HDTenEightyP/NetNews huggingface dataset:
Newsgroups: sci.physics
Subject: Re: What We Don't Know (YET!) 
From: mcirvin@husc8.harvard.edu (Mcirvin)
Date: 10 Sep 92 16:02:40 GMT
 <26182@dog.ee.lbl.gov> <1992Sep10.014816.17123@galois.mit.edu>
Keywords: FAQ, ignorance

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

>Okay, starting with ones that have recently come up, here are
>some things we don't know.  Here's how I would start off the FAQ; of
>course everyone can suggest improvements but Scott is the boss.

It's a nice list.  I'd like to add a few more unknown things: 

What is meant by a "measurement" in quantum mechanics?  Does "wavefunction
collapse" actually happen as a physical process?  If so, how, and under
what conditions?  If not, what happens instead?

What are the gravitational effects, if any, of the immense (possibly
infinite) vacuum energy density seemingly predicted by quantum field
theory?  Is it really that huge?  If so, why doesn't it act like an
enormous cosmological constant?

Why are the galaxies distributed in clumps and filaments?  Is most of the
matter in the universe baryonic?  Is this a matter to be resolved by
new physics?

Why doesn't the flux of solar neutrinos agree with predictions?  Is the
disagreement really significant?  If so, is the discrepancy in models of
the sun, theories of nuclear physics, or theories of neutrinos?  Are
neutrinos really massless? 
-- 
Matt McIrvin, Cambridge, Massachusetts, USA 
Newsgroups: sci.physics
From: schinder@leprss.gsfc.nasa.gov (Paul J. Schinder)
Subject: Re: Black hole + anti-Black hole = ?
Reply-To: schinder@leprss.gsfc.nasa.gov
Organization: Goddard Space Flight Center
Date: Wed, 9 Sep 1992 00:37:50 GMT

In <1992Sep8.222101.9281@math.ucla.edu> barry@arnold.math.ucla.edu (Barry Merriman) writes:


>What happens if you dump some antimatter into a black 
>hole that formed from normal matter? Does it 'cancel out' part of it?

What do you mean by "cancel out"?  If, say, you make a black hole out
of a bunch of electrons and another out of a bunch of positrons, they
have opposite charges.  Combine them, and the charges will cancel.
Remember that both positrons and electrons have positive rest energy,
so the mass of the combination will always increase.

>Or, if I take two black holes, one made from ordinary matter
>and the other made from anti-matter, and merge them, what happens?

The short answer is that once you make them, you can't tell the
difference.  Black holes only respect charge, energy, and angular
momentum conservation.  They don't conserve baryon or lepton number,
so you can't tell the difference between a hole made of anti-protons
or an equivalent number of electrons and enough neutrals to make up
the mass difference.

>Do I get a bigger black hole, or are they somehow annihilated?

Always bigger.  Fuzzy memory tells me that Hawking showed that this
was the second law of thermo for black holes.

>--
>Barry Merriman
>UCLA Dept. of Math
>UCLA Inst. for Fusion and Plasma Research
>barry@math.ucla.edu (Internet; NeXTMail is welcome)
--
--------
Paul J. Schinder
NASA Goddard Space Flight Center
schinder@leprss.gsfc.nasa.gov
Newsgroups: sci.physics
From: litow@csd4.csd.uwm.edu (bruce e litow)
Subject: Boson and Fermion variables
Originator: litow@proclus.csd.uwm.edu
Keywords: infinite/finite
Organization: Computing Services Division, University of Wisconsin - Milwaukee
Date: Wed, 9 Sep 1992 19:16:00 GMT

I seem to recall that Dirac, somewhere, indicated that it is possible
to proceed from the assumption that there are infinitely many fermion
variables (say associated with electrons) and construct boson variables.
The infinity was crucial although somewhat unphysical. Can anyone
give a reference to this or clarify what it is that I think I 
remember?


Bruce Litow
Computing Services Division
P.O. Box 413
Univ. Wisconsin-Milwaukee, Milwaukee, WI, 53201
litow@convex.csd.uwm.edu
Newsgroups: sci.physics
From: pratt@Sunburn.Stanford.EDU (Vaughan R. Pratt)
Subject: Re: Color of electric charges (silly question)
Organization: Computer Science Department,  Stanford University.
Distribution: na
Date: Sun, 13 Sep 1992 21:23:33 GMT

In article <mcirvin.716410389@husc8> mcirvin@husc8.harvard.edu (Mcirvin) writes:
>It's interesting that these color assignments are as strong as
>they are, since they carry no information and have no mnemonic
>value, other than perhaps keeping things straight in my head.
>The only part of all this that seems to be widespread is the
>tendency to paint protons red, and possibly the gray neutrons
>as well.

I figured they were following the usual color coding of positive wires
as red, negative as black, and ground as green.  Maybe the ground and
negative codes got interchanged, or some artist decided green seemed
more complementary to red than black.  Is negative black or green in
Europe?  What about the UK?

-- 
======================================================| God found the positive
Vaughan Pratt   pratt@cs.Stanford.EDU   415-494-2545  | integers, zero was
======================================================| there when He arrived.
Newsgroups: sci.physics
From: moroney@ramblr.enet.dec.com
Subject: Re: Electrons in the body
Organization: Digital Equipment Corporation
Date: Thu, 10 Sep 1992 02:40:22 GMT

In article <79438@ut-emx.uucp>, ofman@zonker.ph.utexas.edu (Leon Ofman) writes...
>In article <00960110.2D669340@Msu.oscs.montana.edu> uchpcjv@Msu.oscs.montana.edu writes:
>>>>Could anyone give me a rough estimate of the percent of mass of a human
>>>>body which is made of electrons? 

>>  ROUGH ESTIMATE:  about 1/2000 of body mass.  Rought estimate.

>Rough estimate: 1/1000 (don't forget the neutrons!)

That would make it about 1/4000 or so.

-Mike
From: sichase@csa3.lbl.gov (SCOTT I CHASE)
Newsgroups: sci.physics
Subject: Re: Did electric/magnetic symmetry "break"?
Date: 7 Sep 92 21:27:38 GMT
Organization: Lawrence Berkeley Laboratory - Berkeley, CA, USA
Distribution: na
Reply-To: sichase@csa3.lbl.gov
NNTP-Posting-Host: 128.3.254.198
News-Software: VAX/VMS VNEWS 1.3-4   

In article <5294@tuegate.tue.nl>, johan@blade.stack.urc.tue.nl (Johan Wevers) writes...

>That it is one force can also be seen from the fact that there exist only
>one kind of photon.

There are 8 kinds of gluons and only one strong interaction.  There are three
kinds of weak boson and there is only one weak interaction.  There happens
to be only one kind of photon, because EM is a gauge interaction with 
U(1) gauge group.

>******************************************************************** 
>* 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\            *
>********************************************************************

Your .sig has inspired me to write something about the status of proton decay 
one of these days.

-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: mcirvin@husc8.harvard.edu (Mcirvin)
Newsgroups: sci.physics
Subject: Re: Hidden variable theories, was: Uncertainty Princi
Date: 10 Sep 92 15:21:24 GMT
Article-I.D.: husc8.mcirvin.716138484

johan@blade.stack.urc.tue.nl (Johan Wevers) writes:

>campo@sunthpi3.difi.unipi.it writes:

>>Also only the hidden variables theory has to
>>give up causality; e.g. quantum electrodynamics strictly respects
>>causality.

>I thought that QED was also a theory which gave it's answers as
>probabilities. Furthermore, I used to see QED as an underlying
>theory for QM which does not contradict with QM on matters as
>uncertancy.

"Causality" here doesn't mean determinism, in the sense of "there is
no effect without a cause" (--Dr. Pangloss); it just means that it's
not possible to transmit a message from event A to event B where B
is outside A's future light cone.  In this sense all of relativistic 
quantum mechanics (at least in Minkowski spacetime) is causal.

Paul Budnik defines causality a little differently, to exclude
correlations of random results over spacelike separations as
well.  By his definition QED doesn't respect causality. 
That's not how the word is used by most physicists. 

-- 
Matt McIrvin, Cambridge, Massachusetts, USA
From: bweiner@ruhets.rutgers.edu (Benjamin Weiner)
Newsgroups: sci.physics
Subject: Re: How old is the universe?
Date: 15 Sep 92 19:57:43 GMT
Organization: Rutgers Univ., New Brunswick, N.J.

ted@physics.Berkeley.EDU (Emory F. Bunn) writes:
>  ...  However, if you look into things
>a little bit more closely, all inflation says is that Omega should be
>very very close to 1.  (The argument actually says that during the
>inflationary period, Omega(t) approaches 1 very rapidly from whatever
>its initial value was.)  So if inflation is right, it's perfectly
>possible that Omega is 0.9999999....99999, or that it's
>1.000000000000....00001.  In the first case, the Universe will
>expand forever, while in the second case it will eventually recollapse
>(although not for an extremely long time).

Yup, in my limited understanding, inflation "blows up" the universe so
much that we can see only a tiny little portion of it, which
naturally looks very flat - but the whole shmeer could actually be 
either open or closed, as you said.  Still, the turnaround time is
so vast that it's essentially meaningless (I have enough trouble
trying to conceive of a megaparsec).  I was trying to emphasize that
the "open vs. closed" issue which used to dominate popular accounts
of cosmology is, for the moment, a non-issue.
From: ric@hpspdla.spd.HP.COM (Ric Peregrino)
Newsgroups: sci.physics
Subject: Re: Why do protons outnumber antiprotons?
Date: 4 Sep 92 18:11:16 GMT
Organization: HP Stanford Park - Palo Alto, CA


I was not thinking logically when I posted:

>For three, is energy not conserved in beta decay?
>If it is then the overall picture remains the same: no imbalance of energy
>results and total particle energy plus total anti-particle energy remains
>constant. Or doesn't it?

Maybe what I should have said was,,,

Consider an empty universe. nothing can happen without negative mass
particles. Assume no such thing for the moment. Now add some photonic
energy. The first thing that can happen is the annihilation of two
photons and a creation of an electron and an anti-electron. These reactions
conserve the total particle MINUS total antiparticle mass at zero.

At higher photon energies, you'll get particle anti-particle creations
of higher energy particles. Say you get a neutron and anti-neutron.
Now say the neutron undergoes beta decay. For the above conservation
to hold, then the mass of the proton plus the electron must equal the
mass of the anti-neutron plus the anti-neutrino. I don't know if this
is the case or not. Do you? Please advise.

I think what I'm trying to say, is that it doesn't have to leave it's
anti-particle, but does have to leave an equal amount of anti-mass.

Anti-bosons? What are the properties of an anti-photon?

--------------------------------------------------------------------------
Ric Peregrino     c/o Hewlett Packard Co.        I represent only myself
ric@spd.hp.com    1501 Page Mill Rd. Bldg. 5M    I may be wrong, maybe not
415-857-7526      Palo Alto, CA 94304            Do DC photons exist?
--------------------------------------------------------------------------
Newsgroups: sci.physics
From: jonwa@ida.liu.se (Jonas Wallgren)
Subject: {pre,sub}quarks.
Organization: CIS Dept, Univ of Linkoping, Sweden
Date: Sun, 13 Sep 1992 17:50:46 GMT

An article in the April 1983 issue of Scientific American gives a description
of some models of quarks and leptons as composed of smaller particles. Two
models presented are the preons from 1974 and the quite beautiful rishons from
1979.

What has happend since then? Are there any new models? Are the old models
refined or discarded? How does this problem relate to the current data
indicating exactly 3 families of particles? How do the models fit together with
W, Z, Higgs, ...?
-------------------------------------------------------------------------------
Jonas Wallgren                                 |                 jwc@ida.liu.se
Department of Computer and Information Science |
Linkoping University                           |-------------------------------
S-581 83  Linkoping                            |Everything that is systematized
Sweden                                         |becomes aesthetic --- B. Becher
-------------------------------------------------------------------------------
Xref: sparky sci.physics:14414 rec.pets.cats:10880
From: exuptr@exu.ericsson.se (exuptr@exu.ericsson.se)
Newsgroups: sci.physics,rec.pets.cats
Subject: Re: Radioactive Cat: How Dangerous is She?
Date: 10 Sep 92 17:44:34 GMT
Organization: Ericsson Network Systems, Inc.

In article <+btn-xl.badboy@netcom.com> badboy@netcom.com (Jay Keller) writes:

>Jay Keller
>Sunnyvale, California
>badboy@netcom.com

I missed the earlier part of your thread.  What was wrong with the cat?

 ----------------------------------------------------------------------------
    "This must be Thursday.  I never could get the hang of Thursdays"
                                                       - Douglas Adams
  - Patrick Taylor                                       (Arthur Dent)
    Ericsson Network Systems
    exuptr@exu.ericsson.se                       "Don't let the .se fool you"
    or exuptr@ZGNews.Lonestar.Org, exu.exuptr@memo.ericsson.se
Newsgroups: sci.physics,sci.math
From: paul@mtnmath.UUCP (Paul Budnik)
Newsgroups: sci.physics
Subject: Re: Hidden variable theories
Date: 14 Sep 92 16:23:28 GMT
Organization: Mountain Math Software, P. O. Box 2124, Saratoga. CA 95070

> ... 
> Since Aspect's 1982 experiment [Aspect, A. (1982). Experimental Realization
> of Einstein-Podolsky-Rosen-Bohm Gedankenexperiment: A New Violation of Bell's
> Inequalities. Physical Review Letters, Vol 49,No.2,P91] agree's with the
> QM predictions and violates Bell's inequality it is assumed that objective
> local theories have been ruled out.

The most serious problem with Aspect's experiment was that there was no direct
measurement of the time delays between changing a polarizer angle and detecting
an affected photon. Franson (Physical Review D, pgs. 2529-2532, Vol. 31, No. 10,
May 1985) first pointed this out and others have noted the same problem since.
We do not know if the correlated events in Aspect's experiment had a space-like
separation. 

>...
> This is not true as briefly mentioned by Mermin on pages 167-169 of his
> book [Mermin, N. D. (1990), Boojums All the Way Through. Cambridge: Cambridge
> University Press]. He says, "detecting the presence of a single photon is not
> an easy feat to accomplish, and the detectors do not always fire when a
> photon enters. In fact, more often than not, they fail to fire." and ... 
> "So if you are stubborn, there is a way to explain the observed data with
> instruction sets, one that can only be ruled out (assuming our current ideas
> about photons and their detectors are in fact correct) by designing photon
> detectors so efficient as to leave no room for such a loophole."
>...

This is interresting and I no doubt should have read your earlier derivation
of a similar result more carefully. I would like to point out that this
has no affect on Bell's inequality. This is a purely mathematical result that
does not depend on physics. Nor does this affect the proof that current
formulations of quantum mechanics predict that Bell's inequality is violated.
What it does do is provide an additional loophole that one would like to
test experimentally.

It is an unlikely loophole. For it postulates that there is some
new property of photons, for which there is no existing experimental
evidence. Yet this property has a significant experimentally observable
affect in EPR experiments.

> Until paired photon experiments of sufficient efficiency have been carried
> out, it is premature to consider issues of "causality".

There will never be an absolutely definitive test of Bell's inequality
because of the loopholes that will always be possible based on faster than light
but still local causes and the possibility of complete predeterminism. The
efficiency issue is a more plausible, but still unlikely loophole. It
is no doubt worth dealing with experimentally, but the main problem is to show
that the manipulations and affected detections have a space-like separation.
You cannot claim to have tested Bell's inequality with out that. (Well I guess
you can claim it since several experimenters have, but the claim is false.)

Paul Budnik
From: kibler@turing.ICS.UCI.EDU (Dennis Kibler)
Subject: Size of neutrino
Newsgroups: sci.physics
Date: 14 Sep 92 18:37:39 GMT

Hi,
  My seven year old is very interested in sizes and speeds of
various things around us. Yesterday he asked me how big
a neutrino was. I have no idea of how to answer him.
Any help appreciated.

A while back we had the following conversation.

 Son: When the astronauts go outside their spaceship,
      they can't talk to each other.
 Me: Why is that?
 Son: Because sound goes at 600 mph and they are going
      at 15,000 mph.
 Me: Hmnn. There isn't any air out is space.
 Son: Well--
       that's another reason why that can't talk to each other.


dennis
Newsgroups: sci.physics
From: prim!dave@germany.eu.net (Dave Griffiths)
Subject: How do we know individual photons exist?
Organization: Primitive Software Ltd.
Date: Tue, 15 Sep 1992 18:06:30 GMT


Having just re-read the description of the 2 slit experiment and the
implications of wave/particle duality, I was wondering how we know
that individual photons exist? I'm under the impression that the answer
is that they cause excitation of an electron from one state to another.

But couldn't the inteference seen in the 2 slit experiment be explained
if instead of just one photon, the source emitted, say, 1000 sub-photons?
The source could be continually spraying out a stream of these sub-photons.
As they travel through space, their phase changes. The electrons in the
target screen act like containers for these photons. Sub-photons of
different phase cancel each other out (gulp). When an electron has collected
1000 sub-photons, it's state changes.

Does the 2 slit experiment definitely correlate an emitted photon at
the source with a detected photon at the screen, or is it just based
on aggregates? (I have in mind that the state of an electron at the
source drops once it has emitted 1000 sub-photons, but such a drop
would not correlate with an excitation at the screen).

The thing I don't understand is when people talk about placing a
detector at one of the slits to determine which of the slits the photon
went through. How is this done? Roger Penrose says that the passage of
the photon is not disturbed, but it's presence is somehow inferred from
detectors placed elsewhere.

Dave Griffiths
Newsgroups: sci.physics
From: dwr2560@zeus.tamu.edu (RING, DAVID WAYNE)
Subject: Re: Is Spacetime Absolute?
News-Software: VAX/VMS VNEWS 1.41    
Organization: Texas A&M University, Academic Computing Services
Date: Sat, 5 Sep 1992 17:31:00 GMT

prim!dave@germany.eu.net (Dave Griffiths) writes...
>I think what I am asking is, is there an objective spacetime fabric out there
>through which all particles move? Or does a different universe exist from the
>perspective of every particle?

Perhaps Quantum gravity will have the answer. :)

>Um... also... how does an object "know" that it is spinning relative to
>the "fixed" stars? (Relative to the object, all it's particles are at rest
>and only the universe is spinning).

This is the gravitational interaction. The effect of distant masses can be
completely described by specifying which frames at each spacetime point
are inertial. Whatever equation tells you what the metric is now, given
the initial conditions is what brings the 'info' to you. I would like to
say it's Einstein's equation, but there's some subtle issues here that
I don't understand, so I won't.

Dave Ring
dwr2560@zeus.tamu.edu
Newsgroups: sci.physics
From: dwr2560@zeus.tamu.edu (RING, DAVID WAYNE)
Subject: Re: Question of Theory of Everything (or Grand Unified theory)
News-Software: VAX/VMS VNEWS 1.41    
Organization: Texas A&M University, Academic Computing Services
Date: Wed, 9 Sep 1992 02:41:00 GMT

matmcinn@nuscc (Mcinnes B T (Dr)) writes:
>>Now: is it not truly astounding that the complexity of the universe
>>is so precisely calibrated to the intelligence of homo sapiens?

Not at all. Life evolved intelligence because understanding nature is
an advantage. And _somebody_ had to be the first to fully understand nature.
Now you might think it astounding that you are alive at the same time as
Witten (:-D) but that is not surprising either, because most of the people
ever to have lived are alive today.

Which reminds me... Consider Galileo, Newton, Einstein. There should
be at least 3 people alive today as brilliant in physics as they were!

Dave Ring
dwr2560@zeus.tamu.edu
Newsgroups: sci.physics
From: raicu@netcom.com (Eugen Raicu)
Subject: Re: skin depth
Date: Sat, 05 Sep 92 05:58:41 GMT
Organization: Netcom - Online Communication Services  (408 241-9760 guest) 
X-Newsreader: Tin 1.1 PL4

pad@galaxy.nsc.com (Paul Denny x8349) writes:
: A textbook practice question on skin depth of electromagnetic
: waves that I was working on recently posed the following 
: question:
: 
: find the skin depth for sea water with rho=.2 0hm.metre for
: frequencies of 30KHz and 30Mhz. How practical is radio
: communication with submarines?
: 
: the formula for skin depth was given as d=(2.rho/u.w)^0.5
: 
: with rho=resistivity u=permeability w=angular frequency
: 
: I plugged in the numbers and came up with d equal to 1.3m
: and 41cm respectively and concluded that submarine comms
: isn't practical at these frequencies which ties in with 
: a vague awareness that radio comms with subs is done but
: at ultralow frequencies. My problem is that there were no 
: worked answers so I may have got it wrong but if I got it
: right then the skin depth for light in sea water must be
: in the micron range - so why isn't sea water opaque (read
: where did I go wrong?:^)) 
: 
: PS My employer doesn't set me homework problems :^)

The formula for skin depth is applicable only to good conductors.
In a good conductor frequency * dielectric constant << conductivity
which allowed you to ignore the dielectric constant in the calculations above.
The resistivity and dielectric constant are not frequency independent.
Even if they were, at high enough frequency, it would cease being
a good conductor.
Sea water is not a good conductor at optical frequencies.
-- 
Eugen Raicu
raicu@netcom.com