Re: New Scientist: Parallel universes make quantum sense
Le 24-sept.-07, à 18:39, Hal Finney wrote (in part) > We see the same thing happening all over again in string theory. I > don't know if you guys are following this at all. String theory is > going through a crisis as it has turned out in the past few years that > it does not predict a single universe, rather a multiverse where there > is a "landscape" of possible sets of parameters, each of which would > correspond to a universe. I think you are confusing two levels. String theory is based on quantum mechanics and presuppose a multiverse. The landscape concerns the "10^500" different string theories with possible different set of parameters; but each theory corresponds already to a multiverse. But I would no deduce from this that string theory leads us toward a multi-multiverse, given there are no reasons (as far as I know) why anything like interference between the multiverses would occur. > The big problem is that there is no natural > or accepted measure (unlike with QM where everyone knew all along that > the measure had to be the Born rule and it was just a matter of how > many hoops you had to jump through to pull it out of your model). As a > result it looks like it might be impossible to get even probabilistic > predictions out of the string theory landscape. In each of them, there is. The problem is more that we don't know which string theory is correct, and given that there are many of them, this can be seen as a big critics. Another problem is that the theory is background dependent, and the geometry seems to fall from the sky. > > AFAIK no one within the community has followed our path and looked > at algorithmic complexity as a source of measure (i.e. the Universal > Distribution, which says that the simplest theories have higher > measure). > Granted, even if that direction were pursued it would probably be > computationally intractable so they still would not be able to pull > much > out in the way of predictions. Yes. But not if you postulate comp explicitly (unlike taking comp just to borrow kolmogorov complexity theory). Once you take comp, it looks worst, at first sight, because although simplest program keep a big role, we cannot avoid the role of big programs. But then we can still use the intrisically computationalist constraints to derive at least the "logic of observable "certainty"" (the case: probability one), and this can be compared to emirical data. In particular, with comp, we know that classical physics is false. QM, up to now, confirms comp. > Neverthless physicists are skilled at the > use of approximation and assumptions to get plausible predictions out > of > even rather opaque mathematics so it's possible they might get > somewhere. > > But at this point it looks like the resistance is too strong. Rather > than string theory making the multiverse respectable as we might hope, > it seems likely that the multiverse will kill string theory. Well, Witten himself is aware that the "wave" aspect of superstring theory is in need of conceptual foundations. But String theories accept multiverse (most of the time implicitly by using QM without collapse). I think the problem in String Theory are more internal to string theory, than in its relation with the interpretation of QM. Bruno http://iridia.ulb.ac.be/~marchal/ --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups "Everything List" group. To post to this group, send email to [EMAIL PROTECTED] To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/everything-list?hl=en -~--~~~~--~~--~--~---
Re: New Scientist: Parallel universes make quantum sense
Here's my comment on David Wallace's 2005 paper, "Quantum Probability from Subjective Likelihood: improving on Deutsch's proof of the probability rule" available at http://philsci-archive.pitt.edu/archive/2302/. I think this is probably one of the main works referred to in the New Scientist article. The main assumption Wallace uses for his derivation of the Born rule is "equivalence", which means that any rational agent must regard equally-weighted events to be equally probable. In my view, the biggest problem with this assumption is, what if the two events have equal weights but different phases? Wallace handles the question in a couple of sentences on page 18: As for phase, this can be incorporated by allowing phase changes in the erasure process: if |'erased(i)', rewardi> is a valid erasure state, so is exp(i theta) |'erased(i)', rewardi>. More directly, it can be incorporated by observing that a phase transformation of an entire branch is completely unobservable, so an agent should be indifferent to it. (end quote) I'd answer that an event being unobservable is not sufficient reason for an agent to be indifferent to it. If it were, then we would all be indifferent to events that will only occur after our death (such as the disposition of our estates) but we clearly are not. Another way to see this is that the phrase "phase change" in the above argument can be replaced with "quantum suicide" and the argument goes through with the same force of logic (or lack thereof). Instead of saying any rational agent must follow the Born rule, I'd reinterpret Wallace's derivation as saying that for any rational agent, if he doesn't care about phase, then he should follow the Born rule. Similarly, for any rational agent who really cares only about what he will observe, he should be indifferent to virtually everything since he can always make the observations come out the way he wants by using quantum suicide. -- From: ""Hal Finney"" <[EMAIL PROTECTED]> Sent: Monday, September 24, 2007 9:39 AM To: <[EMAIL PROTECTED]> Subject: New Scientist: Parallel universes make quantum sense > > New Scientist has an article on parallel universes: > >> David Deutsch at the University of Oxford and colleagues have shown >> that key equations of quantum mechanics arise from the mathematics of >> parallel universes. "This work will go down as one of the most important >> developments in the history of science," says Andy Albrecht, a physicist >> at the University of California at Davis. In one parallel universe, >> at least, it will - whether it does in our one remains to be seen. > > It is behind a paywall at > http://space.newscientist.com/article/mg19526223.700-parallel-universes-make-quantum-sense.html > but I found a copy on Google Groups: > http://groups.google.com/group/alt.kq.p/browse_thread/thread/9631b2e37ba5e7a2/fb3202c9c5b71228?lnk=st&q=%22new+scientist%22+deutsch+albrecht&rnum=1#fb3202c9c5b71228 > > It has a great quote from Tegmark: "The critique of many worlds is > shifting from 'it makes no sense and I hate it' to simply 'I hate it'." > > The thrust of the article is about recent work to fix the two perceived > problems in the MWI: non-uniqueness of basis (the universe splits in all > different ways) and recovering the Born rule. The basis problem is now > considered (by supporters) to be resolved via improved understanding > of decoherence. This work (which was not particularly focused on the > MWI) generally seems to lead to a unique basis for measurement-like > interactions, hence there is no ambiguity in terms of which way the > universe splits. > > As for the Born rule, the article points to the effort begun by Deutsch in > 1999 to base things on decision theory. The idea is that we fundamentally > care about probability insofar as it influences the decisions and choices > we make, so if we can recover a sensible decision theory in the MWI, we > have basically explained probability. I've seen a number of critiques of > Deutsch's paper but according to this article, subsequent work by David > Wallace and Simon Saunders has extended it to the point where things > are pretty solid. > > Hence the two traditional objections to the MWI are now at least arguably > dealt with, and given its advantage in terms of formal simplicity (fewer > axioms), supporters argue that it should be considered the leading > model for QM. This is where we get claims about it being among the most > important discoveries in the history of mankind, etc. > > It's interesting to see the resistance of the physics community to >
Re: New Scientist: Parallel universes make quantum sense
Hal: I usually do not argue your posts (pro or con) because I feel whatever you write is in a 'different' discipline for me (euphemism: for 'above my head'). Now I have a fundamental remark: Whatever you QM etc. abiding minds conclude (including the published science) is within our PRESENT *knowledge-base* (mindset, actual cognitive inventory, naming is open). I don't hold myself above such, just acknowledge that human *k-b* was flimsier in the past and will be less(?) flimsy in the future (but still flimsy), so our likes/dislikes are no proof for the actualities of nature (like: simpler, less axioms, etc.). If there is a 'measure' it is our (present) human figment. MWI: Tegmark is right: (knowledgeable) people hate it at least. I don't, as a matter of fact I apply it in my 'narrative' with a vengeance: in the course of origination I do not specify formational qualia (and the negative is pointing rather to 'ALL may be very very different') so the MW membership is as diverse as it can - beyond our widest imagination (which is still based on this little poor universe we have some experience about.) So those equations derived from mathematical consideration within this one have not too much credit for (potentially) fundamentally different systems. This may be one reason why we know nithing about "them". And this ignorance is the foundation of the 'hate'. People dislike to 'not know'. I include the ignorance of 'most of it' and consider our information very very partial so I can accept the 'rest of it' as unknown/unknowable. Why I accept the possible 'existence' of the multiverse? because I see no reason not to. Our uniqueness and sole existence should be justified in the multitude of everything and so far we could not come up with a good reason for our exclusivity. I know: nescio non est argumentum against, but it is no argument pro either. (This opinion is just as flimsy as the opposite position.) String theory? I don't know the first thing about it (Pun: 1st: what is 'string' - beyond the math-fiction?). A consequence drawn upon it is at least subject to the credibility of the base. (Understandability? that would be too human). I wrote a remark on the new MIT invention that 'spacetime is a liquid' in which I humbly asked about the string-loop vibration as QM-al 'waves' and the straight string endings as the electrically charged subatomix, an explanation using the non-explained. (I know: this may be the route of advancement and I use it myself, - you have to 'dare' to innovate.) The never-never land of substituting math for common sense is disturbing for simpleminded non-mathematicians, no matter how advanced they want to think. Multiverse fits, with enough (non-math) imagination, string does not. This is my way to look at it, I am not ready to defend it. Especially not on the turf of the opponent. Regards John Mikes On 9/24/07, "Hal Finney" <[EMAIL PROTECTED]> wrote: > > > New Scientist has an article on parallel universes: > > > David Deutsch at the University of Oxford and colleagues have shown > > that key equations of quantum mechanics arise from the mathematics of > > parallel universes. "This work will go down as one of the most important > > developments in the history of science," says Andy Albrecht, a physicist > > at the University of California at Davis. In one parallel universe, > > at least, it will - whether it does in our one remains to be seen. > > It is behind a paywall at > > http://space.newscientist.com/article/mg19526223.700-parallel-universes-make-quantum-sense.html > but I found a copy on Google Groups: > > http://groups.google.com/group/alt.kq.p/browse_thread/thread/9631b2e37ba5e7a2/fb3202c9c5b71228?lnk=st&q=%22new+scientist%22+deutsch+albrecht&rnum=1#fb3202c9c5b71228 > > It has a great quote from Tegmark: "The critique of many worlds is > shifting from 'it makes no sense and I hate it' to simply 'I hate it'." > > The thrust of the article is about recent work to fix the two perceived > problems in the MWI: non-uniqueness of basis (the universe splits in all > different ways) and recovering the Born rule. The basis problem is now > considered (by supporters) to be resolved via improved understanding > of decoherence. This work (which was not particularly focused on the > MWI) generally seems to lead to a unique basis for measurement-like > interactions, hence there is no ambiguity in terms of which way the > universe splits. > > As for the Born rule, the article points to the effort begun by Deutsch in > 1999 to base things on decision theory. The idea is that we fundamentally > care about probability insofar as it influences the decisions and choices > we make, so if we can recover a sensible decision theory in the MWI, we > have basically explained probability. I've seen a number of critiques of > Deutsch's paper but according to this article, subsequent work by David > Wallace and Simon Saunders has extended it to the point where things > are pretty solid. > > Hence the
New Scientist: Parallel universes make quantum sense
New Scientist has an article on parallel universes: > David Deutsch at the University of Oxford and colleagues have shown > that key equations of quantum mechanics arise from the mathematics of > parallel universes. "This work will go down as one of the most important > developments in the history of science," says Andy Albrecht, a physicist > at the University of California at Davis. In one parallel universe, > at least, it will - whether it does in our one remains to be seen. It is behind a paywall at http://space.newscientist.com/article/mg19526223.700-parallel-universes-make-quantum-sense.html but I found a copy on Google Groups: http://groups.google.com/group/alt.kq.p/browse_thread/thread/9631b2e37ba5e7a2/fb3202c9c5b71228?lnk=st&q=%22new+scientist%22+deutsch+albrecht&rnum=1#fb3202c9c5b71228 It has a great quote from Tegmark: "The critique of many worlds is shifting from 'it makes no sense and I hate it' to simply 'I hate it'." The thrust of the article is about recent work to fix the two perceived problems in the MWI: non-uniqueness of basis (the universe splits in all different ways) and recovering the Born rule. The basis problem is now considered (by supporters) to be resolved via improved understanding of decoherence. This work (which was not particularly focused on the MWI) generally seems to lead to a unique basis for measurement-like interactions, hence there is no ambiguity in terms of which way the universe splits. As for the Born rule, the article points to the effort begun by Deutsch in 1999 to base things on decision theory. The idea is that we fundamentally care about probability insofar as it influences the decisions and choices we make, so if we can recover a sensible decision theory in the MWI, we have basically explained probability. I've seen a number of critiques of Deutsch's paper but according to this article, subsequent work by David Wallace and Simon Saunders has extended it to the point where things are pretty solid. Hence the two traditional objections to the MWI are now at least arguably dealt with, and given its advantage in terms of formal simplicity (fewer axioms), supporters argue that it should be considered the leading model for QM. This is where we get claims about it being among the most important discoveries in the history of mankind, etc. It's interesting to see the resistance of the physics community to multiverse concepts. It all comes back to the tradition of experimental verification I suppose, which is still pretty much impossible. Really it is more a question of philosophy than of physics as we currently understand these disciplines. We see the same thing happening all over again in string theory. I don't know if you guys are following this at all. String theory is going through a crisis as it has turned out in the past few years that it does not predict a single universe, rather a multiverse where there is a "landscape" of possible sets of parameters, each of which would correspond to a universe. The big problem is that there is no natural or accepted measure (unlike with QM where everyone knew all along that the measure had to be the Born rule and it was just a matter of how many hoops you had to jump through to pull it out of your model). As a result it looks like it might be impossible to get even probabilistic predictions out of the string theory landscape. AFAIK no one within the community has followed our path and looked at algorithmic complexity as a source of measure (i.e. the Universal Distribution, which says that the simplest theories have higher measure). Granted, even if that direction were pursued it would probably be computationally intractable so they still would not be able to pull much out in the way of predictions. Neverthless physicists are skilled at the use of approximation and assumptions to get plausible predictions out of even rather opaque mathematics so it's possible they might get somewhere. But at this point it looks like the resistance is too strong. Rather than string theory making the multiverse respectable as we might hope, it seems likely that the multiverse will kill string theory. Hal Finney --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups "Everything List" group. To post to this group, send email to [EMAIL PROTECTED] To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/everything-list?hl=en -~--~~~~--~~--~--~---
