HDTenEightyP/NetNews huggingface dataset:
From: pratt@Sunburn.Stanford.EDU (Vaughan R. Pratt)
Subject: Re: Report on Philosophies of Physicists
Organization: Computer Science Department,  Stanford University.
Date: Tue, 15 Sep 1992 05:08:49 GMT

In article <1992Sep15.035832.7576@cbnewsm.cb.att.com> mls@cbnewsm.cb.att.com (mike.siemon) writes:
>	- it is VERY important to "break" students from reliance on the
>	  geometry and algebra of their earlier studies as *the* only
>	  matter of a generalized "geometrical" reasoning.  There is such
>	  a wealth of counter-example to expectations in the basic stuff
>	  of a point-set topology course as to open previously closed minds.

This familiar assertion about topology should be contrasted with the
following conclusion to the prefatory "Note to the Reader" from
Munkres' "Topology", Prentice-Hall 1975.

	Now it is all too easy in studying topology to spend too much
	time dealing with "weird counterexamples."  Constructing them
	requires ingenuity, and is often great fun.  But they are not
	really what topology is all about.  Fortunately, one does not
	need too many such counterexamples for a first course; there is
	a fairly short list which will suffice for most purposes.  Let
	me give it here:

	[product, uniform, box topologies on R^n
	 R with basis all [a,b)
	 the order type S_Omega (better known to logicians as omega_1)
	 the lexicographic square]

I would add to this perspective that the "weird counterexamples" (at
least the ones I vaguely recall being put through) are for the most
part the *fault* of a set-theoretic perspective.  Topological spaces
and their continuous maps don't form a closed category (one such that
the set of continuous functions from S to T forms a topological space
in the "obvious" way), forcing one to jump around between spaces and
sets when thinking about maps f:SxT->U and fixing a point in S or T.
For ordinary consumers of topological spaces it's healthiest to go
right to compact Hausdorff spaces without messing around with
non-Hausdorff or non-compact counterexamples---not only is CGHaus
closed but very remarkably it is algebraic, i.e. essentially a variety
or equational class, just like groups or lattices, only with operations
at arities of every cardinality.  For those needing the whole of Top
but cleaner, locales are the clean way to go.  (Cleanliness is next to
godliness.  God I hate it when I get religious.)

Mathematicians who don't see the connection of their stuff with
foundations are muscle-bound programmers who write large grungy codes
without even being aware there's a problem.

-- 
======================================================| God found the positive
Vaughan Pratt   pratt@cs.Stanford.EDU   415-494-2545  | integers, zero was
======================================================| there when He arrived.
-- 
======================================================| God found the positive
Vaughan Pratt   pratt@cs.Stanford.EDU   415-494-2545  | integers, zero was
======================================================| there when He arrived.
From: mcirvin@husc8.harvard.edu (Mcirvin)
Newsgroups: sci.physics
Subject: Re: Hidden variable theories, was: Uncertainty Princi
Date: 10 Sep 92 19:49:34 GMT
Article-I.D.: husc8.mcirvin.716154574

foxd@silver.ucs.indiana.edu (daniel fox) writes:

>While reading these discussions I can't help wondering if there is some sort of
>connection between causality and thermodynamics.  Both seem to define an arrow
>to time.  Might it be that causality is only meaningful for sufficently large
>collections of particles?

Robert Firth caught me essentially inserting the thermodynamic arrow of
time into a definition of causality.  They are in fact quite different.
Causality really only rules out time paradoxes of the sort where you
kill your grandfather before your father's birth; the arrow of time
says in addition that the process corresponding to running the evolution
of a system in reverse will not in general be a probable occurrence.
There's no arrow of time in causality as defined in quantum field
theory.  Furthermore, according to the theory, causality holds for
any physical system. 
-- 
Matt McIrvin, Cambridge, Massachusetts, USA
From: paul@mtnmath.UUCP (Paul Budnik)
Newsgroups: sci.physics
Subject: Re: Hidden variable theories, was: Uncertainty Princi
Summary: You do not seem to understand Bell's inequality.
Date: 11 Sep 92 13:56:40 GMT
Organization: Mountain Math Software, P. O. Box 2124, Saratoga. CA 95070

In article <1992Sep10.195755.1577@newshost.lanl.gov>, jlg@cochiti.lanl.gov (Jim Giles) writes:

> The particles traveling away from their common source carry the
> correlation in an unknown way - whether this be faster-than-light

What is measured in test of Bell's inequality is the correlation between
manipulations of a polarizer and particle detections. The correlations
cannot be carried by the particles because the manipulations do not
occur until after the particles have separated. According to quantum
mechanics manipulating a local polarizer can instantaneously *influence*
what happens a billion light years away. This is experimentally detectable
and the bit rate of data being transferred can be measured. The way this
is verified experimentally is by comparing two sequences of 
detections and two sequences of polarizer manipulations. This can
only be done after the fact. However this after the fact comparison
can *prove* that manipulating a local polarizer instantaneously affected
a distant result. This is a subtle point, but it is the reason why Bell's
result is so important.

Paul Budnik
From: johan@blade.stack.urc.tue.nl (Johan Wevers)
Newsgroups: sci.physics
Subject: Re: Quantitized Length
Date: 9 Sep 92 12:10:05 GMT

cannon@scs.unt.edu (Dustin Cannon (Lab 3460)) writes:

>	I have a question.  I was thinking about the problem of the man 
>walking across a bridge, but he first walks half the distance and then can 
>only walk half the remaining distance and so on.  He never gets to the end, 
>right? 

This is the old Zeno Paradox: the conclusion is not true. If his speed of
walking doesn't decrease, he will (of course) reach the end, mathematically
because the summation 1/2 + 1/4 + 1/8 + 1/16 + ...... is finite.

>	I liked this because it also solves a rather disturbing idea one of 
>my professors once said, which was that as two point charges come in contact 
>with each other they have infinte potential energy due to 1/r.  This, he 
>said, was in his mind a proof of God's exsistence.

Who told you this nonsense? Renormalisation calculus in quantum field
theory knows how to deal with these infinities, and a few time ago
John C. Baez posted a message in which he explained that, even without
QM, the mass would be finite: because gravitation also contributes to
the rest mass, and mass also contributes to the gravitation, we get:

m(r)=m_0 + e^2/r - Gm^2(r)/r

Because in the third term on the left-hand side we have m(r) instead
of m_0 , we receive in the limit r->0: m(r)= e/\sqrt{G}. Finite.

I don't understand what this has to do with a god.

Quantum gravity and superstring deal with quantisized length, but we
don't understand both of these theories yet complete.

******************************************************************** 
* J.C.A. Wevers                *         u\  _\       /e+        2 * 
* johan@blade.stack.urc.tue.nl *     1 |   \ u \  X  /         |   * 
******************************** P = - |    >   >---<     + ...|   * 
*     The only nature of       *     N |   /   /     \         |   * 
*     reality is physics       *         u/   /d     u\            *
********************************************************************
Newsgroups: sci.physics
From: kim@Lise.Unit.NO (Kim Gunnar St|vring \yhus)
Subject: Re: Computability of the universe
Organization: Norwegian Institute of Technology
Date: Fri, 11 Sep 92 17:16:22 GMT

In article <1992Sep11.142213.19269@sei.cmu.edu>, firth@sei.cmu.edu (Robert Firth) writes:

 > 	Every function which would "naturally be regarded as
 > 	computable" can be computed by the universal Turing machine
 > 
 > And that's false.  If I can build a machine to compute something, then
 > that something would naturally be regarded as computable, yes?  For
 > if something exists, it must be possible.  Well, I can build a machine
 > that will compute the function Random(), and out of very simple
 > components - a photon source, a polarising filter, and a detector,
 > for instance.  But a Turing machine cannot compute that function.

This is not true. In Quantum Mechanics, the equation of motion can be used as
basis for a 'simulation', including your components.

-i(d/dt) (QMV) = H (QMV)       QMV:= Quantum-Multi-Verse

QMV must have enough variables, and H (Hamiltonian) must be right for this to
work. There is nothing uncomputable in this formula. A turing machine with
sufficiently good floating point emulation will be able to simulate the
multiverse.

The interesting thing, is that the different outcomes of the random generator
happens simultaneously, in a superposition of all possible random sequences.

Bottom line: Turing machines can run quantum mechanics can run multiverse.

Kim 0yhus
From: burton@cfm.brown.edu (Joshua W. Burton)
Newsgroups: sci.physics
Subject: Re: Hidden variable theories
Date: 14 Sep 1992 17:16:57 GMT
Organization: Brown University Center for Fluid Mechanics
NNTP-Posting-Host: qcd2.het.brown.edu


In article <277@mtnmath.UUCP> paul@mtnmath.UUCP (Paul Budnik) writes:
>
>>... 
>> 
>> Now I am really confused.  Are you saying that you think Bell's
>> inequality is violated or is not?
>
>Sorry. Let me rephrase that.
>
>I will be happy to bet you $50 that by the year 2005 there will be
>substantial experimental evidence that that the correlated events
>observed in tests of Bell's do not have a space-like separation.
>
>Paul Budnik

Whenever anyone starts offering free money, it pays to read the fine print.
Here is the deal so far, as I understand it:

1.) If, before 2005, firm evidence accumulates that the Aspect-type experiments
    performed in the 1980's appeared to violate Bell's inequality only because
    of detector inefficiencies and other loopholes, and that experiments that
    close these loopholes obey Bell's inequality and violate Copenhagen QM,
    Mr. Budnik expects to collect at even odds.

2.) If, by 2005, new experiments clearly show a violation of Bell's inequality
    between events at spacelike separation, at detector efficiencies high
    enough to rule out `nondetection conspiracies', Mr. Budnik proposes to pay
    up at even odds---to his original interlocutor at least, and perhaps to 
    the rest of us if we ask early and politely.  :)

3.) If, in 2005, the experimental situation is unchanged (or, for that matter,
    if the efficiency issue has been resolved but some new objection has
    surfaced which renders the violation of Bell's equality doubtful or
    subject to rationalization), Mr. Budnik _appears_ to be offering to pay
    up anyway.  Since foundations-of-QM experiments have never had a high
    funding priority (if it ain't broke....), this seems like the most likely
    of the three possibilities, so clarifying the terms of the bet seems
    worthwhile.

Anyway, if I have understood the wager correctly, and if the terms are as
stated, I'm in for $20---on the side of QM, of course.  If I have misunderstood
part (3), I still want a piece of the bet...but I want to hash out the terms
and the odds more carefully.  

Actually, I'm pretty sure that Mr. Budnik can get much better than even odds
if he opens the bet up to the whole readership.  If anyone wants either end
of this bet, please e-mail me at <burton@het.brown.edu>.  After a week or so,
I'll figure the odds, and set an interrupt to beep me on the morning of 1 Jan
2006 (my files will have moved from a NeXTcube to a Fujitsu Deathstar by then,
of course, but it will still be Unix!).  Since I'm making book at no
commission, I don't think I'm violating Usenet guidelines or RI state law.

Joshua W. Burton
From: sichase@csa2.lbl.gov (SCOTT I CHASE)
Newsgroups: sci.physics
Subject: Re: Hidden variable theories, was: Uncertainty Princi
Date: 11 Sep 92 20:53:03 GMT
Reply-To: sichase@csa2.lbl.gov
Distribution: na
Organization: Lawrence Berkeley Laboratory - Berkeley, CA, USA
NNTP-Posting-Host: 128.3.254.197
News-Software: VAX/VMS VNEWS 1.3-4

In article <1992Sep11.185356.5600@galois.mit.edu>, jbaez@riesz.mit.edu (John C. Baez) writes...
>I hope Scott Chase is keeping track of these unsolved questions in physics!
>Someone pointed out that pretty near the top of the list should be why the
>signature of spacetime is +--- and not +++-.  (That was a joke, folks. 
>I hope you all know what the real puzzle is: why is there one "time" and
>three "space" dimensions.)  

I'm out here, keeping a list of the suggestions.  But I have been through 
the Hidden variables/Bell's inequality discussion too many times.  I'm too
bored of it to get involved in this particular thread.

-Scott

--------------------
Scott I. Chase			"The question seems to be of such a character
SICHASE@CSA2.LBL.GOV		that if I should come to life after my death
				and some mathematician were to tell me that it
				had been definitely settled, I think I would
				immediately drop dead again."      - Vandiver
Newsgroups: sci.physics
From: jbaez@riesz.mit.edu (John C. Baez)
Subject: Re: How old is the universe?
Organization: MIT Department of Mathematics, Cambridge, MA
Date: Sat, 12 Sep 92 07:10:24 GMT


>C. Taylor Sutherland III writes:
>tolman%asylum.cs.utah.edu@cs.utah.edu (Kenneth Tolman) writes:

>>How old is the universe is seconds?  

>Convert 1.5 E 9 yrs. into seconds.

...and then multiply by about ten if you want an answer close to the
consensus these days.

>>How much time is left before it crunches back together?

>First of all, we're not really sure if it's expanding in the first place, 

Huh?  Conventional wisdom says it is... I'm a cosmological agnostic
myself, but folks who believe they know how old the universe is are typically
believers in the big bang, which entails a belief in the universe's expansion.

>>and
>>if it is we certainly don't have enough data (total mass (including unobserved
>>stars and "dark matter"), total kinetic energy, where the center is[...]

Surely you're joking, Mr. Sutherland!  The "center"?  Everyone knows
that it's in Boston!  Seriously, there is no "center" as far as anyone knows.

>>Where might I find these figures in reference texts?

>Try the Hitchhikers Guide to the Galaxy

Is this where you get your misinformation?


.
From: bweiner@ruhets.rutgers.edu (Benjamin Weiner)
Newsgroups: sci.physics
Subject: Re: Why Do Mirrors Reverse Left/Right and Not Up/Down?
Date: 10 Sep 92 23:00:46 GMT
Organization: Rutgers Univ., New Brunswick, N.J.

I hate to add more to this topic, but recently while driving
(I _do_ live in New Jersey) I found another demonstration that
mirrors do not reverse left to right: when you're looking in the
rear view mirror, and the car behind you is signaling, if the
turn signal that's blinking is on your left, that means it will
turn to your left (except in Boston, because Boston drivers will
do anything to confuse you).  Even though you are looking in a
mirror, the signal is on the "correct" side.

renieW neB
Newsgroups: sci.physics
From: firth@sei.cmu.edu (Robert Firth)
Subject: Re: Probability Question
Organization: Software Engineering Institute
Date: Tue, 15 Sep 1992 12:01:28 GMT

In article <1992Sep14.212528.29098@uwm.edu> gunter@csd4.csd.uwm.edu (David O Gunter) writes:

>But since there are 4-quarters, the total prob. is
>
>                                8 dtheta
>                          P =  -----------
>                                  Pi

There's the error.  There are four quarters, but the probability that the
particle will be in any given quarter is 1/4.  Multiply in that factor,
and you are back to the correct answer of 2dtheta/pi.
Newsgroups: sci.physics
From: sichase@csa2.lbl.gov (SCOTT I CHASE)
Newsgroups: sci.physics
Subject: Re: Report on Philosophies of Physicists
Date: 9 Sep 92 23:05:24 GMT
Reply-To: sichase@csa2.lbl.gov
Followup-To: sci.physics
Distribution: na
Organization: Lawrence Berkeley Laboratory - Berkeley, CA, USA
NNTP-Posting-Host: 128.3.254.197
News-Software: VAX/VMS VNEWS 1.3-4

In article <22218@galaxy.ucr.edu>, baez@ucrmath.ucr.edu (john baez) writes...
> 
>Mathematics is clearly a human activity and as such subject to all the foibles
>of any other human activity, but it is NOT warm and fuzzy.  It is cool and
>smooth.  If you want something warm and fuzzy, raise koala bears.

I suspect that koalas (and pandas) are not nearly as warm and fuzzy (except
in the strictly physiological sense) as the P.R. folks would have us
believe.  Unlike the wonderful koalas who promote QUANTAS and flavored
mineral water, real wild koalas generally are grumpy nasty creatures
who have a strong dislike for mathematicians and physicists, but have a
special distaste for knots and gravity.  You wouldn't like them one bit, John.

Beavers, on the other hand...

-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: dwr2560@zeus.tamu.edu (RING, DAVID WAYNE)
Subject: Re: Did electric/magnetic symmetry "break"?
News-Software: VAX/VMS VNEWS 1.41    
Organization: Texas A&M University, Academic Computing Services
Date: Sun, 6 Sep 1992 00:33:00 GMT

carlip@landau.ucdavis.edu (Steve Carlip) writes...
>The electromagenetic symmetry you are asking about is called duality.  
>In the absence of charged matter, you can freely rotate the electric and
>magnetic fields into each other.  Charged sources provide an _explicit_
>symmetry-breaking, by uniquely picking out one "direction" to couple
>to.  This isn't the kind of broken symmetry you're asking about, I
>think; for instance, there's no phase transition between a symmetric
>and a nonsymmetric ground state. 

'rotate' and 'direction' suggest a continuous symmetry. But taking the dual
is discrete. Is that right?

Dave Ring
dwr2560@zeus.tamu.edu
From: maxc0452@ucselx.sdsu.edu (Legene)
Subject: neutrinos & anti-neutrinos
Summary: A question
Keywords: neutrino, antineutrino,anti-neutrino
Organization: San Diego State University Computing Services
Distribution: global
Date: Wed, 9 Sep 1992 19:10:31 GMT

Could someone please tell me what the annihilation products
of neutrinos and anti-neutrinos are?  I'd appreciate it ever-so-much.


Newsgroups: sci.physics
From: jbaez@riesz.mit.edu (John C. Baez)
Subject: Re: Hidden variable theories, was: Uncertainty Princi
Organization: MIT Department of Mathematics, Cambridge, MA
Date: Fri, 11 Sep 92 18:53:56 GMT

I hope Scott Chase is keeping track of these unsolved questions in physics!
Someone pointed out that pretty near the top of the list should be why the
signature of spacetime is +--- and not +++-.  (That was a joke, folks. 
I hope you all know what the real puzzle is: why is there one "time" and
three "space" dimensions.)  

In the list of mathematical physics questions I left out the cosmic
censorship hypothesis.  I just got a copy of Contemporary Mathematics
132: Mathematical Aspects of Classical Field Theory.  (My own otherwise
magnificent contribution was marred by some dimwit who took my LaTeX
file and decided to get rid of all the boldface characters in the name
of esthetic totalitarianism, so that now my Hamiltonians look just
like my Hilbert spaces, producing some silly sentences like "H psi is
finite whenever psi is H."  Aargh!  But I digress.)  In it is a nice
review article by my pal Piotr Chrusciel entitled "On uniqueness in
the large of solutions of Einstein's equations ("Strong cosmic censorship")".

He notes that two hard problems in general relativity have fallen -
the positive mass conjecture (roughly, that every asymptotically flat
solution of Einstein's equations has positive energy) and the
stability of Minkowski space (roughly, that small perturbations of
flat initial data will send off ripples to infinity and approach
flatness as time goes by, rather than amplifying into nasty singularities).
The cosmic censorship conjecture is still rather problematic.  He states the 
Strong Cosmic Censorship Conjecture as "generic spatially compact or
asymptotically flat initial data sets for the gravitational field
admit a unique maximal vacuum development."  The Weak Cosmic
Censorship Hypothesis he states rather roughly as "for generic collapsing
isolated gravitational systems the singularities that might develop
will be hitten beyond a smooth event horizon."  

The genericity conditions are important because otherwise there are
already counterexamples.  He notes, for example, that Yodzis, Seifert
and Mueller zum Hagen have shown that "naked singularities" can occur
during the collapse of a spherically symmetric dust cloud or for
spherically symmetric perfect fluids.  ("Dust" means that the
stress-energy tensor is of the form T_{mu nu} = rho v_mu v_nu, where
rho is the density of the dust and v_mu is the velocity field of the
dust, which must be timelike (slower than light).  I'll skip the
definition of a perfect fluid.)  He says that these are "shell
crossing singularities," which arise from the crossing of shells of
matter.  Their occurence is stable under spherically symmetric
perturbations.  I guess the hope is that small NON-spherically-
symmetric perturbations would get rid of the singularities.

Does anyone here know what these naked singularities are like?  That
is, what weird physical consequences would they have?

Also check out James Isenberg's article "Strong Cosmic Censorship".



Newsgroups: sci.physics,sci.math
From: G.Joly@cs.ucl.ac.uk (Gordon Joly)
Newsgroups: sci.physics
Subject: Transformations onto Euclidean Space
Date: 10 Sep 92 14:43:23 GMT

David Griffith writes:
 > I apologize in advance for the hopelessly vague nature of this question but...
 > 
 > Can anyone suggest a few mathematical methods to transform or map _something_
 > onto Euclidean or Minkowskian space. In other words, you have some
 > representation or some geometry that describes various points, you apply
 > the mapping and you get points in Euclidean space.
 > 
 > As a for instance, let me make one up - each x, y and z coordinate is
 > actually the modulus of a complex number, so points in this six dimensional
 > complex space map onto the three dimensional real space.
 > 
 > Thanks,
 > 
 > Dave Griffiths
 > 
 > PS: I'd appreciate a _finite_ list! :-)


Here is a map:  (it,x,y,z) <-> (t,x,y,z)

Here is another map:  (it,x,y,z) <-> (-t,x,y,z)

I guess that is is wrong. Try looking a projective geometry
literature, perhaps.

Gordon.
Newsgroups: sci.physics,sci.math