I could be wrong, but from what I’ve read the domain wall should have mass, so it must travel below light speed. However, the energy difference between the two vacuums would put a large force on the wall, rapidly accelerating it to very close to light speed. Collisions with stars and gravitational effects might cause further weirdness, but ignoring that, I think after a while we basically expect constant acceleration, meaning that light cones starting inside the bubble that are at least a certain distance from the wall would never catch up with the wall. So yeah, definitely above 0.95c.
I could be wrong, but from what I’ve read the domain wall should have mass, so it must travel below light speed. However, the energy difference between the two vacuums would put a large force on the wall, rapidly accelerating it to very close to light speed. Collisions with stars and gravitational effects might cause further weirdness, but ignoring that, I think after a while we basically expect constant acceleration, meaning that light cones starting inside the bubble that are at least a certain distance from the wall would never catch up with the wall. So yeah, definitely above 0.95c.