Unified Field Theory

There is a general aesthetic among high energy physicists that the more symmetrical a theory is, the more "beautiful" and "elegant" it is.

The beauty of any complex concept actually lies on that simple, fundamental base that unites them. Like the trunk of the tree that branches into diverse, non-converging concepts.
The most intriguing part, for any physicist, is the attempt to find that trunk that stems out into concepts as divergent as quantum mechanics and the theories of relativity which were proposed by Albert Einstein.
One of the most beautiful descriptions I've ever come that emphasizes this dilemma is quoted below:

"Calling it a cover up would be far too dramatic.But for more than half a century - even in the midst of some of the greatest scientific achievements in history - physicists have been quietly aware of a dark cloud looming on a distant horizon."
(From "The Elegant Universe" by Brian Greeene)

The truth is, this dark cloud looming in the distant horizon, was also responsible for Einstein to trip during his quest for a unified theory, a theory that would connect the two most
antithetical concepts in Physics: Quantum mechanics and the Theory of Relativity.

"Through years of research, physicists have experimentally confirmed to almost unimaginable accuracy virtually all predictions made by each of these theories. But these same theoretical tools inexorably lead to another disturbing conclusion:
As they are currently formulated, general relativity and quantum mechanics cannot both be right. "
(From "The Elegant Universe" by Brian Greeene)

In attempt to briefly describe what the Unified Theory in Physics aims at:

Unified Field Theory, in physics, a theory that proposes to unify the four known interactions, or forces—the strong, electromagnetic, weak, and gravitational forces—by a simple set of general laws. Four distinct forces are known to control all the observed interactions in matter: gravitation, electromagnetism, the strong force (a short-range force that holds atomic nuclei together), and the weak force (the force responsible for slow nuclear processes, such as beta decay). The attempts to develop a unified field theory are grounded in the belief that all physical phenomena should ultimately be explainable by some underlying unity.

Indeed, one of the biggest challenges today would be to find a concrete unifying theory, ironically the simplest and most fundamental explanation of what connects the different aspects of our physical world.

Physics has evolved into such magnanimous proportions that finding the root, the floor of this vast and endless ocean has become even more complex a task.

All concepts, ideas and systems are somehow connected to each other by an invisible thread.