HDTenEightyP/NetNews huggingface dataset:
From: matt@physics.berkeley.edu (Matt Austern)
Newsgroups: sci.physics
Subject: Re: What do we know about choice of groups?
Date: 11 Sep 92 15:04:44 GMT
	<26236@dog.ee.lbl.gov>
Reply-To: matt@physics.berkeley.edu
Distribution: na
Organization: Lawrence Berkeley Laboratory (Theoretical Physics Group)
NNTP-Posting-Host: physics.berkeley.edu
In-reply-to: sichase@csa3.lbl.gov's message of 11 Sep 92 18:35:58 GMT

In article <26236@dog.ee.lbl.gov> sichase@csa3.lbl.gov (SCOTT I CHASE) writes:

> >leaving an infinite number, but a much smaller infinity than without
> >that constraint.                ^^^^^^^^^^^^^^^^^^^^^^^
> 
> ??! Are you sure?  They are a countably-infinite set to start with, no?

I just knew somebody would call me on my choice of wording; I was
hoping that if I used sloppy language, I could get away with not
explaining exactly what I meant.

What I meant was that a priori, if all you know is that you want a
simple Lie group, you could choose any of the classical or exceptional
groups, but after demanding that the group have compex representations
(I forgot about this in my last posting!) and that anomalies cancel,
you can eliminate everything except (if I'm remembering right) E(6),
SU(4n+1), and SO(4n+2).

It certainly is true that you start with a countably infinite set and
you still have a countably infinite set, but if you're making a list
of the possibilities, you'll cross out most of the exceptional groups,
and most of the sequences of classical groups, and even some of the
classical groups in the sequences that remain.
--
Matthew Austern                   Just keep yelling until you attract a
(510) 644-2618                    crowd, then a constituency, a movement, a
austern@lbl.bitnet                faction, an army!  If you don't have any
matt@physics.berkeley.edu         solutions, become a part of the problem!
From: voros@vaxc.cc.monash.edu.au (Joe Voros)
Newsgroups: sci.physics
Subject: Re: AT WHAT HEIGHT IS GRAVITY PERCEPTIBLE?
Date: 15 Sep 92 18:08:07 +1000
Organization: Physics Department, Monash University, Australia.

ritley@uimrl7.mrl.uiuc.edu () writes:
> 
> Given most humans' average athletic ability, musculature, metabolism,
> etc. etc. --- at what altitude will a deviation in gravity from sea level
> become perceptible (to someone)?  Any comments?

Well, astronauts on the Moon don't feel any gravity, 'cos they're so far
away from the Earth.  The only reason they don't float away is because
they wear Heavy Boots.

:)  (for the humour-impaired)

-- 
Joe Voros
Department of Physics, Monash University, Clayton, VIC, 3168, Australia.
voros@physics.monash.edu.au
Quantum Mechanics is God's way of telling you to mind your P_i's and Q_j's.
From: matt@physics.berkeley.edu (Matt Austern)
Newsgroups: sci.physics
Subject: Re: Supersymmetry joke
Date: 13 Sep 92 22:58:18
Organization: Lawrence Berkeley Laboratory (Theoretical Physics Group)
Reply-To: matt@physics.berkeley.edu
NNTP-Posting-Host: physics.berkeley.edu
In-reply-to: allenk@molest.ugcs.caltech.edu's message of Mon, 14 Sep 1992 01:43:26 GMT

In article <allenk.716435006@molest> allenk@molest.ugcs.caltech.edu (Allen Knutson) writes:

> Ascribed to Don Finnell:
> 
> "What do you mean, no evidence for supersymmetry? They've already found
> half the particles!"
> 

Not quite...  They still haven't found the superpartners of the stop
and the higgsino.
--
Matthew Austern                   Just keep yelling until you attract a
(510) 644-2618                    crowd, then a constituency, a movement, a
austern@lbl.bitnet                faction, an army!  If you don't have any
matt@physics.berkeley.edu         solutions, become a part of the problem!
Newsgroups: sci.physics
From: bhv@areaplg2.corp.mot.com (Bronis Vidugiris)
Subject: Re: Defining local, causal etc., was: Hidden variable theories
Organization: Motorola, CCR&D, CORP, Schaumburg, IL
Date: Tue, 15 Sep 1992 23:30:18 GMT

In article <1992Sep14.195331.3379@galois.mit.edu> jbaez@riesz.mit.edu (John C. Baez) writes:

)Good, at last!  Now if you use the usual definition of "state" in
)quantum theory, that is, a unit vector in a Hilbert space, or (better)
)density matrix on a Hilbert space, or (better) normalized positive
)linear functional on a C*-algebra, quantum field theories ARE required 
)to be causal according to the definition you offer!  This is, in fact,
)almost exactly the diamond property (which also specifies how big a
)local region you need).  
)
)I know that now you and Daryl and others will pounce on me, saying
)that I am being seduced by mathematical formalism, and that I am
)ignoring how observations "collapse the wave function" or do
)something, at any rate, different than unitary time evolution.  I will
)not respond to such pouncing since this is an argument that I have
)already engaged in to my heart's content.

Unfortunately, your mathematical formalism goes *right over* my head.
Whoosh!  I think what you're saying when you talk about 'density matrix on
Hilbert space' means something roughly similar to saying the state of the
spin of a particle can be represented by a 2X2 matrix, except that it's much
more general.  I can't even guess what the C* algebra stuff is about. 
However, even if I'm correct in that interpretation, it doesn't answer the
main question.  The evolution of the wave function is certainly local -
however, it's collapse is not.  Before, this was 'handwaved away' by arguing
that observable events were not affected by the non-local and problematical
'collapse of the wave function'.  Now, Bell has proven that if one accepts
QM, observable events *are* affected by the collapse.

If wave functions didn't collapse, the world would be a whole lot different.
Schodinger's half-alive and half-dead cats in a 'mixed state' wandering
around would probably be only the start of the strangeness that would be
occuring.  In real life, we don't run into objects that are 'half there'.
Things are either there or not-there, not in a 'mixed state'.

However, it wouldn't affect the evolution of the wave function at *all*
if the collapse mechanism were different from what was assumed.  The
fact that the collapse mechanism isn't Lorentz invariant seems like
another tip-off that something is very, very wrong.  I'm not sure there
would be much difference in the predictions of QM at all if we were to 
change the 'collapse postulate' a bit.  Probably the biggest problem is
determining how to investigate the matter at all.  Bell has given us at
least the start of a handle on how we could do this.

I'm not sure I really understand the implications of a finite 'speed' of
the collapse of the wave function.  I think this means that a particle could
quite literally be in two places at the same time.  Unpleasant as this may
be, I find it less unpleasant than some of the alternatives.
From: G.Joly@cs.ucl.ac.uk (Gordon Joly)
Newsgroups: sci.physics
Subject: Re: Black hole + anti-Black hole = ?
Date: 10 Sep 92 14:38:24 GMT

Jim Horne writes:
 > In article <18jgmmINNm4g@smaug.West.Sun.COM> Richard.Mathews@West.Sun.COM (Richard M. Mathews) writes:
 > >
 > >Now, it bothers me that Hawking evaporation does not conserve lepton and
 > >baryon number.  Something related to gravity just shouldn't be fooling
 > >with such things.  Personally, I think that a TOE will get rid of the
 > >singularity at the center of a black hole (assuming it doesn't get rid
 > >of black holes completely), and it will replace the singularity with
 > >something which does conserve lepton and baryon number.  That would
 > >mean that black holes would have lepton and baryon numbers, though you
 > >might not be able to directly measure those until the hole evaporates
 > >away.
 > >
 > >     Richard M. Mathews			Lietuva laisva = Free Lithuania
 > >					Brivu Latviju  = Free Latvia
 > >Richard.Mathews@West.Sun.COM		Eesti vabaks   = Free Estonia
 > >					        WE  DID  IT!"!
 > 
 > Actually there's a neat argument that says that it is okay for a black
 > hole to violate baryon and lepton number conservation. I heard it
 > second or third hand, so I'm not sure who originated it, but it may
 > have been Sidney Coleman.
 > 
 > The idea is this: we know (or at least believe) that baryon number is
 > violated at high energy. This is the favorite way to explain why the
 > unierse is made of matter and not anti-matter. A popular energy scale
 > to assume for the symmetry breaking is around the GUT scale, or about
 > 10^15 or so GeV. In other words, above a certain energy, there lots of
 > baryon number violating processes.
 > 
 > Now, consider what should happen when we eventually figure out what
 > string theory is telling us about the nature of the classical
 > singularity. If the singularity somehow gets smoothed out, the
 > smoothing will probably be around the Planck scale, so there will be a
 > blob of Planck scale matter in the middle, instead of a singularity.
 > Since the Planck scale is a few orders of magnitude above the GUT
 > scale, matter-antimatter symmetry will be restored in the blob, and
 > baryon number will be freely violated.
 > 
 > Thus, the fact that black holes violated baryon and lepton numbers
 > is not a real problem.
 > ------------------------------------------------------------------------
 > Jim Horne
 > jhh@cosmic.physics.ucsb.edu
 >                                        
 > 	     "Mars is somewhat the same distance from the sun, which is
 > 	     very important.  We have seen pictures where there are
 > 	     canals, we believe, and water.  If there is water, there
 > 	     is oxygen.  If oxygen, that means we can breathe."
 >                                              Dan Quayle, August 11, 1989

Anybody talked about black hole entropy? I believe that Hawking
proposed this.

Gordon,
____

Gordon Joly      Phone  +44 71 387 7050 ext 3703      FAX  +44 71 387 1397
Internet: G.Joly@cs.ucl.ac.uk        UUCP: ...!{uunet,uknet}!ucl-cs!G.Joly
Computer Science, University College London, Gower Street, LONDON WC1E 6BT
From: exuptr@exu.ericsson.se (exuptr@exu.ericsson.se)
Newsgroups: sci.physics
Subject: Re: How do we know individual photons exist?
Date: 15 Sep 92 21:04:21 GMT
Organization: Ericsson Network Systems, Inc.

In article <10740@sun13.scri.fsu.edu> jac@ds8.scri.fsu.edu (Jim Carr) writes:

>Experiments have been done with very low intensities so that there is 
>at most one photon in the apparatus at a time.  The actual interference 
>pattern requires the accumulation of many events, thus representing 
>an ensemble of incident photons, but the process does occur for one 
>photon at a time.  

I think of it as "photon trail dust".

 ----------------------------------------------------------------------------
    "This must be Thursday.  I never could get the hang of Thursdays"
                                                       - Douglas Adams
  - Patrick Taylor                                       (Arthur Dent)
    Ericsson Network Systems
    exuptr@exu.ericsson.se                       "Don't let the .se fool you"
    or exuptr@ZGNews.Lonestar.Org, exu.exuptr@memo.ericsson.se
Newsgroups: sci.physics
From: prim!dave@germany.eu.net (Dave Griffiths)
Subject: Is Spacetime Absolute?
Organization: Primitive Software Ltd.
Date: Sat, 5 Sep 1992 02:24:49 GMT


I understand that special relativity gets rid of the idea of absolute
3D space and absolute time, but is there any such thing as absolute spacetime?

I think what I am asking is, is there an objective spacetime fabric out there
through which all particles move? Or does a different universe exist from the
perspective of every particle?

Um... also... how does an object "know" that it is spinning relative to
the "fixed" stars? (Relative to the object, all it's particles are at rest
and only the universe is spinning).

Dave Griffiths
Xref: sparky sci.physics:14357 rec.pets.cats:10856
From: sichase@csa2.lbl.gov (SCOTT I CHASE)
Newsgroups: sci.physics,rec.pets.cats
Subject: Re: Radioactive Cat: How Dangerous is She?
Date: 10 Sep 92 00:49:33 GMT
Organization: Lawrence Berkeley Laboratory - Berkeley, CA, USA
Distribution: na
Reply-To: sichase@csa2.lbl.gov
NNTP-Posting-Host: 128.3.254.197
News-Software: VAX/VMS VNEWS 1.3-4   

In article <85snlg+.hank@netcom.com>, hank@netcom.com (Hank Roberts) writes...
>sichase@csa2.lbl.gov (SCOTT I CHASE) writes:
> 
>>That's funny.  I had a radium dial watch about 12 years ago.  One day I was
>....
> 
>>-Scott
> 
>The risk of going out in the car is way higher.  There's a cloud chamber at
>San Francisco's Exploratorium that's very instructive; it's several square

Yes. I know.  The technician who built it worked for my research group 
for about ten years.  We're in the Streamer Chamber / Time Projection Chamber
business.  These are both modern day replacements of the cloud chamber.
I work around radiation from a variety of types and am badged as a radiation
worker by my lab, although the badge mostly sits in my desk nowadays, as 
my experiment is over and I'm mostly analyzing data now.  

>feet of surface with a glass plate over it, and under the plate you can
>see tracks (hundreds each moment, maybe many hundreds) of natural background
>radiation. My dad's old radium-dial watch is in a box somewhere on a shelf,
>along with at least one chunk of uranium-bearing ore from my old rock
>collection; by the time the radioactive cat was down to those levels
>I wouldn't worry much about her.

It's really a matter of exposure.  I don't have hard numbers for the 
flux from my watch, but the Geiger counter sure gave a jump every time
I brought it near.  And I doubt they would have bothered manufacturing such
watches with lead backplates if there were negligible exposure. 

There are other considerations as well.  Alphas from radium do not have 
identical effect on human tissue as cosmic ray muons, etc.  But I figured
that I didn't need the exposure regardless of the details.

-Scott
--------------------
Scott I. Chase			"The question seems to be of such a character
SICHASE@CSA2.LBL.GOV		that if I should come to life after my death
				and some mathematician were to tell me that it
				had been definitely settled, I think I would
				immediately drop dead again."      - Vandiver
From: mikey@ontek.com (euphausia superba)
Newsgroups: sci.physics
Subject: Re: Black hole + anti-Black hole = ?
Date: 10 Sep 92 21:27:14 GMT
Organization: Ontek Corporation -- Laguna Hills, California

In sci.physics, jbaez@riesz.mit.edu (John C. Baez) writes:
| to see exactly what goes on really near the singularity in a black hole
| - if it really IS a singularity - we are using a half-baked mixture of
| classical and quantum physics to answer questions like yours, which
| might account for some of the ugly answers.
| 
| It might be worth setting up a "we don't know list" for the physics FAQ.

I think this should be titled _Frequently Unanswered Questions_.

    the krill
From: gilligan@bldrdoc.gov (Jonathan M. Gilligan)
Newsgroups: sci.physics
Subject: Re: Report on Philosophies of Physicists
Date: 5 Sep 92 01:08:18 GMT
Organization: National Institute of Standards and Technology


I think that a lot of people are being too hard on Mitsu. I agree that
it's not nice to say, ``I could explain this, but I won't because you
would probably misunderstand me,'' but I'd love for a physicist to
explain nonrelativistic quantum mechanics briefly and clearly to
someone who doesn't know much physics and explain it in a way that
will not be misunderstood. 

I agree with Mitsu that it's hard to explain philosophical ideas to
people who don't understand the context of what you are saying.  It's
not so much that the ideas are inexplicable, but that you need to
spend so much time giving context. Hume may be fairly easy to
understand, but without Cartesian ideas to give context, you might
well wonder why he goes on so. And how would you ever understand Kant
without having read Aristotle, Descartes, and Hume? Or Hegel without
Kant? or Marx without Hegel?

The preface of Hegel's Phenomonology of Spirit contains a nice
discussion of the dangers of trying to summarize philosophy as results
separate from the process that gave them birth.

In physics too, even book-length popularizations of physics too often
leave lay readers with fundamental misunderstandings about the
material.

However, if you want concise, I can't beat Wittgenstein:

     Whereof we cannot speak, thereof we must remain silent.

Any questions?


---Jon
-- 

Disclaimer --- The government probably disagrees with my opinions.
Newsgroups: sci.physics
From: kim@Lise.Unit.NO (Kim Gunnar St|vring \yhus)
Subject: Re: Report on Philosophies of Physicists
Organization: Norwegian Institute of Technology
Date: Sun, 6 Sep 92 17:51:44 GMT

I have been following the discussion between Mitsuharu Hadeishi and other
people, including myself. He makes bad statements about western philosophies,
in particular boolean algebra, but refuses to tell what he means by
'eastern philosophies', thus making it impossible to discuss. His only comment
when someone talks about logic, is to agree when someone says it's unclear.
(Which it is not)

This would be equivalent to me saying:
"Scandinavian philosophers are better than eastern."
And then refuse to tell anything about scandinavian philosophers.
I will not discuss with Mitsuharu anymore.


As for philosophy. I'm currently studying Quine. He uses 'meaning' the way
I use 'description', 'definition' the way I use 'renaming', and lots more.
This habit of using words very differently from ordinary language, without
much in the way of explanations or redefinitions, seem to be quite common
for philosophers. THIS IS STUPID!

My personal philosophy is a mix of logic, guesswork, and science.

    Kim 0yhus
Newsgroups: sci.physics,sci.math
From: torkel@sics.se (Torkel Franzen)
Subject: Re: Report on Philosophies of Physicists
Organization: Swedish Institute of Computer Science, Kista
	<1992Sep13.145145.22563@CSD-NewsHost.Stanford.EDU>
	<TORKEL.92Sep13174850@bast.sics.se>
	<1992Sep13.191455.24754@CSD-NewsHost.Stanford.EDU>
Date: Sun, 13 Sep 1992 21:01:16 GMT

In article <1992Sep13.191455.24754@CSD-NewsHost.Stanford.EDU> pratt@Sunburn.
Stanford.EDU (Vaughan R. Pratt) writes:

   >Can we split mathematicians into the chiefs and the indians, or since
   >that's politically incorrect these days, the officers and the troops?

  I'm lost in your flood of metaphor. But then there is little to add.
I'll just invite you to reflect on the relative significance to the
mathematical community in the early decades of the century of 1) the
uses of set theory in topology, measure theory, analysis, and 2) the
(far from clear) prospect of interpreting and justifying all of
mathematics in terms of set theory.  Naturally any serious
investigation of these matters would have to proceed by actual
historical investigation, and my claim that 1) was a lot more
important than 2) in establishing set theory among mathematicians is
indeed based only on considerations of plausibility and the ways of
mathematicians. However, presumably there exists work on this in the
history of mathematics.
Newsgroups: sci.physics,sci.math
From: pratt@Sunburn.Stanford.EDU (Vaughan R. Pratt)
Subject: Re: Applied inconsistency
Organization: Computer Science Department,  Stanford University.
Date: Sun, 13 Sep 1992 22:00:52 GMT

In article <88808@netnews.upenn.edu> weemba@sagi.wistar.upenn.edu (Matthew P Wiener) writes:
>In article <1992Sep13.174721.23818@CSD-NewsHost.Stanford.EDU>, pratt@Sunburn (Vaughan R. Pratt) writes:
>>>[#="ZFC is inconsistent"]
>
>>The meaning of ZFC+# as a foundation for mathematics is no
>>different from say ZFC+V=L (all sets constructible), or any other
>>addition to ZFC.
>
>I'd say # is somewhat different, since it is omega-inconsistent.

As it turned out in my example R, your faith in the falsehood of the
(very complicated) Goedel formula # proved to be misplaced, and #
proved to be true in ZFC+#.  This did not imply the inconsistency of
either ZFC or ZFC+#.  Don't put too much faith in long programs or long
statements, all sorts of things can go wrong with them, minor and
major.  In my example # turned out to be based on a misconception about
proofs (equivalently, about arithmetic), embedded somewhere in Q.
-- 
======================================================| God found the positive
Vaughan Pratt   pratt@cs.Stanford.EDU   415-494-2545  | integers, zero was
======================================================| there when He arrived.
Newsgroups: sci.physics
From: danforth@riacs.edu (Douglas G. Danforth)
Subject: Re: Wave/particle duality
Keywords: photon,particle,dual slits,interference,quantum waves
Organization: RIACS, NASA Ames Research Center
Date: Mon, 14 Sep 92 20:16:01 GMT

In <1992Sep14.032341.19533@asl.dl.nec.com> terry@aslws01.asl.dl.nec.com (Terry Bollinger) writes:

>In article <BuJEy1.Gz5@nntp-sc.Intel.COM>
>bhoughto@sedona.intel.com (Blair P. Houghton) writes:

>> Read Feynman's Lectures on Physics, chapters 1-3 of volume III, carefully,
>> and if you start thinking of particles as waves go back and read them again.

>Dr. Feynman was even more explicit in stating that photons and electrons are
>particles in "QED: The Strange Theory of Light and Matter."  In that delight-
>ful little easy-reading book he begins by pointing out that if human eyes
>were about 10 times more sensitive the classic debate about whether photons
>were particles or waves never would have occurred.  In dim light everyone
>would have been able to SEE individual photons banging on their retinas as
>point-like flashes.

Are the photons point-like or is it our eyes that have point-like regions
of activation?

Consider a gentle wave rolling up a beach on which reside preset mouse
traps.  Some will fire (trigger) and some won't.  Is the wave discrete
or is it the mouse traps?

Doug Danforth 
Xref: sparky sci.physics:14257 sci.astro:9533
From: mcirvin@husc8.harvard.edu (Mcirvin)
Newsgroups: sci.physics,sci.astro
Subject: Re: My son would like to know about photons...
Keywords: photon,size
Date: 8 Sep 92 02:00:14 GMT
 <17u6gpINNs9s@smaug.West.Sun.COM> <1992Sep7.060008.14351@CSD-NewsHost.Stanford.EDU> <7SEP199213475340@zeus.tamu.edu>

dwr2560@zeus.tamu.edu (RING, DAVID WAYNE) writes:

>Hmmm. When I was an undergrad I worked in the Caltech VLBI Processing unit.
>We plugged around 8 hours of data taken from radio telescopes around the
>world into the computer. The data was stored on VCR tapes. Since we were
>measuring interference, I always wondered how the phase information could
>be stored on a VCR tape. I would have thought each photon would go into
>one antenna or the other. Any astrophysicists out there?

I'm not an astrophysicist, but I think it might be helpful to
first think in terms of classical electromagnetism.  In a classical
EM wave there's obviously phase information, but no effects from the
discreteness of photons at all.  In classical E&M there's nothing to
stop you from recording the phase of a wave at two different sites
and getting "interference" by comparing VCR tape.

There's nothing to stop you in quantum electrodynamics either, if
you remember that what the wave really is is something very close to
photons in a *coherent* state.  There are many photons produced, and
their phases are *correlated strongly* in such a way that the phase
from the photons captured in California will yield directional
information when compared with the phase from the photons captured
in Massachusetts or wherever. 

The processes that create strong classical electromagnetic waves are
exactly those that produce something very close to a coherent 
state of photons, since a coherent state is the closest thing to
a classical EM wave that really exists.  Oscillating currents in
a transmitting antenna, for instance, will produce nearly
coherent photons, and so, presumably, would the oscillating
currents involved in whatever astrophysical phenomena are being
imaged.
 
-- 
Matt McIrvin, Cambridge, Massachusetts, USA