>The theory of special relativity was modify by Einstein because of quantum physics. This is why we have both a special theory and relative theory of space time and gravity.

I think you're a little mixed up here.

Here's how I understand it.

We started with Newton's mechanics, the laws of motion and the law of gravity.

Then there were Maxwell's equations for electromagnetic phenomena.

The problem was that Maxwell and Newton didn't totally jive.

So Einstein invented what we call special relativity in 1905. It modifies Newton's laws of motion to play nicely with Maxwell.

However, special relativity didn't play nicely with the law of gravity.

Special relativity also gave us E=mc^2, and the relationship between matter and energy was established. Also in 1905 Einstein was able to explain the photoelectric effect (this was what he won his Nobel Prize for).

As a result of the photoelectric effect and E=mc^2, other scientists, Bohr, Planck, and Heisenberg namely, were able to formulate quantum mechanics. Later on Dirac was able to make QM and SR one in the same. (Sidenote, Einstein never accepted QM, famously saying "God does not play dice!")

The probelm still existing: special relativity didn't work with gravity.

So in 1915, Einstein extended special relativity into general relativity. General relativity describes gravity in a theory that includes special relativity as a subset. So Relativity is really one theory, but in came in pieces, first special, then general.

But there is a new problem: while special relativity works with QM as relativistic quantum field theory, general relativity still hasn't been made to work with it. So there is no quantum theory of gravity.

This is the problem string theory and loop quantum gravity are aiming to rectify.