In article , Uncle Al writes:
"Geoffrey A. Landis" wrote:

Despite a recent article in New Scientist, a solar sail does not break
the laws of physics.
[snip]

Actually, it does as proposed. The sail will come into thermal
equilibrium with the radiation field and emit photons from its other
side, counter-thrusting.

Nope. It radiates from both sides, thus its own emission results in
no momentum change (thus no "counter-thrust). As long as it is
illuminated unisotropically, it'll accelerate. Mind you, this does
not mean that it is practical for any serious purpose, but that's
another matter.

Mati Meron | "When you argue with a fool,
| chances are he is doing just the same"