all line of sight electrons on the surface atoms of all masses/matters/objects are repelling each other with a force f=Ke x ee/rr at all the times.

all atoms are constantly vibrating due to the thermal energy they carry.

that energy/vibrating electrostatic force is instantly shared by all line of sight atoms due to they are directly connected by the force f=Ke x qq/rr.

therefore light speed in vacuum space is infinite, only when transmitting within transparent matter/air/water/glass at limited speed, due to f=ma and the force has to pass every atom.