The claim I made was that world-splitting is not instantaneous. The fact that systems decohere gradually establishes this (if you buy that “world-splitting” is just a consequence of decoherence). I’m not sure I see your worry. Perhaps you can indicate what, specifically, you think is wrong with my initial claim?
This strikes me as an odd thing to say, given the context. You raised what I presume is a criticism of the point I was making. I am trying to clarify the nature of the criticism, since I don’t see the problem yet. If I am able to recognize the force of the criticism, then surely we would have have got somewhere in this conversation. If you realize that the criticism does not work, we would have got somewhere as well. So why do you think we are not getting anywhere? Your comment just leaves me confused.
I can interpret it in a few ways:
(1) “I think our disagreements are sufficiently fundamental that discussing this within the constraints of a blog combox is unlikely to be productive.” It seems to me the particular disagreement at issue, though, isn’t all that fundamental, and can be settled rather quickly once we are both clear on what is being disputed. If you think I am wrong about this meta-point, could you at least give an indication why?
(2) “I do not think you are engaging in good faith, so continuing this is a waste of my time.” All I can do is assure you that I am in fact engaging in good faith. I am very interested in this stuff, and potentially learning more about it is far more valuable to me than “winning” some internet argument.
(3) “You do not possess knowledge sufficient to understand my point, and I do not have the patience to explain it to you.” Given your complaint elsewhere about dilettantes promoting the MWI, I suspect this might be what you intend. I think your point about dilettantism is valid, especially on this site, but it does not apply to me. I have peer-reviewed publications on the foundations of quantum mechanics (not on MWI specifically, but still).
(4) “I realize that my argument doesn’t work, but I don’t want to admit it.” This is a very uncharitable interpretation of your intent, and I mention it only for the sake of completeness. I doubt this is what is really going on.
(5) “I don’t want to talk about this anymore because I’m bored/busy.” If this is the case, please say so (or just don’t respond with anything). I have no problem with people saying this to me, and I will of course refrain from engaging with you further on this.
Which of these is the right one? Or is it something else? I would really appreciate a more informative response from you, because if your actual intent is captured by (1), (2) or (3), it would be beneficial for me to know.
I have peer-reviewed publications on the foundations of quantum mechanics (not on MWI specifically, but still).
I would be interested to see them, provided they were in physics journals (except for the Foundations of Physics, which often publishes stuff that can only be very charitably described as physics), and not in philosophy journals (my opinion of those happens to coincide with that of Feynman).
As for the immediate reason, I pointed out a rather elementary problem with units, which you did not address. Given that we cannot even agree on how propagation rate is defined, I do not see how we can make further progress.
I would be interested to see them, provided they were in physics journals (except for the Foundations of Physics, which often publishes stuff that can only be very charitably described as physics), and not in philosophy journals (my opinion of those happens to coincide with that of Feynman).
Fair enough. I will admit that the only physics journal in which I am published is in fact Foundations of Physics. You may not see this as a worthwhile venue for publication, but I hope that it will at least absolve me of the charge of dilletantism. I’d also point out that while in the past Foundations has had a reputation for encouraging mild crackpottery, its reputation has substantially improved since Gerard ‘t Hooft (I think probably the most insightful contemporary physicist) took charge. My publication in the journal was in the post-’t Hooft era, for what that’s worth. I’d point you to my paper, but I’d like to retain a little anonymity here.
I disagree very strongly with you on the value of (scientifically informed) philosophy, but that is probably a topic on which we genuinely will not get anywhere, so I’ll drop it.
That said, your response was (as I predicted) beneficial. I take it you are expressing surprise (or perhaps skepticism) at my claim to some degree of expertise. When I comment on physics, I try to balance signalling that I know what I’m talking about against being informal and accessible. Perhaps I’m not getting the balance right.
As for the immediate reason, I pointed out a rather elementary problem with units, which you did not address. Given that we cannot even agree on how propagation rate is defined, I do not see how we can make further progress.
Your point about units seems irrelevant to what I was saying. My comment was not intended to be non-responsive. I was trying to make clear what I was actually claiming, in the hope that it would also make clear that the units worry isn’t a problem. Maybe I’ll try again, at slightly greater length.
Look, here’s the dialectic: Someone said that in MWI, world-splitting is global and instantaneous. I responded that it isn’t, since “world-splitting” is just a consequence of decoherence, and decoherence takes time and relies on system-environment interactions, which are constrained by relativity.
At no point do I commit myself to measuring decoherence rates using units of velocity. I did speak of decoherence propagating, and this is what I meant by it: When a system decoheres its dynamics are no longer unitary. But the dynamics of an informationally isolated system are always unitary, so for a system to decohere, it must exchange information with its environment. Relativity constrains the (spatial) propagation of information.
Whether or not a particular quantum process has led to “world-splitting” is, in a sense, relative to an observer. Say I’m observing a Stern-Gerlach experiment. The spin state of the particle decoheres through interaction with the measuring device, From my perspective, though, this doesn’t correspond to a splitting into two worlds with different spin measurements until information from the measuring device propagates to me. This will take a (slight) additional amount of time. To you, standing outside the lab, there wouldn’t have been world-splitting until some portion of that information propagates to you; again, at finite velocity. Until that point, the whole particle-measuring device-me system will be in a state of superposition relative to you. So if we are dealing with localized systems, and we assume that information propagates through space at finite velocity, world-splitting can also be (crudely) thought of as propagating through physical space.
But I should emphasize that this in fact a crude approximation. I’m glossing a number of complications in this sketch. But these complications do not affect my main (in fact, sole) point: world-splitting in MWI is not global and instantaneous. Perhaps you think I’m making some bigger claim here, like MWI is a spatio-remporally local or relativistically invariant interpretation. I am not claiming anything of the sort. I don’t even think the ordinary notion of spatial locality is well-defined in the MWI framework (since physical space is non-fundamental), and I made a comment above explicitly saying that MWI in its current form cannot be easily reconciled with relativity.
First, I did not mean your personally when I was talking about dilettantes who learned from other dilettantes. I meant the people who read the QM sequence as their only in-depth math-free introduction to QM and took it as a self-evident truth, compartmentalizing away everything EY said about guessing the teacher’s password and such. Again, as EY keeps saying, a belief feels like truth from the inside, so it is extremely hard to argue with such people. I am well aware that this applies just as much to me, as to everyone else, having been burned by false beliefs before multiple times.
I agree that under ’t Hooft FoP gotten better, though it is still more philosophy than physics, hence my reservations.
At no point do I commit myself to measuring decoherence rates using units of velocity. [...] To you, standing outside the lab, there wouldn’t have been world-splitting until some portion of that information propagates to you; again, at finite velocity.
I find these two statements in contradiction. If you can measure the degree of decoherence and pinpoint when something is, say, “50%-decohered”, then you can take two observers at two points in space who measure it and calculate the propagation velocity as (x2-x2)/(t1-t1). If you cannot do that, then propagation of decoherence is not ontologically fundamental and is just a feel-good picture.
But these complications do not affect my main (in fact, sole) point: world-splitting in MWI is not global and instantaneous.
My point is that it makes no sense at all to talk about the “world-splitting process” as anything in any sense “real”.
Now, I do not expect you to agree with me, that is why I tried to drop the issue. And the reason I do not expect you to agree with me is a pragmatic one (pun intended): actions speak louder than words. And by “action” I mean an experiment differentiating between our points of view. That’s why I asked you how such an experiment would look. Until this is settled, we can continue back and forth with little hope of coming to an agreement. It might or might not work out better in person, though my observations of metaphysical debates between some rather smart people makes me skeptical that it would.
The claim I made was that world-splitting is not instantaneous. The fact that systems decohere gradually establishes this (if you buy that “world-splitting” is just a consequence of decoherence). I’m not sure I see your worry. Perhaps you can indicate what, specifically, you think is wrong with my initial claim?
Sorry, I don’t think we are getting anywhere...
This strikes me as an odd thing to say, given the context. You raised what I presume is a criticism of the point I was making. I am trying to clarify the nature of the criticism, since I don’t see the problem yet. If I am able to recognize the force of the criticism, then surely we would have have got somewhere in this conversation. If you realize that the criticism does not work, we would have got somewhere as well. So why do you think we are not getting anywhere? Your comment just leaves me confused.
I can interpret it in a few ways:
(1) “I think our disagreements are sufficiently fundamental that discussing this within the constraints of a blog combox is unlikely to be productive.” It seems to me the particular disagreement at issue, though, isn’t all that fundamental, and can be settled rather quickly once we are both clear on what is being disputed. If you think I am wrong about this meta-point, could you at least give an indication why?
(2) “I do not think you are engaging in good faith, so continuing this is a waste of my time.” All I can do is assure you that I am in fact engaging in good faith. I am very interested in this stuff, and potentially learning more about it is far more valuable to me than “winning” some internet argument.
(3) “You do not possess knowledge sufficient to understand my point, and I do not have the patience to explain it to you.” Given your complaint elsewhere about dilettantes promoting the MWI, I suspect this might be what you intend. I think your point about dilettantism is valid, especially on this site, but it does not apply to me. I have peer-reviewed publications on the foundations of quantum mechanics (not on MWI specifically, but still).
(4) “I realize that my argument doesn’t work, but I don’t want to admit it.” This is a very uncharitable interpretation of your intent, and I mention it only for the sake of completeness. I doubt this is what is really going on.
(5) “I don’t want to talk about this anymore because I’m bored/busy.” If this is the case, please say so (or just don’t respond with anything). I have no problem with people saying this to me, and I will of course refrain from engaging with you further on this.
Which of these is the right one? Or is it something else? I would really appreciate a more informative response from you, because if your actual intent is captured by (1), (2) or (3), it would be beneficial for me to know.
I would be interested to see them, provided they were in physics journals (except for the Foundations of Physics, which often publishes stuff that can only be very charitably described as physics), and not in philosophy journals (my opinion of those happens to coincide with that of Feynman).
As for the immediate reason, I pointed out a rather elementary problem with units, which you did not address. Given that we cannot even agree on how propagation rate is defined, I do not see how we can make further progress.
Fair enough. I will admit that the only physics journal in which I am published is in fact Foundations of Physics. You may not see this as a worthwhile venue for publication, but I hope that it will at least absolve me of the charge of dilletantism. I’d also point out that while in the past Foundations has had a reputation for encouraging mild crackpottery, its reputation has substantially improved since Gerard ‘t Hooft (I think probably the most insightful contemporary physicist) took charge. My publication in the journal was in the post-’t Hooft era, for what that’s worth. I’d point you to my paper, but I’d like to retain a little anonymity here.
I disagree very strongly with you on the value of (scientifically informed) philosophy, but that is probably a topic on which we genuinely will not get anywhere, so I’ll drop it.
That said, your response was (as I predicted) beneficial. I take it you are expressing surprise (or perhaps skepticism) at my claim to some degree of expertise. When I comment on physics, I try to balance signalling that I know what I’m talking about against being informal and accessible. Perhaps I’m not getting the balance right.
Your point about units seems irrelevant to what I was saying. My comment was not intended to be non-responsive. I was trying to make clear what I was actually claiming, in the hope that it would also make clear that the units worry isn’t a problem. Maybe I’ll try again, at slightly greater length.
Look, here’s the dialectic: Someone said that in MWI, world-splitting is global and instantaneous. I responded that it isn’t, since “world-splitting” is just a consequence of decoherence, and decoherence takes time and relies on system-environment interactions, which are constrained by relativity.
At no point do I commit myself to measuring decoherence rates using units of velocity. I did speak of decoherence propagating, and this is what I meant by it: When a system decoheres its dynamics are no longer unitary. But the dynamics of an informationally isolated system are always unitary, so for a system to decohere, it must exchange information with its environment. Relativity constrains the (spatial) propagation of information.
Whether or not a particular quantum process has led to “world-splitting” is, in a sense, relative to an observer. Say I’m observing a Stern-Gerlach experiment. The spin state of the particle decoheres through interaction with the measuring device, From my perspective, though, this doesn’t correspond to a splitting into two worlds with different spin measurements until information from the measuring device propagates to me. This will take a (slight) additional amount of time. To you, standing outside the lab, there wouldn’t have been world-splitting until some portion of that information propagates to you; again, at finite velocity. Until that point, the whole particle-measuring device-me system will be in a state of superposition relative to you. So if we are dealing with localized systems, and we assume that information propagates through space at finite velocity, world-splitting can also be (crudely) thought of as propagating through physical space.
But I should emphasize that this in fact a crude approximation. I’m glossing a number of complications in this sketch. But these complications do not affect my main (in fact, sole) point: world-splitting in MWI is not global and instantaneous. Perhaps you think I’m making some bigger claim here, like MWI is a spatio-remporally local or relativistically invariant interpretation. I am not claiming anything of the sort. I don’t even think the ordinary notion of spatial locality is well-defined in the MWI framework (since physical space is non-fundamental), and I made a comment above explicitly saying that MWI in its current form cannot be easily reconciled with relativity.
First, I did not mean your personally when I was talking about dilettantes who learned from other dilettantes. I meant the people who read the QM sequence as their only in-depth math-free introduction to QM and took it as a self-evident truth, compartmentalizing away everything EY said about guessing the teacher’s password and such. Again, as EY keeps saying, a belief feels like truth from the inside, so it is extremely hard to argue with such people. I am well aware that this applies just as much to me, as to everyone else, having been burned by false beliefs before multiple times.
I agree that under ’t Hooft FoP gotten better, though it is still more philosophy than physics, hence my reservations.
I find these two statements in contradiction. If you can measure the degree of decoherence and pinpoint when something is, say, “50%-decohered”, then you can take two observers at two points in space who measure it and calculate the propagation velocity as (x2-x2)/(t1-t1). If you cannot do that, then propagation of decoherence is not ontologically fundamental and is just a feel-good picture.
My point is that it makes no sense at all to talk about the “world-splitting process” as anything in any sense “real”.
Now, I do not expect you to agree with me, that is why I tried to drop the issue. And the reason I do not expect you to agree with me is a pragmatic one (pun intended): actions speak louder than words. And by “action” I mean an experiment differentiating between our points of view. That’s why I asked you how such an experiment would look. Until this is settled, we can continue back and forth with little hope of coming to an agreement. It might or might not work out better in person, though my observations of metaphysical debates between some rather smart people makes me skeptical that it would.