Heisenberg s Uncertainty Principle states that it is not possible to measure both the momentum and position of a particle simultaneously. More specifically, if one knows the precise momentum of the particle, it is impossible to know the precise position, and vice versa. This relationship also applies to energy and time, in that one cannot measure the precise energy of a system in a finite amount of time. Uncertainties in the products of conjugate pairs (momentum/position) and (energy/time) were defined by Heisenberg as having a minimum value corresponding to Planck’s constant divided by 4π. More clearly: ΔpΔx ≥ h/4π ΔtΔE ≥ h/4π Where Δ refers to the uncertainty in that variable and h is Planck s constant.