HDTenEightyP/NetNews huggingface dataset:
From: mab@wdl39.wdl.loral.com (Mark A Biggar)
Subject: Re: Fossil Paradox (was: Structure of Time)
Organization: Loral Western Development Labs
Distribution: sci,talk
Date: Wed, 12 Aug 1992 16:47:03 GMT

In article <1992Aug12.091957.14414@vax5.cit.cornell.edu> cpyy@vax5.cit.cornell.edu writes:
>This paradox is often used in proofs against backward time travel.
>Seemingly, such \ital\free\ital\ time travel mandates what
>physicists dub "violation of causality".
>Intuitively, it seem to suggest a few items:
>1.  You cannot go backward in time.
>2.  You can go back in time, but are locked into a set of
>    events that have already happened (ie predestination).
>3.  You can go back in time, but cannot in anyway communicate
>    with the time you left.  It's akin to never being
>    able to get out of a black hole after passing the event
>    horizon.

Another possibility is that:

1. time travel is possible
2. you can change things
3. eventualy whenever a time machine is invented someone does something
	in the past that prevents the invention of the time machine
4. after iterating this way lots ot time the universe settles to a universe
	where noone ever invents a time machine even though it is possible.

I've heard this called the "fixed point" theory of why ther are no vistors
from the future.  Now all we have to do is show that the sheaf of universes
where noone every get around to inventing time travel is an stable 
attractor and we're done.

--
Mark Biggar
mab@wdl1.wdl.loral.com
From: sichase@csa2.lbl.gov (SCOTT I CHASE)
Newsgroups: sci.physics
Subject: Re: Simple QED question
Date: 21 Aug 92 00:44:49 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 <12950070@hpspdla.spd.HP.COM>, ric@hpspdla.spd.HP.COM (Ric Peregrino) writes...
> 
>I'd like to learn more. Perhaps you could recommend a good book. I've
>got a BSEE and an MSEE, with a lot of math background. I've seen
>some QM, but not quantization of the electromagnetic field. I'd
>like to read and understand something (QED?) at the graduate level.

The first book I learned from, which, IMHO, gave me a good intuitive feel
for QED because I was able to diligently work through everything from cover 
to cover, is J.J. Sakurai's _Advanced Quantum Mechanics_.  It suffers from
being a little out of date notationally.  It uses the Minkowski metric rather
than the more modern real metric with signature -2.  And it doesn't use
the same conventions as more modern books (like Itzykson and Zuber) for
normalizations in a variety of places.  But I think that it's a good place
to start.  You need only a QM background and the math that any EE should
know.  Good luck.  

-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.astro
From: keith@cco.caltech.edu (Keith Allan Schneider)
Subject: Re: Fossil Paradox (was: Structure of Time)
Organization: California Institute of Technology, Pasadena
Date: Mon, 17 Aug 1992 10:57:52 GMT

bedding@physics.su.OZ.AU (Tim Bedding) writes:

>In article <1992Aug17.105608.421@ecc.tased.edu.au> ecc_jim@ecc.tased.edu.au writes:
>>
>>There was a short story like this where a guy trod on a butterfly and totally
>>changed everything. What was it called?
>>
>"The Sound of Thunder", as I recall.  Which was what he heard when he got
>back to the present to find it changed: his travelling partner blew him
>away with a shotgun for being a jerk.  :-)

That wasn't the story I think he was talking about.  If I remember, the
story he mentioned ended just when the man returns to the present (he had
been back in time hunting dinosaurs or something--they would figure out 
when it would die, and then let people shoot it a moment before.  Then, 
the bullets would be collected, etc.  There was this walkway, but
the man stepped off it and onto a butterfly.), finding that the spelling
of a few words on a sign were changed.

I read this story in 8th grade but cannot recall the title.

keith

Newsgroups: sci.physics
From: bhoughto@sedona.intel.com (Blair P. Houghton)
Subject: Re: Parsecs?
Organization: Intel Corp., Chandler, Arizona
Date: Fri, 14 Aug 1992 05:11:55 GMT

In article <1992Aug13.185735.5040@news.uit.no> alvin@stud.cs.uit.no (Alvin Brattli) writes:
>This reminds me of a definition I found in _Physics Handbook_ by
>C. Nordling and J. Oesterman:
>
>"1 light-year = 9.46055e15 m. A corresponding unit, 1 beard-second = 1e-8 m,
> has been suggested for microscopic distances. One beard-second is the
> distance which a standard beard in a standard face grows in one second."

One blairsbeardsec, being the distance at which my beard
subtends one second of arc (on average; well, according to
a small sampling; okay, a sampling of one; I'm not going to
pull ALL my whiskers just to satisfy NIST and the IAU :-{/}),
7420 meters (36.9 furlongs), which, coincidentally, is just
(36^3)/2pi (the sample was exactly 3.6cm long :-{)}).

My moustache, since it is multiplied by a uniform munching
factor, does not give very consistent results...

				--Blair
				  "Finally found my Feynman in the
				   last moving-box I looked through."
Newsgroups: sci.physics
From: sarfatti@well.sf.ca.us (Jack Sarfatti)
Subject: Kosher FTL typo correction &
Organization: Whole Earth 'Lectronic Link
Date: Tue, 18 Aug 1992 09:18:59 GMT



Kosher typo correction&..
z = |I2|^2/|I1|^2

  = [2|r|^2|t|^2-2|r|^2|t|^2 sinB]/[|t|^4+|r|^4+2|r|^2|t|^2 sinB]

= 2x(1 - sinB)/[1 + x^2 + 2xsinB]     this corrects typo error!

Note on unitarity of the computation. One must take the original spin
entangled pair state. Write it as an initial 4x4 spin density matrix
M(i) in two-photon subspace of Fock space of quantum radiation theory.
Then write the final state that is spin-disentangled as a final matrix
M(f). The question then is, can we find a unitary 4x4 matrix U(i,f) such
that

M(f) = U*(f,i)M(i)U(i,f)

where U*(f,i)U(i,f) = U(i,f)U*(f,i) = unit 4x4 matrix

I will do this. Maybe use MATHEMATICA.
Newsgroups: sci.physics
Subject: Re: A "preferred reference frame"
From: mcirvin@husc8.harvard.edu (Mcirvin)
Date: 15 Aug 92 17:49:08 GMT

hinson@maxwell.physics.purdue.edu (Jason W. Hinson) writes:

>The following is a science fictional excursion discussing the possiblity
>of space-time having a preferred frame of reference without violating
>relativity.  My request is that someone tell me how we know that it cannot
>be true.

[description of a physics in which, to paraphrase a bit, instantaneous
communication can occur, but only along a preferred set of spacelike
surfaces]

We do not know that this cannot be true.  Your statement that there would
be no problem with causality is correct, since spacelike communication-->
causality violation depends on the ability to change the spacelike
surface (or in SR, the inertial frame) in which the communication is
instantaneous, and this proposal explicitly removes the possibility.

It does "violate relativity" in the sense that it denies one of the
basic postulates, namely that *all* the laws of physics are the same
in all inertial frames.  It doesn't completely tear it apart, though;
it just turns it into a theory of some special subset of physics,
including all physics currently known.  It doesn't violate causality.

Rather than just say that the "ether" has the property that c is the
same in all frames, I'd say that the "ether" is only an ether for
these extra, instantaneous interactions, and has no relevance to
anything else.

This is, as others and I have pointed out before, a nice self-consistent
way to put faster-than-light travel into science fiction.  It isn't
at odds with any data and doesn't introduce the possibility of time
travel into the past.  All one needs to assume is some nonlocal
phenomenon which disobeys relativity in this way.

The other side of the coin is that there is absolutely no evidence for
any such thing, and no need to introduce it other than that it might
be nice to have.  Relativistic covariance has turned out to be an
extraordinarily successful framework in which to construct a model
of physics, and to most of us, at least, there seems to be no reason
to abandon it.  But nothing currently known from experiment rules out
extra physics of the sort you describe.

-- 
Matt McIrvin, Cambridge, Massachusetts, USA 
Newsgroups: sci.physics
From: johan@blade.stack.urc.tue.nl (Johan Wevers)
Newsgroups: sci.physics
Subject: Re: Origin of universe as quantum fluctuation?
Date: 13 Aug 92 10:03:13 GMT
Organization: MCGV Stack, Eindhoven University of Technology, the Netherlands.

matmcinn@nuscc.nus.sg (Mcinnes B T (Dr)) writes:
>
> This is certainly directly contrary to the singularity theorems of GR,
> which clearly imply that the Universe never "started". :)

The start of the universe must have happened under conditions were GR
is not valid any more. To say that GR contradicts this, is comparable
to say that time dillation contradicts Newtonian mechanics.  This  is
also true, but irrelevant.

 ********************************************************************
 * 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: crb7q@kelvin.seas.Virginia.EDU (Cameron Randale Bass)
Newsgroups: sci.physics
Subject: Re: The dangers in microwaved food...
Date: 20 Aug 92 19:15:47 GMT
Distribution: na
Organization: University of Virginia

In article <25626@dog.ee.lbl.gov> sichase@csa3.lbl.gov writes:
>In article <1992Aug20.161034.2920@murdoch.acc.Virginia.EDU>, crb7q@kelvin.seas.Virginia.EDU (Cameron Randale Bass) writes...
>> 
>>    After rigorous experimentation, I have concluded that it
>>    is difficult to get most eggs to actually explode in the microwave.
>>    Most of them seem to have flaws that rupture before a good
>>    pressure differential can be built up.  Or I could have just
>>    had a bad batch of eggs...
>
>Too much DDT, probably.  But look here for a minute.  It seems to me that
>although there is nothing wrong with a little joking that the original poster
>might be getting the wrong idea.  There is nothing wrong with posing a 
>question about the risks of microwave cooking, either from expose to the 
>microwaves during cooking, or from the consumption of microwaved food.  
>It's a perfectly legitimate concern, which I am sure has been addressed
>at least in part in references which I cannot provide.  From the barrage of
>witty cracks and diversions, you would think that this poor guy was posting
>about space potatos or something.

     Actually mine was a serious report of an experiment that demolished
     a carton of eggs (obviously I have far too much free time today).
     Further results include below 60 second average cracking time at
     high power.  Optimization studies were not performed because my
     egg source agency (my wife) did not seem to think that this was
     as valuable a contribution to science as it was a detriment to 
     our household larder.  My mentioning that cholesterol wasn't good
     for her anyhow did not seem to change her opinion.

     If I was making witty cracks, I would have pointed out your misspelling
     of potatoe.

                                dale bass
-- 
C. R. Bass                                           crb7q@virginia.edu
Department of Mechanical and Aerospace Engineering
University of Virginia
Charlottesville, Virginia                            (804) 924-7926
Newsgroups: sci.physics,sci.astro,sci.philosophy.tech,talk.religion.misc
From: Ari.Huttunen@hut.fi (Ari Juhani Huttunen)
Subject: Re: Fossil Paradox (was: Structure of Time)
Organization: Helsinki University of Technology, Finland
Date: Thu, 13 Aug 1992 01:12:14 GMT

In article <1992Aug11.235257.21903@nosc.mil> clarkk@nosc.mil (Kevin D. Clark) writes:

! It sounds like those questions where one is asked if you could go back and
! kill Adolph Hitler even if it would mean your own death, would you do it?
! This has always sounded logically impossible to me.  If in 1992 I was sent
! back to 1930 (or some such year) to hunt down a man named Hitler and I
! was successful, but I was killed, then none of the atrocities of WWII would
! have happened (in theory).  However, when 1992 rolled around I would never
! be asked to go back and kill Hitler because he would never have committed
! those crimes.  So if I WASN'T sent back, then no one would have killed him
! and he WOULD have committed the crimes.  Aaaugh.....no wonder I majored in
! engineering ...the answers were in the back of the book.

The answer to that problem is simple. A basic law that has not yet been
stated is the law of _causality_. You could travel backwards in time but
you would end up so far away from 'here' that when you traveled back
with the speed of light, it would at best be the present time. That would
also be the reason why time can't go backwards.

That's what I think. I don't have any proof, except that everything we
see works that way. I think that's plenty of proof.

If you can construct an FTL communication device, I will admit I am
wrong. For then you could travel 10 years backwards in time to a place
10 light years away and communicate with someone on Earth with FTL, 
and thus breaking the law of causality. (Hmm... You would only need
one of those devices if you were willing to wait ten years...;)
--
...............................................................................
Ari Huttunen 
...............................................................................
Newsgroups: sci.physics
From: wma6617@tamsun.tamu.edu (William Monroe Ashe          )
Subject: looking for out of print manuals
Organization: Texas A&M University, College Station
Date: Mon, 17 Aug 1992 18:32:03 GMT

	I am in need of assistance.  In my lab we have an old digital
manometer.  The manual for apparatus has been lost.  If anyone out there
in net land has a manual, or any information, I would be deeply indebited
to you.
the appartus is: A Pace Wiancko digital manometer
                 model number DM1
                 Pace Wiancko corp. (division of the Whittaker corp.)
                 N. Hollywood Ca.
Thanks in advance
Bill Ashe
Stored Ion Lab
Department of Physics
Texas A&M University
College Station Texas, USA
77843
ph# 409-845-7861
fax# 409-845-2590
From: ag3l+@andrew.cmu.edu (Arun K. Gupta)
Newsgroups: sci.physics
Subject: Re: Facts and Values
Date: 22 Aug 92 07:56:50 GMT
Organization: Physics, Carnegie Mellon, Pittsburgh, PA


The belief that there is an afterlife makes certain actions logical:

Thus,  the Christian Inquisition was justified on the grounds that the
pain and torture applied to an offender was justified because it was 
far less than anything (s)he would face in the afterlife.

Immolation of widows in India (or witches elsewhere),  dying in an
Islamic Jihad, etc., all are based on the idea that there is heaven, an
afterlife, and so on.

When physics fails to reveal the location of heaven, the existence of
soul, and reveals the insignificant rather than central position of 
human existence in the universe, then all the above lose their logic,
and we begin to find them wrong.  So much so, that a modern person
can barely understand why those practices ever existed and would
outright label them as wrong and evil.  But, within the beliefs and 
knowledge those ancient societies had, those practices were justified.

Thus  science does have an impact on values. 

Another example would be the attempts to give a scientific basis to
racism -- IQ tests,  measuring of head sizes, etc. etc.. The imagined
positive results, and the later discrediting of those results all had an
effect on the legitimacy of racism.

-arun gupta
ag3L@andrew.cmu.edu
Newsgroups: sci.physics
From: mfm0@ellis.uchicago.edu (martin frederic melhus)
Subject: Ranque-Hilsch vortex tubes
Summary: Looking for current state of knowledge
Keywords: Ranque, Hilsch, Vortex, Turbulence (?)
Reply-To: mfm0@midway.uchicago.edu
Organization: University of Chicago Computing Organizations
Date: Sat, 22 Aug 1992 05:48:24 GMT

Is there anyone out there doing active research in the area of 
Ranque-Hilsch vortex tubes?  And what kinds of papers have been
published since 1962 (I have a copy of Sibulkin's paper, and 
a lot of what he referenced, but as is always the case, there
are no references to works in the distant future.)
Any info would be appreciated.  Please followup or e-mail 
(preferred) to mfm0@midway.uchicago.edu.

-- 
                          | You have all the time from when you remove the |
     Martin F. Melhus     | card(s) from your hand until you put it (them) |
 mfm0@midway.uchicago.edu | on the pile to say "Last Card".  If you don't, |
                          | take your two. - Hidden texts, Book of MauMau. |
Newsgroups: sci.physics
From: tjn32113@uxa.cso.uiuc.edu (Thomas J. Nugent)
Subject: Re: "What's New" July-24-1992
Organization: University of Illinois at Urbana
Date: Fri, 14 Aug 1992 20:39:59 GMT

jac@ds8.scri.fsu.edu (Jim Carr) writes:

>My concern is that Freedom has none of the features you describe because 
>it does not exist.  We have spent more than the original proposed cost 
>and have only a design to show for it.  The original-original idea was 

We haven't spent more than 1984$8 Billion, have we?  Besides, I recently 
read that SSF itself will cost actually not more than the original proposal
of ~1984$8 Billion.  The new cost of $40 Billion (unsure what year $$) 
includes the cost of the shuttle flights, etc. etc.  They should (at least
partially) be included in the cost, but technically speaking, the original
estimate wasn't too far off.  One question I raised before which wasn't 
answered is, how much science etc. etc. will be done during the construction
flights?  Most of these flights will be dedicated to putting up Freedom, but
I imagine they will do other things besides.

>I think a space station is a good idea.  I am not sure Freedom is that idea.

I agree.  However, I also think that we are past the point of no return - 
tyring to go to something else now would be worse than just continuing.

"The future is a race between education and catastrophe."
		- H.G. Wells 
-- 
"To be average scares the hell out of me." -- Anonymous
Tom Nugent		e-mail: tjn32113@uxa.cso.uiuc.edu
Xref: sparky sci.physics:12860 sci.math:10286
From: srihari@sodium.cchem.berkeley.edu (Srihari Keshavamurthy)
Newsgroups: sci.physics,sci.math
Subject: Re: Symmetries, groups, and categories
Date: 14 Aug 1992 20:01:04 GMT
Organization: University of California, Berkeley
Distribution: na
NNTP-Posting-Host: sodium.cchem.berkeley.edu

Let me join in to commend John's efforts to make some of the 
abstract mathematics (atleast to me) crystal clear. Thanks.
Now even me, a chemist :), can understand these interesting
topics. By the way, what is a 'functor'?
       
Srihari
Xref: sparky sci.physics:13118 sci.math:10428
From: voros@physics.monash.edu.au (Joe Voros)
Newsgroups: sci.physics,sci.math
Subject: Is the Action a Component of a more general object?
Date: 20 Aug 92 17:39:55 +1000
Organization: Physics Department, Monash University, Australia.

Hi all.

As I was musing with Feynman's path integral approach to QM, I wondered
if the action S is a component of a more general object.  What I have in
mind is something analogous to the energy being connected with the
time-time component of the energy-momentum tensor.  Does anyone know of
anything at all related to these musings?  Work? References?  Ideas?

Cheers,

-- 
Joe Voros
Department of Physics, Monash University, Clayton, VIC, 3168, Australia.

Quantum Mechanics is God's way of telling you to mind your P_i's and Q_j's.
From: moravec@Think.COM (Hans Moravec)
Newsgroups: sci.physics
Subject: Re: Length scales in physics
Date: 23 Aug 1992 03:01:35 GMT
Organization: Thinking Machines Corporation, Cambridge MA, USA
Distribution: world
NNTP-Posting-Host: turing.think.com

In article <Aug.22.21.05.34.1992.26084@ruhets.rutgers.edu>, bweiner@ruhets.rutgers.edu (Benjamin Weiner) writes:
|> responding to B. T. McInnes:
|> 
|> The earlier question of, more-or-less, "why do physicists assume that
|> all constants are less than 10?" is very interesting, because most of
|> the time when you calculate something the constants that emerge are
|> relatively small.  Why?  I don't know, and I don't think it can be
|> fully explained by psychological reasons that determine our units or
|> what quantities we choose to calculate.  There's something there,
|> which explains why you just know, when Jackson says 
|>    show B = 96 pi NI/c (...)
|> that it will be a bitch and a half, because the constant is weird.

Continued fractions are interesting.  They are produced by a "natural"
division and remaindering process that can make any positive integer,
however large, yet most partial quotients in the continued fractions of
almost all numbers are less than 10.  (The probability of a quotient of
size n is proportional to about 1/n^2: about 40% of the quotients are 1).
Every once in a while a big one shows up, just to keep you on your toes.
For instance, here are the first few terms for "typical" real number Pi:

{3, 7, 15, 1, 292, 1, 1, 1, 2, 1, 3, 1, 14, 2, 1, 1, 2, 2, 2, 2, 1, 84, 2, 1, 
  1, 15, 3, 13, 1, 4, 2, 6, 6, 99, 1, 2, 2, 6, 3, 5, 1, 1, 6, 8, 1, 7, 1, 2, 
  3, 7, 1, 2, 1, 1, 12, 1, 1, 1, 3, 1, 1, 8, 1, 1, 2, 1, 6, 1, 1, 5, 2, 2, 3, 
  1, 2, 4, 4, 16, 1, 161, 45, 1, 22, 1, 2, 2, 1, 4, 1, 2, 24, 1, 2, 1, 3, 1, 
  2, 1, 1, 10, 2, 5, 4, 1, 2, 2, 8, 1, 5, 2, 2, 26, 1, 4, 1, 1, 8, 2, 42, 2, 
  1, 7, 3, 3, 1, 1, 7, 2, 4, 9, 7, 2, 3, 1, 57, 1, 18, 1, 9, 19, 1, 2, 18, 1, 
  3, 7, 30, 1, 1, 1, 3, 3, 3, 1, 2, 8, 1, 1, 2, 1, 15, 1, 2, 13, 1, 2, 1, 4, 
  1, 12, 1, 1, 3, 3, 28, 1, 10, 3, 2, 20, 1, 1, 1, 1, 4, 1, 1, 1, 5, 3, 2, 1, 
  6, 1, 4, 1, 120, 2, 1, 1, 3, 1, 23, 1, 15, 1, 3, 7, 1, 16, 1, 2, 1, 21, 2, 
  1, 1, 2, 9, 1, 6, 4, 127, 14, 5, 1, 3, 13, 7, 9, 1, 1, 1, 1, 1, 5, 4, 1, 1, 
  3, 1, 1, 29, 3, 1, 1, 2, 2, 1, 3, 1, 1, 1, 3, 1, 1, 10, 3, 1, 3, 1, 2, 1, 
  12, 1, 4, 1, 1, 1, 1, 7, 1, 1, 2, 1, 11, 3, 1, 7, 1, 4, 1, 48, 16, 1, 4, 5, 
  ...

Actually, each term N in the continued fraction can be viewed as the integer 
part of a real number N+f (0<f<1) formed by collapsing the continued fraction
of that term and all following terms (or more sensibly, not expanding them
in the first place).  It seems to me the distribution of magnitudes of these
real numbers (and their reciprocals) resembles the distribution of constants
I find in basic physics formulas.   (The partial quotients themselves resemble
the number of jellybeans I find in a bunch in my desk or pocket from time to
time).  Can I conclude from this that 40% of all groups in the universe
are singletons, 15% are pairs, 9% are triples, 6% are quads, etc?

			Puzzled  --  Hans Moravec


Newsgroups: sci.physics