[dandotway]

While faster-than-light (FTL) travel is impossible through spacetime as PhD physicists know it (i.e. as "Relativity-confirming experiments reveal it"), there are forms of apparent FTL that have mainstream PhD acceptance, because they don't allow information to travel from point A to point B faster than light and thus do not violate causality.

The expansion of the observable universe itself being apparently FTL is perhaps the most interesting. If we point the Hubble telescope (and soon JWST) towards opposite ends of the observable universe, we observe extreme redshift galaxies receding away from each other in opposite directions greater than twice lightspeed if we measure according to "distance in light years" from earth. But no photons or information from a galaxy at one side of our observable universe can be sent to a galaxy at the opposite end: they are receding away from each other too rapidly, these two galaxies exist Beyond the Cosmological Event Horizon relative to each other and are forever unknowable to each other, and thus causality is not violated.

An advanced alien race in galaxy A might be able to beam a message to earth before galaxy A vanishes Beyond the Cosmological Event Horizon within the next 100 million years earth-time, and likewise galaxy B might beam a message to earth within the next 100 million years earth-time, but earth can't relay the message from A to B or B to A because they have already forever receded from each other and will soon both likewise forever recede away from us.

[lumost]

There is no restriction on relative velocities between objects from a given observer as long as all objects have velocities less than the speed of light. You can point laser pointers in opposite directions and the "front" of the laser pointer will recede at "2x" C from the opposite pointer.

In the case of the expanding universe, our standard "flat" space time represented by minkowski space is warped into de-sitter space. As distances increase apparent acceleration increases up to and beyond the speed of light due to the expansion of space time.