance with Schrodinger's equation.
- whimsicalism 2y ago
  what you are saying is so obviously true to me, i have trouble understanding what people even think is happening with measurement otherwise. i remain dumbfounded that copenhagen is still the preferred interpretation
  - pdonis 2y ago
    > i remain dumbfounded that copenhagen is still the preferred interpretation So you're an MWI proponent, then? If it's "obviously true" to you that everything, including measuring devices and ourselves, always evolves in time exactly according to the Schrodinger equation, no exceptions, then the MWI is your only option as an interpretation. The fact that many people do not think the MWI is a viable interpretation is why interpretations like Copenhagen, which do not rest on the belief that the Schrodinger equation has to be literally true, everywhere, all the time, continue to exist.
    - whimsicalism 2y ago
      I view most people who profess a belief in the Copenhagen interpretation to be expressing a belief in what the role of science is: to predict experiments. Give me an experiment and using the math of QM, I can predict the result of that experiment and everything else is just metaphysics. I can understand that perspective. But once you start trying to really tease apart the potentially metaphysical question of "what's actually happening?" (a question many people believe is just not within the realm of falsifiability/science), traditional collapse theories have a bunch of trouble setting up clear lines of what macroscopic is, how collapse actually occurs, etc. that do not seem to have easy resolutions, especially as we can create bigger and bigger quantum systems.