Solar Sails have been proposed in science fiction and by NASA for years as a means of propulsion for robotic space probes. A huge, mirror-like sail would reflect photons from the Sun or another star while taking on some of the photon's momentum to move the probe. Thomas Gold from Cornell University made a claim recently that solar sails violate the laws of physics. NASA and the ESA have solar sail powered vehicles in development and the Planetary Society hopes to launch their own 100-kilogram sun jammer called Cosmos-1 this September. Gold says they won't work. Most scientists say they will. Place your bets now.