# Contents

## Idea

The distance between two crests? of a wave.

## Definition

For $n \in \mathbb{N}$ and

$\vec x \mapsto e^{2 \pi i \vec k \cdot \vec x}$

a plane wave with wave vector $\vec k \in \mathbb{R}^n$, then its wavelength is the inverse of the norm of $k$:

$\lambda \coloneqq 1/{\vert k\vert} \,.$

The quotient $k/{\vert k \vert} \in S(\mathbb{R}^n)$ is the direction of the plane wave.

The product $2\pi/\lambda$ is also called the wave number.

plane waves on Minkowski spacetime

$\array{ \mathbb{R}^{p,1} &\overset{\psi_k}{\longrightarrow}& \mathbb{C} \\ x &\mapsto& \exp\left( \, i k_\mu x^\mu \, \right) \\ (\vec x, x^0) &\mapsto& \exp\left( \, i \vec k \cdot \vec x + i k_0 x^0 \, \right) \\ (\vec x, c t) &\mapsto& \exp\left( \, i \vec k \cdot \vec x - i \omega t \, \right) }$
symbolname
$c$speed of light

$\hbar$Planck's constant

$\,$$\,$

$m$mass

$\frac{\hbar}{m c}$Compton wavelength

$\,$$\,$

$k$, $\vec k$wave vector

$\lambda = 2\pi/{\vert \vec k \vert}$wave length

${\vert \vec k \vert} = 2\pi/\lambda$wave number

$\omega \coloneqq k^0 c = -k_0 c = 2\pi \nu$angular frequency

$\nu = \omega / 2 \pi$frequency

$p = \hbar k$, $\vec p = \hbar \vec k$momentum

$E = \hbar \omega$energy

$\omega(\vec k) = c \sqrt{ \vec k^2 + \left(\frac{m c}{\hbar}\right)^2 }$Klein-Gordon dispersion relation

$E(\vec p) = \sqrt{ c^2 \vec p^2 + (m c^2)^2 }$energy-momentum relation

</table>

## Examples

Last revised on November 7, 2017 at 08:47:11. See the history of this page for a list of all contributions to it.