HDTenEightyP/NetNews huggingface dataset:
From: paul@mtnmath.UUCP (Paul Budnik)
Newsgroups: sci.physics
Subject: Re: Continuos vs. discrete models Was: The size of electrons, ...
Date: 16 Nov 92 16:40:41 GMT
Organization: Mountain Math Software, P. O. Box 2124, Saratoga. CA 95070

In article <1992Nov16.065208.28725@murdoch.acc.Virginia.EDU>, crb7q@kelvin.seas.Virginia.EDU (Cameron Randale Bass) writes:
> In article <350@mtnmath.UUCP> paul@mtnmath.UUCP (Paul Budnik) writes:
> >In article <1992Nov13.194334.20447@sun0.urz.uni-heidelberg.de>, gsmith@kalliope.iwr.uni-heidelberg.de (Gene W. Smith) writes:
> >> In article <344@mtnmath.UUCP> paul@mtnmath.UUCP (Paul Budnik) writes:
> >> >This is the question. Continuous models are the simplest to work with
> >> >mathematically, but are the simplest possibility as models of physical
> >> >reality? I do not think so.
> >> 
> >> It isn't clear to me that any such distinction can be made.
> >
> >As one simple example consider the difference between a model based on
> >finite difference equations and one based on partial differential
> >equations. 
> 
>     Name a physical system in which the FDE is considered more fundamental
>     than the PDE?  For most of us, we take the 'true' PDE and muck it
>     up, introducing loads of spurious conservation laws and higher
>     order terms, by deriving a finite difference formulation of it. 
>     I'd be interested in a system in which we did the reverse.
> 

I was using this example to show how the distinction between discrete and
continuous models can be made. I know that today physicists do not consider
finite difference equation to be more fundamental. This is part of the problem.
These equations are not often studied as mathematical objects in their own
right, but only as means for approximating differential equations.

I happen to believe that a finite difference approximation to the Klein
Gordon equation will ultimately prove more fundamental then the partial
differential equation. The reason will be that you will not need to muck it
up to introduce these spurious conservation laws. They will be derivable
directly from one simple finite difference equation. The finite difference
approximation when it is fully discretized (for example by being restricted
to integer field values) will be nonlinear and will have chaotic like
behavior that serves to model quantum collapse and the conservation
laws that are obeyed by collapse. Of course this is a speculative idea,
but that is how all new science starts.

Paul Budnik
From: bhoughto@sedona.intel.com (Blair P. Houghton)
Newsgroups: sci.physics
Subject: Re: Continuos vs. discrete models Was: The size of electrons, ...
Date: 16 Nov 1992 22:51:54 GMT
Organization: Intel Corp., Chandler, Arizona
NNTP-Posting-Host: alfalfa.intel.com

In article <1992Nov16.065208.28725@murdoch.acc.Virginia.EDU> crb7q@kelvin.seas.Virginia.EDU (Cameron Randale Bass) writes:
>    Name a physical system in which the FDE is considered more fundamental
>    than the PDE?

Any finite-state machine.

>    For most of us, we take the 'true' PDE and muck it
>    up, introducing loads of spurious conservation laws and higher
>    order terms, by deriving a finite difference formulation of it. 
>    I'd be interested in a system in which we did the reverse.

The load on your machine (if it is a UNIX machine) is a simple example.

A plot of the load vs. time (cf. xload(1X)) appears to
decay exponentially.  The actual load is discrete, and not
very indicative of the load, being simply a difference
equation, and it can be approximated by a continuous
exponential.  Thus it seems the dual of your meta-example:
it is a PDE approximation of a FDE system, and the approximation
introduces spurious knowledge (the idea that a load "decays").

				--Blair
				  "rm -rf /usr/spool/news;
				   I dare you."
Newsgroups: sci.physics,sci.math
From: dwilkins@maths.tcd.ie (David Wilkins)
Subject: Re: Covariant vs. Lie Derivative in Gen. Rel.?
Organization: Dept. of Maths, Trinity College, Dublin, Ireland.
Date: Mon, 16 Nov 1992 11:51:16 GMT

>In article <1992Nov13.213840.10075@galois.mit.edu> jbaez@riesz.mit.edu
>(John C. Baez) writes:
>>As for other cases, I'm suspicious.  Take a look at the proof of the
>>existence and uniqueness of the Levi-Civita connection and see what
>>happens if your metric is replaced by a nondegenerate *skew-symmetric*
>>bilinear form on the tangent bundle.  I'm afraid something will go
>>wrong.  Why?  If nothing did, every symplectic maniold would be blessed
>>with a natural connection analogous to the Levi-Civita connection.  If
>>such a thing existed I should have heard about it, but I haven't.  Of
>>course, it's possible that I am missing out on this crucial facet of
>>symplectic geometry!!
>>
>>Perhaps the symplectic geometers and fans of gravity theories with
>>asymmetric metric tensors can straighten this out in a jiffy.

>
>
>ISN'T IT EASY TO SHOW THAT THE LIE ALGEBRA OF SYMMETRIES OF AN
>AFFINE CONNECTION ON A CONNECTED FINITE-DIMENSIONAL MANIFOLD IS
>FINITE-DIMENSIONAL?  THUS THE LIE ALGEBRA OF INFINITESIMAL
>SYMPLECTOMORPHISMS OF A SYMPLECTIC MANIFOLD IS FAR TOO BIG TO
>PRESERVE AN AFFINE CONNECTION.
>
>
>-JAMES DOLAN

A good reference for this sort of result is
`Transformation groups in differential geometry' by S. Kobayashi

Offhand, there is a possibility that one might require compactness
of the structural group to make things work: one approach for
generalizing the Riemannian result is to define a Riemannian
metric on the total space of the frame bundle in such a way
that connection-preserving maps of the manifold lift to
isometries of the frame bundle.  I seem to recall seeing
something like this in Kobayashi and Nomizu.

DRW
Newsgroups: sci.physics,sci.math
From: phfrom@nyx.uni-konstanz.de (Hartmut Frommert)
Subject: Re: Covariant vs. Lie Derivative in Gen. Rel.?
Organization: Dept. of Physics, University of Constance
Date: Mon, 16 Nov 1992 15:58:53 GMT

jbaez@riesz.mit.edu (John C. Baez) writes:
>anderson@fermi.phys.ualberta.ca (Warren G. Anderson) writes:
>>jbaez@riesz.mit.edu (John C. Baez) writes:

>>> 2) The covariant derivative only requires a tangent vector at one point
>>> of the manifold.  The price you pay is this: to define it you need to
>>> choose a connection on the (tangent bundle of) the manifold.  Of course,
>>> such a connection - the Levi-Civita connection - comes for free if your
>>> manifold has a Riemann metric on it.  
>>
>>Or even a pseudo-Riemannian metric. In fact, wouldn't any way of identifying 
>>the tangent space with it's dual be enough?

>Agreed, pseudo-Riemannian is fine and of course that's what you have in GR.
>As for other cases, I'm suspicious.  [..]
>Perhaps the symplectic geometers and fans of gravity theories with
>asymmetric metric tensors can straighten this out in a jiffy.

Although not totally contained in that set :-)

Your distrust on the determination of a connection G via an asymmetric metric
g is appropriate. While the metricity condition, i.e. vanishing of 
nonmetricity

  0 == Q_{abc} = - g_{ab,c} + g_{db} G^d_{ac} + g_{ad} G^d_{bc}

determines the symmetric part of G, 

  G_{(ab)c} [= g_{d(a} G^d_{b)c}] = (1/2) g_{ab,c} ,

in case of a (pseudo)-orthogonal metric, and thereby in the case of 
vanishing torsion (and in a coordinate frame) the total of G, this is not
true for a non-symmetric g unless this contains a (tensorially invariant)
symmetric part that alone may serve as (pseudo)orthogonal/Riemannian metric,
while the skew-symmetric part may then be treated as independent tensor 
field. You then only have the metricity condition given above, restricting
some components of G, but usually not all. So the case of a symplectic 
manifold you mentioned thus leaves some part of the connection (the 
symmetric one after lowering an index with the symplectic metric j) 
undetermined, so that the connection has a part that is independent of j, 
which cannot be annulled by a reasonable condition like torsion freeness. 

Of course you can still postulate *by hand* that the connection should be 
given by a combination of metric components, but that restricts the theory.
At least the author does not see a reasonable argument for this procedure.

[For those who now quest how the connection G is defined: G comes from the 
covariant derivative of the tangent space base vectors:

    D_a e_b = G^c_{ba} e_c  ]
--
 Hartmut Frommert                 <phfrom@nyx.uni-konstanz.de>
 Dept of Physics, Univ of Constance, P.O.Box 55 60, D-W-7750 Konstanz, Germany
                                           -- Eat whale killers, not whales --
Newsgroups: sci.physics
From: hagerman@ece.cmu.edu (John Hagerman)
Subject: Re: Electric Power Transmission
Organization: Carnegie Mellon University
	<HAGERMAN.92Nov19122352@rx7.ece.cmu.edu>
	<1992Nov19.202817.29139@sfu.ca>
Date: Fri, 20 Nov 1992 01:40:19 GMT

In article <1992Nov19.202817.29139@sfu.ca> palmer@sfu.ca (Leigh Palmer) writes:
>
> Wow. Thanks for the information, John. I hope someone will be able
> to drop the other shoe and tell us where to learn more about this
> twenty-year-old technology.

Your ability to communicate sarcasm without a smiley is nice to see.
But I fear that your comments may mask one important point of my post,
which was to demonstrate that many of the questions asked here can be
sufficiently answered by a tiny bit of research.  Need I explain why
actually doing such research is useful?

I have visited a hydroelectric plant, and it was rather interesting.
Also of interest is the issue of grid phase maintenance, about which
there have been many guesses and few facts posted, and about which my
encyclopedia is mute.

- John
--
hagerman@ece.cmu.edu
Newsgroups: sci.physics
From: wcscps@alfred.carleton.ca (Mike Richardson)
Subject: Anyone checking UNITS? (Abian)
Summary: What about units in his tag-line?
Keywords: Abian,time,inertia,units
Organization: Carleton University
Date: Mon, 23 Nov 1992 19:15:41 GMT

 I was leafing thru the news, and noticed some of what Mr. Abian said
(IF I may quote): "My little finger has more intelligence than Newton
and Einstein put together"
  
 Very impressive (If true).

 Mr. Abian also says (In the tag line of each message), 
"E=mcc (Einstein) must be replaced by E=m(0)exp(-At) (Abian)"
 
 Now, I'm a T.A. for 1'st year physics, and if ANYONE handed this in
they would FAIL.  Not on the basis of theory, but plain UNITS.

[E]=kg*m*m/s*s
[mcc]=kg *(m/s)*(m/s)=[E]
  
 So far so good...
However, Mr. Abian says  E=m(0)exp(-At)

[m(0)]=kg  (of course)
[exp(-At)]=dimensionless

 From his equation, I can deduce that [A]=inverse time, but perhaps, 
Mr. Abian, you missed a proportionality constant somewhere? I may not
be as intelligent as you claim to be, but I propose a slight
modification to your theory...

E=mcc (Einstein) must be replace by E=m(0)C exp(-At) (Abian-DeKok)

Where the C, of course is a constant with [C]=m*m/s*s
  Hopefully waiting for future recognition.

Alan DeKok
(using Physics Society account)

Newsgroups: sci.physics
From: matmcinn@nuscc.nus.sg (Brett McInnes)
Subject: Re: TIME HAS INERTIA - THE ENVIOUS-DESPONDENT REACTION OF CHASE
Organization: National University of Singapore
X-Newsreader: Tin 1.1 PL4
Date: Fri, 20 Nov 1992 05:09:40 GMT

abian@iastate.edu (Alexander Abian) writes:
:   
:  I have to tell you that General Relativity is beta-sigma.  It is a
: unsubstantiated beta-sigma. A group of hallucinating, self-adoring,
: self-massaging,  pseudo-scientists in a total stage of  beta-sigma
: delirium have decided (for the  satisfaction of their own sense of
: warped depravity) that The Cosmos is a semi-differentiable 4 dimensional 
: Riemannian manifold. (Do you want to examine me on the definition of
: a Differentiable manifold again ? Read my last article on that subject
: THE  GIST OF A MANIFOLD).  
:   
:  I don't believe that the Cosmos is a 4-dimensional Manifold - Riemannian 
: or non-Riemannian.  A bunch of self-massaging pseudo-scientists (politi-
: cians), including Einstein and the like, have indoctrinated you people 
: and almost hopelessly paralyzed your brains and mentality.  You are rolling
: slavishly on your bellies in front of their 4, 5, 6, 7, 8 -dimensional beta-
: sigma manifolds !!  What a sham, what a cruel poisoning of minds !  Every
: day they feed you with a new portion of beta-sigma, and, you take it wor-
: shipingly  and licking their hands.

Time to create alt.sex.general relativity?
  : 
:   E = mcc  (Einstein)    must be replaced by    E = m(0) exp(-At) (Abian)
Xref: sparky sci.physics:19501 rec.puzzles:7464
From: sichase@csa3.lbl.gov (SCOTT I CHASE)
Newsgroups: sci.physics,rec.puzzles
Subject: Re: Physics puzzle - antigravity device!
Date: 23 Nov 1992 11:57 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 <1992Nov22.234125.13222@galois.mit.edu>, jbaez@riesz.mit.edu (John C. Baez) writes...
> 
>Part 1 - Place a conducting hollow (and evacuated) spherical
>shell on the table.  Since (at least some) of the electrons are free to
>move in the conductive shell, gravity will pull them downwards a little
>bit.  Of course, when there are more electrons near the bottom of the
>shell, they produce a repulsive electric field.  Thus the electrons will
>come into an equilibrium where there are slightly more electrons near
>the bottom of the shell - distributed in such a way that the electric
>field they produce is just enough to cancel the gravitational pull on 
>the electrons.  (This effect will be very small.)  
> 
>This part is for real, and according to Price this effect has actually
>been observed.  Note that protons or neutrons would fall in this shell
>since they have a different charge/mass ratio.  

Yes.  In fact, this effect is a real problem when doing antimatter gravity/
antigravity experiments.  In the classic, but ambiguous, Fairbanks positron
experiment, he tried to measure the force of gravity on positrons.  To
do so meant shielding the positron from *very* small stray electric fields.
Nanovolts are important here.  Any highly conductive metal shielding will
do, but you need to take into account the effect you mention - there 
is a residual electric field from the shielding pipe itself due to the 
electrons sinking in the gravitational field of the Earth.

-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
Xref: sparky sci.physics:18936 sci.chem:4598 sci.engr.chem:580
From: cervi@oasys.dt.navy.mil (Mark Cervi)
Newsgroups: sci.physics,sci.chem,sci.engr.chem
Subject: Re: Specific Heat
Date: 9 Nov 92 22:36:46 GMT
Article-I.D.: oasys.27359
Followup-To: sci.physics
Distribution: usa
Organization: NSWC, Carderock Div. Det., Annapolis Facility

In article <1992Nov08.184022.19409@radford.vak12ed.edu> kgrossha@radford.vak12ed.edu (Kurt Grosshans) writes:
>jerry@wshb.csms.com  writes:
>>    1) 2740 joules/kg deg.C
>>    2)  848.6 joules/kg deg.C
>> 
>>                             jerry@wshb.csms.com
>
>Am I crazy, or are his units off for numbers of that magnitude?
>=-=-=-=-=-=-=-=-=-==-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-==-=-=-=-=
>Kurt Grosshans
>kgrossha@radford.vak12ed.edu

I get 0.65 for the first and 0.20 for the second in BTU/lb-F.  Aluminum
is 0.23.  The first is near Lithium (0.80).

f
i
l
l
e
r

f
i
l
l
e
r
-- 
	Mark Cervi, CARDEROCKDIV, NSWC Code 2752, Annapolis, MD  21402
	  cervi@oasys.dt.navy.mil, (w) 410-267-2261, (h) 410-647-0990
Newsgroups: sci.physics
From: palmer@sfu.ca (Leigh Palmer)
Subject: Re: _Voltage_ ratings of fuses
Organization: Simon Fraser University
Date: Thu, 19 Nov 1992 22:36:18 GMT

In article <1egpleINNie8@crcnis1.unl.edu> cbettis@unlinfo.unl.edu (clifford
bettis) writes:
>
>The other day the fuse blew in our microwave oven and in the process 
>of replacing it, I noticed it had a voltage as well as a current 
>stamped on it. I'd been aware of this before but never really thought 
>about it. Why is there a voltage rating for a fuse; is it a matter of 
>how much resistance the fuse has, or possibly some sort of breakdown 
>by arcing limitation? If it is a matter of resistance, why not always 
>use the fuse with a lower voltage rating? 

After the fuse blows there may be a voltage drop across it. That's what one has
to worry about.

I have replaced the fuse in my microwave oven twice. To do so I have to take
the whole case off the damn thing - they were too cheap to put on a shielded,
socketed fuse. Do you have the same problem? I note that there is an access
door to the oven light bulbs. 

I'm sure lots of perfectly serviceable microwave ovens get discarded when thay
blow fuses because of this "feature". It is probably due to some unreasonable
radiation requirement for these beasts.

Leigh

Leigh
From: antennae@gn.apc.org
Newsgroups: sci.physics
Subject: Re: Where should beginner begin?
Date: 21 Nov 92 22:10:00 GMT
Nf-ID: #R:gn:1541700004:gn:1541700005:000:185
Nf-From: gn.UUCP!antennae    Nov 21 22:10:00 1992



Thanks to those who've replied.  I'll follow up the books mentioned
and hopefully absorb enough eventually to allow me to follow some of
the discussions on here.

All the best, Indra
From: bweiner@ruhets.rutgers.edu (Benjamin Weiner)
Newsgroups: sci.physics
Subject: Re: energy and mass for the last time
Date: 18 Nov 92 03:28:25 GMT
Organization: Rutgers Univ., New Brunswick, N.J.

abian@iastate.edu (Alexander Abian) writes:
>      Abian answers:

>  The energy is spent irretrievably for moving TIME forward.

No fair, Abian, you replied to something not in Subject: TIME HAS INERTIA.

With best regards,
Ben Weiner
From: voros@physics.monash.edu.au (Joe Voros)
Newsgroups: sci.physics
Subject: Re: Why "p" for momentum?
Date: 16 Nov 92 03:09:08 GMT
Organization: Physics Dept, Monash Uni, Melbourne, Australia.

mox@vpnet.chi.il.us (William Moxley) writes:
> Does anyone know why "p" was chosen to represent momentum?  Other than
> that "m" was already taken?

It is tied to the fact that "q" is used to designate position.  As my
.signature has attested for a bloody long time now, Quantum Mechanics is
God's way of reminding us to mind our P's and Q's.

:)

-- 
Joe Voros
Department of Physics, Monash University, Clayton, VIC, 3168, Australia.
voros@physics.monash.edu.au
Quantum Mechanics is God's way of telling you to mind your P_i's and Q_j's.
Newsgroups: sci.physics,sci.math
From: jbaez@riesz.mit.edu (John C. Baez)
Subject:  Covariant vs. Lie Derivative in Gen. Rel.?
Organization: MIT, Department of Mathematics
Date: Mon, 16 Nov 92 22:11:15 GMT

Ric Peregrino writes:

>I've been struggling with the concept of covariant derivative for some
time.

>For a covariant tensor of 1st rank (order, whatever) A
>
>            j   k
>A   = dA /dx - G  A
> i;j    i       ij k
>
>as I'm sure you all know. 

Fine.  Here G, usually written Gamma, is called the Christoffel symbol
in the context of general relativity.  The left hand side is called the
covariant derivative of A.  

>The "connection" is an additional restraint that need not
>be imposed to insure the tensor character of the resulting tensor.

Huh?  This makes no sense to me, which is probably related to 
the problem you are having.  The "connection" is not a restraint, or
constraint.  There are many ways of thinking about connections but the
most relevant here is that the connection simply IS the entity 

   k
 G  
  ij 

More precisely, the Christoffel symbol expresses the connection in a
given coordinate system (or frame).   It's obvious from this point of
view that one needs a connection to define covariant derivatives.

>>2) The covariant derivative only requires a tangent vector at one point
>>of the manifold.  The price you pay is this: to define it you need to
>>choose a connection on the (tangent bundle of) the manifold.  Of course,
>>such a connection - the Levi-Civita connection - comes for free if your
>>manifold has a Riemann metric on it.

>Hmm.... If I look at the covariant derivative of the scalar I above, all
>I need to know are...

You misunderstood my point since I wasn't precise enough.  To take the
covariant derivative of a tensor A in a given direction v at a certain
point x, all *v* needs to be is a tangent vector at x.  I would write
this covariant derivative as D_v A(x); in coordinates it's
 
 j
v A   (x)

   i;j

Of course to figure this out we need to know A and all its first
derivatives at x and we need to have a choice of connection, that is, we
need to know the Christoffel symbol.  My point was that we only need to
have a tangent vector v at the point x, as opposed to what we need to
compute a Lie derivative, which requires v to be a vector field in a
neighborhood of the point x.  (Well, one can get by with less to compute
a Lie derivative, but please don't anyone point that out and comfuse
things further.)  
Newsgroups: sci.physics
From: crb7q@kelvin.seas.Virginia.EDU (Cameron Randale Bass)
Subject: Re: Higgs Spotted? (really about Mars)
Organization: University of Virginia
Date: Mon, 16 Nov 1992 23:18:44 GMT

In article <1e97msINNe88@chnews.intel.com> bhoughto@sedona.intel.com (Blair P. Houghton) writes:
>In article <1992Nov16.064710.28511@murdoch.acc.Virginia.EDU> crb7q@kelvin.seas.Virginia.EDU (Cameron Randale Bass) writes:
>>>jhh@waldzell.physics.yale.edu (Jim Horne) writes:
>>>> "Mars is somewhat the same distance from the sun, which is
>>>> very important.  We have seen pictures where there are
>>>> canals, we believe, and water.  If there is water, there
>>>> is oxygen.  If oxygen, that means we can breathe."
>>>> 				     Dan Quayle, August 11, 1989
>
>>2) What are the constituent elements of water?
>
>Not, as Danny Boy thinks, anything resembling breathable air.

     Pretty stupid of one to assume air when he said oxygen.
     Oxygen is but one component of air.  I obviously made
     a faulty assumption when I assumed that everyone around here
     knew that.  Should we hoot at you?

>>     It sounds pretty funny when presented the appropriate way, but
>
>You mean it's fucking hilarious when the Vice President of
>the United States of America makes a speech extolling the
>virtues of grandly scoped space travel with utterly
>disingenuous misapplications of facts that any involved (or,
>indeed, sentient) government official would have checked,
>at the very least with a local high-school science teacher.

      Please point out the incorrect assertion.  Spare me the interpretation.

      Or better yet, did you howl when the President of the United States made
      a gaffe in text that should have been checked, at the very least, with
      several German schoolchildren?  Do you honestly think that derision
      is more appropriate than elaborating?  
      
>>     Mr. Quayle was an active head of the National Space Council.
>
>He was a politician in a plastic space helmet playing
>Plan 9 From Outer Space, and losing.
>
>				--Blair
>				  "We have seen pictures where
>				   there are holes in the moon,
>				   and we believe the moon is
>				   made of cheese.  If there is
>				   cheese, there is mildew, and
>				   if mildew, that means we can
>				   have dressing for our salad..."

      However, there *are* apparently pluvial formations on Mars.
      We *do* believe that there is water somewhere (at least some
      of us do), and there have been any number of proposals to use
      that water for oxygen for humans to breathe while on a Mars
      mission.

      Are you saying that the likelyhood of there being water on Mars
      is the same as the likelyhood of the moon being made of cheese?
      I'd have to say that this is wildly at variance with current theory.

                              dale bass

-- 
C. R. Bass                                          crb7q@virginia.edu        
Department of Mechanical, 
     Aerospace and Nuclear Engineering
University of Virginia                              (804) 924-7926
Newsgroups: sci.physics