HDTenEightyP/NetNews huggingface dataset:
From: jbaez@zermelo.mit.edu (John C. Baez)
Subject: Re: Is Space a continuum?
Organization: MIT Department of Mathematics, Cambridge, MA
Date: Fri, 14 Aug 92 21:24:56 GMT

In article <1992Aug14.154321.794@sinix.UUCP> dhg@sinix.UUCP (David Griffith) writes:
>Is space a continuum? In other words, does General Relativity suitably
>adjusted by Quantum Mechanics, treat space-time as infinitely
>sub-divisible? If it's not, how does this affect the mathematics, eg
>calculus which assumes deltas that tend to zero?

Classical - i.e., non-quantum - general relativity treats spacetime as a
continuum.  Nobody knows quite how to "suitably adjust" general
relativity by quantum mechanics yet.  In my favorite approach, the loop
representation of quantum gravity, *knots* play a crucial role and serve
in a sense to replace the continuum by a kind of combinatorial structure
at very small distances (the Planck length).  This is still not as well
understood as one would like, though!

In general assuming that spacetime is a continuum has produced
tremendous successes but also some very nasty infinities, so my opinion
is that it's definitely correct in some sense and wrong in some other
sense.  :-)  The knot picture is one way of having ones cake and eating
it too, it seems.


Xref: sparky sci.physics:12846 sci.math:10273
From: lafave@ial4.jsc.nasa.gov (Dr. Norman J. LaFave)
Newsgroups: sci.physics,sci.math
Subject: Re: Symmetries, groups, and categories
Date: 14 Aug 92 14:47:03 GMT
Organization: Lockheed Engineering & Sciences Co.

In article <1992Aug13.182411.11593@galois.mit.edu>, jbaez@riesz.mit.edu (John C. Baez) writes:
> 
> I will begin with a thoroughly fictionalized account of the quest in
> physics to find bigger and bigger symmetry groups.  Then I will say a
> bit about how that quest has led to some interesting applications of
> category theory.
> 


Outstanding John....

Maybe you could comment on the misconceptions which arise due to the different
usages of the term diffeomorphism (i.e. changing coordinate labels verses
moving points around on the manifold).

Norman

Dr. Norman J. LaFave
From: dmrrsn@math.duke.edu (David R. Morrison)
Newsgroups: sci.physics
Subject: Re: Symmetries, groups, and categories
Date: 17 Aug 92 22:13:54 GMT
Organization: Duke University; Durham, N.C.

In article <1992Aug17.193432.18934@galois.mit.edu> jbaez@euclid.mit.edu (John C. Baez) writes:
>  By the way, I haven't printed out this paper yet since I don't
>have "fizzicks" or whatever they call that package that physicists use
>to do latex.  

send a message to hep-th@xxx.lanl.gov whose subject is ``get phyzzx.tex''

to learn about other macro packages available there, use ``list macros''
From: dabbott@augean.eleceng.adelaide.edu.AU (Derek Abbott)
Newsgroups: sci.physics
Subject: Re: I can travel faster than light (A riddle)
Date: 20 Aug 92 02:48:25 GMT
Organization: Electrical and Electronic Eng., University of Adelaide

In article <0095EFAD.E5086100@Msu.oscs.montana.edu> uchpcjv@Msu.oscs.montana.edu writes:
>In article <1992Aug5.231821.10710@visus.com>, jml@visus.com (Jim Large) writes:
>>
>>I am something you all have seen with your naked eyes.
>>I am a servant you all have employed.
>>I can travel faster than light (you have almost certainly never
>>    seen me do it).
>>
>>What Am I?
>>
>>[Note: this may be a riddle, but it is *NOT* a joke!]
>>
>>-- Jim L.
>
>Okay, if it's NOT a joke, the THING in the "riddle" is the GROUP VELOCITY
>of a wave packet, which can (apparently) travel faster than c.  But it
>can't carry information.  Do I win anything?  Do I get flamed, at least?
 ^^^^^^^^^^^^^^^^^^^^^^
That's what I always thought.


However, guys read this:


IEEE Microwave & Guided Wave Letters Vol. 1, No. 12, Dec. 1991 pp.374-375
                                     Vol. 2, No. 5,  May  1992 pp.199-206


They claim it can be done!!!

Any comments?
From: maggio@amsaa-cleo.brl.mil (Joseph M. Maggio)
Newsgroups: sci.physics
Subject: Re: Super!
Keywords: you'll see
Date: 13 Aug 92 11:46:33 GMT
Organization: Army Materiel Systems Analysis Activity

What about supercalifragilisticexpealodocious?
From: sichase@csa2.lbl.gov (SCOTT I CHASE)
Newsgroups: sci.physics
Subject: Re: Simple QED question
Date: 20 Aug 92 03:41:02 GMT
Organization: Lawrence Berkeley Laboratory - Berkeley, CA, USA
Distribution: na
Reply-To: sichase@csa2.lbl.gov
NNTP-Posting-Host: 128.3.254.197
News-Software: VAX/VMS VNEWS 1.3-4   

In article <12950069@hpspdla.spd.HP.COM>, ric@hpspdla.spd.HP.COM (Ric Peregrino) writes...
>I was reading Feyman's QED and came across the diagram which
>shows one photon splitting into an electron and a positron.
>Then I started thinking (silly me...), what if I transform
>coordinates to the center of mass of the two fermions? Well
>then, here there is no momentum for the two fermions. So then, 
>how could the photon have any momentum in this frame? No 
>momentum for the photon implies no energy for the photon.
>This contradicts conservation of energy and momentum. What gives?

The probability for that process is ZERO.  For exactly the reason that 
you have discovered.  It violates conservation of energy and momentum.  
I.e., there is no phase space for it.  

The diagram you describe can only occur as one part of a larger diagram
in which energy-momentum is conserved.  In photon conversion, whereby 
a phsical photon can become an electron-positron pair, another body, 
typically a heavy nucleus, must participate in the process in order to 
conserve momentum.

-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
From: mcgrew@skid.ps.uci.edu (Clark McGrew)
Subject: Re: SU(5) GUT (was Re: Superbashing ...)
Newsgroups: sci.physics
Organization: Univ. of Calif. Irvine -- Physics, Neutrino Group
Distribution: usa
Date: 22 Aug 92 00:54:09 GMT

matt@physics16.berkeley.edu (Matt Austern) writes:

>"Flipped SU(5)" is just SU(5)xU(1); I don't know why they call it
>"flipped SU(5)".  I also don't really know the motivation for it, but
>some of the more stringy types here at LBL are interested in it.

From a field theoretic point of view the difference between SU(5) and
Flipped SU(5) is mostly just a interchange of the right handed
component of the u and d quarks in the wave function.  The reason, I'm
told, that string people like Flipped SU(5) is that it has been shown
to be derivable from a class of string theories.  This lets low energy
phenomenological predictions be made for string theories which usually
dance at energies up around the planck scale.
--
Clark McGrew                          Internet: mcgrew@skid.ps.uci.edu
Univ of Calif, Irvine                 DECnet:   psroot::mcgrew
Newsgroups: sci.physics
From: jbaez@zermelo.mit.edu (John C. Baez)
Subject: Re: Vector Bosons?
Organization: MIT Department of Mathematics, Cambridge, MA
Distribution: na
Date: Fri, 14 Aug 92 20:55:54 GMT

In article <1992Aug13.224617.1745@asl.dl.nec.com> terry@aslws01.asl.dl.nec.com (Terry Bollinger) writes:

>> ... If the electron were a boson, then all atoms would have the radius
>> of a hydrogen atom.  That certainly would shrink things a bit, but not
>> enough to collapse the Earth into a grape-sized black hole.
>
>Concur fully with your model.  I was flat-out wrong on that statement.

I think Terry may be a lot righter than he thinks.  I seem to recall
that Dyson, Lieb, et al's famous proof of the stability of matter makes
crucial use of the fact that electrons are
fermions.   This theorem is a theorem about Schrodinger's equation and
says roughly that the energy of the lowest-energy state of a system of N
electrons and M nuclei (with the total charge assumed to be zero) is
bounded below by a linear function of N.  This means that if you stick
two hunks of matter together they can't usually do something drastic to
reduce their energy a whole lot.  (Like collapse.)  Recently Lieb and
others even have versions involving gravity, but I just don't remember
if they think that planet Earth would be stable to gravitational
collapse if electrons were bosons.   Maybe someone who's kept up with
this stuff could enlighten me?
From: matt@physics16.berkeley.edu (Matt Austern)
Newsgroups: sci.physics
Subject: Re: SU(5) GUT (was Re: Superbashing ...)
Date: 19 Aug 92 23:02:23
Organization: Lawrence Berkeley Laboratory (Theoretical Physics Group)
Distribution: usa
Reply-To: matt@physics.berkeley.edu
NNTP-Posting-Host: physics16.berkeley.edu
In-reply-to: matmcinn@nuscc.nus.sg's message of Thu, 20 Aug 1992 01:48:25 GMT

In article <1992Aug20.014825.6954@nuscc.nus.sg> matmcinn@nuscc.nus.sg (Mcinnes B T (Dr)) writes:

> Dave, please tell us what happened to flipped SU[5]. [By the way, is
> flipped SU[5] really U[5]?] What is the current position re SO[10] and
> E6? Thanks. Brett McInnes.

"Flipped SU(5)" is just SU(5)xU(1); I don't know why they call it
"flipped SU(5)".  I also don't really know the motivation for it, but
some of the more stringy types here at LBL are interested in it.

SO(10) and E(6) have not been excluded; there are still a number of
viable models.  Unfortunately, these models have somewhat more free
parameters than SU(5) does.
--
Matthew Austern              I dreamt I was being followed by a roving band 
(510) 644-2618               of young Republicans, all wearing the same suit,
matt@physics.berkeley.edu    taunting me and shouting, "Politically correct
austern@theorm.lbl.gov       multiculturist scum!"... They were going to make
austern@lbl.bitnet	     me kiss Jesse Helms's picture when I woke up.
Newsgroups: sci.physics
From: jbaez@euclid.mit.edu (John C. Baez)
Subject: Re: Symmetries, groups, and categories
Organization: MIT Department of Mathematics, Cambridge, MA
Date: Mon, 17 Aug 92 19:34:32 GMT

In article <1992Aug14.221906.18840@Princeton.EDU> mdd@nextc.princeton.edu writes:
>In article <1992Aug14.195651.22652@galois.mit.edu> jbaez@zermelo.mit.edu  
>(John C. Baez) writes:
>> I should make clear that there are only certain things about string
>> theory that bug me, aside from the fact that people make such a big deal
>> about it.  One is that traditionally it has treated strings wiggling
>> around in a background spacetime with a given metric.  

>Well, not having a background independent string field theory is very  
>disturbing to string theorists too. 

I'm glad to hear they feel this way.  I never could understand how they
could talk about strings on a background spacetime with fixed metric
without blushing.

>In fact, one could argue that finding  
>such an animal is the holy grail of string theory. Well, at least one of  
>them :^). 

If this is your personal holy grail I
STRONGLY urge you to take a look at Rovelli and Smolin's approach to
quantum gravity, since 1) it involves loops in R^3, which look awfully like
strings, 2) it is independent of any background metric, and 3) it has a
lot to do with Chern-Simons theory, which figures in Witten's recent
paper.  By the way, I haven't printed out this paper yet since I don't
have "fizzicks" or whatever they call that package that physicists use
to do latex.  

>As for the state of the art: In closed string field theory one  
>writes down a non-polynomial action but this action is written using a  
>particular background. However, one can show that this action is unchanged  
>by certain restricted sets of background shifts. This is not ideal, but it  
>is a start. As for open string field theory, Ed Witten has just put out a  
>paper (last week) that purports to give a background independent  
>formulation. The paper is more of a "maybe we should look in this  
>direction" paper, than a detailed formalism, but Witten promises some
[....]

Any posts summarizing what this paper is attempting to do would be
GREATLY appreciated.
From: jmv@grip.cis.upenn.edu (Jean-Marc Vezien)
Newsgroups: sci.physics
Subject: Re: The dangers in microwaved food...
Date: 20 Aug 92 17:43:44 GMT
Organization: GRASP Lab


> In article <16u7u4INNpbi@agate.berkeley.edu> shirriff@sprite.berkeley.edu (Ken Shirriff) writes:
> 
>There are serious health risks in eating microwaved jelly donuts.
> 

There are serious microwave oven makers.
There are risks to microwave an oven seriously.
There are microwaves which would risk their health
to escape from ovens.


This is, indeed, very serious.


JM.
Newsgroups: sci.physics,sci.skeptic,alt.folklore.science
From: payner@netcom.com (Rich Payne)
Subject: Re: The dangers in microwaved food...
Date: Thu, 20 Aug 92 02:59:27 GMT
Organization: Netcom - Online Communication Services (408 241-9760 guest)

In article <1992Aug20.015531.7842@nuscc.nus.sg> matmcinn@nuscc.nus.sg (Mcinnes B T (Dr)) writes:
>there are serious health risks in eating.

OK, I can't resist any longer...


there are serious health risks in -not- eating.


The only way to be perfectly safe is to be dead, unless of course heaven and
hell await, in which case, there is no safety at all.


Rich

payner@netcom.com



Newsgroups: sci.physics,sci.astro
From: roelle@uars_mag.jhuapl.edu (Curtis Roelle)
Subject: Re: Fossil Paradox (was: Structure of Time)
Organization: Johns Hopkins University
Date: 19 Aug 92 18:39:43 GMT

carl@aoa.aoa.utc.com (Carl Witthoft) writes:

>In article <1992Aug17.105608.421@ecc.tased.edu.au> ecc_jim@ecc.tased.edu.au writes:
>>There was a short story like this where a guy trod on a butterfly and totally
>>changed everything. What was it called?

>[about time travel and all that...]
>I know the story but forget its name.  The premise was that time travellers
>could shoot prehistoric animals.  The guide scoped out the area so
>they only shot animals about to die anyway, and then pulled out the bullet 
>and took off.  I distrusted then (1970 or so) and still distrust
>the idea that killing a butterfly is bad but killing a Tyrannosaurus
>3 seconds early, ripping its guts open, etc. is OK  (from a time-
>travel causality point of view :=) )

Not to mention the impact of constructing the walkway used in the first place.
From: kam@soliton.physics.arizona.edu (Kam-Yuen Kwong)
Newsgroups: sci.physics
Subject: Property of waves
Date: 17 Aug 92 10:54:38 GMT
Organization: University of Arizona - Physics






Greeting:

  Probably somebody would like to enlighten me about this: 'Does
the character, "longitudinal" or "transversal", of a wave come
from empirical observations or the analytical property of the wave
equation and its constraints'? In other words, can we tell a wave
longitudinal or transversal by just looking  into its wave
equation? At least, in the EM wave, analytically, we know the
vector of  E and B is transversal to the Poynting (energy flow)
vector. How about others like string wave, water wave, acoustic
wave etc.?

  Thanks for any comment or explanation, posted or e-mailed.

Hsiu-Ming Chang
(Would like to thank Mr. Kwong allowing me using his address)
kam@soliton.physics.arizona.edu (c/o Hsiu-Ming Chang)
Newsgroups: sci.physics,alt.religion.kibology
From: kibo@world.std.com (James "Kibo" Parry)
Subject: Re: Kibocolliders (was: Re: Super Conducting Supercollider)
Organization: Between a rock and a type specimen sheet, Boston.
Date: Thu, 13 Aug 1992 04:44:28 GMT

In article <1992Aug13.030323.23331@nuscc.nus.sg> matmcinn@nuscc.nus.sg (Mcinnes B T (Dr)) writes:
>Scott: well, for heaven's sake,man, spill the beans! How did Kibo
>explain himself? For my part, I doubt that this person is really Kibo.
>How can you be sure that he is not an impostor?

Of course, the real Kibo would deny making that explanation.

Of course, it would be just like Kibo to forge a posting from himself
saying so.

							-- K.
From: matt@physics2.berkeley.edu (Matt Austern)
Newsgroups: sci.physics
Subject: Re: How to make big bucks using supersymmetry
Date: 20 Aug 92 15:05:12
Organization: Lawrence Berkeley Laboratory (Theoretical Physics Group)
Distribution: na
	<MATT.92Aug19225852@physics16.berkeley.edu> <25625@dog.ee.lbl.gov>
Reply-To: matt@physics.berkeley.edu
NNTP-Posting-Host: physics2.berkeley.edu
In-reply-to: sichase@csa3.lbl.gov's message of 20 Aug 92 19:42:04 GMT

In article <25625@dog.ee.lbl.gov> sichase@csa3.lbl.gov (SCOTT I CHASE) writes:

> For a while, people were talking about a definitive test by
> searching for the lightest MSSM neutral higgs.  The mass was
> supposed to be constrained to be less than the Z mass, if I remember
> correctly.  Unfortunately, someone bothered to calculate the
> radiative corrections, and the whole plan was ruined.  Do you know
> if there is still an upper bound on the mass - or do the corrections
> leave things wide open?

Interestingly enough, I attended a talk on this subject just Monday.
The answer, of course, is a bit more complicated than yes or no---but
then, isn't it always?

It is possible to derive an upper bound on the mass of the lightest
MSSM Higgs, but there are some caveats on that, some of which were
only elucidated only in questions after the talk:
	(1) This bound isn't a number, but a rather complicated plot,
	    the upper bound versus various MSSM parameters.  (The mass
	    of the top, for example, and the ratio of the vevs of the
	    two Higgs doublets.
	(2) The results are only from one-loop calculations.  There is
	    always that nagging questions: if one-loop corrections have
	    a significant effect on the tree-level calculations, then who
	    is to say that the two-loop corrections are small?
	(3) Even according to these calculations, there is a certain 
	    region in paramters space where no existing or planned
	    collider (Tevatron, SppS, SSC, LHC, LEP,...) will be able
	    to detect the lightest MSSM Higgs.
	(4) These calculations make certain assumptions that might not
            be true---for example, they assume that the theory is valid
     	    all the way to the GUT scale, and that the Higgs's 
	    interactions remain weak enough to be treated perturbatively
	    up to that scale.  (This might sound like a technicality,
	    but it makes all the difference in the world.)

By the way, there are some theorists here at LBL who are genuine
experts on this subject.
--
Matthew Austern              I dreamt I was being followed by a roving band 
(510) 644-2618               of young Republicans, all wearing the same suit,
matt@physics.berkeley.edu    taunting me and shouting, "Politically correct
austern@theorm.lbl.gov       multiculturist scum!"... They were going to make
austern@lbl.bitnet	     me kiss Jesse Helms's picture when I woke up.
Newsgroups: sci.physics
From: alvin@stud.cs.uit.no (Alvin Brattli)
Subject: Re: Parsecs?
Followup-To: sci.physics
Organization: University of Tromsoe, Norway
Date: Thu, 13 Aug 1992 18:57:35 GMT

In article <MT87692.92Aug13163609@sotka.cs.tut.fi>, mt87692@cs.tut.fi (Mikko Tsokkinen) writes:
|> attoparsec: n. `atto-' is the standard SI prefix for
|>    multiplication by 10^{-18}.  A parsec (parallax-second) is
|>    3.26 light-years; an attoparsec is thus 3.26 * 10^{-18} light
|>    years, or about 3.1 cm (thus, 1 attoparsec/{microfortnight}
|>    equals about 1 inch/sec).  This unit is reported to be in use
|>    (though probably not very seriously) among hackers in the U.K.  See
|>    {micro-}.

This reminds me of a definition I found in _Physics Handbook_ by
C. Nordling and J. Oesterman:

"1 light-year = 9.46055e15 m. A corresponding unit, 1 beard-second = 1e-8 m,
 has been suggested for microscopic distances. One beard-second is the
 distance which a standard beard in a standard face grows in one second."

-- 
                      I've got two legs from my hips to the ground
Alvin Brattli         And when I move them they walk around
alvin@stud.cs.uit.no  And when I lift them they climb the stairs
                      And when I shave them they ain't got hairs - T.Gilliam
From: flower@hpcc01.corp.hp.com (Graham Flower)
Date: Mon, 17 Aug 1992 23:50:34 GMT
Subject: Re: Order-of-Magnitude problems
Organization: the HP Corporate notes server
Newsgroups: sci.physics

:  
:         Use the uncertainty principle to compute how long an ordinary
:         lead pencil can be balanced upside down on its point.
:                                                 [QM: Das/Melissinos p. 53]
: Any ideas?
:  
  As far as i am aware this problem originated with the book by Dicke and Wittke
  it has been repeated several times. The key is to use the right form of the
  uncertainty principle. You need the angle uncertainty form and start with
  this by considering the minimum angle from the vertical. A torque then can
  be calculated and using the moment of inertia, gravitational acceleration
  and estimated mass of the pencil you can figure how long it'll take to fall.
  the time is quite long as I recall > 1 year, in theory anyway.
  
  This problem is in Ter Der Haars book of solved problems 2nd edition. chapter
  3 It is not in his 3rd edition. Look it up. 

>Well, if I remember correctly, my father, a physicist at Kent State, gave
>a problem similar to this on one of his senior level finals.  His problem 
>involved bouncing a ping-pong ball on top of another, larger ball.  Given
>completely elastic collisions, and the radii of the two balls, estimate how
>many times the ping pong ball can bounce on top of the other ball before it
>falls off, using the uncertainty principle.  The solution of the problem 
 

 This problem is also somewhat famous, it appears in Leonard Schiff's quantum
 mechanics book chapter 1. 

 Graham Flower


Graham Flower ms 90-TT               |  Better to have convictions and act on 
Hewlett-Packard  350 W Trimble Rd    |  them, even if they are wrong, than to  
Microwave Semiconductor Division     |  waffle in indecision.
San Jose, California, 95131          |
 graham_flower@sj.hp.com             |
From: mcirvin@husc8.harvard.edu (Mcirvin)
Newsgroups: sci.physics
Subject: Re: BLACKHOLES IN THE CENTRE OF THE EARTH
Date: 19 Aug 92 22:15:58 GMT

johan@blade.stack.urc.tue.nl (Johan Wevers) writes:

>The situation you describe holds for an empty sphere.

Actually, the previous poster said that the "gravitational attraction
was uniform"; in an empty sphere the gravitational acceleration
is zero.  It's the potential that's uniform.

Getting back to the subject, I'd expect a black hole small enough
not to cause the Earth's orbit major disruption to go straight
through the Earth and come out the other side, if it fell 
straight in from a great distance.  But I don't know how to
do the math, since I think it would depend on the energy
loss in gravitational deformation of the surrounding rock and
metal as the hole passes through.  The hole has to heat the
Earth sufficiently to get its kinetic energy below the amount
required for escape, and that kinetic energy is enormous, 
depending on the mass of the hole.

If the black hole were traveling at typical solar system speeds to
begin with, it might be captured in some sort of multi-body
interaction, like some of the moons of assorted planets.  Then,
if it fell into the Earth, it wouldn't escape upon emergence,
but would instead rise to some enormous height and fall back,
punching repeatedly through the Earth in a series of slowly
damped oscillations.  It would eventually settle in the center
and slowly eat core metal.  But I have no idea how long any
of this would take.
 
-- 
Matt McIrvin, Cambridge, Massachusetts, USA