HDTenEightyP/NetNews huggingface dataset:
From: jbaez@riesz.mit.edu (John C. Baez)
Subject: Re: BAEZIAN Physics and astronomy [was: Space-time IS a semi-Riemannian manifold (?)
Organization: MIT Department of Mathematics, Cambridge, MA
Date: Tue, 6 Oct 92 04:37:20 GMT

In article <1992Oct6.023601.20017@galois.mit.edu> jbaez@riesz.mit.edu (John C. Baez) writes:
McInnes writes:
>>ON THE OTHER HAND I am extremely sceptical of statements such as "at
>>sufficiently small length [huh? what's that?] scales, spacetime is
>>replaced by [wormholes, worms, knots ,loops, strings, etc]. Spacetime is
>>the set of all events. What does it mean to say that events are
>>"replaced" by anything? : 
>
>What's getting replaced is not events but the notion that they are in 
>one might replace this notion WITH, but it's definitely worth keeping in
>
>mind as a possibility.  It would have to be some structure which is good
>at looking like a manifold at larger distance scales.  

Huh?  I HATE using emacs and telnet together.  It sucks.  Try again:

What's getting replaced is not events but the notion that they are in
in one-to-one correspondence with points on a 4-manifold.  It's not
clear what one might replace this notion WITH, but it's definitely worth
keeping in mind as a possibility.  It would have to be some structure which is
good at looking like a manifold at larger distance scales.

Let me add in response to Hartmut Frommert's advocacy of modifications
of GR... it is certainly worth studying these and people have.  No
matter what one does along these lines one will probably want to
quantize the theory eventually, and quantizing old-fashioned Einstein
gravity will probably be good practice.  (Unless these other theories
turn out to be significantly EASIER to quantize.  Occaisionally one
hears this claim but not for torsionful or nonmetric connection
theories.)  

I certainly think it's silly to flounder around trying to replace the
spacetime manifold with strings, worms, sealing-wax, or what-have-you.
The loops, I must emphasize, simply fall out from trying to combine
general relativity and quantum theory without any deliberate quest for
the exotic.  Now the loops start out living in plain-old 3-dimensional
space, a state in quantum gravity simply being a link invariant.  But as
one pursues the mathematics one sees it might be profitable to instead
treat these link invariants purely algebraically, in which case 3-space
gets replaced by something I call the "abstract holonomy algebra".  I am
starting to write up a paper on this.  It's way too
early to take the physical/philosophical implications of this very
seriously; it's all very preliminary and I don't go around saying "The
spacetime manifold MUST DIE!!"
From: baez@ucrmath.ucr.edu (john baez)
Newsgroups: sci.physics
Subject: Re: Simple observation about Quantum Kitty Cats
Date: 30 Sep 92 16:09:12 GMT
Organization: University of California, Riverside

In article <1992Sep29.213854.26085@newshost.lanl.gov> jlg@cochiti.lanl.gov (Jim Giles) writes:
>Of course, the *really* strange thing about QM is the claim that
>a mathematical function *is* the physical object being studied.
>In any other part of science, this would seem rediculous (or,
>at the very least, uninformative).  To derive a function which
>gives a prediction for sky-light as a function of sun angle,
>horizonm angle, wavelength of light, and observer altitude
>should be possible.  To say that the sky really *is* that
>function when you're not looking up is rediculous.  For one
>thing, what does such a claim even *mean*?  Or, consider the
>following function on integers: f(i) = max(0, min(i-1, 13-i))/36.
>This is the probability of rolling `i' as the sum of two dice.
>It is rediculous to say the dice really *are* this function
>while they are rolling and that the function `collapses'
>to a given number when the dice stop rolling.

I agree completely; this is what I was trying to say about "not
identifying the model with reality," but maybe more people will
like this formulation.  Of course, the more comprehensive the model
is, the more tempting it is to identify it with reality.  The cases
you give are of such limited models that few people would make the
mistake.  When we start babbling about "Theories of Everything," 
however, it gets easier to mix things up.  

In mathematically oriented work it is useful to mix up the model
with reality some of the time, to get "into" the model.  It should
be a kind of voluntary suspension of belief, like watching a
good movie or (perhaps a better analogy) playing a good video game.
From: johncobb@ut-emx.cc.utexas.edu (John W. Cobb)
Newsgroups: sci.physics
Subject: Re: Black hole + anti-Black hole = ?
Date: 29 Sep 92 16:27:09 GMT
Reply-To: johncobb@ut-emx.cc.utexas.edu (John W. Cobb)
Organization: The University of Texas at Austin

In article <2358@forty2.physik.unizh.ch>, ks@forty2.physik.unizh.ch
(Kurt Sonnenmoser) writes:
|>In article <1992Sep8.222101.9281@math.ucla.edu> barry@arnold.math.ucla.edu
|>(Barry Merriman) writes:
|>|
|>| What happens if you dump some antimatter into a black 
|>| hole that formed from normal matter? Does it 'cancel out' part of it?
|>|
|>| Or, if I take two black holes, one made from ordinary matter
|>| and the other made from anti-matter, and merge them, what happens?
|>| Do I get a bigger black hole, or are they somehow annihilated?
|>
|>
|>In article <1992Sep9.052443.8026@galois.mit.edu> jbaez@riesz.mit.edu
|>(John C. Baez) writes:
|>>[...]
|>>Anyway, the usual answer is that the "no-hair theorem" shows that the
|>>only properties a black hole has are mass, momentum, angular momentum
|>>and electric charge.  It doesn't know whether you threw matter or
|>>antimatter in.  So if you throw in some matter and then some antimatter,
|>>or a black hole you made out of antimatter, it just keeps getting
|>>bigger.
|>
So what are the implications of this? Does this mean that if a
Quantum no-hair theorem holds that gravitational collapse, ipso facto,
is the source of baryon non-conservation?

Most (All that I have ever seen) "no-hair" theorems are proved for classical
systems. What about quantum systems? If a true quantum description of Hawking
radiation (not just a semi-classical estimate) is finally worked out, is
it not possible for it to depend on "the hair". for example, if a proton/
anti-proton pair is created out of the curvature field just inside the horizon,
will both the proton and anti-proton have exactly the same probability to
tunnel beyond the horizon? Might not these probabilities be affected by the
overall baryon number of the black-hole. Perhaps this is a way to restore
baryon conservation in collapse situations --- then again, black holes may
not respect baryon numbers, even in a complete quantum description.


john w. cobb
"The hair club for Cosmologists". 
      I'm not just the president, but a customer too.
From: exuptr@exu.ericsson.se (Patrick Taylor)
Newsgroups: sci.physics
Subject: Re: Possible?: 2 integers specifying a point in 3D space.
Date: 28 Sep 92 02:45:57 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 <Bv1rAG.LCw@cs.dal.ca> gauthier@ug.cs.dal.ca (Paul Gauthier) writes:
>From: gauthier@ug.cs.dal.ca (Paul Gauthier)
>Subject: Possible?: 2 integers specifying a point in 3D space.
>Date: 23 Sep 92 19:54:15 GMT

>I've been toying with something in my head for a while now and before I
>make an ass of myself by explaining it I'll first ask a related question:

>Is it possible to specify uniquely, an arbitrary point in 3D space using 
>only 2 integers? IE: You point to any point in space (using a conventional
>three-tuple (x, y, z)). Is it possible for me to respond with 2 integers
>which corrispond to that point and no other? You can even use real numbers
>in your three-tuple, but my response has to be two integers. Also, the
>3D space is infinite in all directions, so the values of each component
>of your three-tuple are completely unconstrained. Is it possible for me
>to use some co-ordinate system and label the point you give me uniquely
>with 2 integers?

>Any thoughts, proofs or loud guffaws?

>PG
>-- 
>  ===========================================================================
>                               Paul Gauthier
>  cyclist, rock climber, skydiver, computer scientist (...in order of danger)
>  Electronic: gauthier@ug.cs.dal.ca  Voice: (902)462-8217  Fax: (902)420-1074

Relation to Jon Gauthier?

If my understanding of mathematics is correct, the infinity of real numbers 
is "greater" than the infinity of integers.  Since inf(integer) * 
inf(integer) = inf(integer), your two integers cannot possibly represent even
a single point on a one-dimensional line.  (Think about it, you can 
represent only fractions, but not transcendentals).
 ----------------------------------------------------------------------------
    "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
Newsgroups: sci.physics,sci.astro,sci.math,sci.philosophy.tech
From: crb7q@kelvin.seas.Virginia.EDU (Cameron Randale Bass)
Subject: Re: STRUCTURE OF TIME
Organization: University of Virginia
Date: Sat, 3 Oct 1992 01:13:38 GMT

In article <1992Oct2.230052.25196@hpcvaac.cv.hp.com> billn@hpcvaac.cv.hp.com (bill nelson) writes:
>kim@Lise.Unit.NO (Kim Gunnar St|vring yhus) writes:
>:  > 
>:  >   You don't seem to realize forest from trees. I meant ordinary peoples
>:  >   mental suffering, which is caused by these undeveloped peoples.
>: 
>: Those people I described look quite ordinary to me. By undeveloped peoples
>: I suppose you mean your 'atheistic scientists'. And I have observed and
>: experienced MUCH more suffering from religion than science. I have also
>: observed and experience much more pleasure and happiness from science than
>: from religion.
>
>Not surprising, when much of the Bible teaches fear of God. How can you be
>truly happy when you are in constant fear of an omnipotent being who may,
>out of whim, strike you dead without warning and send you to a place of
>perpetual suffering called Hell?
>
>Bill

    I think you'll find that if you do not use this forum to 
    misinterpret and criticise religion, then it will be easier to keep 
    religion out of this forum.  Physics has nothing to say about
    morality or religion and vice versa.

                              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: jcf@world.std.com (Joseph C Fineman)
Subject: Back to physics!  Joke due to R. P. Feynman
Summary: Disorientation
Keywords: handedness, humor, Feynman
Organization: The World Public Access UNIX, Brookline, MA
Date: Tue, 6 Oct 1992 20:47:54 GMT

If disoriented while traveling, use the following simple rule:  Point
the index finger of your right hand in the direction of motion of the
bus, and the thumb in the direction of motion of exiting passengers.
The middle finger will point *up*.

(In Britain, use the left hand.)

%^)  Joe Fineman  jcf@world.std.com
From: danforth@riacs.edu (Douglas G. Danforth)
Subject: Re: Simple observation about Quantum Kitty Cats
Organization: RIACS, NASA Ames Research Center
Date: Wed, 30 Sep 92 19:02:40 GMT

In <22590@galaxy.ucr.edu> baez@ucrmath.ucr.edu (john baez) writes:

>In mathematically oriented work it is useful to mix up the model
>with reality some of the time, to get "into" the model.  It should
>be a kind of voluntary suspension of belief, like watching a
>good movie or (perhaps a better analogy) playing a good video game.

Yes, this helps greatly in the creative process.  Several recognized
scholars have said they pretend to "be" the thing they are investigating
(e.g. like a cancer cell).

However, I strongly assert that this is NOT the correct approach for
teaching.  One must ALWAYS qualify that a theory is just the best
current working model.  An example of misused (in my opinion) is the
word "law" when associated with Newton.  It comes squeekingly close
to saying our theories are the way the world is.
Newsgroups: sci.physics
From: dhl@mrdog.msl.com (Donald H. Locker)
Subject: Re: Mattel Protest
Keywords: So What?
Organization: Chelsea MSL, Inc., Chelsea, MI
Date: Mon, 5 Oct 92 18:07:29 GMT

In article <stone.718289960@cwis> stone@cwis.unomaha.edu (Travis Stone) writes:
>
>So Mattel is going to market a dollie that says
>"Math class is tough!"---so what?  People have
>been bitching about math classes since the dawn
>of time---boys and girls alike---so obviously
>the vast majority of people out there MUST agree
>with this sentiment; all Mattel is doing is having
>their little plastic pals voice what is undoubtedly
>on every child's mind.  The point is, EVERYONE IS
>ALREADY CONVINCED OF IT, SO WHO CARES IF A TOY
>REPEATS IT?  If a child is going to take a liking
>to math, then he/she/it won't give a tinker's
>damn what some stupid toy has to say about it.
>
[deletia]

The problem (IMO) is not in the expression of difficulty, but the lack
of a resolution, as in "That math class was tough, but I *understand*
the material."  Without a clear indication of tense, children tend to
take the concepts as immediate and with no resolution.

>
>
>T.R. Stone
>University of Nebraska-Omaha
>Where, yes, as you might have guessed, I'm doing
>Grad work in Applied Math...


-- 
Donald.                      Speaking only for myself.

ALL NEW .sig lite - 28% fewer chars, reduced meaning!!
Newsgroups: sci.physics
From: firth@sei.cmu.edu (Robert Firth)
Subject: Re: Questions of transparency
Organization: Software Engineering Institute
Date: Tue, 6 Oct 1992 12:38:10 GMT

In article <1992Oct05.144047.24467@cubic.com> hees@cubic.com (Phil Hees) writes:

>Newton, who first investigated dispersion (the dependence of the angle of
>refraction on the wavelength of the incident light), did consider using
>more that one lens to perform color correction.  Based on what might have
>been too hasty a study of the dispersion characteristics of various
>available glasses, he concluded that such correction was impossible.

The gory details are in the Opticks, Book One, Part I, Experiment 16.
Newton showed how one might correct for spherical aberration by using
two lenses with water in between them (in effect, therefore, three
lenses).  However, he reports

	"But by reason of this different Refrangibility [of colours],
	 I do not yet see any other means of improving Telescopes
	 by Refractions alone, than that of increasing their lengths..."

And, as Phil mentioned, he continues

	"Seeing therefore the Improvement of Telescopes of given
	 lengths by Refractions is desperate; I contrived heretofore
	 a Perspective by Reflexion, using instead of an Object-glass
	 a concave Metal..."

And the rest is history.
From: mcirvin@husc8.harvard.edu (Mcirvin)
Newsgroups: sci.physics
Subject: Re: The H-Bomb secret is out
Date: 2 Oct 92 23:21:41 GMT

steinly@topaz.ucsc.edu (Steinn Sigurdsson) writes:

>someone who knows the answer told me that
>the essence of the problem can be pieced together by
>a _smart_ graduate student with a decent computer in
>6-12 months, and a _good_ student should be able to
>solve the problem given the hints in unclassified literature,
>as opposed to fission bombs which are designable by an 
>average physics grad.

It would probably take me a while to design a working fission bomb
using plutonium... but a bomb using enriched U-235 is quite simple. 

-- 
Matt McIrvin, posting nonsense again 
Newsgroups: sci.physics
From: ramsay@unixg.ubc.ca (Keith Ramsay)
Subject: Re: Defining local, causal etc., was: Hidden variable theories
Organization: University of British Columbia, Vancouver, B.C., Canada
Date: Fri, 2 Oct 1992 01:31:42 GMT

In article <1992Sep29.170356.13002@newshost.lanl.gov> 
jlg@cochiti.lanl.gov (Jim Giles) writes:
|It is not possible to distinguish between wavefunctions that are
|hypothetical entities and  wavefunctions which are real objects.
|Not empirically.  Therefore, their introduction violates Occam's
|razor. 

How do you distinguish between "hypothetical entities" and "real
objects" in any other case?

Keith Ramsay
ramsay@unixg.ubc.ca
Newsgroups: sci.physics
From: knapp@spot.Colorado.EDU (David Knapp)
Subject: Re: Cheap laser possible?
Organization: University of Colorado, Boulder
Date: Mon, 28 Sep 1992 14:19:07 GMT

In article <1992Sep27.164608.13439@ucsu.Colorado.EDU> knapp@spot.Colorado.EDU (David Knapp) writes:
>In article <1992Sep25.122819.29025@alf.uib.no> sigurd@novaja.NoSubdomain.NoDomain (Sigurd Tjelmeland) writes:
>>I have understood that one of the most expensive parts
>>of a laser is the mirror that lets just a little light
>>through. What would happen if one substituted this
>>with a fully reflecting mirror with some small holes
>>drilled in it. Of course this would set up some
>>interference pattern on the beam, but would a laser
>>beam be produced this way?
>>
>>Just curious,
>>
>>Sigurd 
>>e-mail: sigurd@imr.no
>>

Sigurd,

My mail bounced to you again and I cannot finger that node. I'm sure
Norway has more than one computer!  ;-)

To you other questions, mirrors on lasers *do* aid in  making the beam
more directional, but are certainly not required. You can add mirrors
to the Nitrogen laser and simply use edge coupling (two reflective
mirrors with the beam 'leaking' over the edge)

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.

As far as CO2 lasers, I'm building one right now myself!  Their operating
wavelength requires the use of special material for the optics which can
be very expensive. ~300 to 500$ for the optics! This also operates at a 
vacuum (10-30torr) and requires a special gas mix (He, N2, CO2) which can
become cost prohibitive.

The lasing level of the CO2 lasers I am familiar with use a vibrational
state which is excited collisionally by electron impact and excited N2
impact, not from recombinatory processes of CO+O. If you have
references on that, I'd like to hear about it.

Check with your sysadmin about that email address of yours; perhaps then
I can email directly?

btw, I don't mind answering questions and helping out. I enjoy the subject.





-- 
David Knapp                                      University of Colorado, Boulder
Perpetual Student                                   knapp@spot.colorado.edu
From: oser@fermi.wustl.edu (Scott Oser)
Newsgroups: sci.physics
Subject: Re: Can you figure this joke out?
Date: 5 Oct 1992 17:09:58 GMT
Organization: Washington University Astrophysics
NNTP-Posting-Host: fermi.wustl.edu

In article <1992Oct5.144625.22281@bcrka451.bnr.ca> isupstud@bnr.ca (Wayne Hutton) writes:
>
>The integral of 'e' to the 'x' is a function of both 'u' and 'n'.
>If no one can get it I'll post the answer later.
>
>ps. all credit goes to my linear algebra prof (first year college)
>
>-todd.

I won't give it away, but I saw this one carved on a desk at Urbana-Champaign
five or six years ago!
-Scott Oser
From: naturman@uctvax.uct.ac.za
Newsgroups: sci.physics
Subject: Value Rule in QM is false
Date: 5 Oct 92 00:40:31 +0200
Organization: University of Cape Town

Only reply to this if you are deeply familiar with Realism and Locality
paradoxes in Quantum Mechanics.

In the derivation of the Bell Inequallity, is the Value Rule used. The Value
Rule (VR) states that if the probability of an observable Q having the value
q in state \Psi is 0 then Q cannot have the value q in state \Psi.

Physicists realize that VR fails for observables whose corresponding
self-adjoint operator has a continuous spectrum of eigenvalues, since any such
eigenvalue has prob. = 0.

However physicists do not seem to realize that VR can also fail for a discrete
spectrum. Consider the set X = {-1,0,1} and define a probability measure 
p:X-->[0,1] by p(-1) = p(1) = 0.5 and p(0) = 0. Now suppose that Q is an
observable whose operator has eigenvalues X. By VR, Q cannot have the value 0.

To see that this is false let S:R-->X (where R is the set of real numbers) be
the signum function given by 
                                    ( -1 if r<0
                            S(r) =  {  0 if r=0
                                    (  1 if r>0

Let Z denote the position of a particle along some axis corresponding to
operator Z^. Let Q^ = S(Z^). Then Q^ is a self-adjoint operator and PROVIDED
WE ASSUME THAT EVERY SELF-ADJOINT OPERATOR DOES CORRESPOND TO AN OBSERVABLE
there is an observable Q corresponding to Q^. Then the spectrum of Q is X. Let
/Psi be a state where the probability of Z having value z<0 is the same as that
of it having z>0. Then the probability distribution of eigenvalues for Q is
simply p defined above. But if Z has value 0 then so will Q, violating VR.
(PROVIDING we assume that values of Q are related to those of Z by q = S(z).
This assumption does not lead to a Kochen-Specker paradox since Z^ is
non-degenerate.)

If the Bell Inequallity relies on VR for its derivation then if we take a view
of QM which is realist, deterministic, denies VR and denies strong functionality
then this view avoids all locality paradoxes (including the Bell Inequallity),
and avoids the Kochen-Specker paradox.

In fact, since as I've shown above, VR is false I would say that it should
always be denied.

(People with free-will hangups and a morbid desire to preserve non-locality need
not reply to this.)
-- 
*****************************************************************************
* Baby Doc Naturman                                                         *
* USS Enterprise                           "It's life Jim,                  *
* Final Frontier                                  but not as we know it."   *
* naturman@uctvax.uct.ac.za                                                 *
*                                                       Spock of Vulcan     *
*****************************************************************************
Newsgroups: sci.physics
From: COWAN@ssrl01.slac.stanford.edu (Paul L. Cowan)
Subject:  Re: Hannu, the Wood-Duck (was: STRUCTURE)
Organization: CALIFORNIANS ON THE ORIENT EXPRESS
Date: Sun, 4 Oct 1992 00:17:27 GMT
X-News-Reader: VMS NEWS 1.24

In <1992Oct3.012906.27098@nuscc.nus.sg> matmcinn@nuscc.nus.sg writes:

:  What the hell is a wood-duck?

Shouldn't you ask, "Why a duck?" 8^)



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