I have information that time slows down in space. For example if an astronaut is on the Moon or in space for one year, he didn't age. If he returns to Earth he is as young as he left Earth? I don't understand this. If someone travels to another planet (3 months journey through space), I believe he must get older 3 months, or not? And why not? He reached his destination, the other planet and decides to stay for 10 years. After 10 years he travels back to Earth. I am sure people on the other planet (as there might be intelligent life) would age as we do. So he must be 10 years older after 10 years. Hence, if he return to Earth, he must be 10 years older like everyone else on Earth. If you now about the concept of time on other planets and in space, please explain. Does it mean in space time does not exist, so in space no creature will age? I am sure on other planets creatures get old and die too, like on Earth.