Heisenberg uncertainty principle:

 

The Heisenberg uncertainty principle is a mathematical consequence of the treatment of the electron as a wave.  It states the uncertainty of the electron’s position times the uncertainty of the momentum is equal to or greater than the quantity h/4p.  This means that you cannot exactly know both a particle’s position and velocity at the same time.  The physical significance can be described any number of ways. This is a result of the wave-like nature of the electron. To see the frequency or wavelength of a wave, you need to look at it over a certain time or space.  It is not surprising that the Heisenberg uncertainty principle states that a wave will look a little blurry.