http://www.nytimes.com/2007/05/20/books/chapters/0520-1st-isaa.html?ref=books
Walter Isaacson: "The first [paper] deals with radiation and the
energy properties of light and is very revolutionary," he [Einstein]
explained. Yes, it was indeed revolutionary. It argued that light
could be regarded not just as a wave but also as a stream of tiny
particles called quanta. The implications that would eventually arise
from this theory - a cosmos without strict causality or certainty -
would spook him for the rest of his life.

Isaacson could have added: Other implications - the tiny particles
undergo acceleration in a gravitational field and, equivalently, in
the absence of a gravitational field, their speed depends on the
relative speed of the light source and the observer - would eventually
be camouflaged by relativists, in accordance with confessions made by
Einstein himself:

Einstein: "If the speed of light is the least bit affected by the
speed of the light source, then my whole theory of relativity and
theory of gravity is false."

Einstein again: "I consider it quite possible that physics cannot be
based on the field concept, i.e., on continuous structures. In that
case, nothing remains of my entire castle in the air, gravitation
theory included, [and of] the rest of modern physics."