On 10/29/2014 10:00 AM, Bruno Marchal wrote:
On 29 Oct 2014, at 00:15, meekerdb wrote:
On 10/28/2014 8:14 AM, Bruno Marchal wrote:
On 27 Oct 2014, at 20:58, meekerdb wrote:
On 10/27/2014 3:38 AM, LizR wrote:
It would be nice if Mr Clark would EITHER stop joining in with discussions just to
say that he doesn't care about comp, OR state what he agrees or disagrees with in
Bruno's stated argument.
Just saying it's "obviously wrong" doesn't really cut it. So far the only real
(non-sarcastic, non-insult-based) objection I've heard comes down to a semantic
quibble to do with redefining our concept of an individual person. This is exactly
the same redefinition that was brought up by Everett in 1957. It isn't in itself
contentious - a physicist who believes the MWI to be correct will come to the same
conclusions about indeterminacy that someone using Bruno's matter transmitter would
- that it's a phenomenon experienced from a first person perspective because of the
person in question being split into two copies. The phenomena actually map onto each
other, because both comp and Everett allow for the possibility that from the third
person viewpoint the duplication could be observed - quantum computers rely on
precisely that fact.
Quantum computers (of the circuit type) rely on interference to pick out the right
solution. Interference implies superposition in the same world.
Only if you isolate the subsystem well enough. Imagine that I can isolate my room,
where I am, sufficiently, and in that room I succeed in isolating schroedinger cat
(prepared in the alive + dead state) in a box. Then, in my isolated room I look at the
cat (measuring in the alive/dead base) .QM description is that when I do that
measurement, I put myself in the superposition alive + dead. It follows from the
linearity of evolution and of the tensor product. You might say that I am in that
superposed state in *one* world. But if my room is not sufficiently well isolated, or
more normally when I go out of that room, announcing with some joy that the cat is
alive, well soon enough, the environment (the building with that room, then city, and
you coming for a visit) get in the superposition "history of the earth with that
Shroedinger car alive + history of the earth with that Shroedinger car dead.
Would you still say that it is a superposition in *one* world. Yes, the
differentiation of the galaxies will follows, at the speed of light, and I guess there
will be two Milky ways colliding with Andromeda, one with archive describing the fact
that that Schroedinger cat was alive, and one with the fact that that Schroedinger cat
is dead. Would you still say that there is one world? I like to define a physical
world (in the quantum theory) by a set of objects/events close for interaction. That
makes the many world the literal interpretation of QM. Without collapse, I don't see
how the term of the superposition can ever disappear.
The superposition doesn't disappear but it becomes dispersed into the environmental
degrees of freedom, so FAPP there are separate classical worlds. My point is that
superposition is not a defining attribute of different worlds, it's relative
incoherence so subspaces.
I have no problem with that. And despite Everett's own opinion on this, I think it was a
good idea to call that "the relative state theory", instead of the "many worlds", which
can lead to naïve view of multiple aristotelian worlds, which would be doing the
aristotelian error an infinity of times.
In arithmetic also, all we have are the relative states, and their relative measures.
(cf the ASSA/RSSA old discussion, a recurrent theme on the list).
I highly recommend Scott Aaronson's blog http://www.scottaaronson.com/blog/ , for
straight talk about quantum computing (his book "Quantum Computing Since Democritus"
is also very good).
What is his position on Everett?
/(2) One of the first questions anyone asks on learning quantum mechanics is, “OK, but
do all these branches of the wavefunction really exist? or are they just mathematical
constructs used to calculate probabilities?” Roughly speaking, Many-Worlders would say
they do exist, while Copenhagenists would say they don’t. /
Many worlders, when wise avoid the questions, they do exist in the formalism, so if the
tehiry is correct, they can't just simply disappear.
But it is false or ambiguous to say that the /Copenhagenists/ would say they don't
believe that they exist. They believe indeed that one of them exist! That is why they
need a mechanism to make disappearing some term in the wave, and they invented the
collapse, which is simply a way to say that they believe that QM does not apply to ....
them, or the measuring apparatus, or consciousness, etc. They did not find any evidence
that there is a collapse, nor any senseful criteria for something not obeying QM..
/Of course, part of what makes the question slippery is that it’s not even completely
clear what we mean by words like “exist”! /
I am not sure. the real question is "are the terms of the self-superposition as real as
me?".
?? What's the "self-superposition"? I very much doubt that a self is a pure state;
certainly not as modeled by a thread in the UD. For a pure state, "superposition" is just
saying it's relative to some basis other than its eigenstate; it's a state expressed as in
term of the eigenvectors of some other basis. So an UP polarization (which is an
eigenstate of polarization) is a superposition of LEFT and RIGHT polarizations - just a
different basis.
What about accepting to be put in the superposition
sqrt(1/1000000) I punishment> + sqrt(999999/1000000) Ireward>
But that's the general form of a superposition. In general there is some unknown phase
relation between |punish> and |reward>. It's randomization of this phase that makes state
FAPP a classical mixture.
Should that be illegal?
What's it have to do with laws?
/Now, I’d say that quantum computing theory has sharpened the question in many ways,
and actually answered some of the sharpened versions — but interestingly, sometimes the
answer goes one way and sometimes it goes the other! So for example, we have strong
evidence that quantum computers can solve certain specific problems in polynomial time
that would require exponential time to solve using a classical computer. Some
Many-Worlders, most notably David Deutsch, have seized on the apparent exponential
speedups for problems like factoring, as the ultimate proof that the various branches
of the wavefunction must literally exist: “if they don’t exist,” they ask, “then where
was this huge number factored? where did the exponential resources to solve the problem
come from?” /
I thibk it is a good argument, but it has a flaw, and david Deutch knows it, and makes
the correction, you would need to have a quantum brain to get a more driect appraisal of
the many worlds: you can remember visiting different universe, but you need to be
amnesic of the details, but can be aware that there were different.
Yes, I'm aware of Deutsch AI test of MWI, and I'm sure Aaronson is too.
But I am more simple mind on this: if there is a photon in the [1+0] state somewhere in
the universe,
In what basis? In some other basis the same photon is [1/2 1/2] (if I understand your
notation).
I am already in the state [can meet that photon in the state 1 + can meet that photon in
the state 0]. By QM, I don' need to interact.
What does "meet" mean if not to interact?
I thonk david agrees on this, as he prefers the label "differentiation" than
"duplication".
/The trouble is, we’ve also learned that a quantum computer could NOT solve arbitrary
search problems exponentially faster than a classical computer could solve them — /
OK. But logically, you need only one problem which needs the actual parallelism. of
course, we can interact, with the "other computations", but we can do Fourier transform
on all results, and Shor shows that provide an algorithm to solve the factorization problem.
/something you’d probably predict a QC could do, if you thought of all the branches of
the wavefunction as just parallel processors. If you want a quantum speedup, then your
problem needs a particular structure, which (roughly speaking) lets you choreograph a
pattern of constructive and destructive interference involving ALL the branches. /
Indeed, that is the point of the Everettian relativists.
I think you're missing Aaronson's point. Shor's algorithm depends on finding a certain
periodicity. The quantum Fourier transform can does this more efficiently than
conventional computer but having all the non-solutions interfere and cancel out.
Interference means they're happening in the same world (at least by the usual definition
of "world").
Brent
/You can’t just “fan out” and have one branch try each possible solution — twenty years
of popular articles notwithstanding, that’s not how it works! We also know today that
you can’t encode more than about n classical bits into n quantum bits (qubits), in such
a way that you can reliably retrieve any one of the bits afterward. And we have all
lots of other results that make quantum-mechanical amplitudes feel more like “just
souped-up versions of classical probabilities,” and quantum superposition feel more
like just a souped-up kind of potentiality. /
Hmmm looks like a souped-up way to hide the crazyness of QM.
But arithmetic is already crazy ...
/I love how the mathematician Boris Tsirelson summarized the situation: he said that “a
quantum possibility is more real than a classical possibility, but less real than a
classical reality.” It’s an ontological category that our pre-mathematical, pre-quantum
intuitions just don’t have a good name for./
The other self-superposed self branches are as real as our branche(s), but no more
accessible, and thus certainly *seems* less real, but if QM is correct, to say that
those branch are less real than ours, is a bit like the solipsists, who being unable to
feel what an other feels, think those are less real than them. They are, in the first
person views, but they are not, in the 3p views, and I think it is a play of word to
deny the reality of the other terms of the waves, simply because our measuraments makes
them inaccessible. In principle, by amnesia, the terms of the wave can "fuse" again.
Bruno
http://intelligence.org/2013/12/13/aaronson/
Brent
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