That’s not really analogous. What makes distinct MWI branches distinct is that they have ‘decohered’ and can no longer interact in any detectable way.
If the MWI branches are “close” and haven’t completely decohered, it’s possible to detect them. If they’re far away, it’s not. Similarly, if the universes are close by in the fifth dimension, you might be able to make them out. If they’re far away, and you have to look through a hundred universes to make it out, it’s essentially impossible. The method of detecting them is different, the the principle is the same.
However, since the experiment can only end one way, it all takes place within one “branch”.
You can detect it, but it doesn’t happen? Isn’t that like saying that the universe doesn’t exist, but we experience things as if it did?
You need to know the potential energy of every point in configuration space in order to find out the probability of a given event. How can it matter if it isn’t involved?
(Many worlds doesn’t “explain” quantum interference, in spite of what Deutsch might have you believe. I don’t think that was ever its “purpose”, to be fair.)
I don’t understand. It explains it. So does any interpretation beyond pure particle. Its purpose is to explain away waveform collapse and the process of particles getting entangled. The laws regarding those in the Copenhagen interpretation are bizarre, and the results are indistinguishable from just assuming that everything is always entangled, and waveforms never collapse, which is the MWI.
But it’s better to say that the concept of “other worlds” breaks down if you push it too far, than to say we can thereby detect “other worlds”.
We can detect other worlds of they’re close enough, but not if they’re too far away. This isn’t just limited to the MWI. The Copenhagen interpretation follows the same laws with entangled particles. We’ve never been able to detect waveform collapse, so decoherence getting to the point where we can’t detect the interference must happen first.
This is no different than saying that the next twenty branches exist, and maybe a few hundred more, but after a billion, the concept of other branches breaks down.
It’s also like saying that Earth is made of atoms, and the rest of our solar system is made of atoms, but we aren’t remotely capable of discerning atoms in other solar systems, so the concept of “being made of atoms” broke down.
This has largely turned into a semantic dispute about the “correct” meaning of the term “world” in the context of MWI.
You’re using it to mean “summand with respect to the position basis” whereas I’m using it to mean “summand with respect to a decomposition of the Hilbert space into subspaces large enough that elements of two distinct subspaces represent ‘distinct macrostates’”. (Where “macroscopic distinctness” is not and does not pretend to be precisely definable.)
Right after the photon in the Mach-Zehnder apparatus splits, you see two worlds corresponding to the two different positions of the photon, whereas I see only a single world because all macroscopic variables still have determinate values. (Or rather, their values are still as close to being determinate as they ever are.)
In my use of the term “worlds” it is correct to say that the notion of “other worlds” breaks down if you push it too far (ultimately this is because the boundary between the “micro” and “macro” domains cannot be rigorously defined.) In your use of the term “worlds” it is trivially true that, at any given time, the state vector is uniquely expressible as a superposition of “worlds”.
I don’t want to say too much in defense of my usage, except that I think mine is the standard one. You might like to read this by the way. (Not to resolve our dispute, but because it’s awesome.)
However, since the experiment can only end one way, it all takes place within one “branch”.
You can detect it, but it doesn’t happen? Isn’t that like saying that the universe doesn’t exist, but we experience things as if it did?
Sorry, I can’t see how your questions relate to my statement.
I don’t understand. It explains it.
The reason I say it doesn’t explain it is that the notion of “constructive and destructive interference” between different possibilities is deeply bizarre. Simply declaring that all possibilities exist doesn’t explain why two possibilities can cancel each other out. But again, I suspect this is partly just a dispute over the semantics of “explain”.
ETA: I have to acknowledge a bait-and-switch on my part. Whereas in my previous comment I was seeking to characterise worlds directly in terms of decoherence, now I’m characterizing them by way of a third concept, namely “macroscopic distinctness”, which “under normal circumstances (i.e. not doing a two-slit experiment with people)” guarantees decoherence.
Sorry, I can’t see how your questions relate to my statement.
It was a misunderstanding you cleared up by specifying what you meant by “world”.
The reason I say it doesn’t explain it is that the notion of “constructive and destructive interference” between different possibilities is deeply bizarre.
The interference isn’t between probabilities. They don’t contain sufficient information. It’s between the amplitudes. Going from amplitudes to probabilities is the weird part. It’s not explained by any interpretation.
If the MWI branches are “close” and haven’t completely decohered, it’s possible to detect them. If they’re far away, it’s not. Similarly, if the universes are close by in the fifth dimension, you might be able to make them out. If they’re far away, and you have to look through a hundred universes to make it out, it’s essentially impossible. The method of detecting them is different, the the principle is the same.
You can detect it, but it doesn’t happen? Isn’t that like saying that the universe doesn’t exist, but we experience things as if it did?
You need to know the potential energy of every point in configuration space in order to find out the probability of a given event. How can it matter if it isn’t involved?
I don’t understand. It explains it. So does any interpretation beyond pure particle. Its purpose is to explain away waveform collapse and the process of particles getting entangled. The laws regarding those in the Copenhagen interpretation are bizarre, and the results are indistinguishable from just assuming that everything is always entangled, and waveforms never collapse, which is the MWI.
We can detect other worlds of they’re close enough, but not if they’re too far away. This isn’t just limited to the MWI. The Copenhagen interpretation follows the same laws with entangled particles. We’ve never been able to detect waveform collapse, so decoherence getting to the point where we can’t detect the interference must happen first.
This is no different than saying that the next twenty branches exist, and maybe a few hundred more, but after a billion, the concept of other branches breaks down.
It’s also like saying that Earth is made of atoms, and the rest of our solar system is made of atoms, but we aren’t remotely capable of discerning atoms in other solar systems, so the concept of “being made of atoms” broke down.
This has largely turned into a semantic dispute about the “correct” meaning of the term “world” in the context of MWI.
You’re using it to mean “summand with respect to the position basis” whereas I’m using it to mean “summand with respect to a decomposition of the Hilbert space into subspaces large enough that elements of two distinct subspaces represent ‘distinct macrostates’”. (Where “macroscopic distinctness” is not and does not pretend to be precisely definable.)
Right after the photon in the Mach-Zehnder apparatus splits, you see two worlds corresponding to the two different positions of the photon, whereas I see only a single world because all macroscopic variables still have determinate values. (Or rather, their values are still as close to being determinate as they ever are.)
In my use of the term “worlds” it is correct to say that the notion of “other worlds” breaks down if you push it too far (ultimately this is because the boundary between the “micro” and “macro” domains cannot be rigorously defined.) In your use of the term “worlds” it is trivially true that, at any given time, the state vector is uniquely expressible as a superposition of “worlds”.
I don’t want to say too much in defense of my usage, except that I think mine is the standard one. You might like to read this by the way. (Not to resolve our dispute, but because it’s awesome.)
Sorry, I can’t see how your questions relate to my statement.
The reason I say it doesn’t explain it is that the notion of “constructive and destructive interference” between different possibilities is deeply bizarre. Simply declaring that all possibilities exist doesn’t explain why two possibilities can cancel each other out. But again, I suspect this is partly just a dispute over the semantics of “explain”.
ETA: I have to acknowledge a bait-and-switch on my part. Whereas in my previous comment I was seeking to characterise worlds directly in terms of decoherence, now I’m characterizing them by way of a third concept, namely “macroscopic distinctness”, which “under normal circumstances (i.e. not doing a two-slit experiment with people)” guarantees decoherence.
It was a misunderstanding you cleared up by specifying what you meant by “world”.
The interference isn’t between probabilities. They don’t contain sufficient information. It’s between the amplitudes. Going from amplitudes to probabilities is the weird part. It’s not explained by any interpretation.
Good thing I didn’t say that, then!
Above, I said of MWI “I don’t think that was ever its “purpose”.”