Everything Falls Together Because Nothing Is Pulling It Down

Drop a bowling ball and a marble at the same instant and they hit the ground together. Astronauts have dropped hammers and feathers, and physicists have compared blocks of metal in vacuum chambers, and the result is always the same.

For more than 300 years, that sameness looked like a strange coincidence. In the old math of gravity, two very different properties had to line up exactly. One was gravitational mass, or how strongly gravity is supposed to grab an object. The other was inertial mass, or how stubbornly that object resists being pushed. The two cancel out in the equation, which is why everything gets the same acceleration, but nothing explained why they should be equal in the first place. Scientists have now tested that equality to about one part in 10 trillion and found no difference.

The modern explanation is that there is no grab at all. A falling object is not being pulled down. It is coasting, following the straightest possible path through a spacetime that has been curved by the Earth, until something gets in its way.

Picture the inside of a rocket drifting far from any planet. Let go of two objects, heavy and light, and they simply float. If the engine fires and the floor rushes upward, both objects appear to fall to the floor together, not because a force pulled them but because the floor accelerated into them.

Falling on Earth works the same way. A dropped ball and the ground are on different straight paths that happen to intersect. The ball was weightless and unpushed the whole way down. What you feel as weight is the ground interrupting that coast and shoving you upward.