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gravity waves [message #57910] Tue, 07 May 2013 18:19 Go to next message
ARG%SU-AI is currently offline  ARG%SU-AI
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Message-ID: <13393@sri-arpa.UUCP>
Date: Fri, 4-Nov-83 03:47:00 EST
Article-I.D.: sri-arpa.13393
Posted: Fri Nov  4 03:47:00 1983
Date-Received: Tue, 8-Nov-83 21:37:00 EST
Lines: 43

From:  Ron Goldman 

n054  1329  31 Oct 83
BC-SCIENCE-WATCH (UNDATED)
c. 1983 N.Y. Times News Service
    In 1976 the Soviet Union's Crimean Astrophysical Observatory found
that the surface of the sun is heaving up and down every 160 minutes.
''The interpretation of this phenomenon,'' it reported, ''seems to
cause much theoretical difficulty.'' More recently, astronomers have
been puzzled by the enigmatic nature of an extremely powerful
celestial source of gamma rays called Geminga, which also have a
160-minute periodicity.
    Now, George Isaak of the University of Birmingham in England has
proposed that Geminga causes the solar oscillations. Geminga is
believed to be the closest neutron star to the solar system. Isaak
argues that if, like many other stars, Geminga is in a tight orbit
around some companion body, the pair might radiate gravity waves
sufficiently powerful to jostle the core of the sun.
    Einstein's general theory of relativity predicts the existence of
gravity waves, but they have never yet been convincingly detected.
The core of the sun, with a density of 30 tons per cubic foot, should
respond to such waves far more efficiently than the metal cylinders
used in earth-based detection efforts.
    According to the October 20 issue of Nature, Philippe Delache of
France's Nice Observatory and his colleagues have examined five
months' worth of gamma ray emissions from Geminga, recorded by the
satellite COS-B over a seven-year period. They report a 160-minute
variation and also note that tiny earth tremors reach a maximum every
160 minutes, as though the earth were also responding to the gravity
waves.
    As noted by Nature, however, there are several difficulties with
such proposed links. When two massive bodies are circling one another
every 160 minutes, as indicated by the gamma ray variations, gravity
waves should be emitted by each object. The pair would therefore
radiate one every 80 minutes.
    A research group at the University of Rome, led by Eduardo Amaldi,
has used suspended bars of metal to record oscillations that could be
coming from the core of the Milky Way Galaxy, but they are not yet
persuaded the cause is gravitational. Evidence for gravity waves from
the galactic core was reported a number of years ago by Joseph Weber
of the University of Maryland, a pioneer in such observations, but
was never generally accepted.
    
Re: gravity waves [message #57931 is a reply to message #57910] Tue, 07 May 2013 18:19 Go to previous message
gjphw is currently offline  gjphw
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Message-ID: <690@ihuxm.UUCP>
Date: Wed, 9-Nov-83 15:14:10 EST
Article-I.D.: ihuxm.690
Posted: Wed Nov  9 15:14:10 1983
Date-Received: Fri, 11-Nov-83 01:55:35 EST
Organization: AT&T Bell Labs, Naperville, Il
Lines: 26



  This brief note is an attempt to clarify a minor error in the NY Times
article quoted by R. Goldman.  It is a reflection on the intended audience
for the original article.
  
>   Einstein's general theory of relativity predicts the existence of
> gravity waves, but....

  The instructor for my general relativity course claimed that Einstein's
unadulterated theory does not permit gravity waves.  As originally formulated,
general relativity is a nonlinear theory which does not permit waves to
travel far from the source.  A linearized version of general relativity, which
is also easier to work with, does allow gravity waves.
  These comments were made in light of the claims by J. Weber that he had
detected gravity waves.  Einstein's full theory does not permit the generation
of gravity waves, so Weber's observations were considered very interesting.
Since then (1978), other experimenters have constructed equipment similar to
Webers in an attempt to repeat his findings, but none of the other trials have
detected gravity waves.
-- 

                                    Patrick Wyant
                                    AT&T Bell Laboratories (Naperville, IL)
                                    *!ihuxm!gjphw
Re: gravity waves [message #57934 is a reply to message #57910] Tue, 07 May 2013 18:19 Go to previous message
mwe is currently offline  mwe
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Message-ID: <116@astrovax.UUCP>
Date: Thu, 10-Nov-83 11:48:51 EST
Article-I.D.: astrovax.116
Posted: Thu Nov 10 11:48:51 1983
Date-Received: Sat, 12-Nov-83 05:33:56 EST
References: <690@ihuxm.UUCP>
Organization: Princeton Univ. Astrophysics
Lines: 21

RELATIVISTIC JET ON!

I don't know who your instructor was, but hopefully it was you who misunderstood
him, not him making an unforgivable error. 

But because we seem to be quoting authorities here...

My general relativity instructor was Kip Thorne. He said that Einstein's field
equations could describe the propogation of gravity waves. In fact, any change
in the curvature of space time is caused by such waves. He also said that the 
waves are non-linear (because gravity waves carry energy => mass; a similar case
would be if the photon carried electric charge). This means that the equations
can't be easily solved, but it doesn't mean that Einstein's theory doesn't
predict the waves. The linearized equations you saw are the weak-field limit,
which make the approximation that the energy carried in the waves is negligible.
These can be solved, and they represent very closely what happens in Einstein's 
theory in this limit.

					CRAWLING BACK INTO MY BLACK HOLE
					web ewell
					astrovax!mwe
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