The ancient Greeks were the first to assume the existence of the atoms, the smallest particles of the universe. But it didn’t end just there. Over a thousand of years later, the atom was discovered to even be made of protons, neutrons and electrons. And these three subatomic particles are even made of much tinier matter called quarks.
The deeper that we dig into the structure of the universe, the more questions emerge than are answered. Are space and time made of clusters of particles that seem get tinier and tinier that we can’t even see? The mysteries of these particles make them even more fascinating, and because of this, scientists (even up to this day) have assumed certain kinds of particles exist — called theoretical (or hypothetical) particles — but almost all of them haven’t been observed yet.