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

+ 0 like - 0 dislike
158 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.

Is this correct? Where can I read more about it?

asked Dec 13, 2019

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.

Vladimir, I have not asked about or even mentioned the probability of emitting photons. I also have not talked about understanding QED. Why is the sentence "not correct"? What other, corrected sentence is correct then?

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 $\Delta p=p'-p$.

Emission of photon occurs at a single instant of time. The change in momentum has no effect on the phase during one instant!

## Your answer

 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$\hbar$ysicsO$\varnothing$erflowThen 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.