HDTenEightyP/NetNews huggingface dataset:
From: jbaez@riesz.mit.edu (John C. Baez)
Subject: Re: Computability of the universe
Organization: MIT Department of Mathematics, Cambridge, MA
Date: Sun, 13 Sep 92 02:23:28 GMT

paul@mtnmath.UUCP (Paul Budnik) writes:
>In article <1992Sep11.222036.7483@galois.mit.edu>, jbaez@riesz.mit.edu (John C. Baez) writes:

>> ...  Note that the recursivity of the time evolution of the
>> wavefunction does NOT contradict the fact that quantum mechanical
>> observations can be random, hence not computable. ...

>They can be random, but no one knows if they are. That this
>would make them not computable is all the more reason to doubt
>that they are random.

Point taken.  As a mathematical physicist I tend to speak about
theories rather than experiments, so in the above I meant "according
to the standard theory of quantum mechanics."  I leave this out
sometimes since it gets boring to put it in all the time, but this
gets me in trouble on sci.physics occaisionally...

When I said "can be" random rather than "are", I was simply referring
to the fact that quantum mechanics can make *certain* predictions with
100% certainty.

Radioactive decay sure *seems* random - but what are the best
experiments that have been done to find patterns in the seeming
randomness?  As noted a while ago, if I start giving you a series of
bits it will be impossible for you to ever *prove* it is random, so
this is a tricky issue.  

To me, the beauty of quantum mechanics is such that I have no qualms
about its prediction of randomness, but I know some people besides
Paul who find the uncomputability a drawback.   To me, there is no
strong reason why a concept derived from studying what people can
repeatably compute by a systematic procedure should limit the behavior
of nature in this way.  I am quite happy with my results that nature's
behavior is predictable "on average" - expectation values being computable.



.
From: rl@socrates.ucsf.edu (Robert Langridge)
Newsgroups: sci.physics
Subject: Re: WHAT IS LIFE? A BOOK BY SCHRODINGER!!!
Date: 6 Sep 92 00:22:28 GMT
Organization: UCSF Computer Graphics Lab

christos@kuhub.cc.ukans.edu writes:
...
>	In that article there was a brief summary about the author(Schrodinger)
>and it mentioned that Schrodinger has written a book with a title: "What is
>Life?". 

>	I am very interested to find the publishing company of this book so
>that I can order it. Does anybody have any information about this book or any
>information how to get it? Maybe getting the address of Scientific American and
>asking them or a telephone number?

"What is Life" by Erwin Schrodinger was first published by Cambridge University
Press in 1944 and has gone through many printings and editions.  CUP has
recently (1992) reissued it again with another short lecture series (Mind 
and Matter) and some other material.  Your library should have one of the 
printings.

In the mid to late 1940s the book was very influential on, among others, 
Francis Crick, Maurice Wilkins and Seymour Benzer - all ex-physicists
who contributed mightily to the development of molecular biology.

It certainly influenced me when I left physics to work on DNA in the mid
1950s, partly because one of the great men of physics thought that biology
could be interesting to physicists, but more because Schrodinger hoped that 
new physics might come out of research on biological systems.  It hasn't, 
but one can hardly complain that the field has been boring...

Of course, Max Delbruck left physics for biology before Schrodinger gave his
lectures, and was in fact a major influence on Schrodinger's view of the
future of biology - though without his implication that new physics might
appear.

Today, the book should be used more for inspiration than for scientific 
illumination.   But well worth reading...

Robert Langridge			Phone: +1 415 476-2630, -1540, -5128
Computer Graphics Laboratory		               FAX: +1 415 476-0688 
926 Medical Sciences
University of California	                    E-Mail: rl@cgl.ucsf.edu
San Francisco  CA  94143-0446 
Newsgroups: sci.physics
From: attias@ghost.dsi.unimi.it (Isaac Asimov)
Subject: help in pool...PLEASE!!!
Organization: Computer Science Dep. - Milan University
Date: Tue, 15 Sep 1992 13:14:11 GMT


I've a question about pool.
Let'ssay we have two balls colliding.First ball(A) has an initial velocity [VA1x,VA1y],and the second (B)  has [VB1x,VB1y]. They hit with a difference between the two center coordinatess of [dx,dy], and they have same mass.
My problem isto find the two velocity vectors  after the collision.
Could someone help me? Iknow Ihave to preserve cynetic  energy & so on...but I'm not able to  obtain the final formulas.

Please help me !!!!!!

			    Roberto Attias,
			    email: attias@ghost.dsi.unimi.it
From: johan@blade.stack.urc.tue.nl (Johan Wevers)
Newsgroups: sci.physics
Subject: Re: Are redshifts discrete?
Date: 9 Sep 92 12:40:59 GMT

malova@venus.iteb.serpukhov.su writes:
>
>   Some years ago I read about discrete distribution of redshifts. 
>   What is now? Is the idea alive?

Redshift is continious: SRT tells you that the ratio of the observed
frequency f' and the original frquency f from an object that moves w.r.t.
the observer is given by:

f'/f = \gamma(1 - v cos(\phi)/c),

where \gamma = \sqrt{1-v^2/c^2} and \phi is the angle which the movement
makes with the line which connects the object and the observer. Because v
can change continiously, the redshift is continious.

Ofcourse, quantumgravity may change this view when we have discovered it.

******************************************************************** 
* 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\            *
********************************************************************
From: sichase@csa2.lbl.gov (SCOTT I CHASE)
Newsgroups: sci.physics
Subject: Re: quantization of angular momentum
Date: 8 Sep 92 18:34:52 GMT
Organization: Lawrence Berkeley Laboratory - Berkeley, CA, USA
Distribution: na
Reply-To: sichase@csa2.lbl.gov
NNTP-Posting-Host: 128.3.254.197
News-Software: VAX/VMS VNEWS 1.3-4   

In article <1992Sep7.215511.23280@CSD-NewsHost.Stanford.EDU>, pratt@Sunburn.Stanford.EDU (Vaughan R. Pratt) writes...
>In article <25949@dog.ee.lbl.gov> sichase@csa3.lbl.gov writes:
>>>>>Ouch!  L is quantized under all circumstances.  Its eigenvalues are
>>>>>half-integer multiples of hbar, even for free particles.
>>>Angular momentum, though, always has discrete eigenvalues.
>>
>>Angular momentum is not a good quantum number for a plane wave.
> 
>I don't agree.  Plane waves and the trajectory of the particle are

Although L is certainly quantized, even for a plane wave (I don't want to 
start *that* discussion again), a plane wave is not an L eigenstate.  That
means that plane wave states can not be characterized by angular momentum
and, by definition, L is not a good quantum number for a plane wave.

The classical analogy does not hold (the one about cutting the rope on 
a twirling stone) precisely because a plane wave is not localized like 
the stone is.  L becomes a well-defined observable for a classical object
because all classical objects are localized, unlike the plane wave.

- 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,sci.optics
Newsgroups: sci.physics
Subject: Re: Why do protons outnumber antiprotons?
From: mcirvin@husc8.harvard.edu (Mcirvin)
Date: 8 Sep 92 23:46:00 GMT
 <25950@dog.ee.lbl.gov> <3SEP199220131399@zeus.tamu.edu> 
 <26086@dog.ee.lbl.gov> <4SEP199219360305@zeus.tamu.edu> <1992Sep8.225821.12113@sfu.ca>

palmer@sfu.ca (Leigh Palmer) writes:

>I wish to observe that this discussion quickly abandoned the question so
>clearly stated in its title. It seems to me that result is commoner than usual
>in response to this particular question. Could it be that ignorance on this
>subject is as profound as I have always suspected it is?

I think Scott Chase's summary and the corrections thereto pretty much
summed up the knowledge/ignorance of humanity on the subject.  Either
it's the result of weird initial conditions, or it might be the result
of Sakharov's conditions being met, with baryon number nonconservation
coming either from GUT couplings or from the anomalous term in the
electroweak lagrangian.  As to which (if any) alternative to pick, 
ignorance is indeed profound, but there at least exist possibilities
that aren't radically at variance with known physics.

This being stated, the thread digressed massively into the virtues of
hole theory.

-- 
Matt McIrvin, Cambridge, Massachusetts, USA 
Newsgroups: sci.physics
From: gjm11@cus.cam.ac.uk (G.J. McCaughan)
Newsgroups: sci.physics,sci.astro,sci.math,sci.philosophy.tech
Subject: Re: How old is the universe?
Date: 15 Sep 92 23:29:05 GMT
Organization: U of Cambridge, England

In article <1992Sep15.172105.1@tnclus.tele.nokia.fi>, hporopudas@tnclus.tele.nokia.fi writes:

>   Could any one of you check reasonableness of the following figures
>   by computer calculations:
>
>        [stuff about space potatoes, magic particles with negative mass,
>        radiation peripheries, quantization of time, and mysterious
>        properties of diamond]

Aaarrrggghhh!!!

> 
>   Reference for this text and these figures is my article "Structure of Time",
>   which was not accepted to publication by Physical Review newspaper.

I must admit I'm not surprised; it doesn't seem to make any sense. Can you give
some evidence for your theory, and some predictions from it that would enable it
to be tested?

Incidentally, regardless of the correctness of the theory, surely an unpublished
article is no use at all as a *reference*?

-- 
Gareth McCaughan     Dept. of Pure Mathematics & Mathematical Statistics,
gjm11@cus.cam.ac.uk  Cambridge University, England.    [Research student]
From: sichase@csa2.lbl.gov (SCOTT I CHASE)
Newsgroups: sci.physics
Subject: Re: BAROMETERS (was Re: Subject?)
Date: 10 Sep 92 04:49:29 GMT
Organization: Lawrence Berkeley Laboratory - Berkeley, CA, USA
Distribution: na
Reply-To: sichase@csa2.lbl.gov
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In article <1992Sep10.031106.3196@galileo.cc.rochester.edu>, mcia@uhura.cc.rochester.edu (Mike Ciaraldi) writes...

>Actually, you can use the pendulum method without a ruler
>if you have a long enough rope.  Lower the barometer out the
>window until it just clears the ground.  Set it swinging and
>measure the period of oscillation.  You can derive the length of the rope
>from the period.

If the building is tall enough, you are going to need an awfully long and
heavy rope.  This method probably won't work without a scale to weigh the
rope and a more sophisticated formula than sqrt(L/M).

-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: Quantitized Length
Organization: MIT Department of Mathematics, Cambridge, MA
Date: Mon, 7 Sep 92 03:44:33 GMT

While there seem to be plenty of upsetting things that occur in physics
if one assumes that arbitrarily small lengths make sense, it is
important to emphasize that no experiments so far have found anything
like a smallest length.  So the real answer to the question of
quantization of lengths is simply that nobody knows!  I am not trying
to dodge the question - it's important to realize that there are lots
of very good questions that we don't know the answers to.  

I'll email you some stuff I recently posted on length scales in
physics.  In particular, a lot of people think that something weird
happens to space around the "Planck length" - about 10^{-35} meters. 
But again, there is no consensus on WHAT if anything happens.  

The most naive way to obtain a smallest length scale, which goes back
at least to the medieval Arabs (who loved geometric designs) is to
assume that space is a lattice, that is, something like a
checkerboard, on which particles can only move in discrete steps. 
This idea is currently popular among fans of cellular automata, which
are computers (or programs) that simulate worlds in which space is
like this and time also occurs in discrete steps.  The problem with
such theories, apart from the fact that there's no evidence for them,
is that they have less symmetry than our world appears to have - we
don't SEE any preferred "grid" in space, so it is rather upsetting to
most physicists to assume there is one.  Computer scientists, however,
who play with discrete stuff all day and get brainwashed :-), are
often fond of this approach.  The guru of this approach is Ed Fredkin,
a millionaire who is a professor at Boston University but spends much
of his time on an island in the Pacific which he owns.  I kid you not. 
I've met him and argued with him about this topic, but I didn't bother
arguing very hard because I knew it was hopeless, having read an
interview with him in the book "Three Scientists and Their Gods".  He
is passionately convinced that the world is a cellular automaton.  His
disciples, if I may put it that way, include Tom Toffoli and Norm
Margolis at MIT, who just finished building CAM 8, a special-purpose
cellular automaton machine.   This can simulate 3-dimensional cellular
automata and there is a demo I am dying to see which requires one to
wear 3d glasses.  I have spent many happy hours watching cellular
automata on a big-screen TV, run on a CAM 6.  They are mind-blowingly
beautiful and I recommend it to anyone who gets a chance.  But I don't
think the world works that way.  Only time will tell.




From: flower@hpcc01.corp.hp.com (Graham Flower)
Date: Fri, 11 Sep 1992 16:27:31 GMT
Subject: Re: Where do physics graduates look for work?
Organization: the HP Corporate notes server
Newsgroups: sci.physics


>blues).  In any case, we were happy to make lots of money in the markets,
>selling each other the product of other nations, while we merged, disolved,
>and sold our industry to other countries, and spent precious little on real
>R&D (less and less as time went on).  We seem to feel we cannot make money
>trying to compete with the Japanese or the Germans or the <your favorite
>foreign competitor here>.  But we don't have to feel bad about it, its the
>feel-good generation; lets just put more debt on our credit cards...  In
>the meantime, university funding is cut; the number of students entering
>universities is declining.  

  R&D spending has been in decline as a pct of GNP since 1965. These trends have
  a much longer time constant than you seem to imply. They are related to
  corporate profits. Coincidentally 1965 marked the beginning of a trend towards
  lower US industrial profitability. Government support for R&D has been in 
  decline as a pct of total R&D since about 1965 as well. US living standards 
  peaked in 1972-3 and have been in decline with bumps due to local (in time)
  business cycles. Total family income has continued to increase primarily 
  due to the increase in two income families. 

  My company and yours are making alot of efforts to sell overseas. Hewlett
  Packard sells over 50% overseas, I think the IBM percentage is 30% or so.
  The idea that nobody is trying is ludicrous. The auto companies, in case
  you havent noticed have been profitable on their overseas operations and
  have lost money in the US, so why wouldnt they sell overseas. If you dont
  go worldwide these days you are likely to be history. Trade barriers are
  an issue but no less of one is the decline of the currency. This cycle
  is destructive in many subtle ways and extraordinarily difficult to turn
  around, much harder than you seem to think. You can expect the economy
  to be lethargic for a long period, none of the fundamental long term trends
  has changed for 20 years, it will take time to rebalance and pain will 
  likely be invloved. I think you can also expect voter dissatisfaction in
  1996 no matter who is elected, its gonna take more time to fix than 4 years
  and neither candidate is ready to address the deep underlying problems.
  I dont think the American public has really accepted the extent of the
  issue and the politicians therefore wont address it. So dont expect it to
  really be solved by 1996. 

  OK off soapbox, you hit a nerve.


Graham Flower ms 90-TT               |  Better to have convictions and act on 
Hewlett-Packard  350 W Trimble Rd    |  them, even if they are wrong, than to  
Microwave Semiconductor Division     |  waffle in indecision.
San Jose, California, 95131          |
 graham_flower@sj.hp.com             |

Dan
----------
From: bweiner@ruhets.rutgers.edu (Benjamin Weiner)
Newsgroups: sci.physics
Subject: Re: Report on Philosophies of Physicists
Date: 11 Sep 92 21:58:07 GMT
Organization: Rutgers Univ., New Brunswick, N.J.

Greg Nicholls writes:
> [doubt of concrete benefits of "Eastern" mindset, etc.]
> <cheap shot on> 'Western' philosophy, for all it's faults, doesn't
>approve of rolling tanks over students.

It doesn't?  The West, purely aside from Hitler and Stalin, has
nurtured Napoleon, Metternich, the wonderful people who brought us
South Africa, not to mention slavery, and George Armstrong Custer
et al.  The divine right of kings is a long-standing tradition
(Hobbes, Plato).  Let's not pat ourselves on the back, please.  

Greg Nicholls, I know you identified this as a cheap shot, but why
did you even bother making it?  It's plain old xenophobia, or worse
yet, Yellow Peril-ism.  It seems like all your posts are cheap shots
or rants about you'll never let supposed enviro-fascists take away
your car.  Get a new topic.
From: jac@ds8.scri.fsu.edu (Jim Carr)
Newsgroups: sci.physics
Subject: Re: How do we know individual photons exist?
Date: 15 Sep 92 18:24:01 GMT
Reply-To: jac@ds8.scri.fsu.edu (Jim Carr)
Organization: SCRI, Florida State University

In article <1992Sep15.180630.913@prim> prim!dave@germany.eu.net (Dave Griffiths) writes:
>
>Having just re-read the description of the 2 slit experiment and the
>implications of wave/particle duality, I was wondering how we know
>that individual photons exist? I'm under the impression that the answer
>is that they cause excitation of an electron from one state to another.

There are various ways, one being what you describe.  The photoelectric 
effect is the "classic" example, but so are scattering experiments 
like the compton effect.  Many modern experiments at high energy 
use "tagged" photons -- this is where you produce a photon from 
an electron and measure the energy loss of the electron, and then 
look at the scattering of the photon from a target -- where you 
really do follow a single photon through the experiment. 

>But couldn't the inteference seen in the 2 slit experiment be explained
>if instead of just one photon, the source emitted, say, 1000 sub-photons?
> ....

This would be like various pilot-wave theories.  It could, but there 
always seem to be problems with such models.  Most people seek such 
models because they have bigger problems when they try to think about 
how one photon goes through two slits (but wait, whenever you look it 
goes through one or the other, so maybe it goes through only one but 
knows the other is there?) without somehow being cut in half.  I only 
think about these things while watching Monday Night Football and it 
somehow doesn't seem so strange then. 

>Does the 2 slit experiment definitely correlate an emitted photon at
>the source with a detected photon at the screen, or is it just based
>on aggregates?  ....

Experiments have been done with very low intensities so that there is 
at most one photon in the apparatus at a time.  The actual interference 
pattern requires the accumulation of many events, thus representing 
an ensemble of incident photons, but the process does occur for one 
photon at a time.  

--
J. A. Carr                                    |  "The New Frontier of which I  
jac@gw.scri.fsu.edu                           |  speak is not a set of promises
Florida State University  B-186               |  -- it is a set of challenges."
Supercomputer Computations Research Institute |   John F. Kennedy (15 July 60)
From: johan@blade.stack.urc.tue.nl (Johan Wevers)
Newsgroups: sci.physics
Subject: Re: Did electric/magnetic symmetry "break"?
Date: 7 Sep 92 15:11:41 GMT

terry@aslws01.asl.dl.nec.com (Terry Bollinger) writes:

[Something about a symmetry between  electrical and magnetical fields]

Special relativity showed us that electrical and magnetical fields can't be
seen separatedly: the field which is a pure electrical field for one observer,
is a combination between electrical and magnetical fields for another,
and maybe a pure magnetical field for a third one.

That it is one force can also be seen from the fact that there exist only
one kind of photon.

******************************************************************** 
* 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: firth@sei.cmu.edu (Robert Firth)
Subject: Re: Hidden variable theories, was: Uncertainty Princi
Organization: Software Engineering Institute
Date: Fri, 11 Sep 1992 11:59:27 GMT

In article <mcirvin.716153312@husc8> mcirvin@husc8.harvard.edu (Mcirvin) writes:

>I justify my original decision to put in the word "future" by the
>fact that, operationally, that's what it looks like

Fair enough, Matt.  Your amplified statement is one I agree with almost
100%.  The only reservation is that we really haven't looked all that
hard for phenomena that would imply a pastward flow of causality.  But
then, I have very little idea just what kind of phenomenon one would
look for.  Any speculations?
Newsgroups: sci.physics
From: hagerman@ece.cmu.edu (John Hagerman)
Subject: Re: Hidden variable theories, was: Uncertainty Princi
Organization: Carnegie Mellon University
	<1992Sep7.001518.525@prim> <265@mtnmath.UUCP>
	<1992Sep8.144555.455@cine88.cineca.it>
Date: Tue, 8 Sep 1992 21:32:28 GMT

In article <1992Sep8.144555.455@cine88.cineca.it> campo@sunthpi3.difi.unipi.it (Massimo Campostrini) writes:
> 
> Again, instantaneous transmission of information happens in an
> underlying hidden variables theory.

The word "transmission" bothers me.  Why assume that hidden variables
are "somewhere," and that information must be "transmitted"?  Can't
the information already *be* everywhere it is needed?  I envision a
dual universe: in the universe we experience, events are "local" and
hidden variables are "global"; in the dual universe, hidden variables
are "local" and events are "global."  It seems like a mapping between
the two would be simple.  How crazy am I?

- John
--
hagerman@ece.cmu.edu
Newsgroups: sci.physics,sci.math