There’s a simpler way to get FTL in your sci-fi books, and that’s to assume the existence of negative mass and create an Alcubierre drive, which is indeed a well-known and correct solution to Einstein’s equations (if only you grant negative mass).
The reason not to expect negative mass to exist is much weaker than reasons not to expect relativity to generalize, mainly being that it violates a typical assumption of general relativity, effectively that energy density is nowhere negative. However such assumptions have been violated before, eg due to dark energy, and in my understanding, it’s not fundamental to the Einstein field equations themselves.
My impression is that the averaged null energy condition (violated by negative mass) is much more widely accepted than the strong energy condition (violated by dark energy), but yeah, that’s a good point. (Also, I don’t really know why people think the ANEC or something similar has to be true.)
Also, I don’t really know why people think the ANEC or something similar has to be true.
My impression is that its because if it is violated, you get a bunch of crazy shit, like warp drives and perpetual motion (without breaking energy conservation). Plus, it makes the math a lot easier. You need some boundary condition to apply the field equations, and that’s an extremely reasonable one.
There’s a simpler way to get FTL in your sci-fi books, and that’s to assume the existence of negative mass and create an Alcubierre drive, which is indeed a well-known and correct solution to Einstein’s equations (if only you grant negative mass).
The reason not to expect negative mass to exist is much weaker than reasons not to expect relativity to generalize, mainly being that it violates a typical assumption of general relativity, effectively that energy density is nowhere negative. However such assumptions have been violated before, eg due to dark energy, and in my understanding, it’s not fundamental to the Einstein field equations themselves.
My impression is that the averaged null energy condition (violated by negative mass) is much more widely accepted than the strong energy condition (violated by dark energy), but yeah, that’s a good point. (Also, I don’t really know why people think the ANEC or something similar has to be true.)
My impression is that its because if it is violated, you get a bunch of crazy shit, like warp drives and perpetual motion (without breaking energy conservation). Plus, it makes the math a lot easier. You need some boundary condition to apply the field equations, and that’s an extremely reasonable one.