- #1
Wox
- 70
- 0
The classical expression of a plane electromagnetic wave (electric part)
[tex]
\bar{E}(t,\bar{x})=\bar{E}_{0}e^{i(\bar{k}\cdot \bar{x}-\omega t)}
[/tex]
looks a lot like the basis function of the Fourier decomposition in Minkowski space-time
[tex]
\bar{E}(\bar{w})=\int_{-\infty}^{\infty}\hat{\bar{E}}(\bar{\nu})e^{2\pi i\ \eta(\bar{\nu},\bar{w})}d\bar{\nu}
[/tex]
where [itex]\bar{E}\colon\mathbb{R}^{4}\to\mathbb{R}^{4}[/itex] and [itex]\bar{w}=(ct,\bar{x})[/itex]. If I write [itex]\bar{\nu}=\frac{\nu}{c}(1,\bar{n})[/itex] with [itex]\left\|\bar{n}\right\|=1[/itex] then we get
[itex]\eta(\bar{\nu},\bar{w})=\frac{\nu}{c}\bar{n}\cdot \bar{x}-\nu t=\frac{1}{2\pi}(\bar{k}\cdot \bar{x}-\omega t)[/itex] and
[tex]
\bar{E}(\bar{w})=\int_{-\infty}^{\infty}\hat{\bar{E}}(\bar{\nu})e^{ i\ (\bar{k}\cdot \bar{x}-\omega t)}d\bar{\nu}
[/tex]
and for a monochromatic wave
[tex]
\bar{E}(\bar{w})=\bar{E}(ct,\bar{x})=\hat{\bar{E}}(\bar{\nu})e^{ i\ (\bar{k}\cdot \bar{x}-\omega t)}
[/tex]
which is close to the classical expression, but not exactly. So the point is, I feel Fourier decomposition in Minkowski space and the classical plane wave are related, but I'm not sure how. Can someone clarify?
[tex]
\bar{E}(t,\bar{x})=\bar{E}_{0}e^{i(\bar{k}\cdot \bar{x}-\omega t)}
[/tex]
looks a lot like the basis function of the Fourier decomposition in Minkowski space-time
[tex]
\bar{E}(\bar{w})=\int_{-\infty}^{\infty}\hat{\bar{E}}(\bar{\nu})e^{2\pi i\ \eta(\bar{\nu},\bar{w})}d\bar{\nu}
[/tex]
where [itex]\bar{E}\colon\mathbb{R}^{4}\to\mathbb{R}^{4}[/itex] and [itex]\bar{w}=(ct,\bar{x})[/itex]. If I write [itex]\bar{\nu}=\frac{\nu}{c}(1,\bar{n})[/itex] with [itex]\left\|\bar{n}\right\|=1[/itex] then we get
[itex]\eta(\bar{\nu},\bar{w})=\frac{\nu}{c}\bar{n}\cdot \bar{x}-\nu t=\frac{1}{2\pi}(\bar{k}\cdot \bar{x}-\omega t)[/itex] and
[tex]
\bar{E}(\bar{w})=\int_{-\infty}^{\infty}\hat{\bar{E}}(\bar{\nu})e^{ i\ (\bar{k}\cdot \bar{x}-\omega t)}d\bar{\nu}
[/tex]
and for a monochromatic wave
[tex]
\bar{E}(\bar{w})=\bar{E}(ct,\bar{x})=\hat{\bar{E}}(\bar{\nu})e^{ i\ (\bar{k}\cdot \bar{x}-\omega t)}
[/tex]
which is close to the classical expression, but not exactly. So the point is, I feel Fourier decomposition in Minkowski space and the classical plane wave are related, but I'm not sure how. Can someone clarify?