From: Leigh Palmer <palmer@sfu.ca>
Subject: Re: The Hole Story
X-Xxmessage-Id: <A75D362C09011C21@rs16-annex3.sfu.ca>
X-Xxdate: Tue, 22 Dec 92 05:16:28 GMT
Organization: Simon Fraser University
X-Useragent: Nuntius v1.1.1d16
Date: Wed, 23 Dec 1992 05:15:29 GMT

In article <STEINLY.92Dec22104345@topaz.ucsc.edu> Steinn Sigurdsson, 
steinly@topaz.ucsc.edu writes:
>In article <1992Dec22.011638.21749@sfu.ca> Leigh Palmer <palmer@sfu.ca> 
writes:
>
>   In article <STEINLY.92Dec20193619@topaz.ucsc.edu> Steinn Sigurdsson, 
>   steinly@topaz.ucsc.edu writes:
>
>   >I suppose I should read the paper, but there are exact solution of
>   >plane gravitational waves for GR. They're literal solution of the
>   >Einstein equation.
>
>   That's interesting. Are gravitational plane waves susceptible to 
>   (linear) Fourier decomposition? Do they comprise a spanning set for 
>   all gravitational wave solutions? If they are not superposable, how 
>   would one generate a gravitational plane wave?
>
>Gravitational waves are not in general superposable because they
>couple to each other - they carry stress-energy. All the exact
>solutions I know of are ones with special symmetry in vacua, although
>I only have a passing familiarity with the subject.

That being the case, one cannot infer from the existence of plane wave 
solutions that waves generated by, for example, a binary compact sytem, 
will exist which are solutions of GR. In electrodynamics the existence of 
plane wave solutions implied the existence of many other sorts of 
solutions by Fourier's Theorem, and it seems that a leap has been made of 
a similar sort which is not justified in the case of GR.

Thus we return to the question of whether a binary compact system can 
radiate. It is not immediately obvious to me that it should radiate plane 
waves (indeed that possibility is ruled out because plane waves are 
infinite in extent). Does a radiative solution to GR exist which has a 
symmetry more appropriate to the case of the binary pulsar?

I'd also like to ask again my previous question: how would one generate a 
gravitational plane wave? I have trouble wraping (or warping) my 
imagination to conceive a possible source geometry. I hasten to add that
I 
can't do it for electromagnetic waves either, but in that case I can 
generate them by decomposition, going to the far-field limit of any
finite 
radiator.

I will also remind everyone that I do not know GR, but I do see holes in 
arguments made here, perhaps more clearly because of my relative 
ignorance. There may, indeed, be a consensus in the community, but I'm
old 
enough to have seen several similar situation collapse in the face, 
particularly, of observation. Madame Wu won a Nobel Prize for Lee and
Yang 
under entirely similar circumstances a couple of weeks after Louis 
Alvarez, my nuclear physics teacher, had explained parity symmetry to us 
in class. He also told us of Lee and Yang's iconoclastic ideas, and in
the 
same semester gave us the new and diametrically opposite description of 
that aspect of Nature which resulted from the discovery. The correct 
answer on the final examination had changed almost overnight!

Some here think that anyone who would gainsay orthodoxy must be 
dangerously close to being a crackpot. That is not the case. One does 
not have to go back to Galileo to instantiate counterexamples. The
scientific process is replete with them.

Leigh
Newsgroups: sci.astro