HDTenEightyP/NetNews huggingface dataset:
From: tk@ai.mit.edu (Tom Knight)
Newsgroups: sci.physics
Subject: Re: quantization of angular momentum
Date: 3 Sep 92 18:23:46 GMT
	<13581.2aa34a03@ohstpy.mps.ohio-state.edu>
	<1992Sep1.203211.2591@galois.mit.edu>
Distribution: sci.physics
Organization: MIT Artificial Intelligence Lab
In-reply-to: jbaez@riesz.mit.edu's message of 1 Sep 92 20:32:11 GMT

In article <1992Sep1.203211.2591@galois.mit.edu> jbaez@riesz.mit.edu (John C. Baez) writes:

   From: jbaez@riesz.mit.edu (John C. Baez)

   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!

I already know these arguments, which are persuasive (to me) for a bound system.

   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...

Yup, this is what I'm interested in.

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

Ordinary rules, as in the definition of L as being r x p, or do you
have in mind some other rules?

   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.  

Is a simple summary of this to say that eigenstates for position and
momentum are not eigenstates of angular momentum, and that therefore a
continuous spectrum of position or momentum leads to a superposition
of angular momentum states, where the expectation value is r x p, but
where each eigenstate still has discrete angular momentum?  If this is
right, then I think I understand it.  I wouldn't turn down additional
insight, however.  Thanks.
From: shoppa@erin.caltech.edu (TIM SHOPPA)
Newsgroups: sci.physics
Subject: Refs on Japaneese spinning weight experiment?
Date: 23 Aug 92 22:58:00 GMT
Organization: California Institute of Technology
News-Software: VAX/VMS VNEWS 1.41

Hi!
	A few years ago (2-4?) the results of a Japaneese experiment that
spun disks in different directions and found different masses was published.
I know that later experiments proved this effect to not be real, but I am
interested in finding the original article.  I was pretty sure it was in
P.R.L.  but I searched through all the indices and didn't find it!  Nobody
else around here seems to know where I can find it either, even though they
all remember it.  Can anybody point me to where I can find the original
article?

					Tim (Shoppa@erin.caltech.edu)
From: andrew@rentec.com (Andrew Mullhaupt)
Newsgroups: sci.physics
Subject: Re: Facts and Values
Date: 24 Aug 92 01:54:21 GMT
Distribution: na
Organization: Renaissance Technologies Corp., Setauket, NY.

In article <25682@dog.ee.lbl.gov> sichase@csa3.lbl.gov writes:
> War
>and violence do not have their justification in religion, though 
>leaders certainly exploit their followers religious beliefs when convenient.

There are significant cases when religion has been co-opted by politics,
for the worse. Physics too, has been co-opted, (in fact ballistics has
been around longer than modern mechanics.)

I'm pretty happy with the U.S. ideal of separatio of church and state. Now
If I could only get the physicists to make like Aurel Wintner always wanted
and stop asking the government for money...

>If there is a day when religion dissappears, I doubt that war or violence
>will fade away as a result.

Followups to sci.tragedy.human-condition ?

Later,
Andrew Mullhaupt
From: sbs@weyl.bu.edu (Stephen Selipsky)
Newsgroups: sci.physics
Subject: Re: Speculation   (on superconductivity)
Date: 4 Sep 92 18:12:50 GMT
Reply-To: sbs@weyl.bu.edu
Organization: Boston University Physics Department


In article <ceZvXoS00VAw40q60q@andrew.cmu.edu>, 
 ag3l+@andrew.cmu.edu (Arun K. Gupta) writes:

|>If we had a theory of electrons of charge -e, and heavy positively
|>charged (say 41 e) particles, then the lowest energy state given
|>that a bunch of these particles was in existence in a certain volume
|>would be: a superconducting crystalline solid, in which the electro-
|>magnetic gauge invariance would be spontaneously broken, at least for
|>energy scales of 1/100 of an eV. What I mean here is that the long-
|>wave length photon has an effective mass.
|>Does anyone else find this weird ? I find it hard to digest. And the
|>question arises: does something similarly wierd happen in the strong
|>interactions, if I have three quarks in a certain volume ?

This describes a crystal of Niobium (atomic number 41).  Niobium does
superconduct, which is weird if you think superconductivity itself is
weird; collective effects aren't necessarily intuitive.  And the strong
interaction at low energies basically IS a set of collective effects.

     -- Stephen Selipsky
From: mcirvin@husc8.harvard.edu (Mcirvin)
Newsgroups: sci.physics
Subject: Re: What is de Broglie radiation and de Broglie wavelength?
Date: 29 Aug 92 03:20:10 GMT

N020BA@tamvm1.tamu.edu writes:

>  What is the de Brogile wavelength? Does de Brogile radiation exsist?
>
The de Broglie wavelength is the wavelength of the quantum-mechanical
wave function corresponding to a particle of a given momentum.  It is
given by the formula lambda = h/p, where lambda is the wavelength,
h is Planck's constant, and p is the momentum.  (I hope I got that
right.  I haven't had the occasion to use this formula in a while.) 

I suppose you could call just about anything "de Broglie radiation."
All particles have wave functions (or, more properly, fields described
by wave equations).
 
-- 
Matt McIrvin, Cambridge, Massachusetts, USA 
Newsgroups: sci.physics
From: raistlin@tartarus.uwa.edu.au (Brett Cuthbertson)
Subject: Re : Everything is Unitary
Organization: University of Western Australia
Distribution: world 
Date: Thu, 27 Aug 1992 01:50:29 GMT

Just a few question refering to Jack's lectures on FTL comm..ie the one
labelled 'EVERYTHING IS UNITARY"...

anyway...
 there are several equations namely the ones (1)-(4)..which describe
step by step each action upon the two photons..

the first 3 steps are fine...I can see what's going on...but I am
a little confused on the 4th one...

ie HMP|1> = -e^iphi(1)cosx|e1> + sinx|E1>

is the transformation from the last term on the right just
        sinx|01> -> sinx|E1> just refering to the fact that because the
O output is rotated by 90 degrees so that it is equivalent to the E
outputs polarization..?

another question..

the probability is of a particle begin between 0 and infinity etc is
always unitary...and this is worked out by generally

        psi* x psi

where psi* is the complex conjugate os psi...psi begin the wave function
of the particle...The effectively removes any imaginary terms and makes
the function real..This has been forced down us students this year...(
my first year of Quantum mech..)...I just want to know what an imaginary
state is not considered to be an option where probability is concerned..

 ie why does the particle have to be always in a real state and so
probability is conserved...

 that last statement was probably not phrased too well...and you may get
the wrong idea...( like I know the particle doesn't have to be always in
a real state...but as far as probability is concerned it seems to)..and
I also no that probably is a real measurement...anyway I'll leave it at
that..as I can't think how to phrase it much better and see what is
said...maybe then I might be able to make it more specific..

till later...

From: ric@hpspdla.spd.HP.COM (Ric Peregrino)
Date: Wed, 2 Sep 1992 00:41:33 GMT
Subject: Re: Why do protons outnumber antiprotons?
Organization: HP Stanford Park - Palo Alto, CA
Newsgroups: sci.physics


I'll stick my neck way out. I don't think they do outnumber their
anti-particles. I think they may appear to in our region of space time,
but that for every particle is an anti-particle, some where some when.

The way I understand our current understanding of say electrons and
positrons is that an empty universe is actually a universe completely
filled with electrons below zero energy minus the energy of an 
electron. If you add at least twice the electrons energy, one electron
can pop up to zero plus the energy of an electron and leave a hole
behind. That hole is a positron. So for every electron there exists
a positron.

--------------------------------------------------------------------------
Ric Peregrino     c/o Hewlett Packard Co.        I represent only myself
ric@spd.hp.com    1501 Page Mill Rd. Bldg. 5M    I may be wrong, maybe not
415-857-7526      Palo Alto, CA 94304            Do DC photons exist?
--------------------------------------------------------------------------
From: dedmunds@selkirk.sfu.ca (Darran Edmundson)
Newsgroups: sci.physics
Subject: Re: LaTeX submission to Phys. Rev. ?
Date: 27 Aug 92 22:33:37 GMT
Distribution: na
Organization: Simon Fraser University, Burnaby, B.C., Canada

Are there reduced page charges for electronically submitted articles?
I would think that the typing is the lion's share of the production
process.

-- 

Darran Edmundson
darran@chaos.phys.sfu.ca
Newsgroups: sci.physics
From: jbaez@riesz.mit.edu (John C. Baez)
Subject: Re: Why do protons outnumber antiprotons?
Keywords: electron positron proton antiproton subatomic particle theory GUT unified
Organization: MIT Department of Mathematics, Cambridge, MA
Distribution: na
Date: Tue, 1 Sep 92 20:34:13 GMT

In article <1992Sep01.152644.18241@CS.ORST.EDU> cavenej@prism.CS.ORST.EDU (Jeff Cavener) writes:
>And for that matter (NPI;-) why do electrons outnumber positrons?

Easy.  If positrons outnumbered electrons we'd call positrons
"electrons", and if neither outnumbered the other they'd all annihilate
each other and we wouldn't be around!
Newsgroups: sci.physics,sci.math
From: matmcinn@nuscc.nus.sg (Mcinnes B T (Dr))
Subject: Re: Less Groups! More Representations! (was: Symmetries, groups, and categories)
Organization: National University of Singapore
Distribution: na
Date: Wed, 26 Aug 1992 07:58:20 GMT

columbus@strident.think.com (Michael Weiss) writes:
: In article <1992Aug25.045603.13611@nuscc.nus.sg> matmcinn@nuscc.nus.sg
: (Mcinnes B T (Dr)) writes: 
: 
:    [stuff omitted]
:    Also: in what way is the holonomy group of a Riemannian manifold to be
:    interpreted as a group of "symmetries"?
: 
: For the normal case, the holonomy group is isomorphic to the group of
: covering transformations (sometimes called deck transformations).
: These qualify as symmetries in my book.
: 
No, only for compact flat manifolds.

  : As to the original topic, "should the first course in abstract algebra
: teach something about group representations", I'd say yes.  In fact such a
: course often does.  No doubt more could be taught.  On the other hand, I
: certainly don't feel the Sylow theorems should be dropped, as John Baez may
: have suggested (am I misinterpreting you, John?)
: 
: And yes, I know grammatically it should be "Fewer Groups..."
From: sichase@csa1.lbl.gov (SCOTT I CHASE)
Newsgroups: sci.physics
Subject: Re: New Ending - Impure Mathematics
Date: 28 Aug 92 18:50:48 GMT
Organization: Lawrence Berkeley Laboratory - Berkeley, CA, USA
Distribution: na
Reply-To: sichase@csa1.lbl.gov
NNTP-Posting-Host: 128.3.254.196
News-Software: VAX/VMS VNEWS 1.3-4   

In article <28AUG92.11340831@enh.nist.gov>, downey@enh.nist.gov writes...
> 
>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.

To put me in the same class as a rapist just because I objected to someone's
critism of a posting is a pretty low blow.  May your conic section 
shrivel and your spheres freeze off.

-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: doug@netcom.com (Doug Merritt)
Newsgroups: sci.physics
Subject: Re: Inertial drive?
Date: 1 Sep 92 19:22:59 GMT
Organization: Netcom - Online Communication Services  (408 241-9760 guest)

In article <1992Sep1.012210.4251@cs.rochester.edu> dietz@cs.rochester.edu (Paul Dietz) writes:
>Be aware that if you accept that physical laws are independent of the
>reference frame, then if you can violate conservation of momentum, you
>can also violate conservation of energy.  "Inertial drives" [sic]
>are really perpetual motion machines of the first kind.

Some proponents of the Dean Drive and such claim that it is a matter
of combining conservation of linear momentum and conservation of
angular momentum into a single conservation law, such that the two
forms of momentum can be interconverted, like matter and energy,
but are still conserved.

I believe this avoids the perpetual motion machine aspect of it, anyway.

The Dean Drive itself has been rather thoroughly debunked, of course.
	Doug
-- 
Doug Merritt	Preferred: doug@netcom.com   (or: doug@eris.berkeley.edu)
Professional Wild-eyed Visionary	Member, Crusaders for a Better Tomorrow
From: sichase@csa3.lbl.gov (SCOTT I CHASE)
Newsgroups: sci.physics
Subject: Re: Axiom of Physics
Date: 26 Aug 92 19:55:10 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 <1992Aug26.174922.6115@pellns.alleg.edu>, frisinv@alleg.edu writes...
>A friend and I have a small disagreement about the existance of an axiom  
>of physics. She claims that all assumptions in physics are made from  
>empirical evidence and therefore there are no axioms in physics. I  
>maintain that the conservation of mass/energy is an axiom. Here is my  
>argument: an axiom must be based on evidence. Euclid didn't just say  
>parallel lines don't intersect, he saw evidence that they didn't and then  
>stated the postulate. We have seen that energy and mass seem to be  
>conserved. There is very strong evidence that they are conserved but (to  
>my limited knowlege) there is no proof that they are conserved in all  
>cases. Thererfore, conservation of mass/energy is an axiom of physics. Can  
>anyone think of other axioms of physics?

Sometimes axioms are used in physics.  Special relativity might be a good
example.  There was evidence that things did not work as expected according
to Newton.  Einstein came along with a new axiom - the speed of light is
the same in all inertial frames of reference - and found that the theory 
which can be derived from this axiom explained some otherwise bizzare 
experiments, and made some verifiable predictions as well (which turned
out to be correct, of course.)  

Whether we would still say, almost 90 years later, that "the speed of light
is the same in all inertial frames" is still an axiom or an experimental 
fact is a different matter.  

Eventually, one hopes that all axioms undergo direct experimental test,
verifying the fundmental assumptions of the theory by direct confrontation
with reality.  At that point, I suppose they loose their status as axioms
and become experimental facts.

-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: drp40@cd.amdahl.com (Douglas R Puchalski)
Newsgroups: sci.physics
Subject: Inertial drive?
Date: 31 Aug 92 20:41:31 GMT
Reply-To: drp40@cd.amdahl.com
Organization: Amdahl Corporation, Sunnyvale, CA

An office mate recently mentioned having heard about something called
an "inertial drive" which was an enclosed device with some sort of motor
and geared arrangement which would produce a force in a single direction
by converting rotational inertia into "linear" (??) inertia.  Sounds 
pretty bizarre.  Anyone have any details on this?

-- 
Doug Puchalski						drp40@cd.amdahl.com
Xref: sparky sci.physics:14107 sci.environment:11080 misc.consumers:16148
From: betel@camelot.bradley.edu (Robert Crawford)
Newsgroups: sci.physics,sci.environment,misc.consumers
Subject: Re: Radioactivity and Superstition; was: Re: Are Your Light Bulbs Radioactive?
Date: 4 Sep 92 17:28:37 GMT
Organization: Bradley University

dean@vexcel.com (Dean Alaska) writes:
>I'll pay $5 for the light bulb and $10 for the smoke detector and $.01
>for a banana (limit 1).  But I insist on getting a video for verification.
>A polaroid might do but its probably also radioactive.  I won't pay for
>ruined teeth or dentures (signed release required).

	Heck, you can't even _buy_ the materials for that much! In any
case, have you ever tried to _find_ the radioactives in smoke
detectors? Let me tell you, it's not easy...

--
Black Hole Stout: A variety of homebrew that is sufficiently dark to
remove light from the surrounding space. Also has an extremely high
finishing gravity.

Robert Crawford 			betel@camelot.bradley.edu
Newsgroups: sci.physics
From: bucknerb@bnr.ca (Brent Buckner)
Subject: Re: FTL Microwave Signal
Organization: Bell-Northern Research, Ontario, Canada
Distribution: na
Date: Thu, 27 Aug 1992 16:06:06 GMT

In article <1992Aug26.234131.28949@murdoch.acc.Virginia.EDU> crb7q@kelvin.seas.Virginia.EDU (Cameron Randale Bass) writes:
>In article <1992Aug26.202707.15463@bnr.ca> bucknerb@bnr.ca (Brent Buckner) writes:
>>In article <25777@dog.ee.lbl.gov> sichase@csa3.lbl.gov writes:
>>>In article <1992Aug26.021649.4507@augean.eleceng.adelaide.edu.AU>, dabbott@augean.eleceng.adelaide.edu.AU (Derek Abbott) writes...
>>>
>>>I think that the point is that if even one bit of information is transmittable
>>>FTL, then we will all go off in search of the correct reformulation of
>>>mechanics.  If we then find such a theory, we presumably would *then*
>>>know how to exploit the effect in a serious way.
>>>
>>
>>Here's a set of assumptions under which the effect could be
>>useful:
>>
>>1.  We can usefully transform the FTL data transfer into backward-
>>    in-time data transfer (essentially, given that the transfer is from
>>    A to B, then we can put A and B into sufficiently
>>    different frames of reference).
>
>     This assumption makes absolutely no sense if we are in possession
>     of a signal that goes faster than light.   Under those circumstances,
>     the assumptions that underlie the theory that gives rise to 
>     backward in time behavior are incorrect.
>

Which assumptions would those be?  We can still do the math for
SR (and GR) using c, whether or not there is FTL signalling.
Certainly, we would have to refine our notion of causality;
this is embedded in assumption 2.

>>2.  We only get closed timelike loops.
>
>     Similar problem.  Timelike makes sense in a SR (or GR) formulation.
>     It does not make much sense if one can exchange signals faster
>     than the assumed limiting speed.  Assuming the 'new' limiting
>     speed is infinite, we could just coordinatize using the 'new' 
>     assumption and arrive at a Galilean relativistic frame in which
>     there is no such thing as a 'closed timelike loop'.
>

We would still be using c in our coordinate transforms.

               [munch]
>
>     The point is, that the assumptions by which we arrived at
>     the 'backward in time' behavior of FTL signals are invalidated
>     by the existence of causal FTL signals and thus the theory
>     would be incorrect.
>

In an appeal to authority, I'll point out that in the wormhole
work by Thorne et al, they were quite willing to have FTL
signals with G.R..

-- 
at Bell-Northern Research
voice:        (613) 765-2739
Canada Post:  P.O. Box 3511, Station C, Ottawa, Canada, K1Y 4H7
I do not claim that BNR holds these views.
From: toon@moene.indiv.nluug.nl (Toon Moene)
Newsgroups: sci.physics
Subject: Re: Report on Philosophies of Physicists
Date: 2 Sep 92 20:53:18 GMT
Organization: Moene Computational Physics, Amsterdam, The Netherlands

In article <mcirvin.715209788@husc8> mcirvin@husc8.harvard.edu (Mcirvin)  
writes:

[ ... ]

> What I meant is that, if you didn't know any better, you would
> consider it probable that the sorts of phenomena you see around
> you every day-- a clear demarcation between space and time; a
> universal notion of simultaneity; arbitrary measurements with
> precision limited only by the delicacy of the apparatus; objects
> occupying definite places in space and possessing definite momenta--
> would also apply to regions where the objects become very small
> or the speeds very large.  The fact that they don't perhaps should
> not be surprising, since the conditions are really so different.
> Yet a person living in a realm of large objects traveling
> at low speeds in a weak gravitational field necessarily has a
> working model of the world that depends on these ideas and shapes
> behavior and beliefs, and some revising of it is necessary if
> one wishes to think with any ease about things happening in
> very different parts of "experiment space."  

And then, try to imagine the 'experiment space' of 17/18th century man:  
Who really wants to believe in a theory that proclaims moving bodies will  
forever go on moving, or heavier objects falling as fast as lighter ones ?  
You sure know 'reality' is different, don't you ...
I agree with Matt that the conceptual leap of QM, GR and QCD, for that  
matter, is oversold - people had to make similar 'jumps' in the past - and  
they did it; even if it cost them a century ...

--
Toon Moene (toon@moene.indiv.nluug.nl)
Kantershof 269, 1104 GN  Amsterdam, The Netherlands
Tel.: + 31 20 6982029; Fax: + 31 20 6003411
No Disclaimers; a NeXT at home protects against this occupational hazard.
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: na
Date: Tue, 1 Sep 92 20:38:30 GMT

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.
From: snyder@henry.ece.cmu.edu (John Snyder)
Newsgroups: sci.physics
Subject: Re: Rotating Bucket of Water in a Gravitation Field...Part #2
Date: 4 Sep 92 08:02:40 GMT
Article-I.D.: fs7.1992Sep4.080240.3300
Organization: Physics Department, Carnegie Mellon University

In article <4SEP199201521179@zeus.tamu.edu> wdb3926@zeus.tamu.edu (BRUTON, WILLIAM DANIEL) writes:
>>Anyone ever proved that the surface of water in a bucket rotating
>>in a gravitational field is a paraboloid? 
>>
>>Dan
>
>Thanks for the replies reminding me how to work this problem.  It was 
>not a homework problem from a class.  I was just trying to determine 
>how fast one needs to rotate a cylinder of molten glass to make telescope
>mirrors of a particular focal length.  Thanks.
>

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?

John
snyder@henry.ece.cmu.edu