A Subatomic Particle

A subatomic particle is an elementary or composite particle smaller than an atom. Particle physics and nuclear physics are concerned with the study of these particles, their interactions, and non-atomic matter. Subatomic particles include the atomic constituents electrons, protons, and neutrons. Protons and neutrons are composite particles, consisting of quarks. A proton contains two up quarks and one down quark, while a neutron consists of one up quark and two down quarks; the quarks are held together in the nucleus by gluons. There are six different types of quark in all ('up', 'down', 'bottom', 'top', 'strange', and 'charm'), as well as other particles including photons and neutrinos which are produced copiously in the sun. Most of the particles that have been discovered are encountered in cosmic rays interacting with matter and are produced by scattering processes in particle accelerators. There are dozens of known subatomic particles. Hydrogen atom (schematic) The picture shows the first few hydrogen atom orbitals (energy eigenfunctions). These are crosssections of the probability density with warmer colors having higher probability.

Introduction to particles In particle physics, the conceptual idea of a particle is one of several concepts inherited from classical physics, the world we experience, that are used to describe how matter and energy behave at the molecular scales of quantum mechanics. As physicists use the term, the meaning of the word "particle" is one which understands how particles are radically different at the quantumlevel, and rather different from the common understanding of the term. The idea of a particle is one which had to undergo serious rethinking in light of experiments which showed that the smallest particles (of light) could behave just like waves. The difference is indeed vast, and required the new concept of wave-particle duality to state that quantum-scale "particles" are understood to behave in a way which resembles both particles and waves. Another new concept, the uncertainty principle, meant that analyzing particles at these scales required a statistical approach. All of these factors combined such that the very notion of a discrete "particle" has been ultimately replaced by the concept of something like wave-packet of an uncertain boundary, whose properties are only known as probabilities, and whose interactions with other "particles" remain largely a mystery, even 80 years after quantum mechanics was established.