For a long time it was known that atoms consisted of protons, electrons and neutrons. It was believed that these sub-atomic particles were the irreducible building blocks of all matter, however, the existence of forces like gravity and magnetism between particles led scientists to believe that these forces themselves might consist of even smaller particles, called quarks.
In 1963, Murray Gell-Mann, a physicist at the California Institute of Technology, building upon the quantum theory of Planck and the relativity theory of Einstein, postulated the existence of quarks, particle forces binding the protons and neutrons of matter. Quarks are particles, e.g. the force of gravity is exerted by the gravitron particle, and light, for example, consists of photon particles or quanta.
Supposed to be pronounced to rhyme with 'corks', but usually pronounced to rhyme with 'larks', quarks differ from other known particles, in that each has a partial positive or negative electrical charge. Quarks bind together in families of three, or triunes, to form pairs of protons and neutrons, in traditional terminology. These groups of quark triplets are known as hadrons, or collectively, as hadronic particles.
These particles are known to have been plentiful during the initial stages of the big bang, and have subsequently been produced by various scientists in laboratories using particle acceleration equipment.
Quarks exist in six different states known as flavours. The first three flavours discovered were up, down and strange. Subsequent research established that there are three more flavours, dubbed bottom, top and charmed. Only the up and down flavours occur naturally in matter. Protons, for example, have two up quarks and one down quark, the electrical charges combining as: + 2/3 + 2/3 - 1/3 = +1. Neutrons are made up of one up quark and two down quarks as follows: + 2/3 - 1/3 - 1/3 = 0; i.e. it is neutral.
Each flavour of quark occurs in three colors (red, green and blue) and each hadron has one quark of each color. The pairing of a quark with an antiquark of the same color is called a meson. According to quantum field theory, matter is made up of the six flavours of quarks and six other kinds of particles called leptons. Leptons are made up of the electron, the muon, and the tau particle, each with it's own neutrino. Furthermore, all the forces between particles of matter are mediated by force-carrying particles called gauge bosons. One of these, the gluon, is responsible for holding quarks together. Other gauge bosons include the photon, associated with light and other electromagnetic forces, and the graviton, a messenger particle of gravity.
The four flavours of quarks that do not occur naturally - strange, charmed, bottom and top - are believed to have existed briefly during the Big Bang which occurred some fifteen billion years ago, but can now only be observed in particle accelerator laboratories.
When protons and antiprotons collide in a particle accelerator at speeds approaching that of light, the resulting annihilation causes these quark particles to exist for a short time, approximately one hundredth of a billionth of a billionth of a second, before they decay into other particles. Since they decay, they leave "footprints" that can be detected and measured, and from this, their mass can be determined.
In March 1995, the top quark was finally identified by scientists at the Fermi National Accelerator Laboratory in Batavia, Illinois, and had more mass than expected, being about the same as that of an atom of gold, which contains nearly 200 protons and neutrons.
The Higgs boson is a theoretical particle believed to endow all the other particles with mass.
Recent research into quantum field theory has indicated that, because of the 'constructive' influence of quarks on the composition of matter, time travel into the past to 'change events' may not be theoretically possible. Quarks are apparently self-destructive in a mathematical construct of time elapsed.
We would not, therefore, according to some leading scientists, be able to alter future events by murdering our ancestors, or eliminating Hitler from the history books. However, many other interesting possibilities of time travel remain to be explored in the world of advanced physics. Short reverse time trips or trips several minutes into the future remain interesting challenges. "There are more things, Horatio"
Time travel into our own future, the exploration of alternative universes, and the concept of universal transmutation through Einstein-Rosen bridges remain intriguing possiblities, as we continue to decipher and unravel the very building blocks of nature.