Sean Carroll’s Mindscape podcast at Preposterous Universe:
Quantum mechanics and general relativity are the two great triumphs of twentieth-century theoretical physics. Unfortunately, they don’t play well together — despite years of effort, we currently lack a completely successful quantum theory of gravity, although there are some promising ideas out there. Carlo Rovelli is a pioneer of one of those ideas, loop quantum gravity, as well as the bestselling author of such books as Seven Brief Lessons on Physics and the recent The Order of Time. We talk about how to make progress on this knotty problem, including whether string theory will play a role (Carlo thinks not).
More here.