I'm sure most people here have heard about the microwave "invisibility cloak" that was made with metamaterials. For those that haven't heard, basically electrodynamics can be rewritten to handle changes in refractive index of materials with GR like tools where instead the background is 'curved'. I even saw a physics colloquim about this, and the guy claimed that maybe even 'blackhole' equivalents could be made. That seemed really strange to me, as it seems to violate the second law of thermodynamics. (for now you truly have a "thermal diode" it seems). I brought this up during Q&A and it turned into a rapid discussion with many professors offering guesses. Sadly the speaker didn't seem to understand the issue, and since his talk wasn't about these 'black-holes' anyway, we moved on. But now, apparently someone has created an actual model (granted only at a certain wavelength and in 2-D) http://www.scientificamerican.com/article.cfm?id=electromagnetic-black-hole Seriously, how does this not violate the second law of thermodynamics? Actually, now that I think of it, the 'cloaking' would still allow light emitted from the center to reach the outside ... so that too seems to allow a "thermal diode" and cause problems as well. How is this possible?