- The dual wave-like and particle-like nature of light is known as the wave-particle duality.
- Electromagnetic radiation is often described in terms of waves. However, the energy imparted by these waves is absorbed at single locations the way particles are absorbed.
- The absorbed energy of an electromagnetic wave is called a photon and represents the quanta of light.
- When a wave of light is absorbed as photons, the energy of the wave collapses to specific locations, and these locations are where the photons “arrive”. This is called the wave function collapse.
- Albert Einstein wrote:
It seems as though we must use sometimes the one theory and sometimes the other, while at times we may use either. We are faced with a new kind of difficulty. We have two contradictory pictures of reality; separately neither of them fully explains the phenomena of light, but together they do.