The inability of scientists to create a theory of quantum gravity arises from long-standing tensions between general relativity and quantum mechanics. There have been few approaches with any success. Don Lincoln explains one of the few promising ideas, called loop quantum gravity, in this 9-minute video.

Despite a century of effort, scientists have had only cursory success in describing the nature of gravity in the quantum realm. Don Lincoln talks about quantum gravity and the need to make advances in this area.