4 ms·

This reply just raises all sorts of questions. Is there an objective definition of "macroscopic" within the framework of QM? How does a system decide whether i

This reply just raises all sorts of questions. Is there an objective definition of "macroscopic" within the framework of QM? How does a system decide whether it's macroscopic or not? As far as I can tell I'm just swimming in a sea of bosons and fermions doing their thing, there's no "macroscopic" label that distinguishes the atoms of iron in my vacuum chamber wall from the atoms of rubidium in my vacuum chamber's magnetic trap. They're both following the exact same laws of physics at any given moment. (Laws which, AFAIK, satisfy time-reversal symmetry.) Of course, some systems have many degrees of freedom, which makes the calculation very difficult and exhausting, but that's our problem, not the system's. When does your calculation get to drop branches of the wavefunction, and when does it have to keep track of them? Deciding this policy seems like an important step of shut-up-and-calculate. And most importantly: which MWI claim contradicts observation?

pdonis 2y ago
> This reply just raises all sorts of questions. Yes. All of those questions are open areas of research in the foundations of QM. There are no generally accepted answers to them, although of course each individual QM interpretation has its own set of preferred answers, and physicists who prefer a particular interpretation will often talk as though their preferred answers are generally accepted--but they're not. > which MWI claim contradicts observation? The fact that we observe measurements to have single results. The MWI claims that every measurement has all possible results, but that this fact is in principle unobservable. That makes the MWI unfalsifiable.
- mitthrowaway2 2y ago
  All QM interpretations are unfalsifiable. That's why they're interpretations. In a different thread you wrote that "as you say, the MWI claims that in each branch of the wave function, the human experiences a single result of a measurement." But here you're saying that MWI makes a claim that contradicts that we observe measurements to have single results. MWI, just like Copenhagen, claims that we will observe measurements to have single results (but that we won't be able to predict in advance which result we will experience observing). MWI's predictions are exactly in alignment with what we observe, and makes no claim that in any way differs from the reality that we experience. If it did, then it would be falsifiable.
  - pdonis 2y ago
    > All QM interpretations are unfalsifiable. I agree. Others (not you) elsewhere in this discussion have said otherwise. > here you're saying that MWI makes a claim that contradicts that we observe measurements to have single results. Yes, overall I think the MWI contradicts itself in this regard. It has to say that measurements have all possible results, because that's what Schrodinger's equation says, but it also has to say that we observe measurements to have single results, because it's clear that that's what we actually observe. I don't think its claimed resolution of that contradiction is valid. But you are correct that that is not an issue that can be resolved by experimental tests.

pdonis 2y ago

> This reply just raises all sorts of questions. Yes. All of those questions are open areas of research in the foundations of QM. There are no generally accepted answers to them, although of course each individual QM interpretation has its own set of preferred answers, and physicists who prefer a particular interpretation will often talk as though their preferred answers are generally accepted--but they're not. > which MWI claim contradicts observation? The fact that we observe measurements to have single results. The MWI claims that every measurement has all possible results, but that this fact is in principle unobservable. That makes the MWI unfalsifiable.

mitthrowaway2 2y ago
All QM interpretations are unfalsifiable. That's why they're interpretations. In a different thread you wrote that "as you say, the MWI claims that in each branch of the wave function, the human experiences a single result of a measurement." But here you're saying that MWI makes a claim that contradicts that we observe measurements to have single results. MWI, just like Copenhagen, claims that we will observe measurements to have single results (but that we won't be able to predict in advance which result we will experience observing). MWI's predictions are exactly in alignment with what we observe, and makes no claim that in any way differs from the reality that we experience. If it did, then it would be falsifiable.
- pdonis 2y ago
  > All QM interpretations are unfalsifiable. I agree. Others (not you) elsewhere in this discussion have said otherwise. > here you're saying that MWI makes a claim that contradicts that we observe measurements to have single results. Yes, overall I think the MWI contradicts itself in this regard. It has to say that measurements have all possible results, because that's what Schrodinger's equation says, but it also has to say that we observe measurements to have single results, because it's clear that that's what we actually observe. I don't think its claimed resolution of that contradiction is valid. But you are correct that that is not an issue that can be resolved by experimental tests.