Just to nitpick, the Casimir effect only produces negative pressures relative to the vacuum energy. They're not truly negative. Just in case anyone reading that misunderstands.
Also 'violates causality' is an awful lot to unpack, and is glossing over so much nuance that I don't think it's really a meaningful thing to say. For example violation of the Bell inequalities does not rule out superdeterminism, and that has a very solid account of causality. It's just not a conventional one.
You left one portion out of the explanation of the Casimir effect
> The Casimir effect shows that quantum field theory allows the energy density in certain regions of space to be negative relative to the ordinary vacuum energy, and it has been shown theoretically that quantum field theory allows states where the energy can be arbitrarily negative at a given point.[57] Many prominent physicists such as Stephen Hawking,[58] Kip Thorne,[59] and others[60][61][62] therefore argue that such effects might make it possible to stabilize a traversable wormhole.
There’s also solutions to FTL travel that don’t have to violate causality. Space itself is expanding faster than light.
My overall point is it’s weird for scientists to shut down the possibility of FTL travel when we have theories that don’t disprove it outright, especially when we don’t really know whether gravity is a bending in spacetime or is governed by the same rules as QFT. The ER=EPR conjecture really intrigues me, and I think following that path may help lead us to a better understanding of what’s possible.
Well it's not that weird to say "no, FTL travel is impossible" compared to the alternative "FTL travel is possible". The prevailing theories clearly say it's not; why would scientists proclaim anything contrary to that? Of course they want as much as anyone to prove the current theories wrong, but it would still be negligent to go around saying anything other than what the theories actually say to the laypeople.
> 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?
Also 'violates causality' is an awful lot to unpack, and is glossing over so much nuance that I don't think it's really a meaningful thing to say. For example violation of the Bell inequalities does not rule out superdeterminism, and that has a very solid account of causality. It's just not a conventional one.