This nuclear force:

- cannot be electrical, because it neutralises electrostatic repulsion without affecting the positive charges of the protons;
- acts as the “stickiness” to bind together subatomic particles, which are within close “sticking distance”;
- acts only when neutrons are present in the nucleus with the protons.

Therefore, the source of radioactive decay is the relations among:

- the binding nuclear force
- electrostatic repulsion
- the motion of the nuclear particles which determines the “sticking distance” and therefore the “stickiness” of the binding nuclear force

According to quantum mechanics, the relations between the particles vary many times a second between certain ranges.

In many atoms in nature with up to eighty three protons and a sufficient number of neutrons, the binding nuclear force keeps the nucleus stable, because no variations in relations are large enough to cause decay.

However, in atoms with more than eighty three protons, irrespective of the number of protons, electrostatic repulsion and variations in relations become large enough to cause decay.

It is then the unpredictable motions of nuclear particles that generate the randomness inherent in radioactive decay. The motion of nuclear particles is unpredictable because it is not possible to measure both their position and velocity at the same time.

This is the measurement problem of quantum mechanics.

### The measurement problem

In 1926, Schrödinger developed the fundamental mathematical equation of quantum mechanics, and this differs fundamentally from Isaac Newton’s laws of motion on which classical physics is based, because it generates only probabilities that a certain particle will be in a given place at a given time.

In 1927, Werner Heisenberg developed his uncertainty principle to show that it is impossible to precisely measure both the position of a subatomic particle and its exact velocity at the same time. The more accurately one measures the position, the less accurately one can measure the velocity, and vice versa.

In the macroscopic world, it is easy to measure both the position and the velocity of everyday objects because the uncertainties are negligible. Hence, it is easy to precisely trace the cause to the effect in the macroscopic world, and, therefore, to develop the deterministic laws of classical physics.

The uncertainties only become significant in the microscopic world of subatomic particles. Trying to measure the velocity of a subatomic particle knocks it about unpredictably, so that its position cannot be reliably measured at the same time. Therefore, one cannot precisely trace the cause of any quantum process to the effect, because this would require knowledge of both the position and momentum as initial conditions, and this is not possible in the microscopic quantum world using macroscopic measuring instruments.