A clue to the physical meaning of the wavefunction Ψ(x,t) is provided by the two-slit interference of monochromatic light (Figure 7.1.1) that behave as electromagnetic waves. The wavefunction of a light wave is given by E(x,t), and its energy density is given by |E|2, where E is the electric field strength. The energy of an individual photon depends only on the frequency of light, ϵphoton=hf, so |E|2 is proportional to the number of photons. When light waves from S1 interfere with light waves from S2 at the viewing screen (a distance D away), an interference pattern is produced (7.1.1a). Bright fringes correspond to points of constructive interference of the light waves, and dark fringes correspond to points of destructive interference of the light waves (7.1.1b).

Quantum Wavefunctions