In the mid-1800s, a Scottish mathematician named James Clerk Maxwell formulated a set of 4 simple equations. These equations, despite their simplicity, were elegant because they unified two separate branches of Physics into one. Those two branches were electricity and magnetism and out of the unification of which, was born Electromagnetism.

Years after that, Physicists began their attempt to unify the force of Electromagnetism with Gravitation to get a unified field theory. Einstein’s Theory of Relativity, which unified space and time into Space-time Continuum, motivated scientists even further to continue their quest to merge the two known forces at that time. Earlier attempts of unification date back to 1919 when a German Mathematician and Physicist, Theodor Kaluza, hypothesized that if the General Theory of Relativity is extended to a five-dimensional spacetime, the equations can be separated out into ordinary four-dimensional gravitation plus an extra set, which is equivalent to Maxwell's equations for the electromagnetic field. Later, in 1926, Swedish physicist, Oskar Klein, came up with the explanation as to why the 5th dimension cannot be seen. He proposed that it might be a small, compact and curved dimension with an incredibly small radius. This attempt, however, was found to be incompatible with Quantum and Nuclear Physics, but it certainly was important because it served as a precursor to many other unified theories that were to come in the future.

With that, it was now clear that the Universe was not easy to explain and our search for the Theory of Everything required a lot of digging. But Physicists never stopped with that. They continued on and on for years and came up with an incredible idea. The idea was to imagine each fundamental particle to be made up of small strings that vibrate in different ways imparting particles with different properties. This was called String Theory. It aims to unite all the four fundamental forces of nature (Gravity, Electromagnetism, Weak and Strong Nuclear force). It’s been five decades since it was first thought up but it still is incomplete. Physicists are still working very hard on this because of its mathematical beauty and it abides by our current most successful theories. This makes it the strongest contender of the Theory of Everything.

The Standard Model is the best unified theory we currently have. It unifies all fundamental forces of nature except gravity. Gravity is very hard to unify because it is very weak and we don’t know much about it. Quantizing gravity is our goal in order to achieve grand unification. But we have put all our hopes in String Theory because even the Standard Model pops out of it. We cannot say for certain whether this will be our final quest for the Theory of Everything, but if it gets completed someday, this would certainly be the greatest breakthrough in the history of Science.