I knew all this but I like the way he explains it.
In 420 BC Democritus argued for the existence of atoms.
"Democritus's argument for the existence of atoms hinged on the idea that it is impossible to keep dividing matter infinitely - and that matter must therefore be made up of extremely tiny particles"
Democritus thought that the universe consisted of atoms and the voids between them.
Until relatively recently, people thought that atoms were invisible. J.J. Thompson, Marie Curie, and Earnest Rutherford showed that atoms could be divided. It took a while to discover protons and neutrons, and people thought that these were also indivisible. It was later discovered that protons and neutrons were made of up and down quarks.
One could argue that quarks and electrons are the smallest (fundamental) units of baryonic (quark) matter, but this is misleading. Every type of subatomic particle has a field associated with it. A field is something that has a value at every point in space. That value represents that amount of excitation of the field at a particular point. There is likely some energy everywhere, because the fields have been shown to be like tiny ripples on a vast ocean, but if the energy is low at any point in space then not much happens. However, if the energy reaches a certain threshold, then a particle exists at that point.
The Standard Model of Particle Physics has 17 fundamental fields. (There is recent new evidence that Dark Matter may be an unknown type of particle. If so, it might require a new type of field.) Some of these fields interact with each other like the way the electric and magnetic fields can make particles move. These interactions between the fields create the laws of physics, although there is currently no quantum theory of gravity.
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