HDTenEightyP/NetNews huggingface dataset:
From: mcdougal@jensen.cc.brandeis.edu (Brendan A McDougall)
Subject: experimentalist issues
Organization: Brandeis University
Date: Thu, 7 Jan 1993 16:28:27 GMT

Hi,

As a grad student experimentalist in a young surface science lab, I'm  
beginning to find that my most valuable instrument is the phone.  Often  
times I need things that are just not easily available and spend days  
searching for sources.  Although the Thomas Register, Physics Today  
buyer's issue, and other guides are helpful, I think the best source of  
information is the person who has already purchased/used what I need and  
can direct me to his/her supplier or has an opinion on the equipment they  
used.  For example, my latest needle in the haystack search was for a  
piece of quartz tubing--5/16"OD X 0.07"ID X few inches long.  My next hunt  
will soon be for an open cycle liquid He refrigerator/cold head for the  
UHV chamber.  There are few suppliers, but who manufactures the most  
reliable, most "easy-to-use" or "grad-student-safe" gear.

There have been monographs on the issue, e.g. Experimetal Methods in Low  
Temp. Physics, which are very helpfu--listing techniques and suppliers.   
If everything was covered in these "ancient" texts, I wouldn't be doing  
research.  

I think there is a need for a more timely forum.  Is there interest in  
starting a sub-group, e.g. sci.hardsci.exp, that would encompass the needs  
of all hard science experimentalists--engineers, chemists, mat sci, et  
al.?  Or should one just post to these groups as they are?
Newsgroups: sci.physics
From: rivero@sol.cie.unizar.es (Alejandro Rivero)
Subject: Re: Newton's birthday
Reply-To: rivero@sol.cie.unizar.es
Organization: Department of Theoretical Physics. University of Zaragoza
Date: Tue, 5 Jan 1993 19:10:35 GMT


When is Issac Newton's birthday?  I have heard from some people its 
12-25, and from others its today (1-4) does anyone here know for sure?

25 december is the day ack by the CERN...

Being Newton as he was, could you expect another day?
From: metzler@pablo.physics.lsa.umich.edu (Chris Metzler)
Newsgroups: sci.physics
Subject: Re: The Big Bang Never Happened
Date: 7 Jan 1993 16:50:33 GMT
Organization: University of Michigan Department of Physics
Distribution: world
NNTP-Posting-Host: pablo.physics.lsa.umich.edu

In article <1993Jan7.090448.14353@nuscc.nus.sg>, scip2124@nusunix1.nus.sg (MARC PAUL JOREF VAN LOO) writes:
|>   To say that there is no observation against the
|>   Big-bang is simply wrong.
|>   Read Sandage's overview paper (1988 or 1989) in
|>   annual review of astronomy and astrophysics
|>   (or something close to that title).
|> 
|> 

I presume that you are referring to Sandage's "Observational Tests
of World Models," Ann Rev Astron Astrophys, v26 pp561-630 (1988).
I have a copy of it bound and above my desk, and I recommend it to
anyone interested in physical cosmology.  This well-written review
essentially goes over the observational techniques used to determine
the free parameters of the hot Big Bang model, and what those
results are.  I repeat what I said earlier -- it is important to
not confuse the hot Big Bang model with certain scientists'
specific versions of the hot Big Bang model.  If \Omega = 1 is
observationally ruled out, for instance, that says nothing about
whether or not the hot Big Bang model is valid.  Sandage makes
it fairly clear in this review that there is certainly uncertainty
in the free parameters of the model (\Omega_0 or q_o, H_o, t_o,
etc.), but remember that these free parameters are tied together
by the fundamental definition of t_o, f(\Omega) * t_o * H_o = 1,
where f is a known function, and within this they are quite
consistent with each other.  Anyway, if there's something else
you get out of this review that you think falsifies the Big Bang,
please let me know, because I don't know what it is, and I definitely
don't get that impression from the review.  In fact, I think
Sandage's personal opinions are made fairly clear in the quote
from the first page:  "In this review a prejudice in favor of the
hot Big Bang can hardly be suppressed, successful as the model
has become in providing an understanding of the abundance of He^4
and the 3K radiation.  Nevertheless, if a description of beginnings
in this sense is to be confined within the methods of science rather
than to be colored by teleological metaphysics, the model must pass
the tests normal to science rather than to be accepted as revealed
truth."  In other words, I don't think Sandage takes the HBB model
on faith; and yet still (and since this review came out) he
argues in favor of the model.

		-- Chris

-- 
SNAILMAIL:                                       AT&TMAIL:
Chris Metzler                                    313-764-4607 (office)
Department of Physics, University of Michigan    313-996-9249 (home)
Randall Lab, 500 E. University
Ann Arbor, MI  48109-1120 USA

E-MAIL:  metzler@pablo.physics.lsa.umich.edu
From: gaetz@head-cfa.harvard.edu (Terrance J. Gaetz)
Newsgroups: sci.physics
Subject: Re: Schrodinger hydrogen atom partition function divergence
Date: 4 Jan 93 20:54:52 GMT
Organization: Harvard-Smithsonian Center for Astrophysics

In article <1i1onuINNgh@gap.caltech.edu> brandt@cco.caltech.edu (William N. Brandt) writes:
>I have a question about the partition function of the Schrodinger
>hydrogen atom. The energy eigenvalues for such an atom go like
>13.6 ev * (1/n^2) so if we compute Z, the partition function,
>
>        Z = Sum[g_n * exp(-E_n/(k*T))]
>
>(g_n is the degeneracy of the nth state, k is Boltzman's constant,
>and T is tempertature) we notice that E_n tends to zero so the
>exponential tends to 1 so we get an explosively diverging series
>since the g_n's tend to increase.
>
>Since Z is not a QM observable this looks at first sight not to be a
>problem. However, since the population of a given level goes as
>1/Z (and this is an observable) this would seem to indicate that
>the Schrodinger hydrogen atom cannot contain an electron.

Peierls, in "Surprises in Theoretical Physics" (Princeton University
Press, 1979) argues that this is the physically correct answer - the
expectation is that a hydrogen alone in the universe will tend to be
in an ionized state, whatever the temperature.  Basically, this is
because the collisional ionization rate is independent of the 
volume per atom, while the radiative recombination rate is 
inversely proportional to the volume per atom.  As the volume
per atom becomes infinite, ionizations dominate over recombinations.

Peierls also points to a discussion in Landau & Lifshitz ("Statistical 
Mechanics") in which the law of mass action is used to obtain 
the degree of ionization of a gas in thermal equilibrium (the 
Saha equation, although I don't think they call it that).  Peierls 
notes that a prediction of the equation is that the degree of
ionization will be complete for a finite number of atoms in 
an infinite volume.

>I know astronomers resolve this problem by lopping off the partition
>function sum when the bohr radius of the nth state is approximately
>the mean atomic spacing, since EM effects would prohibit higher
>states.  However, is there a fundamental resolution to this
>apparent problem? Or is it not really a problem and why? 

Peierls briefly discusses these issues; in a gas with finite volume
per atom, the high n states of free atoms can't be used because 
they overlap the adjacent atoms.  In essence, the perturbations
resulting from the neighboring atoms will cause what would have
been a high-n electron to behave as a free electron instead.
--
Terry Gaetz  --  gaetz@cfa.harvard.edu
Xref: sparky sci.physics:22450 news.groups:25300 sci.misc:2000
From: kermits@cc.uch.gr (Aggelos Keromyths)
Newsgroups: sci.physics,news.groups,sci.misc
Subject: Re: knots and stat.mech.
Date: 11 Jan 93 00:28:40 GMT
Followup-To: sci.physics,news.groups,sci.misc
Organization: University of Crete, Computer Center
X-Newsreader: TIN [version 1.1 PL8]

What ?
Aggelos
From: matt@physics2.berkeley.edu (Matt Austern)
Newsgroups: sci.physics
Subject: Re: Faster then the speed of light?
Date: 7 Jan 93 20:32:59 GMT
Reply-To: matt@physics.berkeley.edu
Organization: Lawrence Berkeley Laboratory (Theoretical Physics Group)
NNTP-Posting-Host: physics2.berkeley.edu
In-reply-to: cburke@nexus.yorku.ca's message of Thu, 7 Jan 1993 19:48:20 GMT

In article <cburke.726436100@yorku.ca> cburke@nexus.yorku.ca (Carolyn Burke) writes:

> In a recent talk I attended, the speaker mentioned a series of
> astronomical observations involving quasars.  Please excuse my
> use of lay-terminology.  The speaker said that using triangulation
> calculations to determine the velocities of two such heavenly objects
> relative to each other over a period of time, scientists observed (or
> inferred) that said relative velocity far exceeded the speed of light,
> in excess of between 400% and 700% (depending on the value assigned to
> the apparently controversial Hubble constant).  The speaker went on from
> there, and if anyone is interested I'll post a follow-up with citations.

Depending on exactly how you define your terms, there is nothing wrong
with the relative velocity of two objects being greater than c.

Definition 1: the relative velocity of object 1 and object 2 is defined
	to be the velocity of object 2 in the rest frame of object 1.

Definition 2: the relative velocity of object 1 and object 2 is defined
	to be the velocity of object 2 with respect to the observer,
	minus the velocity of object 1 with respect to the same
	observer.

In the nonrelativistic limit, these two definitions are the same; in
special relativity, they are not.  Both definitions are useful for
certain purposes, and you have to be sure which one you're talking
about.

Using the first definition, the relative velocity is always less than
c; using the second definition, it isn't.  (Obviously enough, since
you're just subtracting two numbers, and there's nothing wrong with
one of the numbers being .9c and the other being -.9c.)

My guess is that the speaker in this talk was using the second
definition, if only because it's something that would be much easier
to measure.


--
Matthew Austern                   Just keep yelling until you attract a
(510) 644-2618                    crowd, then a constituency, a movement, a
austern@lbl.bitnet                faction, an army!  If you don't have any
matt@physics.berkeley.edu         solutions, become a part of the problem!
From: columbus@strident.think.com (Michael Weiss)
Newsgroups: sci.physics
Subject: The Dirac sea
Date: 11 Jan 93 10:00:52
Organization: Thinking Machines Corporation, Cambridge MA, USA
	<1993Jan8.160818.19578@galois.mit.edu>
	<1993Jan8.171134.29230@ramsey.cs.laurentian.ca>
	<1993Jan8.212715.21449@galois.mit.edu>
NNTP-Posting-Host: strident.think.com
In-reply-to: jbaez@riesz.mit.edu's message of 8 Jan 93 21:27:15 GMT


In article <1993Jan8.212715.21449@galois.mit.edu> jbaez@riesz.mit.edu (John
C. Baez) writes: 

   Please do ask [about why the Dirac sea is not really needed]!  Or maybe
   I will simply go ahead and answer.  One doesn't really need C*-algebras,
   by the way, one just needs a good understanding of the role of complex
   structures -- that is, the number i -- in quantum mechanics.

I meant to do a little more background reading, but since others are
asking, let me add my voice to those asking for elaboration.

You've already explained what you mean by "complex structure".  Namely, let
H be a Hilbert space over C; the complex structure is the mapping v --> iv,
where v is in H and i=sqrt(-1), as usual.

The next obvious question is what is H for Dirac's electrons?  Normally I'd
suppose the answer is 4-spinor fields, or (confusing the representation
with the abstraction) L^2 functions from spacetime to C^4.

However, Dirac comments that he needs four components because of the
negative energy states.  Quoting from his "Principles of QM" (4th edition):

    We saw in section 37 that the spin of the electron requires the wave
    function to have two components.  The fact that our present theory
    gives four is due to our wave equation (7) having twice as many
    solutions as it ought to have, half of them corresponding to states of
    negative energy.

So maybe we want 2-spinors, i.e., spin vectors, for SU(2) to act on?

And what IS the correct complex structure?  And why, mathematically, do you
get the same results by interchanging annihilation and creation operators?
And how does the correct complex structure predict positrons--- or does it?

Inquiring minds want to know.
Newsgroups: sci.physics
From: cochran@kali.enet.dec.com (Michael Cochran)
Subject: Question on Mechanics Books
Organization: Digital Equipment Corporation
Date: Thu, 7 Jan 1993 22:05:58 GMT


I'm thinking of buying some books. The two that I'm looking at are:

               1) Goldstein - Classical Mechanics
               2) Marion - Classical Dynamics

What do you think? Good reading? Are they THE classics that every bookshelf
should have or would there be another choice thats better?

Thanks,
Mike
Newsgroups: sci.physics
From: paul@mtnmath.UUCP (Paul Budnik)
Newsgroups: sci.physics
Subject: Re: hidden variables
Date: 11 Jan 93 16:34:27 GMT
Organization: Mountain Math Software, P. O. Box 2124, Saratoga. CA 95070

In article <1993Jan11.031733.1730@cs.wayne.edu>, atems@igor.physics.wayne.edu (Dale Atems) writes:
> In article <483@mtnmath.UUCP> paul@mtnmath.UUCP (Paul Budnik) writes:
> > [Eberhard's description of locality violation in QM deleted.]
> 
> Consider the Stern-Gerlach-type experiment described in my other
> post. Clearly that situation is not as simple as implied by Eberhard's
> argument. It is not a case of getting one probability distribution
> for spins measured at site 1 if the setting of magnet 2 is 40 degrees,
> and another if it is 90 degrees. You have to use measurements from
> *both* sites on members of a pair to observe the quantum correlations.
>  
> Is there a case where the nonlocality is as obvious and trivial as
> this quote seems to imply?

Eberhard's point is the setting at one site affects the probability
distribution at the other site. The exeriment you sited is slightly different
then the photon experiment Eberhard was talking about. You detect all particles
and sort them by spin direction. Thus you do not have a literal 'knob'.
However it still must be true that the observation made at one site of
each particle affected the observations made at the other site. It does
not matter in which direction this influence flows but it must flow in
at least one direction or you cannot get a violation of Bell's inequality.
The polarizer/photon experiment exactly conforms to the situation
Eberhard describes. It is the one he uses in his analysis.

Paul Budnik
Newsgroups: sci.physics,news.groups
From: crb7q@kelvin.seas.Virginia.EDU (Cameron Randale Bass)
Subject: Re: sci.physics.research: Are there important unresolved issues?
Organization: University of Virginia
Date: Tue, 12 Jan 1993 01:12:51 GMT

In article <1is89oINNlps@ellipse.mps.ohio-state.edu> goedde@math.ohio-state.edu (Chris Goedde) writes:
>
>In any case, I have a couple technical questions and comments.
>
>Will crossposting to sci.physics be allowed or disallowed?
>Personally, I don't see any reason for any articles to be crossposted
>between these two groups---do the moderators agree?
>
>On the other hand, I can see myself wanting to crosspost between
>sci.physics.{research,moderated} and sci.math.research.  I assume that
>this will be possible and the moderators will know how to deal with
>it?

     I think crossposting to sci.physics mostly unnecessary (things like
     'What's New' seem okay).  However, I think other crossposting
     should be strongly discouraged.  As far as crossposting between
     sci.math.research and sci.physics.research, I suppose there could
     be conditions under which that would be appropriate.  I hope those
     conditions do not occur often.  Besides, who wants to deal with two
     moderators for the same post?

                                 dale bass

-- 
C. R. Bass                                          crb7q@virginia.edu        
Department of Mechanical, 
     Aerospace and Nuclear Engineering
University of Virginia                              (804) 924-7926
Newsgroups: sci.physics,alt.sci.physics.new-theories
From: sarfatti@well.sf.ca.us (Jack Sarfatti)
Subject: Wavelets, squeezed states 8 Windowed Fourier Transforms.
Organization: Whole Earth 'Lectronic Link
Date: Sun, 10 Jan 1993 20:16:27 GMT


8.Windowed Fourier Transforms - a new way to do quantum mechanics?

Group G can be translation in space or time (evolution), changes in
reference framr, dilations, frequency shifts in signal analysis. Invariance
of the reproducing kernel K(m',m) under G then means that the transformed
objects (quantum wave functions, classical signals) form a description
equivalent to the original one, i.e. that the transformation changes
nothing of physical significance.

From this point of view a minimally non-unitary non-standard quantum
mechanics that still obeyed conservation of locally measurable probability
is not so objectionable in view of the fact that the measureing process is
non-unitary in the standard model.

A "generalized frame" is a special case of a reproducing-kernel Hilbert
space. Given such a frame {m}, the kernel

K(m',m) = <m'|G^-1|m>   (60)

is a reproducing kernel for the range RT of map T.

Windowed Fourier Transforms
The canonical coherent state of Glauber's quantum optical coherence theory
form a holomorphic frame. The windowed Fourier transform is another kind of
frame which is related to the Glauber frame for "phase space localization".

Let the classical "time signal" f(t) be a real function of real variable t.
It is complex for quantum signal problems. Define a "window function" h.
The standard frequency spectrum is the set of Fourier coefficients if f is
periodic or its Fourier transform if it is not periodic. If f has meaning
like a Mozart concerto the standard Fourier analysis is too crude. We are
not interested in the total amplitude

F(v) = Integral (-+infinite range)[dte^i2pivt f(t)]     (61)

We would be long gone before we got to enjoy the music. The musical meaning
of the signal, though coded into F, is what the late David Bohm called a
"hidden" or "implicate order".  We want to analyse the frequency content of
f in real time - which is how we actually perceive sound (similarly, for
spatial frequencies in vision). At each instant t = s we hear a "spectrum"
F(v,s).

Example, simplistic linear model for hearing.

The ear's output at time s depends on the input f(t) for t in the interval
s - T <= t<= s, T is "lag time" of "ear" (including neural nets). The "ear"
gives different weights to different parts of f(t). The signal to be
analysed is then

fs(t) = h(t - s)*f(t)       (62)

h is the "window function" and it will generally be complex and * means cc.
Having localized the signal around time instant s, take the Fourier
transform.

Fs(v) = Integral (-+infinite range)[dte^i2pivth(t - s)*f(t)]     (63)

which defines the "dynamical spectrum" - a marriage between the Fourier
transform and the convolution.

to be continued.
From: vignat@lnp01.jinr.dubna.su
Newsgroups: sci.physics
Subject: Re: QM question
Date: Tue, 05 Jan 93 00:18:03 GMT
Distribution: world
Organization: unknown
Reply-To: vignat@lnp01.jinr.dubna.su

>   From: nariani@utdallas.edu (Sushil Nariani)
>   Message-ID: <BzuDo8.I9B@utdallas.edu>
>
>   Scott Chase writes:
>   There is a difference between making a measurement of position and a
>   measurement of momentum for a free particle.  Only the momentum is
>   a good quantum number, i.e., position does not commute with the Hamiltonian.
>   That is, position, in general, evolves in time, no matter what you do.
>   The rule you describe only applies when the operator *does* commute
>   with the Hamiltonian for the system.
>
>           So what *does* happen when I make that sort of a measurement? In
>           general, what does measurement mean in QM and what is it's effect
>           on a system? [If this is in FAQ, please indicate without flames :-)
>
>
>   Since kinetic energy is p^2/2m, it will be very hard to construct a system
>   for which x is a good quantum number.  I suppose you could imagine a
>   velocity-dependent potential which cancels the kinetic energy, though I
>   don't know what physical system this would describe.  If position is a
>   good eigenvalue, then it will surely be very strange indeed.
>
>           suppose you could devise such a system. It would still not leave
>                   the particle in a delta function eigenstate, right?
>
>                   Sushil
>
Dear Sushil!

Measurement in QM is capturing of some particle.
Probability to capture a particle is proportional to energy of interaction
with it, and the last is proportional to |\psi function|^2.

You can easily construct a wave function with momentum and coordinate well
defined simultaneously. Don't you believe? Look

\psi = j_0(s|r-vt|)exp(ivr-i\omega t),

where \omega = v^2/2+s^2/2 and j_0 is a spherical Bessel function, or

j_0(x)=(sin x)/x.

This wave function has a precise momentum (v, m=1, as you see) and a position,
which is a point where it has the maximum. You can easily check, that it
satisfies the Shroedinger equation.

-- 
----------------------------------------------------------------------------
Vladimir Ignatovich FLNP JINR,      Tel. (09621)6-33-17 or (09621)4-70-65
141980 Dubna Moscow reg. Russia.  Fax 7(095)-975-23-81 or 7(09621)-65-085
TIME HAS INERTIA (Abian) so the PARTICLES to maintain their status quo must HAVE CONSCIOUSNESS (Nachmanson).



Newsgroups: sci.physics
From: vejcik@daq (Steve Vejcik)
Subject: Re:    TOP in TIME
Date: Thu, 07 Jan 93 10:07:48 EST
Organization: Physics Dept., University of Michigan, Ann Arbor

Hi,
   CDF has observed one e-mu event which is interesting in that
it bears some of the hallmarks expected of a top decay (or t-tbar
more precisely). In addition to the leptons having high momentum,
there is an indication that there may be a displaced vertex in
the event which would indicate the presence of a b quark.  I don't
know what the 2nd event that Time is referring to.  That may be in
reference to our one candidate from the last run.

                           Cheers,

                           Steve 

Newsgroups: sci.physics,news.groups,sci.misc
From: andre@ramsey.cs.laurentian.ca (Andre Roberge)
Subject: Re: sci.physics.research: proposed panel of moderators
Organization: Dept. of Computer Science, Laurentian University, Sudbury, ON
Date: Fri, 8 Jan 1993 17:11:34 GMT

Presuming that people criticising the proposed panel of moderators are
in favour of creating sci.physics.research, why not try to proceed as
fast as possible to create such a group, give a chance to the proposed 
moderators to prove their worth as such and see what happen?...

[Perhaps to keep people happy, one could include a clause in the chapter
of this group for having a mechanism to deal with replacing an
unsuitable moderator -- as decided in a proper forum....]

I'm one of the research physicist who's been following sci.physics on
a *very* irregular basis, mostly because I was turned off by lots
of #### that appeared there.  I can't wait for a Call For Vote to support
such a group and enjoy "good physics" posts.  Who knows, I might get
the nerves to ask publicly one of the moderator to explain what he meant
where he said something to the effect that the Dirac sea explanation
was not needed with the proper use of C* algebra  (or something like that).
Perhaps he already did, but I wasn't reading sci.physics at the time....


I would also like to add that I believe it will be *very* easy to find
more qualified and interested moderators (if the need arise) once this
group is set-up.

Andre Roberge

Newsgroups: sci.physics