HDTenEightyP/NetNews huggingface dataset:
From: dwr2560@zeus.tamu.edu (RING, DAVID WAYNE)
Subject: Re: Hubble constant?
News-Software: VAX/VMS VNEWS 1.41    
Organization: Texas A&M University, Academic Computing Services
Date: Sat, 15 Aug 1992 10:00:00 GMT

scip1061@nuscc.nus.sg (Marc Paul Jozef) writes...
>G(g) is not zero somewhere _does_ imply that it is 
>not zero everywhere _if g is a Friedmann metric_
>(not for general g of course). I urge you both to
>take a look at MTW, section 27.8: for a Friedmann
>metric, the `matter component G_{ss} of the Einstein
>tensor G is a function that only depends on global
>time s. Therefore, if G_{ss} is (non)zero somewhere,
>it is (non)zero everywhere.

Talk about an abuse of logic! Noone in their right mind would claim that
our universe is _exactly_ described by a Friedmann metric! But that is
required for your logical step above!

>Any `toy model' for the universe must have a global 
>metric of the form Friedmann. Now before you start
>complaining that in case of a grid things are different,

they aren't

>remember that my _only alteration_ of the ususal
>Einstein cosmology is another proposal for idealizing
>the stress-energy tensor - not that of a perfect fluid,
>but that of a grid. Now Dave, you didn't find anything
>wrong with that, so don't complain if the mathematical
>consequences don't suit you.

I like the consequences.

>I repeat, if you don't like the consequences, you have
>to reject either the Friedmann shape as a global 
>approximation, my `delta' idealization of the stress-
>energy tensor, or Einstein's equation.

I like the consequences.

>And by the way, why so stubborn?

Because I'm right. :-)

>                                  Your intuition on a
>slow-down seems to be based on a Newtonian deduction
>that you yourself admitted to be unrigorous.

Not at all. I wouldn't have suggested such a thing if I wasn't so confident
about the GR derivation. That's what I meant when I said one could be
unrigorous iff one is right.

>Just forget your prejudices for a moment and assume
>(I know this is totally ridiculous) that experimentalists
>know their job. They tell us that the universe expands
>with constant rate. Still try to forget your prejudices...
>What does GR tell us? It confirms it! (if we use the
>delta idealization). Now if that is not a nice prediction
>of GR, I don't know what is.

Unfortunately, GR doesn't predict that.

You still haven't answered the question raised by my last post. What matter
distribution produces the 'pumpkin' cosmology?

Dave Ring
dwr2560@zeus.tamu.edu






Newsgroups: sci.physics
From: sarfatti@well.sf.ca.us (Jack Sarfatti)
Subject: phase shift beam recombiner Born&Wolf
Organization: Whole Earth 'Lectronic Link
Date: Fri, 21 Aug 1992 08:39:59 GMT


On the phase shift of a beam splitter.
From Born and Wolf Principles of Optics 7.7 p.p.322-4

"For each member of either the reflected or the transmitted set of
waves, the variable part of the phase of the wavefunction differs from
that of the preceding member by an mount which corresponds to a double
traversal of the plate. this phase difference d is"

d =(4pi/lambda)n'h cos(theta')          (1)

lambda is wavelength of light in vacuum, n' is homogeneous index of
refraction of plate, h is thickness of plate, theta' is refractive angle
in plate. Summing over all multiple reflections, the total reflection
amplitude is

A(r) = {(1 - e^id)R^1/2/(1 - Re^id)}A(i)  (8)  (Born&Wolf numbering)

where r^2 = r'^2 = R (4) where r is single external reflection transfer
function from air into plate, r' is internal reflection from plate to
air (from Fresnel eqs.). Similarly, for transmission tt' = T (2)

A(t) = {T/(1 - Re^id)}A(i)     (12)

Therefore

A(r)/A(t) = |A(r)/A(t)|e^i[phi(r)-phi(t)] = |A(r)/A(t)|e^ib

= (1 - e^id)R^1/2/T     (J1)

= R^1/2/T (1 - cosd - isind)

= R^1/2/T {(1 - cosd) - isind}

= R^1/2/T {(1 - cosd)^2 + (sind)^2}^1/2e^iarctan[sind/(1 - cosd)]

= R^1/2/T {(2 - 2cosd}^1/2 e^iarctan[sind/(1 - cosd)]= |A(r)/A(t)|e^ib

Therefore,

b = arctan[sind/(1 - cosd)] where d =(4pi/lambda)n'h cos(theta')

And there is no reason from this to believe that b = pi/2 as claimed by
Aephraim as an objection to my FTL communicator. So what's going on?
From: crb7q@kelvin.seas.Virginia.EDU (Cameron Randale Bass)
Newsgroups: sci.physics
Subject: Re: Snarfy's Equation
Keywords: mathcheck equation
Date: 19 Aug 92 21:04:23 GMT
Organization: University of Virginia

In article <4067@cruzio.santa-cruz.ca.us> snarfy@cruzio.santa-cruz.ca.us writes:
[stuff deleted]
>
>                     R=6.826*(D^-2)
>
>                 Where R = Ohms per 1000ft
>                 and   D = Diameter of round copper conductor in mm.
>
[data points deleted]

     Before we turn this into a universal law, I should point out that your
     resistance per unit length R can also be more usually expressed
     using resistance R as
                     
                    R/l=4 rho / pi D^2

     where rho is the resistivity and l is the length.  

     At 20C 4 rho / pi =  6.512 Ohm mm^2/1000ft
     for elemental copper.  Yours are probably numbers for annealed
     copper wire.  The upshot is, though, that rho depends on temperature.
     So your 'law' is only good for a certain temperature range.

     I would also like to point out that mixing units in this manner
     is not recommended since it usually leads to grievous error.

                                dale bass
-- 
C. R. Bass                                           crb7q@virginia.edu
Department of Mechanical and Aerospace Engineering
University of Virginia
Charlottesville, Virginia                            (804) 924-7926
From: johan@blade.stack.urc.tue.nl (Johan Wevers)
Newsgroups: sci.physics
Subject: Re: BLACKHOLES IN THE CENTRE OF THE EARTH
Date: 19 Aug 92 13:12:03 GMT
Organization: MCGV Stack, Eindhoven University of Technology, the Netherlands.

ecc_jim@ecc.tased.edu.au writes:
>
>Would it necessarily fall to the *centre* of the Earth. I'm no physicist but I
>certainly remember back in my pre-university days being taught in a physics
>class that within a solid spherical body of uniform density the gravitational
>attraction is uniform throughout the body.

That's not correct: the gravitational potential in such a body rises linear
from 0 to V_0 from the centre to the edge, and then falls with V_0/r^2.

The situation you describe holds for an empty sphere.

>Jim Palfreyman

******************************************************************** 
* 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
From: Bruce.Scott@bbs.oit.unc.edu (Bruce Scott)
Subject: Re: Entropy
Organization: Extended Bulletin Board Service
Date: Fri, 21 Aug 1992 13:34:14 GMT

Shapiro and Teukolsky [1] have some nice discussion on the entropy
of black holes. They cite Hawking's proof [2] that in an interaction
involving black holes, the sum of the areas of the holes can never
decrease. This provides the basis for identifying entropy with surface
area. They show as an example that one cannot create a naked singularity
by adding particles to a black hole near critical rotation in an effort
to spin it up. They compute the total energy, U=Mc^2, of a black hole
in terms of the area and then, identifying dU:=TdS, give the entropy
as S=(kc^3/G hbar) (A/4), where k is Boltzmann's constant and A is the
area. Worth a look.

[1] Black Holes, White Dwarfs, and Neutron Stars: The Physics of
    Compact Objects. Wiley, 1983.
[2] Hawking and Ellis, The Large Scale Structure of Space-time.
    Cambridge, 1973.

Gruss,
Dr Bruce Scott                             The deadliest bullshit is
Max-Planck-Institut fuer Plasmaphysik       odorless and transparent
bds at spl6n1.aug.ipp-garching.mpg.de                 -- W Gibson

--
   The opinions expressed are not necessarily those of the University of
     North Carolina at Chapel Hill, the Campus Office for Information
        Technology, or the Experimental Bulletin Board Service.
           internet:  bbs.oit.unc.edu or 152.2.22.80
Newsgroups: sci.physics
From: m14494@mwvm.mitre.org (Mike White)
Subject: Re: Nevada Casino - 200 miles up
Organization: The MITRE Corporation
Date: Mon, 17 Aug 1992 18:37:23 GMT

In article <64161@cup.portal.com> Eric_S_Klien@cup.portal.com writes:
>  I have access to 2026 AD technology.  
>  

At the rate we're going, 2026 AD technology will consist of
fossil fueled cars, coal and fission power plants, and
pocket supercomputers to calculate just exactly how
miserable we all are.  As for powering Supra-Las Vagas,
probably 80% of the total energy budget will go just 
for the neon lights.  But it won't matter; by 2026 AD, 
nobody will have enough money left to gamble, and
the National AeroSpace Plane, which could have lofted
the marks to the casinos, will still be on the drawing
boards.

************************
* These are my opinions only.*
************************
From: flower@hpcc01.corp.hp.com (Graham Flower)
Date: Thu, 13 Aug 1992 17:07:04 GMT
Subject: math for physics
Organization: the HP Corporate notes server
Newsgroups: sci.physics



     I've been methodically working my way through Schiff's Quantum Mechanics
     text for some time now. I find it reasonable but slow, and I find his
     problem collection OK but somewhat in need of supplement. However, one
     thing I find consistently is that I have forgotten most of what I knew
     about special functions and Schiff doesnt really deal with these except
     to mention them and provide some intermediate steps in derivations. while
     I find I can provide these steps, eventually, in doing so I burn alot of
     time, and usually have questions I cannt answer about the special function
     in question. So I guess what Im looking for is a book on mathematical
     physics or two that will give me the framework to answer most of these 
     questions and more that are upcoming. There are some obvious choices I'd
     appreciate any comments you can give me regarding the use of these books
     or point me to others. 


       Text                            Comment


       Morse and Feshbach            looks comprehensive, dont know how readable
				     and user friendly it is. Pretty advanced.

       Courant and Hilbert           appears to emphasize the mathematical 
				     side like existence. no exercizes and old
				     (1925). However both authors esp hilbert
				     are extremely reputable mathematicians.

       Arfken                        looks fairly good, does it go far enough?

       whittaker and watson          shows up in the footnotes of alot of grad
				     qm books. Schiff's being one of them. 
				     old, but appears to have good exercizes.
				     leans to old style analysis.
     
       Weinberger's PDE book         my primary current reference. leans to math                                     is terse but clear. not alot of detail.

       Bukov                         ? looks like primarily an undergrad book

       Boas                          ? 


       All comments and suggestions are welcome. Are there other texts I should
       know about? How are Morse and Feshbach and or Courant and Hilbert to 
       work with? My present inclination is to buy Arfken and one of the top 
       two classics. 

    
       Thanks

       Graham Flower


Graham Flower ms 90-TT               |  Better to have convictions and act on 
Hewlett-Packard  350 W Trimble Rd    |  them, even if they are wrong, than to  
Microwave Semiconductor Division     |  waffle in indecision.
San Jose, California, 95131          |
 graham_flower@sj.hp.com             |

Newsgroups: sci.physics
From: scip1061@nuscc.nus.sg (Marc Paul Jozef)
Subject: Re: Hubble constant?
Organization: National University of Singapore
Date: Thu, 13 Aug 1992 12:20:04 GMT

  Well Dave, you beat me there! A grid of point-masses 
is not the same as empty space...how could I have
possibly overlooked this?
  You had me running to the library to find that our
universe, which looks so cunningly empty at first sight,
is in fact a perfect fluid.
  Please allow me to scramble for excuses.

I said: G(g) = d is _in effect_ a vacuum equation.
The lefthand side is (by smoothness of a Friedmann metric)
a smooth tensor on spacetime. The righthand side is a
delta-tensor which is only smooth (namely identical zero)
outside the worldcurves of the point-masses.
So outside this set of zero volume, G(g) = d reads G(g) = 0.

O.k, I see it coming this time: you say that if g
satisfies G9g) = 0, it can't also satisfy G(g) = d.
True enough. But remember that one obtains a Friedmann
metric g precisely by ignoring all local effects (for
instance those close to the grid-points). So we should
not be surprised that g does not recognize the grid-
points.

A more realistic solution h of Einstein's G(g) = d
for a grid would be some perturbation of g which has
Schwarzschild-bumps around the grid-points. But 
these bumps do not interest me; I want to know
about the mutual behaviour of the grid-points. And
this behaviour is described by g. (which satisfies G(g) = 0).

G Marc van loo.

Newsgroups: sci.physics
From: mcirvin@husc8.harvard.edu (Mcirvin)
Newsgroups: sci.physics
Subject: Re: ORTHODOX SPECIAL RELATIVITY
Date: 15 Aug 92 01:00:38 GMT
Article-I.D.: husc8.mcirvin.713840438
 <Aug.13.18.10.50.1992.26657@ruhets.rutgers.edu> <1992Aug14.211623.23886@galois.mit.edu>

jbaez@zermelo.mit.edu (John C. Baez) writes:

>Note that translations and rotations commute with
>time translation and have conserved quantitites but Lorentz boosts
>don't.

Sidney Coleman said something interesting about this in his quantum
field theory class, namely that if you plug Lorentz boosts into the
actual expression that one uses to extract Noether currents from
symmetries, instead of getting a conserved current, you derive something
that essentially implies conservation of the path of the center of
mass of a system.  This was, he said, not the same thing as
conservation of momentum.  I don't remember precisely how it went,
though.

-- 
Matt McIrvin, professional gradgrind, amateur Usenet drifter 
Newsgroups: sci.physics
From: jbaez@zermelo.mit.edu (John C. Baez)
Subject: Re: Hubble constant?
Organization: MIT Department of Mathematics, Cambridge, MA
Date: Fri, 14 Aug 92 21:10:56 GMT

In article <Aug.13.16.31.25.1992.25521@ruhets.rutgers.edu> bweiner@ruhets.rutgers.edu (Benjamin Weiner) writes:

>I like the 
>baryonic possibilities because we already know that baryons exist,
>and in addition I would rather that dark matter were something
>astronomically interesting, like so-called Pop III star remnants
>or whatever, rather than a bunch of dull photinos.

Okay, my curiosity is piqued: what's a Pop III star remnant?  After a
star pops 3 times all that's left is remnants?  :-)

Photinos don't sound dull to me, unless like all superpartners they are
designed to be utterly indetectible.  

I have a theory that everyone here on usenet has a superpartner: an evil
twin that looks just like them but is 1000 times heavier.  The reason
why nobody has ever seen one of these superpartners is that they never
make their appointments.  :-)

Newsgroups: sci.physics
From: dwr2560@zeus.tamu.edu (RING, DAVID WAYNE)
Subject: Re: SU(5) GUT (was Re: Superbashing ...)
News-Software: VAX/VMS VNEWS 1.41    
Organization: Texas A&M University, Academic Computing Services
Distribution: usa
Date: Sun, 23 Aug 1992 15:44:00 GMT

mcgrew@skid.ps.uci.edu (Clark McGrew) writes...
>>"Flipped SU(5)" is just SU(5)xU(1); I don't know why they call it
>>"flipped SU(5)".  I also don't really know the motivation for it, but
>>some of the more stringy types here at LBL are interested in it.
>
>From a field theoretic point of view the difference between SU(5) and
>Flipped SU(5) is mostly just a interchange of the right handed
>component of the u and d quarks in the wave function.  The reason, I'm
>told, that string people like Flipped SU(5) is that it has been shown
>to be derivable from a class of string theories.  This lets low energy
>phenomenological predictions be made for string theories which usually
>dance at energies up around the planck scale.

Basically, a flipped string should have extra particles in the spectrum
which bend the running of the coupling constants so that they meet closer
to the plank scale, thus solving one of the tougher problems of string
theory (why is the GUT scale so small). When I said flipped SU(5) was
in some trouble, I should have said the flipped string, because it's
difficult to find a string model that works (not because of some experimental
limit). I'm sorry I don't have any better details.

Generic (non-string motivated) flipped SU(5) has an extra U(1) which
'mixes' with the U(1) subgroup of SU(5) to get the hypercharge symmetry.
(just like SU(2)xU(1)-->U(1) I guess). Thus there is an additional coupling
constant and you can no longer predict sin^2(theta) exactly. So it is doing
fine experimentally, but the evidence for it is weaker.

As far as proton decay constraints on regular SUSY SU(5), the 'naive'
parameter space has been more than half covered by the absence of detection
of the kaon modes. But the 'favorable' parameter space is still untouched.
I.e. there are some theoretical reasons to prefer a longer lifetime.
Unfortunately I don't know what they are.

Dave Ring
dwr2560@zeus.tamu.edu
From: h75@nikhefh.nikhef.nl (Henk Uijterwaal)
Newsgroups: sci.physics
Subject: Re: TOP-quark reactions and mass limit question
Date: 21 Aug 92 19:06:08 GMT
Reply-To: h75@nikhefh.nikhef.nl (Henk Uijterwaal)
Followup-To: sci.physics
Distribution: world
Organization: Nikhef-H, Amsterdam (the Netherlands).

In article <1992Aug21.094507.1@tnclus.tele.nokia.fi> hporopudas@tnclus.tele.nokia.fi writes:
 
>As an amateur physicist I would like to ask is any of the following reactions 
>possible. ?
>                  +
>        t -> b + e  + nu_e
>
>                   +
>        t -> b + my + nu_my
>
>                    +
>        t -> b + tau + nu_tau

The W in t -> b W will immediately decay into quarks or leptons, just
as the b will fragment into a jet. The reactions you describe are in fact:

                  t -> b + W     

followed by  decays of the W and b in parallel, for example:

                  W -> e+ + nu_e
                  b -> jet

and are therefore not only possible but in fact very clean signal for 
top-event. After one of the the reactions described by you, you'll find
an isolated lepton, missing energy (from the nu_x) and a jet in your
detector. It shouldn't be to hard to trigger on those kinds of events.
 
>   And if these are possible, then would these affect the limit
>   mentioned first ( > 91 GeV ). ?

No, they are already included in the mass limit.

Henk.
Newsgroups: sci.physics
From: matmcinn@nuscc.nus.sg (Mcinnes B T (Dr))
Subject: Re: Origin of universe as quantum fluctuation?
Organization: National University of Singapore
Distribution: na
Date: Fri, 14 Aug 1992 02:40:55 GMT

Scott: Physics would be impossible if we keep worrying about new physics
around the corner for which there is no evidence. I think we can say the
following.
About the "start" : GR certainly indicates that there was no "start" of
the  universe: the timelike geodesics have no beginning, just as the
open interval (0,1) has no beginning. Now quantum effects may possible
alter this in some way: BUT there is absolutely no reason to expect that
they will replace (0,1) by a closed interval [0,1]. The onus is on those
who believe this to prove it. BUT having your geodesics defined on [0,1]
is the only way to define the "beginning". So it is still reasonable to
think that there was NO beginning. Probably the (0,1) will be replaced
by something far more exotic. But that will not be called a "beginning".
Likewise for "before the BB". It is certainly meaningless in GR, and
there is absolutely no reason to expect that quantum effects will give
it any meaning. So the reasonable attitude is to suspect that "before
the BB" really is meaningless.
Newsgroups: sci.physics
From: dwr2560@zeus.tamu.edu (RING, DAVID WAYNE)
Subject: Re: the nature of exclusion
News-Software: VAX/VMS VNEWS 1.41    
Organization: Texas A&M University, Academic Computing Services
Date: Tue, 18 Aug 1992 13:29:00 GMT

carl@aoa.aoa.utc.com (Carl Witthoft) writes...
>An interesting continuation of this: if you pull enough energy
>out of the right fermionic system and squish it enough, fermions
>occasionally pair off to form boson-like units.  These units then
>drop into a common energy state.  Cold He3 is one example, if I
>remember correctly :=).

This one has always bugged the heck out of me. Say A1 and A2 pair up
and B1 and B2 pair up. And each pair is in the same quantum state, then
either A1 is in the same state as B1, or A1 is in the same state as B2.
Both of which are forbidden. What's wrong?

Dave Ring
dwr2560@zeus.tamu.edu
Newsgroups: sci.physics
From: sichase@csa2.lbl.gov (SCOTT I CHASE)
Newsgroups: sci.physics
Subject: Re: Annihilation?
Date: 13 Aug 92 20:43:57 GMT
Reply-To: sichase@csa2.lbl.gov
Distribution: na
Organization: Lawrence Berkeley Laboratory - Berkeley, CA, USA
NNTP-Posting-Host: 128.3.254.197
News-Software: VAX/VMS VNEWS 1.3-4

In article <mcirvin.713731150@husc8>, mcirvin@husc8.harvard.edu (Mcirvin) writes...
> 
>You said that S-states could only decay into even numbers of 
>photons... in the terminology that I usually use, the designations
>"S" and "P" refer to the spatial part of the state, so both ortho-
>and para-positronium would be S states in their lowest-energy
>incarnations, though only the para version would be the ground
>state.
> 
>Was I wrong to say that the spin-aligned version can decay
>into three photons, even if it's spatially in an S wave?
>I'm trying to think whether parity messes this up, but
>my brain is going fuzzy.  Certainly there are no problems
>with angular momentum conservation.
> 

Sorry.  I should have said J = 0 and J = 1 states.  S and P 
are correctly reserved for the spacial wavefunctions.  
As far as S states decaying into 3 photons, I seem to remember
that it doesn't happen.  Your parity argument may be correct.
To be perfectly honest, I have to go look it up.

-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
Xref: sparky sci.physics:13242 sci.skeptic:14782 alt.folklore.science:3083
From: mstemper@ems.cdc.com (Michael Stemper)
Newsgroups: sci.physics,sci.skeptic,alt.folklore.science
Subject: Re: The dangers in microwaved food...
Date: 21 Aug 92 16:32:58 GMT
Reply-To: mstemper@ems.cdc.com
Followup-To: sci.physics
Organization: Empros Systems International, a division of Ceridian

In article <1992Aug20.200552.12599@elroy.jpl.nasa.gov>, david@euclid.JPL.NASA.GOV (David Bernath) writes:
|> 
|> >>In article <1992Aug20.015531.7842@nuscc.nus.sg> matmcinn@nuscc.nus.sg (Mcinnes B T (Dr)) writes:
|> >>there are serious health risks in eating.
|> >
|> >There are serious health risks.
|> 
|> Health is a serious risk.

Risk is healthy.

-- 
#include <Standard_Disclaimer.h>
Michael F. Stemper
Power Systems Consultant
mstemper@ems.cdc.com
Newsgroups: sci.physics