“Possibility”
Faster-than-light communication is, by Einstein’s theory of relativity, equivalent to time travel. According to Einstein’s theory of special relativity, what we measure as the speed of light in a vacuum is actually the fundamental physical constant c. This means that all observers, regardless of their relative velocity, will always measure zero-mass particles such as photons traveling at c in a vacuum. This result means that measurements of time and velocity in different frames are no longer related simply by constant shifts, but are instead related by Poincaré transformations. These transformations have important implications:
The relativistic momentum of a massive particle would increase with speed in such a way that at the speed of light an object would have infinite momentum.
To accelerate an object of non-zero rest mass to c would require infinite time with any finite acceleration, or infinite acceleration for a finite amount of time.
Either way, such acceleration requires infinite energy. Going beyond the speed of light in a homogeneous space would hence require more than infinite energy, which is not generally considered to be a sensible notion.
Some observers with sub-light relative motion will disagree about which occurs first of any two events that are separated by a space-like interval.[5] In other words, any travel that is faster-than-light will be seen as traveling backwards in time in some other, equally valid, frames of reference, or need to assume the speculative hypothesis of possible Lorentz violations at a presently unobserved scale (for instance the Planck scale). Therefore any theory which permits “true” FTL also has to cope with time travel and all its associated paradoxes,[6] or else to assume the Lorentz invariance to be a symmetry of thermodynamical statistical nature (hence a symmetry broken at some presently unobserved scale).
While Special and general relativity do not allow superluminal speeds locally, non-local means may be possible, which means moving with space rather than moving through space.