How does a physicist see things

News portal - Ruhr University Bochum

What is a body The question is wrongly posed from the point of view of physics. In everyday life we ​​perceive the bodies in our environment through our senses. There is an interaction of particles with this body, which provides us with information about its spatial expansion: be it the light particles when we see or the atoms on the surface of our hand when we touch it. The type of interaction determines the expansion of a body, which is investigated in atomic and nuclear physics in scattering experiments. This involves bombarding atoms or atomic nuclei with certain particles and measuring their deflection and energy loss. Electrons, protons, neutrons or light particles are used as projectiles - and the results differ significantly depending on the type of projectile and its energy. With neutrons one only sees the atomic nucleus, with electrons and light particles rather the atomic shell. So the question of the size of an atom or atomic nucleus has many answers. This interaction is also important on a large scale. The size of a black hole is defined more by the limit of the interaction of light with gravity than by the spatial extent of the heavy celestial body in its interior.

These types of interaction determine how we deal with bodies in everyday life. So holding a book with your hands is actually the interaction of the atoms in your hand with those of the cellulose of the paper the book is made of. One of the most important laws of quantum physics, the Pauli prohibition, states that the atoms of your hands cannot easily penetrate those of the paper. Therefore, the exercise book is stable in your hands and you can perceive this body in its size.