- #1

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- Thread starter exmarine
- Start date

- #1

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- #2

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You can find the Lagrangian, for example, here

- #3

- 17,675

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- #4

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\begin{equation}

L=-\frac{1}{4}F^{2}=-\frac{1}{4}F_{\mu\nu}F^{\mu\nu}=-\frac{1}{4}(\partial_{\mu}A_{\nu}-\partial_{\nu}A_{\mu})^{2}

\end{equation}

- #5

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phi = (const) exp[(i/h_bar)S]

- #6

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Which part ofOK, then how does one calculate the action (S) for the amplitude of a photon?

was unclear? You need to specify exactly what it is you are trying to do.There is no such thing as the lagrangian ofa photon. Photons are quantum excitations of the electromagnetic field,

- #7

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Feynman & Hibbs, p. 29, eqn 2.15:

- #8

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Feynman & Hibbs, p.29, eqn 2.15: phi[x(t)] = const e^(I/h-bar)S[x(t)]

p.26: S = integral[L(x-dot,x,t) dt]

So if a photon has no Lagrangian, how does one calculate the action, amplitude, probability, etc. for a photon?

- #9

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You don't. You compute the action of the electromagnetic field and correlation functions (essentially amplitudes) between different excitations of the field.So if a photon has no Lagrangian, how does one calculate the action, amplitude, probability, etc. for a photon?

- #10

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Feynman & Hibbs, p. 29, eqn 2.15:

Also, you are here assuming that we have the book available and ready to open. This is not getting us anywhere.

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