Secrets of Spacetime and Black Holes
All scenes › Chapter 2 Moving fast slows time
The speed of light
The fastest thing in the universe
View in 3D300,000 km every second
Light travels about 300,000 km every second. That is like going around Earth 7.5 times. Light leaving the Sun takes about 8 minutes 19 seconds to reach Earth. No object, and no message, can travel faster than this.
Why?Everyone measures the same speed of light. Whether you measure it from a fast spaceship or standing on the ground, it is about 300,000 km per second. This strange fact is what makes time slow down, as the next scene shows.
Learn moreThe exact value is 299,792,458 meters per second. Since 1983 this number has been fixed, and the meter is defined the other way around: by how far light travels in a set time.
- Clock we are watching
- A clock on Earth’s surface
- How much slower
- About 0.02 s slower per year
- Clock rate
- 0.9999999993
seconds this clock ticks while a clock far away in empty space ticks one second · calculated with the formulas of relativity
View this scene in 3D →Read more
More in the series
The numbers come from the textbook formulas of relativity (for a non-spinning, ball-shaped mass) and official constants. Sizes, depths and angles in the 3D view are exaggerated so you can see them.