Delving into the Vast Abyss: Fifteen Unsolved Mysteries in Science that Leave Experts Scratching Heads

Quantum Gravity

Speaking of a unified theory, quantum gravity is another unsolved problem in physics. How do we reconcile quantum mechanics, which describes the world of the very small, with general relativity, which describes the world of the very large? Despite various approaches, from string theory to loop quantum gravity, a satisfactory theory of quantum gravity remains elusive.