HDTenEightyP/NetNews huggingface dataset:
From: ted@physics1 (Emory F. Bunn)
Newsgroups: sci.physics
Subject: Re: Gravity & Rubber Sheet Analogy Problem
Followup-To: sci.physics
Date: 12 Jan 1993 03:53:31 GMT
Organization: University of California, Berkeley
Distribution: usa
NNTP-Posting-Host: physics1.berkeley.edu
Keywords: gravity, general relativity

In article <79814@hydra.gatech.EDU> gt1057a@prism.gatech.EDU (gt1057a JOHNSTON,KEITH) writes:

(Description of the "rubber-sheet analogy in GR deleted.)

>But what if the first mass is Earth, and I set the moon in its
>depression, with no initial velocity.  What would pull it "down"
>toward the Earth, whicsits at the b bottom?  Why wouldn't it

The problem is that the rubber-sheet analogy is a terrible one.  (Not that
I can supply a better one, mind you.)  GR says that objects travel on 
geodesics (straight lines) through the 4-dimensional manifold spacetime.
If you draw geodesics on the rubber sheet, they are geodesics on a single
spacelike slice through that manifold, not on the whole manifold.
So "straight lines" on the rubber sheet don't necessarily correspond to
the paths of objects at all.

What you really need to imagine is that the entire spacetime consists of
an infinite number of copies of the rubber sheet, one for each instant of
time, and there is some funny definition of "length of a path" on this
collection of sheets, and the lengths of paths, according to this definition,
have the property that the actual paths of particles moving under the influence
of gravity will be of minimal length.  In this picture, the path that
represents the moon sitting still at some distance from the earth would
not be a geodesic (shortest distance between two points), but the path
representing the moon starting at rest and falling towards the earth
would be.

Unfortunately, if you change the analogy in this way to make it correct,
it's too complicated and un-intuitive to be of any use.  That's what
I meant when I said it's a terrible analogy, and I don't have a better
one.

-Ted


Newsgroups: sci.physics
From: gjm11@cus.cam.ac.uk (G.J. McCaughan)
Subject: Re: TIME HAS INERTIA - GOEDEL's THEOREMS - att: Dr.PRATT, Mc CULLOUGH
Organization: U of Cambridge, England
Date: Tue, 12 Jan 1993 17:51:36 GMT

In article <1993Jan12.050005.23233@nuscc.nus.sg>, matmcinn@nuscc.nus.sg (brett mcinnes) writes:
> gjm11@cus.cam.ac.uk (G.J. McCaughan) writes:
> : 
> : I don't know any way of proving Godel's Theorem that doesn't require quite
> : a bit of technical muchking around. (Or else a lot of non-rigorous handwaving,
> : of course; but one can prove anything given sufficient willingness to wave
> : one's hands.)
>                     Please prove this.

Well, like, it's sort of obvious, isn't it? After all, all you have to do is
wave your hands abou a bit and say things are obvious, and it's pretty clear
that most proofs are made up of lots of obvious steps and all the cleverness
is in the details, so all you have to do is sort of wave your hands on all
the tricky bits and everyone will believe you. See?

-- 
Gareth McCaughan     Dept. of Pure Mathematics & Mathematical Statistics,
gjm11@cus.cam.ac.uk  Cambridge University, England.    [Research student]
From: andrew@rentec.com (Andrew Mullhaupt)
Newsgroups: sci.physics
Subject: Re: Why are elementary particles small?
Date: 4 Jan 93 18:18:24 GMT
Organization: Renaissance Technologies Corp., Setauket, NY.

In article <1993Jan3.235010.17976@math.ucla.edu> barry@arnold.math.ucla.edu (Barry Merriman) writes:
>Why are elementary particles small?

>Clearly, the ones that comprise our bodies must be much smaller than
>ourselves,

According to Schrodinger, this is because our bodies are reliable but elementary
particles are essentially unreliable (probabilistic).

>but why are there no other elementary particles that are
>the size of, say, a baseball?

Umm - how 'big' is a photon? I think by a 'big' elementary particle 
maybe what you mean is one which a human could comfortably and directly
detect. In this direction you can then determine what way the human ought
to sense it and then ask if that is plausible. For example, in order to
see an elementary particle, it would have to interact with lots of photons
in order to look 'big' - if it scatters a single photon and you see it it
will look as 'small' as the photon. In order to be visible as a big object,
the large numbers of photons scattering off the particle can't move it around
too fast - which puts a lower bound on the mass of the particle. A pretty big
lower bound as elementary particles go, etc. In order to touch an elementary
particle, I think it has to be a fermion, but I'm not sure. Audibility puts
somewhat stranger restrictions on the particle, and taste and smell are also
unlikely candidates. But in any case an answer can be got at by taking all
the bounds on the properties of the 'sensible' particle and seeing if such
things are produced by or persist through the generally understood historical
processes of the Universe, (big bang, formation of galaxies and stars, solar
system, etc.). Then you might have a good idea of why there aren't such
particles in your neighborhood, or perhaps at all.

>If there were an elementary particle the size of a baseball,
>what color would it be? What would happen if you touched it?

Later,
Andrew Mullhaupt
Newsgroups: sci.physics
From: hagerman@ece.cmu.edu (John Hagerman)
Subject: Re: Gravity & Rubber Sheet Analogy Problem
Organization: Carnegie Mellon University
	<1993Jan12.212529.21816@novell.com>
Distribution: usa
Date: Wed, 13 Jan 1993 02:13:33 GMT

I don't understand why the rubber sheet analogy is so bad (but maybe I
don't understand the analogy).  The point of the analogy is to explain
how space can be "distorted," because this is a non-trivial concept.
The rubber sheet analogy illustrates this by showing distortions of a
2-dimensional space.  It is not sufficient to show the distorted sheet
to someone and say "see, this is what distorted space looks like."  It
must be explained that one must envision oneself being a 2D creature
confined to the rubber sheet, and that the interesting thing is what
space looks like in the presence of distortions.  The fact that the
distortions occur because the sheet is deformed in 3-space is not part
of the analogy.  Once one begins to understand what a "distortion" is,
the analogy becomes less useful, although it's still fun to drop coins
down the big funnel at the store.

- John
--
hagerman@ece.cmu.edu
From: paul@mtnmath.UUCP (Paul Budnik)
Newsgroups: sci.physics
Subject: Re: hidden variables
Date: 7 Jan 93 16:45:33 GMT
Organization: Mountain Math Software, P. O. Box 2124, Saratoga. CA 95070

In article <1993Jan6.174455.15423@oracorp.com>, daryl@oracorp.com (Daryl McCullough) writes:

>[...]
> The only way to get a hidden variables theory that is consistent with
> quantum mechanics and probability theory is if the value of the spin
> measured in a particular direction for a particle depends on the
> choices of directions of *both* measurement devices (the one for
> measuring the particle, and also the one for measuring its partner).
> In other words, the only way a hidden variables theory can work to
> explain the twin pair experiment is if the orientation of a distant
> measurement device instantaneously affects the measured properties of
> a particle here.

This argument strikes me as bordering on the perverse, not because it is
untrue but because it implys a difference between hidden variable theories
and quantum mechanics that does not exist. Bell's result implys that
quantum mechanics is a nonlocal theory. The observation of at least
one of the two particles in a test of Bell's inequality must be influenced
by *both* measurements to reproduce the predictions of quantum mechanics
PERIOD. Quantum mechanics implys that the observation of one particle
is instantaneously influenced by *both* measurements even if those
measurements are separated by billions of light years. This prediction
of quantum mechanics is not evidence against more complete theories.
On the contrary it is a powerful argument against the arbitrary and completely
unjustified assumption in quantum mechanics that the wave function changes
instantaneously when an observation is made. If this assumption
is false, quantum mechanics *must* be an incomplete theory because there
is an unknown space-time structure to these nonlinear changes in the
wave function.

Paul Budnik
From: dseeman@novell.com (Daniel Seeman)
Newsgroups: sci.physics
Subject: Re: Okay, it's not the inverse sprinkler problem...
Date: 12 Jan 93 18:52:19 GMT
Distribution: sci
Organization: Novell Inc., San Jose, Califonia

In article <schnitzi.726849584@eola.cs.ucf.edu> schnitzi@cs.ucf.edu (Mark Schnitzius) writes:
>I was discussing this problem with the guy I carpool with
>the other day...  It seems to be one of those physics
>problems that can be argued either way.
>
>Suppose you are stopped in your car at a stop light.  In
>your rearview you see an approaching car that is moving
>too fast to stop -- it is going to plow into you.  You
>have just time enough to do one of two things -- apply
>the brake, or apply the clutch.  From a personal survival
>standpoint, which choice would be in your best interest?
>
>At first it seems that "hitting the clutch" would be the
>proper answer, so your car would provide the least resistance
>to the oncoming car.  But consider -- shouldn't your goal
>be to reduce the sudden acceleration that you will be 
>experiencing?  If that's the case, then maybe hitting the
>brake would be the correct answer.
>
>Thoughts, anyone?
>
>
If by putting on the brakes you could make your car very rigid and anchored to
the ground, you might have something there.  But the car is deformable and
compressible and the wheels would skid across the road surface.  So, putting on
the breaks wouldn't do much except provide just enough friction (between the
wheels and the road) to crunch the car's rear only to be thrown into a skid out
into a busy intersection.  When you came to your second stop, your breaks might
be locked into place (the axil may be bent or something like that) so you could
not move and you would be hit again from the perpendicular direction by the cros
sing traffic.

If you employ your clutch, you may get a bit of whip-lash, but your car would
be propelled (after not as bad a crunch to the rear) across the intersection 
where you would then engage the gears and drive to the road side where you could
exit the car and help the poor soul whose front end is crunched.

That is my spin anyway...

dks.
From: sichase@csa3.lbl.gov (SCOTT I CHASE)
Newsgroups: sci.physics
Subject: Re: Budding Physicist
Date: 7 Jan 1993 10:42 PST
Organization: Lawrence Berkeley Laboratory - Berkeley, CA, USA
Distribution: world
NNTP-Posting-Host: 128.3.254.198
News-Software: VAX/VMS VNEWS 1.41    

In article <93007.100220STANTONK@QUCDN.QueensU.CA>, Ken <STANTONK@QUCDN.QueensU.CA> writes...
>My seven year old asked me a question that left me scratching my head.
>Since I am not a physicist, I need your help.  :^)
>His question started with queries about temperature scales, absolute
>zero and so on. That I could handle. :^) Then, he asked what the MAXIMUM
>possible temperature was, according to theory. My answer was, "What?".
>He explained further to me, "Well, I understand that temperature is a measure
>of the speed of the molecules. And you told me that Einstein's theory
>means that if the molecules were travelling at the speed of light, they
>should be energy, not matter. So, what temperature should that be, according
>to the theory?" And I thought questions like this were only supposed to
>start when they reached age 16   :-/

Temperature can go arbitrarily high.  Velocities "saturate" at v = c, but
momenta can increase forever. You need different formulae for temperature in
the relativistic regime.  Hagedorn is probably the physicist most closely 
associated with this stuff, and his book _Relativistic Kinematics_  is 
a must read for students of relativistic heavy ion physics, such as myself.

-Scott
--------------------
Scott I. Chase			"It is not a simple life to be a single cell,
SICHASE@CSA2.LBL.GOV		 although I have no right to say so, having
				 been a single cell so long ago myself that I 
				 have no memory at all of that stage of my 
				 life." - Lewis Thomas
From: diverson@phys.ksu.edu (David Iverson)
Newsgroups: sci.physics
Subject: Re: Gravity & Rubber Sheet Analogy Problem
Date: 12 Jan 1993 19:49:51 GMT
Organization: Kansas State University
Distribution: usa
NNTP-Posting-Host: bohr.phys.ksu.edu
Keywords: gravity, general relativity


O.K. I'll put a new twist on this, not an answer, more like a continuation
of the question.

Take two balls (you choose the size) and sandwich them between two rubber
sheets.  Do this in the SpaceShuttle to avoid the nasty business of an
external gravity.  I imagine that the balls would be pushed towards each
other as the elastic sheets attempt to minimize their energy.  Encompassing
both balls in one deformation would take less energy than placing each one
in it's own.

So what do you think about this?  Can space-time be characterized as being
elastic?  Does it attempt to minimize some quantity.  (does 'energy' still
hold as the quantity to minimize?)

It's still an imperfect analogy, but maybe it raises a different set of
questions.

-David "and what happens when 'they' find gravitons?" Iverson

--
diverson@phys.ksu.edu
From: dseeman@novell.com (Daniel Seeman)
Newsgroups: sci.physics
Subject: Re: bubble in container
Date: 4 Jan 93 17:03:25 GMT
Organization: Novell Inc., San Jose, Califonia

In article <1JAN199302310655@zeus.tamu.edu> dwr2560@zeus.tamu.edu (RING, DAVID WAYNE) writes:
>bhoughto@sedona.intel.com (Blair P. Houghton) writes...
>>>The final state has the same fluid in the same volume but different
>>>pressure. In fact one can repeat the procedure ad infinitum to get
>>>as high a pressure as one likes.
>>
>>There's no paradox, only a misapprehension.
>
>? A paradox _requires_ a misapprehension (or an inconsistency).
>
>>The pressure in the bubble can not change unless the number
>>of atoms of gas change, the temperature of the bubble
>>changes, or the volume of the bubble changes.
>
What if you cool the bubble.  Does the pressure change then?

dks
Newsgroups: sci.physics,news.groups,sci.misc
From: markc@smsc.sony.com (Mark Corscadden)
Subject: Re: sci.physics.research: proposed panel of moderators
Organization: Sony Microsystems Corp, San Jose, CA
Date: Fri, 8 Jan 93 21:51:27 GMT

In article <1993Jan8.160818.19578@galois.mit.edu> jbaez@riesz.mit.edu (John C. Baez) writes:
>...  We will be excluding such things as: *bian's
>endless thread, discussions of religion and politics (which threads on
>sci.physics often turn into), endless repeats of questions that are in
>the FAQ, re-re-rehashes of discussions ofthe interpretations of quantum
>mechanics, etc..

How did re-re-rehashes of the interpretations of quantum mechanics make
it's way onto the scrap heap?  How does eliminating such discussions fit
in with the goal of making sci.physics.research "lightly" moderated?
(No, I did not miss the "re-re-re" in "re-re-rehashes".)

I'm looking at the original proposal from Matt Austern, and the goal
seems to be to eliminate clearly inappropriate articles, that is, noise
having nothing to do with legitimate physics.  Do discussions of the
interpretations of quantum mechanics really fit that category, in all
fairness?  Things covered in the FAQ, yes; but a comprehensive FAQ on
QM interpretations doesn't exist.  Maybe that's because there isn't
enough consensus to allow a comprehensive FAQ entry to be written.

I'll grant that such discussions may be of no interest to professionals
since they've "heard it all before", but then what is the real agenda for
sci.physics.research, to eliminate clearly inappropriate articles or to
do something else?

I've found the discussions of the interpretations of quantum mechanics
to be very valuable and educational, and other discussions which would
be of little interest to professionals.  Are people who are intensely
interested in physics but committed to some other career path (like
software engineering) going to find sci.physics.research to be a
more-or-less hostile environment where their curiosity is not welcome?
There are always going to be new readers as well; will they find that
they are not very welcome too since their topics of interest were already
discussed last year and the year before (no re-re-rehashes)?

Maybe, and that would not necessarily be bad.  Sci.math.research has no
elementary discussion in it and its a good enough group, if somewhat dry
and low volume.  Is that really what is wanted for sci.physics.research,
though?  So far it doesn't seem that way.  So far it seems like most
people envision sci.physics.research being a lot more open and lively
than sci.math.research.

What about a compromise?  For certain topics like the interpretations
of quantum mechanics the moderators could mandate a standard subject
line, requiring that it start with "QMI" for example, to allow a simple
killfile entry to be used by the non-interested.  Would that be enough?

Mark Corscadden
markc@smsc.sony.com
work: (408)944-4086
Newsgroups: sci.physics
From: wengland@stephsf.com (Bill England)
Subject: Re: infinite universe
Date: Fri, 8 Jan 1993 16:54:02 GMT
Organization: Stephen Software Systems Inc., Tacoma/Seattle, +1 800 829 1684
X-Bytes: 1231

In article <1993Jan4.184114.151@vms.huji.ac.il> tabitha@vms.huji.ac.il writes:
>Another question from a non-physicist.
>
>I frequently read that cosmologists debate whether the
>universe has infinite size.  If the Big Bang started
>at a definite time in the past, and has since expanded
>at a finite speed, how can it be infinite?  What am
>I missing?

  The BB is still speculation and in fact may never have
  happened. Observational results are tending to refute
  it and other explanations are possible to explain
  both the Hubble expansion and the 3 degree background
  radiation.  In fact recent observations (Sci AM Dec 92)
  indicate that recession redshifts are QUANTIZED.  This is
  difficut to explain by simple recession of the light 
  source. 

  For better details read "The Big Bang Never Happend"
  by Mike Lener I believe.
  

  (Titles prediced to be out this decade " The Big Bang Goes Bust")
-- 
 +-  Bill England,  wengland@stephsf.COM -----------------------------------+
 |   * *      H -> He +24MeV                                                |
 |  * * * ... Oooo, we're having so much fun making itty bitty suns *       |
 |__ * * ___________________________________________________________________|
From: leffler@physics.ubc.ca (Steve Leffler )
Newsgroups: sci.physics
Subject: Re: in favor of a moderated physics group
Date: 11 Jan 1993 21:35:59 GMT
Organization: The University of British Columbia
Distribution: world
NNTP-Posting-Host: physics.ubc.ca

dseeman@novell.com (Daniel Seeman) writes:

>What is "junk?"  Who are the "crackpots?"  I can understand completely that you
>do not like to read some posts on the net, but maybe I do.  I do not think it
>unreasonable to ask you to press the 'n' key a few dozen (hundred, thousand,
>etc...) times, or to set up your kill file appropriately.  "Junk" as you (or
>maybe as i) would describe it is not so to others, and there arguably are NO
>"crackpots" in the world (please allow me to play devil's ---read Abian's---
>advocate for just a moment).

>You are your own best moderator.  If you don't like what your are reading, 
>either sound off and try to point out what is wrong, or just don't read it.  But
>do not try to get it banned from the net as you may be curtailing the interest
>of another.

   Whoa!  Nobody is trying to ban ANYTHING from the net.  The moderation 
discussion is about creating a new group to supplement sci.physics, not
replacing sci.physics with a moderated group.  Those who want to read junk and
crackpot articles are welcome to continue reading them on sci.physics.  Those
of us who do not want to have to push the n key a few hundred times to skip
over junk can read serious physics on sci.physics.research.

				     ---Steven Leffler
					leffler@physics.ubc.ca

Newsgroups: sci.physics,news.groups
From: dseeman@novell.com (Daniel Seeman)
Subject: Re: in favor of a moderated physics group (sci.physics.research)
Organization: Novell Inc., San Jose, Califonia
Date: Tue, 12 Jan 1993 23:30:42 GMT

In article <1iva8aINNhef@iskut.ucs.ubc.ca> leffler@physics.ubc.ca (Steve Leffler ) writes:
>dseeman@novell.com (Daniel Seeman) writes:
>
>>I know you are not proposing to "touch" SCI.PHYSICS but rather to introduce
>>SCI.PHYSICS.RESEARCH.  But in the body of the first posting, the statement
>>was made that SCI.PHYSICS.RESEARCH absolutely has the possibility of becomming
>>as "wild" or rather "speculative" as this forum (SCI.PHYSICS) is today.  
>
>>In the attempt to keep SCI.PHYSICS.RESEARCH "clean," you will at some point have
>>to filter a posting or two from that forum.  It is this process that I think is
>>doomed to failure before you start.  It just doesn't make sense to stem the free
>>flow of information, no matter how "non-serious" you happen to believe it is.
>
>   Why not?  It's done all the time.  Scientific journals have very stringent
>rules on what material they'll accept, for example.  Sci.physics.research will
>be an intermediate medium between the complete freedom (and anarchy) of 
>sci.physics, and the very restricted state of a scientific journal.  That seems
>to be just what we need to complement sci.physics. 
>   Free flow of information (and garbage) is wonderful, and I for one will 
>continue reading sci.physics as long as I can afford the time, but there's no
>reason why one can't have places for more controlled flow of information as
>long as there are places where free flow is not stifled.
>

Yes, journals do it all the time, your point is well taken and understood.  But
I still am left unsettled when the community is divided along the lines of who
is "serious" and who is not.  If you really want to control the flow of info.,
wouldn't you just publish your own trade rag?  

Again, I understand what you are saying (and truthfully I am beginning to be
swayed---*in theory only*).  But I am still uneasy with this whole subject.  
The whole "seperate but equal" idea or rather segregation based on one's
technical ability to write articulate ideas smacks of elitism (I do not like
those "---ism" labels, but could not think of a better term at the moment).

As dumb as we are sometimes, we still deserve and retain the right to be heard.
And not just by others like us, but by those who would catagorize us dumb as 
well.  True, the trade rags do it all the time.  But that does not make it 
right.  The net is one of the last places to ask questions and get direct 
answers.  When (if) we reduce the field of readers, and divide our most precious
and collective resourse (our minds) we diminish our ability to continue the
dynamic education process.  That in deed would be a shame.

dks.

ps.  Teachers learn; Learners teach;  The relationship is symbiotic.
Newsgroups: sci.physics,soc.culture.soviet,misc.headlines,sci.energy
Organization: Queen's University at Kingston
Date: Thu, 7 Jan 1993 17:00:43 EST
From: Ken <STANTONK@QUCDN.QueensU.CA>
Newsgroups: sci.physics
Subject: Re: Budding Physicist
 <93007.112134BAV2@psuvm.psu.edu>

Thank you all for the great responses!  If my son isn't interested in
the job offers, perhaps you'll consider extending the offer to me, if
I promise to bring him along?   ;^)   Especially if you are posting from
somewhere warm.   Ken.Stanton@QueensU.CA
Xref: sparky sci.physics:22376 alt.sci.physics.new-theories:2719 alt.conspiracy:13876 sci.skeptic:22238 alt.paranormal:2767 alt.alien.visitors:9706