In outer space, even though all the masses in the Universe gravitate just as normal, there is no ‘up’ or ‘down’ as there is on Earth, as the spacecraft and everyone on board accelerates due to gravity at the same rate. Image credit: NASA / ESA / ISS Expedition 37.

Why Don’t We Have Artificial Gravity In Space?

All sorts of futuristic technologies have come true. So why are astronauts all still weightless?

Put a human being up in space, away from the gravitational bonds of the surface of the Earth, and they’ll experience weightlessness. Although all the masses in the Universe are still pulling on them gravitationally, they pull on whatever spaceship you’re in equally, too, and so you float. In TV shows and movies like Star Trek, Star Wars, Battlestar Galactica and many others, though, you always see the ship’s crewmembers stably on the “floor” of the starship, regardless of any other conditions. This would require some type of artificial gravity to be physically possible, but that’s a tall order for the laws of science as we presently know them.

Captain Gabriel Lorca aboard the bridge of the Discovery, during a simulated combat mission with the Klingons. The entire crew is pulled ‘down’ by artificial gravity, which is firmly a science fiction technology today. Image credit: Jan Thijs/CBS © 2017 CBS Interactive.

For gravitation, the big lesson from Einstein is the equivalence principle: that a uniformly accelerating reference frame is indistinguishable from a gravitational field. If you were in a rocket ship, and unable to view the Universe outside of your surroundings, you’d have no way of knowing which one was going on: do you feel the downward force due to gravity, or do you feel…