Einstein showed that absolute time had to be replaced by a new absolute: the speed of light. Einstein went against the grain and totally dismissed the "Old Physics." He envisioned a world where space and time are relative and the speed of light is absolute (at the time, it was believed that space and time were absolute and the speed of light was relative).
He asserted the equivalence of mass and energy, which would lead to the famous formula E=mc
Einstein challenged the wave theory of light, suggesting that light could also be regarded as a collection of particles. This helped to open the door to a whole new world--that of quantum physics. For ideas in this paper, he won the Nobel Prize in 1921.