According to Max Planck the velocity of electromagnetic waves equals to one Planck length per Planck time; the limit to which photon can travel.
Planck time ~ 5.39×10^−44 s.
Planck length ~ 1.61626×10^−35 m.
Therefore, speed of electromagnetic wave is constant through the equations of Max Planck and Combined with Albert Einstein.
c = ~3x10^8 m/s = fλ = √E/m.
