### Re: collapsing quantum wave function

Russell Standish writes: [quoting Norman Samish] Suppose we take ten apparently identical ball bearings and put stickers on each with the identifiers 1 through 10. We leave the room where the balls with stickers are, and a robot removes the stickers and mixes the balls up so that we don't which ball is which. However, the robot remembers which sticker belongs on which ball. We come back into the room and pick one ball at random to destroy by melting it in an electric furnace. If at this point we ask What is the probability that the destroyed ball is ball '3'? we can truthfully answer My memory tells me that the destroyed ball has a one in ten probability of being '3.' However, by reviewing the robot's record we can see that 6 was, in fact, the one destroyed. Does this mean that the quantum wave functions of all ten balls collapsed at the moment we viewed the record and observed what happened to 6? Or did the wave function never exist, since the robot's record always showed the identity of the destroyed ball, irrespective of whether a human observed this identity or not? Yes and no. In a 3rd person description of the situation, the Multiverse has decohered into 10 distinct universes at the moment the robot decides which ball it picks up. What about the 1st person description? According to the interpretation I follow, the observer is in fact superposed over all 10 branches, and only collapses into a single branch the moment the observer becomes aware of the robot's record. A more conventional physics interpretation would have the conscious observer as belonging to a definite branch since the Multiverse decohered, but not knowing which. I understand that David Deutsch holds this interpretation, for example. There is certainly no 3rd person experiment that can be done to distinguish between these two interpretations, and the only 1st person experiment I can think of relates to tests of quantum immortality. I find it hard to believe the no cul-de-sac conjecture would hold in the latter case. If you accept that it makes no first person difference whether there is one or many instantiations of the same observer moment - that it is all one observer moment - then it becomes meaningless to ask whether the observer belongs to just one or to a superposition of all of the instantiations. How would QTI distinguish between the two interpretations? --Stathis Papaioannou _ Single? Start dating at Lavalife. Try our 7 day FREE trial! http://lavalife9.ninemsn.com.au/clickthru/clickthru.act?context=an99locale=en_AUa=19179

### Re: collapsing quantum wave function

On Sun, Jun 12, 2005 at 09:14:11PM +1000, Stathis Papaioannou wrote: There is certainly no 3rd person experiment that can be done to distinguish between these two interpretations, and the only 1st person experiment I can think of relates to tests of quantum immortality. I find it hard to believe the no cul-de-sac conjecture would hold in the latter case. If you accept that it makes no first person difference whether there is one or many instantiations of the same observer moment - that it is all one observer moment - then it becomes meaningless to ask whether the observer belongs to just one or to a superposition of all of the instantiations. How would QTI distinguish between the two interpretations? --Stathis Papaioannou I think the latter interpretation would see that there _is_ a difference between identical instantiations. Since I tend to follow the first interpretation, as do you by the sounds of things, the second interpretation looks a little inconsistent, and smacks of hidden variables. However I note it, as not everyone sees the world in the same way I do. -- *PS: A number of people ask me about the attachment to my email, which is of type application/pgp-signature. Don't worry, it is not a virus. It is an electronic signature, that may be used to verify this email came from me if you have PGP or GPG installed. Otherwise, you may safely ignore this attachment. A/Prof Russell Standish Phone 8308 3119 (mobile) Mathematics0425 253119 () UNSW SYDNEY 2052 [EMAIL PROTECTED] Australiahttp://parallel.hpc.unsw.edu.au/rks International prefix +612, Interstate prefix 02 pgpRpunZpZq4i.pgp Description: PGP signature

### Re: collapsing quantum wave function

On Thu, 9 Jun 2005, Norman Samish wrote: Jonathan Colvin wrote: If I take a loaf of bread, chop it half, put one half in one room and one half in the other, and then ask the question where is the loaf of bread?, we can likely agree that the question is ill-posed. Depending on definitions, this may indeed be an ill-posed question. On the other hand, with appropriate definitions, the question might be answered by The loaf is half in one room and half in the other, or The loaf no longer exists. This reminds me of my problems trying to understand the collapsing quantum wave function. I've heard of SchrÃ¶dinger's Cat, which I'm told is half alive - half dead until the box is opened and the cat is observed. This observation collapses the quantum wave function, and the cat at that point is either alive or dead. Here's a variation. Is my interpretation correct? Suppose we take ten apparently identical ball bearings and put stickers on each with the identifiers 1 through 10. We leave the room where the balls with stickers are, and a robot removes the stickers and mixes the balls up so that we don't which ball is which. However, the robot remembers which sticker belongs on which ball. We come back into the room and pick one ball at random to destroy by melting it in an electric furnace. If at this point we ask What is the probability that the destroyed ball is ball '3'? we can truthfully answer My memory tells me that the destroyed ball has a one in ten probability of being '3.' However, by reviewing the robot's record we can see that 6 was, in fact, the one destroyed. Does this mean that the quantum wave functions of all ten balls collapsed at the moment we viewed the record and observed what happened to 6? Or did the wave function never exist, since the robot's record always showed the identity of the destroyed ball, irrespective of whether a human observed this identity or not? No this is not a quantum problem at all. The wavefunction does not encode ordinary lack-of-information uncertainty. Even if there was no robot, ball bearings are complicated enough that no two of them are genuinely identical, so there is always a fact of the matter about which was destroyed. Quantum uncertainty is better thought of as both at once rather than either or. Here's a quantum analogue of your experiment. Take ten electrons held in a row of Penning traps (magnetic bottles that can hold single electrons) labelled 1 to 10 (the label is attached to the trap). Introduce an anti-electron into trap number 3, causing an annihilation, so we now have 9 electrons, held in traps 1, 2 and 4 to 10. Does this mean that electron number 3 was destroyed? No, because since electrons *are* genuinely identical, they are not individuals. The wavefunction for any group of electrons is always a perfect mixture of all possible identity assignments, e.g. electron 1 in trap 1, 2 in trap 2 etc plus electron 2 in trap 1, 1 in trap 2 etc. This may sound ridiculous, but without this feature matter as we know it simply wouldn't exist, since it underlies the Pauli exclusion principle and hence the structure of atoms and all chemical properties. Paddy Leahy

### Re: collapsing quantum wave function

On Thu, Jun 09, 2005 at 04:09:15PM -0700, Norman Samish wrote: Does this mean that the quantum wave functions of all ten balls collapsed at the moment we viewed the record and observed what happened to 6? Or did the wave function never exist, since the robot's record always showed the identity of the destroyed ball, irrespective of whether a human observed this identity or not? In QM, it is not possible to distinguish featureless balls (systems in the same quantum state). Storing labels in an external system (robot) would perturb the systems, stopping them being featureless and/or precisely localized. Experimental limitations currently prevent experiments with system sizes much larger than a buckyball, IIRC. If you're talking about entangling several such systems (qubits), manipulating them by the robot should cause collapse of the total wavefunction -- you need to do it in QC to be able to read the result. IANAP, though, so above may be wrong. -- Eugen* Leitl a href=http://leitl.org;leitl/a __ ICBM: 48.07100, 11.36820http://www.leitl.org 8B29F6BE: 099D 78BA 2FD3 B014 B08A 7779 75B0 2443 8B29 F6BE signature.asc Description: Digital signature

### Re: collapsing quantum wave function

Thank you for the fascinating quantum analogue of my ten ball experiment, where you use electrons instead of steel balls. You destroy the electron in the third Penning trap and then point out that electron number 3 was NOT destroyed, because electrons are not individuals. Instead, (If I interpret correctly) we have 9 electrons distributed among ten Penning traps, with equal probability in their distribution. If we now examine each of the Penning traps for the existence of an electron, what do we find? My guess is that we would find nine electrons in the ten traps, and one empty trap. The identity of the empty trap would presumably be unpredictable. Is my guess correct? I don't dispute this, but you are certainly correct when you say This may sound ridiculous. . . This vividly demonstrates quantum weirdness. Norman Samish - Original Message - Patrick Leahy wrote: Quantum uncertainty is better thought of as both at once rather than either or. Here's a quantum analogue of your experiment. Take ten electrons held in a row of Penning traps (magnetic bottles that can hold single electrons) labelled 1 to 10 (the label is attached to the trap). Introduce an anti-electron into trap number 3, causing an annihilation, so we now have 9 electrons, held in traps 1, 2 and 4 to 10. Does this mean that electron number 3 was destroyed? No, because since electrons *are* genuinely identical, they are not individuals. The wavefunction for any group of electrons is always a perfect mixture of all possible identity assignments, e.g. electron 1 in trap 1, 2 in trap 2 etc plus electron 2 in trap 1, 1 in trap 2 etc. This may sound ridiculous, but without this feature matter as we know it simply wouldn't exist, since it underlies the Pauli exclusion principle and hence the structure of atoms and all chemical properties. Paddy Leahy

### Re: collapsing quantum wave function

From: Norman Samish This reminds me of my problems trying to understand the collapsing quantum wave function. Einstein was very interested in collapsing wave functions (see Solvay Congr. 1927) and developed many experiments about it (well before the EPR paper). One of these experiments was Einstein's 'gun powder' experiment (which then became the poor Schroedinger's cat). Another one was Einstein's boxes (then it bacame de Broglie's boxes). In the briefcase of Straycat http://briefcase.yahoo.com/straycat_md you can find the 'Travis Norsen's boxes paper' folder, which has two very interesting papers (pdf) about 'collapse', and 'alternative' collapse (factorizable superpositions), one written by Travis, one by Shimony. Interesting also the other side, when 'collapse' is forbidden. A good paper might be this one by Michael http://research.imb.uq.edu.au/~m.gagen/pubs/thesis.html s. Can a dog collapse a state vector? -Christopher Alan Fuchs

### Re: collapsing quantum wave function

In the briefcase of Straycat http://briefcase.yahoo.com/straycat_md you can find the 'Travis Norsen's boxes paper' folder, which has two very interesting papers (pdf) about 'collapse', and 'alternative' collapse (factorizable superpositions), one written by Travis, one by Shimony. One of the papers above is also at http://www.arxiv.org/abs/quant-ph/0404016

### Re: collapsing quantum wave function

On Thu, Jun 09, 2005 at 04:09:15PM -0700, Norman Samish wrote: Here's a variation. Is my interpretation correct? Suppose we take ten apparently identical ball bearings and put stickers on each with the identifiers 1 through 10. We leave the room where the balls with stickers are, and a robot removes the stickers and mixes the balls up so that we don't which ball is which. However, the robot remembers which sticker belongs on which ball. We come back into the room and pick one ball at random to destroy by melting it in an electric furnace. If at this point we ask What is the probability that the destroyed ball is ball '3'? we can truthfully answer My memory tells me that the destroyed ball has a one in ten probability of being '3.' However, by reviewing the robot's record we can see that 6 was, in fact, the one destroyed. Does this mean that the quantum wave functions of all ten balls collapsed at the moment we viewed the record and observed what happened to 6? Or did the wave function never exist, since the robot's record always showed the identity of the destroyed ball, irrespective of whether a human observed this identity or not? Yes and no. In a 3rd person description of the situation, the Multiverse has decohered into 10 distinct universes at the moment the robot decides which ball it picks up. What about the 1st person description? According to the interpretation I follow, the observer is in fact superposed over all 10 branches, and only collapses into a single branch the moment the observer becomes aware of the robot's record. A more conventional physics interpretation would have the conscious observer as belonging to a definite branch since the Multiverse decohered, but not knowing which. I understand that David Deutsch holds this interpretation, for example. There is certainly no 3rd person experiment that can be done to distinguish between these two interpretations, and the only 1st person experiment I can think of relates to tests of quantum immortality. I find it hard to believe the no cul-de-sac conjecture would hold in the latter case. Cheers -- *PS: A number of people ask me about the attachment to my email, which is of type application/pgp-signature. Don't worry, it is not a virus. It is an electronic signature, that may be used to verify this email came from me if you have PGP or GPG installed. Otherwise, you may safely ignore this attachment. A/Prof Russell Standish Phone 8308 3119 (mobile) Mathematics0425 253119 () UNSW SYDNEY 2052 [EMAIL PROTECTED] Australiahttp://parallel.hpc.unsw.edu.au/rks International prefix +612, Interstate prefix 02 pgp77oZWTfd0k.pgp Description: PGP signature