HDTenEightyP/NetNews huggingface dataset:
From: ted@physics.Berkeley.EDU (Emory F. Bunn)
Newsgroups: sci.physics
Subject: Re: photons and gravity
Date: 4 Sep 1992 01:02:57 GMT
Organization: /etc/organization
Distribution: na
NNTP-Posting-Host: physics.berkeley.edu

In article <v4lnjpp@lynx.unm.edu> jfreter@triton.unm.edu (The Myth) writes:

>We know that photons have energy and carry momentum.  We also know that
>these photons are deflected by gravity.  Even though photons have zero
>rest mass, you can calculate an effective mass for any photon (a function
>of frequency).

>Since the photons are attracted by gravity can a massive object (like a
>person or planet) be attracted to the photon?  That is, can the photon
>flux in the universe be enough to close the universe?  Or am I way off
>in my reasoning?


Yes.  The energy in electromagnetic radiation (photons) does indeed 
"gravitate."  In principle, if you had a powerful enough source of light,
you could measure the gravitational force on massive objects near that
light.  (In practice, the effect is way too small.)

At the moment, the energy density of the photons in the Universe is
much smaller than the energy density of the matter, so the question
of whether the density of the Universe is great enough to close the
Universe can be answered (in principle) by measuring only the matter
density, and ignoring radiation.  However, in the early Universe,
the energy density of the photons was much higher, and the Universe
was "radiation dominated."  So the fact that photons are sources of
the gravitational field is very important for people who study
the early Universe.

By the way, the reason the photon energy density got to be so much
smaller than the matter energy density is that photons redshift, and
lose energy, as the Universe expands.  Protons (and other massive
particles) always have their rest mass, so when the Universe had
expanded enough, the massive particles came to dominate the energy
density.

-ted
From: wdb3926@zeus.tamu.edu (BRUTON, WILLIAM DANIEL)
Subject: Rotating Bucket of Water in a Gravitation Field
News-Software: VAX/VMS VNEWS 1.41    
Organization: Texas A&M University, Academic Computing Services
Date: Mon, 31 Aug 1992 03:56:00 GMT

Anyone ever proved that the surface of water in a bucket rotating
in a gravitational field is a paraboloid? 
I remember seeing this problem worked out is some text, but I can't seem to
relocated it.  I seem to remember using Bernoulli's Equation....but
the form of Bernoulli's Equation that I have seen is not gereralized
to rotational motion.
If you could point me to a text or remind me how to solve it that 
would be great.

Thanks,
Dan
From: protonen@daimi.aau.dk (Lars J|dal)
Newsgroups: sci.physics
Subject: Re: My son would like to know about photons...
Date: 28 Aug 92 11:06:04 GMT
Organization: DAIMI: Computer Science Department, Aarhus University, Denmark

phys169@csc.canterbury.ac.nz writes:

>My son asked...
>> If you can split atoms, can you split photons?

[Summery of nice analogies deleted]

>The difficult part was definately explaining high-energy photons producing an
>electron/positron pair.

[More stuff deleted]

>Mark Aitchison.

I'll try an analogy too.
Imagine the photon like a lump of clay. The one-photon-into-two process
would then be like splitting the big lump into two. This will give you
two smaller lumps of clay (two photons with less energy), both like the
original (i.e. both photons).
Now imagine the original lump is not just split into two lumps, the two
lumps are formed like (say) two little men of clay. The pair of men
corresponds to the electron/positron pair. The little men is not just
lump-halves, and the original lump was not made up of two little men.

My point is that although both the original lump (the photon) and the
little men (the electron/positron pair) are made of clay (which would
amount to energy in both cases if you use E=mc^2) none can be called
constituents of the other.

Perhaps somebody can give a better analogy? What about something like
"plastic is made from oil and still oil is not plastic"?

Good luck!

+--------------------------------------------------------------------------+
| Lars J|dal                  | Q: What's the difference between a quantum |
| email: protonen@daimi.aau.dk|    mechanic and an automechanic?           |
|                             | A: A quantum mechanic can get his car into |
| Aarhus University           |    the garage without opening the door.    |
| Denmark                     |                    -- David Kra            |
+--------------------------------------------------------------------------+
                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                                Try explaining this one to your son if you
                                dare (I guess I wouldn't dare myself)!
From: gilligan@bldrdoc.gov (Jonathan Gilligan 303-497-3861)
Newsgroups: sci.physics
Subject: Re: Report on Philosophies of Physicists
Date: 31 Aug 92 21:04:22 GMT
Organization: National Institute of Standards and Technology

In article <1992Aug30.045247.19483@math.ucla.edu> barry@arnold.math.ucla.edu (Barry Merriman) writes:
>In article <1992Aug28.211530.12229@u.washington.edu>  
>mcfarlan@corona.math.washington.edu (Thomas J. McFarlane) writes:
>> It is sad to see scientists display such a disrespectful and arrogant
>> attitude toward philosophy. 
>
>I display and indeed hold such an attitude, and I won't abandon it
>until someone shows me what philosophers have contributed to 
>our understanding of the physical universe.

Please explain how to discuss the problem of measurement in quantum
mechanics (does the wave function collapse?) without entering into the
realm of philosophy?

More fundamentally, try to justify the scientific method and explain
its superiority to religious pictures of nature (assuming, of course,
that you think science _is_ superior ;-) without recourse to
philosophy. We're all philosophers some of the time, even when we have
our scientist hats on. It's just that some of us think that we might
go farther by building on the work of those who have gone before,
rather than reinventing philosophical wheels in ignorance.

Philosophers have not contributed so much to our understanding of the
universe (although Aristotle made some surprisingly astute
observations) as to our understanding of the way we understand the
universe (i.e., how we can justify statements about the universe).
The idea of logical thinking, governed by codified rules of inference,
is only one of those contributions.

---Jon
-- 

Disclaimer --- The government probably disagrees with my opinions.
Newsgroups: sci.physics
From: phfrom@nyx.uni-konstanz.de (Hartmut Frommert)
Subject: Re: fermion in curved space (In e)
Keywords: fermion
Organization: Dept. of Physics, University of Constance
Date: Wed, 26 Aug 1992 12:08:41 GMT

a62178a@ccsparc01.center.osaka-u.ac.jp (kikkawa lab) writes:

>I am studying a behavior of fermions in curved spacetime. In curved
>spacetime fermions couple to spin connectios. I checked the
>hermiticity of the coupling terms( psi*omega*psi ) in several cases 
>( in the case two dimensional sphere and Schwartzshilt metric ).
>Contraly to my expectations, they are anti-hermite. I think this 
>anti-hermitean property of the coupling terms causes disaster. Tell 
>me a remedy of it. Or is my caluculation wrong? 

Since nobody else answered ...

Probably you missed or lossed an "i" somewhere, but since you didn't present
your calculation ...

Th coupling term fermions--gravity in the Lagrangian density reads (in TeX)
$$
L_{fg} = i\hbar * |g|^{1/2} * \omega_{ij\mu} * e_k^\mu *
         \bar\psi (\gamma^3)^{[ijk]} \psi                               (1)
$$     %          ^^^^^^^^^^^^^^^^^^
       %   $\gamma^{[i} * \gamma^j * \gamma^{k]}
where 
  g           metric det
  \gamma^i    (standard) Dirac matrices, $(\gamma^2)^{(ij)}=\eta^{ij}$
  \eta..      Minkowski metric 
  e_i^\mu     tetrad components
  \omega_...  spin connection components, defined by
              $$
              \omega_{ij\mu} = \eta_{ik} \omega^k_{j\mu}
              \omega^i_{j\mu} = e^i_\kappa * (\partial_\mu e_j^\kappa +
                                \Gamma^\kappa_{\lambda\mu} e_j^\lambda)
              $$
  \Gamma^._.. Christoffel connection components

The Lagrangian term (1) is clearly hermitian since
$$
\bar L_{fg} = (-i) \hbar * |g|^{1/2} * \omega_{ij\mu} * e_k^\mu *
                 % ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ all real
              \bar( [\bar\psi (\gamma^3)^{[ijk]} \psi] )
            % ^----------------------------------------^
            % ^= \bar\psi (\gamma^3)^{[kji]} \psi 
            %             ^^^^^^^^^^^^^^^^^^ = - (\gamma^3)^{[ijk]}
            = (-i) ... \bar\psi [ - (\gamma^3)^{[ijk]} ] \psi
            = L_{fg}                                             (!!)
$$
qed. So no disaster, sorry.
--
 Hartmut Frommert, Physics, Univ of Constance, | + Whale killing is murder. +
 P.O.Box 55 60, D-W-7750 Konstanz, Germany | + Eat whale killers, not whales.
 E-Mail: <phfrom@dknkurz1.bitnet> or <phfrom@nyx.uni-konstanz.de>
+    "Windows NoT" expands in German to "Windows Noch Teurer"
+                                                ^even   ^more expensive
Newsgroups: sci.physics
From: kaltef@theo-physik.uni-kiel.dbp.de (Roland Kaltefleiter)
Newsgroups: sci.physics,sci.math,comp.sys.sun.wanted
Subject: Looking for solid-surface-display Software
Keywords: solid,surface,hermann
Date: 27 Aug 92 13:21:44 GMT
Followup-To: sci.physics
Organization: Inst.f.Theoretische Physik, Universitaet Kiel, Germany

Hi !

We are looking for a special software for displaying 
solid-surfaces. There is (?) a software written by "Mr. Hermann"
or so, coming from Berlin (?) (Germany).
Does anybody know where we can get this software ?

We would like to know, if there is some other software doing the same:
- constructing and displaying solid surfaces
- Brillouinzone determination (and display)

Please reply via e-Mail, I will summarize.

Thanks in advande, Roland.

-- 
Roland Kaltefleiter | OFFICE: kaltef@theo-physik.uni-kiel.dbp.de
D-W2303 Tuettendorf | PRIVAT: roland@tpki.toppoint.de
+49  4346  4639     |
In an other world in an other time to come, there won't be MS-DOS.
From: nicho@VNET.IBM.COM
Newsgroups: sci.physics
Subject: Re: Impure Mathematics
Date: 1 Sep 92 09:59:54 GMT
Reply-To: nicho@vnet.ibm.com

In <1992Aug26.220526.9695@noao.edu> Beatrice Muller writes:
>Well, I am sure you could use mathematical terms in a funny way without
>reference to rape. Rape is never funny or cute!
 However the very essence of comedy is treating serious subjects in
a non-serious manner.
 -----------------------------------------------------------------
               ** Of course I don't speak for IBM **
Greg Nicholls ... nicho@vnet.ibm.com or nicho@cix.compulink.co.uk
                  voice/fax: 44-794-516038
Newsgroups: sci.physics
From: zowie@daedalus.stanford.edu (Craig "Powderkeg" DeForest)
Subject: Re: BAROMETERS (was Re: Subject?)
Summary:  off topic but... (note followups!)
Followups-To: talk.politics, talk.bizarre
Organization: Stanford Center for Space Science and Astrophysics
	<ZOWIE.92Sep1122151@daedalus.stanford.edu>
	<1992Sep2.190759.6383@sfu.ca>
Date: 2 Sep 92 09:40:47

In article <1992Sep2.190759.6383@sfu.ca> palmer@sfu.ca (Leigh Palmer) writes:
   zowie@daedalus.stanford.edu [ I ] write:
   >*Everyone* should read at least one economics text.  No exceptions.

   How 'bout those among us who have robust relevant prejudices which require 
   no reinforcement?

Debunk, debunk, debunk!  There're enough conflicting theories out there, that
even a jaded or jaundiced gent like yourself should find no lack of laughable
lunacy in the local library.   By viewing someone else's theory, you just may
change your own preconceptions -- unless, of course, they're well thought out
and researched, in which case, you've probably perused at least one economics
text!

If everyone knew more about economics, they might be less inclined to believe
every liar who comes along claiming to be able to balance the federal budget,
increase spending, *and* not raise taxes...
--
zowie@banneker.stanford.edu  "Tell your senator to fund the MSSTA program!"

 The world would be much better if more physicists read Strunk and White, 
 and if more fuzzies read Tipler.   *Everyone* should read and understand
 at least one economics text.  No exceptions.       -- zowie
Newsgroups: sci.physics,sci.environment,misc.consumers
From: betel@camelot.bradley.edu (Robert Crawford)
Subject: Re: Radioactivity and Superstition; was: Re: Are Your Light Bulbs Radioactive?
Organization: Bradley University
Date:  2 Sep 92 19:07:56 GMT

de5@ORNL.GOV (Dave Sill) writes:

>>	This is not true; ALL organic foods are radioactive (carbon-14,
>>remember?), and potassium contains 0.01% of K-40... so an eight-year-old
>>child (just about hammer-wielding age) has a 'safe and adequate'
>>recommended dietary intake of circa 1 gram of potassium per day...
>>which comes to about two microcuries.

>Which of my statements is not true?  Do you consider organic foods
>concentrated sources of radioactivity?  I think they are only in the literal
>sense, i.e., they're more radioactive than air or water.  But if they are as
>concentrated as the sources in smoke detectors and compact fluorescents, why
>don't the manufacturers just use a chunk of cucumber and remove the warning
>label?

	The reason they don't use a piece of cucumber is obvious --
the cucumber contains an unknown amount of radioactives, while the
piece of laboratory-grade potassium has a known radioactivity. Also,
a cucumber has _more_ radioactive isotopes than a smoke detector.

	Besides, if they put in the cucumber, they'd have to put a
warning on it about how the cucumber will spoil in a while, and would
be unsafe to eat, despite having once been a cucumber.

--
     We'll dream as lovers under the stars:
     Of civilizations raging afar.
     And the ragged dawn breaks on your battle scars
     As you walk home cold and alone upon Velvet Green.
		- "Velvet Green", Jethro Tull
Robert Crawford 			betel@camelot.bradley.edu
Newsgroups: sci.physics
Subject: Re: quantization of angular momentum
From: mcirvin@husc8.harvard.edu (Mcirvin)
Date: 2 Sep 92 00:14:53 GMT
 <1992Sep1.203830.2793@galois.mit.edu> <1992Sep1.222955.21343@riacs.edu>
Distribution: na

danforth@riacs.edu (Douglas G. Danforth) writes:

>In <1992Sep1.203830.2793@galois.mit.edu> jbaez@riesz.mit.edu (John C. Baez) writes:

>>Ouch!  L is quantized under all circumstances.  Its eigenvalues are
>>half-integer multiples of hbar, even for free particles.

>Is the impact parameter in particle scattering quantized?

No, its eigenvalues are continuous; it's just a component of
spatial position.  (And it's only an operator in nonrelativistic QM.) 

Angular momentum, though, always has discrete eigenvalues.

The basic idea is that you can decompose any wave function, whether
it's of a bound electron or a particle traveling freely, into
a sum of waves whose angular variation is described by spherical
harmonics.  The spherical harmonics form a complete set of complex
functions of spatial angle, and they correspond to different discrete
values of angular momentum.  It doesn't matter where you put the
center from which you measure angles, or which way you decide to
point the z axis; you can always do this.  So any spatial wave
function is a sum of discrete angular momentum eigenstates, and
spin is discrete as well.

High-energy physicists often speak of "scattering in the
s wave" or "the p wave" or some other wave, where the letters
mean the same thing they do in atomic spectroscopy.  This kind
of picture is what they are talking about.

Incidentally, picky person that I am, I hereby make a motion
to replace the word "quantized" with "discrete" in this discussion.
"Quantized" is often used to mean "made into a quantum operator,"
rather than "possessing discrete eigenvalues."
-- 
Matt McIrvin, Cambridge, Massachusetts, USA 
Newsgroups: sci.physics
From: dedmunds@selkirk.sfu.ca (Darran Edmundson)
Subject: LaTeX submission to Phys. Rev. ?
Organization: Simon Fraser University, Burnaby, B.C., Canada
Distribution: na
Date: Wed, 26 Aug 1992 23:56:24 GMT

Has anyone actually submitted a paper to Phys. Rev. electronically in
the LaTeX format?

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?

Thanks very kindly,
-- 

Darran Edmundson
darran@chaos.phys.sfu.ca

Newsgroups: sci.physics
From: kumar@ug.cs.dal.ca (kumar yelubandi)
Subject: Re: Subject?
Organization: Math, Stats & CS, Dalhousie University, Halifax, NS, Canada
Distribution: na
Date: Thu, 3 Sep 1992 00:40:46 GMT

In article <1992Aug31.184707.12086@murdoch.acc.Virginia.EDU> crb7q@kelvin.seas.Virginia.EDU (Cameron Randale Bass) writes:
>In article <10524@sun13.scri.fsu.edu> jac@ds8.scri.fsu.edu (Jim Carr) writes:
>>In article <17mijiINN7de@matt.ksu.ksu.edu> lyn@matt.ksu.ksu.edu (Myself) writes:
>>>
>>>    Terminal Velocity- the typing speed at which your keyboard starts to smoke,
>>>causing you to either A) slow down to just below said velocity, or B) talk to
>>>rec.pyrotechnics.
>>>
>>>	Well, that clears that up. On to other things (like another type of 
>>>							terminal velocity ;-}  )
>>
>>Not quite.  Terminal velocity is the maximum speed of a terminal dropped 
>>from a great height. 
>
>     Wouldn't that be 'terminal terminal velocity', or 'terminal^2 velocity'?
>
>                               dale bass



	Unless, of course, the terminal is connected to two other terminals.
	Then you have:    (terminal + terminal + terminal) terminal velocity
	which is just:    3terminal^2 velocity
	which is really:  the velocity of a [cubic terminal changing 
			  with respect to time].     .

        Let's see...if I wait long enough, maybe a terminal shaped like
	Sophia Loren will come crashing down on me.     :)



			Kumar

-- 
                                  *******************************************
   Kumar Yelubandi                 **  I don't believe in a lot           **
   (good wines > good times!)      **  of things. And I quit thinking     **
   ...in the year 2525...          **  six years ago, so...DON'T BOTHER ME!!! 
Newsgroups: sci.physics
From: crb7q@kelvin.seas.Virginia.EDU (Cameron Randale Bass)
Subject: Re: Axiom of Physics
Organization: University of Virginia
Date: Thu, 27 Aug 1992 12:52:30 GMT

In article <5196@tuegate.tue.nl> johan@blade.stack.urc.tue.nl (Johan Wevers) writes:
>frisinv@alleg.edu writes:
>
>>I maintain that the conservation of mass/energy is an axiom.
>
>The conservation of energy is the simple result from the laws of physics
>being invariant w.r.t. the choise of the beginning point in time.
>E.g. as you transform the time coordinate t -> t+a, then all the physics
>will remain the same.
>
>In general, all conservation laws can be derived from some symmetry:
>The conservation from momentum can be derived from the invariance
>from the physican laws w.r.t. (x,y,z)->(x+a,y+b,z+c), charge conservation
>can be derived from the invariance from the Maxwell equations (or the
>QED lagrangian density) w.r.t. gauge transformations, etc.

      I see no problem with the process of assuming the conservation laws to 
      imply the symmetries.  The fact that conservation laws can
      be derived from symmetries certainly does not mean that the
      signposts cannot be placed elsewhere with similar
      consequences.

      'Which is more fundamental' seems like an exercise in semantics
      sometimes.

                                 dale bass

-- 
C. R. Bass                                           crb7q@virginia.edu
Department of Mechanical and Aerospace Engineering
University of Virginia
Charlottesville, Virginia                            (804) 924-7926
From: raicu@netcom.com (Eugen Raicu)
Newsgroups: sci.physics
Subject: Re: Electrons in the body
Date: 28 Aug 92 17:39:48 GMT
Organization: Netcom - Online Communication Services  (408 241-9760 guest)
X-Newsreader: Tin 1.1 PL4

bwallet@apssgi.nswc.navy.mil (Brad Wallet) writes:
: Could anyone give me a rough estimate of the percent of mass of a human
: body which is made of electrons?  Not important, just curious.
: 
: Brad
: No ideas, no thoughts, no observations, no disclaimer

Assuming equal numbers of electrons, protons and neutrons and
mass of proton = mass of neutron = 2000 * mass of electron we
get mass of electrons = total mass / 4000.
-- 
Eugen Raicu
raicu@netcom.com
From: sichase@csa3.lbl.gov (SCOTT I CHASE)
Newsgroups: sci.physics
Subject: Re: My son would like to know about photons...
Date: 26 Aug 92 19:41:12 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 <1992Aug26.142916.533@csc.canterbury.ac.nz>, phys169@csc.canterbury.ac.nz writes...
>I have a question on behalf of my 9-year old son...
> 
>If you can split atoms, can you split photons?

The simple answer (not completely satisfactory from an adult point of view)
would be "No."  "Splitting an atom" refers to breaking up its nucleus, which
is a composite object composed of neutrons and protons.  But a photon
is fundamental.  It has no constituents and therefore cannot be split
anymore than an electron or quark (so far as we know) can be split.

-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
Newsgroups: sci.physics
From: markh@csd4.csd.uwm.edu (Mark)
Subject: Re: Nevada Casino - 200 miles up
Organization: Computing Services Division, University of Wisconsin - Milwaukee
Date: Sun, 30 Aug 1992 17:37:45 GMT

In article <64161@cup.portal.com> Eric_S_Klien@cup.portal.com writes:
>I have some questions that people don't seem to be able to answer in 
>sci.space.
> 
>Situation:  I need to place a casino 200 miles over Nevada with a 
>tether below it for elevators.  I have access to 2026 AD technology.  
> 
>Questions:  What amount of power would the casino need to stay over 
>one spot in Nevada?  What would be a good source of this power?  What 
>should the tether be composed of?  What will be the weight capacity 
>of the tether?  

Attach the casino by a series of cables to large massive buoys placed up in
geosynchronous orbit.  The structure will be self-supporting if the marierials
can handle the stresses.
Newsgroups: sci.physics
From: bhoughto@sedona.intel.com (Blair P. Houghton)
Subject: Re: Radar Invisibility
Keywords: Snarfy's Street Sheet Tech Briefs
Organization: Intel Corp., Chandler, Arizona
Date: Wed, 26 Aug 1992 16:11:52 GMT

In article <4103@cruzio.santa-cruz.ca.us> snarfy@cruzio.santa-cruz.ca.us writes:
-   In this regard,
-   it is interesting to note that magnetic resonance drives the electrons in
-   an iron specimen (such as a Navy destroyer) into a condition  of  uniform
-   precession.  The precession of an electron describes a cone. A precession
-   cone describes a vortex.
-
-     Electrons in magnetized iron precess at the frequency:
-
-   eq.3                           Wp = yUoH
-
-     Where (H) is the applied magnetic field and  (y)  is  the  magnetogyric
-     ratio (e/m) . Uo is the permeability constant.
-
-                     Transcribed from a QPKD fax from Malnex

In other words, the Philadelphia Experiment confirmed the
idea that you can cook an entire ship and crew with
microwaves.

				--Blair
				  "'Precess?'  I thought you said
				   'recess,' so I started a game
				   of dodge-ball..."
Xref: sparky sci.physics:14008 sci.environment:11008 misc.consumers:16031