EmDrive (by alaric)
A British chappy claims to have built an reactionless engine, the EmDrive - I just read about it in New Scientist today, so threw up the Wikipedia page about it.
Any physicists around here who are able to do the maths and see if his claim (that a truncated-conical resonant cavity full of microwaves will experience an asymmetric photon pressure due to the group velocity of the waves changing as the local diameter of the tube varies, thanks to some relativistic effects) holds water?
And if it does, what becomes of conservation of momentum?
Thu 7th Sep 2006 12:45 pm 
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By Olly Butters, Tue 3rd Oct 2006 @ 2:32 pm
The simplest analogy for why I don't think this works is that the operation of the device may be considered equivalent to the construction of a ship with a large sail at one end and a small sail at the other end, then standing in the middle and blowing uniformly in all directions; this would only create forces within the boat rather than a force capable of propelling the boat away from any fixed body.