Insights into String Theory
An exciting theory that has emerged in the last few decades is String Theory. It is by far the most promising candidate for a unified theory of everything. In other words, this theory describes the fundamental particles and forces of nature including gravity. Other theories, like the Standard Model, fail to explain or include the effects of gravity.
String Theory seems to be the best hope scientists have to explain the quantum behavior of black holes, underlying symmetries of nature and the quantum treatment of singularities. It could also answer questions such as what the nature is of quantum mechanics and space & time.
This theory also brings all the forces and particles into one 'Theory of Everything', just like Einstein and many theorists of the time have wished to be able to do.
Based on a simple premise that at micro-small scales called Planckian scales, (where the effects of quantum gravity are strongest) particles are extended objects that are one-dimensional, or strings. These strings emit particles that are the result of the excitations of the strings. By their different oscillations strings emit what, to the observer, may be a photon, an electron, a quark or whichever. If correct, this theory would suggest that everything is made of strings.
As of yet, there is no evidence deduced from experiments that string theory is correct, but it does seem to fit the model quite well. Scientists are still developing it and hope to find some proof in the very near future.
Sources:
http://www.nuclecu.unam.mx/~alberto/physics/string.html
http://staff.science.uva.nl/~rhd/string_theory.html