It's true you can generate thrust by throwing photons out one end, but that's not what this device does. It bounces microwaves around inside a closed, superconducting chamber, with one end wider than the other.
Oh, it's that device? The one that was on the cover of New Scientist at some point? We (i.e. the lecturer) mocked that in physics lectures (mostly on a "look at the shit New Scientist publishes..." sidetrack). It may also have claimed perpetual motion, while it was at it.
If there really is some quantum interaction, then this becomes interesting, but from momentum alone the contributions from the sides of the box always exactly cancel the resultant from the mismatched plates (by definition of a closed box).
If you've got constant thrust from constant energy input, that pretty much implies perpetual motion, since energy input increases linearly with time and kinetic energy with the square of time.
If you want to say you get less thrust as velocity increases then you run into trouble with the principle of relativity.
So I'm skeptical too, though I think it's worth continuing experiments.
Sure, you can only find the mistake while repeating the experiments (perhaps, as someone else suggested, in a vacuum might be a plan).
I hadn't noticed the constant thrust problem you mention, I'm now recursing back through the equations I remember to try and work out why it costs more energy to push something that's already moving fast... wait, force applied was never anything to do with energy to start with, impulse/power were. Brain-fart resolved.
Oh right, that makes sense; constant acceleration implies constant force, and work is force*distance. As the meters tick by more rapidly, the motor performs the same work in less time, and thus the required power increases.
Which means, "a reactionless drive is like a car in space" would be a nonsensical concept without a preferred reference frame.
Wait, I get what you're saying (0.5mv^2), but isn't it relatively straightforward to get constant thrust from constant energy in other situations? Laser --> lightsail, for example.
To reply to myself, the thrust you'd get from a laser that shoots at you would in fact diminish as you accelerate away from it, as the light would redshift and thus carry less energy to you.
indeed, my PhD supervisor is often wrong about stuff. I don't believe my lecturers per se, but rather I remember the argument about cancelling edge effects (which certainly seems to apply here.)
It's already a kind of well known concept in SciFi to bounce the photon back and forth a lot, getting a little hit of momentum each time (and draining its energy, thus changing its wavelength). Keeping the reflecting pair on the rocket and trying to use asymmetry to pull more off on one side than the other seems a pretty straightforward thing to try.
Exactly right. It's an apparent violation of Newton's Third Law, unless the photons are pushing against virtual particle pairs as suggested in the article.
