This is the fundamental theory of physics that explains what happens to objects as small as atoms. It was developed by a large group of physicists in the 1930’s, and it has changed our technological world. What is says is that there are limits to measurements. If we measure something very small, the more accurate we make our measurement, the less accurate will the momentum (i.e., the speed) of the object be. This is Heisenberg’s Uncertainty Principle:

 

Δp Δx > h,

 

where h is a constant of nature called Planck’s constant. The hydrogen atom is the simplest atom, consisting of a proton and an electron. The size of the atom is given by Heisenberg’s principle, where the uncertainty in the momentum p is just given by the binding energy holding the atom together. Although the electric attraction of the proton and electron would pull them together, they cannot get any closer than the uncertainty principle.

 

Let us put some numbers in. The size of the hydrogen atom is 10-10 meters, and the size of the proton is 10-15 meters. This means that the atom is 100,000 times as big as the proton. This does not mean that the atom is mostly empty space! What it means is that the proton is so small because the nuclear force is so very much larger than the atomic force. We know this, as atom bombs are far more powerful than chemical bombs.