# What is mean by an elementary particle ?

1. Jan 24, 2007

### 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?

2. Jan 24, 2007

### dextercioby

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.

3. Jan 24, 2007

### 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:rofl:

4. Jan 25, 2007

### 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).

$$\psi (r,t)$$

Last edited: Jan 25, 2007