What Is Gravity?
QUICK ANSWER
Gravity is the force that pulls objects with mass toward each other. It's what keeps you on the ground, holds Earth in orbit around the Sun, and shapes galaxies. Einstein's general relativity describes gravity as the curving of spacetime caused by mass and energy, rather than a force in the classical sense.
Gravity is what keeps everything together. It's the force that holds you on the ground, keeps Earth orbiting the Sun, and shapes the largest structures in the universe. Newton described it as an attractive force between masses; Einstein later showed it's actually the curving of spacetime itself. Both descriptions work, but Einstein's is more accurate.
How does gravity work?
Mass attracts other mass. Every object with mass exerts a gravitational pull on every other object with mass, with the strength depending on the masses involved and the distance between them. The more massive an object, the stronger its gravitational pull. The closer two objects are, the stronger their mutual attraction. Earth's gravity is strong enough at the surface to give us weight, but weak compared to the Sun's, which holds the whole solar system in orbit. Gravity follows an inverse-square law: doubling the distance cuts the pull to one-fourth.
What did Newton get right?
The math, mostly. Isaac Newton's law of universal gravitation (published in 1687) describes how gravitational force scales with mass and distance. The law accurately predicts planetary orbits, falling apples, tides, and almost every gravitational effect we experience in daily life. Newton's formulation works well at speeds and gravitational strengths we encounter normally. It's still used for spacecraft trajectories and most everyday physics. Newton thought of gravity as an attractive force acting at a distance, without explaining what gravity actually is.
What did Einstein change?
He explained what gravity really is. Albert Einstein's general theory of relativity (1915) showed that gravity isn't a force pulling objects, but the curvature of spacetime caused by mass and energy. Massive objects warp the fabric of spacetime around them, and other objects move along the resulting curves. Einstein's theory makes very different predictions than Newton's near very massive objects or at very high speeds, and those predictions have been confirmed many times. GPS satellites have to account for relativistic effects to work correctly.
Why does gravity exist?
We don't fully know. Gravity emerges from the curvature of spacetime, but why mass and energy produce that curvature isn't explained by Einstein's theory. The deeper question of why gravity exists in the first place is one of the biggest open problems in physics. Scientists are searching for a theory of quantum gravity that would unify general relativity (which describes gravity) with quantum mechanics (which describes everything else). String theory and loop quantum gravity are two candidates, but neither has been confirmed experimentally.
Gravity is the force that pulls objects with mass toward each other. Newton described how it works mathematically; Einstein later showed it's actually the curvature of spacetime caused by mass. Gravity is responsible for everything from falling apples to galaxy formation. Why it exists in the first place remains an open question in physics, one of the biggest unsolved problems in science.
More Space Basics Questions
Mystery Question?
Mystery Question?
Mystery Question?