 It is important to note that while it is now accepted that this emitted radiation is a photon, Bohr himself was surprisingly skeptical of the photon concept up until as late as the mid-1920s (Stachel 2009). Bohr preferred to think of the emitted or absorbed radiation as a wave, rather than as a particle. Bohr’s hesitation in accepting the existence of photons during this period seems to arise from his concern that such a particle conception of light would be irreconcilable with familiar interference phenomena. For example, Bohr writes in 1921,