How does light cause matter to move? For example, when a photon collides with an atom, an electron absorbs the photon and moves to a higher energy state. If the energy is not used then the electron falls back to a lower energy state and emits radiation. I am unsure of how the photon in the above example causes the motion of an atom. A more specific question is how does sunlight increase temperature, or speed up the motion of the gas particles in the atmosphere.