What is the point of saying that MWI is falsified while Copenhagen is not?DrChinese said:
Not necessarily. You are assuming that every single Planck scale spacetime "cell" is decohered from every other. But that's not the case. The MWI does not say that every single quantum degree of freedom is branching at every Planck time. It only says branching occurs when an interaction takes place that results in decoherence, and the only branches are the decohered ones. So, for example, in a Schrodinger's Cat experiment, there would be only two branches, "cat alive" and "cat dead", since those are the two decohered outcomes. There would not be a different branch for every single microscale interaction between the cat's atoms, since those don't decohere separate branches; they just cause the cat to behave classically in the two branches caused by the experiment, "alive" and "dead".Roberto Pavani said:
Please do not pursue this subthread further. What I said in post #27 is all that can be said about it in this forum.javisot said:
If it is, I don't think it would be for the same reason, since the vacuum energy counting assumes a single universe, not many worlds. It's simply a comparison of the simple, obvious way to calculate the ground state energy of the QFT vacuum with a Planck scale cutoff, with the value we actually observe based on the acceleration of the cosmological expansion. That ground state energy is the energy of a single state in a single universe.Roberto Pavani said:
Dale said:
martinbn said:
A local hidden variable theory isn't an interpretation of QM, it's a different theory--because it doesn't (and can't) predict Bell inequality violations, and QM does. What experimentally confirming the QM predictions of Bell inequality violations did was to dash the hopes of people who were clinging to the idea that QM might end up not being quite right in this regime, and some kind of more classical-like theory would win out. No such luck.bhobba said:
PeterDonis said:
Gleason's Theorem doesn't depend on any particular interpretation of QM: it just says that, given the basic math of QM, if you want to compute something from the quantum state that has the desired properties of a "probability", you have to use the Born rule (more precisely, you have to compute ##\text{tr} \rho A## where ##\rho## is the density operator for the state and ##A## is whatever observable you're interested in). The theorem says nothing about what the thing you compute that has the desired properties of a "probability" means physically. That's what has to be filled in by QM interpretations, and different ones of course fill it in very differently. But in this respect the MWI is not in a different position from any other interpretation--it has its own way of doing the filling in, but so do all the other interpretations.bhobba said:
Why is this any different than very large fluctuations being observed in local gas pressure in statistical mechanics? All micro-states are possible. We just don’t observe ones like these because they are just too rare.Roberto Pavani said:
Although I agree with the general gist of statements made in this post (my read: decoherence drives branching, we don't branch off of every quantum d.o.f.), I think saying there's just *two* branches for Schrodinger's cat is oversimplifying things. Decoherence is not a sharp line. You still have to define what is the sub system and what is the environment the subsystem gets entangled with. Further, the decoherence typically has a time scale through which the off-diagonal terms decay. It's not clear to me how you set a threshold for when a "full decoherence" has even happened.PeterDonis said:
DrChinese said:
bhobba said:
Matterwave said:
Matterwave said:
The premise of the thought experiment is that "alive" and "dead" are two distinct, macroscopically distinguishable cat states, and that there is no third one. Of course neither of these cat states are simple, and of course the cat is not the entire universe. But the premise of the thought experiment is that there are no other macroscopically distinguishable outcomes: just "poison released, cat dead" and "poison not released, cat alive".Matterwave said:
Not really, no. You don't need to have an exact accounting of which atoms are part of the cat and which are part of the environment in order to observe whether the cat is alive or dead.Matterwave said:
The heuristic answer we have now is "when macroscopic outcomes can be irreversibly distinguished". In this case, when we can tell whether the cat is alive or dead. Of course it takes a finite time for the poison, if it's released, to kill the cat. But by that time the "poison released" vs. "poison not released" decoherence has already happened; the decoherence time for that is much shorter than the time it takes for a poisoned cat to die. So actually, by the time the cat dies, in the branch where it does, a macroscopically distinguishable outcome has already occurred--the cat dying is just a further classical consequence of it.Matterwave said:
Which is how the MWI defines branching. See above.Matterwave said:
In the general case, no, because not all observables have a discrete spectrum, and at least on its face, the math for observables with a continuous spectrum leads to a continuous infinity of branches. And even with observables that have a discrete spectrum, it might have a countably infinite number of possible outcomes (for example, energy levels of bound states of electrons in an atom).Matterwave said:
Didn't you say that after message 27 we couldn't talk about this anymore and that everything had already been said?PeterDonis said:
No. I said that about the claim that the MWI has been falsified. That's not what's being discussed in the post you quoted.javisot said:
