X-Message-Number: 11578
From: Thomas Donaldson <>
Subject: For Damien Broderick: experimental proof remains VERY scanty
Date: Mon, 19 Apr 1999 23:51:25 +1000 (EST)

To Damien Broderick:

I too have noticed the theoretical work (and workers) who aim to form a
theory containing both quantum mechanics and general relativity. I've even
written about such things in ANALOG, though that was several years ago
and I'm sure that Witten and others have come up with new and better
ideas.

HOWEVER one unhappy characteristic of such theories is that so far they
are almost impossible to actually prove or disprove. I say "almost"
here quite consciously: several workers have quite recently worked out
one parameter (predicted by such theories) which they can actually test.
You may wish to look at G. Amelino-Carnelia, in NATURE (398(1999) 216-218)
or KC Littrel et al in PHYSICAL REVIEW A (56(1997) 1767ff). The issue of
NATURE containing Amelino-Carnelia's paper gives some other places to 
look. (I discuss this in a sidebar in the 1 March 1999 issue of my 
newsletter PERIASTRON --- which is mostly about scientific matters
relating to cryonics).

It is interesting that even now such experiments exclude some possible
theories. Our tools remain too gross to test others, but even so there
has begun to be an EXPERIMENTAL handle on quantum gravity. This is very
pleasing and important, though I doubt that it will prolong our lives.

I point this out for the simple reason that we can't really claim to 
understand how quantum theory and general relativity combine until we 
have actual experimental evidence for our ideas. No amount of purely
theoretical mumbo-jumbo can bring us even a nanometer closer to a theory
which contains both of them. 

			Best and long long life,

				Thomas Donaldson

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