[Spaceships] Your preferences regarding plausible/playable Reactionless Drives

[teviet]

Alcubierre warp drives explicitly require contramatter (negative mass) of some form. You can also use them as time machines. So I'm not sure if that's what you want.

Originally Posted by vicky_molokh

... one Planck length per Planck time...

In other words, the speed of light? :)

Basically you have two possibilities: either energy/momentum conservation is truly being violated, or there's some mystery field or intangible medium that absorbs the difference. Neither of these is a fundamental impossibility. The first obviously rules out general relativity, so you are basically left with a contrivance: "The Universe has a preferred frame, and certain interactions depend on this frame, but the rest of the laws of physics have been arranged in such a way as to conceal its existence". Still, it's not impossible.

Also, if you can create momentum, you can create energy for free. That much is a mathematical certainty, or else modern-day generators wouldn't function as they do.

An "intangible medium" does less damage to the laws of physics, and you can tune the "intangibility" so that the medium is dragged with local matter. But if it comprises any substantial fraction of the mass of a galaxy (say the cold dark matter component), we would notice it. And cold dark matter is already so tenuous that you either have to reach out to huge distances to grab enough of it to impart significant momentum, or you need to throw the smaller amount near you at relativistic speeds. Which basically gives the same operating characteristics as a photon/neutrino drive.

I didn't read the whole atomic rocket site; what problem, if any, do they have with non-reactionless "reactionless" drives? My preferred handwavium is a mechanism that converts baryons into leptons, specifically neutrinos, and preferentially emitted in one direction with the recoil passing to the mechanism. Technically this is three handwaves, but it gives you a "reactionless" total conversion drive (i.e. no noticeable exhaust) that is inefficient as a power plant.

TeV