How do we know everything is made of particles?

This is the question an 8th grade student of mine asked me yesterday. I love it when they ask such fundamental questions. Because in the process of explaining such seemingly obvious concept, I discover a novel way of understanding the world around me. Or, I end up in existential crisis if tugging at string of reality reveals more mess than truth.

My first instinct was to answer that everything is not made of particles, but disturbance in higgs field. I refrained because my job as teacher is not to shine the torch of knowledge in their face, but to illuminate the world around them. One blinds, other reveals.

This is how I answered, roughly.
We know everything is made of these small particles- atoms because we can see (observe) them, using an electron microscope. But we knew about these atoms long before such microscopes. Earliest mention of atoms are believed to be by greek philosophers. And they gave philosophical evidence of such a thing as atom. If you cut any matter into smaller & smaller units eventually you will have a smallest unit (otherwise infinite regression ensues), which they called atom. Then came scientists who confirmed this claim by some cool experiments. One of which is called rutherford’s experiment. (Followed by a crude explanation of the experiment)

I would say that is a sufficient answer. It led me to face the incongruity between human rationale & physical reality. As a thought machine, we cannot allow infinite regression. Yet, without infinite regression, without cutting matter into infinitely smaller bits, we get waves out of matter. I know that there is purely mathematical way, that transcends limits of human thought, of explaining the subject. But why is human thought limited in capability to understand the foundations of universe. It would not be surprising if we can’t understand convoluted interactions arising after numerous levels of structural hierarchy. But the base of this elaborate structure must be simple, and thus fairly easy to get hold of.

The implication of this thought is that maybe we are not getting complex emergent structures out of simple primaries but we are getting simple emergent structures out of complex primaries. When universe stacks group of atoms together to form a brain, it does not make something smarter than those atoms but something dumber.