The Michael Cuffaro associated paper is a thesis of David Deutsch at Oxford from 20 years ago (and more). Deutsch also holds that we cannot in principle contact our own past, but an exact, parallel Earth is doable (in theory), so you can assassinate your clone's grandfather. For me, my imaginary fun time, side thinks, trade and adventure between earths. In the same spirit as trade and adventure crossing the galaxy. The Deutsch thing on alternate cosmos computing power sounds phenomenal too, but that is too real world for me.
-----Original Message----- From: Telmo Menezes <te...@telmomenezes.com> To: everything-list <everything-list@googlegroups.com> Sent: Sun, Jun 18, 2017 6:43 am Subject: Re: A thought on MWI and its alternative(s) > 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. > > > I have come across an interesting paper that discusses these questions, and > comes to the conclusion that it is problematic to see quantum computing as > accessing the computing power of other worlds. > > Michael Cuffaro, http://arxiv.org/abs/1110.2514v2 Thanks for the paper, I finally had some time to read it. I also write in reply to Brent, I think we are all talking about the same thing. First of all: I was too quick in accepting your definition of world. I think this is where our disagreement starts. You define a world bottom-up, by saying that if two thing can interact, then they belong to the same world. I would say that this is a good definition for classical worlds, but it becomes useless when it is not longer clear what "things" are these that can interact. I prefer this definition: a world is the set of things that can be observed. My definition forces one to invite theories of mind into the discussion. This is another thing I was too quick to accept: to talk about "just physics". When we are discussing interpretations of QM, it's no longer "just physics". Such a requirement makes the discussion non-sensical. To be clear, let us consider the double-slit experiment. Simplistically, under my definition there are three possible worlds: the two ones where you know which sensor was activated and there is no interference, and the one where you do not know and there is interference. The knowing/now knowing distinction is key here. The world-as-what-can-be-observed can supervene on different subsets of the totality, depending on which degrees of freedom are conserved. If I can know which sensor was activated, then the world where I'm in is not compatible with a superposition of states on the electron, and no interference is observable. This is the fundamental breakdown of "thingness" that QM brings to the table. So back to quantum computation: what I think that QC demonstrates (independently of it being realised by network models or cluster states) is that the superposition of states really does mean that the various states *exist*. They are necessarily things, because they provide a subtract for computation that does not exist otherwise. If you wanted to deny this, you would have to be able to show me that your interpretation of QC can be used to implement an equally powerful algorithm in a classical computer. But you cannot do that, cluster state or not. This is what makes purely probabilistic interpretations awkward, and I think this is the meat of Deutsch's intuition. I think that the preferred basis problem operates at a lower level than what I think is a useful definition of world. It's just a matter of frame of reference. It's like refuting the idea that the Earth follows and approximately elliptical orbit around the Sun by placing the frame of reference in Venus. Both descriptions are valid, but the first makes it easier to apprehend the actual underlying phenomenon. For me, the underlying phenomenon here is about what mind can supervene on. Refusing to do this exercise seems absurd, because the very point of interpreting quantum mechanics is to figure out what is the reality that the equations describe, taking into account the reality that we can observe. If we remove the problem of mind from the effort, there is no ground to stand on. It's just a popularity contest between equally unfalsifiable hypothesis. > The explanation for exponential speedup is: > "On this view, quantum computers are faster than classical computers because > they perform fewer, not more, computations. This is just circular reasoning, taking advantage of ambiguity on how to count computations -- and begging the question when deciding how to count them. Otherwise, give me the algorithm so that I can test it here, on my laptop. Telmo. -- 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. 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