What the hell is Quantum Gravity?
Gravity was the first fundamental force that humanity recognized, yet it remains the least understood. Physicists can predict the influence of gravity on bowling balls, stars and planets with exquisite accuracy, but no one knows how the force interacts with minute particles, or quanta.
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.