Quantum Mechanics

Introduction: Concepts

The theory of quantum mechanics asserts that with every possibility for an event in nature to take place, there is a quantity called **amplitude** associated with each **alternative**.
Furthermore, the amplitude associated with the overall event is obtained by adding the amplitudes of each of the alternatives.
The **probability** that the event will happen is equal to the square of the absolute value of the overall amplitude.
Thus, if
and
are the amplitudes of the two possibilities for a particular event to take place,
the amplitude for the total event is

and the probability for the event to occur is given by

In the macroscopic world the total probability for an event to take place is given by

the sum of the probabilities of each alternative. In quantum mechanics

The two additional terms are due to the **interference** of
alternatives. If the event is interrupted before its conclusion, for
example by determining if the event takes place through alternative 1,
the amplitudes of all other alternatives can no longer be added to the
total amplitude.