What is mean by an elementary particle ?

[bchui]

What is mean by an "elementary particle"?

I have always been intriguing about the definition of an "elementary paticle". Can we actually "define" a photon as a wave function $\psi(r,t)$ solution of the Maxwell Equation and "define" an electron as a wave function solution of the Klein-Gordan equation and so on?
How about the "definition" of photons and neutrons and the others?

 

[dextercioby]

I have always been intriguing about the definition of an "elementary paticle". Can we actually "define" a photon as a wave function $\psi(r,t)$ solution of the Maxwell Equation and "define" an electron as a wave function solution of the Klein-Gordan equation and so on?
How about the "definition" of photons and neutrons and the others?

Applying KG equation to the electron leads to erroneous results, as the KG equation is valid only for a field associated to a spin 0 particle.
There's no universal definition to an "elementary particle". I like the one which involves the covering group of the Poicare' group and its irreducible representations.

 

[bchui]

So, how about Quantum Field Theory which tells us particles can be divided into Ferminions and Bosons. Should we actually take a wave function $\psi(r,t)$ as a particle for different $(r,t)$? There must be a precise meaning before we work out QFT

 

[Gib Z]

No Universal Definition to elementary particle? I must have learned physics differently because I always thought that an elementary particle was one which has no inner-substructure. A proton is made up of quarks, so it isn't elementary. An electron is a lepton, made up of nothing else, so it is elementary.

Btw: On PF you use [ tex ] and [ /tex ] tags after our math code (without the spaces).

\psi (r,t)