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 about accepting to be put in the superposition
sqrt(1/1000000) I punishment> + sqrt(999999/1000000) Ireward>
Should that be illegal?
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.
But I am more simple mind on this: if there is a photon in the [1+0]
state somewhere in the universe, 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. 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.
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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