On 29 Oct 2014, at 22:35, meekerdb wrote:
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"?
The first factor in the tensorial product "ME up + Me-down", written
in the {"ME", up, down} base.
Of course, the pure state "ME up + Me-down" is technically not
isolable from the environment, but the macro-complexity can make the
wave non linear, if QM is universally (for the physical realm) correct.
One world with a particle in the state up + down, is the same as an
infinity of worlds with up and down states, fro similar position.
I very much doubt that a self is a pure state;
That follows from QM without collapse.
certainly not as modeled by a thread in the UD.
I agree, that is why the physical reality is not a computable things.
It is the invariant of consciousness with respect to the observable,
and it is a logic on the accessible states by the FPI. The UD cannot
predict in advnce the result of the personla indeterminacies, but a
Löbian machine can works its mathematical structure, and compared with
her observations.
For a pure state, "superposition" is just saying it's relative to
some basis other than its eigenstate;
Yes.
it's a state expressed as in term of the eigenvectors of some other
basis.
No doubt on this.
So an UP polarization (which is an eigenstate of polarization) is a
superposition of LEFT and RIGHT polarizations - just a different
basis.
But as Everett showed, the prediction of the machine, having a
machinery based on some pure states in some bases, will not depend on
the base chosen. So, no problem with this, unless we defend a "naïve"
conception of worlds. Use of the notion of histories is less misleading.
I think that with computationalism we have that the whole of
mathematics is not a mathematical object, and the physical universe is
not a physical object. They inherit this from the fact that
arithmetical truth is not definable in arithmetic, (yet still
pointable too, in diverses ways, with caution).
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?
Because if someone put itself in the state sqrt(1/1000000) I hell> +
sqrt(999999/1000000) I heaven>, there is a sense to say that it sends
someone in hell, which I am not sure that should be legal, although in
this case, if you agree with John Clark's notion of personal identity,
like me, you can still say that it yourself that you send to Hell,
with some low probability for your first person expectation, and that
might only concern yourself.
Bruno
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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