HDTenEightyP/NetNews huggingface dataset:
From: minsky@media.mit.edu (Marvin Minsky)
Newsgroups: sci.physics
Subject: Re: how do you do the one about an infinite mesh of 1ohm resistors ...
Date: 24 Jul 92 16:55:35 GMT
Organization: MIT Media Laboratory
Cc: minsky

In article <2798@ucl-cs.uucp> O.MostynOwen@cs.ucl.ac.uk writes:
>
>There's a problem I was told about years ago which I never managed to solve:
>
>You've got an infinite 2D grid if 1 ohm resistors. What's the resistance
>across 1 of them (no it's not 1ohm, 0 or infinity).
>
>              |                  |                   |
>         ------------1ohm-----------------1ohm------------
>              |                  |                   |
>              |                  |                   |
> .....      1ohm               1ohm                1ohm     .....
>              |                  |                   |
>              | A                | B                 |
>         ------------1ohm-----------------1ohm------------
>              |                  |                   |
>              |                  |                   |
>>
>I'd be grateful if someone laid this one to rest since it keeps on coming
>back to haunt me.

It's a superposition trick.  Imagine attaching a current source
between points A and B, and forcing 1 ampere through the circuit.
There's a theorem (I forget the name) which says that this is
equivalent to the sum of two separate experiments of forcing 1 amp
into A and of sucking 1 amp out of B.  The first experiment would push
1/4 amp into the resistor from A to B, and so would the second
experiment!  So we find that 1/2 amp flows through the resistor, hence
the voltage between A and B is 1/2 volt.  Then because R = E/I, we get
the resistance must be 1/2 volt over 1 amp at the terminals, so the
resistance is 1/2 ohm.  Wonderful example of a sort of circular reasoning.
Newsgroups: sci.physics
From: dwr2560@zeus.tamu.edu (RING, DAVID WAYNE)
Subject: Re: Trapped!
News-Software: VAX/VMS VNEWS 1.41    
Organization: Texas A&M University, Academic Computing Services
Date: Thu, 30 Jul 1992 23:02:00 GMT

baez@ucrmath.ucr.edu (john baez) writes...
>Smolin said this idea was the opposite of the anthropic principle in a
>sense.

It is if you consider anthropic principles to be fundamental. But I would
say that an anthropic principle just demonstrates our ignorance. Before
astronomy one might have felt lucky that earth had air to support life. One
might have argued that if it had been any other way,
we wouldn't be here to ask the question. But then when we learn that there
are many planets in the universe with various atmospheres, the question
seems a bit silly. 

Dave Ring
dwr2560@zeus.tamu.edu
Newsgroups: sci.physics
From: farrell@rhea.trl.oz.au (Peter Farrell)
Subject: Re: Noah's formation: The rainbow
Organization: Telecom Australia Research Labs
Date: Wed, 22 Jul 1992 00:26:55 GMT

Robert Greenler has written a wonderful book called _Rainbows , Haloes and
Glories_ which gives good explanations of the formation of rainbows and other
related phenomena with photographs, drawings, historical material and 
references. Highly recommended.
Peter.
From: matmcinn@nuscc.nus.sg (Mcinnes B T (Dr))
Newsgroups: sci.physics
Subject: Re: Aristotle and the Modern Physicist
Date: 27 Jul 92 05:02:37 GMT
Organization: National University of Singapore

Dave Ring: The gravitational constant measures the correlation between
the Einstein tensor and the presence of matter. It is not a coupling
constant. In this connection: the Einstein equation is in no way
comparable to, say, Maxwell's equation. There can be no question of
prescribing the sources and then solving for the field.
Feynman was fond of saying many things. Many are best forgotten. If you
had asked Newton why free particles move along straight lines at
constant speed, he would probably have asked you what else they should
do. It is deviation from such motion that requires explanation. This is
also the point of view of MTW. Or at least of MT.
Schrodinger's Massive Cat. Yes, this is a real problem, and I would like
to see much more thought expended on it. No, I don't want to equate the
Einstein tensor to the expectation value of T. That would be pathetic,
and there are known problems. Still more pathetic would be to turn the
metric tensor into some kind of operator: that would be a wretched fate
for GR, a worthless formal game far more stupid than the much maligned
work of Einstein's later years. No, this is a hard problem. Let us begin
with something a little easier. If the idea of "quantizing spacetime"
makes any sense, then it must make sense for all spacetimes. Among these
is Minkowski space. What would "quantized Minkowski space" be like?
From: bweiner@ruhets.rutgers.edu (Benjamin Weiner)
Newsgroups: sci.physics
Subject: Re: Defining Photons
Date: 27 Jul 92 20:18:59 GMT
Distribution: na
Organization: Rutgers Univ., New Brunswick, N.J.

Jim Carr writes:
>And it also follows that large numbers of neutrinos would act more like
>electrons than photons, despite the fact that they are massless.

Considerations of putative massive neutrinos as dark matter in
galactic halos have to take seriously Pauli Exclusion Principle
effects.  Sounds insane, I know, but the phase space _is_ limited
(in velocity too) and you need a _lot_ of neutrinos to make the halos
heavy enough. 

Ben Weiner
Xref: sparky sci.physics:11904 sci.astro:8431 sci.philosophy.tech:2896 talk.religion.misc:12900
From: psyrobtw@ubvmsb.cc.buffalo.edu (Robert Weiss)
Newsgroups: sci.physics,sci.astro,sci.philosophy.tech,talk.religion.misc
Subject: Re: Structure of Time
Date: 29 Jul 92 03:32:00 GMT
Organization: University at Buffalo
News-Software: VAX/VMS VNEWS 1.41

In article <1992Jul28.175239.10109@hpcvaac.cv.hp.com>, billn@hpcvaac.cv.hp.com (bill nelson) 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.

 	Bill,

		Try to keep this in perspective.

		You're talking about someone losing their job and 
livelihood as being less important than you having to hit the spacebar.
Newsgroups: sci.physics
From: jbaez@riesz.mit.edu (John C. Baez)
Subject: Re: Quantum Cosmological Boundaries and Determinisim?
Keywords: Quantum cosmology
Organization: MIT Department of Mathematics, Cambridge, MA
Date: Wed, 22 Jul 92 15:31:15 GMT

In article <braham.711770201@physics.ubc.ca> braham@physics.ubc.ca (Stephen Braham) writes:

>My first remark would be that modern quantum cosmology doesn't use
>a wavefunction, or even a density matrix. The alternative decohered
>histories approach does not have an intermediate state in general (at
>best a density matrix, which has many superselection sectors, and
>thus describes, roughly, an ensemble of states). 

What do you mean by an "intermediate state"?

By the way, lots of mathematicians use "state" to refer both to pure
states (typically represented by unit vectors in Hilbert space) and
mixed states (aka density matrices).

What is the most lucid and interesting single reference on the
alternative decohered histories approach?  I've read a bit about it but
could stand some more.
Newsgroups: sci.physics
Subject: Re: Converting the masses
From: mcirvin@husc10.harvard.edu (Mcirvin)
Date: 28 Jul 92 15:40:00 GMT
 <131516@lll-winken.LLNL.GOV> <1992Jul28.004259.9052@smsc.sony.com>

markc@smsc.sony.com (Mark Corscadden) writes:

>The original thread has always been about the problems associated
>with using the notion of relativistic mass.  The general recommendation
>was that relativistic mass is an idea who's time has come and gone and
>that you should use the word "mass" to mean "rest mass" or the intrinsic
>mass of a particle or a system.

A number of people have already objected to the term "intrinsic"...
the word you're thinking of may be "invariant," which specifically
means Lorentz invariant.  The rest mass is often called the invariant
mass because it is the same in all inertial frames.  If you add
energy to the system which doesn't change its overall momentum,
though, the invariant mass can change.

>However I'm still
>puzzled because (as far as I can tell) it requires you, among other things,
>to treat the kinetic energy of the parts of the system, measured relative
>to the system as a whole, as mass.  I'm puzzled because at first I though
>that treating kinetic energy as mass was not kosher, period.

Just think of the mass as the energy of the system in the whole
system's rest frame.  This isn't necessarily the rest frame of
any of the parts.
 
>question 1:  Am I using the word "mass" correctly according to the
>folks like David Knapp who want to get away from the notion of
>"relativistic mass"?

>question 2:  Are physicists in general who use "mass" to mean "rest mass"
>or "intrinsic mass" really all in agreement as to how the concept works?
>Specifically, would the vast majority of such physicists reach the same
>answers that I reach below?

Yes to both questions, in your description of the cannonball
situation.  Even people who use "mass" to mean total energy would
agree if you replaced "mass" with "rest mass" everywhere.

You might, though, replace the word "intrinsic" with "Lorentz
invariant."

-- 
Matt McIrvin  mcirvin@husc.harvard.edu 
Newsgroups: sci.physics
From: tolman%asylum.cs.utah.edu@cs.utah.edu (Kenneth Tolman)
Subject: Re: Blue Sky
Date: 24 Jul 92 17:28:12 MDT
Organization: University of Utah, CompSci Dept

>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! 

  A blue animal would stand out too vividly and be a target in most areas.
The birds- having few predators- have again and again picked up on sexual
selection and run wild with it.  Thus the birds end up with fantastic and
useless (except to attract mates) plumages.  Flowers, again, want to attract
for sexual reasons, but bees mainly see in different wavelengths than we
humans- flowers would be even more spectacular if we could see as a bee.
However, I would bet money there are blue animals besides those in the
ocean, such as some snails, some lizards, and some amphibeans.

Xref: sparky sci.physics:11843 sci.astro:8412 sci.philosophy.tech:2885 talk.religion.misc:12840
From: billn@hpcvaac.cv.hp.com (bill nelson)
Newsgroups: sci.physics,sci.astro,sci.philosophy.tech,talk.religion.misc
Subject: Re: Structure of Time
Date: 28 Jul 92 17:52:39 GMT
Article-I.D.: hpcvaac.1992Jul28.175239.10109
Organization: Hewlett-Packard Company, Corvallis, Oregon USA

hporopudas@tnclus.tele.nokia.fi writes:
: 
:  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.

I can't say I am sorry for you. It would be nice of you restricted you
postings to alt.paranormal or alt.kids.with.imaginations.and.gullible.
parents or alt.overimaginative.parents.  

What you have posted does not even begin to follow what is called the 
scientific method. Physicists love the truth, but random babbling is
not truth.

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.

Bill
From: mcirvin@husc8.harvard.edu (Mcirvin)
Newsgroups: sci.physics
Subject: Converting the masses
Summary: Oh, by the way...
Keywords: special relativity
Date: 26 Jul 92 03:03:39 GMT
Article-I.D.: husc3.1992Jul25.230340.14179
Distribution: world
Organization: Harvard University Science Center

By the way, there are at least two other ways, not unrelated, in
which my parable of the three-momenta is hideously slimy and
unfair.  Find them for extra credit!

The argument on which everything I've said rests is that the
proper way to teach SR is via a four-vector approach, such as
that in Taylor and Wheeler, instead of using the arguments that 
appear in most intro books.  In my opinion the definition-
of-mass issue is by comparison quite cosmetic, though a clear
preference does follow from the four-vector treatment.

However, there's a glaring flaw in all of this, namely:  I've
never actually taught a class in special relativity!  I've
suffered through a traditional treatment of the subject, only to
be illuminated later reading, of all things, Misner, Thorne, and
Wheeler's _Gravitation_ (a path I would not recommend for those
who only want to learn SR-- their weird take on differential
forms boggled me).  But I don't have any experience as a
teacher of the subject, and Leigh Palmer, for instance, 
obviously does.  So, really, I'm quite unqualified to argue 
about any of this.

Does anyone out there have actual experience teaching SR via the
Taylor and Wheeler approach, or, better yet, both that and the
more traditional treatment using mostly three-dimensional quantities?
How do they actually compare in practice?  As we theorists get
reminded several times a week in this newsgroup, the only real
test of truth is experiment!  

-- 
Matt McIrvin  mcirvin@husc.harvard.edu
From: aephraim@physics.Berkeley.EDU (Aephraim M. Steinberg)
Newsgroups: sci.physics
Subject: Re: Aristotle and the Modern Physicist
Date: 27 Jul 1992 17:06:19 GMT
Organization: University of California, Berkeley
NNTP-Posting-Host: physics.berkeley.edu

In article <24JUL199220140602@zeus.tamu.edu> dwr2560@zeus.tamu.edu (RING, DAVID WAYNE) writes:
>Consider a Schroedinger's Cat apparatus where the box is large and contains
>a mass distibution instead of a cat, and a mechanism to alter the mass
>distribution if the nucleus decays. After a time the mass distribution
>will be in a superposition of states. How will a test particle outside the
>apparatus know how to fall?

Well, loads of disclaimer to begin this since I know no GR really, but
I think reasons like this are exactly why certain people (e.g. Roger
Penrose) believe the solution to the quantum measurement problem may
lie in the direction of quantum gravity, and sometimes even say that a
system will behave like a "macroscopic" one as soon as it reaches the
Planck mass.  (A prediction which I wager will be disproved within the
next 10 years, btw.)  
Anyway, I'm not convinced that the center of mass of a system can be 
different in two parts of a coherent superposition.  I'd be slightly
more inclined to believe that you could superpose two distributions with
different QUADRUPOLE moments or something like that, affecting more subtle
things than the simple force on a nearby object.  Then again, perhaps all
moments of the mass need to be conserved, I just don't know.  It does seem
to me that if your apparatus is just a big box with a 2-ton weight in it,
and upon radioactive decay shifts the weight a foot to the right, the box
will shift to the left sufficiently to maintain the center of mass, but the
quadrupole moment will be altered?
The reason I really respond is just because it's amusing that you come
up with this particular example.  I wonder if you're aware that it's exactly
what Aharonov uses in one of his latest proposals?  In conjunction with his
theory of "weak measurements," he uses such a system, in which the rate of
a clock depends on the state of the mass shell and can thus be placed in
a superposition state, to create a time machine.  
I won't go on, not really understanding the proposal, but I just wanted to
mention it.  The basic idea of weak measurements is that if in addition to
pre-selecting (i.e., preparing) a state, you post-select a subensemble,
then the expectation value of some observable at a time INTERMEDIATE to the
pre- and post-selections can sometimes have anomalous values, e.g., larger
than any eigenvalue in its spectrum.  Thus even though the difference in
clock rates is very small, once in a while, a huge shift in time may be
produced.


-- 
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
From: jtwamley@physics.adelaide.edu.au (Jason Twamley)
Newsgroups: sci.physics
Subject: Quantum Cosmological Boundaries and Determinisim?
Summary: Quantum cosmology and determinism
Keywords: Quantum cosmology
Date: 22 Jul 92 00:57:29 GMT

Question:
Assume the the while universe can be described by a quantum theory.ie. there
exists a wave function for the universe. There have been a number of proposals
for the quantum boundary conditions for this wavefunction at the begining of
the universe. If one of these boundary conditions succeed in specifiying
a unique wavefunction what does this say concerning the uncertainty in the
evolution of the everyday classical world and free will? Frequently the 
wavefunction of the universe is called on to calculate the characteristics
of large structures ie. inflation, density perturbations etc. However,
in principle, how far can the information content of this wavefunction reach?
Can it (is it suposed to?) describe the milk mixing in my tea? The standard
probabalistic interpretation of QM is not clear here as we are attempting to
describe the one universe by a single wavefunction and attempting to make
predictions. Or is the Many-world description more appropriate? To put my
question another way.. do the correlations contained in the quantum 
cosmological boundary conditions contain all the information necessary to
describe the complete future of the `classical' world deterministically?

Jason Twamley
Newsgroups: sci.physics
From: mazzucch@ghost.dsi.unimi.it (massimo mazzucchi)
Subject: microvawe
Keywords: microvawe
Organization: Computer Science Dep. - Milan University
Date: Mon, 27 Jul 1992 11:54:23 GMT

I iam  a student of   science of   information  in   Milan ITALY 
i am   interested to have information about 

MICROVAWE:

imy friendswork    in telecomunication and satellite
and want  to know   information about the caracterizaction
in continue  
of  FET  HEMT
 Sorry   for my english but  i   have the  i  problem
 with the line of communication

 Thanks  for   your help and   if  you  can  send  the  mail myu  adress
 is

  MAZZUCCH@HP1.SM.DSI.UNIMI.IT


  BYE
Xref: sparky sci.physics:11877 sci.materials:570
From: sundar@fiber-one.ai.mit.edu (Sundar Narasimhan)
Newsgroups: sci.physics,sci.materials
Subject: density of commonly used materials
Date: 28 Jul 92 22:10:45 GMT
Reply-To: sundar@ai.mit.edu
Followup-To: sci.physics
Organization: MIT Artificial Intelligence Laboratory

Hi, I am interested in finding out the densities (ranges) of commonly used 
materials (starting from things like Aluminium, Steel, Wood etc. to
rubbers and plastics). Is there a handbook of physical constants I can
refer to? Is any such information available online?

Thanks much.
From: sichase@csa2.lbl.gov (SCOTT I CHASE)
Newsgroups: sci.physics
Subject: Re: Defining Photons
Date: 28 Jul 92 20:05:10 GMT
Organization: Lawrence Berkeley Laboratory - Berkeley, CA, USA
Distribution: na
Reply-To: sichase@csa2.lbl.gov
NNTP-Posting-Host: 128.3.254.197
Keywords: Relating photons E=MC^2 criticism
News-Software: VAX/VMS VNEWS 1.3-4   

In article <mcirvin.712335342@husc10>, mcirvin@husc10.harvard.edu (Mcirvin) writes...
> 
>Or hydrogen, for that matter.  A professor in my department   
>has discussed the possibility of doing "optics" with atoms.  I
>don't know how close it is to being feasible.

If I understand correctly, then the recent discussion of atomic "optics"
does not have anything to do with the statistical properties of atoms, but
rather that the technology of diffraction gratings has advanced to the 
point of allowing people to construct atomic interferometers - which among
other things would provide incredibly sensitive position and motion
sensors since the de Broglie wavelength of an atom is orders of magnitude 
shorter than that of visible light.  

This would work for atoms of all spins.

-Scott
--------------------
Scott I. Chase			"The question seems to be of such a character
SICHASE@CSA2.LBL.GOV		that if I should come to life after my death
				and some mathematician were to tell me that it
				had been definitely settled, I think I would
				immediately drop dead again."      - Vandiver
From: u894793@bruny.cc.utas.edu.au (Timothy D Little)
Newsgroups: sci.physics
Subject: Re: The Bubbles
Date: 30 Jul 92 03:10:19 GMT
Organization: University of Tasmania, Australia.

clwu@Uz.nthu.edu.tw (Ching-Long Wu (PHYS U790315)) writes:

>Hello everyone!
>   I am quite interested in the behavior of the bubbles that floating
>on water's surface. I have several questions:

>1. What's the shape of it? Is it a perfect semi-sphere?

It can't be a perfect semi-sphere due to the effect of surface tension at
the edges.  Furthermore, the internal pressure of the bubble would make
the 'flat' bottom slightly curved.

>2. Why does it break? And what's the machanism of it's breaking?

I read once that it was evaporation of the bubble film.  I don't know
how much weight to give this, since it was a 'popular science' book and
not a technical one.

>3. I suppose there are some relation between a bubble's 'life' and 'size'.
>   I think of an experiment like this:
> [details deleted]
>   When a bubble appears on the surface, mesure its diameter immediately and
>start the time counting till it breaks. Has any one done such kind of
>experiment? What's it look like?

I haven't read of any such experiment.  The results should be derivable,
but confirmation would be good.

>4. What if the bubbles are floating in the air? If there is no gravitation,
>will them break?

If the mechanism for breakage is evaporation, then yes they would.

>   I hope you are also interested in these questions...

Fairly much.  I'm more interested in the 'antibubbles' you get by skimming
small droplets of water across the surface, consisting of a glob of water
separated from the main mass by a thin film of air (I assume).
--
Timothy D Little   a.k.a.   u894793@bruny.cc.utas.edu.au
"I'm a Tasmanian." - Yahoo Serious, in the film Young Einstein.
From: weemba@sagi.wistar.upenn.edu (Matthew P Wiener)
Newsgroups: sci.physics
Subject: Re: QPKD and Quantum Communications
Keywords: Communications Public Snide Remarks
Date: 22 Jul 92 14:11:17 GMT
Reply-To: weemba@sagi.wistar.upenn.edu (Matthew P Wiener)
Organization: The Wistar Institute of Anatomy and Biology
In-reply-to: snarfy@cruzio.santa-cruz.ca.us

In article <3925@cruzio.santa-cruz.ca.us>, snarfy@cruzio writes:
>> >  Mr Weiner says:
>> >  > This has nothing to do with FTL anything.

>> >  Dogmatic  sort  aren't  you ?  Instantaneous is by definition faster than
>> >  light.

>> Look, bozo, if you're going to quote private e-mail, get it right...

>       Do you consider the sci.physics forum to be your Private E-Mail?

>                        >....starting with my name.

>       A thousand pardons ,Dick , I mean Frank , I mean Mr. Wiener, There
>       hows that?

Ben Weiner sent me e-mail--that was his posting apparently.  I apologize
for the implied accusations.  Anyway, you still don't know what you are
talking about.
-- 
-Matthew P Wiener (weemba@sagi.wistar.upenn.edu)
Newsgroups: sci.physics,sci.astro
From: jcj@tellabs.com (J. Johnson)
Subject: Re^2: Structure of Time (answers to some questions)
Organization: Huh?
Date: Wed, 22 Jul 1992 13:51:39 GMT

So life is based on what kind of neutrinos God uses to cook 
the space potato?  Does this also imply that cottage fries 
are *evil*?

Newsgroups: sci.physics