From: baez@guitar.ucr.edu (john baez)
Newsgroups: sci.physics
Subject: sci.physics.research: research-level only?
Date: 8 Jan 93 22:17:52 GMT
Organization: University of California, Riverside

Michael Weiss writes:

Do the proposed moderators for sci.physics.research regard research-level
questions only as appropriate, or is any "real physics" suitable, so long
as it is not in the FAQ?

A few examples, to make the question more concrete:

1.  There have been a few posts recently on Huygens' principle.  John Baez
    posted at his usual erudite level on two ways to see that HP holds for
    all odd dimensions, except 1, and fails in all even dimensions.  I was
    puzzled about the exception of dimension 1, and Herbert Kranzer
    straightened me out.  There have also been a couple of posts on
    Hadamard's "method of descent".  (Dave Ring's question on the
    descent from 5 to 3 dimensions remains unanswered.)

    Little of this could be called current research, I would think, since
    most of it is in Courant-Hilbert.  (John: is the conformal invariance
    stuff somewhere in Courant-Hilbert?  How old is Lax's stuff?)

--
The conformal approach is considerably newer than Courant-Hilbert.
Lax's stuff (actually Lax/Phillips) is 1978, and my favorite paper on
the subject, Branson's "Group Reps Arising from Lorentz Conformal
Geometry", is in the 1987 Journal of Functional Analysis (vol. 73, don't
know what pages).  So I see no reason to exclude this stuff from
sci.physics.research.  Note that even old questions can admit new and
interesting answers.  The moderators will exclude questions that have
been asked 10^6 or more times on sci.physics (and, I hope, continue to
compile a list of such questions), but not questions that have been
dealt with in (e.g.) Courant-Hilbert.  The moderators also get to decide
whether *answers* should be posted, emailed to the questioner, or posted
on sci.physics.

2.  About a year ago, someone posted a paradox involving a collision
    between an infinitely massive object and an object of finite mass. The
    resolution hinged on the fact that momentum depends linearly on
    velocity (in Newtonian dynamics) but energy depends quadratically.

    The level here is high-school physics, the math just algebra.  I found
    it a fun puzzle to work out; I wish I'd seen it in high-school.

--
A borderline case in my mind.  What do other moderators think?  I 
would be inclined to let it in but exclude all but one article that
resolved the puzzle - or perhaps, if I was feeling energetic, I would
include it and append a brief resolution myself.  Real physicists can 
stand an article like this, but not what often occurs on sci.physics - a 
protracted thread, all too often full of invective and misinformation.

3.  I asked recently about the QM explanation of ferro-magnetism, and got a
    couple of very informative posts.

--
This seems fine to me.  As with 1, a REALLY GOOD answer could easily work its
way up to research-level physics.

4.  QM at all levels generates a lot of questions.  Some recent examples:
    (a) What is the "size" of an elementary particle?  (b) What is the
    difference between angular momentum in classical physics and in QM?
    (c) Why do eigenstates of the position operator "spread out" with time,
    while eigenstates of the momentum operator do not?  (d) Why is the
    angular momentum of a free particle quantized, when the momentum isn't?

--
In the best of worlds all of these would be in the FAQ, but that'd require
a FAQ that's pretty close to a course on quantum theory.  In the meantime,
I think that sufficiently informative answers to these things deserve to be 
posted.  What do other moderators think?  

5.  GR also generates a lot of questions.  I'll give one example, from
    maybe a year ago: does it make any sense to ask whether the universe as
    a whole is rotating (Mach's principle, Newton's buckets)?

--
This is a hoary old chestnut -- precisely the sort of thing that tends to lead
to endless pseudophilosophical divagation -- so the basic question should be
in the FAQ, and fairly stringent requirements should be placed on further
discussion of it.  (In general, I guess I want to be tougher on topics that
lead to murky philosophizing -- "does time really exist?" -- and gentler on 
topics that, while elementary, are clearly physics and admit terse and
correct answers -- "what is a radionuclide?"  In the latter case I would admit
the question but encourage answers via email.)

I too think that sci.physics.moderated would be a better name for what
I'm after, but somehow when I came back from Christmas break sci.physics.research
is what it was called; I don't care about the name so much but I would
like other moderators to say a bit more about what they think the group 
should be like.  There seems to be a sentiment among the moderators that
about 20 posts a day is a nice volume level, and if that were a goal 
each moderator would aim to accept about 5 posts a day, and deal with the
quality issue accordingly, though one shouldn't be too constipated about this
sort of thing. 

 
Newsgroups: sci.physics,alt.sci.physics.new-theories