Both Quantum Mechanics and General Relativity claim to represent the truth. In 1927, Bohr and his cronies proclaimed QM to be a complete theory or description of the subatomic world:
“ We regard quantum mechanics as a complete theory for which the fundamental physical and mathematical hypotheses are no longer susceptible of modification.”
Paper delivered by Heisenberg and Born at the Solvay Congress of 1927
Curiously, Einstein was just as confident about his macro-world relativity theory a few years earlier when Eddington verified his prediction. “ The theory is correct.” he boasted proudly. Of course he wasn't remotely as cocky just before he died, telling a friend:
" I consider it quite possible that physics cannot be based on the field concept, i.e., on continuous structures. In that case, nothing remains of my entire castle in the air, gravitation theory included, [and of] the rest of modern physics."
[Einstein Letter to Besso, 1954]
However, consensus is that these two mathematical theories cannot be reconciled:
“ The two theories have obtained solid success and vast experimental corroboration, and can now be considered established knowledge. Each of the two theories modifies the conceptual foundation of classical physics in an (more or less) internally consistent manner, but we do not have a novel conceptual foundation capable of supporting both theories.” (p. 7) 
The casual reader may conclude that our mathematicians simply need to develop some yet to be discovered equations to resolve the discrepancies. This is false. QM and GR are conceptually irreconcilable. It is impossible to merge them into a single theory. This has a little bit to do with the fact that QM deals with the micro world and relativity with the macro world, but more to do with the fact that a QM particle is the epitome of the ‘discrete’ and GR’s space-time is the epitome of the ‘continuous’. Quantum explains gravity as a force, a 'particle' that serves as an interface between two objects. Relativity explains gravity as warped space. These physical interpretations are as distant from each other as the Earth from the nearest black hole. Neither can explain both micro and macro phenomena. So which version should you choose to explain gravity to your son meanwhile: QM or GR? The new generations of mathematicians have voted with their feet. They ignore both GR and QM and, instead, are working feverishly to integrate features of the two theories into yet another, so-called Theory of Quantum Gravity:
“ We want to combine what we have learnt about our world from the two theories and to find a new synthesis.” (p. 4) 
String Theory (ST) is a promising field that is sucking up resources and tax dollars. It is ‘promising’ because ST will forever remain an IOU. ST has no chance of delivering the goods or graduating in Science. It has no chance because String Theory has absolutely nothing to do with relativity and is conceptually no different than Quantum Mechanics. Specifically, string theorists are busy developing equations to show that space-time is ‘quantized’ (i.e., is made of tiny components).
“ The commonsense picture of space and time is rather like that of a canvas on which the activity of the world is painted. Einstein showed that the canvas itself can move about and suffer distortions - spacetime comes alive. Quantum theory predicts that if we could examine the surface of the canvas with a supermicroscope we should observe that it is not smooth, but has a texture or graininess caused by random and unpredictable quantum distortions in the spacetime fabric on an ultramicroscopic scale.” 
That quantization is driving contemporary Mathematical Physics is mind boggling (actually hilarious) because relativists have always defined space-time as a quantized entity:
“ The four-dimensional space whose points are events.” (p. 186) 
where an event is:
“ A point in space-time, specified by its time and place.” (p. 184) 
Thus, from a conceptual point of view, space-time has never been defined to be ‘smooth’ (i.e., made of single piece) as now alleged by the string idiots. Space-time has been conceived to be ‘grainy’ from day one. String theorists simply need to read up on the basics of Einstein’s theory. Furthermore, the idiots of String Mathematics admittedly have no idea what they're talking about:
“ There are conceptual problems -- what does it mean to quantize geometry, or space-time? ”
Therefore, our string numskulls are off to an inauspicious start if their sole purpose in life is to prove that space-time is made of discrete entities. I urge you not to hold your breath while the string theorists deliberate. The graininess or quantization of space-time that string mathematicians are feverishly working on will not resolve anything. Assuming the new breeds are finally able to ‘prove’ that space-time is made of vibrating strings, in what way would this change the physical interpretations that QM and GR offer for gravity? For instance, imagine that the mathematicians finally discover the equations that merge QM and GR into a single theory of quantum gravity. What physical interpretation will they now give their equations? Will they say that the Earth rolls around the Sun because the space between these objects is warped or will they say that the Sun attracts the Earth by pelting it with negative-momentum carrying stones? How will the graininess of space-time change the gravity-well explanation or the graviton-pitching mechanism in any way? Or take a simple discrepancy such as whether black holes should spit out material. Maldacena tells us that:
“ Einstein’s theory of gravity says that nothing should come out of black holes while quantum mechanics says that some things do come out of black holes.” 
What is the ‘unified’ theory going to resolve? If relativity is correct, QM is incorrect. And if there is a third option, both GR and QM were wrong all these years. String Theory actually confirms that Mathematics is the wrong tool to use to decipher Physics. No amount of Math is ever going to bridge the qualitative gap between Einstein and Bohr. You should reject all three.