HDTenEightyP/NetNews huggingface dataset:
From: prim!dave@germany.eu.net (Dave Griffiths)
Subject: Re: Questions of transparency
Organization: Primitive Software Ltd.
Date: Tue, 29 Sep 1992 09:36:46 GMT

In article <1992Sep25.073432.29995@hplb.hpl.hp.com> davids@spira.bri.hp.com (david sixsmith (contractor)) writes:
>1. What is (are) the inherent qualitie(s) of a substance, such as glass,
>perspex, diamond, & water, which make it transparent ?
>
>2. What is the mechanism which makes the speed of light lower when travelling
>in such a medium as opposed to traveling in a vacuum ?
>
>I only ask these questions because they seem to me simple questions which
>I would expect to know the answer to, but I having asked a number of graduate
>scientists, I can't get a sensible answer. I think I know how (2) will be
>answered, but I've got a follow up.
>
>This isn't in any way homework. Am I getting no response because no-one knows ?
>
>It seems sci.physics is dominated by arcane quantum mechanists, abstruse
>general relativationists with a good mixture of non-scientists thrown in.
>

I was just wondering about the same questions this evening! I assume the
photon is being absorbed and re-emitted en route?

3. What are the mechanics of the change of direction which occurs at the
boundary between two substances?

Dave Griffiths
Newsgroups: sci.physics
From: frisinv@alleg.edu
Subject: Re: Another Cute Math Joke  (explanation of)
Organization: Allegheny College
Date: Fri, 2 Oct 1992 22:00:23 GMT

In article <1992Oct1.233811.8760@lmpsbbs.comm.mot.com>  
bhv@areaplg2.corp.mot.com (Bronis Vidugiris) writes:
> In article <marc.717947769@vieta.math.uni-sb.de>  
marc@vieta.math.uni-sb.de (Marc Conrad) writes:
> )dms@krang.vis.citri.edu.au (David Mcgregor SQUIRE) writes:
> )
> )>Q: What do you get if you cross an elephant with a grape?
> )
> )>A: |elephant||grape|sin(theta)
> )I'm stupid, but can someone explain this to me ??
> )Marc
> 
> Hmm.  Well, the reason it's funny is that the joke implies you are
> taking a CROSS product of an elephant and a grape, but the math shows
> a DOT product of an elephant and a grape!
> 
> (if A and B are vectors, |A| * |B| * sin(theta) is one expression for  
the
> dot product || -> absolute value, theta is the angle between the  
vectors).
> 
Hate to break it to you, but that is the magnitude of the CROSS product as  
promised.
Newsgroups: sci.physics
From: ddixon@nyx.cs.du.edu (David Dixon)
Subject: Lawsonian Elves Growing Space Potatos
Organization: Nyx, Public Access Unix @ U. of Denver Math/CS dept.
Date: Fri, 2 Oct 92 19:03:59 GMT

Just a brief diatribe.

First, if you don't know what you're talking about, please don't post long
theories categorically stating your warped (and probably incorrect) view.
Initiating a discussion is one thing.  Shooting off your mouth just to show
everyone how smart you are is a waste of net time and net money.

Second, what I'm about to say will be lost on the target audience, but
what the heck.  Maybe some reasonable soul will pay attention.  Nobody cares
about your theory if you can't back it up.  I can very easily say that a
possible mechanism for gamma-ray bursters involves the burping of space
elves who have consumed to many space potatos.  But it's a useless theory
until I provide some experimental test.  So to Hannu, McElwaine, and the
other fringe types: spare us your lunacy until such proof is available.

Finally, since those referred to above will undoubtedly ignore my pleas,.
I will plead with the rational people to IGNORE THE WEENIES!  If someone
posts a stupid theory, don't flame, don't make fun, don't comment.  And
as we saw with Hannu, don't even e-mail, because you'll make a martyr out
of the said person, and they'll never go away.  If we ignore silly people,
then their silliness may be taken elsewhere.  Otherwise, we're liable to
get long summaries of email, previous posts, etc., with the martyr's choice
comments.

Post finally, if you read the sci.physics FAQ, you'll see that this group
is NOT for the discussion of off the wall theories, the existence of God,
the psychological stability of Hannu's daughter, etc.  Other groups and
email exist for these purposes.  Kindly don't clutter up my, or anyone
elses's reader with useless crap.

Thank you for your support.

					Dave

DIXON@UCRPH0.UCR.EDU
Newsgroups: sci.physics
From: phfrom@nyx.uni-konstanz.de (Hartmut Frommert)
Subject: Re: What is the Speed of Exclusion
Organization: Dept. of Physics, University of Constance
Date: Fri, 2 Oct 1992 15:26:50 GMT

mbk@hamilton (Matt Kennel) writes:
>phfrom@nyx.uni-konstanz.de (Hartmut Frommert) writes:
>: matmcinn@nuscc.nus.sg (Mcinnes B T (Dr)) writes:
>: 
>: >[..]Does "gravity" propagate at the speed of light near
>: >a black hole?
>: 
>: To my knowledge, Einsteinian gravity waves always propagate at the same
>: velocity as "classical" light, i.e. mass- and structureless point particles
>: [which do not exist] along null geodesics.

[BTW: That's not the constant velocity c of course.]

>What's the speed of propagation of the Pauli exclusion "force"?

First of all, the fermions observing the Pauli exclusion are of course *not*
mass- and structureless point particles. So it is not trivial that 
Neutrinos, or even bosonic photons (which both have spin and NU's even weak 
SU(2) charge) propagate along null geodesics. So, as you indicated in the 
header, this is another subject.

In relativistic QFT the "Pauli Exclusion Force (PEF)" should propagate
with velocity no larger than c. This follows from the vanishing of 
anticommutators and cross section expectation values over spacelike 
intervals, i.e. causality.

>I.e. you have a macroscopic degenerate system.  All of a sudden one particle
>decays into other stuff (you measure the decay products and so localize the
>position of the ex-particle) and leaves a state free.  How long is it before
>the other side notices?

The sudden annihilation of one particle in the totally skew-symmetric fermion
Fock space is provided by an annihilation operator which does not touch the
antisymmetry of the system, i.e. the N fermion system is "transformed" to
a N-1 fermion system. Since [under not too strange assumptions] the laws of
Special Relativity stay alive, the time for the "other" particles to 
"notice" that process is certainly not greater than their distance to the 
annihilated one, divided by c. But I must leave a detailed demonstration
or outline of that to someone with more expertise in this field :-) .

>Would this be a physical effect of wavefunction "collapse"?

Left to the one called above :-)

 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: eric@reed.edu (eric)
Newsgroups: sci.physics
Subject: cool physics patches
Date: 4 Oct 92 08:19:21 GMT
Article-I.D.: reed.1992Oct4.081921.557
Organization: Reed College, Portland OR

I'm looking for cool patches to decorate my lab coat with.  So far I've sent
letters off to the following organizations:
hp, sun, next, macintosh, ibm, tektronix, spectra physics, lanl (los alamos
national laboratories), sfi, fermi labs, slac (stanford linear accelerator
center), cray, dec, merck labs, wolfram, motoralla, intel, sequent
what did I miss?
Also, I need email addresses for the following:
tektronix, spectra physics, fermi labs, slac, dec, merck labs, sequent

thanks,
eric


-- 

_______________
Eric Hennings / eric@reed.edu
Newsgroups: sci.physics
From: cpg@maths.nott.ac.uk (Chris Gill)
Newsgroups: sci.physics,sci.math
Subject: Re: How do you draw a straight line?
Date: 6 Oct 92 09:32:07 GMT
Reply-To: cpg@maths.nott.ac.uk (Chris Gill)
Organization: Maths Dept., Nott'm Univ., UK.

In article <1992Oct6.030213.20215@galois.mit.edu> jbaez@riesz.mit.edu (John C. Baez) writes:
>In article <1992Oct5.154211.21663@ecrc.de> micha@ecrc.de writes:
>>In article 24242@access.usask.ca, choy@skorpio.usask.ca (I am a terminator.) writes:
>>>How do you know that the line you draw is really straight? What
>>>defines straightness?
>>
>>This is something I've been wondering about since a long time. Although we can
>>make a circle as precise as we want, I think we cannot make a really
>>precise straight line
>>
>>	    [...]
>>							 IMHO there is no
>>process to create a straight line directly. Or is it?
>
>The compass is nice because it works straight from the definition of a
>circle, while a ruler, as you note, is not so nice since it does not
>work from the definition of a straight line as the shortest path between
>two points.  However, there is a machine that has been built which draws
>straight lines "by definition."  Alas, I forget how it works.
>
>	[...]

I'm sure this isn't what you were thinking of, but out in our garden, we
often make straight lines based directly upon the geodesic principle.  That
is, we take a piece of string, and stretch it, so that it takes the shortest
path between the two points.  Not very high tech, but it seems to work well
enough for the garden, and I would imagine the basic technique could be
improved to give the sort of thing you were asking about.

Chris.
-- 

Chris Gill, Postgraduate Group Theorist
Department of Mathematics, University of Nottingham, UK.
From: johan@blade.stack.urc.tue.nl (Johan Wevers)
Newsgroups: sci.physics
Subject: Re: Questions of transparency
Date: 29 Sep 92 13:10:08 GMT

davids@spira.bri.hp.com (david sixsmith (contractor)) writes:

>1. What is (are) the inherent qualitie(s) of a substance, such as glass,
>perspex, diamond, & water, which make it transparent ?

The differential equation for an EM wave traveling in matter is given by
(For E only, a similiar equation holds for B):

\nabla^2 E = \ddot{E}/c^2 + \mu\dot{E}/\rho.

were \mu is the permeability and \rho the resistance per unit of length.
This equation has plane wave solutions:

E=E_0 exp(-\alpha x) cos(kx-\omega t)

here, k=\alpha=\sqrt{\mu\omega/2\rho}. So, if \alpha is small, the wave
can penetrate deeply wthout much absorption. This happens if \rho is large
(bad conductor, like glass and perspex, and/or \mu is small (usually approx 
\mu_r:=4\pi 10^{-7} H/m for this kind of materials).

>2. What is the mechanism which makes the speed of light lower when travelling
>in such a medium as opposed to traveling in a vacuum ?

The interaction between the photons and the atoms in the medium.

>This isn't in any way homework. Am I getting no response because no-one knows ?

I'm affraid you just asked the wrong people.
-- 
********************************************************** 
* J.C.A. Wevers                *   The only nature of    * 
* johan@blade.stack.urc.tue.nl *   reality is physics.   * 
**********************************************************
From: mcirvin@husc8.harvard.edu (Mcirvin)
Newsgroups: sci.physics
Subject: Re: Spin
Date: 6 Oct 92 18:12:18 GMT
Article-I.D.: husc8.mcirvin.718395138

metares@well.sf.ca.us (Tom Van Flandern) writes:

>     If gravitation propagated at the speed of light or anything comparable,
>it too would be subject to aberration.  If an attractive force eminates from
>the Sun with some speed g, then we can represent the force by a velocity
>vector from the Earth toward the true Sun with magnitude g.  Call this vector
><EG>.  Then on a moving Earth with velocity <EV>, the apparent direction of
>the force will be <EV> + <EG>.  Observations flatly contradict this, so we
>can be sure that gravity does not propagate at the speed of light or anything
>comparable.

You seem committed to using this set of terms to describe the phenomenon,
so we ought to at least be careful to note that this doesn't require
gravitational fields to behave in an acausal manner, or to consist of
tachyons, or any such thing, any more than the absence of aberration of
the electrostatic force due to a charge moving in a straight line (the
SR equivalent of gravitational free fall, after all!) implies such things
for the electromagnetic field. 
 
> A distant point in the system would feel slight
>variations in the strength of the gravitational force because the system has
>a small dipole component, since the two stars are separate bodies instead of
>concentrated at their center of mass.  But the dipole variations are felt
>without detectable delay.

Wouldn't the correction be from the *quadrupole* component?  The dipole
component of a system of masses is zero in the center of mass frame.

The same term produces the gravitational waves.  One way of saying all
of this is to point out that the gravitational waves emitted are much
smaller in magnitude than you'd expect from unaccelerated extrapolations 
of the retarded position. 

I don't really mind statements to the effect that static fields (of
any sort) don't propagate.  It helps to counter the excessively literalistic
image, fostered by cursory descriptions of quantum field theory, of
virtual particles spraying out from the source at the speed of propagation
of the field-- which leads in turn to some of the straw-man arguments against 
quantum gravity. 

-- 
Matt McIrvin, posting nonsense again
From: crb7q@kelvin.seas.Virginia.EDU (Cameron Randale Bass)
Newsgroups: sci.physics
Subject: Re: Spin
Date: 29 Sep 92 04:24:51 GMT
Organization: University of Virginia

In article <1992Sep29.003556.3472@sjsumcs.sjsu.edu> b5249-23@mathcs.sjsu.edu (Kurt Stocklmeir) writes:
>John Baez
> his article
>
>You must be doing a lot of homework at MIT.  By the time you get
>out, you will be worn down and not ever be able to do any good research.

     Methings Mr. Baez gives a bit better than he gets these days.

>Gravitational Action        Constant
>Gravitation                 Misner Thorne Wheller P. 177 and other parts
>Look at any books about computer programs of finding paths of planets
>in a solar system.  All componets of gravity have an infinite velocity.

     I've got a computer program that puts a huge yellow bird
     on my screen.   How the heck did that bird get in my computer?

                                dale bass

-- 
C. R. Bass                                           crb7q@virginia.edu
Department of Mechanical and Aerospace Engineering
University of Virginia
Charlottesville, Virginia                            (804) 924-7926
Newsgroups: sci.physics
From: mcirvin@husc8.harvard.edu (Mcirvin)
Newsgroups: sci.physics
Subject: Re: Spontaneous Symmetry Breaking
Date: 6 Oct 92 21:14:00 GMT
Article-I.D.: husc8.mcirvin.718406040

aankrom@nyx.cs.du.edu (Anthony Ankrom) writes:

> I have never read this group so I have no idea if it has been sloshed
>around before, butI would like to know, in a nutshell, just what
>Spontaneous SymmetryBreaking is. I read an article in a quantum chemistry
>journal that discussed SSB in the visual cortex in relationship to viual
>hallucinations. (I can provide a reference if it would be handy. I have
>studied verylitlle quantum mechanics, but feel free to use technical
>terms...) This would put an interesting perspective on my study of
>neurology.

SSB is a very simple idea, and not necessarily a quantum mechanical one.
The following examples are swiped from Physics Today (the pencil) and
Sidney Coleman (the ferromagnet):

Imagine that you have a pencil lying on a flat table.  The laws of
physics for this system are completely rotationally invariant; the
pencil behaves the same way no matter how you point it.  However, the
lowest-energy configuration (in which the pencil is lying on the table,
rather than, say, standing on its point) is not rotationally symmetric.
The pencil has to point in *some* direction.  This is a very simple
example of SSB; though the physics is rotationally symmetric, the ground
state is not.  The rotational symmetry is "spontaneously broken."

The same thing happens in, for instance, a ferromagnet.  The spins of
adjoining atoms are all aligned in the lowest-energy configuration.  So
even though the laws of physics are rotationally invariant, in the ground
state the ferromagnet has a net magnetization in some direction.  If
you lived inside the ferromagnet, it would be hard for you to tell that
the underlying symmetry existed unless you heated the magnet beyond its
Curie point.

The spontaneously broken symmetries spoken of by particle physicists are
usually not of spatial rotations but of rotations in some "internal" space
of components of the field value.  It's the same basic idea, though.
The laws of physics possess a symmetry that the possible ground states 
(which particle physicists call the vacua) do not.  With a sufficiently
enormous particle accelerator or a Big Bang,  one might be able to do the
equivalent of heating the ferromagnet, and see the underlying symmetry.
-- 
Matt McIrvin, posting nonsense again
From: sichase@csa1.lbl.gov (SCOTT I CHASE)
Newsgroups: sci.physics
Subject: Re: LARSONIAN Physics and Astronomy
Date: 29 Sep 1992 13:19 PST
Organization: Lawrence Berkeley Laboratory - Berkeley, CA, USA
Distribution: world
NNTP-Posting-Host: 128.3.254.196
News-Software: VAX/VMS VNEWS 1.41    

In article <1992Sep28.222259.18699@galois.mit.edu>, jbaez@riesz.mit.edu (John C. Baez) writes...
>In article <28SEP199211153430@csa1.lbl.gov> sichase@csa1.lbl.gov (SCOTT I CHASE) writes:
>>
>>>               A SELF-CONSISTENT Theory is MUCH MORE than the ORTHODOX 
>>>          physicists and astronomers have!  They CLAIM to be looking 
>>
>>If by self-consistent, you mean that the theory make one and only one
>>well-defined prediction for any observable, which then turns out to 
>>match the experimental evidence, then modern physics is certainly 
>>self-consistent.
> 
>I think you are being rather optimistic here.  For example, QED, or the
>standard model, is not known to be consistent.  Nor are they known to be
>inconsistent.

Perhaps.  My tendency to be "optimistic" in this sense is well known 
to all.  I would prefer to say that QED is not *proven* to be consistent,
though it is known(*) to be so.  Certainly it is widely believed to be so.

(*) According to the Oracle at Berkeley.

-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: jbaez@riesz.mit.edu (John C. Baez)
Subject: Re: Spin
Organization: MIT Department of Mathematics, Cambridge, MA
Date: Tue, 29 Sep 92 19:46:51 GMT

In article <1992Sep29.115605.10858@sei.cmu.edu> firth@sei.cmu.edu (Robert Firth) writes:

>And I'm still waiting for somebody to cite the passage in the Principia
>where Newton says gravity travels with infinite speed.

In my copy it's on page 177:

Gravity travelling with infinite speed, it follows that I will abandon
my attempts to construct a theory of mechanics in which all disturbances
propagate within the cone traced out the path of light emanating from 
the source of the disturbance.

This set back the discovery of special relativity for centuries.  :-(

Seriously, there are some fascinating physical speculations in the
Principia that seem far ahead of their time.  Unfortunately I can't
remember them - I believe there are a bunch collected into one section
somewhere.   If anyone would post some I'd be very happy.  

Does Newton actually say anything concerning the speed of light?
I believe he may have made some speculations in the section I read....
Newsgroups: sci.physics
From: choy@skorpio.usask.ca (I am a terminator.)
Subject: Nuclear equations
Organization: University of Saskatchewan, Saskatoon, Canada
Date: Fri, 2 Oct 1992 23:04:47 GMT

What do we know for closed form equations describing or modelling
the activity experienced by subatomic particles? How about recursive
equations or series? Do we tend to talk about collections of
particles or can we talk about each individual particle as it
interacts with other particles? Can we predict what happens at
a particular point in space as time passes? I'm wondering about the
extent of any generalization that has been done from experimental
results. Is there a handbook of formulas available? in the works?
Anyone interested in compiling one?

Henry Choy
choy@cs.usask.ca
From: exuptr@exu.ericsson.se (Patrick Taylor)
Newsgroups: sci.physics
Subject: Re: Do black holes destroy information?
Date: 28 Sep 92 02:37:19 GMT
Organization: Ericsson Network Systems, Inc.
X-Disclaimer: This article was posted by a user at Ericsson in North America.
              The opinions expressed are strictly those of the user and
              not necessarily those of Ericsson.

In article <mcirvin.717461651@husc8> mcirvin@husc8.harvard.edu (Mcirvin) writes:

>It depends, of course, on the encyclopedia.  You could toss some
>of them into the aforementioned black hole and get no net 
>information loss.

Well I bet it would make a real mess of the new Madonna CD.  But how much 
information does THAT contain?
 ----------------------------------------------------------------------------
    "This must be Thursday.  I never could get the hang of Thursdays"
                                                       - Douglas Adams
  - Patrick Taylor                                       (Arthur Dent)
    Ericsson Network Systems
    exuptr@exu.ericsson.se                       "Don't let the .se fool you"
    or exuptr@ZGNews.Lonestar.Org, exu.exuptr@memo.ericsson.se
From: sarfatti@well.sf.ca.us (Jack Sarfatti)
Newsgroups: sci.physics
Subject: TIME TRAVEL 3
Date: 28 Sep 92 01:58:20 GMT
Organization: Whole Earth 'Lectronic Link


12.	Robert Forward of the Hughes Research Laboratory in Malibu,
California ... Forward's design for a 'vacuum fluctuation
battery' consists of a helix of ultrathin aluminium foil
charged with electricity - rather like the toy known as a
slinky. The positive electric charge holds the leaves of
foil apart, while the Casimir force tries to pull them
together... if the whole thing is allowed to collapse
slowly like an accordian being squeezed, energy from the
Casimir force will be released as usable electricity. Once
the 'accordian' has collapsed, the 'battery' can be
recharged using electricity from an outside source, just
like an ordinary rechargable battery." p.179

13.	Sarfatti Commentary: What about mobile pi electrons moving
along RNA and DNA helixes? Does the quantum biocomputer for
our immediate mental self-awareness use the Casimir force?
As computers get faster and smaller, the Casimir force will
come into play as noise or as something else? The Casimir
force will impact on nanomachines.
From: John.C..Baez@mailbox.bison.mb.ca (John C. Baez)
Newsgroups: sci.physics
Subject: Re: Defining local, causal etc., was: Hidden variable theories
Date: 25 Sep 92 07:20:19 GMT

Organization: MIT Department of Mathematics, Cambridge, MA

In article <1992Sep23.211346.551@oracorp.com> daryl@oracorp.com (Daryl McCullough) writes:

>I still don't understand your answer about why you find "wave function
>collapse" more problematic than "measuring such and such a value with
>such and such a probability".

Having written reams about this in the last few weeks, I can only 
concede defeat.


> In the MWI, these are equally illusory;
>there is no collapse and there are no probabilities (everything is
>deterministic).

A version of quantum mechanics which does not allow one to calculate
probabilities of experimental outcomes is useless.  Regardless of
"the MWI," whatever you take that to be, in the interpretation of
QM I have been outlining for the last few weeks I have been emphasizing
the role the wavefunction plays as an intrument for calculating
probabilities.  

 * Origin: The Electronic Mailbox (1:348/7.0)
Newsgroups: sci.physics