# Key Einstein principle survives quantum test

## Equivalence of gravity, acceleration applies even for atoms in superposition of energy states

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Particles with mind-bending quantum properties still follow a standard gravitational rule, at least as far as scientists can tell.

The equivalence principle — one of the central tenets of Einstein’s theory of gravity — survived a quantum test, scientists report online April 7 at arXiv.org.

In Einstein’s gravity theory — the general theory of relativity — gravity and acceleration are two sides of the same coin. According to the equivalence principle, the gravitational mass of an object, which determines the strength of gravity’s pull, is the same as its inertial mass, which determines how much an object accelerates when given a push (*SN: 10/17/15, p. 16*). As a result, two objects dropped on Earth’s surface should accelerate at the same rate (neglecting air resistance),