The theory that purports to unify two branches of
physics - quantum mechanics and the theory of relativity,
to give a consistent description of nature over all
time, mass and length scales. Sometimes referred to as
TOE -"Theory of Everything".
String theory is a potential formulation of quantum gravity.
quantum mechanics
The branch of physics that describes nature at small scales.
The formulation of quantum mechanics is considered one of the
greatest intellectual achievements of 20th century, with
great scientists like Dirac, Einstein, Bohr amongst many others contributing
to its development.
quark
Quarks are elementary particles
that make up protons and
neutrons in atomic nuclei.