The ancient Greeks proposed that the Universe was made of tiny indivisible "atoms" and scientists have long searched for an answer to the question: what is the Universe made of? The search for an answer led to the discovery that atoms are made up of smaller particles, a nucleus of neutrons and protons surrounded by electrons, and that the neutrons and protons are in turn composed of quarks and gluons. Along the way has come the recognition of the periodic table of elements, atomic theory, nuclear physics and quantum mechanics. Such developments have been fundamental in understanding how the Universe evolved.
Experiments and theory research continues is ongoing as many puzzles remain unsolved. For example why do we see more matter than antimatter; what is the nature of the force that binds quarks, and nucleons, together; what are the limits of this force; are forces unified at high energies; where does the mass of particles come from; what is the missing dark matter which seems to make up about a quarter of the Universe; and what is the "Dark Energy" which may drive the expansion of the Universe? Particle accelerators along with arrays of sensitive underground detectors, and astrophysical observations, let scientists peer into the fundamental structure of nature and back towards the big bang.