From: palmer@sfu.ca (Leigh Palmer)
Subject: Re: The Hole Story
Organization: Simon Fraser University
Date: Fri, 18 Dec 1992 19:24:14 GMT

In article <1992Dec18.162839.1529@cs.ucf.edu> clarke@acme.ucf.edu (Thomas
Clarke) writes:
>> >                                                      ...When 
>> >something changes, only the retarded solutions propgagate and
>> >thus radiation appears to comes from only the retarded position.  
>> >Why only retarded solutions? - ask the philosophers :-)
>> 
>> For heaven's sake, take off your blinders!
>> 
>This was an allusion to a poorly remembered book (Davies?) 
>that discussed incoming and outgoing (advanced and retarded) 
>electromagnetic waves from an accelerated charge in terms of
>time's arrow, our apparent perception of an asymetry in time.  

I don't think I misunderstood you, Thomas, but of course it's
possible. I understand that you would rather consider a static
field to be something replaceable by a Fourier decomposition in
harmonic functions of time. That is fair enough, and it would
probably win me over if the limits on the decomposition were 
always the same, but as you point out the advanced terms are
arbitrarily excluded from the radiation case. I'm saying that
one can arbitrarily calculate static effects (those due to 
bodies moving solely under the influence of gravitational
forces) using an infinite-speed action-at-a-distance formalism.
As Tom Van Flandern correctly points out, and as philosophically 
distasteful as this may be to some, it is absolutely (!) 
isomorphic to Nature. There is not the smallest residual anomaly
to suggest this is not *a* correct way to look at the universe.
The fact that the solar system has not discorporated in a grand
show of contempt for the law of conservation of angular 
momentum over the last five billion years is evidence enough.

The question of whether this is "true" is a philosophical one,
and that piece of metaphysics seems to be what we are always
arguing about, understandably without resolution. Some of us
have been, as I pointed out before, guilty of the intellectual
crime of reification. We ascribe to a mathematical formalism an
intrinsic reality which it ought not to be considered to have.
Now I'm going to exempt myself from this group. I used to make
this error; I no longer do.

Perhaps an example of a noncontroversial type can illuminate my
point. I've just finished teaching a sophomore electricity and
magnetism course. I showed the students that it is possible to
show that the Joule heat produced in a resistive current-
carrying wire may be attributed to the flux of electromagnetic
energy into the wire as computed by using Poynting's vector. I 
think we all can agree that, while this gives the right answer,
we'd *rather* look at the source of the energy as being the 
current supply, but we cannot unambiguously attribute to that
source a causal role! That would be a metaphysical judgement,
and we don't even have poetic licence, much less philosophical
licence to do so. Nonetheless, most all of us will go along
with the current source as causal.

Im'm afraid your incoming gravitational waves (if that's what 
you advocate, a point about which I am unclear) are in the same
class as the incoming Poynting flux. I have a distaste for them
in much the same way, but I won't say that they are "untrue",
or that they "don't exist". That is beyond my competence, and, 
I believe, beyond that of any mortal.

Bill Burke said it better than any other I have seen:

   "The goal of abstraction is to find common structure in
   different concrete situations, and then to discuss this
   structure independently of the specific situations. Done
   properly, this increases one's knowledge by pooling 
   information from diverse situations. But be careful.
   Excessive abstraction is a very common error. Keep the
   references to concrete instances in mind, but do not 
   give the abstract structures an existence of their own.
   Treating ideas as things (reification), done to excess
   in politics and religion, has no doubt murdered more
   people than any other cognitive error."

If I could write like that you guys wouldn't get it for free.

Leigh
Newsgroups: sci.astro,sci.physics