While we’re on the topic of quantum physics, here is a nifty illustration from Wikipedia of the elementary particles of the Standard Model. “Atom” means indivisible, as atoms were originally thought to be the smallest parts of the universe, the bits that compose everything else but are not themselves composed of smaller particles. As physics advanced, scientists found that atoms consisted of even smaller particles, and these are the smallest, atomic (indivisible) parts of reality as far as we know today, according to the most accurate and experimentally verified theory of physics as of 2014. Notably missing is the graviton, a particle hypothesized to be the carrier of the elementary force of gravitation, but as of today physicists have been unable to create a theory that unifies the three forces of the Standard Model—the electromagnetic force, the strong and the weak nuclear force—with gravity.
The fact that these particles are regarded as elementary doesn’t necessarily mean that they aren’t composed of even smaller particles. It could be that in the future, likely when we can study even higher energies than those in our most powerful particle accelerators—big machines that collide particles at enormous velocities, generating extreme energies in order, basically, to see what happens, what comes of the collision—we will discover that these particles are composed of even smaller constituents. But as it stands right now, these are the smallest things we know exist, and as of now, based on the information we possess from experiments and mathematical theories, we think they’re indivisible. Nothing, as far as we know, is smaller than those particles up there.
Many hypotheses have been put forth which bring further or smaller elementary particles into the fray, notably string theory, but these are so far only mathematical fantasies, hypotheses which have yet to be tested and verified. Science is a process, not an end goal.
If you’re missing the familiar protons and neutrons, they are composed of quarks, held together by the strong nuclear force, which is mediated by the gluon. The electron, however, swirling about the atomic nucleus, is believed to be elementary. Perhaps one day we’ll peek further into the depths of the quantum world and discover smaller things, but that’s where it stands right now.
The pre-Socratic philosopher Democritus is often credited as the father of atomism, the theory that everything is composed of tiny, tiny things that are themselves indivisible and indestructible. This view is, on the face of it, a lucky guess that hints at modern physics; on the other hand, Democritus imagined atoms as solids; some of them could lock together with hooks and become very durable, like iron, while others were slippery and constantly in motion, like water or air. Of course, the Ancient Greeks had no way of investigating this; modern technology and high energies are required to observe the atomic and subatomic world.
ahh, it’s so satisfying to see Higgs up there in full colour, no longer greyed out staying “theoretical”