The point of the LHC as I understand it is to determine what the conditions were after the Big Bang. Problem is, the Big Bang itself was not the start of it all. There was Inflation which may have caused the Big Bang and happened after it. Since there is now debate going on as to how exactly the Universe began, how can we determine a Unified Theory until we solve this problem? Big Bang suggests there was nothing beforehand, that the Universe started from an infinitely small point. In mathematics, infinity is basically giving up, or cheating. This does not provide a satisfactory answer. "Everything from nothing" is God-talk, it doesn't work. Finding out how particles behaved at a certain point in time will help, but I don't think the LHC will tell us much about gravity. There is also Quantum Gravity.