Floating in zero gravity (zero-G) is something that many people have fantasized about. The idea of drifting through the air without the weighty pull of Earth's gravity is, for some, incredibly appealing. But how high above Earth do you have to go to escape its gravitational tug and experience weightlessness?
Technically, "you can experience weightlessness at any altitude," said Lewis Dartnell, author and professor of science communication at the University of Westminster in the United Kingdom. The key, he said, is that you must be "freely accelerating towards the ground at the acceleration of gravity before air resistance builds up too much."
In other words, given that Earth's gravitational acceleration is 9.807 meters/seconds^2, a person falling at that same rate anywhere on our planet would experience a flash of weightlessness.
"Weightlessness depends on your flight path, not your altitude or weight," Steven Collicott, a professor at the School of Aeronautics and Astronautics at Purdue University in Indiana, told Live Science in an email.
Dartnell agreed, noting that the idea of "weightlessness" is easily misunderstood. "Weightlessness is more correctly known as 'microgravity,'" he said.
"Experiencing weightlessness doesn't mean the absence of gravity, just that you are freely accelerating with gravity," Dartnell told Live Science in an email. "You can experience weightlessness just by jumping off a step — before you hit the ground, your body will be in freefall for a very short period."
Even regular aircraft can take people on a microgravity ride. "Airplanes can fly a special wavy up-and-down trajectory, known as parabolic flight, and this produces weightlessness for about thirty seconds at a time," he added.
However, the best way to experience an extended period of weightlessness is to become an astronaut and spend time on the International Space Station (ISS), Dartnell said.
"The ISS is in orbit, which means it is moving so quickly that even though it is constantly falling towards the Earth, it keeps 'missing' because of the curvature of the planet," Dartnell said. "The ISS and the astronauts inside are in perpetual freefall, and so experience microgravity 'weightlessness.'"
Of course, if you were to leave Earth's atmosphere and travel into the depths of space, our home planet's gravity would have little to no impact on you. However, regardless of where in the cosmos you find yourself, there is, according to an article in Yale Scientific (opens in new tab), "no such thing as zero gravity in space. Gravity is everywhere." You would, therefore, find yourself being pulled somewhere by gravity, be it toward a planet, star or black hole, although it could take years to reach your ultimate destination. You would, in such a situation, feel weightless, but would not in fact be weightless.
While the idea of being weightless might seem like an attractive proposition, Dartnell added that it can have significant downsides.
"Although floating around in zero-G looks like a load of fun, when astronauts spend several months, or longer, in weightlessness, it can have several negative effects on their health. Without having to constantly work against the weight of your own body, the muscles begin to weaken — especially the heart muscles as they no longer have to pump blood uphill.
"The skeleton responds to weightlessness by 'demineralising' and losing calcium, which leads to fragile bones and osteoporosis," Dartnell said. "Astronauts try to combat these effects by doing lots of exercise while in space against the resistance of bungee cords, but even so, once they return to Earth they cannot stand up at first, and it takes them a long while to recover." Extended periods of weightlessness for months at a time has also distorted tissues in astronauts' eyes, causing optic nerve damage, and has even led to "extensive" changes in the gray and white matter of astronauts' brains, Live Science previously reported.
However, according to Collicott, who has experienced weightlessness numerous times himself in parabolic flight, these negative impacts are unlikely to affect someone who only experiences zero-G for a brief time.
"Short-term zero-G from a Virgin Galactic or Blue Origin suborbital space flight, for example, appears to have very little effect, either immediate or lasting, on the body. You might see your heart rate immediately increase, or experience other reactions related to stress or danger, but even these can be reduced by training before your flight so that the change in environment is already a bit familiar."
In fact, Collicott says that, if the opportunity arises, anyone with even a passing interest in experiencing zero-G should give it a go.
"I would encourage everyone, young or old, to try weightlessness if given the chance," he said.
Originally published on Live Science.