HDTenEightyP/NetNews huggingface dataset:
From: westes@sti.com (Will Estes)
Subject: Question On Physics Of Sailboards
Organization: Mail Group
Date: Wed, 9 Sep 1992 05:53:33 GMT

I had an interesting discussion with someone recently regarding the
physics of sailboards in two distinct situations.  I wanted to submit
the situations to this group for further discussion.

A windsurfer is moving down the river in two distinct situations:

Situation one: The current is moving at 5 knots/hour, in the same direction 
as the wind itself.  The wind is moving at 30 mph.  The windsurfer is moving 
with the current at 35 mph relative to an observer on land.

Situation two: The current is moving at 5 knots per/hour, but in the
opposite direction of the wind itself.  The wind is moving at 30 mph.
The windsurfer is moving against the direction of the current, and with
the direction of the wind, at 35 mph relative to an observer on land. 

Now, here's the question: if the windsurfer's board were to separate
from the windsurfer and his rig in both of the situations above, would 
the windsurfer have more difficulty catching up to the board in situation one?

One of us argued as follows: "In situation one, both the board and
windsurfer are moving at 5 knots/hour in the same direction.  Therefore,
the windsurfer will be able to catch up to his board at the same
relative speed that he would in situation two."

The other of us argued as follows: "In situation one, the board has far
less surface friction when lying flat on the water than does the
windsurfer.  An object in motion tends to stay in motion, and in
situation one both the current of the river and the wind will tend to
keep the board in motion for a longer period of time than in situation
one.  Therefore the windsurfer will take longer to catch up to his board
in situation one than in situation two."

Which of us is right? (Probably neither of us, but we're here to
learn....)

Another question: assuming that both the sailor and the board are
initially at rest, would there be any reason to believe that in
situation one the board would reach a higher speed relative to an
observer on land than would the windsurfer (due, again, to the
relatively lower surface friction of the board)?
-- 
Will Estes		Internet: westes@netcom.com
Newsgroups: sci.physics
From: terry@aslws01.asl.dl.nec.com (Terry Bollinger)
Subject: Re: Wave/particle duality
Keywords: photon,particle,dual slits,interference,quantum waves
Organization: NEC America, Inc. Irving, Texas
Date: Mon, 14 Sep 1992 03:23:41 GMT

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.

(One wonders how the particle-wave debate would have unfolded had it first
been undertaken by wise old owls instead of half-blind humans...)

				Cheers,
				Terry Bollinger
From: sichase@csa2.lbl.gov (SCOTT I CHASE)
Newsgroups: sci.physics
Subject: What We Don't Know (YET!) (Was: Black hole + anti-Black hole = ?)
Date: 9 Sep 92 20:10:45 GMT
Organization: Lawrence Berkeley Laboratory - Berkeley, CA, USA
Distribution: world
Reply-To: sichase@csa2.lbl.gov
NNTP-Posting-Host: 128.3.254.197
Keywords: FAQ, ignorance
News-Software: VAX/VMS VNEWS 1.3-4   

In article <1992Sep9.052443.8026@galois.mit.edu>, jbaez@riesz.mit.edu (John C. Baez) writes...
> 
>It might be worth setting up a "we don't know list" for the physics FAQ.
> 

I'm game.  Any suggestions?  While we're at it, I was thinking that we
might start a "Jargon File" entry as well.  Anyone who cares to float 
suggestions on that topic as well are hereby invited to do so.

-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: jbaez@riesz.mit.edu (John C. Baez)
Newsgroups: sci.physics
Subject: Re: Did electric/magnetic symmetry "break"?
Date: 7 Sep 92 21:42:35 GMT
Organization: MIT Department of Mathematics, Cambridge, MA

To repeat myself, I don't think there is any asymmetry between electric and
magnetic charges of the form "magnetic charges (if they exist) must be
68.5 times as big as electric charges."  This seeming asymmetry is
just an artifact of a particular system of units.  

Recall Dirac's argument.  If you move an electric charge counterclockwise
around a loop through a magnetic field its wavefunction is multiplied by
a phase

exp(ieF/hbar)

where e is its charge and F is the magnetic flux through the surface
spanned by the loop.  

Now suppose our electric charge moves around on the surface of a
sphere of unit radius enclosing a magnetic monopole of magnetic charge m.
Then the magnetic field is normal to the surface of the sphere and of
strength m.  If we move our charge around a loop enclosing an area A, 
the flux enclosed is mA so the phase shift is

exp(iemA/hbar)

But, as I explained more carefully in my posts on braids (hint,
hint! - they're free!), we can equally well think of this loop as going 
clockwise around an area 4pi - A.  Here 4pi is the area of the sphere, and 
the point is that if you take a bike tour counterclockwise 
around the border of Russia you can equally well say you're going
clockwise on a tour around the border of "all of the world
that's NOT Russia".  So we can alternatively compute the phase shift
to be

exp(iem(A - 4pi)/hbar)

These two have to agree so we must have

exp(4 pi iem/hbar) = 1

or in other words, 2em/hbar must be a multiple of an integer.   Note that
this condition is PERFECTLY SYMMETRICAL BETWEEN MAGNETIC AND ELECTRIC
CHARGES.  Indeed, we could equally have ran the argument the other way
and thought about moving a magnetic monopole around a electric charge.

Okay, so I got that weird factor of 2 that's floating around.  Where's
the fine structure constant coming from?  That must be an artifact of
your units!   The argument does NOT say that magnetic charges are
bigger than electric ones!  It says that the bigger the fundamental
unit of electric charge is, the smaller the fundamental unit of
magnetic charge is.

In case anyone feels like flaming, yes, I know that nobody has seen a
magnetic monopole, and no, I don't believe in them.  This is a summary
of some speculations by Dirac on WHAT IF there were magnetic monopoles.
From: platt@watson.ibm.com (Daniel E. Platt)
Subject: Re: Where do physics graduates look for work?
Date: Thu, 10 Sep 1992 19:18:50 GMT
Distribution: na
Disclaimer: This posting represents the poster's views, not necessarily those of IBM
Organization: IBM T.J. Watson Research Center

In article <1992Sep10.172502.1750@linus.mitre.org>, m14494@mwvm.mitre.org (Mike White) writes:
|> In article <1992Sep10.153848.1215@nntpd.lkg.dec.com> 
|> abbasi@star.enet.dec.com  writes:
|> > Ok, you worked hard to get your physics degree, now what do you do?
|> > where do you look for work? 
|> 
|> Job training time: repeat after me...
|> 
|> "Do you want fries with that?"
|> 
|> ************************
|> * These are my opinions only.*
|> ************************

There's a folk song called "I Don't Know Where I'm Going, But I'm Going
Nowhere in a Hurry Blues," whose first verse goes something like:

Beverly Jones got a PhD in Physics, 
 and went to town to look for some work.
They told her, she was qualified 
 to be a secretary, or a clerk.
The word was out on the day she was born,
 but she was 20 years getting the news...
I don't know where I'm going, but
 I'm going nowhere in a hurry blues.

Its sort of funny... we were so happy to have Reagan for president (well,
some Americans, anyway) because he seemed so much more upbeat than
Carter, who seemed so depressing and guilt ridden (shake off those watergate
blues).  In any case, we were happy to make lots of money in the markets,
selling each other the product of other nations, while we merged, disolved,
and sold our industry to other countries, and spent precious little on real
R&D (less and less as time went on).  We seem to feel we cannot make money
trying to compete with the Japanese or the Germans or the <your favorite
foreign competitor here>.  But we don't have to feel bad about it, its the
feel-good generation; lets just put more debt on our credit cards...  In
the meantime, university funding is cut; the number of students entering
universities is declining.  

My hope: it won't last forever.  There's still good physics to do, and places
to do it in.  If the economy takes much longer to turn around, the only way it
could is if people start making new things to sell to each other competitively.
It will take some good science to do that.

Dan
Newsgroups: sci.physics,sci.math
From: lfoard@Turing.ORG (Lawrence C. Foard)
Subject: Computability of the universe
Organization: The Turing Project, Charlottesville Virginia.
Date: Thu, 10 Sep 1992 02:19:39 GMT

I've been arguing with several people over the "reality" of irrational
numbers. By reality I mean a process in the real world that "operates"
on irrational numbers. This is not to say that irrational numbers are
meaningless since they represent the limiting case of many "real" things as
the number of trials go to infinity. 

My argument is that any given single expermental trial must be
able to be >>exactly<< simulated by a finite turing machine in finite
time. 

If this is not the case we have to ask what we have left out of logic
such that its not sufficient to explain the universe. In other words
a world that cannot run on a finite turing machine is no better than
assuming that some God above logic and reason pushs the particles
around :-)

I would like to go even further and say:
The computing power available to us in 1 gram of matter in one cubic meter
of space is exactly sufficient to simulate 1 gram of matter in one cubic
meter of space. In other words there is no inaccessable hidden
reality/machinery. 

In the past problems an incompleteness in physical theories have always
brought revolutions in physics. Maxwells equations not working in Newtonian
relativity, etc.

Who ever solves this puzzle (making finite computable quantum mechanics),
will get Nobel prize, I just wish I knew where to start...  

If you do it remember where you heard it first :-)
-- 
------          Join the Pythagorean Reform Church!               .
\    /        Repent of your evil irrational numbers             . .
 \  /   and bean eating ways. Accept 10 into your heart!        . . .
  \/   Call the Pythagorean Reform Church BBS at 508-793-9568  . . . .
    
Xref: sparky sci.physics:14210 rec.pets.cats:10733
From: sichase@csa2.lbl.gov (SCOTT I CHASE)
Newsgroups: sci.physics,rec.pets.cats
Subject: Re: Radioactive Cat: How Dangerous is She?
Date: 6 Sep 92 19:04:21 GMT
Organization: Lawrence Berkeley Laboratory - Berkeley, CA, USA
Distribution: na
Reply-To: sichase@csa2.lbl.gov
NNTP-Posting-Host: 128.3.254.197
Summary: Questions about hyperthyroidal cat doped with radioisotope
News-Software: VAX/VMS VNEWS 1.3-4   

In article <yfpnc!g.badboy@netcom.com>, badboy@netcom.com (Jay Keller) writes...
>One of my cats has a severe case of hyperthyroidism.  In less than a year
>(she's 9) she's lost over half her weight and is literally wasting away due
>to the extremely high metabolism caused by the disease.  At this point she is
>just about skin and bones although she eats 3 meals a day.
> 
>What questions should I ask of the radiologist?  

I would want to know how long will there be significant radioisotope in 
the animal's feces and urine.  That's a likely source of exposure for young
children, who get messy and ingest anything. 

BTW:  My Nuclear Wallet Card lists only various beta decay modes for 
the isotopes of iodine.  There is no alpha decay listed.

-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: mcirvin@husc8.harvard.edu (Mcirvin)
Newsgroups: sci.physics
Subject: Re: Uncertainty Principle [T.Bollinger => LONG]
Date: 5 Sep 92 20:48:30 GMT

mcirvin@husc8.harvard.edu (Mcirvin) writes:

>[Terry Bollinger's description of Feynman's demonstration of
>the irrelevance of irreversible processes deleted]

I just read the part of the Feynman lectures that actually
deals with this, and discovered that Feynman said more or
less the opposite of what I thought he said-- that in the
blocked Stern-Gerlach apparatus the loss of information from
the presence of the blocking mask is vitally important.
So what he wrote actually agrees with what I said.  The
"disturbance of the particle" that comes from the Stern-
Gerlach apparatus isn't where the event occurs about which
interpretations diverge; it's the blocking mask that does
that, and, of course, the blocking mask only disturbs the
particle in one of the two possibilities.
-- 
Matt McIrvin, Cambridge, Massachusetts, USA 
Newsgroups: sci.physics
From: baez@ucrmath.ucr.edu (john baez)
Newsgroups: sci.physics
Subject: Re: Why do protons outnumber antiprotons?
Date: 5 Sep 92 00:35:11 GMT
Organization: University of California, Riverside

In article <12950076@hpspdla.spd.HP.COM> ric@hpspdla.spd.HP.COM (Ric Peregrino) writes:
>Anti-bosons? What are the properties of an anti-photon?

The party line has it that the photon is its own antiparticle, that is, 
it is invariant under the charge conjugation operator (C).  Irving Segal, 
who holds many heretical views, some of them true, has told me that one
can split up the space of solutions of Maxwell's equations into two summands
in a Lorentz-invariant, nay conformally invariant manner (I guess these must 
be left and right helicity photon states), and that on group-theoretic
grounds it makes some sense to call one of these the photons and the other
the anti-photons (though it's only a matter of convention as to who is the
"anti").   

I don't have a ref on the latter, by the way, though I suppose one of the
series of Segal and Paneitz on "Analysis on Spacetime Bundles" would
do the job.

Anyway, no matter how you go on this erudite issue, antiphotons are just
like photons.
>Ric Peregrino     c/o Hewlett Packard Co.        I represent only myself
>ric@spd.hp.com    1501 Page Mill Rd. Bldg. 5M    I may be wrong, maybe not
>415-857-7526      Palo Alto, CA 94304            Do DC photons exist?
>--------------------------------------------------------------------------
From: raicu@netcom.com (Eugen Raicu)
Newsgroups: sci.physics
Subject: Re: Liquid mirrors (was Re: Rotating Bucket of Water ...)
Date: 10 Sep 92 05:41:35 GMT
Organization: Netcom - Online Communication Services  (408 241-9760 guest)
X-Newsreader: Tin 1.1 PL4

m14494@mwvm.mitre.org (Mike White) writes:
: Emory F. Bunn writes:
: >these [liquid mirror] telescopes are not pointable, which is a problem.  
: > On the other hand, neither is the Arecibo radio dish
: 
: Ummm.... I think it is.  If memory serves, the feed horn is movable over 
: quite a wide range, allowing the beam to be offset from center by
: a considerable angle.

Why not do the same thing with the liquid telescopes?
-- 
Eugen Raicu
raicu@netcom.com
From: m14494@mwvm.mitre.org (Mike White)
Newsgroups: sci.physics
Subject: Re: Liquid mirrors (was Re: Rotating Bucket of Water ...)
Date: 8 Sep 92 17:16:54 GMT
Organization: The MITRE Corporation

Emory F. Bunn writes:
>these [liquid mirror] telescopes are not pointable, which is a problem.  
> On the other hand, neither is the Arecibo radio dish

Ummm.... I think it is.  If memory serves, the feed horn is movable over 
quite a wide range, allowing the beam to be offset from center by
a considerable angle.

************************
* These are my opinions only.*
************************
From: mcirvin@husc8.harvard.edu (Mcirvin)
Newsgroups: sci.physics
Subject: Re: Color of electric charges (silly question)
Date: 13 Sep 92 18:53:09 GMT
Article-I.D.: husc8.mcirvin.716410389
Distribution: na

allenk@harry.ugcs.caltech.edu (Allen Knutson) writes:

>Whenever I see pictures of electrons and protons, electrons are green and
>protons are red. (Please don't anyone confuse this with colors of quarks!)
>I remember it being that way in Mr. Tomkins, I think: does the history go
>back further than that? Has anyone seen the convention reversed?

Because of a science book I read when I was about eight years old,
to this day I see protons as a dull burgundy color and neutrons as
gray.  Electrons are either yellow, or just black dots.  Quarks have
colors associated with their colors, except when I'm thinking about
flavors.  Then, the up and the top are both yellowish, the down and
the bottom are reddish (the top and bottom are bigger and more brown),
the strange is grayish blue, and the charm is pale green.  These
images of quarks probably came from a Scientific American article
or something similar, but I don't know what.  The muon is blue,
and the tau is bright yellow.  The neutrinos are all gray.

Anything associated with gravity is deep black, probably because
of the color of the covers of MTW and Weinberg.

It's interesting that these color assignments are as strong as
they are, since they carry no information and have no mnemonic
value, other than perhaps keeping things straight in my head.
The only part of all this that seems to be widespread is the
tendency to paint protons red, and possibly the gray neutrons
as well.

-- 
Matt McIrvin, Cambridge, Massachusetts, USA 
Newsgroups: sci.physics
From: phfrom@nyx.uni-konstanz.de (Hartmut Frommert)
Subject: Yet another FUQ's (was Re: What We Don't Know (YET!))
Keywords: FAQ, ignorance
Organization: Dept. of Physics, University of Constance
Date: Fri, 11 Sep 1992 13:47:33 GMT

I'll adopt the term Frequently Unanswered Questions (FUQ)..

jbaez@riesz.mit.edu (John C. Baez) writes:

[10 questions: >~ 4 related to GR]

>And [3] more theoretical questions [..]

Since a larger percentage of your FUQ's concerns General Relativity, just one
more:

*  Is Einstein theory of gravity (classical GR) also correct in the 
   microscopic limit, or are there modifications possible/required
   which co-incide in the observed limit(s),  

  [I think of R^2 terms, scalar tensor theories, and non-Riemannian effects]

   or is it completely wrong, i.e.: Is gravity really curvature, or what 
   else -- and why does it then look like curvature ?
--
 Hartmut Frommert                 <phfrom@nyx.uni-konstanz.de>
 Dept. of Physics, Univ of Constance, P.O.Box 55 60, D-W-7750 Konstanz, Germany
                                            -- Eat whale killers, not whales --
Newsgroups: sci.physics
From: matmcinn@nuscc.nus.sg (Mcinnes B T (Dr))
Subject: Re: What do we know about choice of groups?
Organization: National University of Singapore
Distribution: na
Date: Sat, 12 Sep 1992 05:05:57 GMT

matt@physics.berkeley.edu (Matt Austern) writes:
: 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
Yes, no doubt avoiding anomalies, having complex reps etc will guide you
towards the True Group. But it would be nicer if we could arrive at the
TG by some route that would help us to understand what gauge "symmetry"
really IS. I am thinking of what happens in string theory, where you get
E6 as a sort of extended symmetry group of the geometry of the internal
space, at least in the old Calabi-Yau approach.

 
: matt@physics.berkeley.edu         solutions, become a part of the problem!
Xref: sparky sci.physics:14377 sci.math:11195
From: moulding@fnali.fnal.gov (Steven M Moulding)
Subject: Re: Quantitized Length
News-Software: VAX/VMS VNEWS 1.4-a4  
Reply-To: moulding@fnali.fnal.gov
Organization: Fermilab
Distribution:  world
Date: Fri, 11 Sep 1992 03:21:52 GMT

A naive question which I've often wondered about ?

johan@blade.stack.urc.tue.nl (Johan Wevers) says
:>	Quantum gravity and superstring deal with quantisized length
			    ****************************************

How do extended objects like strings fit onto a space-time lattice ?
I can see how point-like particles can sit at discrete points, but what about
strings ? Any insight would be welcome...! Thanks

				Steve

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*            q  /         \ LQ                                                *
*              /           \                    leptoquarks                   *
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