# Is the fine structure constant the phase change when a photon is emitted?

+ 0 like - 0 dislike
169 views

Feynman beautifully explained how QED works.

Reading his book, it seems that the fine structure constant $\alpha$ can be seen as that change of phase angle of an electron that occurs whenever a photon is emitted.

It is not correct. Alpha is just a number, but the probability of emitting a photon depends also on some other dimensionless variable combinations, say, on $\hbar\omega/mc^2$ or so; thus $\alpha$ is not a clue for understanding QED.
When a real photon is emitted, the electron changes its momentum. This change is a quantitative thing. The momentum is involved in the "pases" of the electron wave function: $\psi(x,t)\propto\text{e}^{ipx}$. If the final momentum is $p'$, the electron phase has changed, but it is not solely $\alpha$ who determines $\Delta p=p'-p$.
 Please use answers only to (at least partly) answer questions. To comment, discuss, or ask for clarification, leave a comment instead. To mask links under text, please type your text, highlight it, and click the "link" button. You can then enter your link URL. Please consult the FAQ for as to how to format your post. This is the answer box; if you want to write a comment instead, please use the 'add comment' button. Live preview (may slow down editor)   Preview Your name to display (optional): Email me at this address if my answer is selected or commented on: Privacy: Your email address will only be used for sending these notifications. Anti-spam verification: If you are a human please identify the position of the character covered by the symbol $\varnothing$ in the following word:p$\hbar$y$\varnothing$icsOverflowThen drag the red bullet below over the corresponding character of our banner. When you drop it there, the bullet changes to green (on slow internet connections after a few seconds). To avoid this verification in future, please log in or register.