Since there are particles which have momentum, but no mass..(physicists differ)... might it be the case that certain particles would not be affected by light speed? The neutrino has very little, if any mass, and it goes very fast.
Since there are particles which go 'almost' C, and there are *theoretical* particles which, if they exist, may have no mass....what would be the *theoretical* speed limit? Photons travel AT C, and have no 'mass' in the usual sense, yet it seems to be accepted that they could be used as a light sail.

I think there is much to be learned yet....including the effect all the "dark matter" that seems to be logically required has on very fast particles...even on photons.