What is Quantum Gravity?

Answer 1

In a word. No. Grand unification is also commonly called the Theory of everything. Which in a sense, there would exist an equation of a set of equations that every other physics equation can be derived from. A quantum theory of gravity would only help to better blend quantum mechanics and classical mechanics, not necessarily leading to a theory of everything, though it would be another step toward it.

Answer 2

Quantum gravity is a hypothetical theory that would combine quantum mechanics with Einstein's theory of general relativity (i.e. gravity). At present these are two different theories with their own domains of applicability and they do not mix. Quantum gravity is a quantum mechanical description of gravity.

At this moment no such theory is known (or has been adequately tested and verified).

Quantum gravity is desired because several objects, such as black holes, require the union of gravity with quantum mechanics to be made sense of. Without quantum gravity we can only get approximate answers.

There are some models which claim to contain quantum gravity, such as string theory, but these have not yet been verified. String theory in particular is notorious for not having made any testable claims yet.

Answer 3

Our best model of gravity is general relativity, which allows us to make predictions that are shown to be accurate to ten significant digits. That's the equivalent to being able to predict the U.S. federal deficit in 2015, exact to the penny!

Our best model for everything else is quantum electrodynamics (QED), which ALSO allows us to make predictions to the above accuracy.

The problem is that, despite decades of attempts by the greatest minds of the world (most definitely including Einstein), we've not been able to combine the two into one model. More precisely, the two models are completely incompatible with each other -- if we start with the assumptions of GR, we make QED impossible; and vice-versa.

So it MIGHT be possible that quantum gravity might work in our Universe. Or it might turn that QED is only a useful approximation, but that GR is a better starting point. At this point in our search to understand our Universe, we can't know.

Answer 4

The quantum theory of gravity is that they are made up of particles called gravitons. This theory is in the early stages, though.