What are the elementary particles?

Since the wavelength of light is much larger than the size of an atom, we cannot hope to “look” at the parts of an atom in the ordinary way. We need to use something with a much smaller wavelength. 

quantum mechanics tells us that all particles are in fact waves, and that the higher the energy of a particle, the smaller the wavelength of the corresponding wave. So the best answer we can give to our question depends on how high a particle energy we have at our disposal, because this determines on how small a length scale we can look.

These particle energies are usually measured in units called electron volts. 

In the nineteenth century, when the only particle energies that people knew how to use were the low energies of a few electron volts generated by chemical reactions such as burning, it was thought that atoms were the smallest unit. In Rutherford’s experiment, the alphaparticles had energies of millions of electron volts. More recently, we have learned how to use electromagnetic fields to give particles energiesof at first millions and then thousands of millions of electron volts. And so we know that particles that were thought to be “elementary” thirty years ago are, in fact, made up of smaller particles. May these, as we go to still higher energies, in turn be found to be made from still smaller particles? This is certainly possible, but we do have some theoretical reasons for believing that we have, or are very near to, a knowledge of the ultimate building blocks of nature.