Then on the other hand in the relm of the very small we have what is called the Standard Model of Particle Physics, which is similar to the Periodic Table of elements, by grouping the different particles and forces we can show how they interact and do what they do. The standard model and quantum mechanics go hand in hand, QM is simply the laws by which these particles interact. These laws are difficult to wrap your head around and are counter intuitive to everyone. The ultimate feat of the standard model and quantum mechanics wa explaining radioactive decay of elements, in particular beta decay. We have been able to use this to revolutionise medicine through radiotherapy and MRI machines again no small feat of a theory.
The problem that remains in physics is having one theory that predicts both of these theories, one law from which Relativity and The Standard Model fall out. As with every physics theory that comes forward the mathematics used to describe them is more baffling than the last, but with nature there is always what physicists call beauty. Beauty from our stand point is after all the mathematics the end result is wonderfully simplistic, when I first derived E=mc^2 as a homework exercise there was 5 pages of equations, relationships and calculus that just seemed to be invented to destroy the soul, but when all was said and done, out popped this wonderfully simplistic formula to describe the relationship between mass and energy. The same can be said about Quantum Mechanics, the maths is again quite difficult and you seem to wonder how it was thought in the first place but after hours of toiling you end up with a simple equation with 4 terms, 1 is the energy of the system, 1 is a natural constant, then the other two are derivatives with respect to time and with respect to position. o you can know the relationship between position and time through a particles energy and a constant of proportionality. This is what we consider beauty.
The front runner for a grand unified theory is called String Theory, although this theory does the job it is not beautiful. It has the appearance of been given the answer and working backwards. The result seems contrived and does not show the natural simplicity of nature that always appears from great works. I may be wrong and it could be proved right but I hope not. Another theory is called E8, this is a theory of particle physics that uses the E8 group in mathematics. http://www.aimath.org/E8/mcmullen.html <-- The picture on that show the set, it has 240 points each of which is a particle and the lines joining them are how they interact. This E8 model is one of the two most beautiful sets in mathematics, the other being the Mandelbrot set. Some physicists argue that these is the grand unified theory, there are currently 22 empty places where we have not found particles, but if CERN can find them then hopefully the theory will gather more mainstream acceptance. Here is a representation of the particles as they interact in 8 Dimensional Space(not actual physical dimensions simply mathematical notation)
Also falling out from this theory is one equation with 10 terms that describes everything, from gravity to the positron and how they all interact.