system
Given the following post, respond as if you're commenting on Reddit:
human
How does a hypothetical Alcubierre drive solve any problems with relativity at all?

It seems to me that the "Alcubierre drive" doesn't actually solve any problems that it attempts to.  It's supposed to allow faster than light travel because the spaceship using it isn't actually moving with respect to the space around it, but why does that matter?   The space inside the bubble including the ship, would still be moving relativistically with respect to everything else in the universe, and would still be limited by c.  Isn't that the only thing that matters?

The contraction of space that an Alcubierre drive creates is kinda like Lorentz contraction, in that it would allow something to traverse more space in less time. Which is how muons created in the upper atmosphere make it to Earth's surface before they decay.   However, Lorentz contraction still has an upper limit at the speed of light, and it still requires exponentially more energy the more contraction you want.

I don't get why this was even a popular idea in the first place?
gpt
It can still be used to communicate back in time as part of a "tachyonic anti-telephone." If two things outside each others' light cones can communicate (it doesn't matter how, or what tricks are used), then with the right choice of reference frames they can communicate back in time.

It also violates the energy conditions of the universe, requires negative-energy-density material, and a host of other issues.

Alcubierre did not conceive of this because he thought it could be made. He did it because it was an amusing trick to do with the mathematics of general relativity. Most of his other work involves simulations of black holes colliding, which is also really cool.

edit: One other thing: people, including Alcubierre, often cite the Casimir effect as evidence of negative energy density. It is not. It is a relativistic van der Waals attraction, which can be derived much more easily in a non-rigorous way using a toy model of negative energy and vacuum fluctuations.