Towards a more and more complete theory..an endless journey it seems!

The hunt for a complete fundamental theory of Physics is not new, it was one of Einstein's unfulfilled dream or may be many Great minds also dreamed of it earlier. Of course it sounds so amazing that just one theory could possibly explain everything around you, but sometimes I feel if this expectation or dream is just a wish or is there any physical necessity. I mean why can't we describe two different observed phenomena using two different theories. Yes we can, but there is no guarantee that these two observed phenomena always happen separately. There may be some situations where both these phenomena are happening simultaneously (in a non-independent way because the two different systems may interact with each other) and we have no clue which theory we should use to describe them. Hence we always wish if we had a theory which can explain everything using one master equation, say. But the question is how far have we been in this really long journey of four or five decades. String theorists are doing a great job of course in developing such an elegant theory which can describe all the four fundamental forces(gravity, electromagnetic, strong and weak nuclear force) in the Universe together. There is no other theory where we can talk about all four forces. In particle physics we can talk about the later three using gauge theories, but gravity is a real bitch in such theories which (if we include) make everything meaningless. Particle physicists that's why live with these three forces only which serve their purposes also because within the region of their interests gravity is negligible. So in particle physics, a complete theory means a theory which can describe these three forces together, the so called Grand Unified Theories (GUT). There have been tremendous works in the last three and half decades on these theories. They look beautiful of course since they have strong predictivities. You write your GUT theory at very high energy and see what it predicts at low energy accessible to experimental detection. There are many models based on different gauge groups which can give rise to standard model of particle physics at low energy and also predict most of the experimental results so far. The best thing is that you start with a theory where there is only one force, only one type of particles at very high energy, and as a output you get a theory with three different forces and many different particles at low energy. But still lots of works need to be done to have a complete theory. Although the achievements in both string theory and such GUT models are tremendous so far, I am still confused whether the real goal of having such a fundamental theory is achieved (even partially) or not. Like GUT people do not talk about gravity, string theories also do not uniquely predict the observed phenomena at low energy. Recently there have been lots of enthusiasm in arriving at a GUT model starting with string theory. But to make the theory internally consistent the GUT models or any particle physics model people arrive at from string theory constructions contain many more particles than a minimal particle physics model. Thus predictivity is lost if we consider such non-minimal models. Hope people will continue such works with more and more enthusiasm and soon we will see some success in this direction.