Time dilation and the time dimension

Think of a person travelling so fast that time goes ten times slower. He ages one year in ten years, meaning that he gets only one year older when ten years have passed on the planet Earth. He comes back to Earth. Is he one year into the future or ten years? Has he two clocks? How does it actually work, technically, physically? Why does time slow down at high speed?

Learn about it in the book A New Understanding of the Universe. You will be able to see it from a four dimensional perspective. You will understand how time is linked to space.