We haven't got the most basic physical theory, and the most basic material composition is still uncertain.
As far as we know, matter is made up of atoms, and atoms are made up of protons, neutrons and electrons. Electrons are considered as elementary particles and cannot be subdivided. But protons and neutrons are made up of smaller quarks, which, like electrons, are regarded as inseparable elementary particles. So how small are electrons and quarks?
At the microscopic level, the behavior of particles is quite different from our common sense. Micro-particles such as electrons and quarks (although there are no free quarks due to color limitation) have wave-particle duality. According to the standard model of particle physics, electrons are point particles with point charges and have no spatial range. However, it is very useful to define the electron radius in the atomic scale interaction problem. According to the definition of classical electron radius, the radius of an electron is about 2.8× 10- 15 meters, that is, 28 millionths of a meter. But this definition ignores the influence of quantum mechanics, which has nothing to do with the real basic structure of electrons. According to the measurement results of Pan Ning ion trap, the upper limit of electron radius is about 10-22 meters. But from the point of energy uncertainty, the upper limit of electron radius is about 10- 18m.
Just like electrons, quarks should theoretically be point-like and infinitesimal. According to the experimental data, the quark radius is less than 4.3× 10- 17m and greater than 10- 19m. In other words, electrons and quarks are on the same scale.
In addition to the basic particles that make up matter, there are smaller basic particles, such as neutrinos. It is estimated that the charge radius of electron neutrinos is10-19m, which is slightly smaller than that of electrons and quarks.
In addition, from the perspective of string theory, elementary particles are all composed of smaller one-dimensional strings, and their size is the smallest scale, that is, Planck length, that is, 10-35 meters. Because it involves the smallest scale, we can't directly observe one-dimensional strings.