HDTenEightyP/NetNews huggingface dataset:
Newsgroups: sci.physics
Subject: Re: Magnetic lenses
From: mcirvin@husc8.harvard.edu (Mcirvin)
Date: 28 Jul 92 23:57:42 GMT

gr1c+@andrew.cmu.edu (Greg Howard Rhodes) writes:

>Would it be possible to use a strong stationary E and/or M field to bend
>light in such a way to mimic an eyeglass? And if it would be possible, how
>strong would the field have to be? (and, from a consumer standpoint, how 
>small could it be made?

No, not at any human-feasible scale, because electromagnetic
fields carry no electric charge or magnetic moment, and therefore
do not interact with themselves (see qualifications below!)  Therefore
you can superpose electromagnetic fields linearly in classical E&M;
light beams do not scatter off of each other; and light beams are
not bent by electromagnetic fields.

Qualification 1:  Electromagnetic fields *DO* self-interact
quantum-mechanically, by the exchange of charged particle-
antiparticle pairs.  However, this effect is extremely feeble,
since the leading term in the coupling is proportional to the 
square of the fine structure constant 1/137, and scattering
probabilities for photons would be proportional to the square
of *that*.  I don't know if the effect has even been observed
experimentally.

Qualification 2:  Electromagnetic fields also self-interact
gravitationally, but this effect is much tinier: for rough
order-of-magnitude calculations you can replace the energy in
the field with mass E/c^2 and consider the resultant
gravitational lensing.  (Though, to avoid rehashing arguments
we've been having for weeks, I must stress that this will 
*only* give you order-of-magnitude estimates.)

To a very good approximation, then, light is
not bent by electric or magnetic fields.  It's the same
approximation you're doing when you use Maxwell's equations
classically, so that fields superimpose linearly.

-- 
Matt McIrvin  mcirvin@husc.harvard.edu
From: jbaez@riesz.mit.edu (John C. Baez)
Subject: Calculating the mass of a charged point particle
Organization: MIT Department of Mathematics, Cambridge, MA
Date: Tue, 28 Jul 92 22:55:12 GMT

NOTE: John C. Baez is the author of this article.  I am only using my
account to post this article for John as a favor - Mark Corscadden

I found the following amusing argument in New Perspectives in Canonical
Gravity by Abhay Ashtekar, a book which I recommend to everyone
interested in classical and especially quantum gravity.  It's rather
hard to get, alas; it's put out by Bibliopolis, a firm in Naples.

Don't take it too seriously.  It's an attempt at deriving the mass of a
charged point particle only using a little of the philosophy of GR, and
no quantum theory.  Say one has a little spherical shell of "bare mass"
m and charge e, and radius r.  Then the total energy of the shell is the
energy due to the mass plus the energy due to the electric field; if we
set c = 1 we get that the "total mass" (due to the total energy) of the
shell and its accompanying field is

	m(r) = m + e^2/r .

Clearly this approaches infinity as r -> 0.  This is of course the old
problem of the self-energy of the electron, which bugged Lorenz long
before quantum field theory was around.  But say we also keep track of
the potential energy due to gravity... i.e. the gravitational
self-energy.  Then

	m(r) = m + e^2/r - Gm^2/r .

This again diverges as r -> 0 unless we fine-tune the bare mass and the charge
so that e^2 = Gm^2, i.e.  m = e/sqrt(G).  But now let's steal an idea
from general relativity and say that ALL energy contributes to the
Status: O

source of the gravitational field.  Then we get

	m(r) = m + e^2/r - Gm(r)^2/r !

This is trickier but we can solve it for m(r) and get 

	m(r) = r/2G(-1 + sqrt(1 + (4G/r)(m + e^2/r)) !

Now as r -> 0 we get 

	m(r) -> e/sqrt(G) ,

the result we had to get by "fine-tuning" before.  As Ashtekar points
out,

1) The answer is finite; gravity automatically regularizes the limit.

2) The answer is independent of the bare mass m.

3) The answer is crucially nonperturbative: if we expand m(r) as a
Taylor series in G before taking the limit as r -> 0, each term diverges.

Beginning physicists shouldn't take this calculation too seriously: it
leaves out the strong and weak forces and, much more importantly, all
quantum effects, and only uses a little bit of the idea of general
relativity.  However, it is rather interesting, and hints at the
potential power of nonperturbative quantum gravity in helping out with
the problem of infinite self-energies.

John Baez
Newsgroups: sci.physics,sci.astro,sci.philosophy.tech,talk.religion.misc
From: billn@hpcvaac.cv.hp.com (bill nelson)
Subject: Re: Structure of Time
Organization: Hewlett-Packard Company, Corvallis, Oregon USA
Date: Wed, 29 Jul 1992 00:26:23 GMT

st0o+@andrew.cmu.edu (Steven Timm) writes:
: Could it be that the reason fewer young ladies are interested in 
: physics and cosmology nowadays is because they receive such rough
: treatment at the hands of know-it-all netters?  It seems to me that for
: a little 
: girl of 5 years old to even know about neutrinos and radiation and
: electricity  is quite a bit to ask.

And, just how much does she really know, excepts some words that her
doting father "interprets" for us? Expecting us to believe that such
a young child could have the slightest idea of what she it babbling
about is asking too much - at least for me.

This stuff belongs on one of the alt.* groups not in a sci group.

Bill
From: palmer@sfu.ca (Leigh Palmer)
Subject: Re: Converting the masses
Organization: Simon Fraser University
Date: Wed, 22 Jul 1992 19:38:37 GMT

In article <9868@sun13.scri.fsu.edu> jac@ds8.scri.fsu.edu (Jim Carr) writes:

>It should be added that I do not know of any physicist who works wiht 
>relativistic kinematics -- either nuclear physicists, astrophysicists, 
>or particle physicists -- who use this first definition.  There is the 
>variable W = sqrt(s), where s is one of the Mandelstam variables, known 
>as the total energy that can be used for such purposes. 

Well, Jim, now you do. In the context of those disciplines the conventional
definition of mass is *now* that which you advocate. I surely hope that you
do not use that definition in teaching elementary physics, however, which 
is how some of us astrophysicists make our livings. In order to illustrate
my point, do you claim that a lump of condensed matter has a the same mass
as the sum of the masses of its elementary constituents? Of course you don't.
That only begins the parade of difficulties attendant to using the currently
fashionable definition outside its proper area of use. "Mass" as you use it
is equal to neither inertial nor gravitational mass as those terms apply to
any system more complicated than a particle at rest! To further confuse the
beginning physics student you could explain that the mass of that lump of
matter is independent of its temperature. You could then define a "relativ-
istic mass" which just happens to be identical to its "inertial mass" and,
by the way, to its "gravitational mass". A more parsimonious observer might
argue that, if those three entities are always equivalent to one another,
perhaps it would be conceptually simpler to designate them as the "mass"
and define a related parameter intrinsic to a particle, its "rest mass",
as the derivative, less "fundamental", entity.

For the benefit of those too young to know I will point out that this con-
vention has changed over the years. It caught on about 25 years ago and has
been a problem ever since, especially conceptually. People actually believe
that there is *scientific* justification for their positions regarding this
convention. It is exactly as scientific as the observation that the bird we
North Americans call a "robin" is not a *true* robin! Actually the *only*
justification for the current convention is that one would have to use the 
term "rest mass" rather more frequently in particle contexts than the term 
"relativistic mass". In earlier times both terms were used to minimize con-
fusion.

Leigh
From: melin@hlrz24.hlrz.kfa-juelich.de (Stephan Melin)
Newsgroups: sci.physics
Subject: Re: The Bubbles
Date: 31 Jul 92 16:19:11 GMT
Organization: Forschungszentrum Juelich GmbH (KFA), Germany

In article <Bs9Bts.263@news.larc.nasa.gov>, mark@cmb00.larc.nasa.gov (Mark Flanagan) writes:
|> 
|> Just another bubble question that has been annoying me for some time.......
|> In carbonated beverages, the bubbles of CO2 rise from distinct points
|> in the liquid, usually on the inside surface of the glass.  Why?  What is
|> so special about the surface, and why specific points on the surface that
|> yield a stream of bubbles?
|> 

Nucleation. Its the same reason why water in the gaseous phase forms 
little droplets (condensation) on surfaces.  

-- 
Stephan Melin

melin@hlrsun.hlrz.kfa-juelich.de   ||    hkf418@djukfa11.bitnet
From: sichase@csa2.lbl.gov (SCOTT I CHASE)
Newsgroups: sci.physics
Subject: Re: mass of quarks?
Date: 29 Jul 92 18:48:09 GMT
Organization: Lawrence Berkeley Laboratory - Berkeley, CA, USA
Distribution: usa
Reply-To: sichase@csa2.lbl.gov
NNTP-Posting-Host: 128.3.254.197
Keywords: quark property
News-Software: VAX/VMS VNEWS 1.3-4   

In article <1992Jul29.130925.1147@samba.oit.unc.edu>, John.Matylonek@bbs.oit.unc.edu (John Matylonek) writes...
>has anyone yet determined the mass of a quark?	
> 

Sure.  But it is much more complicated than you would think to assign an
unambiguous number to that mass.

One simple way is to declare that the mass of a quark is 1/2 of the mass
of the lightest meson composed of a quark-antiquark pair of the appropriate
type.  So for example, the J/psi (c - cbar pair) is 3.1 GeV/c^2, so the 
mass of the charm quark could be taken to be 1.55 GeV/c^2.  Similarly,
the mass of the Upsilon (b - bbar pair) is roughly 9 GeV/c^2, so the 
bottom quark is 4.5 GeV/c^2.

But there are other possible definitions.  What I have describe is, roughly,
the "constituent" mass. There is also the "current" mass, and others.
It gets messy. Since nobody has ever trapped a free quark, the definition of
mass in not unambiguous. 

To make things worse, if you could trap a free quark, you might very well find
that they are massless!  That's because of "chiral symmetry restoration," which
may or may not occur near the quark deconfinement phase boundary of QCD. 
Loosely speaking, you heat up some matter until the quarks and qluons are
liberated. If they are massive, then you heat things up some more and when
chiral symmetry is restored they lose their mass.  Cute, huh? 

-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: rmathews@zeus.calpoly.edu (Robert B. Mathews (bob))
Newsgroups: sci.physics
Subject: Re: The Bubbles
Date: 28 Jul 92 21:39:10 GMT
Organization: California Polytechnic State University, San Luis Obispo

mdturner@riker.acs.calpoly.edu  writes:
>Ching-Long Wu (PHYS U790315) writes
>>  I am quite interested in the behavior of the bubbles that floating
>>on water's surface. I have several questions:
>> 1. What's the shape of it? Is it a perfect semi-sphere?
>
>If the water surface were stationary it would have to be a perfect hemisphere.   
>The base of the bubble would change to eliptical as the water's motion  
>incresed.  Size depends on the radius of the bubble (the volume of gas) in  
>comparison to the curvature of the wave. 

Are you sure of this?  I seem to remember, from looking at bubbles,
that the water tends to get pulled up the side of the bubble by surface
tension.  This distorts the bubble, especially with small bubbles.  I
would not expect to find a nice right angle corner where the bubble
meets the water surface...  You would need one to have a "perfect
hemisphere."

swehtam bob
From: jac@ds8.scri.fsu.edu (Jim Carr)
Newsgroups: sci.physics
Subject: Re: Defining Photons
Keywords: Energy transfer instant communications inquisition hearing
Date: 28 Jul 92 19:55:38 GMT
Reply-To: jac@ds8.scri.fsu.edu (Jim Carr)
Organization: SCRI, Florida State University

In article <3946@cruzio.santa-cruz.ca.us> snarfy@cruzio.santa-cruz.ca.us writes:
>
>                       SNARFY'S INQUISITION HEARING

  [most amusing dialog deleted ... thanks, I needed a chuckle today]

>          Arrgh!  If this is so a mass  doesn't  gain  ANYTHING  by  having
>   photons  (Electromagnetic Radiation) incident upon it-zero gain in terms
>   of M as as M relates to E.  Bullhockey!

I never said or implied anything of the sort.  A mass can definitely 
absorb energy from a photon, the simplest and clearest method being 
via Compton scattering where the loss of E and p by the photon appears 
as recoil momentum of the mass.  Both E and vector p are conserved 
and the mass is otherwise unchanged.

>                                           I do not share  your  Faithe  in
>   such  a  dogma,  Frere  Carr, whether or not it be Canonized by the holy
>   Einstein Himself . 

It takes little faith to note the results of experiments.  It should be 
reiterated that E^2 = p^2c^2 + m^2c^4 is accepted because it agrees with 
the results of many experiments for massive and massless particles.  It 
is not that hard to measure E and p for a given m and see the effect; 
just drop by your local accelerator and give it a try! 

>                       This theory means that  things  (massive  ,food-like
>   objects)  do  not  get  warm  (  gain  E , the equivalent of M times the
>   constant C^2) when you cook them in your microwave.   I  have  disproved
>   this  False  Doctrine  hundreds  of  times in numerous Experiments in my
>   Laboratory of Culinary Exorcism with my Miraculous  Device  marked  with
>   the mysterious inscription: ``Sears''.

No it does not.  Your warm food has more momentum and energy (in the thermal 
motion) that it gained by absorbing the microwave photons energy and momentum. 

>   Tortured by self doubt, however ,snarfy concedes:

I doubt it ... at least not until snarfy has something better to do 
than pull our collective leg from the other coast.

--
J. A. Carr                                    |  "The New Frontier of which I  
jac@gw.scri.fsu.edu                           |  speak is not a set of promises
Florida State University  B-186               |  -- it is a set of challenges."
Supercomputer Computations Research Institute |   John F. Kennedy (15 July 60)
From: Richard.Mathews@West.Sun.COM (Richard M. Mathews)
Newsgroups: sci.physics
Subject: Re: Aristotle and the Modern Physicist
Date: 28 Jul 1992 18:16:27 GMT
Organization: Sun Microsystems, Inc.
NNTP-Posting-Host: astro
Originator: richard@astro.West.Sun.COM

matmcinn@nuscc.nus.sg (Mcinnes B T (Dr)) writes:
>But I do claim that many people
>think of gravitation as an "interaction". Which it is NOT; this being
>the main point of GR....
>as Aristotle said, the Earth goes around the Sun on an
>approxiamtely elliptical orbit NOT because it is being "forced" to do
>so, NOT because it is"interacting" with the Sun, but rather because it
>is NOT interacting with the Sun.

GR says that matter "interacts" with the surrounding space-time by probing
its shape to find a geodesic.  GR also says that space-time "interacts"
with surrounding space-time and matter to determine the shape of that
piece of space-time.  I would say that GR does describe an interaction
between the Earth and the Sun with the shape of space-time acting as the
intermediary agent.

     Richard M. Mathews			G eorge
					 D epression
Richard.Mathews@West.Sun.COM		  B ush casts a
					   G loom on us all
Xref: sparky sci.physics:11652 sci.math:9549
From: andrew@rentec.com (Andrew Mullhaupt)
Newsgroups: sci.physics,sci.math
Subject: Re: Chaos
Date: 24 Jul 92 21:40:55 GMT
Followup-To: sci.physics
Organization: Renaissance Technologies Corp., Setauket, NY.

In article <1992Jul21.211921.17976@galois.mit.edu> jbaez@nevanlinna.mit.edu (John C. Baez) writes:
>In article <1992Jul20.153122.29180@murdoch.acc.Virginia.EDU> crb7q@kelvin.seas.Virginia.EDU (Cameron Randale Bass) writes:
>>In article <1076@kepler1.rentec.com> andrew@rentec.com (Andrew Mullhaupt) writes:
>>>OK but there is still a universal attractor for the N-S equations as
>>>rigorously proved by Foias et. al. 

The hard core theory seems to be well known in 2 space dimensions. I hadn't
remembered this, but a quick look at the literature shows that over the past
ten years, the 2-D case is pretty well worked out. The 3-D case is not done,
but you can get pretty close - to get the 3-D case you need to know that the
do not develop singularites. (Global regularity). In the 3-D case, you can
do stuff, such as Ghidaglia and Temam "Lower bound for the dimension of the
attractor for the Navier Stokes equations in space dimension 3" in the
collection: _Mechanics, analysis and geometry: 200 years after Lagrange_,
M. Francaviglia, ed. North-Holland 1991.

>>     Is this the 'universal attractor' for 2-D NS with periodic and
>>     dirichlet BC's?  

OK, so the rigorous stuff is still at 2-D, but the hope that there
won't be an attractor in the 3-D case looks a bit thin, and getting
thinner as time goes by. Note that there are more different 2-D problems
which have been worked out. I think that helically symmetric 3-D N-S solutions
are an invariant subspace to which this theory applies, too.

>Could someone elaborate a bit more on this idea and what precisely was
>proved?  I find it rather odd.  I seem to recall that the 2-D nonlinear
>Schrodinger equation with cubic nonlinearity is completely integrable
>(let's take periodic boundary conditions, say).  What sort of
>nonlinearities does Foias consider, and what is a "universal attractor"?

Real nonlinearities - like the Navier Stokes equations. You can also
do stuff with complex Ginzburg-Landau, etc.

Later,
Andrew Mullhaupt
Xref: sparky sci.physics:12016 sci.astro:8471 sci.philosophy.tech:2907 talk.religion.misc:13022
From: bhoughto@sedona.intel.com (Blair P. Houghton)
Newsgroups: sci.physics,sci.astro,sci.philosophy.tech,talk.religion.misc
Subject: Re: Structure of Time
Date: 29 Jul 92 22:50:27 GMT
Organization: Intel Corp., Chandler, Arizona

In article <28JUL199218561752@zeus.tamu.edu> dwr2560@zeus.tamu.edu (RING, DAVID WAYNE) writes:
>Entertaining he is. But sci.physics is not a forum for entertainment.

Up yours, junior.

sci.physics is more fun than a barn full of bosons.

				--Blair
				  "Now, about the dippy-bird..."
Newsgroups: sci.physics
From: u108502@beta.lanl.gov (Andrew Poutiatine)
Subject: Re: Noah's formation: The rainbow
Organization: Los Alamos National Laboratory
Distribution: sci
Date: Thu, 23 Jul 1992 14:53:31 GMT



  With all of this talking of rainbows, I was wondering if anyone has seen
in a photo or actuality, a rain-hoop.  That is, from an elevated vantage point,
a closed circular rainbow.  I haven't bothered to try and work out the 
geometry, but it seems intuitively possible if one were in, say, an airplane.

  Perhaps it isn't possible, any comments?
 	-AIP
From: jac@ds8.scri.fsu.edu (Jim Carr)
Newsgroups: sci.physics
Subject: Re: Noah's formation: The rainbow
Date: 21 Jul 92 14:32:52 GMT
Reply-To: jac@ds8.scri.fsu.edu (Jim Carr)
Organization: SCRI, Florida State University

In article <1992Jul20.224509.15546@fs7.ece.cmu.edu> snyder@henry.ece.cmu.edu (John Snyder) writes:
>
>So, in simple form, what is the correct explanation (including the double
>and triple rainbows)?

If it were simple, it would not be a problem of such long and interesting 
history.  But I will try anyway.  I think a good optics book will discuss 
it, and it can also be found in scattering theory books because of its
role in certain nuclear physics phenomena. 

What happens is that a light ray entering a (assume spherical) drop is 
first refracted towards the normal, reflected from the inside, then 
refracted away from the normal as it leaves.  If you follow a large 
number of rays hitting a drop a different places, you will observe a 
curious phenomenon: there are angles where no rays come out, and there 
is an angle where many rays appear to pile up as they all come out in 
the same direction.  This is the rainbow angle, and leads to a bright 
band with a sharp edge (more or less, this is where the Airy functions 
and numerical work comes in) leading to a dark region.  A second bright
band then appears after the dark region, as a result of TWO reflections 
inside the drop.  There are also supernumerary arcs in the dark region 
between the bows, but these are fainter than the second bow.  

You can convince yourself of some of this by working in 2-D with a 
circle as the raindrop.  It is rather convincing if you are careful. 

The color occurs because water is dispersive and hence the rainbow 
angle depends on color.  The second bow is reversed for reasons that 
one can see only by working out the angles themselves, but it turns 
out that the angles of the first and second bow move away from the 
common center dark region as the wavelength changes. 

--
J. A. Carr                                    |  "The New Frontier of which I  
jac@gw.scri.fsu.edu                           |  speak is not a set of promises
Florida State University  B-186               |  -- it is a set of challenges."
Supercomputer Computations Research Institute |   John F. Kennedy (15 July 60)
From: gl8f@fermi.clas.Virginia.EDU (Greg Lindahl)
Newsgroups: sci.physics
Subject: Re: ZERO Nuclear impact (was: Is car pooling for real? etc)
Date: 25 Jul 92 20:44:00 GMT
Organization: Department of Astronomy, University of Virginia

In article <1992Jul25.195246.6135@murdoch.acc.Virginia.EDU> crb7q@kelvin.seas.Virginia.EDU (Cameron Randale Bass) writes:

>>Please rebut all the Scientific American articles that people have
>>been refering to.
>
>     Sure, if you'll rebut every argument made in AEC-NRC documents over
>     the last 40 years.

Dale, I haven't been taking part in that argument at all. My only
participation has been to point out that you've been making many
claims, without any facts, that contradict the literature, namely the
9-90 Scientific American issue and an additional Scientific American
article on the merits and drawbacks of general use of hydrogen as
fuel. I have made no claims or arguments other than that. I don't see
why I should feel obligated to rebut documents that have nothing to do
with what I've been talking about.

If you like, I could give you a copy of the Scientific American issue
in question. But I'm not holding my breath.

>     However, feel free to present in this forum what you think valid 
>     arguments against what I have said, or for some position you think
>     plausible, and I will be sure to consider a response.

Valid arguments against many things you have said may be found in the
literature, mainly the 9-90 issue of Scientific American. Please read
it. This is my last post on the topic, we're now going in circles
(repeatedly).