David Deutsch gives this convincing argument against a single world:
that one can't explain how quantum computers work without postulating
other universes.

The evidence for the multiverse, according to Deutsch, is equally
overwhelming. "Admittedly, it's indirect," he says. "But then, we can
detect pterodactyls and quarks only indirectly too. The evidence that
other universes exist is at least as strong as the evidence for
pterodactyls or quarks."

Perhaps the sceptics will be convinced by a practical demonstration of
the multiverse. And Deutsch thinks he knows how. By building a quantum
computer, he says, we can reach out and mould the multiverse.

"One day, a quantum computer will be built which does more
simultaneous calculations than there are particles in the Universe,"
says Deutsch. "Since the Universe as we see it lacks the computational
resources to do the calculations, where are they being done?" It can
only be in other universes, he says. "Quantum computers share
information with huge numbers of versions of themselves throughout the

Imagine that you have a quantum PC and you set it a problem.  What
happens is that a huge number of versions of your PC split off from
this Universe into their own separate, local universes, and work on
parallel strands of the problem. A split second later, the pocket
universes recombine into one, and those strands are pulled together to
provide the answer that pops up on your screen.
"Quantum computers are the first machines humans have ever built to
exploit the multiverse directly," says Deutsch.

At the moment, even the biggest quantum computers can only work their
magic on about 6 bits of information, which in Deutsch's view means
they exploit copies of themselves in 26 universes-that's just 64 of
them. Because the computational feats of such computers are puny,
people can choose to ignore the multiverse. "But something will happen
when the number of parallel calculations becomes very large," says
Deutsch. "If the number is 64, people can shut their eyes but if it's
1064, they will no longer be able to pretend."


On Fri, May 15, 2009 at 10:50 AM, Bruno Marchal <marc...@ulb.ac.be> wrote:
> On 15 May 2009, at 14:27, ronaldheld wrote:
>> I still do not see any arguments against what I read, that one
>> Universe fits observations better than the MWI.
> Just comp predicts many worlds/histories and the fact they play a key
> role in the statistics of experiences.
> But with QM, many worlds seems to me to be  a direct consequence of
> a) linearity of evolution
> b) linearity of the tensor product
> c) superposition of states
> d) and nothing else (that is "only quantum physical histories", no
> Bohm potential, no classical isolated computations, etc.)
> In this, comp is a problem for "d":  the comp supervenience asks for
> *all* histories, and to solve the mind body problem (or just the body
> problem) we have to either justify completely "a, b, c, and d, from a
> measure extracted from classical computer science", or to reject comp
> or QM.
> But nature, both the observable one, and the one which proceeds by the
> richness of the structure of the integers, suggests that "Many" is
> much simpler than "One". The Mandelbrot set illustrates this too: a
> very simple iteration leads to incredibly complex; self-similar,
> repetitive (and probably universal) structure. Even without QM and/or
> mechanism, the unicity of "anything" is rather doubtful. This is the
> starting idea of the everything list.
> I also disagree a bit technically on some points in Kent's paper, and
> generally I disagree even with MWI partisan. I have never understood
> the Copenhagian Wave collapse. Even when you give a special dualist
> role of consciousness: it does not work. Once you abandon the wave
> collapse, or better, once you agree that physicist obeys to QM, it
> seems to me that the many world cannot be avoided at all. Kent
> criticizes it on the fact that we don't yet recover the Born rules,
> but in my opinion this follows from Gleason Theorem + comp
> indeterminacy. A very old book by Paulette Fevrier (a pioneer in
> quantum logic) already suggests this (without really going through
> Gleason-like theorem).
> It is the equivalent of such a Gleason's theorem that comp is still
> lacking, and that is why I hope the Z1* and X1* logic(s) gives the
> right quantum logics capable of realizing von Neumann's dream to
> extract the quantum proba from the quantum logic. Z1* and X1* are
> quite promising with that respect, but a lot of work still remains to
> be done.
> Now, I don't understand why Wallace introduces a notion of fuzzyness,
> and some passage of Kent's paper remains a bit obscur. Perhaps you
> could tell us what precisely makes you feel (in Kent's paper, or by
> other way) that QM is still consistent with the idea of one  world
> without introducing a non (quantum) mechanical selection principle.
> Kent is the author of many paper "against Everett", and none have ever
> convinced me. Give me time I read it less diagonally though ...
> Bruno
>> On May 15, 1:01 am, daddycay...@msn.com wrote:
>>> On May 14, 9:47 pm, daddycay...@msn.com wrote:
>>>> On May 14, 4:45 pm, Colin Hales <c.ha...@pgrad.unimelb.edu.au>
>>>> wrote:
>>>>> At the same time  position 1 completely fails to explain an
>>>>> observer of the kind able to do 1a.
>>>> I would say that position 2 fails to explain the observer too, you
>>>> have to actually explain the observer to claim that a position
>>>> explains the observer.  But position 2 at least provides the
>>>> topology
>>>> to allow doubt, so that there is room for an observer to be
>>>> explained
>>>> in the future.
>>>>> ...
>>>>> Yet position 1 behaviour stops you from finding position 2 ...
>>>>> and problems unsolved because they are only solvable by position 2
>>>>> remain unsolved merely because of 1b religiosity.
>>>> If what you mean by religiosity is the disallowance of doubt, then
>>>> yes
>>>> by definition position 1 has religiosity and position 2 does not.  I
>>>> agree that disallowance of doubt is not a good thing to have.  I
>>>> think
>>>> you said that physicists would also agree, but that they don't
>>>> practice that way.  I think it's just a matter of frame of mind.  In
>>>> math we do that a lot, where we suppose that something is true and
>>>> see
>>>> where it leads.  I guess in physics the supposing just lasts longer.
>>>> And the supposing in physics is in the form of math.  What other
>>>> form
>>>> could supposing in physics possibly take?  It seems that anything
>>>> you
>>>> suppose true you can put in the form of a mathematics statement.  I
>>>> think it all boils down to the fact that we have to keep remembering
>>>> that we were just supposing, and be able to step back out of it and
>>>> suppose something else.  I think that's where having lots of
>>>> people it
>>>> an advantage, some people are the really dedicated logical inference
>>>> one step at a time see where the supposition leads, do many
>>>> experiments, etc.  Other people are the broad brush outside of the
>>>> box
>>>> thinkers that think up lots of different possibilites.
>>>>> Hmmm. Just in case there's a misunderstanding of position 2, here's
>>>>> their contrast rather more pointedly:
>>>>> Position 1
>>>>> 1a There's a mathematics which describes how the natural world
>>>>> behaves
>>>>> when we look.
>>>>> 1b Reality is literally made of the mathematics 1a. (I act as if
>>>>> this
>>>>> were the case)
>>>>> Position 2
>>>>> 1a There's a mathematics which describes how the natural world
>>>>> behaves
>>>>> when we look.
>>>>> 1b There's a *separate* mathematics of an underlying reality which
>>>>> operates to produce an observer who sees the reality behaving as
>>>>> per 1a
>>>>> maths.
>>>>> 1c There's the actual underlying reality, which is doubted (not
>>>>> claimed)
>>>>> to 'be' 1b or 1a.
>>>> I think that your first description of position 2 seemed to
>>>> necessitate some kind of basic matter that things are made of.
>>>> But I
>>>> think your second description of position 2 (above, by the way, 2a,
>>>> 2b, 2c typo above) doesn't necessarily require that.  In face your
>>>> 2c
>>>> above says that the underlying reality is doubted to be 1b or 1a.  I
>>>> think that your doubt and underlying reality could all be placed
>>>> in 2b
>>>> instead and you could get rid of 2c.  I think that Bruno's G might
>>>> correspond to 2a and G* might correspond to 2b, and viola, comp!
>>>> Tom>
>>> i.e. in the case where you put the doubt and underlying reality into
>>> 2b, then G* could correspond to 2b.- Hide quoted text -
>>> - Show quoted text -
>> >
> http://iridia.ulb.ac.be/~marchal/
> >

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