From: Lee Corbin (lcorbin@tsoft.com)
Date: Thu Sep 12 2002 - 01:46:50 MDT
Dan writes
> "The probability function combines objective and subjective elements. It
> contains statements about possibilities or better tendencies ('potentia'
> in Aristotelian philosophy), and these statements are completely
> objective, they do not depend on any observer; and it contains statements
> about our knowledge of the system, which of course are subjective in so
> far as they may be different for different observers. In ideal cases the
> subjective element in the probability function may be practically
> negligible as compared with the objective one. The physicists then speak
> of a 'pure case'." [ -Werner Heisenberg ]
Well, if local knowledge is considered subjective, then I
must concede the argument: indeed, languages employing
subjectivity are extremely useful on this reading. But
I worry that this may be going further than we want to here.
> With that said, Bohr's complementarity principle was explicitly
> subjectivist, though it did reify uncertainty: uncertainty under
> complementarity is a thing in the world (because the world is
> nothing more than our perceptions/measurements/observations).
Do you believe that "the world is nothing more than our
perceptions/measurements/observations"? Then we should
say that distant galaxies have no existence until we
homo sapiens observe them? I think that you'll agree
that the realist model has lots of advantages.
But Amara writes about your paragraph here
> According to Edwin Jaynes, Bohr was thinking on the epistemological
> level, not describing reality but, instead, information about reality.
with which I agree. There is this constant problem: some, like
Bohr and the postmodernists prefer on many occasions to describe
the epistemology (i.e., *our* concepts, our perceptions, our
symbols, etc.) and others, like we realists, prefer always to
talk about the ultimate referents whenever possible.
Dan writes
> Bohr said: "There is no quantum world. There is only an
> abstract quantum physical description. It is wrong to
> think that the task of physics is to find out how nature
> _is_. Physics concerns what we can say about nature."
It's too bad that MWI had to wait until 1957, two years
after Einstein's death. I think that physics took a long
unnecessary detour through non-realism due to that.
> > To David Deutsch and the MWI crowd, the other worlds are as observable
> > as atoms were (until very recently): namely, that although not directly
> > observable, their effects certainly are! Interference, for example.
>
> Well, the follow-up punch to MWI would be that it doesn't do anything the
> Copenhagen interpretation doesn't do, (it's just an interpretation, after
> all!) and so is on weaker ground because it posits unobservable entities
> to do its work.
The Copenhagen interpretation has terrible problems.
What is the wave function, and how does it collapse?
Why should consciousness intersect physics? These
are real physics questions that the C interpretation
cannot address. By comparison, MWI is quite unproblematical.
Moreover, it retains noble realism with all its advantages.
> [Like I say, I think that Occam's Razor is a wash here;
> I think MWI has its strengths and Copenhagen has its
> strengths, and you can use either as you like.]
I'm actually leery of appeal to Occam's Razor: it's a
fine way to describe what good thinking is about, whether
it be by dentists, mystery writers, or anyone else guessing
and conjecturing about how the world works. But if you'd
mentioned it to Newton, Galileo, Faraday, or Franklin,
they wouldn't have known what you were talking about.
As formulaic recipes for making predictions, QM got well
worked out for the most part between 1925 and 1950. The
only problem *was* the interpretation. MWI just is a
most suitable solution for realists.
> But still, you could imagine a "magical fairy" theory of physics: every
> time an atomic event occurs, a tiny invisible fairy in a green dress and
> pointed shoes waves her magic wand over the observation in question,
> collapsing the wave function in agreement with fay caprice.
>
> You can see how very unconvincing it would be to say in defense of this
> theory: "Of course the magical fairies aren't directly observable, but
> their effects certainly are!" It would be unconvincing because we'll
> accept arguments of this kind only when all the alternatives are much
> worse.
Of course. That's what taste in physics is all about. "Magical
fairies" would raise more questions than they answered. The MWI
doesn't do that; its worst problem is the philosophical problem
of identity: Namely, that it makes a number of physicists
quite uncomfortable to suppose that there are other versions of
themselves who saw a different outcome to the experiment. That,
in my opinion, is the great stumbling block to its acceptance.
Lee
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