Friday, February 08, 2013
Passing the laugh test
Some scientific claims are so outlandish that they do not pass the "laugh test". That is, for these claims to be true it would require throwing out physical principles that have been tested in excruciating detail for decades if not hundreds of years. Perpetual motion machines based on magnets are one example. Another is the "EM Drive". Depressingly, the latter has reappeared, featured in the UK edition of Wired. The idea is that one can make a microwave resonator shaped like a truncated cone, and that somehow when this resonator is pumped with lots of electromagnetic radiation, it will experience a net thrust in one direction, despite the fact that nothing (including photons) is being exhausted. Why is this absurd on its face? Well, put a box around the system, and it clearly violates conservation of momentum, a principle that has been tested with extreme precision for hundreds of years. Despite double-talk about group vs. phase velocity, reference frames, and relativistic effects, the fact remains that the theory of electricity and magnetism, upon which this device allegedly relies, does not violate conservation of momentum, and neither does the quantum version. The reason this has come up again is that a Chinese researcher claims to have experimentally verified that the effect exists. No offense to her particular institution, but call me when people at Beijing or USTC or Tsinghua have done this. I won't be holding my breath.
Posted by Douglas Natelson at 5:12 PM