I QED question: Photons absorbed and emitted by electrons

[dsaun777]

According to QED photons can be absorbed or emitted by electrons, and this process results in em forces via virtual photons. What determines the emitted photon frequency, and are they fully absorbed by electrons assuming photons are discrete and must be in quantized packets? How fast are photons absorbed, instantaneously because all the energy must be transferred? How fast are they emitted? Meaning is there a delta t measuring the energy/time process.

 

[weirdoguy]

and this process results in em forces via virtual photons.

If you are asking in the context of virtual photons, then this article is a good start:
https://www.physicsforums.com/insights/misconceptions-virtual-particles/

 

[dsaun777]

If you are asking in the context of virtual photons, then this article is a good start:
https://www.physicsforums.com/insights/misconceptions-virtual-particles/

Putting virtual photons aside for now what about real photons being absorbed and their time.

 

[mfb]

It is in general not meaningful to talk about a time for that process.

 

[dsaun777]

It is in general not meaningful to talk about a time for that process.

So it is unknown...

 

[weirdoguy]

"Not meaningfull" is something different than "unknown". For example, where is the 'north' direction on the north pole? Do you think it's meaningfull to talk about that?

 

[dsaun777]

"Not meaningfull" is something different than "unknown". For example, where is the 'north' direction on the north pole? Do you think it's meaningfull to talk about that?

Yes, if it is meaningless then surely it must have meaning as to why its meaningless.

 

[weirdoguy]

surely it must have meaning as to why its meaningless.

I would say it's contradictio in adiecto.

 

[dsaun777]

I would say it's contradictio in adiecto.

Maybe time is not the right word but electrons do interact with photons and I'm interested in these dynamics.

 

[mfb]

Then you'll have to learn a lot of quantum field theory.

 

[vanhees71]

"Not meaningfull" is something different than "unknown". For example, where is the 'north' direction on the north pole? Do you think it's meaningfull to talk about that?

Interesting question ;-)). I'd say it's perpendicular up!

 

[vanhees71]

Maybe time is not the right word but electrons do interact with photons and I'm interested in these dynamics.

As @mfb is saying, then you have to learn QFT (it's fun and addictive ;-)). To answer the question qualitatively: It is impossible to intepret the QFT dynamics in terms of particles during the "interaction process". That's why what's usually calculated with QFT are socalled S-matrix elements, describing the probalities that in a scattering process a given "asymptotic free incoming state" (for technical reasons usually two particles like the two protons colliding in the LHC, far away from each other so that you can assume them to be non-interacting) goes into a given other "asymptotic free outgoing state", i.e., some particles that are far enough from each other so that you can consider them as non-interacting.

For times "at the scattering process", i.e., when the incoming and procuced particles are close to each other it is not clear, how to intepret the field dynamics in terms of particles at all, i.e., it's even a bit schizophrenic to formulate the first half of this sentence ;-))).

 

[dsaun777]

Then you'll have to learn a lot of quantum field theory.

QFT or QED? I want to know photon electron interactions nothing else for now.

 

[weirdoguy]

Well, one usually starts learning QFT from QED so Anyway, if you really want to delve smoothly into technicalities I recommend Klaubers Student Friendly Quantum Field Theory. It focuses on QED only, most of the derivations are outlined in great details and Klauber devotes one whole chapter to show that pop-sci myth about virtual particles (or whatever) popping in and out of existence has no basis in QFT.

 

[dsaun777]

Well, one usually starts learning QFT from QED so Anyway, if you really want to delve smoothly into technicalities I recommend Klaubers Student Friendly Quantum Field Theory. It focuses on QED only, most of the derivations are outlined in great details and Klauber devotes one whole chapter to show that pop-sci myth about virtual particles (or whatever) popping in and out of existence has no basis in QFT.

How well does nutshell cover qed and qft in comparison?

 

[weirdoguy]

Well, I paused for a while after reading the first chapter (I want to finish his group theory book first), but some people say (well, @vanhees71 says ) that Zee tried to fit too much in his nutshell and it didn't end up well. It may be a good read, but after you know something on the subject, so that you won't be distracted by some things that didn't end up well didactically.

 

[mfb]

QED is the easiest QFT that describes an interaction in our world.

 

[vanhees71]

How well does nutshell cover qed and qft in comparison?

You mean Zee's book? It's funny to read if you know QFT already. I've no clue, how one can understand it if you don't already know it from this book. It's too brief and partly superficial. My favorite intro book is

M. D. Schwartz, Quantum field theory and the Standard
Model, Cambridge University Press, Cambridge, New York
(2014).

 

[dsaun777]

You mean Zee's book? It's funny to read if you know QFT already. I've no clue, how one can understand it if you don't already know it from this book. It's too brief and partly superficial. My favorite intro book is

M. D. Schwartz, Quantum field theory and the Standard
Model, Cambridge University Press, Cambridge, New York
(2014).

Why Schwartz? Is he a relative or something. I have a friend that is sending me Kaku's quantum field theory a modern introduction, any thoughts on that?

 

[vanhees71]

Kaku is good too. I'm not related to Schwartz in any way. It's just that I think it's a very good QFT book at the introductory level. If you prefer a path-integral-only approach, another one is Bailin, Love, Gauge theories.