© Adam Kleppner.
Ripples on the surface of a lake can be created by adding energy to the surface, for example, by dropping in a pebble. The waves will move at a characteristic speed, carrying energy across the lake. Information about how the waves behave and what waves are possible is already "encoded" in the lake before the pebble falls in. The ripples and lake are analogous to particles and fields. The fields contain the information about the particle. If energy is put into the field, particles are created. Mathematically, the particles take the form of waves. (Unit: 2)