QED Coupling Constant

The coupling constant (aka the fine-structure constant), alpha, is used in quantum electrodynamics to determine the probability an exchange will occur between a charged particle (fermion) such as an electron or a quark and the force-mediating boson such as the photon or W-boson.

 

This is a testament to the remarkable achievement of Richard Feynman who shared in the 1965 Nobel Prize in Physics for his contribution to the theory of QED.

 

The coupling constant can be measured by measuring the anomalous magnetic moment of an electron precessing in a magnetic field.

 

The 2012 value for alpha obtained via QED and the measurement of the electron's anomalous magnetic moment is: 1/(137.035999173(35))

 

That level of agreement between experiment and theory is unheard of in science making QED one of the most precise theories ever developed.

 

(It's also a bit interesting that such a predominant constant of nature would be ~ 1/137 .)

 

For a very interesting lecture series by Richard Feynman on QED (for dummies) see:

www.youtube.com/watch?v=xdZMXWmlp9g

www.youtube.com/watch?v=kMSgE62S6oo

www.youtube.com/watch?v=jNNXD7fuE5E

www.youtube.com/watch?v=UigjOJm6F9o

 

Note: In the 3rd lecture (~37:00), Feynman talks about the coupling constant although he refers to it as c^2.

Done