While there are many challenges facing modern particle physics, perhaps the ultimate one (and certainly among the most difficult) is to describe the nature of gravity in the quantum realm.  Despite a century of effort, scientists have had only the most cursory of success.  In this video, Fermilab’s Dr. Don Lincoln talks about the idea of quantum gravity and sketches out the need for this difficult advance. Related videos: https://www.youtube.com/watch?v=XYcw8nV_GTs https://www.youtube.com/watch?v=5UDUNqwWuNs https://www.youtube.com/watch?v=CaQnC_UmxA4