Light Waves… or Particles:
Originally, when Newton conducted his experiments, it suggested light was very simply demonstrated as a ray (and later on a wave that required no medium of travel). However when Einstein came up with his theory of the photoelectric effect (shooting light at metal made electrons absorb the energy then escape the atom), it suggested that light concentrated energy in pockets - or photons
Every since then, it has angered the science community that both perceptions of light exist. Both are proved yet they cannot live side-by-side.
However, it came as a great shock when Einstein wrote his papers on relativity and described light as a net of waves when he previously acknowledged them as particles. It is known Einstein embraced the idea of Wave-Particle Duality. Meaning he accepted light behaved in both ways and used whichever that best explained/fitted the circumstances.
There is now the idea in quantum mechanics that some particles can exhibit the characteristics of a wave.