Matter
Matter can be considered as a general term for the substance of which a physical object is composed. The material substance occupies space and has mass. The theory that matter consists of discrete units began as a philosophical concept in ancient Greek with the work of Leucippus (~490 BC) and Democritus (~460-370 BC).
Over time an increasingly fine structure of matter was discovered: objects are made from molecules, molecules consist of atoms, which in turn consist of interacting subatomic particles like electrons and protons, demonstrated by Rutherford's famous experiment.
Since the middle of 1920s, researchers have predicted and/or confirmed the existence of several hundred other particles, many of which only came into existence under extreme conditions and for very short times. Protons and neutrons themselves appeared to be composite objects, consisting of quarks and gluons.
The current state of knowledge about the constituents of matter (elementary particles) and their interactions (strong, weak, electromagnetic) is shown in the Standard Model. The overarching goal, which is pursued in several distinct ways, is to find and understand what physics may lie beyond the Standard Model. There are several experimental reasons to expect new physics, including Dark Matter, the Higgs boson and supersymmetric particles.
Matter | Dark Matter | Higgs-Particle | 4th Generation | Heavy Quarks