HDTenEightyP/NetNews huggingface dataset:
From: mcirvin@husc8.harvard.edu (Mcirvin)
Newsgroups: sci.physics
Subject: Re: Abian and the Fundamental Theorem o
Date: 22 Nov 92 19:34:11 GMT

antennae@gn.apc.org writes:

>Well now, how about that for a voice of reason?

>May I ask an ignorant question?  If space-time is a continuum, then
>how is it that we can move in many directions in space but only one
>direction in time?  Or is this an illusion?  Or does my question have
>no meaning?

>Indra

Nobody knows, but the non-answer you get depends on what you mean.

If you're asking where the arrow of time comes from, that's something
we dearly love to argue about here.  But I think you mean the following:

"If space and time can be transformed into each other by a change of 
reference frame, why is it that there are three spatial dimensions but
only one temporal one?"

Here's a partial non-answer:

In relativity we model spacetime as a four-dimensional manifold with a
"metric" associated with it; this essentially describes the local equivalent
of the Pythagorean formula for distances along a line, or lengths of
vectors.  In Euclidean four-dimensional space the formula would be

l^2 = w^2 + x^2 + y^2 + z^2

where x,y,z, and w are the components of the vector in four orthogonal
directions and l is the length.  This is just the Pythagorean theorem
extended to four dimensions.  But in the simplest sort of relativistic
theory, SR, spacetime has the following metric:

l^2 = ct^2 - x^2 - y^2 - z^2

There are three minus signs and one term without a minus sign.  (You
can also define it so that only the ct term has a minus sign; that's
a matter of convention.)  Directions are "timelike" or "spacelike" 
depending on whether l is real or imaginary (respectively, with this
convention).  You can only travel in a "timelike" direction; this
corresponds to velocities less than c.  If you integrate l from this formula
to find the length of a timelike curve, the result is c times the proper
time experienced along that route. 

The Lorentz transform can mix, to some extent, the four components, but
it's constructed in such a way that timelike directions stay timelike,
spacelike directions stay spacelike, and "lightlike" directions (l=0)
stay lightlike.  This last is Einstein's postulate of the constancy of
the speed of light.  So even though spacetime is a single manifold,
there's a distinction between timelike and spacelike directions; and
if you choose an orthogonal basis of non-lightlike vectors, one will 
always be timelike and three spacelike.

Why?  Nobody knows.  But that's the model that seems to correspond
to reality, and it's mathematically consistent. 

-- 
Matt McIrvin
From: antennae@gn.apc.org
Newsgroups: sci.physics
Subject: Re: Detecting crackpots - for laymen?
Date: 21 Nov 92 22:47:00 GMT
Nf-ID: #R:1992Nov17.231944.13221@meteor.wi:-450683850:gn:1541700008:000:516
Nf-From: gn.UUCP!antennae    Nov 21 22:47:00 1992



Dear Scott, please don't say things like "technipions".  English *is*
something I know about (I have made my living from writing ever since
leaving Cambridge in the mid seventies).  If you really want to reach
laymen, it might be a good idea to translate as much physics as you
can into simple lay language.  

PS:  Probably the wrong discussion group in which to ask this
question, but has anyone heard talk about resurrecting Sanskrit for use
as a 'computer language'?  Now where could I have heard that?

Indra
Newsgroups: sci.physics
From: sarfatti@well.sf.ca.us (Jack Sarfatti)
Subject: PS re:Ramsay's objections etc.
Organization: Whole Earth 'Lectronic Link
Date: Mon, 16 Nov 1992 20:59:27 GMT


I forgot to add on your remark "for all relevant choices" - that only
applies to one-photon problem, not at all relavant to actual photon
pair problem, as I show in detail above. Also, even for one-photon
problem - the formal "all possible choices" suppose a kind of gauge
symmetry which may or may not be physically correct. It has to be tested.
For example, in one-photon case, send |a,e,+> and |a,o,+> through a
beam recombiner with two counters getting each of the two output
interferograms - if "fringes" are seen in the count rates, then your
remark <a,e,+|a,o,+> = 0 is disproved experimentally in the one-photon
problem! I'll show this in detail later.
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: Tue, 17 Nov 1992 09:25:05 GMT

rscott@libws3.ic.sunysb.edu (Robert Scott) writes:

>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.

You confuse me a bit :)

If I understand right, the covariant derivative must only preserve the 
symplectic metric j with components

  j_{ab} = j_{[ab]} = - j_{ba} , 

not the set of all symplectic transformations, to obtain a metricity 
condition analogous to the Riemannian: There the Levi-Civita connection only 
leaves (pseudo)-orthogonal g invariant, not all elements of the Lorentz 
group. The symplectic metricity condition reads explicitely

  0 == - j_{ab;c} = - j_{ab,c} + j_{db} G^d_{ac} + j_{ad} G^d_{bc} .
                                                   ^^^^^^
                                                 = - j_{da}

The connection is then a 1-form with values in the symplectic Lie 
algebra which is defined as the set of all generators of transformations 
that leave j invariant, as the Riemannian is contained in the (local, 
[pseudo]-orthogonal) invariance group of g. As I tried to line out in a 
previous posting, I do not see a reasonable argument for uniquely fixing a 
symplectic-metric connection, which happens to be possible for the 
Riemannian by the demand of vanishing torsion, so that there remain 
connection components independent of j.

BTW: The symplectic Lie algebra Sp(D,j) is of course finite-dimensional at 
  each point, and the j-metric connection is contained in it by def. It is
  only infinite-dimensional (like the space of any scalar, vector, tensor, 
  spinor, or isotensor fields, i.e. the corresponding bundle) when viewed 
  non-locally, i.e. in some neighborhood, etc. Dimension of Sp(D,j) is   
  D*(D+1)/2  if D is the dimension of the manifold under consideration.
--
 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 --
From: bhoughto@sedona.intel.com (Blair P. Houghton)
Newsgroups: sci.physics
Subject: Re: Continuos vs. discrete models Was: The size of electrons, ...
Date: 17 Nov 1992 20:43:04 GMT
Organization: Intel Corp., Chandler, Arizona
NNTP-Posting-Host: alfalfa.intel.com

In article <1992Nov17.003058.127@murdoch.acc.Virginia.EDU> crb7q@kelvin.seas.Virginia.EDU (Cameron Randale Bass) writes:
>In article <1e98maINNebq@chnews.intel.com> bhoughto@sedona.intel.com (Blair P. Houghton) writes:
>>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.
>
>     I actually had 'nature' in mind.  I can *create* any number of systems

All systems are "natural."  There are no physical phenomena
that are "unnatural," certainly not the interaction of
electromagnetism and quantum mechanics that constitutes
modern computational electronics.

The string example someone else gave is a devised system of
organic fibers, but those fibers are themselves no less
devised (by the plant on which they grew).

And recall your Calculus I.  All of this continuous
analysis is merely the effect of taking the limit as the
problem is raised to an infinite number of finite
analyses.  You've probably never seen a truly continuous
system in your life (including quantum gravity).

>     I do not recall finite state machines described 
>     by FDE's in our current description of nature.

Then you don't see cells as part of it?

>     Enlighten me.

That's something you can do for yourself; read on.

>     Interesting analogy.  However, my load doesn't decay at all.  It
>     seems to be a monotonically increasing sequence.

That explains a great number of things; Corky, you need to
take a shit.

				--Blair
				  "In the name of the Father, of the
				   Son, and of the Holy Spirit, Amen."
Newsgroups: sci.physics
From: kkretsch@unix1.tcd.ie (kevin patrick kretsch)
Subject: Re: UFO EVIDENCE VS. Carl Sagan
Organization: Trinity College, Dublin
Date: Mon, 16 Nov 1992 16:50:25 GMT

About two years ago I read in a newsgroup (alt.paranormal  
I think ) files released by the U.S. government under the
freedom of information act (FOIA).
         In these files were letters from USAF officers
to mainly independant investigators, 'confirming' that
UFOs do exist and the US government does indeed have in
their posession a number of cadavers and wreckages from
crashed UFOs.
         The most interesting point about these letters
was one that always stuck in my mind and I'm wondering
if anybody has heard anything about this:
         Apparrently, the most closely guarded secret
in the U.S. government regards how the UFOs were 
powered. This, I believe, involves harnessing the
potential energy of the earth's magnetic field.
The theory of this seems to explain the motion of
observed UFOs including the incredible acceleration
in any direction and very high manouverability.
         Does anyone know if this is possible?
         Is this a big hoax?
         Or,
         Should we be starting research into what
could be the greatest advance in propulsion that
mankind has ever known, more exciting than cold fusion
(if it worked ) and potentially more useful?

Any comments would be read with great interest.

Kev.
From: sichase@csa2.lbl.gov (SCOTT I CHASE)
Newsgroups: sci.physics
Subject: Re: Continuos vs. discrete models Was: The size of electrons, ...
Date: 16 Nov 1992 10:36 PST
Organization: Lawrence Berkeley Laboratory - Berkeley, CA, USA
Distribution: world
NNTP-Posting-Host: 128.3.254.197
News-Software: VAX/VMS VNEWS 1.41    

In article <1992Nov16.065208.28725@murdoch.acc.Virginia.EDU>, crb7q@kelvin.seas.Virginia.EDU (Cameron Randale Bass) writes...
>>
>>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.

How about your favorite and mine - the flexible string.  Since the string
is really atomic at the smallest scale, the "most" appropriate equation
is the FDE.  It is only in the approximation that the discrete nature of the
string is irrelevant (a damn good approximation, I admit) that the PDE
becomes a useful description.  

In older textbooks, like Morse and Feshbach, they put more of an emphasis
on these distinctions than modern books do, which tend to be more abstract. 
M&F go to some length to emphasize that the PDE's are not the "true"
models of many systems.  They make a clear distinction between physical
systems which are inseparable from their description in terms of fields
(i.e., PDE's), such as electromagnetic fields, and systems for which 
the fields *are* separable from the physical system, such as the string,
where it is really the finite number atomic positions which are fundamental,
the field being a useful characterization but not one that is intrinsic
to the system, which is properly a discrete system.

-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: sichase@csa2.lbl.gov (SCOTT I CHASE)
Newsgroups: sci.physics
Subject: Re:  TIME HAS INERTIA - THE ENVIOUS REACTION OF TALBOT
Date: 16 Nov 1992 11:04 PST
Organization: Lawrence Berkeley Laboratory - Berkeley, CA, USA
Distribution: world
NNTP-Posting-Host: 128.3.254.197
Keywords: TIME HAS INERTIA,  i.e., TIME IS MATTER
News-Software: VAX/VMS VNEWS 1.41    

In article <abian.721860217@pv343f.vincent.iastate.edu> abian@iastate.edu (Alexander Abian) writes:
>(A2)   TIME HAS INERTIA, i.e., TIME IS MATTER  and that some energy
						         ^^^^
How much ?  Some is a little bit vague.

>       is irretrievably spent by Cosmos to move TIME forward. Thus,
>       in particular, the Principle of Conservation of Energy must be
>       rejected. 

Apologies to Indra, but Abian, you are a blithering fool.  If you would
take a few minutes to learn some real physics before trying to revolutionize
the world, you would save us all a good deal of time and wasted energy.

Everyone who has studied General Relativity knows full well that 
conservation of energy, though valid locally, is not believed to be 
valid on a cosmological scale.  In other words, everyone but you seems to
know that energy is not conserved in the Universe according to our best
model of how these things work.

I suggest that your "sacred principle" is a figment of your own imagination,
born of your complete ignorance of the physics which you are pretending
to discuss.  

Anyone who wants to learn something real about conservation of energy
is invited to read the FAQ, which has an article entitled "Red Shift
and Conservation of Energy," which is the summary of a thread on this 
subject which we had about nine months ago.  It contains a fair summary
of the collective understanding of the readers of this group at the time,
and some references to texts which discuss the idea further.

-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: hougen@focus.csl.uiuc.edu (Darrell Roy Hougen)
Newsgroups: sci.physics
Subject: Tesst
Date: 17 Nov 1992 18:04:14 GMT
Organization: Center for Reliable and High-Performance Computing, University of Illinois at Urbana-Champaign
NNTP-Posting-Host: focus.csl.uiuc.edu
Summary: test
Keywords: test

Why didn't this work before?

Newsgroups: sci.physics
From: bhv@areaplg2.corp.mot.com (Bronis Vidugiris)
Subject: Re: moderated sci.physics
Organization: Motorola, CCR&D, CORP, Schaumburg, IL
Date: Mon, 16 Nov 1992 18:12:16 GMT

In article <Bxpx3C.BDB@well.sf.ca.us> sarfatti@well.sf.ca.us (Jack Sarfatti) writes:
)
)What does moderated actually mean? Is it not a euphemism for censorship?
)I agree that this whatever you call it is filled with noise but that is
)the price for freedom of expression - and no one is forced to read what
)they do not want. It is easy to skip over it. I have not read one thing
)by or about Abian, for example. Also the bit cost is trivial as some
)one has already pointed out.
)
)The danger is that the moderator's bias could cause him or her to
)perceive an "unorthodox" view as "crackpot" 

...

)fight it here! This is a new medium with new rules and new opportunities
)to connect scientist all over the world - it is not meant to be the stodgy
)pages of a peer-reviewed journal. Let the battle of ideas proceed - don't
)impose your ideas of "orthodox" on others. Let there be new wine for new
)bottles - keep the vinegar of "moderation" and "orthodoxy" in the old
)bottles of paper journals. This is a new medium of communication. Keep
)it free! FREEDOM!

Actually, I would *not* want to see sci.physics disappear if a new moderated
group were created.  However, I have no objection to the creation of an
aditional moderated group in parallel.  I suspect the probability of finding
a moderator (esp. a qualified moderator) is very low (perhaps negligible
:-)), however.
Xref: sparky sci.physics:19486 sci.math:15412
Organization: Penn State University
Date: Mon, 23 Nov 1992 11:16:33 EST
From: <BAV2@psuvm.psu.edu>
Newsgroups: sci.physics,sci.math
Subject: Re: Advice Please: What Geometry Course?

In article:  <1emgjbINNiep@agate.berkeley.edu>

      jhcooper@ocf.berkeley.edu (John Hutton Cooper) writes:
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
I am a sophomore majoring in physics.  I am interested in special relativity,
and might make the topic my specialty in physics.  Special relativity uses
a lot of non-Euclidean geometry.  I am interested in taking a course dealing
with non-Euclidean geometry at UC Berkeley, and I welcome any course
suggestions.  I will have completed the 1A/1B 50A/50B sequence at the end of
this semester.  Thanks for the advice.
--

My own opinions, etc.                                 John Hutton Cooper
                                                      jhcooper@ocf.Berkeley.EDU
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

I can give an advice about standard textbooks    used to teach
Theoretical Physicists in the former USSR.

A. The fundamentals (and hopefully all you need if you are an average
theoretician not specializing in relativity) you'll  find in  L.D.Landau
& YE.M.Lifshits _Field Theory_ (a lot of Engl translations are available)
It's a 2nd vol of their Course of Theoretical Physics. Maybe you'll
find reading this course difficult for the first time but when you
understand their style you'll  see that it is worth reading. The first
3 volumes and the fifth one (_Mechanics_, _Field Theory_, _Quantum
Mecdhanics_ & _Statistical Physics, Pt 1_) are brilliant and any
theoretician must read them

B. There is a book by Dubrovin, Novikov & Fomenko _Modern Geometry_. It
seems it was translated in Engl. Try also to locate other works by
Fomenko. He is a good paedagog. Besides his drawings are excellent. A
good half of _Modern Geometry_ is devoted to relativistic geometry
and this book is a very good intro for a physicist specializing in
relativity

Good luck

-Dr. Boris Veytsman
Newsgroups: sci.physics
From: u108502@beta.lanl.gov (Andrew Poutiatine)
Subject: Re: pressure questions
Organization: Los Alamos National Laboratory
Date: Tue, 17 Nov 1992 15:51:56 GMT

In article <16NOV199214241024@csa3.lbl.gov> sichase@csa3.lbl.gov (SCOTT I CHASE) writes:
>surely know more about this than I do.  But I suspect that when the 
>atmospheric pressure approaches the pressure you heart can generate, that
>you have circulatory problems.  Your heart will have to work harder, 
>and your blood vessels may not be able to take the pressure increase.

This is all great until this last sentence.  Your body is less like a rigid
steel container, and more like a highly incompressible fluid.  Even though 
under high ambient pressure your body does not compress significantly, it 
finds a system-wide equilibrium that brings your tissue and fluid pressures to
the ambient.  The heart does not need to fight the increased pressure, since
that pressure is at inlet and outlet to this pump of yours, and in fact the 
muscle of the heart is at that same pressure also.  I do not know how much
pressure the heart generates, nor how deep divers have gone, but I am fairly
confident that the pressures that deep divers regularly see is much greater
than the pressure differential through your heart.

-AIP

Newsgroups: sci.physics
From: cerikson@occs.cs.oberlin.edu (Carl Erikson)
Subject: Double Pendulum
Organization: Oberlin College Computer Science
Date: Tue, 17 Nov 1992 22:06:53 GMT
Distribution: sci
X-Posted-From: occs.cs.oberlin.edu
NNTP-Posting-Host: sol.ctr.columbia.edu

Hello,
	I am currently involved in a software project to create a simulation
of a double pendulum. A double pendulum has two axis of motion:

                 .
                  \
                 A1\ L1
                    \
                     o M1
                  A2/
                   / L2
                  /
                 o M2  
It consists of two pivot points of mass M1 and M2 and two levers of length
L1 and L2. The angles between the two pivot points are A1 and A2. During
the simulation, only A1 and A2 change.
	I found some equations that describe this system. They are of
the form:
A1'' = ...
A2'' = ...
	I used these equations in a prototype and found them to produce
some very weird behavior (I think even weird for a double pendulum). I used
the Runge Kutta method (4-step) for estimating integration. I do not have the
physics background to determine if the equations I have are correct. I'm sure
someone has already produced error free equations of the double pendulum and
I would appreciate it greatly if I could compare mine with them. So, if you
have worked with the double pendulum before, please e-mail me at
cerikson@occs.cs.oberlin.edu with any advice that you have. It will be
greatly appreciated!

Carl Erikson (cerikson@occs.cs.oberlin.edu)
Newsgroups: sci.physics
Newsgroups: sci.physics
Subject: Re: Flying fast enough and becoming a black hole
From: mcirvin@husc8.harvard.edu (Mcirvin)
Date: 21 Nov 92 19:29:45 GMT
Distribution: sci.physics

Steven Timm <st0o+@andrew.cmu.edu> writes:

>The idea of increasing mass with increasing velocity is one of the more 
>common fallacies.  Consider the following:  There are some quasars in the
>universe whose redshifts indicate they are moving away from us at .99c
>due to the expansion of the universe.  It follows that earth, and the solar
>system, and the local galaxy, are going .99c in their rest frame.

>Since our mass must be the same in our reference frame or theirs, and we've
>not turned into a black hole in either case, it follows that we are not 
>in danger of turning into a black hole through excess velocity.

The conclusion is true, but the argument is suspect-- the recessional
velocity of distant objects due to the expansion of the universe is
a rather different sort of thing from a relative velocity of nearby
objects.  There is, for instance, nothing to prevent recessional
velocities from exceeding c, according to some ways of reckoning the
velocity.  (I think the recessional velocities usually quoted are
calculated backwards from the redshift using the special-relativity
Doppler formula, though, so they'd have to be < c if the object is
visible.)

The simplest argument is simply Leigh Palmer's statement that "black
holiness" is invariant under boosts.  A more pedantic one would involve
actually examining the stress-energy-momentum tensor associated with moving
matter and determining that you don't get anything like a black hole--
it does make the result much more plausible if you realize that what
couples to gravity is neither the rest nor the "relativistic" mass, but
the whole tensor. 

Incidentally, I just found out that the French term for rest mass is
"masse propre."  This strikes me as a much better term than "rest mass,"
one which dovetails nicely with terms like "proper time" and "proper 
length."
-- 
Matt McIrvin