HDTenEightyP/NetNews huggingface dataset:
Newsgroups: sci.physics
Subject: Re: de Broglie wavelength.....
From: mcirvin@husc8.harvard.edu (Mcirvin)
Date: 27 Aug 92 12:28:08 GMT

sci20035@nusunix3.nus.sg (LIM WOOI BENG) writes:

>I want to pose this question which my tutor asked my tutorial group. He
>said that a de Broglie wavelength does not have a corresponding
>wavelength because it does not 'understand' time being in nature a
 ^^^^^^^^^^ I assume you mean "frequency"
>standing wave. Now I would like to ask the people in this group..is that
>a fact....? 

No, it isn't.  Quantum-mechanical wave functions don't have to
be standing waves; they can travel.  Furthermore, whether or
not the wave travels, if it is an energy eigenstate it has an
oscillatory frequency of E/h.  That frequency is ill-defined in
the sense that one can redefine the zero of energy, but *relative*
frequencies between states of different energy are important.

When you solve the time-independent Schrodinger equation to find
a standing wave, what you get is usually defined to be a real
function, and time doesn't appear anywhere in it.  This might be
what your tutor is referring to.  But it's misleading, because
the wave will solve the equation if you give it any complex 
phase, and when you look at relations between different energy
eigenstates it becomes very important that the phase of each
wave is actually rotating with a frequency E/h (or angular
frequency E/hbar).  The time-independent Schrodinger equation
is just a consequence of the time-dependent Schrodinger
equation, which enforces this phase rotation in the complex
plane. 

After all, the standing waves you can make in a telephone
cord oscillate in time too, even though they don't go anywhere.

If all you want to do is find the energy levels in a static
potential, this isn't important.  If you want to find out
how a certain initial state evolves, it's critical.

-- 
Matt McIrvin, Cambridge, Massachusetts, USA 
Newsgroups: sci.physics
From: danforth@riacs.edu (Douglas G. Danforth)
Subject: Is coulomb scattering unique?
Keywords: nonlinear field interactions
Organization: RIACS, NASA Ames Research Center
Date: Fri, 4 Sep 92 19:50:42 GMT


Does the differential scattering cross section for
coulomb scattering force a point particle interpretation
of the interaction process?

Is it possible to construct an extended (to some extent)
nonlinear field interaction (in the small) that gives 
the coulomb scattering cross section (in the large).

If so, what is the class of nonlinear fields that admit
such solutions?

- D. G. Danforth

Newsgroups: sci.physics
From: larsen@mace.Princeton.EDU (Michael Larsen)
Subject: Re: Less Groups! More Representations! (was: Symmetries, groups, and categories)
Organization: Princeton University
Distribution: na
Date: Fri, 4 Sep 1992 03:10:08 GMT

In article <22035@galaxy.ucr.edu> baez@ucrmath.ucr.edu (john baez) writes:
>In article <COLUMBUS.92Aug25114146@strident.think.com> columbus@strident.think.com (Michael Weiss) writes:
>
]As to the original topic, "should the first course in abstract algebra
]teach something about group representations", I'd say yes.  In fact such a
]course often does. 
>
>Often?  You're lucky.  I've never run across it.
>
>I would be happy with a little, as opposed to none, which is all I've
>ever seen.  Glad to know there are some better schools than the ones
>I've been to.  :-)
>
Well, Michael Artin's algebra text certainly discusses representation
theory, even going so far as classifying the irreducible representations
of SU_2.  I believe the book grew out of course notes for the undergraduate
algebra course at MIT.

>I only suggest this because the standard excuse for not including any
>group rep theory is that there's not enough time.  If it was a matter of
>one or the other I'd skip the Sylow stuff.  
>
I will be teaching the "Abstract Algebra" course at U. Penn next year,
using Artin as the text.  I hope to cover the Sylow theorems, but 
representation theory is non-negotiable.

						-Michael Larsen
From: ghenzie@phad.hsc.usc.edu (Gregory M. Henzie)
Newsgroups: sci.physics
Subject: Magnetic Resonance, T1, and T2
Date: 30 Aug 1992 18:52:06 -0700
Organization: University of Southern California, Los Angeles, CA
NNTP-Posting-Host: phad.hsc.usc.edu



A simple question on magnetic resonance:

Why does T1 for a substance typically increase with increasing magnetic
-- 
"All you people of Earth are IDIOTS!"           | ghenzie@phad.hsc.usc.edu
                   -Eros                        | All opinions expressed herein
                   "Plan Nine From Outer Space" | are solely mine!
From: andrew@rentec.com (Andrew Mullhaupt)
Newsgroups: sci.physics
Subject: Re: Axiom of Physics
Date: 28 Aug 92 02:04:56 GMT
Organization: Renaissance Technologies Corp., Setauket, NY.

In article <1992Aug26.174922.6115@pellns.alleg.edu> frisinv@alleg.edu writes:
>A friend and I have a small disagreement about the existance of an axiom  
>of physics. She claims that all assumptions in physics are made from  
>empirical evidence and therefore there are no axioms in physics. I  
>maintain that the conservation of mass/energy is an axiom. Here is my  
>argument: an axiom must be based on evidence. Euclid didn't just say  
>parallel lines don't intersect, he saw evidence that they didn't and then  
>stated the postulate. We have seen that energy and mass seem to be  
>conserved. There is very strong evidence that they are conserved but (to  
>my limited knowlege) there is no proof that they are conserved in all  
>cases. Thererfore, conservation of mass/energy is an axiom of physics. Can  
>anyone think of other axioms of physics?

Quantum mechanics is often phrased in terms of axioms, but even the most
ardent proponent of the quantum theory would have to admit that the axiom is
part of the theory. The experimental connection to reality is _very_ impressive
for quantum mechanics, but in some sense, to the extent that science is
falsifiable, it cannot be axiomatic like say, associativity in mathematics.
Whether you can have non-falsifiable statements in science is a function of
which philosophy of science you subscribe to. If every scientifically
meaningful statement is supposed to be falsifiable, then there are no axioms.

Later,
Andrew Mullhaupt
Newsgroups: sci.physics,alt.sex
From: k044477@hobbes.kzoo.edu (Jamie R. McCarthy)
Subject: Re: BAROMETERS (was Re: Subject?)
Followup-To: alt.barometers
Organization: Kalamazoo College
Distribution: na
Date: Wed, 2 Sep 1992 17:25:13 GMT

jfreter@triton.unm.edu (The Myth) writes:
>zowie@banneker.stanford.edu writes:
>>You are given
>>an accurate barometer.  Your task is to determine the height of the
>>building.  Name at least six ways to accomplish this task.
>
>1) go to the building superintendant.  Tel him (her?), "I will give this
>2) climb to the top of the building.  Throw the barometer off and time how
>3) pace a certain distance out from the building.  Put the barometer on
>4) tie a rope to the barometer and lower it off of the top of the building.
>5) As above, but swing the barometer in pendulum fashion.
>6) Measure air pressure at the bottom and at the top.  find the density
>7) Build an adjustable catapault (variable launch speeds and angles).  put
>
>More?

8) Stand the barometer on the ground.  Measure its shadow, its height,
and the building's shadow.  Similar triangles.
-- 
 Jamie McCarthy      Internet: k044477@kzoo.edu      AppleLink: j.mccarthy
 So I'm rattling the bars around this drink-tank discreetly;  I should pour up
 through the keyhole or evaporate completely, but there'd be no percentage and
 there'd be no proof, and the sound upon the roof is only water...      - TMBG
Newsgroups: sci.physics
From: schinder@leprss.gsfc.nasa.gov (Paul J. Schinder)
Subject: Re: Facts and Values (was Where it came from)
Reply-To: schinder@leprss.gsfc.nasa.gov
Organization: Goddard Space Flight Center
Distribution: na
Date: Tue, 25 Aug 1992 23:54:53 GMT

In <MATT.92Aug25140738@physics16.berkeley.edu> matt@physics16.berkeley.edu (Matt Austern) writes:

>In article <schinder.714773737@leprss.gsfc.nasa.gov> schinder@leprss.gsfc.nasa.gov (Paul J. Schinder) writes:

>> >(3) 1 year = 10^7 seconds
>> 
>> Probably because it's a little more important to astrophysics to get
>> closer to the right number, astrophysics grad students learn that 1
>> year = pi x 10^7 sec (which is almost right).  Along with pi^2 = 10,
>> it comes in very useful.

>Actually, Scott was just slightly imprecise; what he should have said
>is that every high-energy grad student learns that one year is 10^7
>seconds.  

>This is more nearly correct that pi x 10^7 seconds; the point is that
>in one calendar year, it is realistic to assume that you will be
>taking data for about 10^7 seconds.

You're joking!  You mean HEP grad students get to *SLEEP*!!!!  Gee, I
never knew what an incredibly soft field it is!

:-)

>--
>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!
--
--------
Paul J. Schinder
NASA Goddard Space Flight Center
schinder@leprss.gsfc.nasa.gov
From: mcirvin@husc8.harvard.edu (Mcirvin)
Newsgroups: sci.physics
Subject: Re: Quarks, Neutrons, and Mesons...
Date: 2 Sep 92 22:03:40 GMT
Article-I.D.: husc8.mcirvin.715471420
Distribution: usa

seove@mars.lerc.nasa.gov (ERIC OVERTON) writes:

>"Quarks, Neutrinos, Mesons.  All those damn particles you can't
>see.  That's what drove me to drink.  But _now_ I _can_ see them!"

>--S. Harris

I'll have to drink more.

-- 
Matt McIrvin, Cambridge, Massachusetts, USA
From: sichase@csa3.lbl.gov (SCOTT I CHASE)
Newsgroups: sci.physics
Subject: Re: Report on Philosophies of Physicists
Date: 4 Sep 92 03:13:55 GMT
Organization: Lawrence Berkeley Laboratory - Berkeley, CA, USA
Distribution: na
Reply-To: sichase@csa3.lbl.gov
NNTP-Posting-Host: 128.3.254.198
News-Software: VAX/VMS VNEWS 1.3-4   

In article <2726@news.cerf.net>, mitsu@nic.cerf.net (Mitsuharu Hadeishi) writes...
> 
>	Believe me, I have tried to address these issues using
>brief discussions before, and I could do so now if I wanted to, but in
>my experience I have had very little success communicating the
>basic ideas to someone who has not already tried to think about
>these issues in depth.  Although the basic concepts seem rather
>simple and "obvious", I have found that when attempting
>to discuss them with people who have not done any serious
>work in philosophy (Western or Eastern), I cannot seem to make
>myself understood clearly.  I believe the reason is simply that there...
> 
>	In sum, the problems are so subtle and so filled
>with the potential for misunderstanding that I have long since
>given up on trying to explain them in brief.  The only answer

This has got to win the award for the most arrogant post ever to appear
on sci.physics.  Mitsu, that was not easy to do, but you have managed it
anyway.  You are speaking to probably the brightest group of people you
will ever have the good fortune to deal with.  If you can't explain it to them,
then you are probably a complete incompetent.  Since your language skills 
demonstrate that you have a brain, I am forced to conclude that rather 
than incompetent, you are just a self-absorbed fool.

Why did you bother to get involved in this thread in the first place, if you 
knew from the beginning that we would all be unable to grasp the subtleties 
of your wisdom?

If each of us followed your reasoning, and refused to explain anything that
might be too subtle for everyone to grasp every nuance, then there would be
nothing left to post but stupid arguments about funding the SSC and space
potatoes.  Fortunately, we do not.  Rather, we take the attitude, which 
comes from our love of physics, that anyone who wants to play is welcome - 
especially those who are most likely *not* to understand everything, people
who are new to physics but interested enough to want to find out what it's 
about.  Not everyone understands everything, but we have fun.  

-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: baez@ucrmath.ucr.edu (john baez)
Newsgroups: sci.physics
Subject: Re: Length scales in physics 4 - the Planck length
Date: 4 Sep 92 19:42:58 GMT
Article-I.D.: galaxy.22211
Organization: University of California, Riverside

In article <1992Sep2.035552.5982@nuscc.nus.sg> matmcinn@nuscc.nus.sg (Mcinnes B T (Dr)) writes:
>Yes, but what I was getting at was that the target space [in string
theory] was still a
>MANIFOLD, not a bucket of dust or whatever.

Yes, and my point is that this seems to be related with what is WRONG
with string theory, namely, that the strings wiggle around on a
spacetime with a fixed "background" metric.  If you can get strings to
wiggle around on a manifold with no "background" geometrical structure
then you may have a theory of quantum gravity in which 1) the philosophy
of GR is adhered to, namely that all geometrical structures are
dynamical variables and 2) space isn't really all that weird on short
length scales.  But this has not been achieved.

>And it seems to me
>[wrongly?] that in Ashtekarology, you play around with connections and
>holonomies instead of metrics, but everything is still defined on a
>manifold.

Quite true. d

>So there does not seem to be any indication that spacetime
>itself is replaced by anything.

No, it's not replaced by anything.  It is "weird" on the Planck scale,
though, in that its geometry is given not by a metric or connection but
by a linear combination of isotopy classes ( = "topologically different
kinds") of links.  

>Coming back to the metric, though: granted, Ashtekarology does not
>prefer flat metrics. But what exactly happens to proper time?

Ferreting out the dynamics from any quantization of general relativity
is a tricky issue that folks call the "problem of time" - perhaps this
is what you are referring to?  (I'm not sure what your question is
about....)  For now I'll just say that this is hard and various people
in quantum gravity including myself are struggling with it.  In
particular, the isotopy classes of links represent not the geometry of
space at a "given time" but of spacetime!!!   If you ask
something more specific I can try risking a more specific answer.
From: whit@milton.u.washington.edu (John Whitmore)
Newsgroups: sci.physics
Subject: Re: Nevada Casino - 200 miles up
Date: 26 Aug 92 03:21:07 GMT
Distribution: usa
Organization: University of Washington, Seattle

In article <MCGLK.92Aug25023447@bike.rad.washington.edu> mcglk@bike.rad.washingt
on.edu (Ken McGlothlen) writes:
>Eric Klein wants to put a casino 200 miles over Las Vegas, tethered with some
>mystery material.

>One problem is that centrifugal force isn't going to be enough to keep it up
>there.
>at 200 miles, in order for it to stay at 200 miles, must be traveling at around
>17000 mph, which means that it orbits the earth in about (off-the-cuff
>back-of-the-head calculation here) an hour or so.

        That is fine for a single orbiting body; one could, however,
imagine creating a maze of hundreds of orbiting masses, and have the
casino exchange places with one each time it neared the Nevada border.
Because the exchange would be an elastic collision, no fuel or
energy or reaction mass is expended, just a little matter of
connecting a really BIG bngee to a nearby orbiting mass.

	And a small matter of finding enough orbiting matter for
all the counterweights.

        Nevada is roughly 300 mi in each dimension, so you'd need to
attach the bungee every 80 seconds, swing 'around' until the new
station momentum is what the old rock orbit was, in order to keep
'hopping' to a new orbit that keeps it at the right latitude.
By alternating E/W and W/E orbits, you could keep to the right
longitude as well.  Timing the bungee release would be very
important, of course, and the ride would be QUITE jerky.

        Easier, of course, to just engineer a variety of tree that
grows to 200 miles in height...and casts shade on everything
north, up to Tonopah in summer and to Boise in winter.

        Hmm.  That's a political problem, and it suggests an
alternate solution: just have Las Vegas annex the equator, and
use a simple circular orbit.

        John Whitmore
From: tekman@ecn.purdue.edu (Erkan Tekman)
Newsgroups: sci.physics
Subject: Re: LaTeX submission to Phys. Rev. ?
Date: 27 Aug 92 17:24:48 GMT
Distribution: na
Organization: Purdue University Engineering Computer Network

In article <dedmunds.714873384@sfu.ca>, dedmunds@selkirk.sfu.ca (Darran Edmundson) writes:
|> Has anyone actually submitted a paper to Phys. Rev. electronically in
|> the LaTeX format?

Yes I did and I strongly recommend it to everyone.

|> I would be very interested in talking to someone who has been through
|> the process successfully.  Specifically, what style do you use and
|> how do you handle references (BibTeX???) and figure captions?

The best way for electronic submission is to use the macro package REVTEX by
APS staff. Just send a note to tex@aps.org and ask for the details. They will
send you both the macro package and some manuals. The package has all the
necessary thing for referencing, captions etc.

By the way, you may send the figures by e-mail as well, if you have them in
postscript format (not the encapsulated one, though).

Erkan Tekman
tekman@ecn.purdue.edu
Newsgroups: sci.physics
From: wvhorn@magnus.acs.ohio-state.edu (William VanHorne)
Subject: Re: Impure Mathematics
Organization: The Ohio State University
Date: Fri, 28 Aug 1992 13:01:21 GMT

[ discussion of mathematical rape humor crossposted to soc.culture.celtic,
  sci.physics, sci.misc deleted ]

Ok, so tell me, what is it with the title "sci.physics" that makes people
put it in their crossposting lists for no apparent reason? 

Soc.culture.celtic ?

---Bill VanHorne

Who is crossposting from now on to soc.culture.lakers.
From: johan@blade.stack.urc.tue.nl (Johan Wevers)
Newsgroups: sci.physics
Subject: Re: E=mc2?
Date: 31 Aug 92 10:53:39 GMT
Organization: MCGV Stack, Eindhoven University of Technology, the Netherlands.

In article <17sacmINNd2s@darkstar.UCSC.EDU> gross@maxwell.ucsc.edu (Mike Gross) writes:

>But nuclear weapons _do_ turn matter into energy. For a fusion bomb, the key
>point is that a deuterium and a tritium nucleus weigh less than a helium 
>nucleus and a neutron. A gamma ray is also among the fusion products. Thus,
>you have matter + ~10 MeV -> less matter + a lot more energy (grossly
>simplified, of course). This _is_ a conversion from matter to energy. 

The original deuterium and tritium was heavier because it had a larger
binding energy between its parts. That was energy conversed to matter.
You can't separate energy and matter. In nuclear reactions, the binding
energy chanches a lot, so the mass difference is measurable. In 
chemical reactions, the mass-energy  difference is that small that we can't
measure it.

******************************************************************** 
* J.C.A. Wevers                *         u\  _\       /e+        2 * 
* johan@blade.stack.urc.tue.nl *     1 |   \ u \  X  /         |   * 
******************************** P = - |    >   >---<     + ...|   * 
*     The only nature of       *     N |   /   /     \         |   * 
*     reality is physics       *         u/   /d     u\            *
********************************************************************
From: mcirvin@husc8.harvard.edu (Mcirvin)
Newsgroups: sci.physics
Subject: Re: Axiom of Physics
Date: 30 Aug 92 18:19:52 GMT

jac@ds8.scri.fsu.edu (Jim Carr) writes:

>A better example than the one discussed in this thread, the conservation 
>laws, might be the axioms of QCD.  Here one states that the interaction 
>between quarks is governed by the generators of the mathematical "group" 
>known as SU(3), with an empirical coupling constant, and procede to 
>derive or compute the properties of protons etc etc and compare them 
>to experiment.  

If only this could actually be done!  In QCD today, there are usually
a large number of extraneous assumptions that have to be made before the
comparison with experiment can occur, since nobody knows how to calculate
the properties of protons, etc. from first principles.  It is believed
and hoped that all of this will eventually follow from QCD alone, since
QCD is aesthetically appealing and doesn't seem to directly contradict any
of the evidence.  For now we have to rely on things like the parton
model, the infinite-mass approximation for heavy quarks, and other stuff
that is not strictly included in the axioms.  Lattice gauge theory is
closer to doing calculations with QCD directly; it's in its infancy, and
the extent to which it succeeds will depend in part on the availability
of sufficiently capable computers. 

>This is a very abstract starting point.  It is related 
>to the earlier inductive insight into use of the SU(3) group for 
>the description of patterns in the masses of particles, but only in 
>a mostly accidental way.  

For one thing, a different SU(3) is involved.  It's interesting that
the gauge groups that have been incorporated into the standard model 
(SU(3), SU(2), and U(1)) are all groups that originally came up in
different physical contexts (hadron flavors, spin, and nonrelativistic 
wave functions, respectively).  
-- 
Matt McIrvin, Cambridge, Massachusetts, USA
From: mcirvin@husc8.harvard.edu (Mcirvin)
Newsgroups: sci.physics
Subject: Re: FTL
Date: 29 Aug 92 02:58:01 GMT

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

> When you interpret the Dirac equation
>correctly, as a field equation for a field whose "positive-energy modes"
>annihilate particles and whose "negative-energy modes" really create 
>antiparticles (so that it's no longer necessary to have negative energies),
>what you get instead of a Compton-wavelength-sized jitterbug is an
>impossible-to-remove Compton-wavelength-sized uncertainty in particle
>position, which is kind of cute.  All this is done in Sakurai's red book,
>_Advanced Quantum Mechanics._

I should add that Sidney Coleman, in his QFT course, mentioned this
irrevocable uncertainty *in connection* with the problem we are
discussing, though it smelled strongly of handwaving.  He started out
assuming that Klein-Gordon theory was actually a wave theory for single-
particle states, then derived the existence of an exponential tail
outside the light cone for the propagator and stated that, if the
wave equation is taken literally as a single-particle wave equation,
this violates causality.  He then gave as a possible resolution to the
problem the fact that, in the proper interpretation of Klein-Gordon
(or Dirac) theory as a *field* theory, you can't actually set up the
initial condition in which the particle is at a given spot.  If you
try to localize it to within its Compton wavelength or thereabouts,
you will invariably create a hail of particles from the large amounts
of energy required.  I still don't quite understand how this solves
the problem, but it is suggestive.  All Coleman used it for was to
put a nail in the coffin of relativistic QM without field theory.
 
-- 
Matt McIrvin, Cambridge, Massachusetts, USA