The theory of relativity includes two main interrelated theories by Albert Einstein: special relativity and general relativity.
- Special Relativity (published in 1905):
- Applies to physical phenomena in the absence of gravity.
- Based on two key principles:
- The laws of physics are the same in all inertial (constant speed) frames of reference.
- The speed of light in a vacuum is constant and does not depend on the motion of the light source or observer.
- Shows that space and time are linked into a unified four-dimensional entity called spacetime.
- Introduces effects such as time dilation (time slowing down at high speeds) and length contraction (objects contracting in the direction of motion).
- Shows mass and energy are related by the famous equation E=mc2E=mc^2E=mc2.
- General Relativity (published in 1915):
- A theory of gravitation that refines Newton's law of gravity.
- Describes gravity not as a force but as the curvature of spacetime caused by mass and energy.
- Explains gravitational phenomena such as gravitational time dilation (clocks run slower in stronger gravitational fields), deflection of light by gravity, and the expansion of the universe.
- Uses mathematical field equations (Einstein field equations) to relate the curvature of spacetime with energy, momentum, and mass.
- Predicts phenomena like black holes, neutron stars, gravitational waves, and the Big Bang cosmology.
In summary, special relativity addresses objects moving at constant speeds without gravity, while general relativity deals with gravity as the curvature of spacetime affecting the motion of objects and light. Both transformed our understanding of space, time, and gravity fundamentally.
