> Moreover, I'd suggest you review the history of quantum mechanics, because Einstein did not invent field theory, just as Newton did not invent or understand the Lagrange or Hamiltonian formulations, nor statistical mechanics, even though his theory provided the foundation of them all.
First of all, physical fields were a concept far before QFT came in the picture, and they are the same concept as QFT's fields. Einstein was definitely familiar with classical field theories, which were prevalent ways of looking at gravitation and electromagnetism far before even quantum mechanics was discovered.
Secondly, Einstein died some time after QFT had become a real theory, so it is very likely that later in life he could have been at least passingly familiar even with some concepts of quantum fields (though of course, not at the time he wrote his GR papers).
