Relativity
The Equivalence Principle
The principle that gravitational and inertial mass are identical, so that being in free fall is locally indistinguishable from floating in empty space. This insight led Einstein from special to general relativity, recasting gravity as the curvature of spacetime; it is tested to extraordinary precision by lunar laser ranging and dedicated satellites.
Highlights
- ›Free fall feels like empty space — the seed of general relativity
Related physics & astronomy
Knowledge connections
- Associated withGeneral Relativity
- Associated withSpacetime
- Associated withMass–Energy Equivalence
- Associated withThe Fundamental Forces
Sources
The primary and reference sources this topic draws on.
- NASANational Aeronautics and Space Administration
Mission data, planetary science, space telescopes, and public-domain imagery.
Most NASA-produced imagery is in the public domain; individual items are checked for usage terms before publication.