# Why do material particles interact?

• B
Why do fermions exchange bosons with each other?

Related Quantum Physics News on Phys.org
PeterDonis
Mentor
2019 Award
What kind of answer are you looking for? This question is very broad.

bhobba
Do they exhange bosons?

If "an electron" is an excitation of an 'electron field', its electric charge proprerties suggest it excites and interacts with EM field, which is essentially, the photon field.
As such, the excitations of the photon field as result of two electrtons can be intetpreted as "virtual photons" exchanged between the two to determine the momentum differential...

At least, that's my opinion.

Urs Schreiber
Gold Member
Why do fermions exchange bosons with each other?
In quantum field theory, the interactions that fundamental fields/particles have with each other are encoded by the monomials of the field variables that appear in the Lagrangian/action functional that defines the field theory.

For instance the electron-photon interaction

is reflected by the fact that the Lagrangian density of quantum electrodynamics (example 5.11 in the PF QFT notes) contains a monomial of the form

$$\overline{\psi} \gamma^{\mu} \psi a_\mu$$

where ##\psi## corresponds to the electron field and ##a## to the photon field.

So from this perspective your question is this grand question:

1) Why does the Lagrangian density of the standard model of particle physics have the broad form it has? Namely the form of Einstein-Yang-Mills-Dirac-Higgs theory?

That's an excellent question. A related question is:

2) Assuming the Lagrangian density of the standard model of particle physics is of Einstein-Yang-Mills-Dirac-Higgs theory-type, why does it have the precise numerical coeffcients that it has, for the couplings between the particles?

This second question has been much discussed, but remains wide open. The first question, the one that you are effectively asking, is receiving less attention, but regarding the first question there are some intersting hints.

Namely there are deeper principles which one may invoke, that imply that physics is modeled by Einstein-Yang-Mills-Dirac-Higgs theory, even if they do not imply the precise numerical values of masses and couplings.

One such principle is the assumption that virtual particles are secretly strings (see the last paragraphs of Does string theory make predictions? How?). Another such principle is that the action functional is the "spectral action" of a "spectral triple". These two principles are not unrelated.

Hence should these principles be correct principles of nature, they would reduce the question "Why do fermions interact via exchange of bosons the general way we see in experiment?" to something more fundamental. Whether these principles are principles of nature remains open. But part of the interest in these principles is driven by this implication, that they would provide an answer to the question that you are asking.

#### Attachments

• 3 KB Views: 212
Last edited:
ftr
What kind of answer are you looking for? This question is very broad.
I was looking for the kind of answers given here. I will certainly try to take a deeper look into the explanations given here so I can understand physical interactions. Thank you for your replies!