What is gravity?

Gravity is a fundamental force of nature that attracts objects with mass toward one another. It's the invisible force that keeps your feet on the ground, holds the Moon in orbit around Earth, and binds galaxies together. Every object with mass exerts a gravitational pull on every other object, though we typically only notice gravity's effects when at least one object is extremely massive, like a planet or star. Sir Isaac Newton first described gravity mathematically in the 17th century, and Albert Einstein later refined our understanding with his theory of general relativity, which describes gravity as the curvature of spacetime caused by mass and energy.