Zero gravity is often used as a reference to weightlessness, circumstances where objects lose apparent weight and begin floating. This generally occurs in orbit or anywhere in space not close to a celestial body, i.e., astronauts traveling between the Earth and the Moon. Although in orbit the Earth’s gravity still exerts pull, because objects in orbit are in a state of continuous free-fall, this gravity does not press astronauts against the floor. Although objects in orbit are not really experiencing zero gravity, the term as a synonym for weightless has stuck, and will be used throughout the rest of this article.
In zero gravity, everything not tied or bolted down floats. An object at rest stays at rest, but an object in motion continues to move until it hits a wall or another object. Released liquids, such as orange juice, form into bubbles due to surface tension and float around until sucked up. Bubbles can merge together to create larger bubbles.
Zero gravity is not a good place to avoid dust. Imagine if all the dust and clutter on the floors and in the corners of rooms started floating everywhere. This can lead to a messy environment quickly. Thus, air on a space station must be processed and filtered continuously to stay clean.
In zero gravity, flames are more spherical. Usually, carbon dioxide created by a wood flame travels upwards, because this gas has positive buoyancy under surface conditions. In zero gravity, the gas has neutral buoyancy, and lingers in the vicinity of the flame until it smothers itself. However, if there is enough oxygen, flames can still spread and pose a threat to astronauts.
Zero gravity can take a harsh toll on the human body. Without weight pushing us downwards and forcing our bodies to work to against it, our bones and muscles become frail. This is called spaceflight osteopenia. To counteract osteopenia, astronauts must exercise frequently.
Although spaceflight is considered glamorous, the other symptoms of zero gravity on astronauts are anything but. These include a slowing of blood circulation, disorders of balance, a weakened immune system, sleep disturbance, puffiness of the face, and perhaps the most embarrassing: excess flatulence. If we want to colonize space on a larger scale without suffering from constant flatulence and muscle frailty, it seems that we’ll have to create space stations that rotate to simulate gravity. Optimistically, this will be achieved by private companies by 2020, with 2030-2040 perhaps a more realistic time frame.