HDTenEightyP/NetNews huggingface dataset:
From: tycchow@phragmen.mit.edu (Timothy Y. Chow)
Subject: Re: What's a manifold?
Organization: None.  This saves me from writing a disclaimer.
Date: Fri, 6 Nov 92 02:41:42 GMT

In article <SMITH.92Nov5132141@gramian.harvard.edu> smith@gramian.harvard.edu
(Steven Smith) writes:

>No one ever said that arbitrariness is necessarily bad;

Actually, a couple of us have implied it.

>Sorry, but what is your definition specifically?  If manifolds are
>simply retracts of open sets of Euclidean space, then using this
>definition, how is projective space a manifold ?

This is not a problem, as long as you embed in a high enough space.  The
projective plane, for instance, embeds nicely in R^4 and it's easy to make
it into a retract of some tubular neighborhood.

I don't think that people are giving enough credit to the retract
definition.  It is often very convenient to be able to introduce a tubular
neighborhood around a manifold.  The Jordan curve theorem is one example.
With the classical approach, proving that manifolds can be embedded in
Euclidean space is quite a major theorem.  You do get some things almost
for free with the retract definition.  But as has already been pointed
out there are other limitations to this approach.
-- 
Tim Chow     tycchow@math.mit.edu
Where a calculator on the ENIAC is equipped with 18,000 vacuum tubes and weighs
30 tons, computers in the future may have only 1,000 vacuum tubes and weigh
only 1 1/2 tons.                               ---Popular Mechanics, March 1949
From: 01crmeyer@leo.bsuvc.bsu.edu (Craig Meyer)
Newsgroups: sci.physics
Subject: High-Pressure Gas Tanks--How Many PSI?
Date: 9 Nov 92 21:09:09 GMT
Organization: Ball State University, Muncie, In - Univ. Computing Svc's

I'm looking into the concept of running an automobile off of compressed air.

According to my calculations (based on a Gast airmotor catalogue), such a 
vehicle would need air tanks that could hold 100,000 psi.

Is that at all possible?

Thanks for your help,

CM

-- 
       Craig Meyer                 01CRMEYER@LEO.BSUVC.BSU.EDU
       Indiana Academy for Science, Mathematics, and Humaities.
       Muncie, IN  47306                          317-285-7433

       Opinions expressed are mine alone, and not necessarily
       shared by the Indiana Academy.
Newsgroups: sci.physics
From: sarfatti@well.sf.ca.us (Jack Sarfatti)
Subject: Re: Round 3, Superluminal Debate
Organization: Whole Earth 'Lectronic Link
Date: Thu, 5 Nov 1992 22:35:34 GMT


Some notes on FTL signals on quantum connection.
#1 The beam splitter should not make any difference. If the output port
kets are |I> and |II>, then |I><I| + |II><II| = 1 implies that the beam
splitter acts as the identity.

# Perhaps phase compensation plates can be designed so that
<cos(phi + phi(e) - phi(o))> not zero. The phi dependence in the flutuation
signal can be regained if the classical probability distribution for the
phases is not uniform.


Newsgroups: sci.physics,sci.math
From: jbaez@riesz.mit.edu (John C. Baez)
Subject: Re: graphical humping terminology
Organization: MIT Department of Mathematics, Cambridge, MA
Date: Wed, 11 Nov 92 06:33:32 GMT

In article <1992Nov10.190554.11097@sfu.ca> palmer@sfu.ca (Leigh Palmer) writes:
>In article <ETHANB.92Nov9155340@ptolemy.astro.washington.edu>
>ethanb@ptolemy.astro.washington.edu (Ethan Bradford) writes:
>>The simple explaination of why yellow monochromatic light looks the
>>same as equal combinations of green and red light is that the color
>>receptor systems in the eye (the cones) have sensitivity curves which
>>trail off (I remember them as being roughly gaussian).  A signal
>>halfway between the two peaks excites the two receptors equally, as do
>>two signals right on each peak.
>
>This article piqued my old annoyance with the free use of the term "gaussian"
>which is so common among us. In the case mentioned above it is the case that
>none of the three visual response functions looks gaussian to me. I have even
>heard Lorentzian curves described as gaussian by colleagues in an unthinking
>moment.
>
>I believe it is time that we had another term for curves which have
humps.

(Picturesque solutions deleted.)  I agree with your annoyance
completely.  Gaussians are very useful but pretending that every
molehill or mountain is a Gaussian can lead to lots of errors - so it's
good that mathematicians have a technical term for the kind of function
you are referring to.  It's called a "bump function", or "bump".


Newsgroups: sci.physics
From: solman@athena.mit.edu (Jason W Solinsky)
Subject: Re: Is Math Hard?
Organization: Massachusetts Institute of Technology
Date: Sun, 8 Nov 1992 11:57:11 GMT

In article <10673@vice.ICO.TEK.COM>, hall@vice.ICO.TEK.COM (Hal F Lillywhite) writes:
|> 
|> In article <611@alden.UUCP> sgr@alden.UUCP (Stan Ryckman) writes:
|> >In article <10620@vice.ICO.TEK.COM> hall@vice.ICO.TEK.COM (Hal F Lillywhite) writes:
|> >[...]
|> >>Of course we should also listen to the experts in deciding what is 
|> >>taught but that does not mean giving them a free hand in the matter.
|> >>We should take what they say into account then apply our own
|> >>intelligence to the matter.  Otherwise we risk paying for people to
|> >>teach our children the economic theories of Angela Davis or the
|> >>genetic ideas of William Shockley.
|> 
|> >Or, (gasp!) Charles Darwin.
|> 
|> >Just how do we "take what they say into account and then apply our
|> >own intelligence?"  A vote?  I bet creationism still would win out
|> >in a fair portion of the U.S.
|> 
|> 
|> Well, yes we do it by vote.  The only other choice available to us
|> is some form of dictatorship.

Dear g-d, we have here a product of the American education system. There are
thousands of choices available to us besides dictatorship and democracy.
Democracy is a disgusting system wherein the majority rules. Democracy will
always result in a communist economic system. This is its nature because a
majority of people will always covet something a minority has. This is NOT
the way a child's education should be determined. IT CAN NOT BE. The parents
of a child must make that decision.

You are advocating the Hillary Clinton school of thought. Who cares what the
parents think or believe in? The child should be taught what the majority
believes and do what the majority feels is correct and if the parents don't
agree, the child should be taken away from them, or should sue them.
Democratic governments are bad enough, but a democratic education is a
heinous violation of personal freedom.

Jason W. Solinsky
Newsgroups: sci.physics
From: pratt@Sunburn.Stanford.EDU (Vaughan R. Pratt)
Subject: Re: The size of electrons, and Fanciful misc SAGA
Organization: Computer Science Department,  Stanford University.
Date: Mon, 9 Nov 1992 23:01:56 GMT

In article <1992Nov9.155216.18546@prim> dave@prim.demon.co.uk (Dave Griffiths) writes:
>In article <1992Nov8.231641.28334@CSD-NewsHost.Stanford.EDU> pratt@Sunburn.Stanford.EDU (Vaughan R. Pratt) writes:
>>
>>You are forgetting that scalability is a big concern today in CS.
>>Digital models don't scale gracefully, the bits look bigger.  Smooth
>>scalability demands a smooth view of what one is scaling.  A digital
>>view inhibits scalability.
>>
>
>Can you give an example of where scalability becomes a problem? Of course
>things don't look the same on smaller and smaller scales, but that's the
>whole point. If you take a smooth rod of metal, you can keep chopping it
>in half, but eventually you'll run up against a barrier of individual atoms -
>your scalability disappears.

I already gave a perfect example, namely bitmap fonts.  I used to hear
exactly your view expressed for bitmap fonts during the mid-80's.  I
don't hear it any more, there are now too many bits for bitmaps to be
more than the last step before rendering, at least in printers and I
hope at some point for screens.
-- 
Vaughan Pratt
Xref: sparky sci.physics:18172 sci.physics.fusion:2617
From: jtchew@csa3.lbl.gov (Ad absurdum per aspera)
Newsgroups: sci.physics,sci.physics.fusion
Subject: Munich A-bomb kit (was Re: The H-Bomb secret is out)
Followup-To: sci.military
Date: 5 Nov 1992 09:32 PST
Organization: Lawrence Berkeley Laboratory - Berkeley, CA, USA
Distribution: world
NNTP-Posting-Host: 128.3.254.198
News-Software: VAX/VMS VNEWS 1.41    

(Note followups to sci.military, begging its moderator's indulgence)

On sci.physics.fusion, dam@dcs.glasgow.ac.uk (David Morning) writes...

>About 4kgs of what was described as "bomb grade" Plutonium was seized by
>customs official in Germany about two weeks ago. It was being smuggled via
>Poland and its destination appeared to be the Balkans. This is the second
>customs seizure of Plutonium the Germans have made in the last 6 months.
>Scary huh?

Opinions vary; one suspects that, as always, the people who know for
sure aren't able or willing to talk about it.

The seizure, apparently from the trunk of a car in Munich, was 
mentioned only lightly and sporadically in the US news media.  An 
early report which my wife saw (on CBS television, if we both recall 
correctly) had it as more or less a complete do-it-yourself bomb kit, 
plus some unspecified indications that the vendors were willing to
sell anything from special nuclear materials to assembled ex-Soviet
weapons.  

A radio report that I heard a few days later (probably from the BBC 
World Service by way of National Public Radio) said that it was "only" 
a few pounds of U-235, with some conflicting reports from various
officials as to whether it was weapons- or reactor-grade material.
Some nth-hand gossip from the unclassified stem of the interlaboratory 
grapevine (I hold no clearance, and my cleared friends are all a bunch 
of boy scouts, so take this how you will) says it was the latter.

So:  I'd give odds that they did NOT find a paint-by-numbers A-bomb or
immediately usable components thereof.  The scary part, for me, was a
news report that various German officials had dealt with 100 real or
suspected incidents of this type in 1992, up from 29 the previous year.
Perhaps the American media's inattention to this story will be rectified
dramatically and all too soon.  :(

--Joe
"Just another personal opinion from the People's Republic of Berkeley"
From: firth@sei.cmu.edu (Robert Firth)
Subject: Re: Scientists debunk astrology
Organization: Software Engineering Institute
Date: Wed, 11 Nov 1992 13:22:44 GMT

If astrology is all rubbish, then what hitherto unknown scientific
principle allowed Johannes Kepler to cast such accurate horoscopes?
Newsgroups: sci.physics
From: crb7q@kelvin.seas.Virginia.EDU (Cameron Randale Bass)
Subject: Re: Religion & Physics Don't Mix
Organization: University of Virginia
Date: Mon, 9 Nov 1992 01:15:39 GMT

In article <1dk972INNemd@chnews.intel.com> bhoughto@sedona.intel.com (Blair P. Houghton) writes:
>In article <BxBpHs.DtF@unixhub.SLAC.Stanford.EDU> sschaff@roc.SLAC.Stanford.EDU (Stephen F. Schaffner) writes:
>>You simply can't do science without the 
>>"unquestioning belief" (usually unconscious) in the foundations upon which 
>>it is built.
>
>NOT.
>
>One makes assumptions, or alludes to the work of others (which
>also is based on assumptions), and deduces the next level of
>facts[*] from those assumptions.
>
>But, in many cases, logic does not require assumptions of
>any kind, since it can make the assumptions irrelevant to
>the results; i.e., the results support themselves.

     It requires the assumption of logic, if nothing else.

     And as much is it pains me to use this particular overworked 
     example, I believe that Godel showed, at least in one restricted
     system, that the system itself is not capable of proving
     all theorems within the system with a limited number of
     assumptions.  I expect no different behavior from such large and messy
     systems as reality.  In other words, 'ya gotta make assumptions',
     lots of them.  Logic doon't help here, laddie.

>If everywhere in the self-supporting loop there are observable
>and repeatable phenomena, then you have an assumptionless
>fact, and faith is not necessary.

     Fact?  Assumptionless?  Hell, you make any number of assumptions
     in looking at a number on a dial, to say nothing of the assumptions
     that proceed down from the dial to whatever phenomenon you happen to   
     be dialing.

>(Thomas Edison made no assumptions; that's why it took over
>six thousand prototypes to make a profitable incandescent
>light-bulb; there was no faith, there was only risk and
>persistence and a passing observation that electrically-
>heated materials can glow).

     Looks to me like he made assumptions by the metric buttload.

     How many insulators did he try?  Did he try Lake Michigan?
     Jellyfish?  Tuna on rye?  Assistants' nostrils?  Every hair
     on his head?  
     
                            dale bass
-- 
C. R. Bass                                          crb7q@virginia.edu        
Department of Mechanical, 
     Aerospace and Nuclear Engineering
University of Virginia                              (804) 924-7926
Newsgroups: sci.physics,sci.math
From: jbaez@riesz.mit.edu (John C. Baez)
Subject: Re: What's a manifold?
Organization: MIT Department of Mathematics, Cambridge, MA
Date: Thu, 5 Nov 92 21:25:25 GMT

In article <1992Nov5.060400.14203@CSD-NewsHost.Stanford.EDU> pratt@Sunburn.Stanford.EDU (Vaughan R. Pratt) writes:

>Ah, now this is starting to sound very interesting and helpful.  What I
>don't understand here is how "living in R^n" is of itself creating
>complexity and obscurity.  I can see that the arbitrariness of f might
>get in the way.  But where does the complexity and obscurity creep in
>if for example we define a manifold to be a smooth retract of an open
>subset of R^n?  (This is essentially taking the existence of tubular
>neighborhoods as definitive of manifolds, and is how Bill Lawvere likes
>to think of them.)

Are you just playing devil's advocate here?  The devil has enough
advocates already and doesn't need your help.  :-)  But anyway, one
point is that many nice ways of constructing new manifolds from old ones
are a pain in the butt to describe if your manifolds all have to be
living in some R^n.  E.g. - constructing manifolds by surgery (cutting
and pasting).  Just 'cause each of the pieces live in some R^n doesn't
mean that when you stick 'em together you get something that can be
embedded in R^n (for the same n).  You can use a larger value of n, but
you should soon get the feeling, "why am I bothering?  What's so great
about living in R^n, anyway?"  

When you tell folks spacetime is curved they always want at first to
visualize it as sitting inside some "hyperspace," an R^n of higher
dimension.  This is a blatant violation of Occam's razor and leads to
silly questions about using hyperspace as a tricky form of rapid
transportation.  (Note: I'm not saying that one should never consider
these questions - just that, upon thought, it turns out that they are
unproductive.)  The fact is, we have no strong evidence that we are
living in R^3, or R^4 -- all we know is that it looks *locally* like R^3
or R^4, so we might as well face up to the intrinsic notion of manifolds.


Newsgroups: sci.physics,sci.math
From: jbaez@riesz.mit.edu (John C. Baez)
Subject: Re: Covariant vs. Lie Derivative in Gen. Rel.?
Organization: MIT Department of Mathematics, Cambridge, MA
Date: Wed, 11 Nov 92 06:28:53 GMT

In article <1992Nov10.173224.6690@vision.ummed.edu> lml@vision.ummed.edu (Lawrence Mark Lifshitz) writes:

>So, conceptually, what is the difference between the two?
>Does one require a different type of topogical space or
>parameterization?  Mathematically how do they differ?
>thanks in advance.

It always gets me when folks ask math questions on sci.physics and *not*
sci.math.  Is this meant to indicate that the answers mathematicians
give will be too confusing?  Let's see - I'm a mathematician and I will
try not to be too confusing.  I won't repeat the definitions of
covariant vs Lie derivatives of tensor fields; instead, I'll just
emphasize some ways in which they are VERY DIFFERENT.  To begin with,
though, they are both defined for any sort of tensor field on a manifold
- so no "different type of topological space" is involved.

Here are the big differences:

1) To perform a Lie derivative one needs, not just a tangent vector at a
point of the manifold, but a whole vector *field* - at least on some
patch (open set) of the manifold.  This is because one needs to flow the
tensor along the vector field, so to speak, and see at what rate it
changes as it flows past a given point.

2) The covariant derivative only requires a tangent vector at one point
of the manifold.  The price you pay is this: to define it you need to
choose a connection on the (tangent bundle of) the manifold.  Of course,
such a connection - the Levi-Civita connection - comes for free if your
manifold has a Riemann metric on it.  It is crucial to note that some
*extra geometrical structure* (the connection) is involved in the
covariant derivative that is not needed for the Lie derivative.  

To repeat: The connection allows you to compare tangent vectors at two
points of the manifold given only a curve connecting them; the Lie
derivative requires a whole vector field, to generate a flow that "drags
tensors along". 

Newsgroups: sci.physics
From: sarfatti@well.sf.ca.us (Jack Sarfatti)
Subject: Does Baez understand orthodoc QM?
Organization: Whole Earth 'Lectronic Link
Date: Sat, 14 Nov 1992 02:41:42 GMT


Baez writes to Firth:
I already told Robert this.  Perhaps I wasn't sufficiently eloquent to
get my point across.  But let me just say that I agree completely with
Benjamin Weiner's point.  It makes perfect sense to argue about what can
or cannot happen according to orthodox QM without doing any experiments.
If Sarfatti claimed he had a NEW THEORY that contradicted orthodox QM
one would have to see if his theory was consistent and met experimental
tests.  But he seems to be claiming that orthodox QM predicts FTL
communication.  Of course, his way of doing orthodox QM looks very
unorthodox, i.e., wrong.

This indicates to me that Baez does not understand orthodox quantum
mechanics. I am willing to retract my statement if Baez can pinpoint
the deviation of my argument from orthodox qm.

The red herring that |a,e,+> is orthogonal to |a,o,+> is hogwash
and contradicts standard QM and is not required by local unitarity of time
evolution between measurements.  Thinking that they are orthogonal
shows a lack of physical understanding. A half-wave plate rotates plane
of polarization by 90 degrees. Therefore, although |a,e,+> is orthogonal
to |a,o,->, it is not orthogonal to |a,o,+> and this is not a non-
unitary transformation. The unitary transformation is

U(1/2)|a,o,-> = |a,o,+>
U(1/2)|a,o,+> = |a,o,->
U(1.2)|a,e,+> = |a,e,+>
H(1/2)|a,e,-> = |a,e,->
(typo H last line is U)

<a,o,-|a,o,+> = 0

<a,e,+|a,e,-> = 0

<a,e,+|a,o,-> = 0

|<a,e,+|a,o,+>| = 1

|<a,e,-|a,o,->| = 1

If Baez has another objection what is it?

Baze is a good formalist, perhaps. But he totally lacks the physical
understanding (i.e. Bohm's "informal language") that connects the
formalisim of kets and unitary matrices to the physical devices. The
same goes for Ramsay and Weiner. Formalism is like "statistics" you
can prove all kinds of lies with it - and then you can abuse your
opponent by calling him "crackpot" or saying the work is "nonsense".
I am not accusing Baez of the latter - I refer to others.

As Einstein said:"Great spirits have always encountered violent
opposition from mediocre minds."

Baez, I am not referring to you here - but to some rude person from
Skidmore College physics Dept who sent me a gratuitous malicious
and very unprofessional e-mail.
From: crb7q@kelvin.seas.Virginia.EDU (Cameron Randale Bass)
Newsgroups: sci.physics
Subject: Re: No big crunch?
Date: 5 Nov 92 04:58:29 GMT
Organization: University of Virginia

In article <1da56vINNcqk@darkstar.UCSC.EDU> fxt@helios.ucsc.edu (oxide owner) writes:
>look dale. no one is claiming a dark matter universe is the solution. one does
>claim that it is, at present, the best available explanation. cosmology and
>galaxy formation is very speculative at this point in human endeavor, unlike
>the study of fluid flows tied to terrestrial applications. self consistency
>with known physics *is* important, if for the very fact that cosmological
>theories that violate or are inconsistent with known physics are most
>certainly ruled out. your skepticism of modern paradigm is healthy, but your
>insistence of abian-like pixie's as a cosmological theory for galaxy formation
>is very unbecoming of your rather colorful sci.physics personality.

     To the contrary, I hear and read many people of the astrophysical
     persuasion who would have us believe that such concepts as
     'pixie'-like dark matter are far more definite than they actually
     are.  My wife's favorite term 'kludge' seems to come immediately
     to mind.

     About 'pixies', I have not been insisting on them, just pointing
     out that some current theory seems to have pixie-like characteristics.

     I prefer wildebeest as my universal motivating force.

                              dale bass

-- 
C. R. Bass                                           crb7q@virginia.edu
Department of Mechanical and Aerospace Engineering
University of Virginia
Charlottesville, Virginia                            (804) 924-7926
From: matt@physics16.berkeley.edu (Matt Austern)
Newsgroups: sci.physics
Subject: Re: Higgs mass mechanism and e+e- anihilation
Date: 8 Nov 92 22:51:50
Organization: Lawrence Berkeley Laboratory (Theoretical Physics Group)
Reply-To: matt@physics.berkeley.edu
NNTP-Posting-Host: physics16.berkeley.edu
In-reply-to: ddixon@nyx.cs.du.edu's message of Sun, 8 Nov 92 23:37:12 GMT

In article <1992Nov8.233712.14557@mnemosyne.cs.du.edu> ddixon@nyx.cs.du.edu (David Dixon) writes:

> If electron mass comes from the coupling to a scalar Higgs field, then
> what would the mechanism be for converting this mass to the energy in
> a gamma-ray if the electron is annihilated (one n or two?) by a positron?
> Does this also account for the relativistic mass?  How about the
> electromagnetic binding energy of a hydrogen (or other) atom?

Essentially, none of these questions depend at all on the Higgs
mechanism.  (Pretty much all of them can be answered perfectly well
using ordinary QED.)

There's a reason for this which is actually quite general: all of
these questions involve physics at a scale of an MeV or less, but the
mass-generating mechanism (whether a Higgs boson or something else)
involves scales of a couple hundred GeV or so.  It is a general
property of quantum field theories that physics at very high energy
scales decouples from physics at low energy scales.  That's why we
still don't know just what the mass-generating mechanism is:
low-energy experiments don't really probe that sector.

I haven't stated this "decoupling theorem" very precisely; a more
precise statement of it would explain exactly in what sense the
different scales decouple, and it would also explain just what the
conditions are under which it applies.  Still, it is at least a good
rule of thumb that physics at some particular energy scale doesn't
depend very much on what's going on at an energy scale 100,000 times
larger.


--
Matthew Austern                   Just keep yelling until you attract a
(510) 644-2618                    crowd, then a constituency, a movement, a
austern@lbl.bitnet                faction, an army!  If you don't have any
matt@physics.berkeley.edu         solutions, become a part of the problem!
Newsgroups: sci.physics