Rejection of the Light Quantum: The Dark Side of Niels Bohr

Evidence is recalled of the strong opposition of Niels Bohr, at the time of the Old Quantum Theory 1913–1925, to the Lichtquanten hypothesis of Einstein. Some episodes with H. A. Kramers, J. C. Slater, and W. Heisenberg are recollected; Bohr's changing point of view is traced back to some philosophical antecedents and to his endeavor to deduce quantum results from the Correspondence Principle. Some consequences for the future interpretation of Quantum Mechanics, specially to the Complementarity Principle, are considered.