Vacuum
Ancient Greek philosophers debated the existence of a vacuum, or void, in the context of atomism. Lucretius argued for the existence of vacuum in the first century BC. Hero of Alexandria tried unsuccessfully to create an artificial vacuum in the first century AD. Aristotle believed that no void could occur naturally because denser surrounding material would immediately fill any incipient rarity. In his Physics book IV, Aristotle offered numerous arguments against the void. He claimed motion through a medium offering no impediment could continue ad infinitum. There being no reason that something would come to rest anywhere in particular. Medieval Muslim scholars also weighed in on this debate. Al-Farabi wrote a treatise rejecting the existence of the vacuum in the 10th century. He concluded air's volume can expand to fill available space. Therefore the concept of a perfect vacuum was incoherent. Abū Rayhān al-Bīrūnī stated there is no observable evidence that rules out the possibility of vacuum. European scholars such as Roger Bacon focused considerable attention on issues concerning the concept of a vacuum during the 13th and 14th centuries. The commonly held view that nature abhorred a vacuum was called horror vacui. Jean Buridan reported in the 14th century that teams of ten horses could not pull open bellows when the port was sealed.
Evangelista Torricelli produced the first laboratory vacuum in 1643. A Torricellian vacuum is created by filling with mercury a tall glass container closed at one end. Then it is inverted in a bowl to contain the mercury. Blaise Pascal's experiments demonstrated a partial vacuum shortly after. Otto von Guericke invented the first vacuum pump in 1654. He conducted his famous Magdeburg hemispheres experiment showing atmospheric pressure outside the hemispheres prevented separation. Teams of horses could not separate two hemispheres from which the air had been partially evacuated. Robert Boyle improved Guericke's design with the help of Robert Hooke. They further developed vacuum pump technology. Research into the partial vacuum lapsed until 1850 when August Toepler invented the Toepler pump. Heinrich Geissler invented the mercury displacement pump in 1855 achieving a partial vacuum of about 10 Pa. A number of electrical properties became observable at this vacuum level. This renewed interest in further research. The Crookes tube used to discover and study cathode rays was an evolution of the Geissler tube.
Paul Dirac proposed a model of the vacuum as an infinite sea of particles possessing negative energy in 1930. This theory helped refine predictions of his earlier formulated Dirac equation. It successfully predicted the existence of the positron confirmed two years later. Werner Heisenberg's uncertainty principle formulated in 1927 predicted a fundamental limit within which instantaneous position and momentum can be measured. These far-reaching consequences threatened whether the emptiness of space between particles exists. In quantum electrodynamics the vacuum is referred to as QED vacuum. QED vacuum contains vacuum fluctuations virtual particles that hop into and out of existence. Some experimentally verified effects of vacuum fluctuations include spontaneous emission and the Lamb shift. Coulomb's law and the electric potential in vacuum near an electric charge are modified. Theoretically multiple vacuum states can coexist in QCD. String theory is believed to have a huge number of vacua known as the string theory landscape.
Vacuum quality is indicated by the amount of matter remaining in the system. ISO 3529-1:2019 defined ranges according to technology required to achieve it or measure it. Low vacuum pressure ranges from 100 Pa to atmospheric pressure. Medium vacuum spans from 100 Pa down to 0.1 Pa. High vacuum extends below 0.1 Pa. Ultra-high vacuum operates below one trillionth of atmospheric pressure reaching around 100 particles per cubic centimeter. A mercury column manometer measures pressures ranging from 1 torr to above atmospheric. The McLeod gauge isolates a known volume of vacuum and compresses it to multiply height variation. It can measure vacuums as high as 10^-6 torr. Thermal conductivity gauges rely on heat conduction decreasing with pressure. A Pirani gauge uses a single platinum filament as both heated element and RTD. Ionization gauges used in ultrahigh vacuum come in hot cathode and cold cathode versions. Hot cathode gauges are accurate from 10^-3 torr to 10^-10 torr. Cold cathode gauges are accurate from 10^-2 torr to 10^-9 torr.
Vacuum became a valuable industrial tool in the 20th century with the introduction of incandescent light bulbs. Vacuum tubes were also widely adopted during this period. Chemical vapor deposition and physical vapor deposition utilize high to ultra-high vacuum to remove air obstruction. This allows particle beams to deposit or remove materials without contamination. Dry etching is essential to the fabrication of semiconductors and optical coatings. Deep vacuum lowers the boiling point of liquids promoting low temperature outgassing. Freeze drying adhesive preparation distillation and metallurgy all use these principles. Electron microscopes and vacuum tubes including cathode-ray tubes rely on electrical properties of vacuum. Vacuum interrupters are used in electrical switchgear. Vacuum arc processes produce certain grades of steel or high purity materials. The Newcomen steam engine used vacuum instead of pressure to drive a piston. Manifold vacuum drives accessories on automobiles such as the vacuum servo for brakes. Maintaining a vacuum in the condenser is important for efficient operation of steam turbines.
Humans exposed to vacuum will lose consciousness after a few seconds and die of hypoxia within minutes. The reduction in pressure lowers the temperature at which blood and other body fluids boil. Elastic pressure of blood vessels ensures this boiling point remains above internal body temperature of 37 degrees Celsius. Formation of gas bubbles in bodily fluids known as ebullism is still a concern. Gas may bloat the body to twice its normal size and slow circulation. Shuttle astronauts wore a fitted elastic garment called the Crew Altitude Protection Suit preventing ebullism at pressures as low as 2 kPa. Animal experiments show rapid and complete recovery is normal for exposures shorter than 90 seconds. A study by NASA on eight chimpanzees found all survived two and a half minute exposures to vacuum. Limbs may be exposed for much longer if breathing is not impaired. Robert Boyle was first to show in 1660 that vacuum is lethal to small animals. Tardigrades can survive vacuum conditions for periods of days or weeks.
Continue Browsing
Common questions
When did Lucretius argue for the existence of vacuum?
Lucretius argued for the existence of vacuum in the first century BC. This argument was part of ancient Greek philosophical debates on atomism and void.
Who invented the first laboratory vacuum in 1643?
Evangelista Torricelli produced the first laboratory vacuum in 1643. He created a Torricellian vacuum by filling a tall glass container with mercury and inverting it in a bowl to contain the mercury.
What is the definition of ultra-high vacuum according to ISO standards?
Ultra-high vacuum operates below one trillionth of atmospheric pressure reaching around 100 particles per cubic centimeter. ISO 3529-1:2019 defined ranges according to technology required to achieve or measure it.
How long can humans survive exposure to vacuum before losing consciousness?
Humans exposed to vacuum will lose consciousness after a few seconds and die of hypoxia within minutes. Animal experiments show rapid and complete recovery is normal for exposures shorter than 90 seconds.
Why does air expand to fill available space according to Al-Farabi?
Al-Farabi wrote a treatise rejecting the existence of the vacuum in the 10th century. He concluded that air's volume can expand to fill available space making the concept of a perfect vacuum incoherent.