Ralph D, particle physics, and BS
Rahul Mahajan
rahul at hagar.ph.utexas.edu
Sat Jun 17 08:33:11 MDT 1995
Hans Ehrbar wrote:
>Rahul, I agree that deep down physicists think their mathematical
>formulas mean something, and that their hunch is right. The concept
>which you seem to be missing is that reality is layered, and a
>scientific explanation is the unearthing of deeper-lying things which
>generate the empirical phenomena. After the existence of these things
>has been "predicted," these deeper-lying things themselves may become
>the subject of empirics.
Thanks for the agreement, Hans, but I am certainly not missing the layered
view of reality. That is a scientific commonplace, and I was simply
skipping over it, or thinking about going beyond it, without a clear idea
of how to do so. It's an appealing, if pedestrian, view, especially once
one realizes that there's no need for there to be any lowest level.
However, you have slightly misstated it, I think. I am not talking about
levels like that quarks make up protons and neutrons, which make up nuclei.
What you mention below about the quark model is true, but still we observed
the existence of quarks, not of the equations governing them. When we say
those equations are real, what do we mean?
> I am always bringing the example of quarks
>in class when I talk about this and you may correct me if I am wrong
>because it is only hearsay: quarks started as a mathematical device to
>bring more order into the zoo of elementary particles, and after this
>device was invented, physicists thought: perhaps it is more than a
>mathematical device, maybe one can observe them, and they did. I
>understand that the theory of gases as a cloud of atoms swirling about
>started in the same way: first it was simply a "model", a way to make
>ideas from Newtonian mechanics help[ful for an understanding of
>thermodynamics, without claim that gases really were clouds of mass
>points, but at a later time physicists designed experiments to count
>how many molecules are in a given volume of gas.
I don't quite think this is true of the modern atomic theory. I haven't
read anything by Dalton, who reintroduced it into science, but certainly
there were many 19th-century scientists who thought of atoms as real even
before the development of statistical mechanics (stat mech provides the
microscopic theory behind thermodynamics, which deals mostly with macro
phenomena)
> Since Hans Despain
>is talking about Bhaskar in a different context here, I would
>recommend: read at least the beginning pages of Bhaskar's Realist
>Theory of Science. It has what Kuhn is missing.
I don't expect to find enlightenment about any such matters from someone
who has not been doing physics. Maybe it's parochial of me, but I don't
quite see how you can get a good feel for these things without living with
them. Kuhn is missing logic, clarity, and depth, among other things. Of
course, he's a model of clarity compared to some of his successors.
>I have read Feynman's QED and I think it should be on the list.
>Feynman stresses that at present we have formalisms to predict quantum
>elelctro-dynamic phenomena, but these formalisms do not seem to imply
>any plausible mechanisms how these phenomena are generated.
I don't quite understand what this means. Could you expand?
>I am intrigued by your remark that one cannot base quantum mechanics
>on observables alone. Can you elaborate? I expect this to support
>the "depth-realist" theory of a stratified world versus a flat
>empiricist view: there is no necessity that everything real can be
>observed or can be reduced to observable phenomena. Such a view should
>be rejected anyway on the grounds that it is anthropocentric.
First of all, I think that the conflation of positivist
(observer-is-everything) models with anthropocentrism is a fundamental
error that goes all the way back to Bohr, proving that great scientists
need not necessarily be great philosophers of science. There is absolutely
no requirement that observers must be human beings. To the contrary,
although the concept of an observer is ill-defined, it's clear that a cat
can just as well be an observer. Logically speaking, it does not seem to me
that "consciousness" or "life" should make any difference, and that
therefore we may try to define an "observation" as any interaction that is
in some sense "big enough." Roger Penrose once proposed an ad hoc
one-graviton rule, but it's neither here nor there. To me, the question of
what is an observation is the only epistomological question in quantum
mechanics that is unresolved.
Second, how does one build quantum mechanics? In the most abstract and
elegant formalism (which is, however, equivalent to all of the others),
what you do is take classical observable quantities like position and
momentum, which are simply numbers classically, and make them into
(generally infinite-dimensional) matrices which act on a space of vectors,
known as a Hilbert space. Such an underlying vector corresponds to what is
called the quantum state, but the vector itself is in principle
unobservable. It corresponds to what is called the wavefunction in the
Schrodinger formalism, which, again, is unobservable, although its absolute
square and other things you can build from it using the observable
operators are.
As regards the "depth-realist" versus empiricist models, the problem is to
give a definition of "real" that one can use to determine whether a given
object, structure, equation, whatever, is real. "Observable" need not mean
the same thing as "real," but the advantage of it is that we have a usable
definition of it. Of course, "observable by us" is not the same as
"observable," but we keep expanding the sphere of what we can observe, so
we at least have a program for defining it, if not one that will achieve
the goal in finite time. So, what does "real" mean? That was the problem I
alluded to in a tortured way in the previous post -- how can we come up
with a good definition of the word that will at least partially validate
the intuitive feeling that we scientists have?
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