The advantage of the emdrive is that it does not require reaction mass, at the cost of incredibly high power consumption. Unfortunately that makes it not really viable for anything; ion drives are limited by power, not reaction mass, so the emdrive is actually worse because it uses way more in power than it saves in not needing reaction mass.
Since violation of conservation of energy is very unlikely, I'd say that this is a sign that the drive doesn't actually work. Or at least that there is some gotcha that we haven't understood yet.
The EM Drive is an energy reaction engine, rather than a mass reaction engine (if it works as described), so instead of pushing off wake, it uses energy itself to "deepen the fold", as it were, and increase speed (and mass, since the two are exchanged).
That's interesting. I've never considered that the very act of increasing the velocity of the EM Drive would actually increase its mass. Hrm.
And anyway, kinetic energy isn't a conserved quantity. It can be converted into potential energy in a gravity well, or lost entirely in inelastic collisions. Momentum is the quantity that is always conserved, and that is what the emdrive violates directly (though still not in a way that allows for perpetual motion or free power, near as I can tell).
The first internal combustion engines were quite inefficient as well.
By special relativity you can't break the momentum conservation principle without breaking the energy conservation principle.
Somehow most people feel more comfortable dismissing the momentum conservation principle, but they are intertwined.
A carousel with Emdrives like the described in the previous comment should be a perpetual mobile and create energy if it's spinning in the right direction. (It will destroy energy in the reverse direction, so be careful.)
[Anyway, I think that the emdrive doesn't work and the conservation of energy and momentum are safe.]
However, any true reactionless thrust is equivalent to a perpetual motion machine, because reactionless thrust drives produce the same acceleration regardless of speed, but the kinetic energy produced by the same acceleration goes up as the speed goes up.
If you accelerate one kg from 0m/s to 1m/s, you impart 0.5joules of energy on it. If you accelerate it from 1m/s to 2m/s, you impart 1.5joules of energy on it. If you accelerate it from 2m/s to 3m/s, you impart 2.5 joules of energy on it, and so on and so on. Each added m/s costs more in energy.
A reactionless drive working in a system with no preferred frame would add the same amount of acceleration for the same amount of cost, regardless of how much energy there already is. This would mean that eventually it would be going fast enough that the added kinetic energy would be more than however much energy it draws in. Then you can build a gigantic carousel that is spinned on the rim and takes energy from the middle and feeds some back in to move it, and now you have perpetual motion.
This is why no real physicist actually thinks that this will be reactionless thrust. However, that does not necessarily mean it's useless. If it, for example, allows you to push against the earth's magnetic field more weight-efficiently than current magnetic propulsion systems, it would be a major win for satellite stationkeeping.
A) Where is that in the paper? Or am I missing something elementary to this?
B) We don't even know if it produces the same level of thrust as speed increases. If it produces the same level of thrust across all speeds, then we have a problem, because as velocity increases, so does mass, and the same level of thrust would produce less acceleration over time, because of the increase in mass. Of course, that may only effect things at relativistic speeds.
Rockets do that too, but they get away with it because they stored the necessary extra energy into the kinetic energy of the fuel.
If there was a reactionless thruster that did, in fact, get less efficient at higher speeds, then that would also be world-shattering physics news, because then you could measure it's performance after accelerating in different directions and eventually get a true rest frame that is privileged over the rest of the reference frames out of it.
That's another good reason to think it doesn't work.
That's the implication of the EM Drive. I didn't invent it, it's the very first thing that you think of once you violate the momentum conservation principle. This is why it's unlikely to be true, but at the same time an alchemists dream scenario.
It's worth more than any existing or previous theoretical engine. Put this rotating around a center point. Now put 1000s of them. Now we have power generation for outposts in space. The implications of a working EM drive are staggering.