The Heisenberg Uncertainty Principle
Based on the concept of photon - particle collisions, Werner Heisenberg proposed a theory in 1927 known as the uncertainty principle. It argued that since we have to use light to identify the location or motion of an electron, the photon of light will influence the electron's motion and position. The uncertainty principle says the more certain we are about a particle's position, the less certain we are about its momentum, and vice versa. Mathematically, the uncertainty principle looks like:
where 
= the uncertainty in position
= the uncertainty in
momentum
h= Planck's constant
