In 1905, he
published three path-
breaking papers In the
first paper, he introduced
the notion of light quanta
(now called photons) and
used it to explain the
features of photoelectric
effect In the second paper,
he developed a theory of
Brownian 
motion,
confirmed experimentally a
few years later and provided
a convincing evidence of
the atomic picture of matter The third paper gave birth
to the special theory of
relativity