From: hal@finney.org
Date: Mon Jun 25 2001 - 18:17:55 MDT
Amara writes:
> >http://xxx.lanl.gov/abs/astro-ph/0012345
> >Magnetic tension and the geometry of the universe
> >-Christos G. Tsagas (University of Portsmouth)
>
> The implications of this paper is wild. Fascinating, really. I wish I
> could follow the equations, but I never studied magnetohydrodynamics
> in a general relativistic framework, so I had a lot of trouble
> following it.
I haven't tried to read it and I'm sure would not be able to understand
it if I did. But there is nothing new in principle with the idea that
electromagnetism causes gravitation.
My bible is the "telephone book" Gravitation by MTW, from 1973.
They describe in chapter 1 how the metric leads to the Riemann curvature
tensor, and then to the Einstein tensor G. The key equation is then
G = 8 pi T, where T is the stress-energy tensor, the source of gravity.
In chapter 5 they show the formula for T in several simple examples,
including electric and magnetic fields. The 00 "energy" component of
T is (E^2 + B^2) / (8 pi), the well known Maxwell expression for the
electromagnetic energy density.
So EM fields have energy and stress, and these phenomena directly lead
to curved space. I gather that the new work shows how these effects can
build up over large scales to be unexpectedly significant. But there
is no surprise in the basic idea that electromagnetism causes gravity.
Hal
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