I saw this equation on a coffee mug, and I am wondering what it means. I am not far enough along in physics to understand it. Does it actually mean anything or is it gibberish?

enter image description here

I can't embed the image because I am a new user.

(But I can, L.M.)

  • 3
    $\begingroup$ Answer to the embedded question : I don't understand why you chose such an ugly angled typeface to write this question . $\endgroup$ – Frédéric Grosshans May 20 '11 at 10:05

Dear Ganesh, it's a totally valid and legitimate interaction Lagrangian of the electron field as it interacts via the electroweak interactions.

Note that this is just a part of the overall Lagrangian and only includes the electron - and its neutrino - as it interacts by exchanging photons, W-boson, and Z-bosons. Note that the "parts" of the electron that are spinning differently, the left-handed $\psi_{eL}$ and right-handed $\psi_{eR}$ electron, are treated differently. In this fundamental way of writing it, the gauge fields responsible for all the forces are the fields $\vec A_\mu$ for the $SU(2)$ group and $B_\mu$ for the $U(1)$ factor. Other particles and kinetic terms for electrons, the gauge bosons, and other particles have to be added.

Particle physicists would probably not write the explicit $\hbar$ factors because whoever studies the electroweak theory usually uses units in which $\hbar=1$. Also, the claim that the interaction Lagrangian is legit doesn't imply that the creator of the mug understands particle physics. It's more likely that he copied it from somewhere - or, more likely, asked a physicist to give him the text.

  • $\begingroup$ It was a pleasure. $\endgroup$ – Luboš Motl May 19 '11 at 17:42

It's the electroweak Lagrangian. In laymen's terms, it describes how photons, electrons and neutrinos interact with one another. Each term represents a possible interaction. See this wiki page for more info. You will see a similar, equivalent Lagrangian expression there with some more detailed explanations, should you want it.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.