The being of atoms and their elementary particles was not like that of the objects of everyday experience. They live in worlds of potentialities, Heisenberg explained; they are not things, but possibilities. The transition from the “possible” to the “real” only occurred during the act of observation or measurement. There was, therefore, no independently existing quantum reality. Measured as a wave, an electron appeared as such; measured as a particle, it adopted this other form.
