HDTenEightyP/NetNews huggingface dataset:
From: Richard.Mathews@West.Sun.COM (Richard M. Mathews)
Newsgroups: sci.physics
Subject: Re: E=mc2?
Date: 9 Sep 1992 17:48:05 GMT
Organization: Sunsoft Inc., Los Angeles, CA.
NNTP-Posting-Host: astro
Originator: richard@astro.West.Sun.COM

sgooch@uts.amdahl.com (Shelley H. Gooch) writes:
>Having examined Einstein's original letter in the Smithsonian, I was
>amazed to see that such an historically monumental letter consisted of
>only one, or at the most 2 sentences.

Strange.  The abridged copy of the letter which I have contains 10
sentences arranged in 4 paragraphs.  An ellipsis in the middle leads
me to believe that there are additional paragraphs not included in my
copy.  He refers to work by Joliot, Fermi, and Szilard indicating that
"a chain reaction in a large mass of uranium" may generate "vast amounts
of power."  He discusses the possibility of using this in a bomb, adding
that "such bombs might very well prove to be too heavy for transportation
by air."  Finally he talks about Germany stopping the sale of uranium from
Czechoslovakian mines, hinting that this may be realted to the American
work on uranium.

     Richard M. Mathews			Lietuva laisva = Free Lithuania
					Brivu Latviju  = Free Latvia
Richard.Mathews@West.Sun.COM		Eesti vabaks   = Free Estonia
					        WE  DID  IT!!!
From: keith@cco.caltech.edu (Keith Allan Schneider)
Subject: Re: AT WHAT HEIGHT IS GRAVITY PERCEPTIBLE?
Organization: California Institute of Technology, Pasadena
Date: Tue, 15 Sep 1992 05:46:11 GMT

ritley@uimrl7.mrl.uiuc.edu () writes:

>At the risk of breaking with the tradition of using simple assumptions 
>in stating physics problems (spherical cow, etc.), let me ask....

>Given most humans' average athletic ability, musculature, metabolism,
>etc. etc. --- at what altitude will a deviation in gravity from sea level
>become perceptible (to someone)?  Any comments?

Well, I don't know much about the average perceptual abilities of
humans, but let's assume that we can notice a 1% change in the weight of
an object.

Then, (the gravitational force is GMm/r^2) we have

1/r2^2 = .99/r1^2

r1, the (let's say equatorial) radius of the Earth is about 6378km.  So,
at a distance of 6410km from the center of the Earth (that is, 32km or
20 miles), there will be a 1% variation in the weight of an object.

If we are less perceptive, needing 5% or 10% variation to notice a change, the
distance is 102 or 214 miles, respectively.

Now, the highest mountain is about 6.6 miles abouve sea level.  So, unless you
could detect a .3% change in the weight of an object, you will not notice
the difference of gravity, even on Mt. Everest.  (if you weigh 165lbs like I
do, then you'd have to notice 8.8oz change in your body weight, which is
much less than the variation due to food, water, and waste every day)

oh well
keith

Newsgroups: sci.physics
From: felawka@sitka.fnal.gov (Larry Felawka)
Subject: Re: Angular momentum thought experiment
Organization: Fermi National Accelerator Laboratory, Batavia IL
Date: Sun, 6 Sep 1992 21:44:16 GMT

Find the acceleration of m1.  The O's are pulleys.
             __ 
            |m0|_____________
            |__|            O|
--------------------------   |
/////////////////////////|   |
                        /|   |
   All pulleys, ropes,  /|  |O|
   and surfaces are     /|  | |
   frictionless and     /|  | |
   massless.            /| m1 |
                        /|    m2
                        /|

				--Blair
				  "Took me a whole
				   bloody day..."


Solution:

Max Kettner's rules for solving all problems in Mechanics:
 1) choose a system
 2) note all forces acting on the system
 3) f=ma
 4) "You can't push a rope..."

(Max Kettner was my 1st yr Physics Prof.)

So ....

  I) choose mass 1 as system
      T1 - m1.g = m1.a1

      T1 is tension in string connected to mass m1
      g is acceleration due to gravity
      a1 is acceleration of m1 in "up" direction

 II) choose mass 2 as system
      T2 - m2.g = m2.a2

      T2 is tension in string connected to mass m2
      a2 is acceleration of m2 in "up" direction

III) choose masses 1 and 2 as system

      T3 - (m1+m1).g = (m1+m1).ac

      T3 is tension in string conected to pulley which supports both masses
      ac is the acceleration of centre of mass of 1 and 2

 IV) choose mass 0 as the system

      T4 = m0.a0

      a0 is the acceleration of m0 towards the right

Some relationships:
   T1 = T2
   T3 = T4
   a0 = - ac
   ac = (m1.a1+m2.a2)/(m1+m2)

The unknown quantities are T1, a1, T2, a2, T3, ac, T4, a0 (for a total of 8).
We have 8 equations, so we can solve this thing.  The solution is left as an
exercise for the reader :-).


					Larry Felawka

Newsgroups: sci.physics
From: matmcinn@nuscc.nus.sg (Mcinnes B T (Dr))
Subject: Re: Comprehending Theories (of Everything?)
Organization: National University of Singapore
Date: Sat, 12 Sep 1992 05:12:00 GMT

bweiner@ruhets.rutgers.edu (Benjamin Weiner) writes:
: Even if string theory, or loop variables (by the way I have a theory
: which says that deep down, the fundamental structure of the Universe
: is tiny little pieces of duct tape) or anything else, should turn
: out to be both a correct TOE and comprehensible to only a few, that
: would be nothing new.  At some point there were only two people who
: understood calculus (well, maybe a few more, but very few).
: 
: I'm not saying that string theory (et al) will ever be taught to college
: freshmen, but that its difficulty is linked to its status as research
: frontier.  So the incomprehensibility of proposed TOEs is an artifact
: of their newness, not some kind of coincidence with human limits
: (unless you believe, like I do, that people tend to think up the most 
:  COMPLICATED EXPLANATION AVAILABLE)

Well, yes, I do suspect that.I once heard somebody say [not in jest]
that people should have realised that Kaluza-Klein theories must be
wrong on the grounds that they do not involve sufficiently abstruse
mathematics.
Newsgroups: sci.physics
From: pcsg8264@uxa.cso.uiuc.edu (Preston Craig Smith)
Subject: Tri atomic Hydrogen Ion Potential Energy Diagram (sources?)
Organization: University of Illinois at Urbana
Date: Tue, 8 Sep 1992 04:01:41 GMT

In working with the DEGAS code, our group has come across the need for
a PE diagram for H3+.  H and H2 are availible of course, but we cannot
find a reference for H3+.  Any leads?
Newsgroups: sci.physics,sci.astro
From: asnd@reg.triumf.ca (Donald Arseneau)
Subject: Re: My son would like to know about photons...
News-Software: VAX/VMS VNEWS 1.41    
Keywords: photon,size
Organization: TRIUMF: Tri-University Meson Facility
Date: Wed, 9 Sep 1992 09:51:00 GMT

In article <7SEP199213475340@zeus.tamu.edu>, dwr2560@zeus.tamu.edu (RING, DAVID WAYNE) writes...
>pratt@Sunburn.Stanford.EDU (Vaughan R. Pratt) writes...
>>giving the nominal width of the photons.  Typical photon widths ranged
>>from a few feet to hundreds of feet.
> 
> I would have thought each photon would go into
>one antenna or the other. Any astrophysicists out there?

A photon is a particle of light (since it has zero rest mass it is normally
not called a particle, but a quantum).  Interference is a phenomenon of 
waves.  Strangely, wave properties can never be seen in a measurement of
particle properties, and vice-versa.

Photons are not localized point-like objects when you measure interference,
but are as large as your detection device.  They don't come at a particular
time, but arrive for the whole time you observe.

If, however, you try to locate a photon precisely, or time its arrival,
interference and other wave-like behavior disappear!

Donald
Newsgroups: sci.physics
From: matmcinn@nuscc.nus.sg (Mcinnes B T (Dr))
Subject: Re: How old is the universe?
Organization: National University of Singapore
Date: Sat, 12 Sep 1992 02:15:23 GMT

Sorry, something has gone wrong with the hardware here. I am not the
author of the bit about the Physical Review Newspaper.
Newsgroups: sci.physics
From: m15133@mwvm.mitre.org (Graham K. Glover)
Subject: QUESTION: General Relativity
Organization: The MITRE Corporation
Date: Tue, 8 Sep 1992 21:31:20 GMT

A question has come up in my considerations of relativity.  I would 
appreciate any input anyone might have regarding it.

What happens to the frequency of a light wave that has been deflected by 
the gravitational effects of a massive body?

    ------nu~0--->--\ nu~1
                  *  \
                 /    \
    massive body      _\|
                        nu~2

What is nu~1 and nu~2 relative to nu~0?  Why?  Please cite sources, if 
possible.

Please e-mail responses to me.  Thanks in advance for your consideration 
in this matter!  It is appreciated.

----------------
Graham K. Glover
----------------
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
Distribution: na
Date: Thu, 10 Sep 1992 01:39:00 GMT

I write...
>>                                                      most of the people
>>ever to have lived are alive today.

Ridiculous. :)

sichase@csa2.lbl.gov writes...
>There was recently a discussion of this (was it sci.skeptic?) - one estimate
>which was posted is that the total population over all human history is
>roughly 100 Billion (of course it depends on when you start counting).  If
>this is even roughly correct, then your statement is incorrect.

You're right. After some research I think the number in history is ~50b.

>>Which reminds me... Consider Galileo, Newton, Einstein. There should
>>be at least 3 people alive today as brilliant in physics as they were!
> 
>Galileo and Newton were bright, but they were also lucky to be born when 
>you could gain fame and fortune for say, looking through a telescope
>and discovering sun spots, moons, etc.  

It was not luck that Galileo was alive when the telescope was invented!
Perhaps he was lucky to have been alive when noone had heard of the scientific
method, and noone knew to apply _mathematics_ to physical problems, and
noone knew to decide on physical theories on the basis of actually _looking_.
But then there were a lot of others throughout the ages who lived under
those circumstances.

As for Newton, he was 23 when he invented Calculus to solve a physical
problem! Einstein had nothing to compare with this achievement. If he had
invented Reimannian Geometry I might be more impressed.

>                                        They were both certainly visionaries, 
>but I don't know if they were any more intelligent than today's luminaries.
>Einstein is another matter - I think that he is a good example of extreme
>genius performing unexpected nontrivial feats in a time when cutting-edge
>experimental data was much harder to generate, the necessary mathematics
>was much more sophisticated, and the "easy" things had already been done.

I think I should also add Archimedes.

Dave Ring
dwr2560@zeus.tamu.edu
Newsgroups: sci.physics
Newsgroups: sci.physics


For one, because of the behaviour of a photo-multiplier tube, which
is based on the photo-electric effect. As for 1000 sub-photons, this
don't happen, becuase otherwise you could split a monochromatic source
into it's constituents with a grateing.

--------------------------------------------------------------------------
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?
--------------------------------------------------------------------------
From: baez@ucrmath.ucr.edu (john baez)
Newsgroups: sci.physics
Subject: Re: third try
Date: 4 Sep 92 22:27:00 GMT
Organization: University of California, Riverside

In article <1992Sep1.041710.11504@asl.dl.nec.com> terry@aslws01.asl.dl.nec.com (Terry Bollinger) writes:
>Ah well... I'll give it one more try:

>    In a large-scale system you can track conservation of angular momentum
>    can be tracked by attaching angular momentum vectors to the component
>    objects of that system.  The sum of all such vectors will be invariant
>    over time as long as the system is not disturbed from outside, and the
>    magnitude and orientation of such vectors are independent of observers.

True for a "classical system" - i.e., false, but okay as long as we aren't 
interested in knowing the angular momentum very accurately, so that classical
mechanics is a decent approximation.  In short, what you're saying is fine
so far.

>    In an extremely small system you can still track conservation of angular
>    momentum by attaching vectors to the objects, but the vectors will now
>    be quantized (multiples of 1/2 hbar) and, more importantly, the exact
>    orientation of these vectors will depend on HOW they are measured.

Well, here is where I think you're wrong.  One really never measures the
angular momentum VECTOR in quantum mechanics, since the components don't
commute.  This may in fact be exactly what you are referring to.  But I 
think it's better to say that one can pick any axis and measure angular
momentum around that axis.  If one does so accurately and then re-measures
the angular momentum of the WHOLE RELEVANT SYSTEM again along the same axis
one is bound to get the same answer.  By the "whole relevant system" I am
noting that anything which could apply a torque to what you were originally
interested in must also be included.  So if you measure the ang. mom. of
an electron along the x axis, then use a "angularmomentumometer" to measure
the ang. mom. of the electron along the y axis, and then want to check the
ang. mom. along the x axis again to see if it was conserved, one had
really better do the following:

measure the ang. mom. of the electron AND angularmomentumometer #1
along the x axis, using angularmomentumometer #2

measure the ang. mom. of the electron along the y axis, using 
angularmomentumometer #1

measure the ang. mom. of the electron AND angularmomentumometer #1
along the x axis, using angularmomentumometer #2

If you do this I claim that the angular momentum along the x axis WILL be
be conserved!

>    Such a dependence unavoidably leads to the implication that the angular
>    mometum vector sum for the system will no longer invariant over time.
>    It can (and will) change from one set of measurements to the next.

I think that the way out of this puzzle is as stated above.  I agree that
it's an interesting and tricky problem, which is probably why everyone
except me had the sense not to answer!!!! :-)  I have never seen it
before.    
Newsgroups: sci.physics
From: firth@sei.cmu.edu (Robert Firth)
Subject: Re: Computability of the universe
Organization: Software Engineering Institute
Date: Thu, 10 Sep 1992 13:14:37 GMT

In article <1992Sep10.021939.10087@murdoch.acc.Virginia.EDU> lfoard@Turing.ORG (Lawrence C. Foard) writes:

>My argument is that any given single expermental trial must be
>able to be >>exactly<< simulated by a finite turing machine in finite
>time. 

Not so.  True random events cannot be simulated by a Turing machine, and
the universe presents us frequently with true random events (for example
the scintillations on the dial of your radium watch).

>If this is not the case we have to ask what we have left out of logic
>such that its not sufficient to explain the universe.

The leap from "logic" to "Turing machines" is one I confess I'm unable
to follow.  A Turing machine is merely a very simple engine that is
capable of performing a very small subset of feasible computations.
To deify it makes no more sense than to insist the universe must be
explained using only straight edge and compasses.
Newsgroups: sci.physics
From: leffler@physics.ubc.ca (Steve Leffler )
Subject: Re: Question about falling elevator...
Organization: University of British Columbia, Vancouver, B.C., Canada
Date: Fri, 11 Sep 1992 20:40:24 GMT

owens@hilbert.wharton.upenn.edu (Susan Owens) writes:

>  I have a question that I thought maybe someone here could answer.  It
>concerns a falling elevator.  If I was in an elevator that was falling
>say 20 stories what would happen if I jumped right before I hit the
>ground.  I say that I wouldn't be able to jump because of the force
>being exerted against me, some collegues here say that I  would be able
>to jump but that I would not affect the force with which I hit the ground with
>to any degree to be worth mentioning.  I agree with that but I still say
>that I would not be able to jump. 

> And if I am right I am sure that there is a less distance that I  
>could fall that I would be able to jump right before I hit the ground
>(I would say roughly around 4 stories).  Does anyone know the aprox.
>height at which an avarage person would be able to jump before hitting
>the ground. Or maybe I am totally wrong (wouldn't be the first time) 

   If the elevator is not experiencing any friction due to contact with the walls 
of the shaft, etc. you will experience NO force while the elevator is falling
(relative to the reference frame of the moving elevator).  This is because both you
and the elevator are falling freely under the influence of gravity, and so the
downward motion of the elevator under your feet exactly equals the downward motion
of your body due to gravity.  Thus, you would feel like you were in zero gravity,
relative to the elevator. (In fact, this effect is why the "zero-gravity"
state experienced by astronauts in orbit is often referred to as "free-fall".)

   Thus, you would be able to jump, but only if you were already crouched down
before the elevator started to fall.  If you weren't already crouching, you would
not be able to do so: your feet would simply drift up off of the floor of the
elevator when you tried.

   Jumping wouldn't help much, anyway.  When the elevator hit the bottom of the
shaft and stopped, you would soon hit the floor of the elevator at a velocity
equal to the velocity with which the elevator had hit the ground.  There might
be a difference in the amount of injury you would sustain due to the different
nature of the collision, but it isn't obvious to me whether it would be more
or less.  Certainly, the total amount of energy in the collision would be the
same either way.

				      Steven Leffler
				      leffler@physics.ubc.ca

Newsgroups: sci.physics
From: barry@arnold.math.ucla.edu (Barry Merriman)
Subject: Black hole + anti-Black hole = ?
Organization: UCLA, Mathematics Department
Date: Tue, 8 Sep 92 22:21:01 GMT


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

Or, if I take two black holes, one made from ordinary matter
and the other made from anti-matter, and merge them, what happens?
Do I get a bigger black hole, or are they somehow annihilated?

--
Barry Merriman
UCLA Dept. of Math
UCLA Inst. for Fusion and Plasma Research
barry@math.ucla.edu (Internet; NeXTMail is welcome)
From: jcj@tellabs.com (JCJ)
Newsgroups: sci.physics
Subject: Re: Are redshifts discrete?
Date: 14 Sep 92 17:46:31 GMT
Organization: Huh?

In article <5323@tuegate.tue.nl> johan@blade.stack.urc.tue.nl (Johan Wevers) writes:
>malova@venus.iteb.serpukhov.su writes:
>>
>>   Some years ago I read about discrete distribution of redshifts. 
>>   What is now? Is the idea alive?
>
>Redshift is continious: SRT tells you that the ratio of the observed
>frequency f' and the original frquency f from an object that moves w.r.t.
>the observer is given by...

Ah, I believe the original poster is referring to some people claiming
to have found a clustering of redshifts at two "preferred" values.  It's
probably a statistical fluke.
From: davidk@bcsaic.boeing.com (Dave Kerlick)
Newsgroups: sci.physics
Subject: 137, was: Did electric/magnetic symmetry "break"?
Date: 11 Sep 92 17:50:08 GMT
Organization: Boeing Computer Services AI Center, Seattle

In article <1992Sep8.012930.25239@galois.mit.edu> jbaez@riesz.mit.edu (John C. Baez) writes:
>
>Afficionados of those who plunged in where angels feared to tread will
>have to check out Eddington's book in which he tried to "deduce" that
>the fine structure constant was exactly 136.  Then it turned out to be
>137 and he realized he'd left one something-or-other out.  Well, then
>it turned out not to be exactly 137 either.  People can also try out
>Irving Segal's article on the value of the fine structure constant. 
>Sorry, I don't have the reference.  
>
>Myself, I think 137.036 is just fine.  

George Gamow evidently got wind of this, and sent in a joke paper to
Sommerfeld's (?) journal about why the freezing of water is at

(2 / alpha - 1) degrees Celsius.  It got published, to much merriment.


-- 
G. David Kerlick,     Research & Technology Boeing Computer Services  
P.O. Box 24346, MS 7L-24, Seattle, WA 98124-0346
Work phone: 206-865-5051 Fax: 206-865-3327  Email: davidk@espresso.boeing.com
Newsgroups: sci.physics,sci.optics
From: johnp@gagme.chi.il.us (john papiewski)
Subject: Physics as a career!
Originator: johnp@gagme
Organization: Gagme Public Access UNIX, Chicago, Illinois.
Date: Tue, 15 Sep 1992 03:02:34 GMT

I'd like to hear from REAL physicists out there on the net,
about physics as a career.  After a long time doing commercial and
engineering computer work (programming, support, etc) the siren song
of basic science is sounding loudly (85 db) in my ears. If you
respond I'd like to know your impressions on:
1. Satisfaction with research
2. Satisfaction with teaching
3. Recommended university (pref. in Chicago area)
4. Other avenues, like working in a commercial/industrial setting.
5. How you decided on a career in science.
6. Do physicists REALLY peak in their 20's? I'm >30.

Thanks in advance for ANY advice/comments/references!

John Papiewski

Newsgroups: sci.physics
From: gilligan@bldrdoc.gov (Jonathan M. Gilligan)
Newsgroups: sci.physics
Subject: Re: Uncertainty Principle
Date: 5 Sep 92 01:26:15 GMT
Organization: National Institute of Standards and Technology

In article <1992Sep4.170847.235@prim> prim!dave@germany.eu.net (Dave Griffiths) writes:
>
>I just read (Stephen Hawking) a nice explanation of the Uncertainty Principle:
>to measure the position accurately, you need very short wavelength photons
>which will have such a high energy that they will bash the particle so hard
>that it's momentum becomes uncertain.

Karl Popper points out that this argument fails to explain why we
can't first measure the momentum by scattering a low-energy photon of
known momentum (so as not to disturb the momentum of the particle); and
then, an extremely short time later, measure the position as described
above.  His point was not to show any inconsistency in quantum
mechanics, but to show the shortcomings of thinking in terms of
thought experiments.  (from ``On the use and misuse of imaginary
experiments, especially in quantum theory,'' Appendix xi of
_The_Logic_of_Scientific_Discovery_, Harper 1968).

---Jon
-- 

Disclaimer --- The government probably disagrees with my opinions.
Newsgroups: sci.physics
Subject: Re: Terminal velocity of a raindrop?
From: harper@kauri.vuw.ac.nz (John Harper)
Date: Wed, 9 Sep 1992 21:26:59 GMT
Organization: Victoria University of Wellington

In article <1992Sep9.161952.21421@news.uiowa.edu> haferman@icaen.uiowa.edu (Jeff Haferman) writes:
>For an excellent overview of some physics of raindrops, check out
>(ref deleted)

Also: H Pruppacher & JD Klett "Microphysics of clouds and precipitation"
D Reidel Publ Co, Dordrecht, Holland 1978 (I don't know if there is a later
edition)

John Harper Mathematics Dept. Victoria University Wellington New Zealand
Newsgroups: sci.physics,sci.skeptic,alt.folklore.science