Chapter 2 – Wave functions and uncertainty

Superposition

There is a major difference between the friend and the electron. Although the probability distribution for the friend shows that we don’t know exactly where they are, we do assume they are at a position that we can discover by calling them. The electron is not at a specific position until we look. This makes quantum mechanics fundamentally different from the world that we experience.

This change to the probability distribution is called the wavefunction collapsing. The wave function before the observation shows a range of possible positions. the observation collapses it to just showing the observed position.

The important point is that the particle was not in a specific position before being observed. After the observation, the wave function continues to evolve to predict future positions. A particle that can be in many positions is called superposition.

This is sometimes described as the particle being in many places at once but that is not correct. The particle has a possibility of being found in many places but does not have a defined position until it is observed.

A question often asked is whether a human is needed to make the observation that collapses the wave function. Humans are not needed and the same result will be obtained if an automated detector was used even if no human ever looked at the result.