The "filter" doesn't only restrict exiting photons; entering photons are similarly filtered. If the blackbody is in thermal equilibrium with its environment, the incoming photons will match the outgoing ones. Maxwell's demon requires a _one-way_ filter. Franklin T. Adams-Watters -----Original Message----- From: hbaker1@pipeline.com ... This professor suggests that one can put such a photonic crystal "filter" in front of a "blackbody", and thereby allow only the most energetic photons to leave. _Presumably_, the photons that bounce back into the blackbody exchange energy with the blackbody to reconstitute the classic blackbody radiation spectrum, so that the only photons leaving the blackbody are those with high energies. This is not a perpetual motion machine of the first type, because energy is conserved, but isn't it a perpetual motion machine of the second type? ... ________________________________________________________________________ Check Out the new free AIM(R) Mail -- 2 GB of storage and industry-leading spam and email virus protection.