Scientific tragedy of late Einstein. He tried hard to unify all fundamental forces in a framework like his General Relativity. While GR ranks among the greatest achievements of physics, UFT never worked out. According to CF von Weizsäcker, Einstein's UFT was far from explaining sharply separated types of elementary particles, while Heisenberg's attempts on UFT came a little closer.

It's an unsolved problem to fit gravitation and quantum physics into one mathematical framework.

Unified Field Theory, also referred to as the Grand Unified Theory in its more complex state, is a physical theory that attempts to unite the four known forces in nature - the Electrostatic, the Strong Nuclear, the Weak Nuclear, and the Gravitational. Unifying these four forces under one single set of mathematical expressions was long considered the 'Holy Grail' of modern physics, and absorbed the efforts of thousands of physicists for the better part of a century.

Unified Field Theory started out as Albert Einstein's attempts to reconcile his own view of the universe with the emerging field of Quantum Mechanics. Einstein despised quantum theory in its infancy, perceiving it as a threat to the foundations upon which his theories of Special and General Relativity were built. His famous statement, "God does not play dice with the universe", is a reflection of his disposition towards a probabilistic universe. By contrast, all of Relativity is based on Newtonian determinism. Einstein was partially successful in unifying these wildly different forces, but ultimately failed. Heisenberg later took up the gauntlet for the more noble reason of preserving the elegance of physics - he believed that the ultimate goal of physics would be to great an 'equation for everything'. Currently however, there is no theory of gravitation at the quantum mechanical level.

Interest in the Unified Field Theory waned as some of the greatest minds of the twentieth century fell in pursuit of the ultimate equation. Research was recently rekindled however with the theorization of the Higgs Boson, the currently theoretical particle thought to give particles mass. The reason for this is difficult to explain in words, but I will try. Under the Standard Model of particle physics and our current understanding of field theory, we can plot graphs describing each of the four forces. If we plot them on the same axes, at increasing energies, the four lines begin to converge to a point, but without including the Higgs Boson, they miss convergence by a tiny but significant margin. By including the Higgs into the Standard Model, it is possible to unify all four fields, at a very high energy state known as the Unification Energy. This energy level also gives rise to several other 'fringe theories' such an over-unity (free energy) and Magnetic Monopoles.

Currently, the conclusion of the UFT, for good or ill, is still a dream for physicists. However, the construction of ever more powerful particle accelerators may eventually change this situation, perhaps leading to the final discovery of the Higgs and beyond.

There are reasons for suspecting that some sort of Unified Field Theory exists. It can be seen in the equations.

In days of yore, Sir Isaac Newton "discovered" gravity. The force of gravitational attraction between two objects of masses m1 and m2, at a distance of r, is given by the equation

F_g = (g*m₁*m₂)/(r²)
where g is simply a constant. The constant, of course, changes depending on the units of measurement that are chosen. Simply put, g is completely arbitrary and could be eliminated if we chose the right units.

As a side note, the force of gravity felt by each object due to the presence of the other object is identical. The reason that an astronaut falls toward the earth, while the earth does not appear to fall toward the astronaut is an issue of mass. F=m*a where F is force, m is mass, and a is acceleration. The Earth is far more massive than the astronaut, and hence does not accelerate nearly as quickly as the astronaut. In fact, you wouldn't even notice it.

Similarly, there is an equation which describes the amount of force felt (either attraction or repulsion in this case) by a charge due to the presence of another charge at some distance r. Much like gravity, the force felt by each particle due to the presence of the other will be identical.

F_E = (k*q₁*q₂)/(r²)
Where k is another one of those arbitrary constants, and q1 and q2 are the charges on each of the two particles. k is also sometimes expressed as the inverse of 4*pi*E, where E is the permeability of free space and is really the Greek letter which looks like a capital E. Once again, though, it's arbitrary. Change the units, and the constant disappears. Suppose we changed the units for mass, charge, and distance in a way that would eliminate the constant for both equations. We would be left with the following:

F_g = (m₁*m₂)/(r²)
F_E = (q₁*q₂)/(r²)

Gasp! Those equations... look the same. Perhaps mass is related to charge, meaning electricity, in some manner. This is the stuff of Physicists' wet dreams.