Time is Relative
Before Einstein, everyone believed that time was an absolute, ticking cosmic clock that moved at the same rate for everyone in the universe. Special Relativity shattered this idea, proving that time is a local experience.
Time Dilation is the phenomenon where a clock moving at high speeds ticks slower relative to a clock that is at rest. The faster you move through space, the slower you move through time.
The Twin Paradox
If you leave Earth on a spaceship traveling at 99% the speed of light, time for you slows down dramatically. You might travel for 1 year (according to your ship's clock), but when you return to Earth, you will find that 7 years have passed for everyone else. You have effectively time-traveled into the future.
The Formula
Example Calculation
An astronaut travels at 86.6% the speed of light ($v = 259,620,311 , \text{m/s}$) for exactly $10 , \text{years}$ of proper time ($\Delta t_0$).
- Calculate v/c: $0.866$.
- Square it: $0.866^2 \approx 0.75$.
- Subtract from 1: $1 - 0.75 = 0.25$.
- Square Root: $\sqrt{0.25} = 0.5$.
- Divide Proper Time: $10 / 0.5 = 20 , \text{years}$.
While the astronaut aged 10 years, $20 , \text{years}$ passed on Earth.