Exploring quantum gravity and entanglement using pendulums

When it comes to a marriage with quantum theory, gravity is the lone holdout among the four fundamental forces in nature. The three others—the electromagnetic force, the weak force, which is responsible for radioactive decay, and the strong force, which binds neutrons and protons together within the atomic nucleus—have all merged with quantum theory to successfully describe the universe on the tiniest of scales, where the laws of quantum mechanics must play a leading role.