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Curved spacetime
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Mass tells spacetime how to curve; spacetime tells mass how to move.
In general relativity gravity is the curvature of spacetime caused by energy and momentum. Free-falling objects follow geodesics. Wheeler: 'matter tells spacetime how to curve; spacetime tells matter how to move'.
The Moon follows a straight path in curved spacetime.
Space and time are curved, not just space.
In more detail
In general relativity, gravity is described as the curvature of spacetime caused by mass and energy. Objects follow the straightest possible paths, called geodesics, through curved spacetime.
Real-world uses
- Gravitational lensing and the orbits of planets are described by spacetime curvature.
- Satellite navigation accounts for curvature effects.
- Cosmologists model the expansion of the universe using the curvature of spacetime in Einstein's theory.
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Frequently asked questions
Does mass bend space?
Mass bends spacetime, which affects both space and time.
What is a geodesic?
The path followed by a freely falling object, which is locally the straightest path.
What does it mean for spacetime to be curved?
Free bodies follow paths that look straight locally but bend relative to each other because of gravity.
Related topics in Relativity
Gravitational time dilation · Gravitational redshift · GPS and relativity · Einstein field equations · Geodesics · Schwarzschild metric