HDTenEightyP/NetNews huggingface dataset:
From: stephen@mont.cs.missouri.edu (Stephen Montgomery-Smith)
Subject: Re: How do you draw a straight line?
Organization: University of Missouri
Date:  6 Oct 92 07:41:05 GMT

In <1992Oct6.030213.20215@galois.mit.edu> jbaez@riesz.mit.edu (John C. Baez) writes:

>In article <1992Oct5.154211.21663@ecrc.de> micha@ecrc.de writes:
>>In article 24242@access.usask.ca, choy@skorpio.usask.ca (I am a terminator.) writes:
>>>How do you know that the line you draw is really straight? What
>>>defines straightness?
>>
>>This is something I've been wondering about since a long time. Although we can
>>make a circle as precise as we want, I think we cannot make a really
>>precise straight line - every straight line is made from another one or from a tool
>>that has been made using some older straight lines - so it all comes down to
>>copying a line that has been made thousands years ago. Although we have precise
>>instruments and tools, we can only make better and better lines (so that eventually
>>the error is less than an atom, and we are there), but IMHO there is no
>>process to create a straight line directly. Or is it?

>The compass is nice because it works straight from the definition of a
>circle, while a ruler, as you note, is not so nice since it does not
>work from the definition of a straight line as the shortest path between
>two points.  However, there is a machine that has been built which draws
>straight lines "by definition."  Alas, I forget how it works.  Maybe
>someone can remind us or reinvent it.  Of course this is not to say it
>really is better than a good ruler but it is philosophically satisfying.
>I seem to remember that it was built, not for practical reasons, but
>just to show it could be done.  Back in the age of mechanical (as
>opposed to electronic) ingenuity they did this sort of thing.  Some of
>you may know how to built a device which will measure the area of a
>shape if you trace the outline of the shape.  Others may enjoy figuring
>it out.  Nothing electronic allowed!  Big clue: Green's theorem.
>Disclaimer: I would have to figure out the details myself so don't ask....

How about pulling a piece of string taut?  Won't that give a straight line?

Stephen




Newsgroups: sci.physics
From: terry@aslws01.asl.dl.nec.com (Terry Bollinger)
Subject: Re: Simple observation about Quantum Kitty Cats
Organization: NEC America, Inc. Irving, Texas
Date: Fri, 2 Oct 1992 02:12:38 GMT

In article <1992Oct1.125305.13437@oracorp.com>
daryl@oracorp.com (Daryl McCullough) writes:

> It seems clear to me that the wave function is not a physical field,
> in the sense of the classical electromagnetic field...

Just as a sidenote, Bell apparently was intrigued by the idea that the
wave function *was* every bit as real as an electromagnetic field, a cocept
first broached by DeBroglie in 1926 in his pilot wave model.  In the paper
after which his book Speakable and Unspeakable in Quantum Mechanics was
named, Bell makes his fondness for particle *and* wave quite clear by
saying: "Even now the de Broglie-Bohm model is generally ignored, and
is not taught to students.  I think this a great loss.  For that picture
exercises the mind in a very salutary way."

And again: no, I definitely do not subscribe to pilot waves.  I'm just
intrigued by how thoroughly UNconventional Bell was in his QM philosophy.
One of the greatest ironies I've seen regarding this was a headline in
a science article about Bell (I forget where) that described him as "The
Man Who Proved Einstein Wrong."  The excellent irony is that Bell would
have loved nothing more than to have proved Einstein RIGHT about quantum
mechanics.  Bell has nothing but praise for Einstein's approach to the
QM conundrum, and simultaneously Bell appears to regard Bohr's concept
of complementarianism as little more than pompous obfuscation.

Bell was NOT, repeat NOT your everday Copenhagen traditionalist.  He
liked his QM as solid as he could possiblly bake it, and went back to
the very earliest days of QM to find a recipe that suited his tastes.

				Cheers,
				Terry Bollinger
From: jlg@cochiti.lanl.gov (Jim Giles)
Newsgroups: sci.physics
Subject: Re: Simple observation about Quantum Kitty Cats
Date: 29 Sep 92 21:38:54 GMT
Article-I.D.: newshost.1992Sep29.213854.26085
Organization: Los Alamos National Laboratory

In article <1992Sep29.182835.26555@galois.mit.edu>, jbaez@riesz.mit.edu (John C. Baez) writes:
|> [...]
|> Of course, mathematics has been a branch of mysticism ever since the
|> Pythagoreans (if not earlier).  As a mathematician, if one could
|> find a mathematical model from which quantum mechanics and general
|> relativity both "fell out" in some natural manner, it would count
|> as an outstanding achievement even if it had no testable consequences.

Yes.  It's always useful for your model to be easily manipulated.
However, a model by itself isn't a theory.  A theory is a model
*PLUS* a mapping from the model onto measurable aspects of reality.
Those parts of the model which are *not* mapped to measurable aspects
of reality cannot be said to *necessarily* correspond to anything 
physical - no matter how elegant they are.  Any alternative 
model which produces the same measurable predictions with the
same accuracy will do as well - and often in the past, well
regarded models have had to be discarded because new methods
of testing became available which disproved previously untestable
aspects of those models.

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.

-- 
J. Giles
Newsgroups: sci.physics
From: sarfatti@well.sf.ca.us (Jack Sarfatti)
Subject: TIME TRAVEL 1
Organization: Whole Earth 'Lectronic Link
Date: Mon, 28 Sep 1992 00:54:29 GMT


THE TIME TRAVELLER'S HANDBOOK 1.

From John Gribbon's new book UNVEILING THE EDGE OF TIME
(Harmony,1992):
1.	"Pick a big enough black hole, where tidal forces near the
event horizon are not too extreme, and, still without ever
crossing the event horizon, they would be able to use the
region of distorted spacetime around the hole for repeated
journeys through time - but only in one direction, into the
future." p.146

2.	"there seems to be nothing in the laws of physics that
forbids travel through wormholes. The science-fiction
writers were right - hyperspace connections do, at least in
theory, provide a means to travel to distant regions of the
Universe without spending thousands of years pottering
along through ordinary flat space at less than the speed of
light." p.152

3.	"it might indeed be possible to construct travrsable
wormholes artificially .... given a suitably advanced
technological civilization." p.173

4.	One must use negative feed back destructive gravity wave
interference stabilization to prevent the traversable
wormhole time machine fron shutting itself down by the
"blue sheet" barrier. p.174

5.	The Cal Tech consortium of Morris, Yurtsever and Thorne
"started out by constructing the mathematical description
of a geometry that described a traversable wormhole, and
then used the equations of the general theory to work out
what kinds of mattewr and energy would be associated with
such a spacetime... in order for an artificial wormhole to
be held open, its throat must be threaded by some form of
matter, or some form of field, that exerts negative
pressure and has antigravity... the kind of field,
associated with the modern version of the cosmological
constant, thought to have driven the expansion of the very
early Universe ... the negative pressure (tension) exerted
must be greater than the mass-energy density of the
original matter that makes up the black hole....
hypothetical matter that possesses this curious property is
known as 'exotic' matter." p.175

6.	Is the dark missing mass of the Universe exotic matter? It
would have to be if, indeed, the Universe is engineered by
super-intelligence quantum acting at a distance from the
future!


Xref: sparky sci.physics:16042 sci.math:12809
From: chrisman@wheatena.berkeley.edu (chrisman)
Newsgroups: sci.physics,sci.math
Subject: Re: How do you draw a straight line?
Date: 6 Oct 1992 20:13:09 GMT
Organization: U.C. Berkeley Math. Department.
NNTP-Posting-Host: wheatena.berkeley.edu

In article <1992Oct6.142703.20829@b11.b11.ingr.com> craig@jido.b11.ingr.com writes:
>In article <stephen.718357265@mont> stephen@mont.cs.missouri.edu (Stephen Montgomery-Smith) writes:
>   How about pulling a piece of string taut?  Won't that give a straight line?
>   Stephen
>
>Hmmmmmmm ...
>"No power on Earth, however great,
>Can stretch a string, however fine,
>Into a horizontal line
>That shall be absolutely straight."
>-- Author unremembered, it's in _Fantasia Mathematica_.


Indeed, a stretched string won't be completely straight, because
of the influence of gravity (gusts of wind, Brownian motion, ...)
no matter what the tension on the string.

Besides, if we want a machine that uses the "definition" to get
a straight line, how about a laser?  For the physicist (not the
mathematician), I suppose that the path followed by a beam o
light is the closest thing to a definition of a straight line.
From: matmcinn@nuscc.nus.sg (Mcinnes B T (Dr))
Subject: Re: STRUCTURE OF TIME
Organization: National University of Singapore
Date: Sat, 3 Oct 1992 03:09:19 GMT

	Err...mind telling us which law of physics you used to arrive at
this conclusion, Dale?

: 
:                               dale bass
: 
: 
: 
: 
: 
: 
: 
: 
: 
: 
: 
: 
: 
: 
: 
: 
: -- 
: C. R. Bass                                           crb7q@virginia.edu
: Department of Mechanical and Aerospace Engineering
: University of Virginia
: Charlottesville, Virginia                            (804) 924-7926
From: steinly@topaz.ucsc.edu (Steinn Sigurdsson)
Newsgroups: sci.physics
Subject: Re: Expansion
Date: 30 Sep 92 14:39:22
Organization: Lick Observatory/UCO
	<Sep.29.16.54.08.1992.28530@ruhets.rutgers.edu>
	<29SEP199220244986@zeus.tamu.edu> <22594@galaxy.ucr.edu>
NNTP-Posting-Host: topaz.ucsc.edu
In-reply-to: baez@ucrmath.ucr.edu's message of 30 Sep 92 16:31:21 GMT

In article <22594@galaxy.ucr.edu> baez@ucrmath.ucr.edu (john baez) writes:


   In article <29SEP199220244986@zeus.tamu.edu> dwr2560@zeus.tamu.edu (RING, DAVID WAYNE) writes:
   >This makes sense. What I don't understand is why a region of high density
   >homogeneity does not recollapse in a time appropriate to that density. I.e.
   >if the universe were filled with stars, in the density of a galaxy, the
   >universe would have recollapsed long ago. The region of space which is
   >inside a galaxy satisfies the same local einstein equation as the above
   >recollapsing example, so why do galaxies live so long?

   'Cause they're smaller.  I'm sure one can work out the math, but
   it's bound to amount to just that.  For example, one can have
   a fist-sized ball of iron, which will essentially never collapse
   (quantum fluctuations aside), but a galaxy-sized ball of iron
   would collapse mighty fast.

   Galaxies are not all *that* dense and they're spinning around (at least
   lots of them).  So they will take a while to collapse.  It's become
   widely accepted that many galaxies have black holes at their centers.
   These black holes are eating stars at a decent rate and should only
   be billions and billions of years before they suck up most of the
   galaxy, or at least the dense inner part.

   Does anyone have estimates on how long this munching process should
   take and how it will proceed?

See Binney & Tremaine and Blandford, Begelman and Rees.
Some characteristic time scales are the relaxation time
scale and the gravitational radiation time scales
for typical galaxy cores. They vary from 10**9 years
for some systems to 10**13 +++ for more ordinary
systems.
Your typical galaxy will stick around for longer than
the evolution time scale of the individual stars.

*  Steinn Sigurdsson   			Lick Observatory      	*
*  steinly@lick.ucsc.edu		"standard disclaimer"  	*
*  The laws of gravity are very,very strict			*
*  And you're just bending them for your own benefit - B.B. 1988*
Newsgroups: sci.physics
From: phfrom@nyx.uni-konstanz.de (Hartmut Frommert)
Subject: Re: Feynmann diagrams
Organization: Dept. of Physics, University of Constance
Date: Mon, 5 Oct 1992 17:40:12 GMT

rmz@ifi.uio.no (Bj|rn Remseth) writes:

>Are there any computer programs  for drawing 

Different LaTeX and PicTeX progs. Check some ftp server.

>and manipulating Feynmann
>diagrams?

How ? :-) 
If mathematically, there are packages in Computer Algebra languages
(at least in REDUCE) which provide some math'l manipulation/evaluation.

 Hartmut Frommert                 <phfrom@nyx.uni-konstanz.de>
 Dept of Physics, Univ of Constance, P.O.Box 55 60, D-W-7750 Konstanz, Germany
                                           -- Eat whale killers, not whales --
Newsgroups: sci.physics
Subject: Re: TIME HAS INERTIA
From: mcirvin@husc8.harvard.edu (Mcirvin)
Date: 26 Sep 92 16:16:48 GMT

rx1@athena.mit.edu (Stanley H Thompson) writes:

[about Alexander Abian's equation...]

>>	E(t) = m exp (-At)
>	I am only lowly undergraduate, but do the units of the above 
>equation even check?

Yeah, if you define c = 1 and use the right units for A.  The problem
is that he's given absoutely zero justification for writing down that
equation other than something about "time having inertia."  Proof isn't
absolutely necessary-- just SOME reason to think this might be true.
Otherwise, a reasonable response is Dale Bass's-- write down another,
equally unjustified equation and demonstrate that there's just as much
reason to believe that.  (Personally, I think the correct formula is 
E(t) = m exp (iAt).  These other ones are clearly the result of Real
Number Chauvinism.)

-- 
Matt McIrvin, posting nonsense again 
Newsgroups: sci.physics,sci.astro,sci.math,sci.philosophy.tech
From: kim@Lise.Unit.NO (Kim Gunnar St|vring \yhus)
Subject: Re: STRUCTURE OF TIME
Organization: Norwegian Institute of Technology
Date: Mon, 28 Sep 92 12:45:38 GMT

In article <1992Sep28.091054.1@tnclus.tele.nokia.fi>, hporopudas@tnclus.tele.nokia.fi writes:
 > 
 > In article <1992Sep24.102014.1@tnclus.tele.nokia.fi>,
 > hporopudas@tnclus.tele.nokia.fi writes:

 >      "I think that atheistic scientists are fully reponsible for ordinary
 >    peoples sufferings in all over the world, when they have instructed them
 >    to reject God's good doctirine given in The Holy Bible. This doctrine
 >    teaches ordinary people to respect good. Now this kind of respection
 >    does not exist and good peoples who respect good are considered to be mads.
 >    You all "wise scientists" should know that this means only one thing,
 >    namely that all kind of evil will be in full power in all around the world."

So the scientists are responsible for the suffering of all the people who
got vaccinated against rabies and other deaseases, the suffering of the
people not starving because of better crops and fertilizers, the suffering
of the people successfuly operated or medicated, the suffering av women
who don't have to do grueling house-work because of machines, the suffering
of people warm by electricity and fuel, the suffering of learning how the
universe work, and so on.

And as for the 'good' doctrine of God: Have you forgotten that people like
you used to BURN people like me, just for telling truth? The doctrine of
the Bible is being used to kill and exploit indians, oppress women,
overpopulate the world, condemn homosexuals, making disablement of people
just punishment, and learning children lies, for example,
all in the name of God.

No, it's not us atheistic scientists who are evil. We just try to find truth.
You, however, who think you are good, but actually hurt people, are the
evil ones. I have met enough people of your kind to be very certain you 
are bad. It's sad how you'r selfish meme fool nice people into doing bad
while thinking good.

And you want us to be in the eternal flame.

Kim0

Post Scriptum: I know I'm gonna get flamed for this, but it felt nice to be
               totally honest for once.
From: peters@physics.ubc.ca (Dan Peters)
Newsgroups: sci.physics
Subject: Re: TIME TRAVEL 4
Date: 28 Sep 92 21:44:05 GMT
Organization: University of British Columbia, Vancouver, B.C., Canada

sarfatti@well.sf.ca.us (Jack Sarfatti) writes:

>THE TIME TRAVELLER'S HANDBOOK 4

>18.	Precognitive remote viewing in the military operations of
>the First Crusade : "he was called ... R. Salomon ha-
Zarfati (the Frenchman) by Jews outside of France ... p.33
^^^^^^^
any relation?


Drin
--
-----------------
Gutted - Flame NA
From: davids@spira.bri.hp.com (david sixsmith (contractor))
Date: Wed, 30 Sep 1992 07:32:55 GMT
Subject: Re: Questions of transparency
Organization: Hewlett-Packard Laboratories, Bristol, England
Newsgroups: sci.physics
X-Newsreader: TIN [version 1.1.1 PL6]

Johan Wevers (johan@blade.stack.urc.tue.nl) wrote:
: davids@spira.bri.hp.com (david sixsmith (contractor)) writes:
: 
: >1. What is (are) the inherent qualitie(s) of a substance, such as glass,
: >perspex, diamond, & water, which make it transparent ?
: 
: The differential equation for an EM wave traveling in matter is given by
: (For E only, a similiar equation holds for B):
: 
: \nabla^2 E = \ddot{E}/c^2 + \mu\dot{E}/\rho.
: 
: were \mu is the permeability and \rho the resistance per unit of length.
: This equation has plane wave solutions:
: 
: E=E_0 exp(-\alpha x) cos(kx-\omega t)
: 
: here, k=\alpha=\sqrt{\mu\omega/2\rho}. So, if \alpha is small, the wave
: can penetrate deeply wthout much absorption. This happens if \rho is large
: (bad conductor, like glass and perspex, and/or \mu is small (usually approx 
: \mu_r:=4\pi 10^{-7} H/m for this kind of materials).
: 
: >2. What is the mechanism which makes the speed of light lower when travelling
: >in such a medium as opposed to traveling in a vacuum ?
: 
: The interaction between the photons and the atoms in the medium.
: 

Thanks for your response.

I also had some response on e-mail. In fact (some what worryingly) with the
above equations there seem to be 2 rather different ideas (which may be
related);

	1. The equations above.
	2. The idea that transparent materials have gaps in their absorbtion
	   spectra which makes them unable to absorb photons in particular
	   frequency bands.

The second idea I find more convincing. Firstly because it gives me some
feeling for the mechanism involved (rather the just plugging numbers into an
equation), but also because (it seems to me) it answers the two rather puzzling
features of transparency - that materials seems to be either very transparent
or very opaque - and secondly that so few materials are transparent.

The proof of the pudding would be to predict transparency in a material. Does
anyone know if this has been done ?

It seems remarkable that we have here a day-to-day phenomenon which needs
some understanding of QM to give a explanation. Does anyone know what the
classical explanation was; after all questions of lenses etc were well
understood by Newton - did noone have any idea why glass was transparent.

Incidentally - is transparency a proof of the relative smallness of the
nucleous ? Presumably photons will react in a head on collision with a
nucleous, and so if the nucleous was large compared to the atom, transparency
would never occur ? (Is this analysis correct ?)


On the second question answers seem to be shorter, but still varied. Anyone
prepared to be a bit more verbose than the above ? 

------------------------------------------------------------------------------
| Dave Sixsmith                     |  Disclaim, disclaim, disclaim, etc.    |
| Bristol, England                  |                                        |
------------------------------------------------------------------------------
From: elete@vaxc.cc.monash.edu.au
Newsgroups: sci.physics
Subject: REQ: transmission factor calculations
Date: 29 Sep 92 12:26:49 +1000
Organization: Computer Centre, Monash University, Australia

g'day,

i'm having trouble working out the transmission factors (or absorption or 
attenuation) for a rectangular crystal of length 4 cm, width 2.6 cm and 
thickness 1 cm, exposed to a neutron beam with incidence angles varying
from 0 to 100 degrees.

i have worked out the transmission eqaution for an infinite slab but with this
there is the problem of the transmission going to infinity when the incident
angle approaches 90 degrees.

i would appreciate any help from anyone out there who has worked out
transmission factors for a FINITE slab.
thanks in advance,

tunay

Newsgroups: sci.physics
From: matmcinn@nuscc.nus.sg (Mcinnes B T (Dr))
Subject: Re: BAEZZIAN physics and astronomy [was: Space-time IS a semi-Riemannian manifold (?)
Organization: National University of Singapore
Date: Mon, 5 Oct 1992 09:12:34 GMT

jbaez@riesz.mit.edu (John C. Baez) writes:
: 
: I am awed by your certainty.  Many of the best researchers in quantum
: gravity would dearly like to know whether spacetime is a
: semi-riemannian manifold.  What info do you have that they don't? 
: Barring seances with Einstein's ghost, I would prefer to say
: "spacetime is well modelled by a semi-riemannian manifold on
: sufficiently large distance scales."  

Two points. First, nobody in that discussion mentioned quantum effects.
So naturally what I meant was that CLASSICAL spacetime IS a
semi-riemannian manifold. The kind of thing I am criticising is the
speculation that big-bang type singularities are meaningless because no
clock could endure arbitrarily large tides. To that I reply that
CLASSICALLY time is well defined mathematically [as the length of a
timelike worldline] and that I am not interested in clocks. In short, I
was repudiating operationalism, not quantum gravity!
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? : 
: On the other hand, I agree that the idea of time being "defined" by
: clocks is essentially a cop-out unless one has a good theory of what
: counts as a clock and why cesium clocks are regarded as "better"
: clocks than baloney sandwiches.  (In other words, although I am of an
: operationalist bent, I don't think one can weasel out of the issue of
: time simply by defining time to be that which is measured by that
: which we build to measure time.)
: 
: As for whether time "exists," until someone lays out their precise
: definition of "exists" I will use my everyday sloppy one, according to
: which time, numbers, baloney sandwiches and societies all exist, even
: though they are very different sorts of things.   
: 
Sorry about the title, I am just learning how to play with this thing.: 
Newsgroups: sci.physics