Quanta: The Originality of Einstein's Approach to Relativity?
  We suggest that not only quanta may have played a role in Einstein's ideas on relativity, but that they themselves may be related to the dynamical and relativistic behaviour of the electromagnetic field exhibited in a Poincar\'e's 1900 paper, in particular to the identical transformation law of energy and frequency for bounded plane waves. 
Christian Bracco
physics.hist-ph gr-qc