atom10⁻¹⁰ mnucleus10⁻¹⁴ mproton10⁻¹⁵ mquarkunder 10⁻¹⁹ m10,000× closer10× closer10,000×+ closer
Each panel enlarges a small square of the one before. The atom is mostly empty: its nucleus is about 10,000 times smaller across, so if the atom were a football stadium, the nucleus would be a pea on the centre spot. The nucleus is a cluster of protons (red) and neutrons (grey). Each of those is three quarks held together by gluons. No experiment has found any size for a quark, down to 10⁻¹⁹ m.