But in the research fields of reconciling classical and quantum physics, it is arguably the best we have. It is not Ad Hoc like God. It is predicated on mathematical truths. The Higgs particle, as I've already said, is predicated on mathematical truths and quite obviously that is sufficient for over 30 countries to invest billions of dollars into a project meant primarily to confirm it. String Theory is an idea in theoretical physics, but technically it is more of a hypothesis. It is an educate guess that fits the gaping jigsaw hole and is worth investigating. You realize if you argument is testability and experimentation then no answer will be satisfactory to you, because particle physics and the like require massive and new technology, for which we are still waiting.

Also, can you please give me the name of a mainstream physicist that "believes" in string theory, as in thinks it's true or already substantially proven. I have a feeling you'll have a tough time finding one, and here's why: There isn't even a totally agreed upon blue print or definition of what string theory is. And that's just in general terms. String Theory itself has at least 5 versions, and could be expanded to include more. In other words, if one says they "believe" in String Theory, than they must "believe" in one of the 5 versions if not another, after which they would provide a reason for that one and not one of the other four. The problem with that is that nothing really sets the 5 apart in terms of validity. Put simply, for someone to say the "believe" in string theory, the either have no idea what they actually believe in, or are psychic and can see into the future to when we finally are able to test the thing (potentially Summer 2008!).