HDTenEightyP/NetNews huggingface dataset:
From: mcirvin@husc8.harvard.edu (Mcirvin)
Newsgroups: sci.physics
Subject: Re: Converting the masses
Date: 23 Jul 92 15:06:54 GMT
Article-I.D.: husc8.mcirvin.711904014

palmer@sfu.ca (Leigh Palmer) writes:

> "Mass" as you use it
>is equal to neither inertial nor gravitational mass as those terms apply to
>any system more complicated than a particle at rest! 

Which only illustrates that those concepts are only really useful in
the context of Newtonian physics, IMHO.

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

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.

>For the benefit of those too young to know I will point out that this con-
>vention has changed over the years. It caught on about 25 years ago and has
>been a problem ever since, especially conceptually. People actually believe
>that there is *scientific* justification for their positions regarding this
>convention. It is exactly as scientific as the observation that the bird we
>North Americans call a "robin" is not a *true* robin!

Here I do agree with you: the distinction really is semantic, and
the only real justifications for the new convention are pedagogical
or utilitarian.  I think that the new convention *should* be taught
to elementary physics students, along with a four-vector treatment
of SR when we teach them SR, but we must keep in mind that it is a 
convention used because it is more useful than the alternative, and
not a matter of physical fact.
 
>Actually the *only*
>justification for the current convention is that one would have to use the 
>term "rest mass" rather more frequently in particle contexts than the term 
>"relativistic mass". In earlier times both terms were used to minimize con-
>fusion.

One wouldn't use the term "relativistic mass" at all, actually.  It's
useless unless you must hang onto a formulation of relativity in
terms of three-dimensional quantities, and is of limited use even
there.  I do say "rest mass" when I want to be absolutely clear,
though.  There's no chance for ambiguity if you do.

-- 
Matt McIrvin   mcirvin@husc.harvard.edu   Long live short .sigs
Newsgroups: sci.physics
From: tenney@med.unc.edu (Charles R. Tenney)
Subject: Jacob's Ladders (was Re: What are those things called...)
Organization: UNC-CH School of Medicine
Date: Fri, 24 Jul 1992 19:33:06 GMT

In article <1992Jul24.134854.9052@lut.ac.uk> A.J.Robinson@lut.ac.uk (Alan Robinson) writes:
>In article <1992Jul23.214214.8574@microplex.com> hsk@microplex.com (Harjeet Kalsi) writes:
>>
>>I know I've seen them in physics labs (including mine when I was in school) 
>>but forgotten what this "box" with two antennas, that has a high
>>voltage spark travelling between the antennas from bottom to top,
>>is called.
>>
>
>I think they're called Jacob's ladders, but I could be wrong.

Yes, that's what they're called.  I have one at home, made out of a neon
sign transformer and some coathanger wire.  Two wires are attached, one to
each high-voltage terminal, such that they come almost together, then rise
vertically, almost parallel but diverging slightly.  On mine, the gap is
about 1/4 inch at the bottom and 1-1/2 inch at the top (about 2 feet
tall).  The spark forms at the bottom, and the (ionized, therefore
conductive) air in the spark is heated and so rises.  The spark travels up
to the top, and beyond, at which point it ceases to conduct and a new
spark starts. It takes a bit of fiddling (run, unplug, bend wires, plug in
again, etc.) to get it right so the gap is not too wide at the top, the
spark doesn't rise to the top and stay there, etc.  You need substantial
couthangers (not the cheap thin ones) to make it work, the thin stuff has
a tendancey to start vibrating.

Lots of fun, and easy to build if you have a neon sign transformer.  But
if anyone decides to try this, FOR GOD'S SAKE, BE CAREFUL.  15 to 30 kV  
deserves a lot of respect, and due caution.  Especially in an unshielded
configuration.  If you can't be careful, don't try it at all, and don't
blame me for any accidents.


-- 
--
Charles R. Tenney	tenney@med.unc.edu   | What would the UNC school of
					     | Medicine want with my opinions?
	"My karma ran over my dogma."	     | What would I want with theirs?
Newsgroups: sci.physics
From: gast@next.ben-fh.tuwien.ac.at (Gast)
Subject: Re: Relativity and Quantum Mechanics
Organization: Technical University of Vienna
Distribution: usa
Date: Wed, 22 Jul 1992 13:05:07 GMT

In article <1992Jul21.032510.6139@leland.Stanford.EDU>  
zamenhof@leland.Stanford.EDU (Daniel Fish) writes:


> Now, observer A will see one flash happen before the other.  Is there  
not
> some sense in which the second flash is already determined at that time,
> for that observer?  If so, is this a philosophical problem for QM,  
having
> a truly random event, such as a nuclear decay, somehow predetermined?

Here is an explaination:

Both events of flashing are'n simultanious in observer A's system. And  
there is NO chance of being predetermined, because in this case the later  
flashlight had to get the information 'the earlier one has flashed' from  
observer B outside BEFORE it flashes, which is impossible if the signal  
from B moves at c. Therefore the Information of the observer B can not be  
used, there is no predetermination.


But another well-known paradoxa is this:

Imagine a particle with a determine spin which 'explodes' in two particles  
with undetermined spins and equal masses. The seperate from each other in  
a large distance and their spin is undetermined. When they are far away  
their spins are measured simultaniously By observers A and B (in the  
center-of-mass-system, syncronized for example by a flash at the time of  
explosion). Each observer A and B could measure various spins, which are  
determined at the time of measurement. On the other hand these spins have  
to be correlated because of the initial spin of the exploding particle. So  
the particle at A has to know SIMULTANIOUSLY which spin is measured by B,  
the signal has to move with infinity speed, contradictive to the SR.

This is a summary of the EINSTEIN-PODGOLSKY-ROSEN-experiment (I hope I got  
the names right).

So long

Harry
From: aephraim@physics.Berkeley.EDU (Aephraim M. Steinberg)
Newsgroups: sci.physics
Subject: Re: Unprovable true statements (was Structure of Time)
Date: 30 Jul 1992 20:17:05 GMT
Organization: University of California, Berkeley
NNTP-Posting-Host: physics.berkeley.edu

In article <Jul.29.19.56.44.1992.22038@ruhets.rutgers.edu> bweiner@ruhets.rutgers.edu (Benjamin Weiner) writes:
>Dave Chaloux writes:
>>Yaron Sheffer writes:
>>>This one's easy: Truth is measureable in the lab, or observable in the
>>>Universe, and in any case should be consistent and causal with anything
>>>that we have ever observed/measured ...
>>
>>I was under the very definite impression that mathematicians have shown that
>>the number of true statements is a larger order of infinity than the number of
>>proofs and that therefore there are true statements that cannot be proved.
>>If I am wrong, I'm sure this will be pointed out 8), but if true this should
>>make one think twice about statements like the above.
>
>If you're talking about incompleteness theorems, I'm not sure I would
>phrase it the way you did, but it is in general true that with a finite
>system of axioms there are statements which are true but cannot be
>proved (thus the axioms are incomplete, hence the name).  

Yes, this is what Godel's theorem says.  As far as the "order of infinity"
claim, I'm pretty sure that's wrong.  Godel's theorem is premised on axiomatic
systems in which statements and proofs can be coded into finite (but
unlimited, if I can phrase things thusly) strings of a finite number of
characters, so both the set of all true statements and the set of all
valid proofs seem to me to have the same size-- aleph-one, perhaps?
Anyway, that doesn't exclude non-overlapping regions, even if one (true
statements) is known to contain the other (valid proofs).  Cf natural
numbers and even numbers.

-- 
Aephraim M. Steinberg                    | "WHY must I treat the measuring
UCB Physics                              | device classically??  What will
aephraim@physics.berkeley.edu            | happen to me if I don't??"
                                         |       -- Eugene Wigner
Newsgroups: sci.physics
From: gast@next.ben-fh.tuwien.ac.at (Gast)
Subject: Re^2: Twins Paradox Resolved
Organization: Technical University of Vienna
Date: Wed, 22 Jul 1992 14:47:45 GMT

In article <1992Jul22.130948.18912@cs.ucf.edu> clarke@acme.ucf.edu (Thomas  
Clarke) writes:
> In article <BrrztE.J4u@well.sf.ca.us> metares@well.sf.ca.us (Tom Van  
Flandern)  
> writes:
> > 
> > {reiteration deleted}
> >     For those unfamiliar with SR, SR implies that events synchronized  
in one
> >frame will not be synchronized (= simultaneous) in a relatively moving  
frame.
> 
> Not true.

It is true. Two events that happen simultaniously in one system don't in a  
system which is moved in respect to the former system.

Harry
Newsgroups: sci.physics
From: mw@irfu.se (Mattias Waldenvik)
Subject: Re: Noah's formation: The rainbow
Date: Thu, 23 Jul 1992 13:54:57 GMT
Organization: Swedish Institute of Space Physics, Uppsala, Sweden

In article <2A6DEF17.1804@ics.uci.edu> bvickers@ics.uci.edu (Brett J. Vickers) writes:
>peterk@public.sub.org (Peter Kittel) writes:
>>Is it only me or does the sky beneath a rainbow also appear lighter
>>to others than the sky above a rainbow (or wait, was it the other way
>>around?)? But anyway, for my eye there is definitely a jump in
>>brightness of the background sky (normally rain clouds) from beneath
>>to above the rainbow. Any explanation for this?
>
>Optical illusion?  Two fields of the same color, separated by a line
>of a brighter or darker color, give the optical illusion that one half
>is lighter than the other.  The trick is to cover the line and see that
>they are the same.  I've never tried this with a rainbow.
>
>--
> ___            _    _     _  _        _
>(  _) ___ ___ _( )__( )_  ( )( ) o  __( ) _  ___  ___  ___
>(___)(_) (__=) (_)_ (_)_   (__) (_)(_((_)(_'(__=)(_) _(_)
>Brett Vickers (bvickers@ics.uci.edu)

	It is not an illusion, actually it is even more pronounced
	on a photography of rainbows. A set of rays impinging on
	a raindrop and reflected once inside the drop is "bunched"
	in a certain angle, giving rise to the primary rainbow.
	Rays reflected twice inside the drop give rise to the
	secondary rainbow and so on, as explained in earlier posts.
	With this in mind it is then not too hard to understand
	why there is a dark band between the primary and the
	secondary rainbow.

	For this handwaving explanation of the rainbow it is
	not necessary to assume that the raindrops are spherical.
	I read somewhere that raindrops actually are shaped more
	like hamburgerbuns. It would be an interesting problem
	to try to calculate the shape of a raindrop from a given
	rainbow, then again inverse scattering isn't my strong side.

					Cheers, mw
-- 

-----------------------------------------------------------------------------
	Mattias Waldenvik			Phone:	intl.+46 18 303674
	Swedish Institute of Space Physics	Fax:	intl.+46 18 403100
	Uppsala Division
	S-755 90 Uppsala, Sweden		mw@irfu.se
-----------------------------------------------------------------------------
From: kriman@acsu.buffalo.edu (Alfred M. Kriman)
Newsgroups: sci.physics
Subject: Re: Blue Sky
Summary: *** The sky is purple.  ***  People are blue.  ***
Date: 26 Jul 92 06:40:28 GMT
Organization: "UB" = State Univ. of New York at Buffalo

In article <1099@kepler1.rentec.com> Andrew Mullhaupt (andrew@rentec.com)
asked:
>Why is the sky blue?

   In the ravel of thread that followed, a consensus developed for the
standard "correct" answer of Rayleigh scattering.  As has been noted in
many posts, this perception is not just a question of physics.  In fact,
the standard answer would yield not a blue sky but a PURPLE one, if our
eyes were equally sensitive throughout the spectrum of "visible" lights.
(It's why we speak of ultra-_violet_, and not "ultra-blue".)
   It is well known that our eyes are in fact most sensitive in the
_green_.  My understanding (though I am not a biologist) is that the
increasing sensitivity with wavelength, and the decreasing intensity of
Rayleigh-scattered light, are the dominant factors combining to produce
the observation of a blue sky.  Of course, the complex way that we combine
information from three kinds of cones in our retinas to obtain a color
judgement, as well as the frequency-dependence of the solar radiation
filtered to the earth's surface, are also factors.
   The question of blue animals, apart from blue birds, has also arisen.
Clearly, they are less common, and some of the bright examples have been
given.  No one has mentioned people, however.  There are two instances
I can think of, apart from those found in Jazz and in a movie made by a
certain 1960's rock quartet.
(1) The Blue Berbers:  I don't know if this tribe persists, or if it keeps
to its old sartorial habits, but once the group was wont to wear robes dyed
a deep blue with indigo.  The color "rubbed off" (more likely sweated in)
and these people had appreciable amounts of indigo dye in their blood-
streams.  Their skin had a slight blue tinge.
(2) Pale-skinned people of partial color:
 (a) With veins close to the skin.
 (b) With the "Mongolian spot," (although, either through biology or
     through the use of one term for too many phenomena, this is not in all
     cases blue).  (For more details, please ask someone who actually has
     or had this pigmentation phenomenon.  I only know from veins.)

>P. S. I have an idea, but I'd like to collect answers from physicists.
>I sometimes use as a philosophical example 'go ask a physicist why the
>sky is blue, and he'll likely say...' and I would like to be honest
>about it. It's been a while since I actually asked any physicists this
>question, so here goes.

P.S.  Why does everybody forget blueberries when talking about blue foods?
Some crabs?  Aren't blue whales blue?  Do blue-fin tuna have blue fins?
Also, insects are animals, a few of these blue.  They might even be edible,
if you're hungry enow.

P.P.S.  The question was raised, why leaves are green.  Presumably this is
because most chlorophyll absorbs in the red.  But will someone explain
"chlorophyll a" and "chlorophyll b," and the algae colors?

Al_Kriman> cat flames >/dev/null.
From: MEDELMA@cms.cc.wayne.edu (Michael Edelman)
Subject: Re: Cost of public vs. private transportation
Organization: Wayne State University, C&IT
Date: Thu, 23 Jul 1992 13:58:38 GMT

It's certainly impossible to dispute that shared transportation on a
limited number of routes appears cheaper than individual transport on a
wider number of routes, but can be misleading to make that comparison.
First, it's very difficult to assign costs given the difficulty of
determining the cost vs. utility of the various public goods involved
(roads, pollution, etc.) It's easy, though, to look at actual individual
behavior to see how people act in evaluating the relative utility and
cost of the different systems.
 
In public transportation systems the bulk of the cost is born equally
by everyone regardless of its utility to them. I don't think you can
find a public transportation system anywhere in the world that covers
its operation costs from revenues, let alone its capitalization, thus
operating revenues and capital costs must be recovered via general revenues.
This is a strong argument that people would not actually pay the real costs
of public transit if they were assigned to the end users only.
 
But people are willing to pay a larger fraction of the cost of individual
transport, above and beyond capital and operational costs. The pay tax on
the vehicle, license fees, government mandated insurance and so forth.
Whether auto owners actually cover the costs of public roads is debateable,
but the most common form of public transport uses the same roads.
 
That leaves the costs of pollution. This is typically taxed in most states,
too, in the form of air-quality testing and mandated controls.
 
I don't know if it's possible to assign the actual costs of public versus
private transportation in a way that all will agree, but I think a very good
case can be made for the argument that in the case of private transportation
there is more perceived utility and more willingness to assume direct costs.
From: matmcinn@nuscc.nus.sg (Mcinnes B T (Dr))
Newsgroups: sci.physics
Subject: Re: Destroying the Earth
Date: 29 Jul 92 01:55:54 GMT
Organization: National University of Singapore

Dave RIng: Spoilsport. :)   But no, seriously: suppose we use some more
or less realistic version of interior Schwarzschild, and consider the
Earth to have been compressed to a sphere with srface area slightly
greater than 4 pi x [Schwarzschild radius]^2   [Schwarzschild r does
accurately measure area] then this sphere should have a well-defined
radius. I wonder if anybody has estimated it. If,as I suspect, it turns
out to be totally different from the S radius, then that would be rather
interesting.
Organization: Penn State University
Date: Fri, 24 Jul 1992 16:41:28 EDT
From: <MRG3@psuvm.psu.edu>
Newsgroups: sci.physics
Subject: Re: ***********MIND-BLOWING GEDANKENEXPERIMENT**********

If this is indeed the proposal from Physics Essays, then I have a few comments:
That proposal has a fundamental, but subtle flaw, which may remain in this
proposal.

In Sarfatti's Physics Essay article, he uses a spin-flip process to
disentangle the correlated states:
        (|v1>|v2>+|h1>|h2>)/(sqrt(2))
becomes
        (|v1>|v2>+|h1>|v2>)/(sqrt(2))
which is
        (|v1>+|h1>)|v2>/(sqrt(2)).

 This is clearly the source of the problem, for if this REALLY describes
a linear evolution on system 2 only, then it does not in general
conserve probability, as seen by the fact that it implies
     |h2> -> |v2>
     |v2> -> |v2>
so that
     |h2>+|v2>  -> 2|v2>
and
     |h2>-|v2>  -> 0  (normalize this final state ;)

    On the other hand, we can interpret the dynamics as being
     |h1>|h2> -> |h1>|v2>
     |v1>|v2> -> |v1>|v2>
    which, with normal QM results in a transition matrix

    hh  hv  vh  vv
 hh 0   1   0   0
 hv 1   0   0   0
 vh 0   0   1   0
 vv 0   0   0   1

which is nonlocal in that it does not factor into a product involving
independent evolution.  Hence, it is Sarfatti's nonlocal spin-flip
which introduces the  FTL communication possibilities, and not
the original entanglement of the of the two photons.

Surely someone has already pointed this out in the literature.
It seems analogous to the demonstration that you "can't clone
a quantum" (Wooter's & Zurek?). If note, can somebody send me the
editor's adress at Physics Reports. ;)


It might be useful if some quantum optics person where to actually
describe for us the quantum mechanics of polarization rotation.

mike gallis
PENN STATE SCHUYLKILL CAMPUS
200 UNIVERSITY DR
SCHUYLKILL HAVEN, PA 17922
BITNET: MRG3@PSUVM.PSU.EDU
PHONE:
(717) 385-6053 (OFFICE)
(717) 754-3097 (HOME)
From: sichase@csa3.lbl.gov (SCOTT I CHASE)
Newsgroups: sci.physics
Subject: Re: Converting the masses
Date: 21 Jul 92 20:39:44 GMT
Organization: Lawrence Berkeley Laboratory - Berkeley, CA, USA
Distribution: na
Reply-To: sichase@csa3.lbl.gov
NNTP-Posting-Host: 128.3.254.198
Keywords: four-vectors
News-Software: VAX/VMS VNEWS 1.3-4   

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. 
>>
>   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.  Space-time is four-dimensional,
with each point being represented by a 4-vector in some arbitrary coordinate
system as (t,x,y,z).  All the equations of relativity (and any theory 
such as quantum field theory which you want to express in a relativistically
invariant way) are constructed in terms of 4-vectors and 4x4 matricies which
operate on the 4-vectors.  Other examples are the energy-momentum 4-vector
(E,px,py,pz) and the gradiant operator (dt,dx,dy,dz).  

Every four-vector transforms the same way under Lorentz boosts.  Therefore,
energy transforms like the time, while momentum transforms like a length.

When you get down to the nitty-gritty, things get a little more complicated, 
so that my last statement is not exactly true.  There are two classes of
4-vectors:  covariant and contravariant, which transform somewhat differently
under the Lorentz transformations. 

Reference:  Taylor and Wheeler's _Spacetime Physics_ is the classic. 

-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
Newsgroups: sci.image.processing
From: rstewart@ganglia.megatek.uucp (Rich Stewart)
Subject: Re: Spatial versus grey-scale resolution
Reply-To: megatek!rstewart@uunet.uu.net
Organization: Megatek Corporation, San Diego, California
Date: Tue, 21 Jul 1992 17:51:41 GMT

In article <1992Jul17.185546.7669@rz-berlin.mpg.de> van_heel@rz-berlin.mpg.de writes:
>
>      My specific question:  can I use a 512x512x8 bit CCD chip to obtain 
>      a 256x256x10 bit image?
>
>     
>
>   PS.   Please E_mail me your answers/suggestions directly since
>         I will not be at my desk for the next weeks and will
>         thus not be able to read this news-group
>
>
>-------------------------------------------------------------------      
>
>      Marin van Heel 
I did as the author requested, but then I thought this might be also
interesting to the group at large...


No, you can not even use an 8 bit CCD to get a good 8 bit image. They
tend to be horribly non linear in the lower order bits. 
There was a company making something that could get 2k images out
of a 512 ccd. They basically shook it alot and interpolated the data.
The results looked good. Oh wait, here is a idea. You could
take an 8 bit CCD, and if you knew its freq. resp. curve characterizations,
you could capture multiple exposures with different integration times, and
interpolate the color out to a greater bit depth.

Has anyone out there done this? Of course you had better have a still object.
-Rich
  rstewart@megatek.com
  rstewart@megatek.uucp
  ucsd!megatek!rstewart
From: bellutta@cascade.ohsu.EDU (Paolo Bellutta)
Newsgroups: sci.image.processing
Subject: Re: Datacube
Date: 20 Jul 92 22:59:17 GMT
Article-I.D.: ohsu.1992Jul20.225917.2880
Organization: Oregon Health Sciences University

In article <1992Jul20.221850.11457@ctr.columbia.edu>  
sion@sioux.ctr.columbia.edu (Boudi Sahyoun) writes:
> 
> Any datacube experts around here?

There is a datacube mailing list. To be added to the list send e-mail to:
datacube-list@media-lab.media.mit.edu

--
 _   /|  | Paolo Bellutta ---------- bellutta@ohsu.edu
 \'o.O'  | B.I.C.C - Oregon Health Sciences University
 =(___)= | 3181 SW Sam Jackson Park Rd. - Portland, OR
    U    | tel: (503) 494 8404 --- fax: (503) 494 4551
Newsgroups: sci.image.processing