HDTenEightyP/NetNews huggingface dataset:
From: jac@ds8.scri.fsu.edu (Jim Carr)
Newsgroups: sci.physics
Subject: Re: E=mc2?
Date: 4 Sep 92 13:35:48 GMT
Reply-To: jac@ds8.scri.fsu.edu (Jim Carr)
Organization: SCRI, Florida State University

In article <mcirvin.715560320@husc8> mcirvin@husc8.harvard.edu (Mcirvin) writes:

  [answering a reply to whether relation between E=mc^2 and the 
   atomic bomb is a misunderstanding or not....

>It's a matter of emphasis, really.  The formula is very important
>when you calculate the yield from a fission reaction.  What isn't
>true is to say that the formula is the basic physical principle behind
>the bomb, or that special relativity was *the* theory that made the
>bomb possible.  The development of nuclear weapons had more to do with
>the empirical knowledge gained from experimental nuclear physics 
>than anything else.  I think QM had as much to do with it as did 
>relativity.

This is a good point.  Once you accept that the nucleus is made of 
small constituent parts and hence part of its mass can be released  
as energy, the actual physical understanding of the process can be 
handled entirely with non-relativistic quantum mechanics to a very 
good approximation.  

Thus relativistic mechanics is not at the foundation of the physics 
of the bomb.  Indeed, from the perspective of 1943, quantum mechanics 
was hardly required since the models used to make sense of the data 
concerning uranium fission were macroscopic ones and not true quantum 
mechanical calculations.  

--
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: muttiah@stable.ecn.purdue.edu (Ranjan S Muttiah)
Newsgroups: sci.physics
Subject: Re: Report on Philosophies of Physicists
Date: 30 Aug 92 20:11:53 GMT
Organization: Purdue University Engineering Computer Network

In article <mcirvin.715196487@husc8> mcirvin@husc8.harvard.edu (Mcirvin) writes:
>muttiah@stable.ecn.purdue.edu (Ranjan S Muttiah) writes:
>
>>I wonder whether the discoveries in physics (say in terms of QM
>>and relativity) made in the 20th century were really such a big
>>deal after all.  
>They certainly weren't a big deal in the ways they have often been
>made out to be.  QM and relativity are radical ideas, and radically
>at odds with our intuition about the world; and QM, at least, has been
>technologically useful in myriad ways.  But relativity has nothing to
>do with moral or cultural relativism, and QM has nothing to do with
>Taoism or transcendental meditation; just as Darwinism has nothing to
>do with "social Darwinism."

True enough.  But let me ask you why you think these theories are
"radically at odds with our intuition."  These theories gave explanations
for experiments conducted in regions (I'm not sure what else to call it...
"experiment space" ? ;-) never tested by humans before.  The atoms were never 
split pre-20th century, and nor were detailed speed of light experiments 
conducted before.  Sure, Galilei or one of his contemporaries may have roughly
determined the speed.  But it would have been no big deal for them.  It
was only because of Maxwell's work in electromagnetism that the speed
of light was such a big deal.  In fact, I heard that the Michelson-Morley
experiment was originally thought out by Maxwell.  So the new scales of
measurements were totally unexplored areas for which new theories and 
new academic positions :) were developed.
From: ted@physics.Berkeley.EDU (Emory F. Bunn)
Newsgroups: sci.physics
Subject: Liquid mirrors (was Re: Rotating Bucket of Water ...)
Date: 4 Sep 1992 20:53:03 GMT
Organization: Physics Department, U.C.Berkeley.
Distribution: world
NNTP-Posting-Host: physics.berkeley.edu

In article <1992Sep4.080240.3300@fs7.ece.cmu.edu> snyder@henry.ece.cmu.edu (John Snyder) writes:

>Interestingly, I believe I remember hearing about 2 groups who were trying
>to make telescopes with rotating mirrors:  one with Hg for the mirror,
>the other with molten Ga (which melts between 20 and 100 C [I don't
>remember the exact value, I think it is even between 20 and 50 C]).
>Does anyone know the status of these experiments?  They would seem
>to have somewhat limited utility, since they can only look straight
>up, isn't that right?

There's an article in a recent Astrophysical Journal (Borra et. al.,
1992 July 10, 393:829) describing the results of shop tests on a rotating
liquid mirror.  I'm pretty sure it was made of mercury.  They claim some
pretty impressive results:  In particular, they say that their resolution
is diffraction limited.  I don't remember the size or focal length, but
they were both within reasonably useful astronomical ranges.

Borra also recently published an articl in the same journal entitled
"The Case for Liquid Mirrors in Orbiting Telescopes."  (Ap. J. 392:375)
One's first reaction is "But there's no gravity in orbit, so how do
you maintain the mirror's shape?"  Borra proposes the following:
Put the telescope in orbit about the Sun, and give it a big sail, so that
it feels significant radiation pressure.  Then you can put it into
a stable orbit that is always some distance above the ecliptic plane.
Because of the radiation pressure, there is an effective local gravitational
field, and the rotating mirror will maintain a parabolic shape.

I wouldn't hold my breath waiting for funding to get approved for this
project.

As you say, these telescopes are not pointable, which is a problem.  On
the other hand, neither is the Arecibo radio dish, and it does a lot
of first-rate astronomy.  You wait for the object you're looking at to
pass near the zenith, and you move the detectors and imaging optics around
to get it even if it's not right at the zenith.  There's some loss of
resolution, but it's still useful.

-Ted
From: sichase@csa3.lbl.gov (SCOTT I CHASE)
Newsgroups: sci.physics
Subject: Re: quantization of angular momentum
Date: 2 Sep 92 19:27:03 GMT
Organization: Lawrence Berkeley Laboratory - Berkeley, CA, USA
Distribution: na
Reply-To: sichase@csa3.lbl.gov
NNTP-Posting-Host: 128.3.254.198
News-Software: VAX/VMS VNEWS 1.3-4   

In article <1992Sep1.203830.2793@galois.mit.edu>, jbaez@riesz.mit.edu (John C. Baez) writes...
>In article <25903@dog.ee.lbl.gov> sichase@csa2.lbl.gov writes:
>>L is not quantized under all circumstances.  For a free particle, 
>>none of r,p, and L are quantized.  
> 
>Ouch!  L is quantized under all circumstances.  Its eigenvalues are
>half-integer multiples of hbar, even for free particles.

Am I off base here?  If you have a free scalar particle with wave function
exp(-iEt+px), how is L quantized?

-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
From: art@physics.berkeley.edu (Arthur Ferruzzi)
Newsgroups: sci.physics
Subject: Code request - magnetic fields
Followup-To: sci.physics
Date: 29 Aug 1992 00:12:37 GMT
Organization: U.C. Berkeley Physics Department
Distribution: world
NNTP-Posting-Host: lec3mac18.berkeley.edu

Posted for a friend witout Usenet access.

David Hotz (david@cicese.mx) would like to know if there is
any p.d. code to calculate the magnetic fields of steady
currents. I am posting this for him, and request that you
direct replies/queries to david@cicese.mx.

Naturally, if you are aware of some code that is of interest
to the members of this newsgroup, please post to the net.

Art Ferruzzi

// standard disclaimers apply
Newsgroups: sci.physics,alt.sex
From: snyder@henry.ece.cmu.edu (John Snyder)
Subject: Re: BAROMETERS (was Re: Subject?)
Organization: Physics Department, Carnegie Mellon University
Date: Wed, 2 Sep 1992 19:22:05 GMT

In article <ZOWIE.92Sep1122151@daedalus.stanford.edu> zowie@banneker.stanford.edu writes:
>Lots of people write:
>	<stuff about people foolishly jumping out of windows>
>
>This whole thread reminds me of the age-old physics exam question:
>
>You are taken to a large, impressive-looking office building.  You may
>wander the building and its environs at will <etc. etc.> You are given
>an accurate barometer.  Your task is to determine the height of the
>building.
>
>Name at least six ways to accomplish this task. [before breakfast! ;-]
>
>--
>zowie@banneker.stanford.edu  "Tell your senator to fund the MSSTA program!"
>
>The world would be much better if more physicists read Strunk and White, 
>and more fuzzies read Tipler.  *Everyone* should read at least one 
>economics text.  No exceptions.


1)  Use the barometer to measure the air pressure differences between
the bottom and the top of the building.  Calculate the height from
the pressure difference.

2)  Tie a long string to the barometer.  Lower it slowly from the top
of the building.  Note the length of string when the barometer touches
the ground.

3)  Climb the building, measuring the height in barometers.  Measure
the barometer's length and convert.

4)  Drop the barometer off the top of the building, timing its fall.
Calculate the height from the time.

5)  Sit the barometer upright.  Measure its height and the length of its
shadow.  Measure the length of the shadow of the building.  Calculate
the height by similar triangles.

6)  Measure the height of the barometer.  Hold at a distance from you that
you can sight along the bottom and see the bottom of the building, and see
along the top to the top of the building.  Measure the distance that you are
holding it from you.  Calculate the building height from 
geometry/trigonometry.

7)  Go talk to the building manager.  Tell him, "I'll give you this very
nice barometer if you tell me how high your building is."

[Does anyone know where this question and answers originate?  Was it
actually asked and the answers published?  Or is it just an urban legend?]

John
snyder@henry.ece.cmu.edu
From: andrew@rentec.com (Andrew Mullhaupt)
Newsgroups: sci.physics
Subject: Re: Symmetries, groups, and categories
Date: 24 Aug 92 01:09:20 GMT
Distribution: na
Organization: Renaissance Technologies Corp., Setauket, NY.

In article <1992Aug21.181701.27612@galois.mit.edu> jbaez@riesz.mit.edu (John C. Baez) writes:
>In article <mcirvin.714344140@husc8> mcirvin@husc8.harvard.edu (Mcirvin) writes:
>>andrew@rentec.com (Andrew Mullhaupt) writes:
>>
>>>Hey while we're hammering physics for ill-chosen terminology, can we at least
>>>change it to 'renormalization monoid'?

>Well, scaling is a monoid (the real numbers in (0,1] form a
>monoid under multiplication), or if you allow "scaling up," a group (the
>real numbers > 0 form a group under multiplication).  But I am probably
>one of millions of mathematicians who were sorely disappointed to find
>out that the "renormalization group" was such a boring group.  What's
>interesting is not this group per se but its ACTION on the physical
>system one is studying (the "renormalization group flow" on some space
>of coupling constants).  So I agree that it's a bad term.

Actually, there are more interesting renormlization groups which pop into
your consciousness as soon as you get past the idea that a renormalization
theory is only supposed to give you values for critical exponents -  there
is fine structure in a lot of things which renormalize and the renormalization
group can have a big influence on the structure of these asymptotics. (E.g
Karamata theory, etc.) Ultimately, we will want to  deal with the generalization
of the renormalizaton theory to situations other than a hyperbolic fixed point.

Then again the monoid action is more interesting than the monoid, but this
isn't news, right?

Later,
Andrew Mullhaupt
Newsgroups: sci.physics
From: crb7q@kelvin.seas.Virginia.EDU (Cameron Randale Bass)
Subject: Re: Facts and Values (was Where it came from)
Organization: University of Virginia
Date: Wed, 26 Aug 1992 20:45:19 GMT

In article <1992Aug26.202330.1264@cs.ucf.edu> clarke@acme.ucf.edu (Thomas Clarke) writes:
>I missed the start of this thread.
>
>Did someone read "Lilith" by 
>	Robert (Zen and the Art of Motorcycle Maintenance) Pirsig?
>
>In a philosophy book disguised as a novel, Robert Pirsig tries to
>show how science has a morality.  He calls it the "metaphysics of
>quality."  The world is made of two principles, the dynamic and the
>static.  The dynamic is unknowable, mystic, etc.  When science
>explains something it passes from dynamic to static.  Morality 
>comes in since it is wrong to try to hold back the dynamic using
>the static.

    All the more reason to not get ideas about science from Mr. Pirsig.
    Fire, water, earth and air is just about as plausable and as helpful.

    *Warning*, personal value-laden commentary about Mr. Pirsig approaching...

    He is an idiot.

                           dale bass
-- 
C. R. Bass                                           crb7q@virginia.edu
Department of Mechanical and Aerospace Engineering
University of Virginia
Charlottesville, Virginia                            (804) 924-7926
From: sichase@csa3.lbl.gov (SCOTT I CHASE)
Newsgroups: sci.physics
Subject: Re: My son would like to know about photons...
Date: 27 Aug 92 01:58:32 GMT
Organization: Lawrence Berkeley Laboratory - Berkeley, CA, USA
Distribution: na
Reply-To: sichase@csa3.lbl.gov
NNTP-Posting-Host: 128.3.254.198
News-Software: VAX/VMS VNEWS 1.3-4   

In article <1992Aug27.103741.551@csc.canterbury.ac.nz>, phys169@csc.canterbury.ac.nz writes...
>The difficult part was definately explaining high-energy photons producing an
>electron/positron pair.  The problem I'm left with is this: if you fire a
>photon at an atom, you get an electron and protons and stuff (I got a bit
>bogged down explaining ions and neutons and such like so I skipped it). Fine.
>But if that gamma photon happens to hit another photon, and you get e+ and e-,
>why can't you also say these were constituent bits of the photon, like we said
>with an atom? I extended the bank-account analogy there, suggesting an account
>for positrons and electrons, but that was stretching things a bit far.

This is very important.  It is at the heart of modern particle physics.  If you
accelerate an e+ and e- and collide them at very high energy, you can make 
very massive particles such as protons and even much heavier things.  Clearly 
they weren't in the original electron and positron which weigh only 1/1836 part 
of a proton mass each.

Here's an analogy.  If you pluck a certain piano wire you get middle C.
Now imagine crossing this wire with another at right angles so they almost
touch somewhere near the middle.  This other wire is tuned to G above middle C.
Now pluck the C.  If you pluck strongly enough, the wires will touch and the
G will be excited to some extent, so that afer the amplitudes have died down
enough that the wires can no longer touch you have two pure tones - C and G.
All you did was pluck C.  But you made some G as well.  Clearly the G was never
in the C wire.  

When you collide an electron and a positron there is a finite probability 
that the event will excite a vibration in a set of quantum fields which 
we identify as a proton at times large compared to the collision time.
There is non-zero coupling between the initial and final states because of 
(primarily) the electromagnetic interaction.  But the final state proton 
was never in either of the initial particles.

-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
From: mcirvin@husc8.harvard.edu (Mcirvin)
Newsgroups: sci.physics
Subject: Re: My son would like to know about photons...
Date: 27 Aug 92 12:23:08 GMT

ric@hpspdla.spd.HP.COM (Ric Peregrino) writes:

>What about beta decay? This doesn't "split" a quark, but it does transform
>one quark into another with the release of an electron and it's antineutrino
>(I think?). So in some sense the original quark was broken into constituents.

Yeah, that's what it does.  The products aren't consistuents of
the original quark in the usual sense of the word; a down quark
isn't a bound state of an up quark, an electron and an antineutrino.

-- 
Matt McIrvin, Cambridge, Massachusetts, USA
From: downey@enh.nist.gov
Newsgroups: sci.physics
Subject: New Ending - Impure Mathematics
Date: 28 Aug 92 15:34:08 GMT
Organization: NIST


From: downey@enh.nist.gov
Date: 28-AUG-1992 14:53:42
Description: New Ending - Impure Mathematics


It seems reason and downright outrage are not recognized by
Darryl (the original poster of "Impure Mathematics"), or others
who find the story "funny."  Here is a new ending which
results in a much more equitable and judicious disposition.

When Curly Pi attempted improper integration, Polly was so outraged
that she raised herself to the nth degree and pulled out a .357
magnum.  She then threatened to blow off Curly Pi's conic section
and relative spheres whereupon his full extrapolation shrivelled to
an infinitesimal imaginary number.  While keeping her exponents
applied to the trigger, Polly summoned the matrix police and
Curly Pi was brought up on charges of attempted improper integration
and sentenced to hard differentiation for infinity; where he
repeatedly became a zero, thus rendering him incapable of ever
attempting improper integration again.

More of the Story:  Attempted improper integration may result in
loss of conic section and relative spheres and definitely results
in loss of any degree of freedom.

Epilogue:  While Curly Pi served his time in infinity, he ran
into a few other zero's named Darryl, Fred, Scott & Johan,
among others, who had been sentenced for masquerading as
higher-order equations and grossly offending other members
of mathkind.
From: cavenej@prism.CS.ORST.EDU (Jeff Cavener)
Newsgroups: sci.physics
Subject: Why do protons outnumber antiprotons?
Keywords: electron positron proton antiproton subatomic particle theory GUT unified
Date: 1 Sep 92 15:26:44 GMT
Article-I.D.: CS.1992Sep01.152644.18241
Distribution: na
Organization: Oregon State University, Computer Science Dept.

And for that matter (NPI;-) why do electrons outnumber positrons?
From: snarfy@cruzio.santa-cruz.ca.us
Newsgroups: sci.physics
Subject: snarfy's program
Keywords: correction
Date: 26 Aug 92 14:55:21 GMT
Reply-To: snarfy@cruzio.santa-cruz.ca.us


                           Correction:

   Command 1650 of the program I posted yesterday reads:

   1650 PRINT "for the new value of VARs/T(delay) after the news of the "

   It should read:

   1650 PRINT "for the new value of VARs*T(delay) after the news of the "

   Excuuuuuse Me ! (I was drunk when I wrote that command line)

   Cheerio !

   Snarfy
Newsgroups: sci.physics,alt.sex
From: franklin@ug.cs.dal.ca (Steve Franklin)
Subject: Re: Subject?
Organization: Math, Stats & CS, Dalhousie University, Halifax, NS, Canada
Distribution: na
Date: Tue, 1 Sep 1992 21:40:50 GMT

In <1579@dsinet> heinzl@hpw2 (Heinz Lottermoser) writes:

>Do any of you even know what "terminal velocity" is???  The higher you are
>does NOT mean the faster you fall unless you are in a friction free 
>environment, or the coef. of friction is so low that it does not overcome
>the acceleration.  

   Well, I think that you are under a false presime here my friend. Although
you will not be in a friction free environment, you are in a friction
lessened environment. Any ol' physicist can tell you that the density 
of the atmosphere decreases on average (devoid of any abrupt atmospheric
changes like thunderclouds, hurricanes, etc) as you go higher up. Therefore,
the coefficient of friction that a fallin body would encounter is LESS
at higher regions of the atmosphere. Since terminal velocity will mainly
depend on the surface area of the falling body, the shape of the falling
body, and the coefficient of friction (viscosity/air resistance) the falling
body encounters, it is clear why at higher regions, the individual
will certainly move more quickly (assuming the same shape is held).

steve

>Sorry, just can't stand bad physics...

   hypocrite!

>The Howler...
   yes, I probably would too
-- 
aasdSteveFranklin-Subliminal Psychology Major.ks;dlasBlueJaysRULEkasdfeahsdbfl
sd;lfaswoq[eBuyMeAQuadra!!!mbnZMXCNdfsba;KdSPAMiuroqiyetIBMSuxiweuryth'ewr;mxn
qpuepriuPartyOneqtuj;,n.,xnc,kjasFlameMeNot!;lkj;lkgkjd;askElvisLivesjhfquweru
zx.cfranklin@ug.cs.dal.ca,sk;t;lrut[Superboy@ac.dal.cav.zx,Physics!eq3rwkh;oHA
Newsgroups: sci.physics
From: dwr2560@zeus.tamu.edu (RING, DAVID WAYNE)
Subject: Re: E=mc2?
News-Software: VAX/VMS VNEWS 1.41    
Organization: Texas A&M University, Academic Computing Services
Date: Mon, 31 Aug 1992 17:01:00 GMT

gross@maxwell.ucsc.edu (Mike Gross) writes...
>But nuclear weapons _do_ turn matter into energy. For a fusion bomb, the key
>point is that a deuterium and a tritium nucleus weigh less than a helium 
>nucleus and a neutron. A gamma ray is also among the fusion products. Thus,
>you have matter + ~10 MeV -> less matter + a lot more energy (grossly
>simplified, of course). This _is_ a conversion from matter to energy. 

Springs do the same thing. A compressed spring has kx^2/2c^2 more mass than
a relaxed one. So releasing a spring turns mass into energy.

Dave Ring
dwr2560@zeus.tamu.edu
Newsgroups: sci.physics
From: jbaez@riesz.mit.edu (John C. Baez)
Subject: Re: quantization of angular momentum
Organization: MIT Department of Mathematics, Cambridge, MA
Distribution: sci.physics
Date: Tue, 1 Sep 92 20:32:11 GMT

In article <13581.2aa34a03@ohstpy.mps.ohio-state.edu> balbes@ohstpy.mps.ohio-state.edu writes:
>In article <TK.92Aug31202517@wheat-chex.ai.mit.edu>, tk@ai.mit.edu (Tom Knight) writes:
>> I'd like to understand the quantization of angular momentum better.
>> On the one hand, we are told that L is quantized, but we (naively)
>> recall that L = r x p, and note that neither the position nor the
>> momentum is quantized; presumably, the error or complexity lies in the
>> classical definition of the angular momentum, and if we had only
>> turned these into operators on the wave function "it would all be
>> clear."  Perhaps that's sufficient for some of you, but I'd like a
>> little better insight.  Maybe I'm just asking for insight into
>> something which is intrinsically not amenable to insight.  If so,
>> perhaps that will be some consolation.  Thanks.

>It's because we are taught to think in terms of Schroedinger's 
>version of QM where the operators are constant and the wave function
>evolves in time.

I doubt that'll help Tom.  His question, as I see it, is this.
In QM position has a continuous spectrum and can take any value
whatsoever.  Ditto for momentum.  So how come angular momentum, which
is r x p, can only take values which are integer multiples of hbar/2?
Good question.  This is a way to make it very hard to understand why
angular momentum has a discrete spectrum.  If what you want to do is
understand why it has a discrete spectrum, other routes are much easier!
For example, noting that it comes from a representation of the group of 
rotations will do the job -- perhaps someone could mail Tom some posts
from an earlier thread where we went over this.

But if you really want to take the bull by the horns and ask how a
cross product of 2 quantities with continuous spectrum can have a
discrete spectrum...

the main thing to note is the position and momentum do not commute, so
the ordinary rules do not apply!

A similar example is the harmonic oscillator.  H = p^2 + q^2.  Both
the operators p^2 and q^2 have a continuous spectrum but H has a
discrete spectrum.  It's a fairly common phenomenon.  

Perhaps someone with more energy can turn this into a real "explanation"
that Tom will like.