Carl De Torres

To get ahead in life, spend some time on the International Space Station. Why? Well, according to the theory of relativity, astronauts on the ISS age more slowly due to the spacecraft's high orbital speed. It's called time dilation, and it means that when they return they're a bit younger than they would have been—as if they've traveled into the future. (The effect is very small—it would take more than 100 years on the ISS to warp ahead by just one second.) But not all space travel will keep you young. Like speed, gravity also slows time, so your clock revs up as you get farther from a large mass like Earth. As a result, satellites in higher orbits age more quickly. Got your heart set on space travel but want to age at a normal, earthly pace? Good news! There's a sweet spot, 3,174 kilometers above Earth's surface, where the effects of increased speed and reduced gravity cancel each other out. You can hang out there as long as you like without fear of relativistic shenanigans.