HDTenEightyP/NetNews huggingface dataset:
From: bweiner@ruhets.rutgers.edu (Benjamin Weiner)
Newsgroups: sci.physics
Subject: Re: Black Holes, Hawking Radiation, and Entropy
Date: 15 Oct 92 22:23:33 GMT
Organization: Rutgers Univ., New Brunswick, N.J.

Matt Austern writes:
>Hawking radiation.  This is just thermal black-body radiation, i.e.,
>the radiation is described by a density matrix given by the Boltzmann
>factor.  It certainly appears, at any rate, as if what is happening is
>that a pure state is evolving into a mixed state.

[This is why people worry about this, because it's not time-reversible.]

>So what's the solution?  I don't know.  Some people have suggested
>that quantum mechanics has to be modified in such a way so that it is
>possible for pure states to evolve into mixed states.  My own feeling
>is that since we haven't even observed black holes at all, let alone
>Hawking radiation, it's a bit premature to start modifying quantum
>mechanics on the basis of how Hawking radiation works.

I'm sympathetic to this, but there do seem to be a few causes for
concern.  First, plain vanilla black holes can have an event horizon
out where the curvature of space is Not Terribly Large (NTL), so
that semiclassical calculations (such as the existence of the horizon,
and more tenuously, Hawking radiation) shouldn't be too badly wrong.

Then, if you drop junk into a black hole, it comes out as thermal
Hawking radiation; unless that radiation is really carrying the
information out through some kind of jiggered-up higher-order
fabulously subtle correlations, which seems too contrived, then the
black hole evaporates down almost to nothing with all the information
still inside, meaning that a remnant of arbitrarily small size
has a complex enough interior structure to encode all the information.

This is ugly, and some people feel it's ruled out (by experiment!)
since then there would be an infinite phase-space density of remnants
and they would be created as virtual particles.  However, I just saw a
talk by Andy Strominger in which he claimed that there's a way around
it for "dilaton" black holes, but I'm way out of my depth here.
Regardless, notice that this is before, and independent of, what
happens at the putative final "evaporation," which is good since
no-one can claim to know anything about that.

There was a nice review paper by John Preskill on this very subject
on the hep-th preprint server last month; thanks to John Baez who
originally posted a notice of that paper.
From: ric@hpspdla.spd.HP.COM (Ric Peregrino)
Date: Wed, 7 Oct 1992 18:06:07 GMT
Subject: Re: How do you draw a straight line?
Organization: HP Stanford Park - Palo Alto, CA
Newsgroups: sci.physics


Concerning the use of a laser as a reference for a straight line.

If you use the definition of a laser beam as a straight line,
since it is geodesic, then you might as well use the trajectory
of say the moon, since it too is a geodesic. This is probably not
what the original poster had in mind, but I suggest that the
geodesic of an Euclidean space was what was intended. A laser beam
does not provide such a geodesic in the presence of a gravitational
field, as doesn't the taught string, for arbitrary directions in
relation to the gravity, but only in the direction of "up and down".
But for practicle purposes, both work fine.

--------------------------------------------------------------------
Ric Peregrino   c/o Hewlett Packard Co.    I represent only myself
ric@spd.hp.com  1501 Page Mill Rd Bldg 5M  I may be wrong, maybe nit
415-857-7526    Palo Alto, CA 94304        Are DC photons detectable?
--------------------------------------------------------------------

Newsgroups: sci.physics
From: bhv@areaplg2.corp.mot.com (Bronis Vidugiris)
Subject: Re: Quantum reality silliness
Organization: Motorola, CCR&D, CORP, Schaumburg, IL
Date: Tue, 13 Oct 1992 17:43:45 GMT

In article <1992Oct10.025445.14017@mnemosyne.cs.du.edu> ddixon@nyx.cs.du.edu (David Dixon) writes:
)AAAAAAAAAAAAAAAAAAUUUUUUUUUUUUURGH!  I can't take it anymore!  Bell's
)inequality to the left of me, wave function collapse to the right!  I
)think I'm going ... MAD!
)
)It seems to me that this situation has become more complicated than it needs
)to be, largely because (I think) of prejudice that the world is necessarily
)dterministic.  Look, folks, just because we live in a world macroscopically
)inhabited by ping-pong ball like objects does NOT mean that there is any
)correlation implying that such "determinism" exists in the microscopic
)world.

...

)I think a lot of the confusion about quantum mechanics occurs because we
)have been imbued with this belief in the wave-particle duality, as if
)sub-atomic particles somehow consisted of a "wave" which carried along a
)tiny point-like particle with it.  Baloney.  The proper way to think of it
)is that the wave function is a field which tells you probabilities of a
)certain amount of energy or momentum being exchanged at a certain point
)in space-time.  Nothing mystical about it.

The issue isn't one of determinism.  Non-deterministic theories that are
local and realistic also have the same problem.

If you accept classical definitions of probability, and also believe that
trees do make a sound when they fall in a forest even if there is no one
to hear it :-) (and particles do have a spin direction even if they haven't
been measured yet), you run into the problem with QM.

The experimental evidence is, of course, the key issue.  If locality or
realism had been definitely disproved, that would be one thing.   The
current status is not quite that clear.

Newsgroups: sci.physics
From: pratt@Sunburn.Stanford.EDU (Vaughan R. Pratt)
Subject: Re: Can Information Have Physical Units?
Organization: Computer Science Department,  Stanford University.
Date: Wed, 7 Oct 1992 22:18:52 GMT

In article <1992Oct5.153852.12046@asl.dl.nec.com> terry@aslws01.asl.dl.nec.com (Terry Bollinger) writes:
>A CHALLENGE REPEATED:  HOW ABOUT PHYSICAL UNITS FOR "INFORMATION?"
>
>I was also very much serious about whether someone out there might have any
>ideas on how to link units of information to other units in physics, using
>some link to, say, changes in QM interference effects.  It's an interesting
>exercise, and one with some promise of real formalization, not just hand-
>waving.  (Whether you would be able to get anyone to *agree* to your
>formalization is another issue!)

It would be very convenient from an information-processing perspective
if one could, at least isothermally, equate information to energy.  For
in physics time is conjugate to energy, while in computation time is
conjugate to information.  For the latter, observe that in the typical
alternation of a (presumably isothermal) computer between events and
states, events hold time fixed while changing information, while states
hold information fixed while changing time.  Large events may take
nonzero time, while long-duration states may vary a little in their
information, but this is just to say that events can become state-like
while states can become event-like; the ideal event takes no time while
the ideal state changes no information.

For nonisothermal computation the relevant equation is dS = dQ/T: a
packet of information (aka entropy) equals a packet of energy divided
by the temperature.  ("Packet" here can be any size provided only that
T is sufficiently close to being constant for the duration of the
packet.  For oversized packets one may treat this formula as an
approximation whose accuracy can be improved by taking T to be a
suitable average of the prevailing temperature during the packet
exchange.)

A nice information-processing interpretation of temperature is as the
noise/signal ratio, which you can think of as measuring how hard you
have to yell (i.e. how much energy to put into the yell) to communicate
a yes or a no to someone.  Stock exchanges and mating couples operate
at higher temperatures than poker games and confessionals.  We may look
forward one day to weather reports that list more than just the air
temperatures of major cities.

-- 
=================================================== In short, I am floundering
Vaughan Pratt   pratt@cs.Stanford.EDU  415-494-2545 around and don't take what
=================================================== I say seriously.
From: aws@ms.uky.edu (Albert Schueller)
Newsgroups: sci.physics
Subject: Planck Length?
Keywords: discrete space-time
Date: 15 Oct 92 18:24:09 GMT
Article-I.D.: ms.1992Oct15.142409.22128
Organization: University Of Kentucky, Dept. of Math Sciences

A colleague and I were discussing this notion of discrete distances and
time, and we have some questions:

1)  What is the current standing of theories that describe the universe
as having finite precision in space and time?  Are there any?

2)  What questions do such theories attempt to answer?  (read: Why
consider finite precision?  Why can't the universe be a continuum in
space-time?)

3)  Has any work been done in the development of a finite precision
calculus?  (number theoretic, abstract measure theory etc.)

We would appreciate any references you might have pertaining to these
areas.  (please e-mail, as I don't want to clutter the net with such
things)  Thanks all.



-- 
Albert W. Schueller				University of Kentucky, Math

"And now for something completely different..."  
Xref: sparky sci.physics:16389 sci.math:13082 soc.men:17647 soc.women:17636
From: pepke@ds1.scri.fsu.edu (Eric Pepke)
Newsgroups: sci.physics,sci.math,soc.men,soc.women
Subject: Re: Mattel on women
Date: 13 Oct 92 01:38:45 GMT
Reply-To: pepke@ds1.scri.fsu.edu (Eric Pepke)
Followup-To: sci.physics
Organization: Florida State University, but I don't speak for them

In article <1992Oct12.173039.3065@tellab5.tellabs.com> chrz@tellabs.com (Peter Chrzanowski) writes:
>In fairness, it might be noted that a lot of 20th century science is either
>counter-intuitive, or just difficult to understand.  Einstein's mechanics of
>motion is less intuitive than Newton's, and molecular biology is less
>accessible than Darwin.

Ah, but the major part of this guy's thesis was that during the 19th and 
early 20th centuries popularizers of science concentrated (in my view 
correctly) on the methodology of science rather than on collections of facts.

If you have the methodology, you can always determine the state of research.
If you don't have the methodology, it doesn't matter how many facts you have
been fed; they all seem like magic.

-EMP
Newsgroups: sci.physics
From: dwr2560@zeus.tamu.edu (RING, DAVID WAYNE)
Subject: Re: How to get preprints in latex form electronically
News-Software: VAX/VMS VNEWS 1.41    
Organization: Texas A&M University, Academic Computing Services
Date: Wed, 14 Oct 1992 17:09:00 GMT

jbaez@riesz.mit.edu (John C. Baez) writes...
>I was going to to refuse to tell anyone how to get things from 
>gr-qc, since this has come up so often, but someone I like asked me
>so I will post the recipe and save it in a file so I never have to type this
>again.

I think this stuff deserves a place on the FAQL

Dave Ring
dwr2560@zeus.tamu.edu
From: terry@aslws01.asl.dl.nec.com (Terry Bollinger)
Newsgroups: sci.physics
Subject: Re: Time to develop a crackpot index?
Date: 16 Oct 92 14:39:06 GMT
Organization: NEC America, Inc Irving TX

Howdy ya'll,

In article <1992Oct16.042744.22785@galois.mit.edu>
jbaez@riesz.mit.edu (John C. Baez) writes:
> In article <1992Oct15.181831.13283@asl.dl.nec.com>
> terry@aslws01.asl.dl.nec.com (Terry Bollinger) writes:

> | The statement you are now reading is clearly false.

> Your statement is false, but not clearly so...

My hat is off to you, sir.  Your innovative logic is refreshing.  Most folks
would never think of breaking the unity of the assertion to arrive at a way
to break the trap.  There is a curious mental habit most of us have of
setting up all sorts of little "rules" and constraints about how we should
go about solving problems -- rules that often keep us *from* solving them.

Example: I once posted a quiz on my wall and added "a really big hint is
posted right on this same wall."  There were several other older quizzes,
which everyone diligiently went crazy searching through for the Hint.
(My prizes were always big bags of chocolate, the world's one and only
*truly* effective research incentive.)  For a period of weeks, nary a soul
paid any attention whatsoever to my name plate, since it had been there
long before any of the quizzes.  The answer to the quiz was "Bullinger."

Anywho, my expectations are now high, Dr. Baez.  When may we expect you to
publish a GUT theory showing similar logical innovation, a GUT theory that
does more than just rummage through the toybox of group theory like a kid
looking for the "right" toy?

				Cheers,
				Terry

P.S. - Dale Bass: Grad student, hmm?  Would you believe I had you pegged
       mentally as a curmudgeonly 60+ year old mechanical engineering prof
       out to give young whippersnappers a hard time?  Nets are amazing
       things -- in the absence of solid info the imagination wanders wildly.

       But please don't toss out history like some old cookies.  It has its
       place, even in science, because the idea that we are islands to our-
       selves is very much an illusion.  It never hurts at least to know
       where the foundation stones are a laid, even if you insist that where
       they were quarried and the texture of the stone is irrelevant.
       
       (For those curious:  I am a 37 year old father of four, Masters and
       Bachelors in Computer Science, a best paper award from a leading
       publication in my own field, and known on occassion for gently (?)
       harassing physicists.  (Well, I *did* send a raspberry to a Nobel
       Laureate once via the net, but how was I to know that some guy named
       Schwinger was of any note?  I never heard of him in *my* field.  His
       idea was stupid anyway, and I was right anyway, so what the heck...)

       (Hey, does correcting a Laureate even when he's being assinine count
       for anything on the crackpot index??)
Newsgroups: sci.physics,sci.math
From: jim@cs.UAlberta.CA (Jim Easton)
Subject: Re: How do you draw a straight line?
Organization: University of Alberta, Edmonton, Canada
Date: Thu, 8 Oct 1992 23:42:27 GMT

tekman@ecn.purdue.edu (Erkan Tekman) writes:

>What is the definition for a straight line anyhow?

Well any machinist has a pretty good idea of what a straight line is
and for practical purposes can be generated in a variety of ways.

As for a definition didn't Einstein define it as "the path
light takes".

	Jim
Newsgroups: sci.physics,sci.math
From: pratt@Sunburn.Stanford.EDU (Vaughan R. Pratt)
Subject: Re: How do you draw a straight line?
Organization: Computer Science Department,  Stanford University.
Date: Fri, 9 Oct 1992 05:03:17 GMT

In article <jim.718586962@st-michael> jim@cs.UAlberta.CA (Jim Easton) writes:
>Since it doesn't look like anyone else is going to answer this I
>guess I will.  There is a linkage which will draw a straight line.
>I tried to draw it in ascii but it didn't work very well so I wrote
>a little postscript program which will draw it which I have put at
>the end of this article.

Your diagram is exactly the Peaucellier cell that Jim Reeds mentioned
(via John Baez) a few hours back.

So Jim, what has the little industry of 3-space linkages in robotics
produced that will draw a straight line, other than those that already
work in 2-space?
-- 
Vaughan Pratt   pratt@cs.Stanford.EDU     exp(n pi sqrt(163)/3) for n=1..30
From: lnh@soliton.physics.arizona.edu (sometimes a Wombat)
Newsgroups: sci.physics
Subject: Re: TIME HAS INERTIA AND THE PRINCIPLE OF TENDENCY OF MAINTAINING THE
Date: 11 Oct 92 20:05:00 GMT
Distribution: na
Organization: Society for the Appreciation of Janni Lee Simner

Alexander Abian writes:
>    In no Physics book there is a convincing explanation  of why heat is
>produced when a pair of fingers rub a piece of fur.  I know all the
> nonconvincing thermodynamical explanations - changing the levels of 
>energy,etc, etc.  I say that the fur produces heat in order to burn the
>fingers so that they stop bugging and rubbing it.  

Of course, another person could say that the fur LIKES being rubbed,
and the heat is produced to warm the fingers so they will keep rubbing
it.  Maybe even that the warmth is an erotic come-on.

The problem with unquantified (and unquantifiable) analogies in science
is that a similar one with an opposite explanation can be created that
is equally plausible and equally (not) falsifiable.

	Larry "Give us equations or go away" Hammer
--

LNH@physics.arizona.edu     \   People ought to fight for their law as
GEnie: L.HAMMER2             \  for a wall.  -- Heraclitus, #100
From: seh@neutron.physics.arizona.edu (Steven E. Hoell)
Newsgroups: sci.physics
Subject: Re: 1992 Nobel Prizes: a prediction
Date: 8 Oct 92 18:25:06 GMT
Distribution: na
Organization: University of Arizona, Tucson AZ

Having T.A'd for Donald Huffman, I hope your prediction
comes true.

When do they announce the winners? 

Steve Hoell			seh@neutron.physics.arizona.edu
Newsgroups: sci.physics
From: phfrom@nyx.uni-konstanz.de (Hartmut Frommert)
Subject: Re: OQ (Open Question) on particles
Keywords: OQ, (Elementary) particles
Organization: Dept. of Physics, University of Constance
Date: Tue, 13 Oct 1992 13:38:16 GMT

jbaez@riesz.mit.edu (John C. Baez) writes:
>phfrom@nyx.uni-konstanz.de (Hartmut Frommert) writes:
>>* What is a particle really ?

>For quantum field theorists one common definition is: an eigenvector of
>the mass operator (the square root of the operator energy^2 -
>momentum^2).  

If I understood right, the mass operator is usually applied to quantum
states (Qst's) which can be only identified with "a particle" if you are
in one-(or few-) particle theory. Then the particle(s) is (are) described
by fields which are more or less classical with regard to 2nd quantization.

The difficulty of figuring out what "a particle" is in QFT was at least 
mentioned by Bjorken/Drell and Streater/Wightman who point out that their
formalism is good for the large-distance limit (e.g. cross sections) but
somewhat incomplete at short distance and "really local" considerations,
due to Heisenberg relations, of course. So you can say that there are, say, 
22 particles (so, what ?), in a configuration, but I still do not see what
one (or each) of them is. 

>While abstract, this definition has some advantages:
>1) it applies to all *stable* particles and stable bound states thereof,
>2) it makes sense whenever your field theory gives a unitary
>representation of the Poincare group, 

(which BTW may be generalized to affine if one wants. This seems to be only 
necessary for theories with nonmetricity)

>3) it bears some relation to how
>we look for particles in detector (looking for peaks at certain values
>of mass).  

Although I regard my question still as open, thanx, John, for your in a
certain sense enlightning discussion.
--
 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: Richard.Mathews@West.Sun.COM (Richard M. Mathews)
Newsgroups: sci.physics
Subject: Re: Black Holes, Hawking Radiation, and Entropy
Date: 15 Oct 92 23:10:01 GMT
Organization: Sunsoft Inc., Los Angeles, CA.
NNTP-Posting-Host: astro
Originator: richard@astro.West.Sun.COM

matt@physics2.berkeley.edu (Matt Austern) writes:

>Now consider a black hole.  Suppose something falls into a black
>hole---something described by a pure quantum-mechanical state....

>So what's the solution?

It seems to me that the solution must be that the black hole is not a
pure state.  In fact, it can't be.  If the hole can evaporate at all,
then it can change with time.  Nothing which can change with time can be
an eigenstate of the Hamiltonian.  Thus black holes are not pure states.
It is some incredible mixture of all of the states corresponding to all
possible decays.  And the coefficient on each of those states must be a
function of only M, Q, and S if the no-hair theorem holds.  But it is
still a mixed state.

     Richard M. Mathews			G eorge
					 D epression
Richard.Mathews@West.Sun.COM		  B ush casts a
					   G loom on us all
Newsgroups: sci.physics
From: bhv@areaplg2.corp.mot.com (Bronis Vidugiris)
Subject: Re: TIME HAS INERTIA AND THE PRINCIPLE OF TENDENCY OF MAINTAINING THE
Organization: Motorola, CCR&D, CORP, Schaumburg, IL
Date: Thu, 15 Oct 1992 16:50:21 GMT

In article <abian.719117674@pv343f.vincent.iastate.edu> abian@iastate.edu (Alexander Abian) writes:

)Yes, I am the real Professor Abian who states that
)           
)                 TIME HAS INERTIA    and that
)  
) E = mcc  (Einstein)   must be replaced by    E = m(0) exp(-At)  (Abian)
)    
)and that our decadent  Solar System must be altered by reshuffling some
)planets.
)

On a slightly more serious note - an abstract from July 1992 'Science"
"Chaotic Evolution of the Solar System" (p 56)

"The evolution of the entire planetary system has been numerically integrated
for a time span of nearly 100 million years.  This calculation confirms that
the evolution of the solar system as a whole is chaotic, with a time scale of
exponential diveregence of about 4 million years.  Additional numerical
experiments indicate that the Jovian planet subsystem is chaotic, although
some small variations in the model can yield quasiperiodic motion.  The
motion of Pluto is independently and robustly chaotic."

Also

"Another unsettling feature of the chaotic behavior we observe in long-term
planetary integrations is that nothing dramatic happens.  This is compounded
by the fact that in no case have we unambiguously identified the mechanism
responsible for the chaotic behavior.  This lack of mechanism and lack of
obvious irregular behavior is in marked contrast to the clearly understood
mechanisms and irregular character observed in other examples of chaotic
behavior in the solar system, for example, asteroids on chaotic trajectories
near commensurabilities...."

Anyway, it appears that if you wait enough millions of years, the inclination
and orbit of the Earth may well shift by itself, though whether it will shift
enough to satisfy you is hard to say.
Xref: sparky sci.physics:16611 sci.math:13282
From: lpeters@postmaster@hq.af.mil (Leslie D Peters)
Newsgroups: sci.physics,sci.math
Subject: Re: Mattel on women
Keywords: Targetting females once again.
Date: 13 Oct 92 14:47:35 GMT
Reply-To: lpeters@marge.hq.af.mil
Followup-To: sci.physics
Distribution: na
Organization: 7th Communications Group

Would that be the thinking being's version of "Wheel of Fortune"?
-- 
**********************************************************************
* Les Peters (lpeters@marge.hq.af.mil): a small fish in a big pond,  *
*                                                 but growing...     *
**********************************************************************