Ask Dr. Universe

Dear Dr. Universe: In space, which way is up? –Pablo, 10, Spokane, WA

Dear Pablo,

We might not always think about it, but every day gravity keeps us pulled to the Earth. It’s what brings us back down when we jump on a trampoline. It’s why a Slinky tumbles down stairs.

Now think about what it would be like to live in a place with very little gravity. Let’s say you were 200 miles off the ground, orbiting earth in the International Space Station. Here, the idea of up and down really gets flipped around.

On Earth, the human balance system helps the head figure out how move up and down under the fo...