Re: Original Sin

On Dec 18, 1:32 am, Gareth McCaughan <Gareth.McCaug...@xxxxxxxxx>
wrote:
DianelosGeorgoudis wrote:
[snip]
that quantum mechanics appears to imply that physical reality is *not*
observer independent, which is a polite way of saying that physical
reality is not objective.

I don't think quantum mechanics implies any such thing.

Doesn't it bother you that extremely knowledgeable physicists even
today think it does?

The fact that some extremely knowledgeable physicists think
it does is evidence that it does. The fact that some extremely
knowledgeable physicists think it doesn't is evidence that it
doesn't. I'm not sure why I should be *bothered* by any of
this. (If there were any reason to believe that the great
majority of people who've thought hard about this stuff
disagree with me, *that* would be reason to be bothered.
If there is such reason, I haven't seen it.)

Well, I'd put this way: Those physicists who write books about the
ontological implications of quantum mechanics do in their majority
think that these implications are deeply paradoxical and that it is
hard to describe physical reality in a way that is observer
independent.

In this context, how do you explain Wheeler's
delayedchoice experiment? (The most concise explanation of that
experiment I know is to be found on the diagram on page 165 of Nick
Herberts "Quantum Reality", which you can read here by clicking on
that page here:
http://www.amazon.com/gp/reader/0385235690/ref=sib_dp_srch_pop?v=sear...
).

I don't see that there's any problem. Sorry if I'm being dim.
The caption talks about "a photon" taking one path or two
paths around a distant galaxy, but obviously that's nonsense;
photons taking paths are merely a (very) convenient approximation;
do the actual calculations and you get the results shown in
that diagram; what's the difficulty, exactly?

There is not difficultly there, as there is no difficulty with quantum
mechanics whatsoever. Calculations do indeed beautifully describe or
predict our observations of the relevant physical phenomena. The
question is how to describe an objectively existing physical reality
that would produce these results. To my knowledge physicists who tried
to describe what kind of physical reality could produce the results of
Wheeler's delayed choice experiment [1] found it difficult to do so. I
mean I have never read any such description. If you can offer any such
ontological description please do so.

[1] That's precisely why John Wheeler, an eminent physicist by any
measure, proposed that experiment in the first place. My understanding
of the situation is as follows: Even the classical double slit
experiment is ontologically paradoxical. Individual photons normally
behave like waves interfering with themselves, but if it is possible
to obtain knowledge about which slit a photon actually passed that
interference disappears and now individual photons behave like
particles. Some think that in order to know through which slit the
photon passed we must somehow "disturb" it and hence affect its future
behavior. That explanation does not work very well because even if we
only measure what happens at the left slit, photons that pass through
the right slit will modify their behavior even though one has not
disturbed them. Still one could hypothesize that the photon behaves
like a spread-out wave before being measured and thus the photon
somehow senses that it is being measured at the left slit which causes
it to collapse into a particle that passes through the right slit.
Wheeler's idea was to suggest an experimental configuration in which
any measurement (and hence any "disturbance") happens long after the
photon has passed the slits and indeed far way from them. In the case
of using a gravitational lens what we do with the photon happens
billions of light years away from the corresponding "slits" and
billions of years after it has passed through them. The paradox
consists in the fact that we must give contradictory ontological
descriptions about what happened so long ago and so far away depending
on what we do here and now. But it can't be that what we do here and
now affects what happened in physical reality there and then, or, if
it does affect it then in what sense is physical reality independent
from us? But perhaps you disagree with my claim that we "must give
contradictory ontological descriptions" above; perhaps you can give a
coherent ontological description of what happened then and there
independently of what we do here and now. If so I am curious to know
about it.

(I think that if you take the experiment as shown there at
face value -- an actual galaxy, an actual quasar, etc. --
then you won't see anything like the resu0lts described
because of decoherence, but I may be being dim.)

To my knowledge photons traveling through space do not decohere. And
anyway it's not like a decohered photon stays decohered. So, for
example, if you put two double-slit screens one after the other and
measure through which slit of the first screen a photon passed thus
destroying the interference pattern, it's not like the interference
pattern won't reappear after the second screen. Incidentally, table-
top delayed choice experiments have been performed, and there is some
discussion about doing the same at cosmic scale (see:
http://www.seti.org/news/features/quantum-astronomy-cosmic-scale.php
). The point though is that whatever the practical difficulties nobody
really doubts what the results of such an experiment would be. The
wave-particle duality of matter is well established. It has been
demonstrated not only with photons and electrons but even with large
molecules. Indeed, as the authors of "Quantum Enigma" explain, there
is no reason to suspect that it won't be technically feasible to
demonstrate the wave-particle nature of matter with objects large
enough to be visible with the naked eye.

[snip]

I haven't seen anything like a survey of Great Physicists
on this point, if that's what you mean. But I'll cite
Gell-Mann and Feynman as examples of unquestionably
great physicists of recent years for whom QM is weird
rather than paradoxical, and who have (had, alas, in
Feynman's case) no truck with the idea of making
consciousness, or conscious observation, a fundamental
notion in physics.

My take on Feynmann's ontological beliefs is that even though he was a
materialist he was an agnostic about what really is happening out
there. It's those physicists who do try to describe what is happening
in physical reality that find it difficult to do so in a way that is
independent from the conscious observer. Our difference is that you
seem to be saying that this used to be a problem but isn't any more,
whereas I say that the ontological implications of quantum mechanics
are as paradoxical today as they were when the founders of the theory
first tried to deal with them.

[snip]

Any fact about our observations of the world that ceases to be
"paradoxical" if you regard our world as a computer simulation,
or a divine creation, is ipso facto not really paradoxical.

They are paradoxical in the context of scientific naturalism, i.e. the
ontological view that physics describes not only phenomenal reality
but also the objective reality that produces it. The computer
simulation hypothesis contradicts scientific naturalism.

You want naturalists to give a full, detailed explanation
of how and why the world is as it is, and in so far as that's
difficult you say "aha, paradoxes". But for opposing views
you're content to stop when the explanation reaches "computer
simulation" or "mind of God" -- thus leaving all the same
things unexplained as any naturalist might -- but you have
no problem with that. As I say: double standards.

I claim that the ontological implications of quantum mechanics are
paradoxical for scientific naturalism but are not paradoxical for
other ontologies such as for the computer simulation hypothesis or for
idealistic theism. So where's the double standard?

As for where the explanation "stops" I am not sure what you mean by
that. All scientific explanations about phenomenal reality are as
valid in any of these three ontologies. If you know of anything that
scientific naturalism explains over and beyond science, and which
would then confer it any advantage in comparison to the other two
ontological theories, please present it. I claim that idealistic
theism explains some facts of our condition above and beyond what
science can explain. But even if I am wrong in this we would be left
comparing three ontologies that explain exactly the same but one of
which is paradoxical and hence less reasonable than the other two.
.

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