On 15 Sep 2015, at 22:33, smitra wrote:
On 12-09-2015 10:26, Bruno Marchal wrote:
On 11 Sep 2015, at 18:17, smitra wrote:
It seems to me that COMP should lead to MWI plus a preferred
basis where the latter derives from well defined computational
states. Many of the problems with the MWI should not arise here,
they are an artifact of the theory never defining what an
observation is, appealing to ad hoc intuitive notions that are
never formulated from within the theory itself.
The notion that the environment plays a fundamental role should
be rejected on physical grounds, it just explains the effective
physics we observe just like air resistance explains why Newton's
laws were not all that obvious to people who lived many centuries
ago.
The only way you can explain Newton's law to students is by
letting them contemplate a perfect vacuum. It doesn't matter here
how physically unrealistic that perfect vacuum is or isn't. The
same is true for quantum mechanics. You'll never make process if
you always invoke the environment and environment induced
decoherence to try to define fundamental concepts, because Nature
cannot possibly work that way on the fundamental level.
Instead, within quantum mechanics (i.e. if we forget about the
desire to derive QM from COMP or some other deeper theory)
defining observers as computations, means that they should be
represented as operators of the form:
sum over input of |output><input|
which leads to a preferred basis when you introduce an environment.
An environment or a universal machine, with or without oracle(s).
I think we agree.
I hope you agree that we agree here.
Yes, and I think you could make a lot of progress by trying to
deconstruct QM in terms of algorithms.
Algorithm cannot be enough.
Assuming Mechanism, the doctrine that there is a physical universe is
deconstructed, and with Church thesis, the deconstruction is partially
constructive, as it shows what physics has to be given by the global
FPI calculus on the computations/sigma_1 sentences.
But the FPI calculus does not rely exclusively on the computations
(modeled by the true sigma_1 sentences), but on the logic of correct
self-reference with respect to those propositions, or logic of
provability (and its intensional variants) with the atomic
propositions being the sigma_1 arithmetical sentences. Despite
provability, unlike computability, is a relative notion, depending on
the machine or subject, as long as it is supportable by a machine, and
arithmetically correct, the general laws of self-reference (captured
by G*) will apply, and physics depends only on that.
And so I think that the work is entirely done, at least at the
propositional level. QM proposition calculus is entirely given by the
logics of []p & <>t (& p). The FPI is not algorithmic, even if the
distribution of probability is algorithmic with the simple protocol,
but even the simple FPI is no more algorithmic on the universal
dovetailing (or on the sigma_1 propositions) as we cannot recognize
them as such algorithmically. This makers very nice that the
propositional logic of observable is decidable (and close to a Quantum
Logic).
Note that the quanta appears at the star-level (in X1* minus X1),
making quanta into special case of qualia, which is coherent with
Everett's superposition of collection of people (first person plural)
and with the idea that the "absolute 3p reality is a multi-dreams (and
note a many-worlds). This shows that even with the Everett "MWI", we
don't have any world: only sharable first person experiences. If the
quanta would have appeared in Z1 or X1 (and not in the proper star-
extension) a notion of apparent global physical reality would have
made sense, but it looks we lost this.
I recall the 8 povs or "hypostases";
1) p (truth of p)
2) [0]p = []p = bewesibar('p'), with p a (sigma_1) arithmetical
sentence.
3) [1]p = []p & p (the knower, or soul or inner god)
4) [2]p = []p & <>t (the observer, gambler, ...)
5) [3]p = [2]p & p (the "senser").
which can be put in this diagram:
1=1*
2 2*
3=3*
4 4*
5 5*
We have that
1=1*
2 2*
3=3*
is the basic propositional theory of mind/soul (1= One, 2 =
Intellect, 3 = Soul)
and
4 4*
5 5*
gives the "two sorts of matter": 4 = intelligible matter, 5 = sensible
matter.
Quantizations appear at 3*, 4*, and 5*. That suggests 3 sorts of
logics structuring (slightly?) differently the physical reality. I
guess that 3* is "heaven physics" (the physics of the soul which has
not yet felt), and 4*, like 5*, are the physics of "earth", when we
sin in the bet on the non justifiable "Reality" (<>t).
So we can not only test mechanism, but we can test if we are in heaven
or not :)
No need to take this too much seriously. A lot of research needs to
be pursued to clarify all this. At the quantified logical level, we
know that both 2 and 2* are highly undecidable, and I expect it to be
like that for 3, 3*, 4, 4*, 5 and 5* too.
That is technically annoying, but if the whole quantified logic were
decidable, I would have doubted that comp is true, because the whole
physics and theology would have become decidable, which I cannot
really imagine. In fact the miracle is that at the *propositional*
level, those logics *are* decidable.
Now I am aware that not much people have the background in logic, to
get this straight, and without asking question it is hard for me to
say much more. To get an intuition, I can only suggest to read the
neoplatonists or the mystics, or to try to find out by themselves by
meditation, or other "perturbation of the brain" technic, in some
(non dangerous) way. People have to be careful because those technic
can also be used for brainwashing and to deepen the "illusion", but
then everything can be misused, even logic.
Bruno
Saibal
Bruno
Saibal
On 11-09-2015 17:07, Bruno Marchal wrote:
On 11 Sep 2015, at 03:10, Bruce Kellett wrote:
On 11/09/2015 5:00 am, Bruno Marchal wrote:
On 10 Sep 2015, at 01:20, Bruce Kellett wrote:
On 10/09/2015 7:42 am, Brent Meeker wrote:
On 9/9/2015 10:27 AM, Bruno Marchal wrote:
On 09 Sep 2015, at 07:55, Quentin Anciaux wrote:
As for Bruce, could you then be honest, and simply say
you don't believe in the many world interpretation and
don't want to explore it... yes we're talking mostly
metaphysics on this list, if you dislike it, I wonder
what you're doing here.
Indeed the point is notably that we can reason about this,
that is doing science, so that we never disagree except
about the choice of the assumptions.
Now, I disagree with Bruce, and I guess many philosophers
and scientists, except Deutsch (on this), but I do think
that QM (without collapse) is a theory of many worlds (in
a perhaps admittedly more abstract than usual notion of
world).
If we define a physical world by a set of events close for
interaction,
But can computationalism give a coherent account of this?
Doesn't the UD imply at every set of events will have many
(countably many?) causal histories and infinitely many
causal futures.
then the "many-world" is a consequence of the linearity of
the wave evolution together with the linearity of the
tensor product.
But they are only "many" FAPP. Decoherence suppresses
cross terms in the density matrix, but it doesn't make them
zero - and I don't think it's even provable that there is a
unique basis in which it diagonalized FAPP. And of course
we have no theory of quantum spacetime. QM assumes a
continuous spacetime, so QM is not the last word and if
computationalism only reproduces QM it will fail when QM
fails.
I think it is clear that Bruno does not understand either QM
or the MWI. MWI is not a consequence of the linearity of the
wave function.
It is when you define a world by the maximal consistent
extension close for the local observable interactions.
That is not a consequence of linearity. Linearity gives
superpositions. You only escape from the superpositions to
distinct non-interacting worlds by imposing some non-linearity
somewhere. In MWI this is hidden in the trace over
environmental states. But this is just as much a non-linear
collapse as in any other collapse model.
On the contrary, linearity of the tensor product gives the
superposition, and linearity of the wave evolution assures that the
terms of the superposition behaves like we see pure states, when in
fact we are ourself superposed. It assures also the non
interaction of
the terms, but it does not imply the lack of interference. Then
decoherence explains the *hardness* (and the need of amnesia) of
realizing the interference of the branches in which we "belong".
Superposition is the consequence of linearity,
OK. And if the computations done can interfere, they have an
equivalent physical reality, and determined alternate
accessible realities, but if entangling oneself with them, we
loss or make very hard the ability to see the interference.
Just because you can't see it it does not follow that it is not
there.
Yes. That's my point.
and superposition implies interactions between outcomes.
?
I would say interference between the outcomes.
Many-worlds requires decoherence in a preferred basis,
I would say that classical macroscopic brain or universal
machine requires a classical-enough base, which benefits of
that decoherence, although with quantum computing we can
exploit the ignorance by changing the base (which is still
rather mysterious from the comp pov).
There is no such thing as a "classical" basis for Hilbert
space. Quantum computing is irrelevant here.
?
All linear space have bases (if you are OK with the axiom of
choice).
A basis is a classical notion. All basis are classical.
with actual zeroing of the off-diagonal terms in the density
matrix. Indeed, this latter step is just the standard
"collapse" postulate in a different guise. So, far from
eliminating "collapse", MWI relies on it as much as any
other interpretation of QM.
Not at all. There is no physical collapse, just an
epistemological differentiation when one get entangled in the
other's business.
You appear to be referring to Everett's original 'relative
state' interpretation,
I refer (here) to any theory which assumes that the SWE apply to
both
the particles and the observers.
Well, to tell you the truth, I believe that just computationalism
implies the "many-dreams" in arithmetic. No need to know quantum
mechanics. I do not assume quantum mechanics at all once we assume
computationalism. I just say that the SWE (or MWI, which is
logically
equivalent) confirms the many-dreams theory (arithmetic "seen from
inside") up to now.
in which there was only ever one world --
... or zero world. "world" are never really defined.
the other parts of the wave function played no role. But this
was soon realized to be unworkable. You really should read up
on modern versions of MWI. I recommend Shlosshauer, Rev. Mod.
Phys. 76 (2004) 1267. Or
http://arxiv.org/abs/quant-ph/0312059
or his book on the subject.
I have no problem with that paper. It looks it confirms what I
said.
Maybe you can elaborate, as I am not sure why you refer to it. I
read
most of Griffith papers, and Omnes' books. I agree with a lot in
them,
except that they lost me very often in the philosophical
conclusion(s) where they lack rigor, and seems to believe in some
primary universe, which is useless, and contradicted (my job) by
computationalism (which is my starting hypothesis).
Bruno
Bruce
The real difference between interpretations is whether this
"collapse" is a physical process or merely an epistemological
one.
In the MWI, actually in Everett theory, there is only the
SWE. Sating "there is no collapse", means, for a logician,
that we don't add the collapse postulate (unlike many
textbook). So the collapse is necessarily an epistemological,
even indexical, and relative, notion.
In MWI, which reifies the wave function
Which is indeed an error, at least with the mind-body problem
in mind, but physicists do this very often.
and the elements of the superposition, the collapse is
definitely physical.
?
So it is, after all, no different in this respect from the
von Neumann Copenhagen interpretation.
I have a problem. In Everett theory there is no postulation
of collapse. The collapse is explained by the postluation of
universal machine, or at least good approximation of
universal machine.
Copenhague:
- SWE
- Collapse
- Dualist theory of mind and matter
Everett:
- SWE
- COMP
And what I try to explain is that COMP ->. [](COMP -> SWE)
& (COMP -> SWE), so "my" theory is just
- COMP
Formally it is just any theory which is Turing universal, and
observation is defined by the logic of self-reference (of
rcher entities living there) and the intensional variants.
This is not supposed to compete with physics, but to supply
the qualia, and the range of non communicable, but true,
realities.
Bruno
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