nothing with mass can reach the speed of light

Criticism of the theory of relativity

Michelson-Morley experiment null result

Gravitational lensing formalism

Light bends around massive objects due to spacetime curvature

Schwarzschild metric

Schwarzschild radius at r=2GM/c² marks the event horizon

Einstein's photoelectric explanation used Planck's E=hf to predict that higher frequency light ejects faster electrons

Einstein's photoelectric equation E=hf predicts faster electron ejection with higher frequency light

Special relativity

Albert Einstein's special relativity paper introduced time dilation

Time dilation

Clocks run slower in stronger gravitational fields