Path tracing is not Ray tracing, though they do share some core concepts. Or at least I think they do, this is all pretty techy stuff. Above is a teaser for Brigade, a real-time Path tracing engine that you really need to see to understand. Because Path tracing intrinsically allows for reflection, global illumination, depth of field, shadows, motion blue, caustics and ambient occlusion, the end result is nothing short of amazing. But to get this kind of computationally complex thing running at real-time, even on dual CUDA-capable cards, there are some drawbacks. Mainly, a kind of ‘grainy’ look which results from certain “rays” not having made it back to the camera yet, either because they took too long to bounce around the scene, or because they were killed off early for the sake of speed (the Russian Roulette method).
You can read more about what the Bridage Engine is on the official site. If you can’t see the YouTube above, here are some screenshots to get the idea across. Remember, this is 30fps, real-time.