Quarks and leptons are currently recognized as the smallest known building blocks of matter. When arranged in an organized manner, they reveal a pattern that hints at the potential existence of even smaller subatomic particles. It remains uncertain whether these smaller particles exist or if the observed pattern can be explained by other means. The question regarding the most fundamental nature of matter has intrigued thinkers for over 2,500 years, with Greek philosophers like Democritus and his mentor Leucippus proposing a model that resembles modern scientific views. They suggested that, at the tiniest scale, the universe is composed of "atomos," which translates to "uncuttable" in Greek.
However, it is important to note that "atomos" differs from our current understanding of atoms. While "atomos" referred to the smallest unit of matter, we now know that atoms themselves are constructed from smaller particles: protons, neutrons, and electrons. Beginning in 1964, scientists discovered that protons and neutrons are further made up of even smaller entities called quarks. In contrast, the electron is considered an elementary particle and belongs to a category known as leptons. Leptons come in two forms: charged and neutral, with the neutral leptons being classified as neutrinos.
Currently, there are six known types of quarks, whimsically named: up, down, charm, strange, top, and bottom. The up and down quarks are components of protons and neutrons (with protons consisting of two up quarks and one down quark, and neutrons composed of one up quark and two down quarks). Additionally, there are six types of leptons, including three charged leptons (the electron, muon, and tau) and three neutral leptons (the electron neutrino, muon neutrino, and tau neutrino).
A system can be established where the proton has a charge of +1, the electron has a charge of -1, and the neutron has no charge. Within this framework, up, charm, and top quarks carry a charge of +2/3, while down, strange, and bottom quarks possess a charge of -1/3. The electron, muon, and tau leptons each have a charge of -1, and neutrinos are neutral.
These particles can be categorized into three distinct groups termed "generations." The first generation consists of the up and down quarks, the electron, and the electron neutrino. The second generation includes the charm and strange quarks, the muon, and the muon neutrino. Lastly, the third generation comprises the top and bottom quarks, the tau lepton, and the tau neutrino.
All commonplace matter is formed from first-generation particles. The particles belonging to the second and third generations are unstable and tend to decay rapidly into first-generation particles, with each successive generation being more massive than its predecessors.
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