Einstein's Theory of Relativity Explained
Einstein developed two theories of relativity that revolutionized physics.
Special Relativity (1905)
The starting point: The speed of light is constant for all observers, regardless of their motion.
This seems simple but leads to mind-bending conclusions:
#### Time Dilation
Moving clocks run slower. The faster you go, the slower time passes for you.
Example: If you traveled at 90% light speed for 10 years (your time), 23 years would pass on Earth.
#### Length Contraction
Moving objects shrink in the direction of motion.
#### Mass Increase
Objects gain mass as they accelerate. At light speed, mass would be infinite — which is why nothing with mass can reach light speed.
#### E = mc²
Energy equals mass times the speed of light squared.
This reveals that matter is concentrated energy. A small amount of mass contains enormous energy (basis of nuclear power and weapons).
General Relativity (1915)
Special relativity didn't include gravity. General relativity took 10 years to develop.
The insight: Gravity isn't a force pulling objects together. Mass curves spacetime, and objects follow the curved paths.
Analogy: A bowling ball on a trampoline creates a dip. A marble rolled nearby curves toward it — not because of a "force," but because of the curved surface.
- Gravitational time dilation: Clocks run slower in stronger gravity (GPS satellites must account for this)
- Light bending: Light curves around massive objects
- Gravitational waves: Ripples in spacetime (detected 2015)
- Black holes: Extreme curvature traps everything
Why It Matters
- GPS requires relativistic corrections
- Particle accelerators confirm mass increase
- Nuclear energy proves E=mc²
- Cosmology depends on general relativity
Einstein's thought experiments became engineering reality.
Related Reading
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