HDTenEightyP/NetNews huggingface dataset:
From: gast@next.ben-fh.tuwien.ac.at (Gast)
Subject: Re: A long-winded primer on four-vectors (part 1)
Organization: Technical University of Vienna
Date: Wed, 22 Jul 1992 12:34:54 GMT

In article <1992Jul21.182314.14031@husc3.harvard.edu>  
mcirvin@husc8.harvard.edu (Mcirvin) writes:

> Likewise, a four-vector in the xt plane (t = time!) transforms
> like this under a velocity boost with "rapidity parameter" phi:
> 
> x -> x' = x cosh phi + t sinh phi
> t -> t' = x sinh phi + t cosh phi 
> 
> where by x and t, I mean the corresponding vector components.
> 
> Cosh phi is the famous time dilation factor, gamma, which
> is 1/sqrt(1-v^2/c^2), with v the relative velocity.  Sinh phi
> is gamma times v/c, or just gamma*v if c = 1.  Quantities
> such as velocity, energy, and momentum can be expressed in terms
> of four-vectors, making notation more compact and easy to
> handle, and making it obvious when something is a relativistic
> invariant and when it isn't.  

The article was a prety good overview about the subject of four-vectors.  
Yet, two short remarks:

Remark 1:
If you don't set c=1, the coordinates of a point in a Minkowsky-space are  
(if any doubt, consider the units):

 a
x = (ct,x,y,z)  (a is an upper index)

Therefore the transfromation above has to be

   x -> x' = x cosh phi   + ct sinh phi
   t -> t' = x/c sinh phi +  t cosh phi 

Remark 2:
Because of the metric there are two kinds of coordinates neccessary. For  
example the space-vector is given as
 
                    a
   contravariant:  x  = (ct, x, y, z)  (a is an upper index)  

   covariant:      x  = (ct,-x,-y,-z)  (a is a lower index)
                    a

The relationship between a contravariant and a covariant vector is given  
as
                  b
    A    = g   .A      where g    is the described metric tensor
      a      ab                ab

The dot product is aways defined as the product of a covariant and a  
contravariant vector, which explains the minus sign:

              a              a
    A.B :=  A  .B   = A   .B
                  a     a

For example the absolut square of the space-vector is:
      a
    x  .x   = (ct).(ct) + (x).(-x) + (y).(-y) + (z).(-z)
          a

      a        2 2    2    2    2
    x  .x   = c t  - x  - y  - z
          a

I hope this two remarks are comprehensible, too.

--
Harry
Newsgroups: sci.physics
From: matmcinn@nuscc.nus.sg (Mcinnes B T (Dr))
Subject: Re: Twins Paradox Resolved
Organization: National University of Singapore
Date: Thu, 23 Jul 1992 05:24:21 GMT

[continued]...I wonder what happens to the twins when spacetime is flat
but the spatial sections are flat three-folds of non-trivial holonomy?
From: jac@ds8.scri.fsu.edu (Jim Carr)
Newsgroups: sci.physics
Subject: Re: scientific literature
Date: 27 Jul 92 21:11:59 GMT
Reply-To: jac@ds8.scri.fsu.edu (Jim Carr)
Distribution: na
Organization: SCRI, Florida State University

In article <JMC.92Jul26142559@SAIL.Stanford.EDU> jmc@cs.Stanford.EDU writes:
>The critical criterion for a scientific journal these days is whether
>the articles are subjected to peer review as a criterion for being
>published.  _Scientific American_ doesn't do this, and the articles

I would not consider S-A to be a "journal" because of the level of 
their articles, but they are reviewed rather carefully.  I think they 
might even exceed the level of editorial intervention in the "Annual 
Review of Nuclear and Particle Science", which is a journal where the 
authors are selected for a given subject based on their track record 
in the peer-reviewed literature.  I know someone who has been published 
in Sci-American, and should ask him about the experience.  I do know 
that the article was a spin-off of a slightly more technical article 
in Nature that was itself a spin-off of a *very* technical paper in 
Rev. Mod. Phys.  In some ways, Sci-American does meet your criteria 
below concerning what role a referee should have in the process. 

>in the _News and Comment_ section of _Science_ aren't either.  Neither
>are the articles in _Technology Review_ or the articles in the
>National Academies' _Issues in Science and Technology_.  My opinion
>is that there should be a refereed magazine dealing in popular
>language with issues arising out of science and technology.  The

This is difficult, since the very act of simplifying language can 
lead to lack of clarity and the attendant conflicts over content. 
The letters to Sci-American where the authors reply that they had 
intended to discuss <matter x> but it was cut by the editors are 
clear indications of the hazards in such an endeavor.

>refereeing might have a different character than standard scientific
>refereeing.  The referees couldn't reject an article on the grounds
>that the author was wrong, but they could make him deal with a
>consideration he was ignoring.

I think you would have a hard time finding people to referee papers 
under those conditions.  It is an onerous enough task as it is (said 
as I take a break from 50 pages of text and figures that I am re-reading 
before writing my report later this evening) let alone under such 
circumstances.  But there *is* at least one such journal at present. 

And no, I will not name it on the net ....

--
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)
Newsgroups: sci.physics
From: bj368@cleveland.Freenet.Edu (Mike E. Romano)
Subject: Re: Low Tech is Best
Organization: Case Western Reserve University, Cleveland, Ohio, (USA)
Date: Thu, 23 Jul 92 03:38:18 GMT


Actually my original question is poorly worded.
I am not an engineering major so I do not know the applicable formulas.
Also my title is misleading and probably creates wrong impression.
The physics problem is simply this:
can a suitable wire transfer mechanical or work energy with less loss
over a long distance (say a quarter mile) than an electric line of
similar length?
I am not stating that human labor is superior to machine labor, nor
that we should return to the pre industrial era.
-- 
            Mike Romano     Univ. Calif. Berkeley
Newsgroups: sci.physics,sci.astro,sci.philosophy.tech,talk.religion.misc
From: billn@hpcvaac.cv.hp.com (bill nelson)
Subject: Re: Structure of Time
Organization: Hewlett-Packard Company, Corvallis, Oregon USA
Date: Wed, 29 Jul 1992 01:50:45 GMT

crb7q@kelvin.seas.Virginia.EDU (Cameron Randale Bass) writes:
: >
: >You were asked a number of times to take your postings somewhere else
: >where they would be appreciated. You ignored the requests - you deserve
: >to suffer the consequences - whatever they may be.
: 
:      Just curious.  Too much coffee?
: 
:                               dale bass

Nope - don't drink the stuff. Just tired of junk like that being posted
to a sci group. But then, all the stuff we are posting doesn't further
the cause of science either.

I think it is time to terminate the thread and return control of the
television to the watcher.

Bill
From: jbaez@riesz.mit.edu (John C. Baez)
Newsgroups: sci.physics
Subject: Re: Cost of public vs. private transportation
Date: 31 Jul 92 14:08:17 GMT
Organization: MIT Department of Mathematics, Cambridge, MA

In article <1992Jul30.142935.7199@ke4zv.uucp> gary@ke4zv.UUCP (Gary Coffman) writes:
>In article <1992Jul28.155151.3676@aero.org> foy@aero.org (Richard Foy) writes:
>>Do the figures of cost of highways include the cost of highway patrol, and of
>>a fair share of the judicial system?
>
>At least in Georgia, highway patrol and traffic court systems are net
>revenue producers. In many smaller jurisdictions, speeding fines are
>the sole source of revenue for local government. Georgia, home of the 
>original speed trap run by local parasites.

Could someone explain to me why this is in sci.physics, except for
reasons of tradition?   I'm getting tired of this newsgroup being
dominated by public policy disputes -- for the SSC it makes some sense,
but what the #$%#^ do speed traps in Georgia have to do with physics.

Of course, there's the old excuse, "I'm sorry officer, but the light was
blue-shifted so much it looked GREEN to me, not RED!"
Newsgroups: sci.physics,sci.astro,sci.philosophy.tech,talk.religion.misc
From: hporopudas@tnclus.tele.nokia.fi
Subject: Re: Structure of Time
Organization: Nokia Telecommunications.
Date: Tue, 28 Jul 1992 08:24:29 GMT


 Hi !

 Re: Structure of Time


   I'am very sorry that I have encounter here many peoples who seems to be
somekind of representative of "inquisition". I always belived that just
physicists love the truth most, what ever the truth is.
   These "inquisitors" have contacted to my employer and they have tried
to insalt me and my paper. My employment is in danger at the moment.



Oulu  -  Finland  28.7.1992  Hannu K. J. Poropudas

         "I promised never to lie to God"
From: steinly@topaz.ucsc.edu (Steinn Sigurdsson)
Newsgroups: sci.physics
Subject: Re: Converting the masses
Date: 22 Jul 92 17:25:38
Organization: Lick Observatory/UCO
	<1992Jul22.193837.18095@sfu.ca> <131163@lll-winken.LLNL.GOV>
NNTP-Posting-Host: topaz.ucsc.edu
In-reply-to: dk@imager's message of 22 Jul 92 22:32:18 GMT

In article <131163@lll-winken.LLNL.GOV> dk@imager (Dave Knapp) writes:



   In Article <1992Jul22.193837.18095@sfu.ca> palmer@sfu.ca 
   (Leigh Palmer) writes:

   > In order to illustrate my point, do you claim that a lump of
   > condensed matter has a the same mass as the sum of the masses of
   > its elementary constituents? Of course you don't.  That only
   > begins the parade of difficulties attendant to using the currently
   > fashionable definition outside its proper area of use.

   > To further confuse the beginning physics student you could explain
   > that the mass of that lump of matter is independent of its
   > temperature.

     This caricature of the "currently fashionable definition of mass"
   is pretty twisted.  Surely you can't be claiming that the use of
   "rest mass" as "mass" implies that one must use the sum of
   constituent masses to obtain the mass of an object?  If you are, then
   how do you think particle physicists define the proton mass?  As the
   sum of the masses of the constituent quarks?  Not likely.

     Hmmph.  I think I smell a straw man.  -- Dave

Nope. Define the mass of a neutron star, and consider that
most astrophycists will respond if asked: "baryonic mass
or gravitational mass?".
	Now for the tricky bit: given the distinction, explain
why a black hole's gravitational mass if non-zero and give an
operational definition...

*  Steinn Sigurdsson   			Lick Observatory      	*
* steinly@helios.ucsc.edu		"standard disclaimer"  	*
*  The laws of gravity are very,very strict			*
*  And you're just bending them for your own benefit - B.B. 1988*
From: mcirvin@husc8.harvard.edu (Mcirvin)
Newsgroups: sci.physics
Subject: Re: Converting the masses
Date: 24 Jul 92 16:16:37 GMT
Article-I.D.: husc8.mcirvin.711994597
 <9868@sun13.scri.fsu.edu> <1992Jul22.193837.18095@sfu.ca> <mcirvin.711904014@husc8> <24826@dog.ee.lbl.gov>
Distribution: na

sichase@csa2.lbl.gov (SCOTT I CHASE) writes:

>In article <mcirvin.711904014@husc8>, mcirvin@husc8.harvard.edu (Mcirvin) writes...
>> 
>>Actually, neither definition of mass would be temperature-independent,
>>if you define it for the whole lump of coal.  When you raise the
>>temperature, the energy in the rest frame increases!  The sum of
>>the masses of all the particles is perhaps temperature-independent,
>>but as you complained before, that's not the mass of the lump.

>But inertial mass *can* be termperature dependent.
[description of experiments with hydrogen]

That's what I said...  Oh, you mean of the individual constituents of
the object.  Yes, I imagine so; I was talking about the idealized
picture of atoms as billiard balls, not the situation in which they
have internal degrees of freedom.

This just illustrates further the fact that *no* reasonable definition
of mass, "rest" or "relativistic," is temperature-independent for an
object with internal structure.

-- 
Matt McIrvin   mcirvin@husc.harvard.edu   Long live short .sigs
From: flower@hpcc01.corp.hp.com (Graham Flower)
Date: Wed, 22 Jul 1992 18:33:24 GMT
Subject: Re: Helium Ballons in a Car (was Re: Air bubbles in a universe of water)
Organization: the HP Corporate notes server
Newsgroups: sci.physics


>One of my old physics Professors, Robert Romer at Amherst College, told
>our mechanics class about how he actually tried this, and showed his
>child/ren (I don't recall how many) how it worked that way, braking and
>accelerating, with the balloon behaving as described above.  As he turned
>onto his street going home, he heard an "Oh my God!" from the back seat as
>the balloon was observed leaning toward the INSIDE of the turn.  He hadn't
>anticipated that one, but it's obvious in hindsight.

>balloon doing the above behavior.  

  Your physics prof was nuts. There is a very easy way to demonstrate
  this effect to a class. Take an old Miracle whip jar and fill it with
  water attach a wine bottle cork to the lid using tape and allow it to
  float up in the water on a piece of string so that it replicates the
  balloon in the car scenario. (candle wax also makes a good attach to
  the lid) Then slide this rascal around on a table. It'll convince you 
  of the correctness of your expectations. 

  I got asked this question on my hp interview, the interviewer was less
  certain of the answer than I was so the above demo served to convince 
  him some monthes later.

  Try it. It works well.


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 endlessly.
San Jose, California, 95131          |
 graham_flower@sj.hp.com             |

Newsgroups: sci.physics
From: pyacm@trentu.ca (A Colin Morton)
Subject: Re: Blue Sky
Organization: Trent University, Ontario
Date: Thu, 23 Jul 1992 17:15:44 GMT

In article <1992Jul23.010953.6388@math.ucla.edu> barry@arnold.math.ucla.edu (Barry Merriman) writes:
>In article <10018@vice.ICO.TEK.COM> hall@vice.ICO.TEK.COM (Hal Lillywhite)  
>writes:
>> In article <9930@sun13.scri.fsu.edu> jac@ds8.scri.fsu.edu (Jim Carr) writes:
>> 
>> ....
>> >George did that routine before blue-corn became popular enough to 
>> >show up as corn flakes as well as tortillas, or squid-ink pasta made 
>> >it into american grocery stores.  Interesting that there are blue birds 
>> >and flowers but not blue animals; where is a biologist when we need one! 
>> 
>> And I find it peculiar that although there are blue birds, there are
>> no blue raptors that I know of.  Can you imagine the advantage a sky-
>> blue hawk would have?  His prey would have a very difficult time seeing 
>> him until it was too late.  I wonder why such an obvious advantage 
>> seems not to have developed.
>
>Actually, he should be blue on the bottom and dark on top,
>so that he ends up blending in when viewed from above or below.
>Thats "why" fish are silver on the bottom and dark on top, perhaps
>
Most raptors are, in fact, white or very light gray on their undersides,
with mottled brown top coats.  In most parts of the world inhabited by
hawks and the like, partly cloudy or hazy days far outnumber the
perfectly clear ones, so this actually works better than a blue
underside would -- white shows up less distinctly on a blue background
than vice versa.

Colin.
From: jac@ds8.scri.fsu.edu (Jim Carr)
Newsgroups: sci.physics
Subject: Re: Converting the masses
Keywords: four-vectors
Date: 21 Jul 92 18:57:24 GMT
Reply-To: jac@ds8.scri.fsu.edu (Jim Carr)
Organization: SCRI, Florida State University

In article <1992Jul21.141253.17366@jlc.mv.com> john@jlc.mv.com (John Leslie) writes:
>In article <mcirvin.711673227@husc8> mcirvin@husc8.harvard.edu (Mcirvin) writes:
>>dk@imager (Dave Knapp) writes:
>>
>>In fact, I think that a more important issue than the definition of
>>mass is the use of four-vectors in introductory classes teaching SR,
>>which I think should be encouraged, since it brings beauty and
>>simplicity to something which otherwise looks like an algebraic junkheap  
>>built on a shifting foundation of paradoxes. 

Nice statement.  The "algebraic junkheap" was how I viewed it when I first 
tried to work through SR back in high school.  Of course, the following 
query tells you why intro classes do not use this particular formulation...

>   Could someone have mercy on those of us whose college physics is
>twenty or more years in the past?  What is "four-vectors"?

A "four-vector" is a vector with 4 components, normally used in physics 
when one wants to treat space and time as the 4 components of a single 
vector space called "space-time" for short.  It works just like regular 
geometry with "three-vectors" except the meaning of the distance between 
two points is altered in a significant way.  What is nice about this 
approach (besides the fact that it is crucial to use it if you want to 
do general relativity) is that it makes it very clear that the Lorentz 
transforms are just a rotation in this 4-space, and nothing more.

--
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: jac@ds8.scri.fsu.edu (Jim Carr)
Newsgroups: sci.physics
Subject: Re: Defining Photons
Keywords: Street Sheet Tech Briefs # 2
Date: 23 Jul 92 14:46:49 GMT
Reply-To: jac@ds8.scri.fsu.edu (Jim Carr)
Organization: SCRI, Florida State University

In article <3931@cruzio.santa-cruz.ca.us> snarfy@cruzio.santa-cruz.ca.us writes:
>
>                         STREET SHEET TECH BRIEF #2
>                       A QPKD FAX from Malnex at G-net
>                     Forwarded to the sci.physics forum by
>                               James Ostrowski
>                          (..netcom!cruzio!snarfy!)
>
>                Fundamentals of the Nature of Light and Matter
>
>        The  concept  of  the  ``photon'' seems to be a central issue in
>       discussions   we've   monitored   concerning   the   nature    of
>       electromagnetic  radiation  (EMR).   Your  renowned mathematician
>       and physicist, Einstein,postulated that a photon has no  ``rest''
>       mass.   We  are  faced  ,then,  with  the  task of relating these
>       theoretical ``particles'' that do not have a rest masses  to  the
>       equation E=Mc^2 since it is assumed that M represents a rest mass
>       value.

                   [ long argument based on wrong equation deleted ]

 The equation is 
                   E^2 = m^2c^4 + p^2c^2 

 where m is the mass, p is the momentum (vector), E is the total energy, 
 and c is the speed of light.  E=mc^2 is a specialized case of this 
 equation, and can be used to tell you the total energy of a massive 
 particle at rest.  It should not be applied to a massless particle 
 such as a photon or neutrino. 

 For massless particles, it is the case that E=pc.

 I find it odd that someone can spend a lot of time working on such a 
 document that was posted here and never take the time to read enough 
 of Einstein to know the actual equations he used.  

--
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)
Newsgroups: sci.physics
From: jmc@SAIL.Stanford.EDU (John McCarthy)
Subject: Re: "What's New" July-24-1992
Reply-To: jmc@cs.Stanford.EDU
Organization: Computer Science Department, Stanford University
	<24909@dog.ee.lbl.gov>
Distribution: na
Date: 26 Jul 92 12:42:13

Did I misread, or did the physicists oppose the Space Station, rather
than just say that, considered as science, it wasn't worth the money?
--
John McCarthy, Computer Science Department, Stanford, CA 94305
*
He who refuses to do arithmetic is doomed to talk nonsense.

Newsgroups: sci.physics
From: arw4@cunixb.cc.columbia.edu (Aaron R Wininger)
Subject: inertial fusion
Reply-To: arw4@cunixb.cc.columbia.edu (Aaron R Wininger)
Organization: Columbia University
Date: Mon, 27 Jul 1992 16:19:02 GMT

Does anyone know the state of research of inertial fusion is at?
How close to breakeven, compared to tokomaks? Is anyone besides LLNL is US or
world doing research on inertial fusion?
Thanks

_______________________________________________________________________________
Aaron Wininger                               Columbia Plasma Physics Laboratory
arw4@cunixb.cc.columbia.edu                                  New York, NY 10027
_______________________________________________________________________________
From: mcirvin@husc8.harvard.edu (Mcirvin)
Newsgroups: sci.physics
Subject: Re: Defining Photons
Date: 29 Jul 92 15:15:38 GMT
Article-I.D.: husc8.mcirvin.712422938

franl@centerline.com (Fran Litterio) writes:

>I'm not an expert on the subject, but I could swear that I've heard
>that Ohm's Law was never an exact description of reality in the first
>place (even before QM and relativity).  If so, the obvious question
>is: Does whatever passes for the modern replacement for Ohm's Law (if
>such exists) also lack a time parameter?

It's there even in the old-fashioned version of Ohm's Law.  The
voltage-current relation is derived, with various assumptions, from
the *local* statement E = j*rho, where E is the electric field,
j is the current density, and rho is the resistivity, all 
evaluated at the same place and time in a material for which a 
resistivity can actually be defined.  It's nonlocal to the extent
that you're averaging over atomic phenomena and over the time
required for transient effects to go away, but that's it.

You are right:  Ohm's Law was never interpreted as more than an
approximate description of a certain class of materials.

-- 
Matt McIrvin  mcirvin@husc.harvard.edu
From: vgurarie@phoenix.Princeton.EDU (Victor V. Gurarie)
Newsgroups: sci.physics
Subject: Re: The Modern Physicist in Calculus I
Date: 27 Jul 92 16:39:35 GMT
Organization: Princeton University
Originator: news@ernie.Princeton.EDU

In article <1992Jul27.054053.19462@nuscc.nus.sg> matmcinn@nuscc.nus.sg (Mcinnes B T (Dr)) writes:
>TA: And here we have the graph of y = 1/x, x>0. As you can readily
>verify, this is a perfectly well-behaved, continuous, indeed, infinitely
>differentiable function on the open set (0, infinity).
>Modern Physicist [excitedly] Clearly, we have here a SINGULARITY!
>y=infinity at x=0. This is totally unacceptable!
>TA: As I said, the domain is an open set. x=0 is excluded. There is
>nothing remarkable about that.
>MP: Nonsense! Next thing you'll be saying that there is nothing
>remarkable about the SINGULARITY at the beginning of the Universe! Then
>you will try to tell us that time is defined on an open set, and that
>there is nothing remarkable about that either!
>TA: Quite.
>MP: No! Everybody knows that the prediction about the singularity shows
>that "GR contains the seeds of its own destruction" [tm]. And now I
>begin to suspect that the graph of y = 1/x proves that freshman calculus
>also contains the seeds of its own destruction......
>
>Moral: Time is defined on an open set. Spacetime has no singularities.


   What a nonsense all that is! Look at this: if y=1/x, x belongs to
(0,infinity), then for any M there exist epsilon such that for all x
less than epsilon (and still belonging to the set) y(x)>M. This is a
singularity. The writer of the posting above should refresh his knowledge
of freshman calculus!
From: leon@unixg.ubc.ca (Leon ter Beek)
Subject: Gyromagnetic ratio of the proton
Organization: University of British Columbia, Vancouver, B.C., Canada
Date: Mon, 27 Jul 1992 19:15:52 GMT


Can someone indicate where I can find an accurate number for the
gyromagnetic ratio of the proton in SI-units [1/s*T].   

Leon