Certain pairs of physical properties, such as:

- position and momentum
- time and energy

cannot be simultaneously known to arbitrarily high precision.

approximate | more precise | |
---|---|---|

distance/momentum | Δx Δp < h | σ_{x}σ_{p}<= h/2 |

time/energy | ΔE Δt < h | σ_{E}σ_{t} <= h/2 |

where:

- x = distance
- t = time
- p = momentum
- E = energy
- h = (h in h/2 should have line drawn through bar of h)
- σ = standard deviation