‘Physical impossibility’ based on current understanding of the way the Universe works. In 4d spacetime the speed of light is a speed limit, but Physicists already know ‘something’ travels faster than light speed in order to communicate between two particle, so there is a distinct possibility that dimensional limits may be breeched, allow something ‘not in 4D spacetime’ to move about or effect uate at greater than light speed. If Guth is correct, the entire universe once moved faster than light speed.
“Physicists already know ‘something’ travels faster than light speed in order to communicate between two particle”
Not quite. There is the “spooky action at a distance” going on in quantum physics, but that doesn’t necessarily equate to anything traveling faster than light. It may appear that way to us, but it doesn’t mean that is the true explanation. To a photon, any travel would appear instantaneous, but that is not what is happening from the perspective of an outside observer. So just because something appears to violate an inviolable rule from one perspective, does not mean it is actually doing so.
Also, even if we could demonstrate that something can travel faster than light, it wouldn’t change the fact that we, being massive objects, can never hope to do the same. We’re stuck obeying the laws that apply to matter, not the laws that might apply to some theoretical thing that can’t be either matter or energy, and that we really have no clue what it might be or how we might go about detecting it.