HDTenEightyP/NetNews huggingface dataset:
From: scip1061@nuscc.nus.sg (Marc Paul Jozef)
Subject: Re: Local expansion
Organization: National University of Singapore
Date: Wed, 30 Sep 1992 14:16:29 GMT

About pg 739 of MTW (a discrete grid-universe)...

I admit I fail to see why the `geometry in a cell'
(around each grid-point) must be Schwarzschild,
because of some succesfull approximation in solid-
state (!) physics. Each cell completely isolated from
the influence of the other grid-points or what?

I would love to see a rigorous proof of the assertion
that the Schwarzschild-cell-geometries `match up smoothly'
at the boundaries between cells (that would mean a
beautiful new solution of Einstein's equations; so
nice of MTW to leave that discovery to the eager reader).
But most of all, I would like to see some serious definitions
instead of that sloppy picture.

Just to show where sloppiness can lead to, consider
the grid in a compact hyperbolic universe (angle-deficit
for the sum of observed angles in a triangle consisting
of 3 grid-points, instead of angle-excess, as automatically
assumed by MTW). Follow MTW's argument once more, and
come out with the conclusion that a hyperbolic universe
eventually recontracts.

Now how is that for an `agreement to 4% or better' with
the standard perfect-fluid model?

I repeat my claim (of the former thread `Hubble-constant')
that there is no proof whatsoever that a discrete grid-
universe behaves the same as a perfect fluid universe
with the same mean density.

marc van loo.
From: bhoughto@sedona.intel.com (Blair P. Houghton)
Subject: Re: TIME HAS INERTIA
Organization: Intel Corp., Chandler, Arizona
Date: Sun, 27 Sep 1992 20:07:04 GMT

In article <5648@tuegate.tue.nl> johan@blade.stack.urc.tue.nl (Johan Wevers) writes:
>abian@iastate.edu (Alexander Abian) writes:
>>         TIME HAS INERTIA AND SOME ENERGY IS IRRETRIEVABLY DISSIPATED
>>                          ON MOVING TIME FORWARD
>I'd say, time is a coordinate, just as space. Why doesn't space have
>inertia?

I'd say time is a dimension, just like distance, color, and
understanding; why doesn't space have any common sense?

				--Blair
				  "If only I had an Adamsian Thumb..."
From: choy@skorpio.usask.ca (I am a terminator.)
Newsgroups: sci.physics
Subject: How do you draw a straight line?
Date: 2 Oct 92 22:42:20 GMT
Organization: University of Saskatchewan, Saskatoon, Canada

How do you know that the line you draw is really straight? What
defines straightness? If you look down the line and you don't
see wobbling, is it straight? Can you transfer that line to
a piece of metal, cut it out and use that metal as a
straightedge for drawings? More fundamentally, how do we come
to trust our empirical work? When a really complicated gadget
like a particle accelerator is running, how much error is
there?

Henry Choy
choy@cs.usask.ca
From: johno@sdd.hp.com (John Ongtooguk)
Newsgroups: sci.physics
Subject: Re: How do you draw a straight line?
Date: 6 Oct 1992 19:47:55 GMT
Organization: Hewlett-Packard, San Diego Division
Distribution: world
NNTP-Posting-Host: hpsdlg10.sdd.hp.com

In article <Bvpr2n.F9@news.larc.nasa.gov>, mark@uab15.larc.nasa.gov (Mark Flanagan) writes:
|> In article <1asiu6INNf5k@agate.berkeley.edu> aephraim@physics.Berkeley.EDU (Aephraim M. Steinberg) writes:
|> 
|> [taut string for a straight line...]
|> 
|> >if the string has any mass and is in any gravitational field
|> >whatever, then any finite tension will still leave it a catenary, just
|> >a straighter and straighter one.  I believe the question was one of
|> >principle.
|> >
|> How about making the string parallel to the local gravitational gradient?

   Would it eliminate the tendency of the string to resonate ? It
   probably wouldn't be any better than filling a long tray with water,
   floating a pen holder in it, and drawing the line by drawing the
   'boat'. One could also drop ink from a stationary container in a
   still cave onto an inclined plane, and lower the plane to generate
   the line, but even with two nice pivot points at the base of the
   plane the rope used to lower the plane would suffer from the same
   problem. If one were to float the plane in a long tray and draw
   it against a pen....or set the plane in a tray of water and 
   carefully place some dye in the water....or roll an inked ball
   down an inclined plane....I guess that's why a taut string is 
   traditionally used. 

   John Ongtooguk (johno@sdd.hp.com)
From: firth@sei.cmu.edu (Robert Firth)
Newsgroups: sci.physics
Subject: Re: How do you draw a straight line?
Date: 6 Oct 92 11:56:19 GMT
Organization: Software Engineering Institute

In article <1aqd0hINNsm1@hpsdlss3.sdd.hp.com> johno@sdd.hp.com (John Ongtooguk) writes:

>   I seem to recall that the Mormans used long trays of water when
>   laying out the pitch of their irrigation systems and that it was
>   remarkably accurate over a long distance.

Yup.  So did the Romans and Egyptians, and probably many more civilisations.
This method has the advantage of working, since it recognises that the
Earth is round and you want to survey a great circle, not a straight line.
Over the length of an aqueduct, that matters!
Newsgroups: sci.physics
From: sarfatti@well.sf.ca.us (Jack Sarfatti)
Subject: quantum computers 1
Organization: Whole Earth 'Lectronic Link
Date: Fri, 2 Oct 1992 07:13:08 GMT


Charles H. Bennett of IBM in 1981 wrote: "Computers may be thought of as
engines for transforming free energy into waste heat and mathematical
work... the essential irreversible step, which prevents the [Maxwell] demon
from breaking the second law [of thermodynamics], is not the making of a
measurement (which in principle can be done reversibly) but rather the
logically irreversible act of erasing the record of one measurement to make
room for the next. ... a tape full of zeros, or ones containing some
pseudorandom sequence such as pi, has fuel value and can be made to do
useful thermodynamic work as it randomizes itself. A tape containing an
alogorithmically random sequence lacks this ability."

A quantum computer acting between a hot negative temperature and a cold
positive temperature has no waste heat.  Experiments must be done to see if
strings of individual quantum events (e.g., detections of polarizations of
a sequence of photons - one at a time in the system - is really random or
pseudorandom with nonlocal hidden variables giving them "fuel value" - that
would, it seems, be sufficient for faster-than-light communication though
not necessary.
Newsgroups: sci.physics
From: bhv@areaplg2.corp.mot.com (Bronis Vidugiris)
Subject: Re: Defining local, causal etc., was: Hidden variable theories
Organization: Motorola, CCR&D, CORP, Schaumburg, IL
Date: Tue, 6 Oct 1992 22:04:20 GMT

In article <1992Oct2.191819.29150@newshost.lanl.gov> jlg@cochiti.lanl.gov (Jim Giles) writes:
)In article <1992Oct1.224027.8421@lmpsbbs.comm.mot.com>, bhv@areaplg2.corp.mot.com (Bronis Vidugiris) writes:
)|> [...]
)|> Anyway, if you set up an experiment with a pair of photons in the 'singlet'
)|> state (i.e. opposite spins) and measure the spin of  both photons along
)|> an arbitrary axis with an angle from the vertical of theta1 (for detector1)
)|> and theta2 (for detector2)
)|> 
)|> detector 1     <======     source           =======>    detector 2
)|> 
)|> 
)|> you get the following result from QM
)|> 
)|> p(theta1,theta2) = p1(delta) = cos^2(theta2-theta1)
)
)This is actually:
)
)   p(theta1,theta2) = p1(delta) = cos^2(theta2-theta1)/2
)                                                      ^^
)
)Otherwise, just by lining up the two detectors, *all* the photons
)must start being detected!  And we know that each observer actually
)only sees *half* the photons on average.

Nope.  Two photons are generated per event.  Cascade photons are but one
example of a process that generates two photons with opposite spins
heading in opposite directions - *pairs* of photons in the 'singlet state' -
which is the idea behind this experiment.

I *was* assuming 100% detector efficiencies - if you want the really rigorous
analysis which includes detector efficiences and suchlike,  you'll have to
track downthe paper by Clauser et al that I referenced (the one that has
escaped my filling system).

)Note also that the above predicts a probability *distribution*.  It
)does not predict specific events.  There is no reason to expect that
)the photons are each - individually - reifications of the function
)at all.

Yeah, we've been going around on that one for a while.  So that's why
I started talking about things that can be measured.  Probability
distributions can be measured.  You just have to repeat the experiment
several times.

)|> Anyway, there *is* a way to distinguish between the two condtions I
)|> was describing.  Local Realistic theories predict that you will have a
)|> constraint on p1(delta).  A simple 'speed-of-light-collapse' theory predicts
)|> that p1(delta) *will* change its value when the spins are measured in a
)|> 'timelike' manner (i.e within a lightcone) vs a 'spacelike' manner.
)
)This is like being able to distinguish between "leprechauns 
)have red  hair" and "leprechauns have green hair" without first 
)demonstrating that leprechauns exist at all!

p1(delta) is measureable, so it's not (IMO) a leperchaun or like a
leperchaun.
Xref: sparky sci.physics:15962 sci.astro:10429 sci.math:12735 sci.philosophy.tech:3556
From: newberry@kepler.as.arizona.edu (Mike Newberry)
Newsgroups: sci.physics,sci.astro,sci.math,sci.philosophy.tech
Subject: Re: Hannu is a wood-duck
Date: 5 Oct 92 22:41:51 GMT
Organization: University of Arizona, Tucson, AZ

In article <1992Oct5.120355.18354@aoa.aoa.utc.com> carl@aoa.aoa.utc.com (Carl Witthoft) writes:
>In article <1992Oct1.172815.1@tnclus.tele.nokia.fi> hporopudas@tnclus.tele.nokia.fi writes:
>> I ment by these sufferings that when man is unhappy he suffers mentally.
>x
>Fine. but that has nothing whatsoever to do with scientists
>or the alleged existence of god.  
>In any case, would people please edit the followup-to line?
>
>
>-- 
>Carl Witthoft @ Adaptive Optics Associates
>aoa!carl@bbn.com  carl@aoa.utc.com
>54 CambridgePark Drive, Cambridge,MA 02140 617-864-0201
>"My Karma just ran over my Dogma!"

*******************************************************

OK, what does this thread have to do with ASTRONOMY ???

*******************************************************
From: jbaez@riesz.mit.edu (John C. Baez)
Subject: Re: How old is the universe?
Organization: MIT Department of Mathematics, Cambridge, MA
Date: Mon, 28 Sep 92 20:49:58 GMT

In article <1a3j6vINNsh9@agate.berkeley.edu> ted@physics.Berkeley.EDU (Emory F. Bunn) writes:
>In article <17584@ucdavis.ucdavis.edu> carlip@landau.ucdavis.edu (Steve Carlip) writes:
>>In article <19tid9INNo1h@agate.berkeley.edu> ted@physics.Berkeley.EDU (Emory F. Bunn) writes:
>>>[much deleted...]
>[more deleted...]
>>> What bothers me about
>>>this is that there is no natural measure one can impose on the set
>>>of possible initial conditions for Universes in order to make that
>>>statement meaningful.
>>>[...]
>[more deleted...]
>>
>>If I understand you correctly, you are claiming that there is no
>>possible measure on the space of three-geometries (or maybe
>>three-geometries plus initial configurations of matter fields).
>>This seems unlikely to me; do you have a proof or a reference?
>>Would you argue that a path integral is impossible in principle
>>in general relativity, for instance?

>I was making the assertion you attribute to me, and I made it with
>more confidence than I probably should have.  I believe, based on my
>admittedly limited understanding of measure theory, that the space
>of 3-geometries is simply "too big" to admit a well-behaved measure
>that would allow one to talk about probabilites.  (I have formed
>some vague arguments in my mind in support of this position,
>but they're far from being rigorous enough to convince anyone else.)

>I hope that I am wrong about this, as I think it would be very nice 
>to have such a measure.  Is there anyone out there who can be more 
>definitive about this than I can?

There is certainly nothing definitive known about this question.
It's best to begin by pondering the situation with field theories
that are a lot better understood than quantum gravity.
Honest-to-goodness measures on some space of Euclidean field 
configurations have only been constructed in 2 or 3 spacetime
dimensions.  I hear that Balaban, a student of Jaffe, claims to have
done it for 4d Yang-Mills theory, but that the proof was so long
he isn't going to bother publishing it (in a curious twist on 
Fermat's last theorem).  

Of course, people can calculate perturbatively in ordinary QFT
quite well as if these measures really existed.

On the other hand, every set has lots of measures on it, and being
"big" is no obstacle.  What we want in physics is measures satisfying
certain properties, and one can only discuss whether they exist or
not after we have some idea of what properties we want.  That's
what happened in ordinary QFT: the Osterwalder-Schroeder axioms
state what your measure should satisfy, and people work on
constructing measures that satisfy those axioms.  In quantum gravity
I doubt it is even known what the "axioms" should be.

By the way, don't you want a measure on 4-geometries, rather than
3-geometries, if you're doing path integration... and you live in
3+1 dimensions (unlike Steve :-)).
From: hporopudas@tnclus.tele.nokia.fi
Subject: Re: Lawsonian Elves Growing Space Potatos
Organization: Nokia Telecommunications.
Date: Sun, 4 Oct 1992 10:19:15 GMT


In article <1992Oct2.190359.18885@mnemosyne.cs.du.edu>,
ddixon@nyx.cs.du.edu (David Dixon) writes:
> Just a brief diatribe.
>

  ...deleted stuff...
>
> Thank you for your support.
>
> 					Dave
>
> DIXON@UCRPH0.UCR.EDU

 I don't like at all this kind of stupid 'net-psychologist'. Try to
 concentrate instead to matter proposed (not to persons).

 ---Hannu

 "Thrown to ignorance men give themselves to work and employment and by
  keeping themselves sensible and learned they stagger without goal like
  blinds lead by blinds."

           (Indian wisdom, from Kat'ha upanisad)
From: ap1i+@andrew.cmu.edu (Andrew C. Plotkin)
Newsgroups: sci.physics
Subject: Re: Make time stop?
Date: 30 Sep 92 09:47:53 GMT
Article-I.D.: andrew.MemSV9W00gpIAzckgm
	<1992Sep30.024508.15587@nuscc.nus.sg>
Organization: School of Computer Science, Carnegie Mellon, Pittsburgh, PA

tolman%mindblow.cs.utah.edu@cs.utah.edu (Kenneth Tolman) writes:
:   A frame of reference moving very very fast has a time dilation, correct?
: (That is, if we are still and looking at someone moving they are "slow")
: When we look out into the universe- all galaxies are moving away from us,
: and the very far away galaxies are moving near the speed of light.
: 
: Therefore, THEIR TIME HAS BARELY BEGUN.  Their civilization's have not 
: started, and they live in a "young" universe.  Thus, if we could travel
: faster than light, we could jump backwards and live this whole universe
: through once again.  Of course, the converse is true just as well from
: their perspective.  Is this analysis somewhat correct?
: 

Excerpts from netnews.sci.physics: 30-Sep-92 Re: Make time stop? Mcinnes
B T @nuscc.nus.s (731)

> 				No.

Oh, be a little nice. IF you assume FTL travel, it *is* true; SR says
that FTL is equivalent to time travel, for just about this reason. 

To be accurate, SR says that a pair of events separated by a spacelike
interval in one reference frame will have an undefined ordering; which
comes "first" will depend on your reference frame. Thus, anything that
looks like FTL (jumping from the first event to the second) will look
like time travel from another reference frame. 

Andromeda is moving away from us; assume that space-time is flat, and it
passed us a billion years ago (by our clocks.) If you consider an event
whose position is there and whose time is "now" (using our local
definition of "now" and the coordinate system of our ref. frame), that
event will be in the past (in the sense that that event will have
experienced less than a billion years, Andromeda time, since the
galaxies passed.)

Of course, this all shows the meaninglessness of "now" more than
anything else, but it does demonstrate all the problems that Star Trek
blithely warps over. :-)

--Z

"And Aholibamah bare Jeush, and Jaalam, and Korah: these were the borogoves..."
From: srctran@world.std.com (Gregory Aharonian)
Newsgroups: sci.physics,sci.logic
Subject: Anyone have an axiomization of electromagnetism?
Date: 6 Oct 92 12:39:11 GMT
Article-I.D.: world.Bvp9tC.Itv
Organization: The World Public Access UNIX, Brookline, MA


     Does anyone know of any articles that explore the issue of providing
a predicate logic axiomization of electromagnetism, or any similar simple
aspect of non-relativistic physics?
     Any email responses to    srctran@world.std.com    will be appreciated.

Thanks,

Greg Aharonian
Source Translation & Optimization
srctran@world.std.com
-- 
**************************************************************************
Greg Aharonian
Source Translation & Optimiztion
P.O. Box 404, Belmont, MA 02178
Xref: sparky sci.physics:15948 sci.chem:3824
From: rl@socrates.ucsf.edu (Robert Langridge)
Newsgroups: sci.physics,sci.chem
Subject: Re: Rosalind Franklin (was: Meitner and Hahn)
Date: 5 Oct 92 21:36:45 GMT
Organization: UCSF Computer Graphics Lab

aw3@ukc.ac.uk (A.Wilson) writes:

>In article <rl.717712058@cgl.ucsf.edu> rl@socrates.ucsf.edu (Robert Langridge) writes:
>>jac@ds8.scri.fsu.edu (Jim Carr) writes:
>>[...discussion of Hahn/Meitner...]
>>>
>>>Not nearly as clear-cut a case as in the DNA story, where Rosalind (?) 
>>>Franklin actually made the measurements and the correct interpretation 
>>>of the measurements.  The excuse there is that she had died by the 
>>>time the award was made, and was thus not eligible, but begs the 
>>>question of why others who did not make the real discovery were 
>>>considered eligible! 
>>>[Carr]

>>There is certainly a case to be made that Franklin, if she had lived,
>>should have shared the Nobel Prize with Crick, Watson and Wilkins.
>>This would have given the Nobel Committee serious problems since the 
>>award is restricted to no more than three individuals.  As jac says,
>>no award is made posthumously, but to say that the three who got the
>>award did not make the real discovery is utter nonsense.  As in much of
>>science, no one person deserves the credit.
>>[Langridge]

>Can I add my 2p worth, before this thread takes off? This subject was
>discussed some six months ago in sci.chem - perhaps some kind individual
>who kept all the posts can summarise (I read a few, then headed for the
>KILL file......)
>[Wilson]

I e-mailed Wilson a while ago to ask if he had a pointer to an archive of 
the discussion in sci.chem but have not heard from him.  If anyone has this 
I would appreciate receiving it by e-mail.

This brings up again the issue of when, and if, one should post comments,
particularly on a subject which is as misrepresented as the DNA structure 
discovery was here.  It is of little help to respond as Wilson did if the 
previous discussion is no longer available.  Many of us can read net.news 
of various flavo(u)rs only irregularly, and the chances of missing exchanges 
on any given sci.* are high.

-rl
Newsgroups: sci.physics
From: ramsay@unixg.ubc.ca (Keith Ramsay)
Subject: Re: Simple observation about Quantum Kitty Cats
Organization: University of British Columbia, Vancouver, B.C., Canada
Date: Sat, 3 Oct 1992 01:23:08 GMT

In article <303@mtnmath.UUCP> paul@mtnmath.UUCP (Paul Budnik) writes:
>In QM there is a disconnect between the theory, which talks only about
>probabilities, and experimental observations. It is this disconnect
>that is the source of the problems of interpretation. One literally
>does not know what one is talking about when one starts discussing
>inherently random processes, as opposed to statistical models that result
>from incomplete knowledge or an incomplete model.

I'm afraid that all I can get out of these comments (and the ones
which followed) is that you, seemingly, agree with Einstein that "God
does not play dice with the universe". 

But what if the universe just *has* randomly behaving components,
anyway, in spite of your wanting a theory which is deterministically
linked to observations? What if it there simply is no correct
deterministic theory? Then asking for a probabilistic theory to be
"formalized" so as to take the form of a deterministic theory is
not necessary.

Keith Ramsay
ramsay@unixg.ubc.ca
Newsgroups: sci.physics
From: jbaez@riesz.mit.edu (John C. Baez)
Subject: Re: TIME TRAVEL 4
Organization: MIT Department of Mathematics, Cambridge, MA
Date: Tue, 29 Sep 92 01:44:46 GMT

In article <peters.717716645@physics.ubc.ca> peters@physics.ubc.ca (Dan Peters) writes:
>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?

No, it's clearly THE SAME SARFATTI having used his faster-than-light
communication system to beam himself back to the Crusades.  This PROVES
that it works!
Newsgroups: sci.physics
From: pratt@Sunburn.Stanford.EDU (Vaughan R. Pratt)
Subject: Re: Computability of the universe
Organization: Computer Science Department,  Stanford University.
Date: Sat, 26 Sep 1992 22:09:18 GMT

In article <Bv53wy.L9r@news.cso.uiuc.edu> jjt@uihepa.hep.uiuc.edu writes:
>In article <1992Sep25.065628.25017@CSD-NewsHost.Stanford.EDU>, pratt@Sunburn.Stanford.EDU (Vaughan R. Pratt) writes:
>
>   (...stuff deleted for brevity...)
>
>> We constructed several hypotheses about what the coefficients of a
>> formula might be, and tested them against the data to get some idea of
>> the robustness of the different formulae being used to model the
>> sequence.
>
>This sounds to me like the caterpillar in "Alice in Wonderland."  Webster
>notwithstanding, in scientific research "experiment" implies observation of 
>the external world, not computation of the results of a mathematical model.  
>
>Suppose you are trying to determine the roots of x**2 +x -2 , and  you use
>an approximation method to determine that one root is about 0.997. Is that
>an experimentally determined quantity?  Not in the scientific sense.

By this argument Mandelbrot's preliminary exploration of the shape of
the Mandelbrot set could not be considered "experimental."  Sounds like
you've defined "experiment" so as to rule out altogether the
possibility of experimental math.

I can think of one reason you might want to do so, namely because it is
"clear" that physics and math are about different worlds, natural and
Platonic.  But that would mean that your argument, that math and
physics are as different as you say, is circular, mediated by what you
and not the dictionary believe a word *should* mean, with your belief
in turn based on a premise you are now trying to prove.

Does the term "experimental math" create any problem for you besides
conflict with an old prejudice about the meaning of "experiment" that
has now been outdated by the advent of the computer?

Neither mathematics nor physics will ever be fully understood, and for
the same reason: they are both too complicated.  Moreover the
complexity has the same basic roots:  in mathematics there are too many
things that can happen when theorems interact, and dually when
structures interact, for us ever to know them all.   Likewise in
physics when particles interact, and dually when waves interact, the
full consequences are unknowable.  Anyone who doubts either of these is
seriously confused about that subject.

It follows that we should respect both the theoreticians and the
experimentalists in both subjects.  Backing one kind to the exclusion
of the other would greatly impede the progress of science.

-- 
=================================================== In short, I am floundering
Vaughan Pratt   pratt@cs.Stanford.EDU  415-494-2545 around and don't take what
=================================================== I say seriously.