Energy-Time Uncertainty

\Delta E \cdot \Delta t \geq \frac{\hbar}{2}

Energy and time cannot both be precisely determined. Related to spectral line widths.

Variables

ΔE

Energy uncertainty

Δt

Time uncertainty

ℏ

Reduced Planck constant

J·s

Your notes

0/5000

Constants in this formula

ℏ

Reduced Planck Constant

1.054 571 817… × 10⁻³⁴. Exact by definition.

J·s

Other modern physics formulas with the same quantities

Time-Dependent Schrödinger Equation (Quantum Mechanics) shares Reduced Planck constant
Fermi Energy (Quantum Mechanics) shares Reduced Planck constant
Bohr Radius (Atomic Physics) shares Reduced Planck constant

Where this formula is listed

Modern Physics formulas, under Quantum Mechanics, alongside Photon Energy (Planck), Photoelectric Effect, Stopping Potential, de Broglie Wavelength and Particle in a Box Energy Levels.
In the modern physics list it comes after Heisenberg Uncertainty Principle and before Time-Dependent Schrödinger Equation.
Modern Physics formula sheet, one of 41 formulas printed with symbol keys and SI units.
The full formula index, grouped by category and topic.

Common questions

What is the Energy-Time Uncertainty formula?

Energy-Time Uncertainty is written ΔE · Δt ≥ ℏ/2. Energy and time cannot both be precisely determined. Related to spectral line widths. It belongs to Modern Physics, under Quantum Mechanics.

What are the units in ΔE · Δt ≥ ℏ/2?

In SI units, ΔE is energy uncertainty, measured in J; Δt is time uncertainty, measured in s; ℏ is reduced planck constant, measured in J·s.