Louis de Broglie hypothesized that all matter exhibits wave-like properties. The wavelength ($\lambda$) associated with a particle of momentum $p$ is: $\lambda =\frac{h}{p}$ where $h$ is Planck's constant.

• For a particle of mass $m$ and velocity $v$, $p=mv$, so $\lambda =\frac{h}{mv}$.
• This duality is only noticeable for microscopic particles like electrons due to the extremely small value of $h$.