I don’t expect the general climate of opinion on this site to change except as a result of new intellectual developments in the larger world of physics and philosophy of physics, which is where the question will be decided anyway.
If they do an experiment where they detect waveform collapse, and it’s repeated by other labs with different equipment, then we’ll change our opinions.
it is with the version of Many Worlds which says there’s no actual number of worlds.
It’s common to define “world” as a blob in configuration space. It’s similar to the idea of an ink blot. It is not something ontologically fundamental. I’m told that this is the standard definition, but I don’t really know.
Another definition is a point in configuration space. As far as anyone can tell, configuration space is a continuum, and there are uncountably infinite of them. This one is precisely defined, and the answer may very well be uncountably infinite. It could even be bigger than a continuum, for that matter.
I suppose that in a few people’s heads, there’s a rapid movement from “science (or materialism) is correct” to “quantum mechanics is correct” to “Many Worlds is correct” to “the Oxford school of MWI is correct”.
I can’t speak for the rest of us, but I follow those because each step has been pinned down extremely well.
because that opens the possibility that there is a right definition of “world”
There is no possibility. It has no inherent meaning. I suspect you’re thinking of something with specific properties. If so, the definition that compares it to ink blots isn’t that. It’s not meant to be that.
If they do an experiment where they detect waveform collapse, and it’s repeated by other labs with different equipment, then we’ll change our opinions.
The crucial issue is whether you need to suppose the actual existence of parallel worlds (or parallel “parts-of-world”) in order to explain experiment.
Classical probability can be expressed as a sum over histories, but that is not taken as evidence that the other histories do exist or must exist. The entirety of the reason for believing in the actual existence of other quantum histories is the interference of probability amplitudes—destructive interference, as in the double-slit experiment, is especially clear. You have things that don’t happen, or that happen rarely, “because” there are two ways in which they can happen, but the amplitudes cancel.
Nonetheless, the ontological significance of this is not nailed down. One class of quantum interpretations is retrocausal: there are causal chains heading from future to past as well as from past to future. If you have classical probabilistic dependence that is bidirectional in time, can you get destructive interference? I don’t know, and I think nobody knows.
Also, the arrival statistics (interference patterns) produced in a double-slit experiment provide information about the center-of-mass motion of the object which goes through the slits. It may be possible to get double-slit behavior, even from large objects (I mean containing thousands of atoms), from something like Bohmian mechanics, in which there is an extra potential arising from the double-slit apparatus, which induces a Bohmian trajectory in the center-of-mass motion. The other degrees of freedom of the complex object would be essentially independent of this coupling. Possibly such an explanation would require a deviation from quantum mechanics; again, I don’t think this line of thought has been pursued.
Even if we reach the point of believing in many worlds, we still might want to consider something that looks like many Bohmian worlds, but in which there is no guiding wavefunction—rather, the ensemble of worlds itself would provide the guiding influence for each of the member worlds. Here you would have many worlds which were genuinely interacting with their neighbors in configuration space.
I don’t claim that this remotely exhausts the theoretical possibilities or issues that one might wish to think about. What I do claim is that there is almost no reason to consider the “possibility” that “worlds exist but they don’t definitely exist”, or however it is that one chooses to express the Oxford school’s position, because this position resists even being stated in a way that makes sense. As I just said to kilobug, it makes sense to say that there is no right definition of “blob”, but it does not make sense to say that there is no right definition of “world”, because the existence of the blob depends on the definition, but the existence of the world does not.
The crucial issue is whether you need to suppose the actual existence of parallel worlds (or parallel “parts-of-world”) in order to explain experiment.
According to timeless physics, the past and future are just other parallel worlds. They might not actually exist, but since we can’t really do anything unless they do, we might as well assume they exist.
Even without that, Assuming that a specific path through the waveform happens is pretty silly. All of it is vital to figuring out what happens, so why assume on piece of the past exists? If I were going to assume that it was mostly just reality conforming to a random point in a waveform, I’d expect it’s one random point. Why would it be a path of them?
Bohmian mechanics
From what I can gather about that, it still assumes a waveform. In order for it to make the same predictions as quantum mechanics, which have been very thoroughly tested, it would have to have waveforms of huge numbers of dimensions. It would either have to have laws about how the waveform gets entangled, like the Copenhagen interpretation, or it would have to have the waveform include the position of every particle. In short, it assumes some other interpretation of quantum mechanics, and then adds particles on top of that.
Am I misunderstanding it?
One possibility I have considered is that the waveform is made of a huge number of interacting particles.
Oxford school’s position
I don’t actually know what that position is. My position is that the entire waveform exists. I don’t know why the Born probabilities are what they are, but I wouldn’t know no matter what they were.
it makes sense to say that there is no right definition of “blob”, but it does not make sense to say that there is no right definition of “world”, because the existence of the blob depends on the definition, but the existence of the world does not.
You’re reading too much into that word. The terminology is a bit misleading. It’s like a blob, not what you think of when you think “world”.
I’d say the world, in the sense of what actually happens, is the entire configuration space. I don’t know what makes us “experience” a piece of it, but it’s as much a question of neurons as it is of amplitudes.
If they do an experiment where they detect waveform collapse, and it’s repeated by other labs with different equipment, then we’ll change our opinions.
It’s common to define “world” as a blob in configuration space. It’s similar to the idea of an ink blot. It is not something ontologically fundamental. I’m told that this is the standard definition, but I don’t really know.
Another definition is a point in configuration space. As far as anyone can tell, configuration space is a continuum, and there are uncountably infinite of them. This one is precisely defined, and the answer may very well be uncountably infinite. It could even be bigger than a continuum, for that matter.
I can’t speak for the rest of us, but I follow those because each step has been pinned down extremely well.
There is no possibility. It has no inherent meaning. I suspect you’re thinking of something with specific properties. If so, the definition that compares it to ink blots isn’t that. It’s not meant to be that.
The crucial issue is whether you need to suppose the actual existence of parallel worlds (or parallel “parts-of-world”) in order to explain experiment.
Classical probability can be expressed as a sum over histories, but that is not taken as evidence that the other histories do exist or must exist. The entirety of the reason for believing in the actual existence of other quantum histories is the interference of probability amplitudes—destructive interference, as in the double-slit experiment, is especially clear. You have things that don’t happen, or that happen rarely, “because” there are two ways in which they can happen, but the amplitudes cancel.
Nonetheless, the ontological significance of this is not nailed down. One class of quantum interpretations is retrocausal: there are causal chains heading from future to past as well as from past to future. If you have classical probabilistic dependence that is bidirectional in time, can you get destructive interference? I don’t know, and I think nobody knows.
Also, the arrival statistics (interference patterns) produced in a double-slit experiment provide information about the center-of-mass motion of the object which goes through the slits. It may be possible to get double-slit behavior, even from large objects (I mean containing thousands of atoms), from something like Bohmian mechanics, in which there is an extra potential arising from the double-slit apparatus, which induces a Bohmian trajectory in the center-of-mass motion. The other degrees of freedom of the complex object would be essentially independent of this coupling. Possibly such an explanation would require a deviation from quantum mechanics; again, I don’t think this line of thought has been pursued.
Even if we reach the point of believing in many worlds, we still might want to consider something that looks like many Bohmian worlds, but in which there is no guiding wavefunction—rather, the ensemble of worlds itself would provide the guiding influence for each of the member worlds. Here you would have many worlds which were genuinely interacting with their neighbors in configuration space.
I don’t claim that this remotely exhausts the theoretical possibilities or issues that one might wish to think about. What I do claim is that there is almost no reason to consider the “possibility” that “worlds exist but they don’t definitely exist”, or however it is that one chooses to express the Oxford school’s position, because this position resists even being stated in a way that makes sense. As I just said to kilobug, it makes sense to say that there is no right definition of “blob”, but it does not make sense to say that there is no right definition of “world”, because the existence of the blob depends on the definition, but the existence of the world does not.
According to timeless physics, the past and future are just other parallel worlds. They might not actually exist, but since we can’t really do anything unless they do, we might as well assume they exist.
Even without that, Assuming that a specific path through the waveform happens is pretty silly. All of it is vital to figuring out what happens, so why assume on piece of the past exists? If I were going to assume that it was mostly just reality conforming to a random point in a waveform, I’d expect it’s one random point. Why would it be a path of them?
From what I can gather about that, it still assumes a waveform. In order for it to make the same predictions as quantum mechanics, which have been very thoroughly tested, it would have to have waveforms of huge numbers of dimensions. It would either have to have laws about how the waveform gets entangled, like the Copenhagen interpretation, or it would have to have the waveform include the position of every particle. In short, it assumes some other interpretation of quantum mechanics, and then adds particles on top of that.
Am I misunderstanding it?
One possibility I have considered is that the waveform is made of a huge number of interacting particles.
I don’t actually know what that position is. My position is that the entire waveform exists. I don’t know why the Born probabilities are what they are, but I wouldn’t know no matter what they were.
You’re reading too much into that word. The terminology is a bit misleading. It’s like a blob, not what you think of when you think “world”.
I’d say the world, in the sense of what actually happens, is the entire configuration space. I don’t know what makes us “experience” a piece of it, but it’s as much a question of neurons as it is of amplitudes.