HDTenEightyP/NetNews huggingface dataset:
From: aephraim@physics.Berkeley.EDU (Aephraim M. Steinberg)
Newsgroups: sci.physics
Subject: Re: How do you draw a straight line?
Date: 6 Oct 1992 17:38:14 GMT
Organization: University of California, Berkeley
NNTP-Posting-Host: physics.berkeley.edu

In article <12950087@hpspdla.spd.HP.COM> ric@hpspdla.spd.HP.COM (Ric Peregrino) writes:
>
>How about a taught string?

Exactly, but I think the question was: how do you teach it?

(Besides, if the string has any mass and is in any gravitational field
whatever, then any finite tension will still leave it a catenary, just
a straighter and straighter one.  I believe the question was one of
principle.)


-- 
Aephraim M. Steinberg                    | "WHY must I treat the measuring
UCB Physics                              | device classically??  What will
aephraim@physics.berkeley.edu            | happen to me if I don't??"
                                         |       -- Eugene Wigner
Newsgroups: sci.physics
From: jbaez@riesz.mit.edu (John C. Baez)
Subject: Re: Simple observation about Quantum Kitty Cats
Organization: MIT Department of Mathematics, Cambridge, MA
Date: Fri, 2 Oct 92 20:22:49 GMT

In article <299@mtnmath.UUCP> paul@mtnmath.UUCP (Paul Budnik) writes:
>In article <22592@galaxy.ucr.edu>, baez@ucrmath.ucr.edu (john baez) writes:
>> 
>> That may be how philosophy works - pitting argument against argument -
>> but it's not how physics works; there one pits model against model.
>> Just saying "quantum collapse as a physical local process" won't stack
>> up against a well-developed formalism that people have successfully
>> used for decades.  You need to lay out a precise model of quantum
>> collapse as a physical local process and show how one can calculate
>> all sorts of things with it.  I.e., you have to match the competition.
>> OR you have to get ahold of an experiment that shows the existing formalism
>> makes wrong predictions.  
>
>But my formalism makes the same predictions of quantum mechanics with
>the exception of tests of Bell's inequality. 

Let's see your formalism - where are the equations?  What precisely does
it predict in situations where QM violates Bell's inequality?  Not
words, numbers.  Show how to do some QFT-type calculations using this
formalism (since QFT combines relativity and QM) - say electron-electron
scattering.
From: jbaez@riesz.mit.edu (John C. Baez)
Newsgroups: sci.physics
Subject: Re: Simple observation about Quantum Kitty Cats
Date: 29 Sep 92 18:28:35 GMT
Organization: MIT Department of Mathematics, Cambridge, MA

In article <717712154.5@mailbox.bison.mb> Jim.Giles@mailbox.bison.mb.ca (Jim Giles) writes:
>Organization: Los Alamos National Laboratory
>
>In article <1992Sep24.190216.13493@riacs.edu>, danforth@riacs.edu (Douglas G. Danforth) writes:
>|> [...]
>|> If by hypothesizing a new structure that subsumes two other descriptive
>|> models then the new structure gains significance via its generality
>|> and reduction in parts.  The possibility of a unified field that
>|> corresponds with QM and GR leads one to look for such an explanation. 
>
>Only if that new hypothesis has *testable* consequences.  If not, it's
>an exercise in mysticism.  Now, don't get me wrong - have nothing against
>mysticism.  Imagination and wishful thinking may *lead* to testable
>ideas.  I just oppose mysticism being promoted as known fact.

Of course, mathematics has been a branch of mysticism ever since the
Pythagoreans (if not earlier).  As a mathematician, if one could
find a mathematical model from which quantum mechanics and general
relativity both "fell out" in some natural manner, it would count
as an outstanding achievement even if it had no testable consequences.
Elegance, generality and "reduction in parts" are very important in
mathematics and also physics to the extent that it is mathematical!
This is indeed the mystical side of physics, relying as it does on
the faith that "mathematics is the language of nature" (to paraphrase
Galileo) which yields the "unreasonable effectiveness of mathematics"
(to quote Wigner).  However, this mystical faith is time-tested and
proven; one need only study how Kepler arrived at his 3 laws, or how
Einstein arrived at general relativity, to see that the pursuit of
mathematical beauty, in conjunction with painstaking attention to the
empirical clues provided by nature, can lead to theories that *later*
turn out to have empirical consequences.  One should not be in too much
of a rush to demand testable consequences; mathematics that is both
rigorous and elegant has a strong tendenccy to come in handy eventually.
Newsgroups: sci.physics
From: pratt@Sunburn.Stanford.EDU (Vaughan R. Pratt)
Subject: Re: Understand...!!!!
Organization: Computer Science Department,  Stanford University.
Date: Thu, 1 Oct 1992 06:55:19 GMT

In article <1992Oct1.044951.18999@nuscc.nus.sg> matmcinn@nuscc.nus.sg (Mcinnes B T (Dr)) writes:
>I am a serious person with a vast store of good will. But you know that
>baloney is not a clock because you know that it doesn't measure time.
>That's because you know that time exists independently of devices used
>to measure it. It's about time [so to speak] to drive a stake [or is
>that steak?] through the heart of operationalism. .

1.  Which alternative did you have in mind?  Both in mathematics and
physics, Platonism postulates a reality independent of our
interpretation of that reality (the falling tree must make a sound).
Rationalism was Chomsky's alternative to Skinner's behaviorism,
advocating the explanation of observed phenomena in terms of postulated
unobserved phenomena.

I'm no great fan of Platonism, as my previous posts have indicated.  I
do however enormously like rationalism, which seems to me not only a
marvellously sensible way to do science but how most of us actually do
it in practice, whether or not consciously.  From that perspective
Platonism can be seen as merely a mental crutch allowing us to refer
all postulates to an imagined "reality," against which we imagine
ourselves to be testing those postulates.  This crutch seems very
effective, but the nature of that effectiveness is purely
psychological, reassuring us in much the same way that we are reassured
by looking out a window and seeing ground and buildings in their usual
places.

Instead of debating the unanswerable question of whether time has any
existence, would it not be better to focus on explanations of observed
temporal phenomena?

Such a line of investigation leads away from the rigid world of "one
time to bind them all" to a variety of notions of time.  This is done
for example in the paper "Temporal Structures", Mathematical Structures
in Computer Science 1:2, 179-214, July 1991, by Casley, Crew, Meseguer
and myself, where a variety of notions of time are defined, only some
of which assume that time is a continuum.  A similar theme is pursued
in Winfree's book "When Time Breaks Down", Princeton U. Press, 1987.

2.  Again let me ask: what does any of this discussion have to do with
time per se?  It seems to me that the points that have been made so far
on this topic could be applied to the observation and independent
existence of *any* observable.

-- 
=================================================== In short, I am floundering
Vaughan Pratt   pratt@cs.Stanford.EDU  415-494-2545 around and don't take what
=================================================== I say seriously.
Newsgroups: sci.physics
From: scip1061@nuscc.nus.sg (Marc Paul Jozef)
Subject: Re: Information on author F. David Peat (Einstein's Moon)
Organization: National University of Singapore
Date: Tue, 6 Oct 1992 12:37:18 GMT

Is that the same Peat as the one who wrote a book on
superstrings and twistor-theory?
I hope not, because that guy understands his topics
about as well as Hannu understands her potatoes.
From: daryl@oracorp.com (Daryl McCullough)
Newsgroups: sci.physics
Subject: Quantum Zeno Effect, Part 1.
Date: 3 Oct 92 13:46:53 GMT
Organization: ORA Corporation

In quantum mechanics, it seems literally to be the case that a watched
pot never boils. More specifically, if an observable A is measured
frequently enough, it is possible to prevent the value of A from
changing. In this posting, I will give a nonrigorous argument for
why this is true.

This effect, which is sometimes called the "quantum Zeno effect" is
derivable from elementary quantum mechanics. If a quantum system starts
in an eigenstate |a> of observable A with eigenvalue a, then its state
time t later will be given by (approximately, for small t)

    |Psi(t)> = |a> - it/h-bar H |a>

where H is the Hamiltonian. The probability at time t of measuring
observable A to have value b different from a is approximately

    P(b,t) = t^2 (h-bar|<b|H|a>|)^2 = C t^2
    (where C is independent of time)

If you observe eigenvalue a, then that means that the system is still
in state |a>, which means that the probability of observing b at time
2t, given that you observed a at time t is the same as P(b,t) above.
Therefore, the probability that you will observe A to have value b
different from a in any of N measurements spaced at intervals t is
given approximately by: (letting the product Nt be T)

    P(b,T) = N P(b,t) = Nt^2 C = T^2 C/N

In the limit as N -> infinity, keeping T fixed, we get P(b,T) = 0. In
other words, if you measure a value often enough, you can prevent it
from changing. An example where the quantum zeno effect applies is in
observation of alpha decay. As I understand it, "watching" a
radioactive atom closely can make the rate of alpha decay go to zero,
and this has actually been observed.

Now, this effect is easily explained using the collapse of the wave
function; every time you observe the state of the particle, you
collapse its state back into an eigenstate of the observable. However,
it seems that most physicists these days don't really believe in the
collapse of the wave function as a physical effect. Some view it as
simply a matter of a change of knowledge; that is, collapsing the wave
function simply represents a collapse in the set of possibilities, and
has no more physical meaning than the corresponding collapse that
occurs when you peak at a coin after you have flipped it. However, it
is hard to reconcile a change in knowledge with an actual physical
effect such as the slowing of the decay rates of radioactive
particles. Regardless of interpretation, it is a real, observable
effect.

Daryl McCullough
ORA Corp.
Ithaca, NY
From: matt@physics16.berkeley.edu (Matt Austern)
Newsgroups: sci.physics
Subject: Re: I'm no radical
Date: 5 Oct 92 10:51:09
Organization: Lawrence Berkeley Laboratory (Theoretical Physics Group)
Reply-To: matt@physics.berkeley.edu
NNTP-Posting-Host: physics16.berkeley.edu
In-reply-to: paul@mtnmath.UUCP's message of 5 Oct 92 17:33:35 GMT

In article <308@mtnmath.UUCP> paul@mtnmath.UUCP (Paul Budnik) writes:

> In reviewing your posts it was general relativity not
> quantum mechanics that you said may require change at
> small distances.

Almost everyone believe this, not just Dr. Baez.  General Relativity
is a classical theory, just like (for example) classical
electromagnetism.  It is generally believed that at short distances,
it will instead be necessary to use a quantum-mechanical theory of
gravity.  

A great many people are working on quantizing gravity.  It is a
difficult problem, and as far as I can tell (this work is very
technical, and I am not involved in it) it hasn't been terribly
successful yet.

--
Matthew Austern                   Just keep yelling until you attract a
(510) 644-2618                    crowd, then a constituency, a movement, a
austern@lbl.bitnet                faction, an army!  If you don't have any
matt@physics.berkeley.edu         solutions, become a part of the problem!
Newsgroups: sci.physics
From: m14494@mwvm.mitre.org (Mike White)
Subject: Re: NOVA is about Leo Szilard
Organization: The MITRE Corporation
Distribution: usa
Date: Mon, 28 Sep 1992 15:59:48 GMT

Jim Carr writes:
> Just a program note...
> ...NOVA on PBS is featuring a story about Leo 
> Szilard and his involvement in the development of the bomb.

Thanks.  This is great; I just hope they do the subject justice.

> Szilard is less well known for his scientific contributions.
> Perhaps the most important was his effort to get truely pure
> graphite for cross section tests...

This is of course true and very important, but for me, his really
epoch-making discovery was the nuclear chain reaction, which
he theorized, and later experimentally verfied.  When he saw the
results of his neutron multiplication experiment, and realized that
there was enough multiplication for a self-sustaining reaction, he said
"I think the world is in for a very bad time".  How right he was.

************************
* These are my opinions only.*
************************
From: bwallet@apssgi.nswc.navy.mil (Brad Wallet)
Newsgroups: sci.physics
Subject: Re: Cheap laser possible?
Date: 28 Sep 92 15:50:14 GMT
Organization: Naval Surface Warfare Center

In article <1992Sep28.141907.29179@ucsu.Colorado.EDU>, knapp@spot.Colorado.EDU (David Knapp) writes:
|> You might try to check out a Scientific American article of several years
|> ago (maybe many years ago, now '79??) where a nitrogen laser is described
|> for home building in detail. It is certainly the most affordable and
|> easiest.

That was in Scientific American issue June, 1974 in the Amature Scientist
column.

Brad
Newsgroups: sci.physics
From: evans@ftp.phy.uab.edu (Kervin Orlando Evans)
Subject: Determining Fluorescence Properties By Bilot-Kawski Equation
Organization: University of Alabama at Birmingham
Date: Mon, 28 Sep 1992 18:27:42 GMT

The fluorescence properties of molecules in solvents can be determined by using
the Bilot-Kawski equation, which depends on the static dielectric constant and 
the frequency-dependent refractive index of the solvent.  However, all of the
literature found so far give different versions.  So, if anyone has an idea of
the best version to use, or where to look for it(along with a reasonable   
explaination of derivation), please contact me ASAP.
From: rwa@aupair.cs.athabascau.ca (Ross Alexander)
Newsgroups: sci.physics
Subject: Re: Response to PUTTING VENUS IN AN ORBIT ... and TIME HAS INERTIA
Date: 2 Oct 92 18:01:17 GMT
Article-I.D.: aupair.rwa.718048877

abian@iastate.edu (Alexander Abian) writes:

	[pompous bombast elided; this is a family group]

>   People should study my proposals and further develop them.  Their 
>implementation is inevitable.

Alex, if they really are inevitable, shouldn't people instead just lie
back and let them happen by themselves?  It would save a lot of work!

ob joke:  how many supply siders does it take to change a light bulb?
    ans:  none; the darkness will cause the creation of another.

tally ho,
Ross

--
Ross Alexander  rwa@cs.athabascau.ca  (403) 675 6311  ve6pdq@ve6mgs.ampr.org
From: matt@physics.berkeley.edu (Matt Austern)
Newsgroups: sci.physics
Subject: Re: Spin
Date: 6 Oct 92 15:26:43
Organization: Lawrence Berkeley Laboratory (Theoretical Physics Group)
	<1992Oct5.013734.29341@unixg.ubc.ca> <Bvon89.I70@well.sf.ca.us>
	<mcirvin.718395138@husc8> <mcirvin.718405900@husc8>
Reply-To: matt@physics.berkeley.edu
NNTP-Posting-Host: physics.berkeley.edu
In-reply-to: mcirvin@husc8.harvard.edu's message of 6 Oct 92 21:11:40 GMT

In article <mcirvin.718405900@husc8> mcirvin@husc8.harvard.edu (Mcirvin) writes:

> >I don't really mind statements to the effect that static fields (of
> >any sort) don't propagate. 
> 
> I reminded myself after I posted this that the fields in the solar
> system aren't static.  "Radiation-free" is a better term.

In my opinion, "radiation-free" isn't too bad a definition of
"static."  

After all, just think of the electromagnetic field produced by a
nonaccelerating point charge; the fields are time-varying if it is
moving in the lab frame, but they aren't if it is at rest in the lab
frame.  That is: whether or not the fields are time-varying is not a
Lorentz-invariant distinction.

(And, of course, the electromagnetic "field lines" from a point charge
moving with constant velocity will always point to the present, not
retarded, position of the charge.  This does not mean that
electromagnetic forces travel faster than light.)
--
Matthew Austern                   Just keep yelling until you attract a
(510) 644-2618                    crowd, then a constituency, a movement, a
austern@lbl.bitnet                faction, an army!  If you don't have any
matt@physics.berkeley.edu         solutions, become a part of the problem!
Newsgroups: sci.physics
From: clarke@acme.ucf.edu (Thomas Clarke)
Subject: Re: How do you draw a straight line?
Organization: University of Central Florida
Date: Tue, 6 Oct 1992 13:01:24 GMT

How about the carpenter's chalk line?
Stretch a string coated with chalk dust where you
want the line to be and then give it a snap. leaving a
linear chalk mark.

You should be able to asymptotically approach a straight
line.  Let string tension go to infinity, let chalk dust
size go to zero, and let amplitude of snap go to zero.
--
Thomas Clarke
Institute for Simulation and Training, University of Central FL
12424 Research Parkway, Suite 300, Orlando, FL 32826
(407)658-5030, FAX: (407)658-5059, clarke@acme.ucf.edu
Newsgroups: sci.physics,sci.math
From: jbaez@riesz.mit.edu (John C. Baez)
Subject: Re: Mattel protest
Organization: MIT Department of Mathematics, Cambridge, MA
Distribution: usa
Date: Tue, 6 Oct 92 03:15:56 GMT


>     I take it then that y'all did not find math to be tough?
>
>                               dale bass

No.  Honest, most things in life are more tough for me than math.
I can just imagine more realistic Barbies:

"Getting enough money to put a down-payment on a house these days is tough!"
"Dealing with my personality differences with Ken is tough!"
"Reconciling quantum theory and general relativity is tough!"
"Facing up to my mortality and existential angst is tough!"
From: baez@ucrmath.ucr.edu (john baez)
Newsgroups: sci.physics
Subject: Re: Expansion
Date: 30 Sep 92 16:31:21 GMT
Organization: University of California, Riverside

In article <29SEP199220244986@zeus.tamu.edu> dwr2560@zeus.tamu.edu (RING, DAVID WAYNE) writes:
>This makes sense. What I don't understand is why a region of high density
>homogeneity does not recollapse in a time appropriate to that density. I.e.
>if the universe were filled with stars, in the density of a galaxy, the
>universe would have recollapsed long ago. The region of space which is
>inside a galaxy satisfies the same local einstein equation as the above
>recollapsing example, so why do galaxies live so long?

'Cause they're smaller.  I'm sure one can work out the math, but
it's bound to amount to just that.  For example, one can have
a fist-sized ball of iron, which will essentially never collapse
(quantum fluctuations aside), but a galaxy-sized ball of iron
would collapse mighty fast.

Galaxies are not all *that* dense and they're spinning around (at least
lots of them).  So they will take a while to collapse.  It's become
widely accepted that many galaxies have black holes at their centers.
These black holes are eating stars at a decent rate and should only
be billions and billions of years before they suck up most of the
galaxy, or at least the dense inner part.

Does anyone have estimates on how long this munching process should
take and how it will proceed?
Xref: sparky sci.physics:15989 sci.astro:10437 sci.math:12758 sci.philosophy.tech:3562
From: bunner@vms.macc.wisc.edu (Dana A. Bunner)
Newsgroups: sci.physics,sci.astro,sci.math,sci.philosophy.tech
Subject: Re: Hannu is a wood-duck
Date: 6 Oct 92 04:50:59 GMT
Organization: University of Wisconsin Academic Computing Center

In article <1992Oct5.224151.13702@organpipe.uug.arizona.edu>, newberry@kepler.as.arizona.edu (Mike Newberry) writes...
>*******************************************************
>OK, what does this thread have to do with ASTRONOMY ???
>*******************************************************

True enough.  The original poster should have called Hannu a Wild Duck.

Dana
From: mvb@chopin.udel.edu (Maurice V. Barnhill)
Newsgroups: sci.physics
Subject: Re: Rishon
Date: 1 Oct 92 11:42:22 GMT
Article-I.D.: news.BvFxun.626
Distribution: na
Organization: University of Delaware

In article <1992Sep29.173039.5945@galileo.physics.arizona.edu> seh@neutron.physics.arizona.edu writes
>Does anyone know what a "rishon" is? Someone asked me about this a while
>ago and I couldn't find it in the "Particle Data Handbook." Sounds pretty
>exotic, though...
>
>Thanks,
>Steve Hoell		seh@neutron.physics.arizona.edu

Rishons were hypothesized as constituents of quarks.  The general idea was to
explain the prolification of quarks by describing them as the bound states
of a smaller number of constitutent particles.  The proposal didn't lead
anywhere useful and the idea was abandoned.
    Maurice Barnhill
    University of Delaware
Newsgroups: sci.physics,rec.pets.cats
From: zowie@daedalus.stanford.edu (Craig "Powderkeg" DeForest)
Subject: Amusing Radiation Regs (was Re: Radioactive Cat: How Dangerous ... ?)
Organization: Stanford Center for Space Science and Astrophysics
	<1992Sep9.225426.20316@hsv3.lsil.com>
	<1992Sep25.182429.29289@bnlux1.bnl.gov>
Date: 27 Sep 92 13:00:36

schroede@bnlux1.bnl.gov (gary l. schroeder) writes:
   mvp@hsv3.lsil.com (Mike Van Pelt) writes:
   >An old high-school friend of mine went to work at a nuclear plant after
   >he got out of the Navy, and he had a story or two to tell about I131
   >treatments.  
	...
   Radionuclides used in patient therapy such as iodine-131, are 
   non-regulated in that the material that leaves the patient via excreta
   is non-regulted. 

It's amusing to read 10CFR20, the Federal regulations on radiation dose,
and find the passage about tagging radioactive sources.  At one point, the
regs say that any object with more than <x> activity must be clearly 
labelled and placed in a radiation restricted zone, unless the object in 
question is a patient undergoing radiotherapy (!)

--
...Behind me, the crowd was still cheering as Cal kicked off the 3rd quarter.
   One of the cops examined my band field pass; two more stood ready in case I
   bludgeoned the fourth with my flute.  He snickered and said, "You'll 
   *never* ride a motorcycle in this stadium *again*!"
Newsgroups: sci.physics
From: bhv@areaplg2.corp.mot.com (Bronis Vidugiris)
Subject: Re: TIME TRAVEL 4
Organization: Motorola, CCR&D, CORP, Schaumburg, IL
Date: Tue, 29 Sep 1992 20:39:48 GMT

In article <1992Sep29.014446.20218@galois.mit.edu> jbaez@riesz.mit.edu (John C. Baez) writes:

)No, it's clearly THE SAME SARFATTI having used his faster-than-light
)communication system to beam himself back to the Crusades.  This PROVES
)that it works!

Even if it hasn't happened - YET.

:-)

Newsgroups: sci.physics