HDTenEightyP/NetNews huggingface dataset:
From: abbasi@star.enet.dec.com 
Subject: Where do physics graduates look for work?
Organization: Digital Equipment Corporation
Date: Thu, 10 Sep 1992 15:36:40 GMT


Ok, you worked hard to get your physics degree, now what do you do?
where do you look for work? when I mean work, I mean physics/science
related, not flipping burgers.

are there actually physics/science work out there?

what is best references/papers/magazines to help in this regard?

thank you,
/Nasser
From: dwr2560@rigel.tamu.edu (RING, DAVID WAYNE)
Subject: Re: VLBI (was: My son would like to know about photons...)
News-Software: VAX/VMS VNEWS 1.41    
Keywords: photon,size
Organization: Texas A&M University, Academic Computing Services
Date: Fri, 11 Sep 1992 17:44:00 GMT

ryba@ll.mit.edu (Marty Ryba) writes...
>|> I think I understand this explanation, except that I don't see why separate
>|> photons should be correlated since in cases of interest the measured
>|> radiation is thermal.
> 
>   Thermal or nonthermal is no matter - a collection of accelerating charges -
>a classical time-varying current - will radiate a whole mess of photons
>*coherently* creating a spherical plane wave *at a given frequency*.  Thermal
>noise means that the phases of each frequency are uncorrelated, and the
>amplitudes follow some statistical distribution.  Since

Things are getting clearer, but I'm not there yet :-)  I don't see where
the "collection of accelerating charges - a classical time-varying current"
comes in when we are essentially looking at just a hot gas. Or maybe that's
the point of radio astronomy, that we are looking at the currents?

Dave Ring
dwr2560@zeus.tamu.edu
From: G.Joly@cs.ucl.ac.uk (Gordon Joly)
Newsgroups: sci.physics
Subject: Re: Is Spacetime Absolute?
Date: 9 Sep 92 10:40:09 GMT

Dave Griffiths writes:
 > In article <mcirvin.715719878@husc8> mcirvin@husc8.harvard.edu (Mcirvin) writes:
 > >prim!dave@germany.eu.net (Dave Griffiths) writes:
 > >
 > >>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?
 > >
 > >In special and general relativity there isn't a preferred coordinate
 > >frame with which to express positions in spacetime, but there is a
 > >single manifold through which everything moves.  The geometry of
 > >that single spacetime in general relativity depends on the distribution
 > >of energies, momenta, and forces, but statements about the curvature
 > >that results can be expressed in such a way that they are the same
 > >for everybody.  In that sense there is absolute spacetime in these
 > >theories.  What happens when gravity is quantized is less clear.
 > >
 > 
 > Just to muddy the waters, here is a quote from Einstein's Relativity:
 > 
 > "There is no such thing as an empty space, i.e. a space without field.
 > Space-time does not claim existence on its own, but only as a structural
 > quality of the [gravitional] field."

Sounds like the first glimmer of superstring theory (in which
spacetime is made of superstring, as are all particles).
 
 > Part of my confusion results from trying to imagine 4D spacetime. I imagine
 > first of all Euclidean space with the Universe as a big 3D cube, then
 > extend that to a 4D hypercube where it is still possible to assign
 > coordinates (x, y, z, t) to every event and where this 4D spacetime still
 > has an objective existence.

Psuedo Riemannian with signature (+,+,+,-) : think of Minkowski, not Hawking!

 > (Not to mention the problem of, "if spacetime is curved, in what dimension
 > is it curving?" :-)
 > 
 > Where am I going wrong?
 > 
 > Dave Griffiths

It has intrinsic curvature. Like the surface of the globe (globally speaking:-).

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
Newsgroups: sci.physics,sci.math
From: rabjab@golem.ucsd.edu (Jeff Bytof)
Newsgroups: sci.physics
Subject: Not quite so Black Holes...
Date: 13 Sep 1992 03:03:05 GMT
Organization: sio
NNTP-Posting-Host: lutherlab.ucsd.edu

If an alternative to General Relativity is developed, and leads to
a prediction that collapsed stars do not end up getting crunched into
a singularity, what might be the resulting physics of such an object,
which might be much denser than a neutron star?


Newsgroups: sci.physics
From: adamsd@crash.cts.com (Adams Douglas)
Subject: Re: AT WHAT HEIGHT IS GRAVITY PERCEPTIBLE?
Date: 15 Sep 92 02:56:05 GMT

In <BuL1qx.CDz@news.cso.uiuc.edu> 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?

That's really a subjective question. Most humans can detect a change in
acceleration of about a Gal (1 cm/sec) when riding in an elevator
for example. But a gradual change in the gravity field would probably
take a much bigger change to notice.

I guess you're assuming that the subject is in a vehicle which is not in free-fall
and is not rising or falling on the vertical axis, such as a high-altitude
aircraft or a super-tall building. Gravity would drop 10 percent (to .9 G)
on a super-tall imaginary building about 200 miles high. One _might_ notice
that, but I think it would also depend on what G forces the subject felt
on the way up there.

Newsgroups: sci.physics
From: mfm0@ellis.uchicago.edu (martin frederic melhus)
Subject: Re: Size of neutrino
Reply-To: mfm0@midway.uchicago.edu
Organization: University of Chicago Computing Organizations
Date: Tue, 15 Sep 1992 06:46:18 GMT

mcirvin@husc8.harvard.edu (Mcirvin) writes:
(concerning the size of a neutrino - MFM)
>
>Nobody knows!  The only way (outside of something like string
>theory in which particles are treated as extended, floppy
>objects) that a particle can have any size at all is for it to
>consist of smaller components, as long as relativity holds.
>An atom is the size it is because of the distribution of its
>electrons, for instance.  In the Standard Model of particle
>physics, neutrinos (and electrons!) are treated as truly
>fundamental particles, so they have no extension at all;
>they are points.  This doesn't cause physicists much worry
>since most of them believe that the smooth geometry of space
>breaks down anyway at scales below 10^-33 cm, so this picture
>of neutrinos as points rests on an approximation.  But it
>does appear from the data that the picture of electrons, at
>least, as point particles is good to the limit of experimental
>precision.  Neutrinos are harder to deal with.

I seem to remember a upper bound on the size of an electron,
a statement like "we know that an electron is smaller than
10^-x cm in diameter.  Any info on this?  And is there a similar
statement about neutrinos?  It seems likely that they are smaller
than beach balls, but has anyone shown this?  Or are they just too
evasive?
-- 
                          | You have all the time from when you remove the |
     Martin F. Melhus     | card(s) from your hand until you put it (them) |
 mfm0@midway.uchicago.edu | on the pile to say "Last Card".  If you don't, |
                          | take your two. - Hidden texts, Book of MauMau. |
Newsgroups: sci.physics
From: jbaez@riesz.mit.edu (John C. Baez)
Subject: Re: Black hole + anti-Black hole = ?
Organization: MIT Department of Mathematics, Cambridge, MA
Date: Wed, 9 Sep 92 05:24:43 GMT

In article <1992Sep8.222101.9281@math.ucla.edu> barry@arnold.math.ucla.edu (Barry Merriman) writes:

>What happens if you dump some antimatter into a black 
>hole that formed from normal matter? Does it 'cancel out' part of it?

>Or, if I take two black holes, one made from ordinary matter
>and the other made from anti-matter, and merge them, what happens?
>Do I get a bigger black hole, or are they somehow annihilated?

Nobody has ever done these experiments so we don't know.

There - see? - I can act like a wet-blanket experimentalist just as well
as the next guy!  It *is* worth noting, though, that we're talking about
some heavy-duty extrapolations beyond what has been seen, and there are
some very fishy points lurking in this issue.

Anyway, the usual answer is that the "no-hair theorem" shows that the
only properties a black hole has are mass, momentum, angular momentum
and electric charge.  It doesn't know whether you threw matter or
antimatter in.  So if you throw in some matter and then some antimatter,
or a black hole you made out of antimatter, it just keeps getting
bigger.

Of course this is rather upsetting since it means that black holes
violate all the particle conservation laws we know and love, like
conservation of electron number.  I would take it all with a grain of
salt: these particle conservation laws are essentially beasts of
quantum field theory, so until we have a quantum field theory of gravity
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.
From: baez@ucrmath.ucr.edu (john baez)
Newsgroups: sci.physics
Subject: Re: quantization of angular momentum
Date: 4 Sep 92 22:47:35 GMT
Distribution: na
Organization: University of California, Riverside

In article <1992Sep1.222955.21343@riacs.edu> danforth@riacs.edu (Douglas G. Danforth) writes:
>Is the impact parameter in particle scattering quantized?
>D. Danforth

Dunno.  Write it down in terms of position and momentum operators
and I'll tell you - or else ask Scott!  If it's a function of angular 
momentum, it's quantized.

Of course, I sense the answer you're looking for is "no".
From: abbasi@star.enet.dec.com (My name is Nasser Abbasi)
Newsgroups: sci.physics
Subject: Question of Theory of Everything (or Grand Unified theory)
Date: 7 Sep 92 02:20:20 GMT
Organization: Digital Equipment Corporation

Hi,

 read somewhere that a Theory of Everything, or the Grand Unified theory,
 or whatever you want to call it (that will unify the four forces of nature
 in one theory), will be found soon, may be in the next 10-20 years ?!

 my question , will this theory be based on ?
 ie. SuperStrings? relativistic quantum mechanics or what?

 I mean what is currently the most promising direction that people think
 will lead to the unified theory?

 thanks,
/Nasser
Newsgroups: sci.physics
From: haferman@icaen.uiowa.edu (Jeff Haferman)
Subject: Re: Terminal velocity of a raindrop?
Date: Wed, 9 Sep 1992 16:19:52 GMT
Organization: University of Iowa, Iowa City, IA, USA

From article <10647@sun13.scri.fsu.edu>, by jac@ds8.scri.fsu.edu (Jim Carr):
> In article <1992Sep4.122013.9635@den.mmc.com> carlm@iplmail.orl.mmc.com (Carl Morris) writes:
>>After reading some of the posts to this group I'm sure someone
>>out there can help me with my question: what's the terminal
>>velocity of a raindrop?
> 
> I asked my favorite consulting meteorologist (and immortalized-in-a-
> NOVA-program tornado chaser) this at lunch today. 
> 
> As you might guess, he said the answer depends on the size of the 
> raindrop, since some are so small that they are carried around on 
> updrafts inside the storm until they become large enough to fall. 
> With that caveat, the basic answer is that most fall at a speed of 
> "a few" meters per second.  
> 
> I asked him if they had defined a "standard" raindrop and he just 
> laughed.  (Although their storm models distinguish between "rain" 
> and "graupel" and other forms of water, the models are not sufficiently 
> microscopic to worry about the actual drop size.)  He did add that 
> the *shape* of a raindrop is not what most people think it looks 
> like: it is more of an oblate spheroid falling along the symmetry 
> axis, that is, flat side down, rather than an elongated "drop".
> 

There is a common approximation used for spherical raindrops, namely

     V(r) = 965 - 1030 exp[-12 r]

where V is the terminal velocity in cm/s, and r is the droplet radius,
in cm.  [Note that this is valid for droplets with radii greater than 
0.0054 cm, smaller droplets produce a negative velocity in this 
formulation].

For an excellent overview of some physics of raindrops, check out

  T. Oguchi, "Electromagnetic Wave Propagation and Scattering in
Rain and Other Hydrometeors." Proc. IEEE Vol. 71, p.1029 (1983).



Jeff Haferman                            internet: haferman@icaen.uiowa.edu
Department of Mechanical Engineering     DoD 0186  BMWMOA 44469  AMA 460140
The University of Iowa
Iowa City, IA  52242                                 '76 R90S
From: baez@ucrmath.ucr.edu (john baez)
Newsgroups: sci.physics
Subject: Re: Uncertainty Principle
Date: 4 Sep 92 22:57:25 GMT
Organization: University of California, Riverside

In article <5273@tuegate.tue.nl> johan@blade.stack.urc.tue.nl (Johan Wevers) writes:
>From the formalism of QM, you can derive the Robertson equation:
>
>\Delta A \Delta B \geq \frac{1}{2}|<[A,B]>|

Robertson??? Who's he? Was he the first one to note this general fact?
In every class I've taught (and in the book I'm writing) I just call
this the uncertainty principle (making no claims as to any historical
justification for this name -- it just *should* be called the uncertainty
principal).  If it's due to some dude Robertson I'd like to give him 
credit -- even if Cauchy-Schwarz-Bunyakowski-etc-etc-etc deserve most
of the credit, since it's an easy corollary of their inequality.
Newsgroups: sci.physics
From: A. Satish Pai <Pai-Satish@CS.Yale.Edu> 
Subject: Poynting power flux wrong?? 
Originator: pai@opal.CS.Yale.Edu
Organization: Yale University Computer Science Dept., New Haven CT 06520, USA
Date: Fri, 11 Sep 1992 00:26:57 GMT


In the September 1992 issue of SIAM Review, there is an article, "A New 
Conservation Law for Electrodynamics" by Clark Jeffries of Clemson University.

In this, it is claimed that the power flux calculated from the Poynting vector
does not really measure the flow of energy in many systems, and that better
calculations (that start out with the potentials \phi and A) give the right
answers. 

1. For a region of space with static electric and magnetic fields, the Poynting
   vector predicts non-zero power flux even if the fields are maintained by 
   static charges and permanent magnets. 

2. For a radiating antenna, the Poynting vector apparently predicts half the 
   actual power flux. Has this been experimentally observed?

I have a couple of questions. Is the Poynting vector method generally accepted
as being correct? If so, how does it get reconciled with the conservation of
energy (in 1 above)? If not, how come it is often used for calculating power
flux in textbooks? 

-Satish


--
-------------------------------------------------------------------------------
Internet: Pai-Satish@CS.Yale.Edu                       | A. Satish Pai
UUCP:     ...!{uunet,harvard,decvax,ucbvax}!yale!pai   |
Bitnet:   Pai@YaleCS                                   | +1 203 432 1217 [Off.]
Mail:     Box 2158, Yale Station, New Haven, CT 06520  | +1 203 776 7069 [Res.]
-------------------------------------------------------------------------------
Newsgroups: sci.physics,rec.pets.cats
From: rg@msel.unh.edu (Roger Gonzalez)
Subject: deep question.. (was Re: Radioactive Cat)
Organization: Denning Mobile Robotics
	<t#rnaf+.hank@netcom.com>
Date: Thu, 10 Sep 1992 23:45:40 GMT


>>>>> "Hank" == Hank Roberts <hank@netcom.com> intones:

Hank> Me, I'd still keep the kids away for a couple extra half-lives before
Hank> letting the cats sleep with the kids; an extra few days.


Hmm.  I assume that a cat has 18 half-lives....


--
ARTIFICIAL FLOWERS:  Pieces of plastic and metal, crudely fashioned to
  bear a limited, superficial resemblance to real flowers, but with no
  credible attempt to match their internal complexity in terms of form,
  function, or behavior.

ARTIFICIAL INTELLIGENCE: Really smart computers.

Roger Gonzalez - rg@msel.unh.edu     (508) 658-7800 (fax -2492)
Denning Mobile Robotics, 13 Concord Street, Wilmington MA 01887


Newsgroups: sci.physics
From: firth@sei.cmu.edu (Robert Firth)
Subject: Re: And another thing (was Re: QUESTION: General Relativity)
Organization: Software Engineering Institute
Date: Fri, 11 Sep 1992 21:25:10 GMT

In article <11SEP199213115299@utahep.uta.edu> sawyer@utahep.uta.edu (Lee Sawyer) writes:

>  Does gravity bend different frequencies of light by different amounts,

I'd say no, it doesn't.  If it did, wouldn't that violate the Principle
of Equivalence?

Incidentally, doesn't Newton prove this somewhere in his Opticks?  It's
been a long time, and I may misremember.
From: mcirvin@husc8.harvard.edu (Mcirvin)
Newsgroups: sci.physics
Subject: Re: Did electric/magnetic symmetry "break"?
Date: 5 Sep 92 16:21:47 GMT
Article-I.D.: husc8.mcirvin.715710107

terry@aslws01.asl.dl.nec.com (Terry Bollinger) writes:

> o  However, they are highly assymmetrical in their relationship towards
>    matter.  E.g., the electric field has associated with it two particles
>    (among others) called the electron and positron, with opposite charges
>    of (say) 1 unit each.  The equivalent particles for the magnetic field,
>    if they exist at all, would have to have charges with magnitudes about
>    63 times as great.

In what units?  I don't think this is the case if hbar=c=1.

> o  Can the assymmetry of [electric:1] and [magnetic:63] be defined
>    mathematically as a "broken symmetry" -- that is, that at some time
>    very early in the history of the universe *either* of the two fields
>    could have been associated with charges of one unit, with the other
>    one being relegated off to the lesser role of what we now call the
>    "magnetic" field?

In the language of particle physics there is no asymmetry here.  The
different behavior of electric and magnetic fields originates in the fact
that they are derived in different ways from a single four-vector
potential, made up of the electric scalar potential and the magnetic
vector potential.  This four-vector possesses an exact Lorentz symmetry,
and its coupling to matter is described by one quantity, the electric
charge.  Magnetic moments are derivable from there.  The difference
between the electric and magnetic potentials is precisely analogous to
the difference between time and space, or energy and momentum; they 
mix with each other under changes of inertial frame.  

On the other hand, in the standard model spontaneously broken symmetry
is responsible for the difference between electromagnetism and the weak
interactions.

Magnetic monopoles are created in the early universe in some GUTs, but
they are quite different beasts from electrically charged particles, even
when created.
 
-- 
Matt McIrvin, Cambridge, Massachusetts, USA 
Newsgroups: sci.physics
From: firth@sei.cmu.edu (Robert Firth)
Subject: Re: Eating habits; was: Radioactivity and Superstition; 
Organization: Software Engineering Institute
Date: Tue, 8 Sep 1992 12:53:01 GMT

In article <4SEP199208255406@rover.uchicago.edu> frank@rover.uchicago.edu writes:

>	Side note: If you die in our hospital but are a labratory animal
>	rather than a human, we can't bury you normally, but have to send
>	you to a low-level radioactive waste disposal facility.

Really?  I thought all the labs now used lawyers for experimental
purposes - the technicians don't get so attached to them.  But
your comment prompts the thought that, thanks to the population
explosion, the largest source of radioactivity on the planet is
probably humans.

People worried about this fearful invisible killer can therefore
ameliorate the problem by volunteering to be buried in geologically
stable formations.  Form an orderly line on the rim of the Grand
Canyon, please.
Newsgroups: sci.physics
From: tolman%asylum.cs.utah.edu@cs.utah.edu (Kenneth Tolman)
Subject: Re: Computability of the universe
Date: 11 Sep 92 13:06:51 MDT
Organization: University of Utah, CompSci Dept

>This point is important to me, because I care about the real world and
>want to understand it.  And, as best we know, true randomness is a key
>and irreducible component of that world.

Let me make a few comments (I recently wrote a paper to the same effect)
It is possible to deduce that ALL noncompressibility that exists in the
world was produced from quantum amplification.  All information and
complexity arises from this random property.  Computers are incapable of
creating information, they may merely manipulate it.  A nice simple proof
of this is to examine the definition of Kolmogrov complexity.  Our
computers can not take any creative actions at this moment, and hopefully
eventually they will accept this second &*( paper.. 
Imagine the world as unfolding from day one, and imagine the little
crinkles that quantum processes yield.  Some of these become the galaxies,
and much much later it begins in evolution, and each mutation brings
on a richer and richer complexity, until we reach the memetic age of today.
Newsgroups: sci.physics,sci.math