> There’s also solutions to FTL travel that don’t have to violate causality. Space itself is expanding faster than light.
But you can't use expansion of space to move matter or to travel. You could even argue that distant galaxies aren't even moving at all, they just appear to do so because the distance between them and us increases. Comparing velocities of distant objects in curved spacetime is tricky in general.
The Alcubierre drive gets around this by bending the spacetime around a craft so that portion of space is moving and not the craft through space. And beyond that, traversable wormholes aren’t completely ruled out yet
Yes, I will happily concede that time travel and FTL is possible with wormholes. I would even buy into Novikov's self-consistency principle to avoid paradoxes.
However, to manipulate spacetime like that, we'd have to control massive quantities of an never observed type of energy. Like, on the order of the mass of the galaxy, or at least solar masses. And constructing a wormhole between A and B will still take longer than light travels between the endpoints, so I'm not exactly holding my breath.
The Alcubierre drive (assuming it's feasible) will still violate causality though, and the self-consistency principle does not apply, so I'm convinced that's a bust.
Our prevailing theory of quantum mechanics is QFT which suggests that there aren’t actually any individual particles, but fields that experience excitations which act like individual particles. If we find that gravity is also just a field and gravitons are excitations within the field, who’s to say that perhaps every excitation in that field is entangled in some sort, and to create a traversable wormhole to the other end of the galaxy, we only need to impact the gravitons around us?
But you can't use expansion of space to move matter or to travel. You could even argue that distant galaxies aren't even moving at all, they just appear to do so because the distance between them and us increases. Comparing velocities of distant objects in curved spacetime is tricky in general.