The proton is a subatomic particle with a positive electric charge of +1e, which is found in the nucleus of every atom. It is one of the three fundamental particles that make up atoms, along with the electron and neutron. Protons are much heavier than electrons, weighing about 1836 times as much. The name “proton” comes from the Greek word for “first”, because it was first discovered in 1918 by Ernest Rutherford.
Rutherford showed that the atom consists of a small, dense nucleus composed of protons and neutrons surrounded by electrons in orbit around it. He also demonstrated that when atoms collide, they sometimes bounce off each other like billiard balls – an effect that he called “scattering”. This led to his famous gold foil experiment, in which he bombarded a sheet of gold with alpha particles and observed their scattering pattern. From this he deduced that the vast majority of an atom’s mass must be concentrated in its nucleus, with its electrons orbiting around it like planets around a star.
Today we know that protons are one type of hadron – a class of particles that includes both mesons and baryons (such as neutrons). Hadrons are held together by the strong nuclear force, which is mediated by bosons known as gluons. The strong force is incredibly powerful: it can hold quarks together against immense repulsive forces – such as those generated by the electrostatic repulsion between protons – and it overcomes the electromagnetic forces trying to push nuclei apart. In fact, it is so strong that even when two nuclei collide at high speeds (as happens inside stars), they will often pass right through each other without fusion taking place. Only if they happen to hit dead-on will they fuse together into a single larger nucleus.
Protons are not indestructible: when exposed to extremely high energies (such as those found near black holes or during collisions between cosmic rays), they can be destroyed by what are known as proton decay processes. These include weak interactions such as beta decay (in which a proton decays into a neutron) or positron emission (in which a proton emits an anti-electron/positron). However, these processes are very slow compared to the typical lifespan of an isolated proton, which is on the order of 10^34 years – making them effectively immortal on human time scales!