Page "Identical particles" Paragraph 97

We let the composite system evolve in time, interacting with a noisy environment.

Because the and states are energetically equivalent, neither state is favored, so this process has the effect of randomizing the states.

( This is discussed in the article on quantum entanglement.

) After some time, the composite system will have an equal probability of occupying each of the states available to it.

We then measure the particle states.