String theory, and its latest exponent M-wave theory, are indeed the "hot" thing, but as I understand it we need a particle accelerator the size of the solar system to confirm the predictions it makes experimentally. There are some indirect things we might observe but even that needs substantially higher energy accelerators.
On the issue of gravitons, I think they are indeed supposed to be massless, much like photons. Not sure how that works exactly though.
To get back to the original question, I have always found the analogy of the plane flying over a hilly area useful. On the 2-dimensional surface of the hills, the shadow of the plane seems to follow a very curved path. Through the 3-dimensional space it is following a straight line however.
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