Protons are positively charged particles that sit at the heart of every atom.
They belong to the baryon family, meaning they’re made of 3 quarks held together by the strong nuclear force. Specifically, a proton is composed of 2 up quarks and 1 down quark (uud), bound so tightly by gluons that they can never escape. This internal structure makes protons incredibly stable, and unlike neutrons, which can decay outside a nucleus, protons seem to last forever, at least, as far as we know. Some theories predict that protons might eventually decay after an absurdly long time (longer than the age of the universe!), but so far, they appear to be immortal.
Being positively charged, protons play a crucial role in determining an atom’s identity. The number of protons in an atom’s nucleus is what defines an element: 1 proton makes hydrogen, 2 make helium, 6 make carbon, and so on.
Their precise size is the subject of ongoing debate (the “proton radius puzzle”), and their deep internal structure is far more complex than just 3 quarks sitting inside. They’re more like a swirling sea of quarks, antiquarks, and gluons, constantly shifting in a dance dictated by quantum chromodynamics.