# What is a "structure-less particle"?

## Main Question or Discussion Point

I have a stupid question:

I saw the term "structureless Particle".

What is a "structureless particle"? Please explain to me like I am a 4th grader.

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quasar987
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It all depends on the context of course, but I would guess it means a particle that is not made up of more particles. Fundamentally, a proton is not a structureless particle because it is made up of 3 quarks. However, a quark would fit in this category and so would an electron, because as far as we know, they are not made up of anything else.

Structureless particle? Maybe it has not internal quantum numbers? I.e. no spin.

Hootenanny
Staff Emeritus
Gold Member
Structureless particle? Maybe it has not internal quantum numbers? I.e. no spin.
Both electrons and quarks [as far as we know] are elementary particles (have no internal structure), both are also fermions and hence have half integer spin (i.e $\pm1/2, \pm3/2, \pm5/2,...$). However, I do agree with quasar987's interpretation. If you google 'elementary particle' you should find some more information.

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According my opinion, structureless particles haven't its mass, size and aren't made up of more particles. For example, photon, neutrino are the structureless particles. However, they are still influenced by interactions (fundamental force as weak,electromagnetic, gravitational, strong ..).

Hootenanny
Staff Emeritus
Gold Member
According my opinion, structureless particles haven't its mass, size and aren't made up of more particles. For example, photon, neutrino are the structureless particles. However, they are still influenced by interactions (fundamental force as weak,electromagnetic, gravitational, strong ..).
According to current theory and experimental evidence, neutrinos have a small but finite mass. Out of curiosity why do you require that a structureless particle must be massless?

Both electrons and quarks [as far as we know] are elementary particles (have no internal structure), both are also fermions and hence have half integer spin
I know quite a bit about electrons and quarks:) I guess "structureless" is pretty ambiguous. I took structureless to mean without any internal quantum numbers, and spin is internal in the sense that it is intrinsic. I've never seen an electron called a "structureless" particle, only "fundamental" particle. It would be nice to see some context, I guess.

And 5/2 isn't an allowed spin for fundamental particles:)

Structureless particle? Maybe it has not internal quantum numbers? I.e. no spin.
Do you think that is an answer a 4-th grader would understand?

Pete

In my country, one call pmb_phy 's post above is a spam. And you are spamer. It isn't contructive.