yeah? What "physics" is that? Care to elaborate on the "physics" you claim that says the whole concept will fail?
I would say that the Iron Dome and the Patriot system have shown spectacularly that the "Physics" DOES work, and quite well too. You just have to scale it up, and that can be easily done... And as for cost, all you have to do is stop ONE missle loaded with a NBC warhead to recoup the cost, easily, and prevent WWIII from breaking out!