On the issue of many-world, I must just be slow because I can’t see how it is “obviously” correct. It certainly seems both self consistent and consistent with observation, but I don’t see how this in particular puts it so far ahead of other ways of understanding QM as to be the default view. If anyone knows of a really good summary for somebody who’s actually studied physics on why MWI is so great (and sadly, Eliezer’s posts here and on overcomingbias don’t do it for me) I would greatly appreciate the pointer.
In particular, two things that I have a hard time wrapping my head around are:
-If multiple worlds really are “splitting” from our own how is this accomplished without serious violations of mass and energy conservation. (I’m sure somebody has treated this somewhere since it’s so basic, but I’ve never seen it.)
-Even assuming everything else is fine, the actual mechanism for which world diverge has to be spelled out. (Maybe it is somewhere, if so please help me end my ignorance.)
I’ll admit that I haven’t actually spent a great deal of time considering the issue, but I’ve never come across answers to basic questions of this sort.
What if instead of talking about “many worlds” we just said “no collapse”? If there’s just this state and it evolves according to Schroedinger’s equation. Then then of course there’s conservation of energy.
Sure, I’m certainly not saying that the Copenhagen interpretation is correct, and my understanding is that a decoherence view is both more useful and simpler. MWI (at least as I understand it) is a significantly stronger claim. When we take the probabilities that come from wave state amplitudes as observed frequencies among actually existing “worlds” then we are claiming that there are many different versions of me that actually exist. It’s this last part that I find a bit of a stretch.
If many different versions of you existing bothers you, does Schroedinger’s cat bother you?
The extent to which MWI is a stronger claim than “no collapse,” it’s purely interpretative. It certainly doesn’t posit any “splitting” beyond vanilla QM. Questions about conservation of energy suggest that you don’t get this.
Thank you, this is exactly the type of linking that I was looking for. Unfortunately, the FAQ that you so kindly provided isn’t providing the rigor that I’m looking for. In fact, for the energy conservation portion, I think (although I’m by no means certain) that the argument has been simplified to the point that the explanation being offered isn’t true.
I guess what I’d really like is an explanation of MWI that actually ties the math and the explanations together closely. (I think that I’m expressing myself poorly, so I’m sorry if my point seems muddled, but I’d actually like to really understand what Eliezer seems to find so obvious.)
“the law conservation of energy is based on observations within each world. All observations within each world are consistent with conservation of energy, therefore energy is conserved.”
Conservation of energy takes place within worlds, not between them.
FWIW, I first learned about the MWI from: Paul C.W. Davies’ book: “Other Worlds”—waay back in the 1980s. It was quite readable—and one of the better popular books on QM from that era. It succeeded in conveying the “Occam” advantage of the theory.
OK, if that’s really what it takes I guess I’ll leave it at that. But I don’t see the loss of generality from conservation laws operating on any closed system as a good thing, and I can’t understand how weighting a world (that is claimed to actually exist) by a probability measure (that I’ve seen claimed to be meant as observed frequencies) is actually a reasonable thing to do.
I would actually like to understand this, and I suspect strongly that I’m missing something basic. Unfortunately, I don’t have the time to make my ignorance suitable for public consumption, but if anyone would like to help enlighten me privately, I’d be delighted.
Ok, but this isn’t actually making the case for MWI better to my mind. Instead of mass and energy being conserved in any closed system it is now only conserved on closed systems up to the “size” of a “world”. I don’t see how this loss of generality (especially since “worlds” tend to “split” into things that must now be treated independently despite coming from the same source) is a good thing.
I actually want to understand this correctly and I strongly suspect that I’m missing something basic. Unfortunately, I don’t really have the time to express my ignorance well in a public forum, but if anyone is willing to discuss privately, I’d be delighted.
If anyone knows of a really good summary for somebody who’s actually studied physics on why MWI is so great (and sadly, Eliezer’s posts here and on overcomingbias don’t do it for me) I would greatly appreciate the pointer.
You say Eliezer’s posts didn’t do it for you, but how much of it did you read? In particular, the point about parsimony favoring MWI is explained in “Decoherence is Simple”. As for the mechanism of world divergence, I think the answer is that “worlds” are not an ontologically basic element of the theory. Rather, the theory is about complex amplitude in configuration space, and then from our perspective embedded within the physics, the evolution of the wavefunction seems like “worlds” “splitting.”
You say Eliezer’s posts didn’t do it for you, but how much of it did you read?
I have read every post on overcomingbias and I’m pretty sure I’ve ready every top-level post by Eliezer on less wrong. Although I very much enjoyed Eliezer’s posts on the issue, they were intended for a wide audience and I’m looking for a technical discussion.
I think that the many world hypothesis is aesthetic because it doesn’t break symmetry. Suppose that in some set-up a particle can move down one path to the right or another path to the left and there are exactly equal probabilities of either path being taken. Choosing one of the paths—by any mechanism—seems arbitrary. It is more logical that both paths are taken. But the two possibilities can’t interact: two different worlds.
In the world we experience, objects do occasionally move to the right. If there is not an alternate reality in which the object moved to the left, eventually, with either that object’s movement, or the object that pushed it, or the object that pushed that, and so on, you have to explain how symmetry was ever broken in the first place.
Physicists don’t like spontaneous breaking of symmetry. So much so, that the idea of many worlds suddenly seems totally reasonable.
Later edit: This is similar to the argument Eliezer made, in more detail and with more physics here.
In my understanding, what you have presented is an argument for why MWI is interesting (is has strong aesthetic appeal) and why it’s worth looking into seriously (it doesn’t seem to have spontaneous breaking of symmetry).
What I’m looking for is a compilation of reasons that I should believe that it is true, basically a list of problems with other interpretations and how MWI fixes it along with refutations of common objections to MWI. I should also note that I’m explicitly asking for rigorous arguments (I actually am a physicist and I’d like to see the math) and not just casual arguments that make things seem plausible.
I should also note that I’m explicitly asking for rigorous arguments
Many worlds is an interpretation of quantum mechanics. QM stays exactly the same; mathematics, evidence and everything. Whether an interpretation is plausible really just depends on what is aesthetic and what makes sense to you. I explained why some other physicists find Many Worlds reasonable. It’s always going to be this nebulous opinion-based “support” because it’s not a matter of empirical fact—unless it ever turned out there is some way the worlds interact.
In my understanding, what you have presented is an argument for why MWI is interesting (is has strong aesthetic appeal) and why it’s worth looking into seriously (it doesn’t seem to have spontaneous breaking of symmetry).
You’ve made a distinction between MWI being aesthetic and MWI being worth looking into seriously, which makes it sounds like you view that the argument to avoid spontaneous breaking of symmetry is more than just an aesthetic one. Can you pinpoint the physical reason why we like to avoid it? (I was wondering before.)
And then a question for the physical materialists: Why do you feel comfortable discussing multiple worlds; with it being an interpretation rather than an empirical fact? Or do you think there could ever be evidence one way or the other? (I just read Decoherence is Falsifiable and Testable and I believe Eliezer is saying that Many Worlds is a logical deduction of QM, so that having a non-many-world-theory would require additional postulates and evidence.)
“Many worlds is often referred to as a theory, rather than just an interpretation, by those who propose that many worlds can make testable predictions (such as David Deutsch) or is falsifiable (such as Everett)”
It mostly revolves around the idea of collapse. There’s no expermental evidence for a collapse. In the MWI, there’s no collapse. If we find evidence for a collapse someday, we will have to discard the MWI. However, people have been looking for a while now—and there’s no sign of a collapse so far. So, applying Occam’s razor, you get the MWI—or something similar.
On the issue of many-world, I must just be slow because I can’t see how it is “obviously” correct. It certainly seems both self consistent and consistent with observation, but I don’t see how this in particular puts it so far ahead of other ways of understanding QM as to be the default view. If anyone knows of a really good summary for somebody who’s actually studied physics on why MWI is so great (and sadly, Eliezer’s posts here and on overcomingbias don’t do it for me) I would greatly appreciate the pointer.
In particular, two things that I have a hard time wrapping my head around are: -If multiple worlds really are “splitting” from our own how is this accomplished without serious violations of mass and energy conservation. (I’m sure somebody has treated this somewhere since it’s so basic, but I’ve never seen it.) -Even assuming everything else is fine, the actual mechanism for which world diverge has to be spelled out. (Maybe it is somewhere, if so please help me end my ignorance.)
I’ll admit that I haven’t actually spent a great deal of time considering the issue, but I’ve never come across answers to basic questions of this sort.
What if instead of talking about “many worlds” we just said “no collapse”? If there’s just this state and it evolves according to Schroedinger’s equation. Then then of course there’s conservation of energy.
Sure, I’m certainly not saying that the Copenhagen interpretation is correct, and my understanding is that a decoherence view is both more useful and simpler. MWI (at least as I understand it) is a significantly stronger claim. When we take the probabilities that come from wave state amplitudes as observed frequencies among actually existing “worlds” then we are claiming that there are many different versions of me that actually exist. It’s this last part that I find a bit of a stretch.
If many different versions of you existing bothers you, does Schroedinger’s cat bother you?
The extent to which MWI is a stronger claim than “no collapse,” it’s purely interpretative. It certainly doesn’t posit any “splitting” beyond vanilla QM. Questions about conservation of energy suggest that you don’t get this.
For energy conservation see:
http://www.hedweb.com/manworld.htm#violate
The main reason for following the MWI is Occam’s razor:
http://www.hedweb.com/manworld.htm#ockham%27s
Thank you, this is exactly the type of linking that I was looking for. Unfortunately, the FAQ that you so kindly provided isn’t providing the rigor that I’m looking for. In fact, for the energy conservation portion, I think (although I’m by no means certain) that the argument has been simplified to the point that the explanation being offered isn’t true.
I guess what I’d really like is an explanation of MWI that actually ties the math and the explanations together closely. (I think that I’m expressing myself poorly, so I’m sorry if my point seems muddled, but I’d actually like to really understand what Eliezer seems to find so obvious.)
The first sentence lays out the issue:
“the law conservation of energy is based on observations within each world. All observations within each world are consistent with conservation of energy, therefore energy is conserved.”
Conservation of energy takes place within worlds, not between them.
FWIW, I first learned about the MWI from: Paul C.W. Davies’ book: “Other Worlds”—waay back in the 1980s. It was quite readable—and one of the better popular books on QM from that era. It succeeded in conveying the “Occam” advantage of the theory.
OK, if that’s really what it takes I guess I’ll leave it at that. But I don’t see the loss of generality from conservation laws operating on any closed system as a good thing, and I can’t understand how weighting a world (that is claimed to actually exist) by a probability measure (that I’ve seen claimed to be meant as observed frequencies) is actually a reasonable thing to do.
I would actually like to understand this, and I suspect strongly that I’m missing something basic. Unfortunately, I don’t have the time to make my ignorance suitable for public consumption, but if anyone would like to help enlighten me privately, I’d be delighted.
Ok, but this isn’t actually making the case for MWI better to my mind. Instead of mass and energy being conserved in any closed system it is now only conserved on closed systems up to the “size” of a “world”. I don’t see how this loss of generality (especially since “worlds” tend to “split” into things that must now be treated independently despite coming from the same source) is a good thing.
I actually want to understand this correctly and I strongly suspect that I’m missing something basic. Unfortunately, I don’t really have the time to express my ignorance well in a public forum, but if anyone is willing to discuss privately, I’d be delighted.
You say Eliezer’s posts didn’t do it for you, but how much of it did you read? In particular, the point about parsimony favoring MWI is explained in “Decoherence is Simple”. As for the mechanism of world divergence, I think the answer is that “worlds” are not an ontologically basic element of the theory. Rather, the theory is about complex amplitude in configuration space, and then from our perspective embedded within the physics, the evolution of the wavefunction seems like “worlds” “splitting.”
I have read every post on overcomingbias and I’m pretty sure I’ve ready every top-level post by Eliezer on less wrong. Although I very much enjoyed Eliezer’s posts on the issue, they were intended for a wide audience and I’m looking for a technical discussion.
I think that the many world hypothesis is aesthetic because it doesn’t break symmetry. Suppose that in some set-up a particle can move down one path to the right or another path to the left and there are exactly equal probabilities of either path being taken. Choosing one of the paths—by any mechanism—seems arbitrary. It is more logical that both paths are taken. But the two possibilities can’t interact: two different worlds.
In the world we experience, objects do occasionally move to the right. If there is not an alternate reality in which the object moved to the left, eventually, with either that object’s movement, or the object that pushed it, or the object that pushed that, and so on, you have to explain how symmetry was ever broken in the first place.
Physicists don’t like spontaneous breaking of symmetry. So much so, that the idea of many worlds suddenly seems totally reasonable.
Later edit: This is similar to the argument Eliezer made, in more detail and with more physics here.
In my understanding, what you have presented is an argument for why MWI is interesting (is has strong aesthetic appeal) and why it’s worth looking into seriously (it doesn’t seem to have spontaneous breaking of symmetry).
What I’m looking for is a compilation of reasons that I should believe that it is true, basically a list of problems with other interpretations and how MWI fixes it along with refutations of common objections to MWI. I should also note that I’m explicitly asking for rigorous arguments (I actually am a physicist and I’d like to see the math) and not just casual arguments that make things seem plausible.
Many worlds is an interpretation of quantum mechanics. QM stays exactly the same; mathematics, evidence and everything. Whether an interpretation is plausible really just depends on what is aesthetic and what makes sense to you. I explained why some other physicists find Many Worlds reasonable. It’s always going to be this nebulous opinion-based “support” because it’s not a matter of empirical fact—unless it ever turned out there is some way the worlds interact.
You’ve made a distinction between MWI being aesthetic and MWI being worth looking into seriously, which makes it sounds like you view that the argument to avoid spontaneous breaking of symmetry is more than just an aesthetic one. Can you pinpoint the physical reason why we like to avoid it? (I was wondering before.)
And then a question for the physical materialists: Why do you feel comfortable discussing multiple worlds; with it being an interpretation rather than an empirical fact? Or do you think there could ever be evidence one way or the other? (I just read Decoherence is Falsifiable and Testable and I believe Eliezer is saying that Many Worlds is a logical deduction of QM, so that having a non-many-world-theory would require additional postulates and evidence.)
Uh huh. See:
“What unique predictions does many-worlds make?”
http://www.hedweb.com/manworld.htm#unique
“Could we detect other Everett-worlds?”
http://www.hedweb.com/manworld.htm#detect
“Many worlds is often referred to as a theory, rather than just an interpretation, by those who propose that many worlds can make testable predictions (such as David Deutsch) or is falsifiable (such as Everett)”
http://en.wikipedia.org/wiki/Many-worlds_interpretation
OK, thanks. I see that many-worlds could be falsifiable, if the many-worlds interact (or interfere). I really didn’t know that was on the table.
It mostly revolves around the idea of collapse. There’s no expermental evidence for a collapse. In the MWI, there’s no collapse. If we find evidence for a collapse someday, we will have to discard the MWI. However, people have been looking for a while now—and there’s no sign of a collapse so far. So, applying Occam’s razor, you get the MWI—or something similar.