A vacuum is a volume of space that is essentially empty of matter. The word comes from the Latin term for â€œempty,â€ but in reality, no volume of space can ever be perfectly empty. A perfect vacuum with a gaseous pressure of absolute zero is a philosophical concept that is never observed in practice. Physicists often use the term â€œvacuumâ€ to discuss ideal test results that would occur in a perfect vacuum, which they simply call â€œvacuumâ€ or â€œfree spaceâ€ in this context, and use the term partial vacuum to refer to the imperfect vacuo realized in practice. The Latin term in vacuo is also used to describe an object as being in what would otherwise be a vacuum.
The quality of a vacuum refers to how closely it approaches a perfect vacuum. The residual gas pressure is the primary indicator of quality, and is most commonly measured in units called torr, even in metric contexts. Lower pressures indicate higher quality, although other variables must also be taken into account. Quantum theory sets limits for the best possible quality of vacuum, predicting that no volume of space can be perfectly empty. Outer space is a natural high quality vacuum, mostly of much higher quality than what can be created artificially with current technology. Low quality artificial vacuums have been used for suction for thousands of years.
Evangelista Torricelli produced the first sustained artificial vacuum in 1643, and other experimental techniques were developed as a result of his theories of atmospheric pressure. The vacuum became a valuable industrial tool in the 20th century with the introduction of incandescent light bulbs and vacuum tubes, and a wide array of vacuum technology has since become available. The recent development of human spaceflight has raised interest in the impact of vacuum on human health, and on life forms in general.