Message #204405

[Jennifer Murdoch]

 The inverse Compton effect lifts low-energy photons to high energies
       in collisions with relativistic electrons,  while  gamma  and  X-ray
       photons lose energy  by  the direct Compton effect.   The  radiation
       reaching the observer  thus bears the imprint of both the source and
       the accidents of its passage though space.

       The Universe observable  with  electromagnetic  radiation  is  five-
       dimensional.  Within this   phase,  four  dimensions   -   frequency
       coverage plus spatial,  spectral,  and temporal resolutions - should
       properly be measured logarithmically with each unit corresponding to
       one decade (Tarter,  1984).  The fifth  dimension  is  polarization,
       which has four possible states:  Circular, linear,  elliptical,  and
       unpolarized.

       This increases the volume of logarithmic phase space fourfold.