Re: Are Gravitational Waves Electromagnetic waves?

From: Bilge (dubious_at_radioactivex.lebesque-al.net)
Date: 03/07/05 

Date: Mon, 07 Mar 2005 14:09:40 GMT

 David Cross:
>May I ask how one can suppose that electromagnetism, based on the
>presence and motion of charges, can be superficially claimed to also
>have its origin in gravitation, which is based on the presence of
>interacting masses?

  You can't, since mass is a poincare invariant in special relativity,
which manifestly does not include gravity. That means that mass has a
meaning even in the absence of a gravitational interaction. Whether such a
theory is ultimately self-consistent and physically realizable is a
different question which, as far as I know, has never been proven either
way. However, since there is not a single example of a high energy
experiment in which it has been necessary to include gravity to obtain
agreement with theory, it's a safe bet that gravity isn't relevent at the
TeV scale.

>I grant that unified theories would have the same set of equations
>for both gravity and electromagnetism; however, as I see it that is
>not the same thing as saying the origin of one kind of wave is the
>same as the origin of the other.

  It's not, except in a very remote and abstract way which is not anything
like what was suggested. E&M and gravity can only be the same interaction
in the same limit that the electromagnetic field strength is equivalent to
geometric curvature. The ``curvature'' defined by the electromagnetic
field strength is not a geometric curvature, except in the sense that a
phase can be described using geometric language and calling it a fibre
bundle, or alternatively by appealing to more than four dimensions. If the
universe was ever five-dimensional, the five dimensions have not been on
equal footing for a very long time and have long since split into 4
spacetime dimensions and one ``curled up'' circular dimension. However,
since we already have a theory which unifies the electromagnetic force and
the weak force (and the strong force, more or less), which is known to
work very reliably, the question of unifying E&M and gravity is
essentially moot. The question is unifying gravity with a theory in which
E&M doesn't exist as a force distinct from the strong or weak
interactions.

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