mam@charm.UUCP (Matthew Marcus) (06/11/85)
(E = Mc^2 +- 3dB )
About maximum energies for photons: Take any ol' photon you have lying
around. Now look at it from a frame of reference going very fast in the
direction opposite to said photon. The photon is now blue-shifted to higher
energy. By making your new reference frame move fast enough, you can get any
energy you want, including 10^43 Hz or whatever the last-posted limit was.
Now, 'black-hole-ness' is an invariant, so an energetic photon is never a
black hole. Another way to see this is that black holes are characterized
by three and only three parameters: charge, spin, and mass. This mass is
an invariant, and hence must be in the nature of a rest mass. The rest
mass of a photon, any photon is 0. 'Nuff said.
The argument has been made that a hefty enough electromagnetic
field will gravitate itself into a black hole. Well, Misner, Thorne &
Wheeler, aka the Phone Book, give as a show-that problem the theorem that
two light beams do not attract. While there is energy density in each beam
(T sub 00, where T is the stress-energy tensor), there is also momentum
density (T sub 0i) which cancels out the attractive effects of light upon
light. Therefore, you are not going to get a black hole by shining lots
of light into a small spot.
{BTL}!charm!mam