Stefan Lovgren in the Ntional Geographics:
In his first paper in March 1905, Einstein argued that light is not a wave, as most physicists previously thought, but instead a stream of tiny packets of energy that have since come to be known as photons. The theory won Einstein the Nobel Prize in 1921 and helped lay the foundation for quantum theory, which states that physics cannot make definite predictions. It can only predict the probability that things will turn out one way or another. The quantum theory, with its statistical description of nature at the subatomic scale, has turned out to be right. However, Einstein came to reject the unpredictability of quantum mechanics, famously saying, “God does not play dice with the universe.”
“He couldn’t accept that so deeply woven into the fabric of the cosmos was an element of uncertainty,” said Brian Greene, a physics and mathematics professor at Columbia University in New York. “He hoped the probabilistic framework of quantum mechanics was merely an intermediary point physicists reached in their study. But that doesn’t seem to be the case,” said Greene, who wrote the best-selling The Elegant Universe: Superstrings, Hidden Dimensions, and the Quest for the Ultimate Theory. Einstein never succeeded in his search for a theory of everything. But many people consider string theorists such as Greene to be Einstein’s natural successors. String theory is a physical model that says that the fundamental building blocks of the universe are vibrating filaments of energy within every particle.
More here.