• Register
PhysicsOverflow is a next-generation academic platform for physicists and astronomers, including a community peer review system and a postgraduate-level discussion forum analogous to MathOverflow.

Welcome to PhysicsOverflow! PhysicsOverflow is an open platform for community peer review and graduate-level Physics discussion.

Please help promote PhysicsOverflow ads elsewhere if you like it.


New printer friendly PO pages!

Migration to Bielefeld University was successful!

Please vote for this year's PhysicsOverflow ads!

Please do help out in categorising submissions. Submit a paper to PhysicsOverflow!

... see more

Tools for paper authors

Submit paper
Claim Paper Authorship

Tools for SE users

Search User
Reclaim SE Account
Request Account Merger
Nativise imported posts
Claim post (deleted users)
Import SE post

Users whose questions have been imported from Physics Stack Exchange, Theoretical Physics Stack Exchange, or any other Stack Exchange site are kindly requested to reclaim their account and not to register as a new user.

Public \(\beta\) tools

Report a bug with a feature
Request a new functionality
404 page design
Send feedback


(propose a free ad)

Site Statistics

198 submissions , 156 unreviewed
4,897 questions , 2,075 unanswered
5,311 answers , 22,539 comments
1,470 users with positive rep
802 active unimported users
More ...

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

+ 0 like - 0 dislike

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 in Open problems by Naiveguy [ no revision ]

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):
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:
Then 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.

user contributions licensed under cc by-sa 3.0 with attribution required

Your rights