Re: superposition

[palmer@sfu.ca (Leigh Palmer)]

> Leigh Palmer says:
> > It should be pointed out explicitly that superposition breaks down
> > for the electromagnetic field also at sufficiently extreme limits.
> > That field, too, exhibits nonlinearity, and a consequence of that
> > is that high energy gamma rays cannot be seen from great distances
> > in the universe because they collide with other radiation (the
> > microwave background) in otherwise free space.
>
> Do tell!  What are the other facets of this observation.  I.e. how do we
> know that there should be high energy gamma rays coming from great
> distances, and how is it known that their absence is due to E&M
> non-linearity?

Of course we don't know that high energy gamma rays should be coming
from great distances, but quantum electrodynamics wouldn't let them
travel long distances if they tried because of the cosmic microwave
background. I don't quite understand your question, however. If
the process were linear (i.e. if superposition held) electromagnetic
waves would not interact at all they would pass through one another
in free space without interaction, as indeed they do at lower energies.

Leigh