Time

The fourth dimension

Time - maybe one of the hardest expressions to explain and fully understand! It's called the fourth dimension.

Time is relative!

Albert Einstein showed in his equations that time is relative. That gives the effect that if you are travelling very fast (near the speed of light), then the time will go slower compared to them who not are travelling with this speed.

A high-speed spaceship

If you for example travel from the Earth to another planet system in a high-speed spaceship, and you use 3000 years regarding to your clock, then the people left on the Earth maybe will say: "No, you have used over 5000 years regarding to our clock! (And we have the same kind of clock as the one you have.)" Both are right! Because the time is actually going slower when travelling with high speed.