On Mon, Jun 12, 2017 at 3:43 AM, Bruce Kellett <bhkell...@optusnet.com.au> wrote: > On 11/06/2017 1:31 am, Telmo Menezes wrote: >> >> On Sat, Jun 10, 2017 at 1:11 AM, Bruce Kellett >> <bhkell...@optusnet.com.au> wrote: >>> >>> On 10/06/2017 2:36 am, Telmo Menezes wrote: >>>> >>>> On Fri, Jun 9, 2017 at 12:37 AM, Bruce Kellett >>>> >>>>> The idea that the explanation is epistemological rather that >>>>> ontological >>>>> has >>>>> been my preferred position for a long time. If the wave-function is >>>>> merely >>>>> an epistemological device for calculating probabilities and not a >>>>> really >>>>> existing object, all worries about collapse and action-at-a-distance >>>>> vanish. >>>>> Of course, multi worlds also vanish, but in my opinion that is no bad >>>>> thing. >>>> >>>> So what's your position on Deutsch's argument about quantum computers? >>>> Where does the extra computing power come from? >>> >>> >>> It has long been understood that Deutsch is out to lunch on this. >>> >>> He appears >>> to assume that a quantum computer is just using the same algorithms that >>> a >>> classical computer would use, only executing them in a massively parallel >>> manner. >> >> I find it very hard to believe that David Deutsch does not have a good >> understanding of quantum computers. >> >>> This is manifestly false. Quantum computers operate in a completely >>> different way -- that is why there are so few actual algorithms for >>> quantum >>> computers to execute that gain massive speed improvements. >> >> I think you built a straw man and now you're attacking it. When I >> heard Deutsch make the argument, he was referring explicitly to Shor's >> algorithm. This is sufficient to demonstrate an increase in >> computational power that would be impossible in the classical world. > > > No one is denying that Shor's algorithm on a quantum computer would > factorize numbers exponentially faster that a classical Turing machine could > do it. But that does not mean that a quantum computer is just lot of > classical Turing machines acting in parallel.
No, but it does mean that a quantum computer can have the computational power of a lot of Turing machines acting in parallel, and it is normal to ask "why?", and be unsatisfied with a theory that does not answer this question. >> As for more general speed improvements, there is for example Grover's >> algorithm, that offers a quadratic improvement in searching unsorted >> lists. This has wide applicability in software engineering. >> >> Of course, building more complex quantum computers is still beyond our >> technical abilities. I don't think that's news for anyone... >> >>> As Brent says in his recent post, Scott Aaronson points out: >>> "The way a quantum algorithms work is that they arrange for wrong answers >>> to >>> destructively interfere while the desired answer interferes >>> constructively. >>> Interference requires that they take place in the same world." >> >> Yes, but this is not classical interference, it's interference between >> superpositions of states. So how can this computation happen in the >> physical world? > > > No one is suggesting that this is classical interference. Interference > between superpositions of states does happen in the physical world! Yes, this was a rhetorical question. > Are you > suggesting that two-slit interference does not happen in the physical world? > Interference between qbits happens in the physical world just as much as > two-slit interference. If you define a "world" as something closed to > outside interactions, then interference can only take place in the one > world. > >> For me, that gives more credence to the claim that the >> wave function describes a real object. > > > I don't see how that could follow. The wave function exists in complex > configuration space -- that is not the "real world". Well, I'm no sure about that, but classical mechanics exists in R^3 configuration space that is demonstrably not the real world (although it is the model that most closely matches our day-to-day perception of reality). 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. In other posts you alluded to a purely probabilistic interpretation of quantum mechanics. In that case, I would say that it also becomes awkward to explain the exponential increase in computational power for the quantum Fourier transform. These are all just intuitions, of course. We all have ours. Another problem for me with the purely probabilistic interpretation is that it gives base-level reality to true randomness, and that would also be quite mysterious in my view. My point being: you argue as if probabilistic interpretations remove weirdness from the explanation, but for me true randomness is weirder than many worlds. At least many worlds are already contained in the wave equation, if you take it seriously. Then, with many minds, you explain true randomness, à la Bruno. >>> Classical computers do not have quantum interference. Quantum computing >>> does >>> not prove the existence of parallel worlds -- there is no need for other >>> worlds in which to find the computational power, you just need a modicum >>> of >>> insight into how quantum computing algorithms work. >>> >>> You might claim that Deutsch is a known expert on quantum computing, but >>> more commonly, Deutsch is known for having way out, non-standard ideas on >>> quantum mechanics. >> >> Oh no! Everyone should be kept in line! > > > Physics is full of people who take non-standard positions. On the whole, > that is a good thing, because it provides an opportunity for real advances > in understanding. But that does not mean that all non-standard positions are > 'true' or valuable. Of course. Telmo. > > 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. -- 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.
