HDTenEightyP/NetNews huggingface dataset:
From: holmes@opal.idbsu.edu (Randall Holmes)
Subject: Re: Computability of the universe
Organization: Boise State University Math Dept.
Date: Tue, 15 Sep 1992 23:04:01 GMT

In article <BuHM6A.4Gz@news.cso.uiuc.edu> chappell@symcom.math.uiuc.edu (Glenn Chappell) writes:
>In article <1992Sep11.181736.5324@galois.mit.edu> jbaez@riesz.mit.edu (John C. Baez) writes:
>>In my opinion this fairly pervasive notion that you can only
>>"really" measure lengths that are rational numbers is an outdated
>>remnant of one of the Greeks' less bright moments.  For example:
>>
>>Say we all measured distances with a circular roller that was one foot
>>in diameter.  (I think they do something like this sometimes.)  We
>>measure distances by rolling this thing along and counting the number
>>of revolutions.  Okay, now we are measuring things in units of pi feet.
>>If our driveway looks to be 40 revolutions long, our best guess is
>>that it's 40pi feet long.
>.
>.
>.
>>Rationals are nice in many ways, but the idea
>>that measurements of lengths always give rational numbers is just
>>plain silly.
>
>Strictly speaking, yes, but the idea *is* useful in practice. After
>all, in real life, no length measurement is made without some
>experimental error. The result of a length measurement is actually a
>probability distribution - or, if you like, an interval. Since plain
>ol' numbers are easier to deal with than intervals (and since, in
>practice, they're usually good enough) any dense set of real numbers
>will do for expressing length measurements. The rationals are dense
>in the reals, and they're also generally easy to deal with, so why
>not use them?
>
>Well, interestingly enough, we usually don't. We usually use proper
>subsets of the rationals.
>
>E.g. traditionally, when the English system is used, measurements are
>expressed using rationals that can be written with their denominator
>being a power of 2.
>
>Thus, English system rulers are marked in inches, 1/2's, 1/4's, 1/8's,
>maybe 1/16's and sometimes 1/32's. The same goes for liquid measurements
>(1/2 gallon), etc.
>
>Now, the set of rationals that can be written as a/2^b is still dense in
>the reals, so it's still good enough.
>
>More modern practice tends toward using only those numbers than can be
>expressed as a/10^b. (When was the last time you heard anyone say
>"1/8 meter"?) The set of such numbers is also dense in the reals, so
>it's also good enough.

No, no, use the dyadic rationals (a/2**b).  Their special status is
revealed in Conway's construction of the surreal numbers.  :-)


>
>				Glenn Chappell  <><
>


-- 
The opinions expressed		|     --Sincerely,
above are not the "official"	|     M. Randall Holmes
opinions of any person		|     Math. Dept., Boise State Univ.
or institution.			|     holmes@opal.idbsu.edu
Newsgroups: sci.physics
From: bhoughto@sedona.intel.com (Blair P. Houghton)
Subject: Re: My son would like to know about photons...
Organization: Intel Corp., Chandler, Arizona
Date: Sat, 5 Sep 1992 18:05:21 GMT

In article <3SEP199219540648@zeus.tamu.edu> dwr2560@zeus.tamu.edu (RING, DAVID WAYNE) writes:
>I'm not sure what the reference frame of a photon means, but two photons
>can have the same energy in one frame and different energies in another.

Two photons with the same velocity.

				--Blair
				  "Okay, six of one, half
				   a parsec of another..."
From: sbs@weyl.bu.edu (Stephen Selipsky)
Newsgroups: sci.physics
Subject: Re: 137, was: Did electric/magnetic symmetry "break"?
Date: 14 Sep 92 17:22:36 GMT
Reply-To: sbs@weyl.bu.edu
Organization: Boston University Physics Department


In article <82607@bcsaic.boeing.com>, davidk@bcsaic.boeing.com (Dave Kerlick)
 writes:
|>
|>In article <1992Sep8.012930.25239@galois.mit.edu> jbaez@riesz.mit.edu (John C. Baez) writes:
|>>
|>>Afficionados of those who plunged in where angels feared to tread will
|>>have to check out Eddington's book in which he tried to "deduce" that
|>>the fine structure constant was exactly 136.  Then it turned out to be
|>>137 and he realized he'd left one something-or-other out.  Well, then
|>>it turned out not to be exactly 137 either.  People can also try out
|>>Irving Segal's article on the value of the fine structure constant. 
|>>Sorry, I don't have the reference.  
|>>
|>>Myself, I think 137.036 is just fine.  
|>
|>George Gamow evidently got wind of this, and sent in a joke paper to
|>Sommerfeld's (?) journal about why the freezing of water is at
|>
|>(2 / alpha - 1) degrees Celsius.  It got published, to much merriment.

The paper was by G. Beck, H. Bethe, and W. Reizler, appeared in
Die Naturwissenschaften, 2 (1931) pp.38-39, and is reprinted in
"A Random Walk in Science", ed. R. L. Weber, along with many
other famous physics jokes.  
                             -- Stephen Selipsky, Boston Univ.
From: nicho@VNET.IBM.COM
Newsgroups: sci.physics
Subject: Re: Report on Philosophies of Physicists
Date: 10 Sep 92 12:34:54 GMT
Reply-To: nicho@vnet.ibm.com

In <2760@news.cerf.net> Mitsuharu Hadeishi writes:
> --- previous matter deleted for brevity -----
 This is all very well Mitsu, but the assertion that 'Eastern' modes
of thought are better suited to describing 'neuroscience' 'cognitive
psycology' and 'social science' than 'Western' modes is not one you
have backed up with any facts. I'd be interested in any references
you can provide demonstrating that a scientist using an 'Eastern'
mindset had obtained superior results in the fields you have chosen.
(or any other field of thought for that matter).
 <cheap shot on> 'Western' philosophy, for all it's faults, doesn't
approve of rolling tanks over students.
 -----------------------------------------------------------------
               ** Of course I don't speak for IBM **
Greg Nicholls ... nicho@vnet.ibm.com or nicho@cix.compulink.co.uk
                  voice/fax: 44-794-516038
Newsgroups: sci.physics
From: bhoughto@sedona.intel.com (Blair P. Houghton)
Subject: Re: Angular momentum thought experiment
Organization: Intel Corp., Chandler, Arizona
Date: Sat, 5 Sep 1992 18:19:20 GMT

Find the acceleration of m1.  The O's are pulleys.
             __ 
            |m0|_____________
            |__|            O|
--------------------------   |
/////////////////////////|   |
                        /|   |
   All pulleys, ropes,  /|  |O|
   and surfaces are     /|  | |
   frictionless and     /|  | |
   massless.            /| m1 |
                        /|    m2
                        /|

				--Blair
				  "Took me a whole
				   bloody day..."
From: ofman@zonker.ph.utexas.edu (Leon Ofman)
Newsgroups: sci.physics
Subject: Re: Electrons in the body
Date: 9 Sep 92 23:43:27 GMT
Organization: Institute for Fusion Studies, UT-Austin

In article <00960110.2D669340@Msu.oscs.montana.edu> uchpcjv@Msu.oscs.montana.edu writes:
>In article <1992Aug28.040331.8765@ucc.su.OZ.AU>, yongbai@physics.su.OZ.AU (Yongbai Yin) writes:
>>In article <1992Aug26.122949.10900@relay.nswc.navy.mil> bwallet@apssgi.nswc.navy.mil (Brad Wallet) writes:
>>>Could anyone give me a rough estimate of the percent of mass of a human
>>>body which is made of electrons? 
>>
>>	The number is equal to one's weight divided by the mass of two protons,
>>just approximate.
>>
>
>  ROUGH ESTIMATE:  about 1/2000 of body mass.  Rought estimate.

Rough estimate: 1/1000 (don't forget the neutrons!)
From: nicho@VNET.IBM.COM
Newsgroups: sci.physics
Subject: Re: Report on Philosophies of Physicists
Date: 11 Sep 92 08:54:10 GMT
Reply-To: nicho@vnet.ibm.com

In <2765@news.cerf.net> Mitsuharu Hadeishi writes:
>   It is becoming increasingly evident in the field of artificial
>intelligence that the kinds of analogical and metaphorical reasoning
>used in everyday thought process are not very well describable by
>Boolean logic.
   Aha ! Now we're making progress. You appear to equate 'Western' modes
of thought with boolean logic. This is a naive view. Whilst true that
boolean logic has been developed to a high degree in 'western' societies,
it is by no means the whole. I totally agree that boolean
logic is inappropriate to many classes of problems, however to state
that ipso facto, we must adopt 'eastern' philosophies to deal with these
problems is, I think, unnecessary.
>   This is, however, getting a bit off-topic.
 Yup.
 -----------------------------------------------------------------
               ** Of course I don't speak for IBM **
Greg Nicholls ... nicho@vnet.ibm.com or nicho@cix.compulink.co.uk
                  voice/fax: 44-794-516038
Newsgroups: sci.physics
From: dwr2560@zeus.tamu.edu (RING, DAVID WAYNE)
Subject: Re: Rotating Bucket of Water in a Gravitation Field...Part #2
News-Software: VAX/VMS VNEWS 1.41    
Organization: Texas A&M University, Academic Computing Services
Date: Sat, 5 Sep 1992 16:00:00 GMT

ric@hpspdla.spd.HP.COM (Ric Peregrino) writes...
>I think this is wrong. Say there was only one star, which was just a
>flashlight (not much mass compared to the Earth). Now if the rest of
>the empty universe, containing this flashlight, spun around the Earth,
>why would you expect to see the water move in the bucket? This flashlight
>has very little mass and is far from the Earth; it's really just a marker.

The distant stars in this scenario are replaced by the boundary conditions.

Dave Ring
dwr2560@zeus.tamu.edu
From: m14494@mwvm.mitre.org (Mike White)
Subject: Re: Where do physics graduates look for work?
Organization: The MITRE Corporation
Distribution: na
Date: Thu, 10 Sep 1992 17:25:02 GMT

In article <1992Sep10.153848.1215@nntpd.lkg.dec.com> 
abbasi@star.enet.dec.com  writes:
> Ok, you worked hard to get your physics degree, now what do you do?
> where do you look for work? 

Job training time: repeat after me...

"Do you want fries with that?"

************************
* These are my opinions only.*
************************
Newsgroups: sci.physics
From: rwallace@unix1.tcd.ie (russell wallace)
Subject: Re: Computability of the universe
Organization: Trinity College, Dublin
Date: Thu, 10 Sep 1992 17:09:59 GMT

In <1992Sep10.131437.15148@sei.cmu.edu> firth@sei.cmu.edu (Robert Firth) writes:

>In article <1992Sep10.021939.10087@murdoch.acc.Virginia.EDU> lfoard@Turing.ORG (Lawrence C. Foard) writes:

>>My argument is that any given single expermental trial must be
>>able to be >>exactly<< simulated by a finite turing machine in finite
>>time. 

>Not so.  True random events cannot be simulated by a Turing machine, and
>the universe presents us frequently with true random events (for example
>the scintillations on the dial of your radium watch).

A Turing machine can produce a pseudo-random number sequence that cannot
be distinguished from the real thing (to be precise, for any test for
randomness, there are random number generators that will pass that
test). Therefore we can't know whether quantum events are truly random
or only pseudo-random.

>>If this is not the case we have to ask what we have left out of logic
>>such that its not sufficient to explain the universe.

>The leap from "logic" to "Turing machines" is one I confess I'm unable
>to follow.  A Turing machine is merely a very simple engine that is
>capable of performing a very small subset of feasible computations.
>To deify it makes no more sense than to insist the universe must be
>explained using only straight edge and compasses.

Not so. A Turing machine can perform any feasible computation (the
Church-Turing thesis).

--
"To summarize the summary of the summary: people are a problem"
Russell Wallace, Trinity College, Dublin
rwallace@unix1.tcd.ie
From: jbaez@riesz.mit.edu (John C. Baez)
Subject: Re: Why do protons outnumber antiprotons?
Organization: MIT Department of Mathematics, Cambridge, MA
Date: Sun, 13 Sep 92 17:31:03 GMT

brahm@cco.caltech.edu (David E. Brahm) writes:
matt@physics.berkeley.edu wrote:

>> baryon number violation in the Standard Model proceeds through topological
>> effects, and is suppressed by a factor of something like exp(-1/alpha).

>Matt must have missed my earlier post, so I'll repeat:
>The Standard Model vacua are separated by potential barriers, which you can
>either tunnel through (highly suppressed, as he says) or be thermally
>excited over.  At temperatures above the barrier height (the "sphaleron
>mass", about 10 TeV -- that's not so high) it's very easy to violate baryon
>number.  It's also possible that at comparable energies (i.e. SSC energy)
>B-violation will be seen.

That would be really cool, almost worth $8 billion!  :-)  None of my
measly collection of particle physics books talk about baryon
nonconservation or sphalerons, so I have a couple of questions, which
I hope you could answer in a way comprehensible to someone who loves
gauge theory but can never remember which is the s and which is the t
channel - in short, a mathematical physicist whose practical particle
physics is woefully weak.

1.  What sort of vacua are we talking about here: presumably those
corresponding to different values of some topological charge, but
which?  To be frank, which homotopy group are we talking here?  :-)
Is this pi_3(SU(n)) for n = 1, 2, or 3 (some kind of theta-worlds
deal) or am I thoroughly out of it?   

2.  Why at low temperatures is tunnelling suppressed by exp(-1/alpha)?
I'm puzzled that this is the electromagnetic alpha but the baryon 
number conservation would seem not to be an electromagnetic effect.

A clue, a clue, my kingdom for a clue!


.



Newsgroups: sci.physics
From: bweiner@ruhets.rutgers.edu (Benjamin Weiner)
Newsgroups: sci.physics
Subject: Re: Comprehending Theories (of Everything?)
Date: 11 Sep 92 22:24:23 GMT
Organization: Rutgers Univ., New Brunswick, N.J.

Even if string theory, or loop variables (by the way I have a theory
which says that deep down, the fundamental structure of the Universe
is tiny little pieces of duct tape) or anything else, should turn
out to be both a correct TOE and comprehensible to only a few, that
would be nothing new.  At some point there were only two people who
understood calculus (well, maybe a few more, but very few).

I'm not saying that string theory (et al) will ever be taught to college
freshmen, but that its difficulty is linked to its status as research
frontier.  So the incomprehensibility of proposed TOEs is an artifact
of their newness, not some kind of coincidence with human limits
(unless you believe, like I do, that people tend to think up the most 
complicated explanation available).
From: andrew@rentec.com (Andrew Mullhaupt)
Newsgroups: sci.physics
Subject: Re: Report on Philosophies of Physicists
Date: 12 Sep 92 03:40:23 GMT
Organization: Renaissance Technologies Corp., Setauket, NY.

In article <22218@galaxy.ucr.edu> baez@ucrmath.ucr.edu (john baez) writes:
>In article <1223@kepler1.rentec.com> andrew@rentec.com (Andrew Mullhaupt) writes:
>>In other words, I defy anyone to make sensible the claim that mathematics is
>>_not_ a soft, warm fuzzy, human frailty. 
>
>Mathematics is clearly a human activity and as such subject to all the foibles
>of any other human activity, but it is NOT warm and fuzzy.  It is cool and
>smooth.  If you want something warm and fuzzy, raise koala bears.

Ever checked the claws on those bears? But mathematics is not cool and
smooth unless you want it to be. Note how much traffic in sci.math reflects
the human interest stuff in math - who won what prize, what's your Erdos
number (mine recently went down to 2 on account of a paper on number theory
and piano tuning - I had forgotten all about it when my co-authors sent me
the proofs this past month...)

There are only a very few activities that no civilization seems to manage
without for very long. Mathematics is one of them. It lies very close to
some of the deepest human urges - certainty, truth, beauty, security, you
get them all in math. Presumably, you regard these as "cool and smooth"
and a bit like impersonal Hellenistic abstractions. But in this century,
we find that there are different possibilities for the "true truth" of math-
and we have to _choose_ which one we _want_. Anything as central to human
culture as mathematics is is warm and fuzzy it you look at it close up.

You've made the claim - try making it stick. However, this discussion
might make more sense in sci.philosophy.meta.

Later,
Andrew Mullhaupt
From: jcf@world.std.com (Joseph C Fineman)
Newsgroups: sci.physics
Subject: Re: Poynting power flux wrong??
Date: 13 Sep 92 02:10:25 GMT
Organization: The World Public Access UNIX, Brookline, MA

>1. For a region of space with static electric and magnetic fields, the Poynting
>   vector predicts non-zero power flux even if the fields are maintained by 
>   static charges and permanent magnets. 

It predicts a *circulation* of power flux, but there is no net accumulation
or attenuation of energy in any element of volume.  However, if you divide
that flux by c^2, you get a mass flux, and if you integrate the corresponding
angular-momentum density over all space, you get a total angular momentum
of the field, which is really there.  (E.g., if the permanent magnet is
heated thru its Curie point, so that the field collapses, it is easy to see
that the assembly will end up rotating.)  Hence, it seems to do no harm to
believe in this ghostly power flux in the static case.
From: mcirvin@husc8.harvard.edu (Mcirvin)
Newsgroups: sci.physics
Subject: Re: Is Spacetime Absolute?
Date: 5 Sep 92 19:04:38 GMT

prim!dave@germany.eu.net (Dave Griffiths) writes:

>I understand that special relativity gets rid of the idea of absolute
>3D space and absolute time, but is there any such thing as absolute spacetime?

>I think what I am asking is, is there an objective spacetime fabric out there
>through which all particles move? Or does a different universe exist from the
>perspective of every particle?

In special and general relativity there isn't a preferred coordinate
frame with which to express positions in spacetime, but there is a
single manifold through which everything moves.  The geometry of
that single spacetime in general relativity depends on the distribution
of energies, momenta, and forces, but statements about the curvature
that results can be expressed in such a way that they are the same
for everybody.  In that sense there is absolute spacetime in these
theories.  What happens when gravity is quantized is less clear.

>Um... also... how does an object "know" that it is spinning relative to
>the "fixed" stars? (Relative to the object, all it's particles are at rest
>and only the universe is spinning).

Read the thread on the rotating bucket-- it's fun!  In special
relativity it's clear that acceleration is not a relative thing.
Only non-accelerating (inertial) frames are equivalent to each other,
so you can't expect experiments to come out the same if you express
the results in terms of a nonrotating frame.

Now, this seemed unsatisfactory to both Ernst Mach and Albert
Einstein.  Mach proposed that which frames were inertial actually
depended on how you were moving relative to the bulk of matter
in the universe.  Einstein used this as a guiding principle when
he developed general relativity, but the extent to which it is
actually realized in GR depends on who you're talking to.  The
fact that very massive rotating objects distort spacetime in such
a way as to drag inertial frames with them is very suggestive.
On the other hand, the Minkowski spacetime of special relativity
is a solution of the equations of general relativity, so the
presence of matter clearly isn't *necessary* to define the inertial
frames, provided that you're willing to impose certain boundary
conditions at infinity instead.

-- 
Matt McIrvin, Cambridge, Massachusetts, USA
From: johan@blade.stack.urc.tue.nl (Johan Wevers)
Newsgroups: sci.physics
Subject: Re: Hidden variable theories, was: Uncertainty Princi
Date: 14 Sep 92 13:49:40 GMT

foxd@silver.ucs.indiana.edu (daniel fox) writes:

>While reading these discussions I can't help wondering if there is some sort of
>connection between causality and thermodynamics.  Both seem to define an arrow
>to time.  Might it be that causality is only meaningful for sufficently large
>collections of particles?

I think that thermodynamics is only meaningful for sufficently large
collections of particles and sufficiently long times (t>>interaction times).
If you want to seek for the interpretation of the `direction of time', I
suggest you'd study relativity (both special and general).

BTW, till now, nobody was able to calculate the entropy of a system
were general relativity applies......

******************************************************************** 
* 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,alt.sex
From: bhoughto@sedona.intel.com (Blair P. Houghton)
Subject: Re: BAROMETERS (was Re: Subject?)
Organization: Intel Corp., Chandler, Arizona
Distribution: na
Date: Mon, 7 Sep 1992 19:25:03 GMT

In article <1992Sep6.114724.7327@news.Hawaii.Edu> johnf@uhheph.phys.hawaii.edu (John Flanagan) writes:
>If it's a mercury-column barometer, rip the ruler off the side of the
>barometer, rappel down the side of the building, and measure the height
>by hand.

Which begs the question:  How tall was Torr?

				--Blair
				  "Ob. Sex:  How big was
				   his barometer?"
From: jack@dcs.glasgow.ac.uk (Jack Campin)
Newsgroups: sci.physics
Subject: Re: Computability of the universe
Date: 11 Sep 92 17:29:33 GMT
Reply-To: jack@dcs.glasgow.ac.uk (Jack Campin)
Organization: COMANDOS Project, Glesga Yoonie

rwallace@unix1.tcd.ie (russell wallace) wrote:
> firth@sei.cmu.edu (Robert Firth) writes:
>> The leap from "logic" to "Turing machines" is one I confess I'm unable
>> to follow.  A Turing machine is merely a very simple engine that is
>> capable of performing a very small subset of feasible computations.
>> To deify it makes no more sense than to insist the universe must be
>> explained using only straight edge and compasses.
> Not so.  A Turing machine can perform any feasible computation (the
> Church-Turing thesis).

The C-T thesis is dead.  Defunct.  An ex-theory.  Have a look at this:

   Type of Material: Book
     LC Call Number: QA9.59 .P68 1989
             Author: Pour-El, Marian B. (Marian Boykan), 1928-
              Title: Computability in analysis and physics / Marian B. Pour-El,
                      J. Ian Richards.
   Publication Info: Berlin ; New York : Springer Verlag, c1989.
  Phys. Description: x, 206 p., [1] leaf of plates : ill. ; 25 cm.
        Series Name: Perspectives in mathematical logic
              Notes: Bibliography: p. [195]-200.
           Subjects: Computable functions.
           Subjects: Mathematical analysis.
           Subjects: Physics.
        Other Names: Richards, J. Ian (Jonathan Ian), 1936-
     LC Card Number:    88024880
               ISBN: 0-387-50035-9 (U.S. : alk. paper)

or the papers they wrote before that.  The basic idea is to set up
computable boundary conditions for rather ordinary differential equations
(like the wave equation) which do not have computable solutions.

This should hardly come as a surprise if you remember that an optical
system can do Fourier transforms in constant time.  The analogue computers
Pour-El and Richards describe just sharpen this by solving Turing-undecidable
problems; given how noddy Turing machines are and how complex systems
described by differential equations are, this is not all that surprising.

If you *really* want to forecast the weather accurately, get a planet, not
a parallel processor.

OK, I'm oversimplifying a bit, in that nobody can really build a Pour-El
machine yet; but I'd bet that this work leads to real second-generation
analogue computers some day.

-- 
--  Jack Campin    room G092, Computing Science Department, Glasgow University,
17 Lilybank Gardens, Glasgow G12 8RZ, Scotland   TEL: 041 339 8855 x6854 (work)
INTERNET: jack@dcs.glasgow.ac.uk or via nsfnet-relay.ac.uk    FAX: 041 330 4913
BANG!net: via mcsun and uknet     BITNET: via UKACRL    UUCP: jack@glasgow.uucp