HDTenEightyP/NetNews huggingface dataset:
From: ted@physics.Berkeley.EDU (Emory F. Bunn)
Newsgroups: sci.physics
Subject: Re: Gravity and SR
Date: 2 Sep 1992 05:53:36 GMT
Organization: University of California, Berkeley
Distribution: world
NNTP-Posting-Host: physics.berkeley.edu
Keywords: gravity, relativity

In article <1992Sep1.215708.11691@cco.caltech.edu> stieger@cco.caltech.edu (Ronald David Stieger) writes:
>The other day I was thinking (don't ask me why, I try to avoid it as 
>much as possible :-) about electric fields and how the field of a moving
>charge is not spherically symmetric, and how relativity leads to magnetic
>fields.  Then I started wondering whether or not gravitational fields 
>behave the same way.  

The short answer is that there are indeed "gravitomagnetic" effects in
general relativity.  They're always weak in comparison to the 
ordinary gravitational effects, and as far as I know, they have
never been directly observed.  There's some hope of using extremely
low-temperature technologies to observe gravitomagnetism in superfluid
helium eventually.

>Of course, if I remember correctly, the magnetic
>field arises from the fact that there are both positive and negative
>charges in a wire, and in different frames of reference these can be at
>rest or moving; for gravity, there is only positive mass (unless someone
>has made a new discovery recently! :-).  

That's right.  That's the reason it's possible to produce strong
magnetic fields without simultaneously producing much stronger electric
fields:  You can arrange positive and negative charges in such a 
way that the electric (Coulomb) force is small, but the magnetic effect
is large.  Since there's only positive mass, you can't do the
analogous thing to produce large gravitomagnetic effects without
simultaneously producing extremely large "gravitostatic" effects.

(Stuff deleted.)

>Why is it that mass and gravitational fields curve spacetime?
>Why not charge and electric field?  I suspect that it's more than just
>a convention, but I don't understand why gravity differs from the other
>forces in such a fundamental way.

Here's one way to look at it.  We know that gravity obeys this amazing
principle that says that all test particles fall in the same way
in a gravitational field, independent of the nature of the particle.
This is not true for, say, the electromagnetic force.  (Protons and
electrons move differently in an electric field.)  The fact that
gravity obeys this "Equivalence Principle" means that it is possible
to view gravity in the general-relativity way:  Freely falling 
particles travel along straight lines; it's just that the spacetime
in which they're travelling is curved.  You couldn't form an 
analogous theory for electromagnetism, since the paths of different
sorts of particles in an electromagnetic field are different.

I hope this helps.

-Ted

Newsgroups: sci.physics
From: jarleb@medusa.uio.no (Jarle Brinchmann)
Subject: Re: Gravitational lenses
Reply-To: jarleb@medusa.uio.no (Jarle Brinchmann)
Organization: University of Oslo, Norway
Date: Mon, 31 Aug 1992 08:41:18 GMT

In article <9224413.19986@mulga.cs.mu.OZ.AU>, scienger@ecr.mu.OZ.AU
(Christopher_Robert INNES) writes:
> 
> 
> Greetings,
> I'm currently reading a book called `The Dark Matter' which is 
> dicussing dark matter and methods of detecting it. One of the methods
mentioned
> was using the gravitational lens effect. If I understand it correctly
> foreground galaxies , due to their mass and therefore gravitational
field ,
> 'bend' the light of a background galaxy , which is behind the
foreground
> galaxy , due to einstein's general theory of relativity. I was just
wondering
> if gravitational lensing has been observed by astronomers. 
> 
Well, Yes. The first discovery was made in 1979, with The so called Twin
Quasar,
(sorry I don't recall the name). Though the idea that grav. lensing
could occur,
is as old as from Zwicky i 1937(?). By now quite a few lenses have been
discovered.
I'm not really sure of the number up to date, if you want that you
better ask in
sci.astro, where they love to discuss such objects......

If you want a popular review, I'd recommend Cohens 'Gravitation's
Lens.'


> Also what is the current state of dark matter theory? I mean has
anymore
> evidence in the last few years come to light?
> 
(Here I'm merely referring things I've read lately in Physics World and
Science
and other magazines/publications).


Well, _The_ important evidence lately has been the results from the COBE
satellite.
(Cosmic Background Explorer). Which has measured anisotropies in the 2.7
K background
radiation. Several claims have been made that these observations rule
out Cold Dark
Matter theory, but then again, the data and theory have very large
errorbars, so nothing
has been settled. 	

					Jarle.
From: sajid@jam.wpd.sgi.com (Sajid Zia)
Newsgroups: sci.physics
Subject: E=mc2?
Date: 28 Aug 92 21:55:35 GMT
Reply-To: sajid@jam.wpd.sgi.com (Sajid Zia)
Organization: Silicon Graphics, Inc., Mountain View, CA, USA

Can somebody write to me how Einstein arrived at this
equation, I am extremely curious. Thanks,

Sajid
Newsgroups: sci.physics
From: dwr2560@zeus.tamu.edu (RING, DAVID WAYNE)
Subject: Re: Why do protons outnumber antiprotons?
News-Software: VAX/VMS VNEWS 1.41    
Organization: Texas A&M University, Academic Computing Services
Distribution: na
Date: Fri, 4 Sep 1992 16:02:00 GMT

In article <26069@dog.ee.lbl.gov>, sichase@csa3.lbl.gov writes...
>I don't understand your objection.  Can you elaborate?  You're not 
>just worried that I wrote "nu" for the antineutrino, are you?  In
>my example of beta decay, production of the electron should leave an 
>electron hole, which appears as a positron.  Since this does not happen, 
>I think that this is a pretty good example of what's wrong with thinking
>of antiparticles as the holes left behind when you pop a particle out
>of the Dirac sea.

The point is an electron and a neutrino are just components of one
particle. Consider instead the process N + nu -> P + e- . The lepton
particle is still there above the sea, it has just rotated into a different
component. In your process a lepton was pulled out of its sea and at the same
time rotated. I claim in fact that there is nothing inconsistent about
the hole interpretation for fermions (until you get to supersymmetry).
I don't really know this but I've argued with my advisor about it without
any real conclusion.

Dave Ring
dwr2560@zeus.tamu.edu
Newsgroups: sci.physics
From: matmcinn@nuscc.nus.sg (Mcinnes B T (Dr))
Subject: Re: E=mc2?
Organization: National University of Singapore
Date: Mon, 31 Aug 1992 04:10:26 GMT

sajid@jam.wpd.sgi.com (Sajid Zia) writes:
: Can somebody write to me how Einstein arrived at this
: equation, I am extremely curious. Thanks,
: 
I am also very curious about the origin of the notion that nuclear
weapons are in some special way related to E=mc^2. Even today there are
textbooks which seem to imply that these devices operate by converting
matter into energy. I find it hard to see how such a misunderstanding
could have arisen.

 : Sajid
From: dbc@ecs.soton.ac.uk (Bryan Carpenter)
Newsgroups: sci.physics
Subject: Re: E=mc2?
Date: 3 Sep 92 14:21:38 GMT

In <1992Aug31.041026.17766@nuscc.nus.sg> matmcinn@nuscc.nus.sg (Mcinnes B T (Dr)) writes:

>sajid@jam.wpd.sgi.com (Sajid Zia) writes:
>:...
>I am also very curious about the origin of the notion that nuclear
>weapons are in some special way related to E=mc^2. Even today there are
>textbooks which seem to imply that these devices operate by converting
>matter into energy. I find it hard to see how such a misunderstanding
>could have arisen.

The net rest mass of the the fragments coming out of a Uranium fission
(for example) is less than the mass of the original nucleus (by an
easily measurable amount---getting on for 1% so far as I remember).
The energy liberated can be calculated from E = m c^2.  A natural way of
looking at this is that part of the rest mass of original matter has
been converted to energy.  Why is that a misunderstanding?

> : Sajid

Bryan
From: andrew@rentec.com (Andrew Mullhaupt)
Newsgroups: sci.physics
Subject: Re: Symmetries, groups, and categories
Date: 23 Aug 92 22:59:47 GMT
Distribution: na
Organization: Renaissance Technologies Corp., Setauket, NY.

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'?
>
>And "pseudometric tensor" in relativity.
>
>My algebra's rusty.  What's the difference between a monoid and a
>semigroup?  Some textbooks say that it's really a renormalization
>semigroup.  They give the nature of the composition law as evidence.
>"Monoid" is more general, right?

Other way 'round. Monoids are semigroups with identities. Groups are monoids
with inverses. Note that in the case of renormalization, the identity is
usually (always?) admissible.

>What I find strange is that the term is used even though the
>[monoid/group/semigroup] nature of the beast isn't particularly
>illuminating or important.  The term seems to be the result of
>enthusiasm for group theory bleeding into places where it has
>little relevance.


I think the physicists just didn't feel that the distinction was that big
and they were familiar with groups. 

In the case of most renormalizations, the distinction between group and monoid
translates into global dynamic aspects of the orbits of the renormalization.
Since the bulk of renormalization theory is centered on the properties which
can be deduced from the linearization of the orbits near a fixed point, so
there should be very few instances where the differences are noticable.

Later,
Andrew Mullhaupt
From: ric@hpspdla.spd.HP.COM (Ric Peregrino)
Date: Wed, 2 Sep 1992 00:17:00 GMT
Subject: Re: ELECTRON HELIX : ITS POWER AND POSSIBLITIES
Organization: HP Stanford Park - Palo Alto, CA
Newsgroups: sci.physics


Regarding the electron helix.

This won't work.

You can't make a helix with magnetic fields which produces a bigger 
magnetic field than the sources. 

You can't accelerate with a magnetic field; F = Q V x B.

Q is a scalar, F and V are vectors, B is a pseudo vector and x denotes
the vector cross product. So an ion at rest will feel no force in a
magnetic field (V = 0), and an ion in motion is only deflected and 
the magnitude of V remains constant.

But don't stop thinking and studying,

--------------------------------------------------------------------------
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?
--------------------------------------------------------------------------
Newsgroups: sci.physics
From: crb7q@kelvin.seas.Virginia.EDU (Cameron Randale Bass)
Subject: Re: FTL Microwave Signal
Organization: University of Virginia
Distribution: na
Date: Fri, 28 Aug 1992 16:59:47 GMT

In article <1992Aug28.133333.1478@bnr.ca> bucknerb@bnr.ca (Brent Buckner) writes:
>In article <1992Aug27.182628.26130@murdoch.acc.Virginia.EDU> crb7q@kelvin.seas.Virginia.EDU (Cameron Randale Bass) writes:
>>In article <1992Aug27.160606.7612@bnr.ca> bucknerb@bnr.ca (Brent Buckner) writes:
>>>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:
>>>>>
>>>>>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.
>>
>>    The assumption that there is a limiting signal velocity.
>>
>
>Never having seen this as a basic postulate of SR, I'll have to
>bow out.  

     If there is not a limiting signal velocity, you have to give 
     up causality in SR.  Choose between the two.  Sometimes assumptions
     about reality are not well-stated.  Possession of a causal FTL 
     signal does not mean we can send stuff backwards in time.  
     As far as advanced signalling goes in the absence of causal
     FTL, it is very difficult for me to understand how one 
     expects to 'receive' a signal.

     My point is that you cannot analyze causal FTL signals in SR
     because they do not exist in SR.   

     By the way, I have been assuming all along that we were discussing
     causal signalling as the basis for discussing FTL (since I am 
     completely unsure how advanced 'signalling' would work).  
     Possibly that is the difficulty here?
     
                                dale bass


-- 
C. R. Bass                                           crb7q@virginia.edu
Department of Mechanical and Aerospace Engineering
University of Virginia
Charlottesville, Virginia                            (804) 924-7926
Xref: sparky sci.physics:13904 sci.astro:9365 sci.math:10790 sci.philosophy.tech:3073
From: bwallet@apssgi.nswc.navy.mil (Brad Wallet)
Newsgroups: sci.physics,sci.astro,sci.math,sci.philosophy.tech
Subject: Re: About my papers (Calendar (NEW), Ancient Times, Surface Algebras, Struc
Date: 1 Sep 92 14:35:37 GMT
Organization: Naval Surface Warfare Center

Mr. Space Potato is now proving the existence of God in sci.math by quoting
the Bible.
Newsgroups: sci.physics,sci.electronics
From: chegarty@mickey.WPI.EDU (Chris Hegarty)
Subject: Ionospheric Wave Propagation
Organization: Worcester Polytechnic Institute, Worcester, MA
Date: Wed, 2 Sep 1992 14:07:47 GMT


Does anyone out there know of an impulse response or frequency response 
model characterizing E&M wave propagation (satellite signals) through the 
ionosphere?

Any help would be appreciated.  Please e-mail responses.  I will summarize to
the group if there seems to be interest.

Thanks!
From: pad@galaxy.nsc.com (Paul Denny x8349)
Newsgroups: sci.physics
Subject: fluxgate compasses
Keywords: info sought
Date: 31 Aug 92 22:30:50 GMT
Organization: National Semiconductor, Santa Clara

I am interested in finding out how fluxgate compasses work. in 
particular I should like to understand the means by which they
sense the direction of a stationary magnetic field - I am familiar
with hall probes and their operation but this one has me stumped.
Any replies or literature pointers can be emailed - I will summarise
if there is any interest

Many thanks - Paul
From: baez@ucrmath.ucr.edu (john baez)
Newsgroups: sci.physics
Subject: Re: Axiom of Physics
Date: 28 Aug 92 19:39:32 GMT
Article-I.D.: galaxy.22039
Organization: University of California, Riverside

In article <5206@tuegate.tue.nl> johan@blade.stack.urc.tue.nl (Johan Wevers) writes:
>crb7q@kelvin.seas.Virginia.EDU (Cameron Randale Bass) writes:
>
>> I see no problem with the process of assuming the conservation laws to 
>> imply the symmetries.  

>I have never seen the derivation of a symmetry from a law of conservation,
>but maybe this is possible (Anyone on the net who knows ?). I thought that
>symmetry rules were more fundamental.

In symplectic mechanics, aka Hamiltonian mechanics, a smooth function F on
phase space is a conserved quantity, that is, F is invariant under the
flow generated by a given Hamiltonian H, if and only if it generates a
group of symmetries of the Hamiltonian, that is, H is invariant under
the flow generated by F.  Note the perfect symmetry here.  So neither
viewpoint is more fundamental; what's fundamental is this beautiful but
simple theorem.  Often it is easier to spot symmetries of a Hamiltonian
than to guess conserved quantities, but by this theorem they are
equivalent.

Note that by symmetries here I am only referring to one-parameter groups
of symmetries.
From: diverson@phys.ksu.edu (David Iverson)
Newsgroups: sci.physics
Subject: Re: Nevada Casino - 200 miles up
Date: 26 Aug 1992 18:10:14 GMT
Organization: Kansas State University
NNTP-Posting-Host: bohr.phys.ksu.edu


>Eric_S_Klien@cup.portal.com writes:

>>"I'd recommend trying to figure out the thrust you'd need.  I think it
>>could be a fun problem."
>> 
>>I'm unable to do this.  Can anyone help?  I'd be interested in the 
>>thrust requirements for different attitudes, perhaps 200 miles, 2000 
>>miles, 20000 miles, and 23,000 miles.  
>> 

>You want some large object simply hovering at those attitudes?  Well, to first
>order, that's just the weight of the thing.  You want a 100 ton 'building' to



Hmmm... seems like us mortal humans can't figure out a solution.  Maybe
you'd be better off asking the 'Cloud People' I keep hearing about, seems
they're doing this already.  Or if they won't take your calls you can try to
get in contact with the Nazi's living inside the hollow Earth.  I think
they've shown that it can be done, we're just not smart enough yet.  Or
maybe it's because we don't BELIEVE strongly enough.


-Diverson
-I think I can, I think I can.

--
diverson@phys.ksu.edu
From: crb7q@kelvin.seas.Virginia.EDU (Cameron Randale Bass)
Newsgroups: sci.physics
Subject: Re: ELECTRON HELIX : ITS POWER AND POSSIBLITIES
Date: 1 Sep 92 18:39:19 GMT
Article-I.D.: murdoch.1992Sep1.183919.12341
Organization: University of Virginia

In article <1992Sep1.121501.613@ualr.edu> hdgarner@acs.harding.edu writes:
[bunch of 256 character lines deleted]
>o
>f one of these methods, or a combination of both, I believe the "electron helix" can be formed to produce extremely powerful magnetic fields.
>I believe if the "electron helix" can be formed it will be very beneficial to mankind because of its many potential uses.  It can be used to produce magnetic containment fields to contain fusion reactions or even matter and antimatter reactions to produce
> vast amounts of energy.  It can also be used to propel spacecraft through space to explore regions of space which are now unreachable.  I think the " electron helix" may someday be used to supply the energy needs of the people of the earth.

     They do now.  We usually call them 'generators.' 

                                    dale bass

-- 
C. R. Bass                                           crb7q@virginia.edu
Department of Mechanical and Aerospace Engineering
University of Virginia
Charlottesville, Virginia                            (804) 924-7926
From: matmcinn@nuscc.nus.sg (Mcinnes B T (Dr))
Newsgroups: sci.physics
Subject: Re: New Ending - Impure Mathematics
Date: 29 Aug 92 02:01:44 GMT
Organization: National University of Singapore

downey@enh.nist.gov writes:
: 
: 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.
You're right about the "downright outrage". The experimental evidence
strongly suggests that people like feminists, the religious right, etc
etc, whose moral outrage is easily provoked, are unusually stupid.
True,the original story was also stupid and unfunny.:
From: crb7q@kelvin.seas.Virginia.EDU (Cameron Randale Bass)
Newsgroups: sci.physics
Subject: Re: C. R. BASS
Date: 1 Sep 92 23:50:41 GMT
Organization: University of Virginia

In article <1992Sep1.162814.615@ualr.edu> hdgarner@acs.harding.edu writes:
>GENERATORS???????????
>
>PLEASE EXPLAIN
>
>HDGARNER
>HU

     Certainly.  Devices that often include helical windings around
     metal cores in which rotational energy is turned into electrical
     energy by the motion of said windings in a magnetic field.  This
     field is often produced by a set of permanent magnets.  These devices 
     feature the motion of many trillions of trillions of electrons 
     in electric and magnetic fields, which are not usually quoted
     to 16 significant figures.

     Strangely enough, this device has been used for many many years
     and is the source for the electricity that runs the terminal I
     am typing on.

                               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: quantization of angular momentum
Date: 2 Sep 92 19:43:41 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 <mcirvin.715392893@husc8>, mcirvin@husc8.harvard.edu (Mcirvin) writes...
>>In <1992Sep1.203830.2793@galois.mit.edu> jbaez@riesz.mit.edu (John C. Baez) writes:
> 
>>>Ouch!  L is quantized under all circumstances.  Its eigenvalues are
>>>half-integer multiples of hbar, even for free particles.
> 
>Angular momentum, though, always has discrete eigenvalues.

Angular momentum is not a good quantum number for a plane wave.  So it is not
correct to say that a plane wave has quantized angular momentum.  John
is correct that L only has half-integer eigenvalues (in units of h-bar), but
that is not enough for me to say that a plane wave has quantized L.

-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