Re: A thought on MWI and its alternative(s)
On Tue, Jun 13, 2017 at 7:11 AM, Telmo Menezes wrote: > > If you take the wave function seriously, then you take > > seriously that qubits really do exist in a superposition of states, > > and this explains the exponential increase in computational power as > > you add qubits to the systems in certain configurations. I guess you > > can accept superposition and deny many worlds, but I would say that it > > is quite an awkward move. Actually you can do Quantum Mechanics without making use of the wave equation, Heisenberg found a way of doing it about 6 months before Schrodinger discovered his equation. Both methods produced the same answer but Heisenberg's way was more abstract and for most (but not all) problems the calculations were more complex. Most physicists decided Quantum Mechanics was abstract and complex enough as it is so Schrodinger's Wave Equation is usually their first choice. In the same way if you were a working stiff who made his living writing quantum programs I suppose you could try to find the bug in your incomplete program by visualizing Copenhagen, but I think you'd get a better understanding of how your program works and the errors in it by visualizing Many Worlds. John K Clark -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to everything-list+unsubscr...@googlegroups.com. To post to this group, send email to everything-list@googlegroups.com. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
Re: A thought on MWI and its alternative(s)
On 15 Jun 2017, at 06:59, Bruce Kellett wrote: On Wednesday, June 14, 2017 at 10:19:56 AM UTC+10, Brent wrote 6/13/2017 4:11 AM, Telmo Menezes wrote: > The reason why it would follow is precisely the point of my rhetorical > question above. If you take the wave function seriously, then you take > seriously that qubits really do exist in a superposition of states, > and this explains the exponential increase in computational power as > you add qubits to the systems in certain configurations. I guess you > can accept superposition and deny many worlds, but I would say that it > is quite an awkward move. Being in a superposition is just a matter choosing the basis. If it's a pure state then there's some basis in which it is not a superposition. And if it's not in a superposition, then you can choose another basis in which it is. The basis problem is always going to defeat naive accounts of many worlds. OK. That is why most people now see decoherence as central, since that can give a principle reason for basis selection: the preferred basis is that which is stable against environmental decoherence. That was already well explained in Everett's long text. But the preferred basis is only preferred relatively to a entity/machine. The big picture does not need to choose a special base. That is proven in Everett. He insisted that this makes the notion of subsystem into a relative notion. Separate worlds can only form after irreversible decoherence. The decoherence itself is reversible in QM-without collapse, and it can even been done, theoretically, by memory erasing/discarding. Of course, to have a decent subjective life for some period, it is better (FAPP) to consider the decoherence irreversible. Yet, to avoid conceptual paradoxes, we need to realize that, without collapse, the decoherence is always a local happening and is *in principle reversible* in the big picture. The entire universe (assuming this makes some sense) cannot be subjected to decoherence, as you cannot leak outside the universe, by definition of "universe". Bruno Bruce -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to everything-list+unsubscr...@googlegroups.com. To post to this group, send email to everything-list@googlegroups.com. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout. http://iridia.ulb.ac.be/~marchal/ -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to everything-list+unsubscr...@googlegroups.com. To post to this group, send email to everything-list@googlegroups.com. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
Re: A thought on MWI and its alternative(s)
On 14 Jun 2017, at 19:11, John Clark wrote: On Wed, Jun 14, 2017 at 5:01 AM, Bruno Marchal wrote: >> Even the 2-slit experiment will not produce interference if you remove the photographic plate and just allow the photons to continue into infinite space after they pass the slits because then the world splits but the two never recombine again so no interference. > This is a bit weird. I would say that the interference are still there, but that we can't see them. I don't see why you would say that. We know for a fact from experiment that you CAN place a detector next to one slit so you CAN know which slit the photon went through, but if you do that then the interference pattern disappears. How does the MWI explain that? It says that when the photon approaches the 2 slits the universe splits, but in one universe a record is made (in a computer or a paper notebook or a human memory) that the photon went through the left slot and in the other a record is made that the photon went through the right slot. When the photon hits the photographic plate it's destroyed but the 2 universes are still NOT identical because they have different records, so they never merge back together, there is nothing to interfere with, so nobody in either universe sees a interference pattern. It would work the same way if no record of which slots the photon went through was made but you removed the photographic plate (or brick wall) and so didn't destroy it and allowed the photon to continue on for eternity after they pass the slits. The photons will be on slightly different tracks for infinity and so the two universes will never merge together into one and so there is no interference between the two. > Without the photographic plate, we can still introduce a needle at a position where no photon will ever go, Not after the photon passes the slits you can't, you could never move your needle fast enough to get in front of it. And according to Quantum Mechanics there is no place you can say with certainty the photon will never go, but it can tell you that it is more likely to go some places than others. You could make a calculation beforehand and find a good point to place the needle and bet the photon will not hit it, in most universes you will win your bet but in some you will not. And one needle is not enough, to prove if interference did or did not occur, you'd need lots of photons and lots of needles, although a photographic plate would be much easier to use. OK. But so we agree. > Interferences occur independently of our decision to observe them. Yes, observation has nothing to do with it if the MWI is correct, however interference requires at least 2 things, and if nothing interferes with the universe no interference pattern will be produced; the 2 universes need to merge back together but that will never happen if they remain different (because a record of which slot the photon went through is different or because the path the photon is taking on its infinite voyage is different). OK. Bruno John K Clark -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to everything-list+unsubscr...@googlegroups.com. To post to this group, send email to everything-list@googlegroups.com. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout. http://iridia.ulb.ac.be/~marchal/ -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to everything-list+unsubscr...@googlegroups.com. To post to this group, send email to everything-list@googlegroups.com. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
Re: A thought on MWI and its alternative(s)
On 14 Jun 2017, at 01:06, Bruce Kellett wrote: You seem to be taking the older view of many worlds that is favoured by David Deutsch. This approach has serious problems with the notorious basis problem, and there does not seem to be any principled way from within the theory to select unambiguosly the basis in which all of these worlds form. More recent understandings of MWI take decoherence into account. Decoherence provides a principled dynamical way to solve the basis problem, but it means the worlds do not actually form until there is decoherence -- worlds cannot form until they know what basis is relevant! I recommend the paper I suggested to Telmo: Michael Cuffaro, http://arxiv.org/abs/1110.2514v2 Cuffaro discusses the problems with the older form of MWI and suggests that although many worlds might be a useful heuristic in quantum computing, decoherence is required before worlds could be considered to have any ontological basis. The exponential speedup with a quantum computer is then seen in the fact that the QC manipulates the phases inherent in the entanglement of qbits, and doesn't have to actually calculate the function in question for all possible inputs, as the older many worlds view requires. Oh! I see that my explanation that the MW prevents the need of action at a distance was neo-everettian! I am not sure I understand the paper by Currafo, as I have no single- world interpretation of entanglement and/or quantum phase. At best, it would be a critics of the notion of world (be it single or not), and this would made QM even closer to the physics extracted from computationalism, where there is no world at all, and the differentiation is only a relative differentiation of the consciousness of a person. I guess mechanism is probably neo-neo- everettian, if not neo-neo-neo-Everettian. As I said once, despite Everett seems to disagree, it is better to talk in term of relative state, or relative dreams, instead of world. The worlds, with mechanism, are maximal consistent extensions, and exists only in the mind of the numbers. The FPI are not on the worlds, but on the first person (hopefully plural, as it seems) experience. Probably more on this later, I have still a lot of work to do. Meanwhile, Bruce, or anyone, you might try to explain his cluster quantum computing in a single world, or with collapse. Cuffaro does not provide any explanation of this, and when taken literally, his multi-qubit entanglement requires "MW" (or many minds, many dreams, many numbers, etc.). Bruno Bruce On 14/06/2017 4:09 am, John Clark wrote: On Mon, Jun 12, 2017 at 8:32 PM, Bruce Kellett > wrote: >> I agree Interference must take place in a single world, but where did all the information that produced the interference come from, where did the computations that produced all those wrong answers (and a few correct ones) come from? > What calculations are performed in these parallel worlds? Whatever algorithm you and your doppelgangers decided to run on their quantum computer. > And what performs those calculations? Computers made of matter that obey the laws of physics. > You are the one who insists that calculation is possible only on a physical computer. Yes, but you almost make that sound as if it were a contradiction of some sort. > Who constructed all these physical computers in the parallel worlds? If the MWI is correct and if you're a computer engineer then you and your doppelganger s made the quantum computer, made lots and lots of them actually. >> Even the 2-slit experiment will not produce interference if you remove the photographic plate and just allow the photons to continue into infinite space after they pass the slits because then the world splits but the two never recombine again so no interference. > Of course the interference continues -- for ever if necessary. The screen or photographic plate is only there to enable you to see it. No, in the Many World's theory it doesn't matter if anybody sees the results, in fact a brick wall would work just as well as a screen or a photographic plate, the only thing the MWI is interested in is that all of those things destroy the photon. After the photon passed the slits that photon was the only difference between those 2 universes, when it is destroyed in both universes by a screen or photographic plate or brick wall there is no longer a difference between universes so they merge back together, but indications it went through slot A and indications it went through slot B remain. And that produces the interference pattern. We don't usually see this weird quantum effect in our everyday macro-world because when a large change is made between universes it's hard to arrange things so they evolve together toward the same point, become the identical again, and thus
