Question: why do some particles have mass and others dont?

John Prytherch answered on 16 Mar 2012:

I think the only particles that don’t have mass are photons, which are the particles that make up light (and other electromagnetic radiation like radiowaves or microwaves). All other particles do have mass, even neutrinos, which are so small and have such little mass that millions of them are constantly passing through us without us noticing).

Photons are the particles of light, but light is both wave and particle, and has some very strange behaviour, which we try and understand using quantum mechanics. This is a very important area of modern physics (for instance, the scientists at CERN who work on the Large Hadron Collider are trying to answer the question ‘what causes mass?’), is it something you would like to study after you finish school?