Light is both a particle and a wave, and that is not the same as quantum mechanics, that is describing a natural phenomenon with a best fit model. Quantum mechanics begins when you start defining the physics these particles follow. Even Einstein was too early for that. Newton also believed that light moved from a straight path no matter what (and perhaps that it had an infinite speed, I'm not sure) unless there was reflection, refraction, or absorption. Einstein later disproved this, showing that gravity can displace light, and that the maximum speed of light is 300000 k/s.