What is the significance of the kinetic term in a scalar field theory?

Click For Summary

Discussion Overview

The discussion centers around the significance of the kinetic term in the action of a scalar field theory, specifically questioning its interpretation as kinetic energy, particularly in the context of massless fields like photons.

Discussion Character

  • Exploratory, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant questions the interpretation of the kinetic term in the action, expressing discomfort with the idea of kinetic energy for massless fields.
  • Another participant asks whether a photon has kinetic energy, prompting further exploration of the concept.
  • A different participant suggests that kinetic energy can be understood as energy due to movement, noting that massless particles always move at the speed of light.
  • Some participants acknowledge that while photons have energy expressed as E=hν, they do not typically refer to it as kinetic energy, indicating a distinction in terminology.
  • There is a mention that for massless particles, energy is related to momentum through the equation E=pc, which adds to the discussion on kinetic energy.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of kinetic energy in the context of massless fields, and no consensus is reached regarding the terminology or conceptual understanding.

Contextual Notes

The discussion reflects uncertainty about the definitions and implications of kinetic energy in field theory, particularly for massless particles, and highlights the dependence on classical versus quantum interpretations.

robousy
Messages
332
Reaction score
1
I've been wondering about terms you typically find in the action of a field theory, for example consider the kinetic term of a scalar field

[tex]S=\int d^4x(\partial_\mu\phi\partial^\mu\phi).[/tex]

I've read that it can be thought of as the kinetic energy of the field - but this just doesn't sit to well with me for some reason. I mean the kinetic energy of a massless field seems strange.

Can anyone here provide any deeper insights into this?
 
Physics news on Phys.org
does a photon has kinetic energy?
 
mjsd is right

think the definition (classically also) of what K is?

roughly speaking is the amount of energy that a system has, due just to his movement.

massles particles do move always at c.
 
hmmm... well I know that a photon has energy [tex]E=h\nu[/tex], but I've never called it knietic energy - but I see what you are getting at.
 
robousy said:
hmmm... well I know that a photon has energy [tex]E=h\nu[/tex], but I've never called it knietic energy - but I see what you are getting at.

rember also that for m=0 E=pc
 

Similar threads

Graduate How the mass term of the Hamiltonian for a scalar fields transform?
  • · Replies 1 ·
Replies
1
Views
3K
Graduate Verifying the Relation in Yang-Mills Theory with a Scalar Field
  • · Replies 30 ·
2
Replies
30
Views
6K
Graduate Deducing counter-terms for canonically quantised GR
  • · Replies 2 ·
Replies
2
Views
2K
Graduate Possible decay process for a cubic scalar self-interaction
  • · Replies 3 ·
Replies
3
Views
2K
Graduate Derivation of momentum for the complex scalar field
  • · Replies 8 ·
Replies
8
Views
4K
High School Are real theories undiscoverable from effective field theories?
  • · Replies 4 ·
Replies
4
Views
3K
Graduate Variation of the kinetic term in scalar field theory
  • · Replies 1 ·
Replies
1
Views
1K
Undergrad What does "transforms covariantly" mean here?
  • · Replies 4 ·
Replies
4
Views
1K
Undergrad Scattering of a scalar particle and a Fermion
  • · Replies 2 ·
Replies
2
Views
4K
Undergrad How to determine matching coefficient in Effective Field Theory?
  • · Replies 1 ·
Replies
1
Views
2K