Many people seem to think NASA has secret training rooms in which gravity can be turned off. Aside from the long-running Anti Gravity column in Scientific American, however, there is no such thing as antigravity.
 
Gravity is a force arising among any two masses in the universe. Our most familiar run-in with it is the attraction that pulls our bodies, our houses and everything else in our lives toward the planet Earth beneath us. Even in orbit, where astronauts do not feel the tug of gravity, it is nonetheless abundantly present. Gravity’s draw is simply masked by the free-falling motion of a spacecraft as it circles the planet. Only way out in deep space, beyond the domain of any planets or stars, can you truly escape gravity.
 
As of yet, no technology exists to neutralize the pull of gravity. The best way to approximate the feeling of weightlessness on Earth is to ride onboard a plane flying in parabolic arcs that mimic the shape of Saint Louis’s Gateway Arch. Such planes, nicknamed “vomit comets” because of the queasiness they induce, allow passengers to float for a few moments while the plane is in free fall on the downward swing of the arc. Astronauts use this method to train for spaceflight; it also gave us scenes of a weightless Tom Hanks in the film Apollo 13. You can also experience moments of apparent weightlessness during the drops on roller coasters or Disney World’s Tower of Terror ride, for example. “Both you and your rollercoaster carriage are falling at the same rate,” says Damian Pope, a physicist at the Perimeter Institute for Theoretical Physics in Canada, “so your seat doesn't push against you and you don't feel any support. This mimics what you'd feel if, for some reason, you happened to find yourself in a rollercoaster carriage in deep space.”
 
These examples illustrate how we normally experience gravity. During the rest of a roller coaster ride you feel the upward push of the seat on you. “A physicist would say that the seat was exerting a force on you—they'd call it a normal force,” Pope says. “More generally, the feeling of having weight we experience in daily life is just the feeling of being supported by the ground, a rollercoaster seat etc., and these objects exerting ‘normal forces’ on us.”
 
The lack of antigravity chambers is what makes space-based research valuable. Without a way to turn off gravity on Earth, scientists must launch experiments into orbit to test what happens in weightlessness. The International Space Station, officially designed a U.S. National Laboratory, houses hundreds of projects investigating everything from the effects of weightlessness on viruses (which become more virulent) and crystals (which grow much larger) to human bodies (which suffer bone density degradation and damaged eyesight). Scientists hope medicines developed in the unusual conditions of space can help treat regular health issues on Earth.
 
If humans are to explore deep space in the future, we will need better ways of manipulating gravity than we have now—or at least better tools to fight the ill effects of weightlessness on the human body. In the 16 years since the International Space Station’s first module was launched NASA and its partners have made strides in using specialized exercise equipment and nutrition to maintain astronauts’ fitness. Yet these steps will not be enough to protect crews on space journeys lasting much longer than a year. A popular science fiction trope is the spinning spacecraft that creates artificial gravity via centripetal force, such as the one depicted in the movie 2001: A Space Odyssey. The rotation pulls everything toward the ship’s outside wall, which becomes the floor. The logic behind this plan is sound, but to create gravity similar to that on Earth, such a spacecraft would have to be much larger than any spacefaring vehicle ever built. For now, we might as well enjoy the antigravity aspect of space travel, which is good for, among other things, some very weird yo-yo tricks.