This vacuum means "absent of matter" or "an empty area or space"; for the cleaning appliance, see vacuum cleaner. A vacuum cleaner (in colloquial British English also hoover) is a device that uses an air Pump to create a partial Vacuum to Suck

A vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The volume of any solid plasma vacuum or theoretical object is how much three- Dimensional space it occupies often quantified numerically Space is the extent within which Matter is physically extended and objects and Events have positions relative to one another Matter is commonly defined as being anything that has mass and that takes up space. Pressure (symbol 'p' is the force per unit Area applied to an object in a direction perpendicular to the surface ^[1] The word comes from the Latin term for "empty," 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 discuss ideal test results that would occur in a perfect vacuum, which they simply call "vacuum" or "free space" in this context, and use the term partial vacuum to refer to real vacuum. A physicist is a Scientist who studies or practices Physics. Physicists study a wide range of physical phenomena in many branches of physics spanning In Classical physics, free space is a concept of Electromagnetic theory, corresponding to a theoretically "perfect" Vacuum, and sometimes 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. Pressure (symbol 'p' is the force per unit Area applied to an object in a direction perpendicular to the surface The torr (symbol Torr) is a non- SI unit of Pressure defined as 1/760 of an atmosphere. 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. Quantum mechanics is the study of mechanical systems whose dimensions are close to the Atomic scale such as Molecules Atoms Electrons Outer space is a natural high quality vacuum, mostly of much higher quality than can be created artificially with current technology. Outer space, often simply called space, comprises the relatively empty regions of the Universe outside the escape velocities of Celestial bodies. Low quality artificial vacuums have been used for suction for many years. Suction is the flow of a fluid into a partial Vacuum, or region of low pressure

Vacuum has been a frequent topic of philosophical debate since Ancient Greek times, but was not studied empirically until the 17th century. Philosophy is the study of general problems concerning matters such as existence knowledge truth beauty justice validity mind and language The Ancient Greek language is the historical stage in the development of the Hellenic language family spanning the Archaic (c As a means of recording the passage of Time, the 17th Century was that Century which lasted from 1601 - 1700 in the Gregorian calendar Evangelista Torricelli produced the first laboratory vacuum in 1643, and other experimental techniques were developed as a result of his theories of atmospheric pressure. Evangelista Torricelli ( ( October 15, 1608 &ndash October 25, 1647) was an Italian physicist and mathematician 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 twentieth century of the Common Era began on The incandescent light bulb, incandescent lamp or incandescent light globe is a source of electric Light that works by Incandescence, (a general This article is about the electronic device not an evacuated pipe used for experiments in Free-fall. The recent development of human spaceflight has raised interest in the impact of vacuum on human health, and on life forms in general. A human spaceflight is a Spaceflight with a human crew, and possibly passengers

A large vacuum chamber

Uses

Light bulbs contain a partial vacuum, usually backfilled with argon, which protects the tungsten filament

Vacuum is useful in a variety of processes and devices. vacuum chamber is a rigid enclosure from which air and other gases are removed by a Vacuum pump. The incandescent light bulb, incandescent lamp or incandescent light globe is a source of electric Light that works by Incandescence, (a general This article pertains to the chemical element For other uses see Argon (disambiguation. Tungsten (ˈtʌŋstən also known as wolfram (/ˈwʊlfrəm/ is a Chemical element that has the symbol W and Atomic number 74 Its first widespread use was in the incandescent light bulb to protect the filament from chemical degradation. The incandescent light bulb, incandescent lamp or incandescent light globe is a source of electric Light that works by Incandescence, (a general Its chemical inertness is also useful for electron beam welding, cold welding, vacuum packing and vacuum frying. Electron beam welding (EBW is a fusion Welding process in which a beam of high-velocity Electrons is applied to the materials being joined Cold or contact welding was first recognized as a general materials phenomenon in the 1940s Vacuum packing is a method of storing food and presenting it for sale A Vacuum fryer is a Deep-frying device originally developed for Potato chip production Ultra-high vacuum is used in the study of atomically clean substrates, as only a very good vacuum preserves atomic-scale clean surfaces for a reasonably long time (on the order of minutes to days). Ultra high vacuum (UHV is the Vacuum regime characterised by Pressures lower than about 10−7 pascal or 100 nanopascals (~10−9 High to ultra-high vacuum removes the obstruction of air, allowing particle beams to deposit or remove materials without contamination. This is the principle behind chemical vapor deposition, physical vapor deposition, and dry etching which are essential to the fabrication of semiconductors and optical coatings, and to surface science. Chemical vapor deposition (CVD is a Chemical process used to produce high-purity high-performance solid materials Physical vapor deposition (PVD is a variety of vacuum deposition and is a general term used to describe any of a variety of methods to deposit Thin films by the condensation Dry etching refers to the removal of material typically a masked pattern of Semiconductor material by exposing the material to a bombardment of Ions (usually a Semiconductor device fabrication is the process used to create chips the Integrated circuits that are present in everyday Electrical and electronic An optical coating is a thin layer of material deposited on an optical component such as a lens or Mirror, which alters the way in which the optic Surface science is the study of physical and chemical phenomena that occur at the interface of two phases, including Solid - Liquid The reduction of convection provides the thermal insulation of thermos bottles. Deep vacuum promotes outgassing which is used in freeze drying, adhesive preparation, distillation, metallurgy, and process purging. Outgassing (sometimes called offgassing, particularly when in reference to indoor Air quality is the slow release of a Gas that was trapped Freeze drying (also known as lyophilization or cryodesiccation) is a Dehydration process typically used to preserve a perishable material Glue or adhesive is a compound that adheres or bonds two items together Vacuum distillation is a method of Distillation whereby the pressure above the liquid mixture to be distilled is reduced to less than its Vapor pressure (usually Metallurgy is a domain of Materials science that studies the physical and chemical behavior of metallic elements, their intermetallic compounds, and their The electrical properties of vacuum make electron microscopes and vacuum tubes possible, including cathode ray tubes. An electron microscope is a type of Microscope that uses Electrons to illuminate a specimen and create an enlarged image This article is about the electronic device not an evacuated pipe used for experiments in Free-fall. The cathode ray tube (CRT is a Vacuum tube containing an Electron gun (a source of electrons and a Fluorescent screen with internal or The elimination of air friction is useful for flywheel energy storage and ultracentrifuges. Friction is the Force resisting the relative motion of two Surfaces in contact or a surface in contact with a fluid (e Flywheel Energy Storage (FES works by accelerating a Rotor ( Flywheel) to a very high speed and maintaining the energy in the system as Rotational energy The ultracentrifuge is a Centrifuge optimized for spinning a rotor at very high speeds capable of generating acceleration as high as 1000000 g (9800 km/s²

Vacuums are commonly used to produce suction, which has an even wider variety of applications. Suction is the flow of a fluid into a partial Vacuum, or region of low pressure The Newcomen steam engine used vacuum instead of pressure to drive a piston. The atmospheric engine invented by Thomas Newcomen in 1712 today referred to as a Newcomen steam engine (or simply Newcomen engine was the first practical In the 19th century, vacuum was used for traction on Isambard Kingdom Brunel's experimental atmospheric railway. The 19th century of the Common Era began on January 1, 1801 and ended on December 31, 1900, according to the Gregorian calendar Isambard Kingdom Brunel, FRS (9 April 1806 &ndash 15 September 1859 (ˈɪzəmbɑrd ˈkɪŋdəm brʊˈnɛl was a British Engineer. An atmospheric railway is a Railway that uses air Pressure to provide power for propulsion

Outer space

Main article: Outer space

Outer space is not a perfect vacuum, but a tenuous plasma awash with charged particles, electromagnetic fields, and the occasional star. Outer space, often simply called space, comprises the relatively empty regions of the Universe outside the escape velocities of Celestial bodies. In Physics and Chemistry, plasma is an Ionized Gas, in which a certain proportion of Electrons are free rather than being bound The electromagnetic field is a physical field produced by electrically charged objects. A star is a massive luminous ball of plasma. The nearest star to Earth is the Sun, which is the source of most of the Energy on Earth

Outer space has very low density and pressure, and is the closest physical approximation of a perfect vacuum. Outer space, often simply called space, comprises the relatively empty regions of the Universe outside the escape velocities of Celestial bodies. It has effectively no friction, allowing stars, planets and moons to move freely along ideal gravitational trajectories. Friction is the Force resisting the relative motion of two Surfaces in contact or a surface in contact with a fluid (e A star is a massive luminous ball of plasma. The nearest star to Earth is the Sun, which is the source of most of the Energy on Earth A planet, as defined by the International Astronomical Union (IAU is a celestial body Orbiting a Star or stellar remnant that is But no vacuum is truly perfect, not even in interstellar space where there are still a few hydrogen atoms per cubic centimeter. The deep vacuum of space could make it an attractive environment for certain industrial processes, for instance those that require ultraclean surfaces; however, it is much less costly to create an equivalent vacuum on Earth than to leave the Earth's gravity well. In Physics, a gravity well is the Gravitational potential field around a massive body (a particular kind of Potential well)

Stars, planets and moons keep their atmospheres by gravitational attraction, and as such, atmospheres have no clearly delineated boundary: the density of atmospheric gas simply decreases with distance from the object. An atmosphere (from Greek ατμός - atmos, " Vapor " + σφαίρα - sphaira, " Sphere " The Earth's atmospheric pressure drops to about 1 Pa (10^-3 Torr) at 100 km of altitude, the Kármán line which is a common definition of the boundary with outer space. Beyond this line, isotropic gas pressure rapidly becomes insignificant when compared to radiation pressure from the sun and the dynamic pressure of the solar wind, so the definition of pressure becomes difficult to interpret. Radiation pressure is the Pressure exerted upon any surface exposed to Electromagnetic radiation. The Sun (Sol is the Star at the center of the Solar System. In Fluid dynamics dynamic pressure (indicated with q, or Q, and sometimes called velocity pressure) is the quantity defined by The solar wind is a Stream of charged particles&mdasha plasma &mdashthat are ejected from the upper atmosphere of the Sun. The thermosphere in this range has large gradients of pressure, temperature and composition, and varies greatly due to space weather. The thermosphere is the layer of the Earth's atmosphere directly above the Mesosphere and directly below the Exosphere. Space weather is the concept of changing environmental conditions in Outer space. Astrophysicists prefer to use number density to describe these environments, in units of particles per cubic centimetre. In Physics, Astronomy, and Chemistry, number density is an Intensive quantity used to describe the degree of concentration of Countable

But although it meets the definition of outer space, the atmospheric density within the first few hundred kilometers above the Kármán line is still sufficient to produce significant drag on satellites. In Fluid dynamics, drag (sometimes called fluid resistance) is the force that resists the movement of a Solid object through a Fluid (a This article is about artificial satellites For natural satellites also known as moons see Natural satellite. Most artificial satellites operate in this region called low earth orbit and must fire their engines every few days to maintain orbit. A Low Earth Orbit (LEO is generally defined as an Orbit within the locus extending from the Earth’s surface up to an altitude of 2000 km The drag here is low enough that it could theoretically be overcome by radiation pressure on solar sails, a proposed propulsion system for interplanetary travel. Solar sails (also called light sails or photon sails, especially when they use Light sources other than the Sun) are a proposed form of Planets are too massive for their trajectories to be affected by these forces, although their atmospheres are eroded by the solar winds.

All of the observable universe is filled with large numbers of photons, the so-called cosmic background radiation, and quite likely a correspondingly large number of neutrinos. The Universe is defined as everything that Physically Exists: the entirety of Space and Time, all forms of Matter, Energy In Physics, the photon is the Elementary particle responsible for electromagnetic phenomena Neutrinos are Elementary particles that travel close to the Speed of light, lack an Electric charge, are able to pass through ordinary matter almost The current temperature of this radiation is about 3 K, or -270 degrees Celsius or -454 degrees Fahrenheit. Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic

Effects on humans and animals

See also: Human adaptation to space

This painting, An Experiment on a Bird in the Air Pump by Joseph Wright of Derby, 1768, depicts an experiment performed by Robert Boyle in 1660. Human physiological adaptation to space is a challenge faced in developing Human spaceflight. An Experiment on a Bird in the Air Pump is a 1768 oil-on-canvas painting by Joseph Wright of Derby, part of a series of candlelit scenes that Wright painted Joseph Wright ( 3 September 1734 - 29 August 1797) styled Wright of Derby was an English landscape and portrait painter Robert Boyle was a Natural philosopher, chemist physicist inventor and early Gentleman scientist, noted for his work in Physics and Chemistry

Humans and animals exposed to vacuum will lose consciousness after a few seconds and die of hypoxia within minutes, but the symptoms are not nearly as graphic as commonly shown in pop culture. Consciousness has been defined loosely as a constellation of attributes of Mind such as Subjectivity, Self-awareness, Sentience, and the Blood and other body fluids do boil when their pressure drops below 6. Blood is a specialized Bodily fluid that delivers necessary substances to the body's cells ��such as nutrients and oxygen—and transports Waste products 3 kPa, (47 Torr,) the vapour pressure of water at body temperature. Vapor pressure (also known as equilibrium vapor pressure or saturation vapor pressure) is the Pressure of a Vapor in equilibrium ^[2] This condition is called ebullism. Ebullism is the formation of Gas bubbles in Bodily fluids due to reduced environmental pressure for example at high Altitude. The steam may bloat the body to twice its normal size and slow circulation, but tissues are elastic and porous enough to prevent rupture. Ebullism is slowed by the pressure containment of blood vessels, so some blood remains liquid. ^[3][4] Swelling and ebullism can be restrained by containment in a flight suit. flight suit is a full body garment worn while flying a powered Aircraft such as Military airplanes and helicopters Shuttle astronauts wear a fitted elastic garment called the Crew Altitude Protection Suit (CAPS) which prevents ebullism at pressures as low as 2 kPa (15 Torr). NASA 's Space Shuttle, officially called Space Transportation System ( STS) is the United States government's current manned Launch ^[5] Rapid evaporative cooling of the skin will create frost, particularly in the mouth, but this is not a significant hazard.

Animal experiments show that rapid and complete recovery is the norm for exposures shorter than 90 seconds, while longer full-body exposures are fatal and resuscitation has never been successful. ^[6] There is only a limited amount of data available from human accidents, but it is consistent with animal data. Limbs may be exposed for much longer if breathing is not impaired. ^[2] Robert Boyle was the first to show in 1660 that vacuum is lethal to small animals. Robert Boyle was a Natural philosopher, chemist physicist inventor and early Gentleman scientist, noted for his work in Physics and Chemistry In 1942, in one of a series of experiments on human subjects for the Luftwaffe, the Nazi regime tortured Dachau concentration camp prisoners by exposing them to vacuum in order to determine the human body's capacity to survive high-altitude conditions. Year 1942 ( MCMXLII) was a Common year starting on Thursday (the link will display the full 1942 calendar of the Gregorian calendar. Nazi human experimentation was a series of controversial medical experiments on large numbers of prisoners by the German Nazi regime in its Concentration ( German 'luftvafe is a generic German term for an Air force. Nazism, which was a short name for National Socialism (Nationalsozialismus refers primarily to the Ideology and practices of the National Socialist German Dachau was a Nazi German Concentration camp, and the first one opened in Germany located on the grounds of an abandoned munitions Factory near the

Cold or oxygen-rich atmospheres can sustain life at pressures much lower than atmospheric, as long as the density of oxygen is similar to that of standard sea-level atmosphere. The colder air temperatures found at altitudes of up to 3 km generally compensate for the lower pressures there. ^[2] Above this altitude, oxygen enrichment is necessary to prevent altitude sickness, and spacesuits are necessary to prevent ebullism above 19 km. Altitude sickness, also known as acute mountain sickness ( AMS) altitude illness, or soroche, is a pathological condition that is caused by acute A space suit is a complex system of Garments equipment and environmental systems designed to keep a person alive and comfortable in the harsh environment of outer space ^[2] Most spacesuits use only 20 kPa (150 Torr) of pure oxygen, just enough to sustain full consciousness. This pressure is high enough to prevent ebullism, but simple evaporation of blood can still cause decompression sickness and gas embolisms if not managed. Evaporation is the process by which Molecules in a Liquid state (e Decompression sickness (DCS, the diver’s disease, the bends, caisson disease is the name given to a variety of symptoms suffered by a person An air embolism, or more generally gas embolism, is a medical condition caused by Gas bubbles in the bloodstream ( embolism in a medical context refers to

Rapid decompression can be much more dangerous than vacuum exposure itself. Even if the victim does not hold his breath, venting through the windpipe may be too slow to prevent the fatal rupture of the delicate alveoli of the lungs. An alveolus (plural alveoli, from Latin alveolus, "little cavity" is an anatomical structure that has the form of a hollow cavity lung is the essential Respiration organ in air-breathing Animals including most Tetrapods a few Fish and a few Snails The most primitive ^[2] Eardrums and sinuses may be ruptured by rapid decompression, soft tissues may bruise and seep blood, and the stress of shock will accelerate oxygen consumption leading to hypoxia. The tympanic membrane (also tympanum or myrinx is a thin membrane that separates the External ear from the Middle ear. ^[7] Injuries caused by rapid decompression are called barotrauma. Barotrauma is physical damage to body tissues caused by a difference in Pressure between an air space inside or beside the body and the surrounding Gas or Liquid A pressure drop as small as 100 Torr, (13 kPa,) which produces no symptoms if it is gradual, may be fatal if occurs suddenly. ^[2]

Some extremophile microrganisms, such as Tardigrades, can survive vacuum for a period of years. An extremophile is an Organism that thrives in and may even require Physically or Geochemically extreme conditions that are detrimental to the Tardigrades (commonly known as water bears) form the Phylum Tardigrada, part of the superphylum Ecdysozoa.

Historical interpretation

Historically, there has been much dispute over whether such a thing as a vacuum can exist. A controversy or dispute is a commencement of a conflict between statements of accepted fact and a new or unaccepted proposal that disagrees with argues against Ancient Greek philosophers did not like to admit the existence of a vacuum, asking themselves "how can 'nothing' be something?". The term ancient Greece refers to the period of Greek history lasting from the Greek Dark Ages ca Philosophy is the study of general problems concerning matters such as existence knowledge truth beauty justice validity mind and language Plato found the idea of a vacuum inconceivable. Biography Early life Birth and family Plato was born in Athens Greece He believed that all physical things were instantiations of an abstract Platonic ideal, and he could not conceive of an "ideal" form of a vacuum. The phrase Platonic idealism usually refers to Plato's theory of forms or doctrine of ideas the exact philosophical meaning of which is perhaps one of the most disputed questions Similarly, Aristotle considered the creation of a vacuum impossible — nothing could not be something. Aristotle (Greek Aristotélēs) (384 BC – 322 BC was a Greek philosopher a student of Plato and teacher of Alexander the Great. Later Greek philosophers thought that a vacuum could exist outside the cosmos, but not within it. In its most general sense a cosmos is an orderly or harmonious system

Hero of Alexandria was the first to challenge this belief in the first century AD, but his attempts to create an artificial vacuum failed. Hero (or Heron) of Alexandria ( Ήρων ο Αλεξανδρεύς) (c ^[8] The philosopher Al-Farabi (872 - 950 CE) appears to have carried out the first experiments concerning the existence of vacuum, in which he investigated handheld plungers in water. Philosophy is the study of general problems concerning matters such as existence knowledge truth beauty justice validity mind and language TemplateInfobox Muslim scholars --> Abū Nasr Muhammad ibn al-Farakh al-Fārābi ( Nastaliq:) or Abū Nasr al-Fārābi ^[9] He concluded that air's volume can expand to fill available space, and he suggested that the concept of perfect vacuum was incoherent. ^[10]

Torricelli's mercury barometer produced one of the first sustained vacuums in a laboratory. Mercury (ˈmɜrkjʊri also called quicksilver or hydrargyrum, is a Chemical element with the symbol Hg ( Latinized hydrargyrum History The first barometer is thought to have been built unintentionally by Gasparo Berti, sometime between 1640 and 1643

In the Middle Ages, the Catholic Church held the idea of a vacuum to be immoral or even heretical. The absence of anything implied the absence of God, and harkened back to the void prior to the creation story in the book of Genesis. God is the principal or sole Deity in Religions and other belief systems that worship one deity. Medieval thought experiments into the idea of a vacuum considered whether a vacuum was present, if only for an instant, between two flat plates when they were rapidly separated. A thought experiment (from the German Gedankenexperiment) is a proposal for an Experiment that would test a Hypothesis or Theory There was much discussion of whether the air moved in quickly enough as the plates were separated, or, as Walter Burley postulated, whether a 'celestial agent' prevented the vacuum arising. Walter Burley (or Burleigh c1275-1344/5 was a Medieval English Logician. The commonly held view that nature abhorred a vacuum was called horror vacui. In Philosophy the horror vacui stands for a theory initially proposed by Aristotle stating that nature “fears” empty space This speculation was shut down by the 1277 Paris condemnations of Bishop Etienne Tempier, which required there to be no restrictions on the powers of God, which led to the conclusion that God could create a vacuum if he so wished. The Condemnations at the medieval University of Paris were enacted to restrict certain teachings as being heretical A bishop is an ordained or consecrated member of the Christian clergy who is generally entrusted with a position of authority and oversight Étienne (Stephen Tempier (also known as Stephanus of Orleans) (died September 3 1279 was a French Bishop of Paris during the thirteenth century ^[11] René Descartes also argued against the existence of a vacuum, arguing along the following lines:“Space is identical with extension, but extension is connected with bodies; thus there is no space without bodies and hence no empty space (vacuum)”. In spite of this, opposition to the idea of a vacuum existing in nature continued into the Scientific Revolution, with scholars such as Paolo Casati taking an anti-vacuist position. The period which many historians of science call the Scientific Revolution can be roughly dated as having begun in 1543 the year in which Nicolaus Copernicus published Jean Buridan reported in the 14th century that teams of ten horses could not pull open bellows when the port was sealed, apparently because of horror vacui. Jean Buridan (in Latin, Johannes Buridanus; ca 1295 &ndash 1358 was a French Priest who sowed the seeds of the Copernican revolution A bellows is a device for delivering pressurized Air in a controlled quantity to a controlled location ^[8]

The Crookes tube, used to discover and study cathode rays, was an evolution of the Geissler tube. A Crookes tube is an early experimental Discharge tube, invented by British physicist William Crookes and others around 1875 in which Cathode rays Cathode rays (also called an electron beam or e-beam) are streams of Electrons observed in Vacuum tubes i The Geissler tube is a glass tube for demonstrating the principles of electrical Glow discharge.

The belief in horror vacui was overthrown in the 17th century. Water pump designs had improved by then to the point that they produced measurable vacuums, but this was not immediately understood. What was known was that suction pumps could not pull water beyond a certain height: 18 Florentine yards according to a measurement taken around 1635. (The conversion to metres is uncertain, but it would be about 9 or 10 metres. ) This limit was a concern to irrigation projects, mine drainage, and decorative water fountains planned by the Duke of Tuscany, so the Duke commissioned Galileo to investigate the problem. Galileo Galilei (15 February 1564 &ndash 8 January 1642 was a Tuscan ( Italian) Physicist, Mathematician, Astronomer, and Philosopher Galileo advertised the puzzle to other scientists, including Gaspar Berti who replicated it by building the first water barometer in Rome in 1639. ^[12] Berti's barometer produced a vacuum above the water column, but he could not explain it. The breakthrough was made by Evangelista Torricelli in 1643. Evangelista Torricelli ( ( October 15, 1608 &ndash October 25, 1647) was an Italian physicist and mathematician Building upon Galileo's notes, he built the first mercury barometer and wrote a convincing argument that the space at the top was a vacuum. Mercury (ˈmɜrkjʊri also called quicksilver or hydrargyrum, is a Chemical element with the symbol Hg ( Latinized hydrargyrum History The first barometer is thought to have been built unintentionally by Gasparo Berti, sometime between 1640 and 1643 The height of the column was then limited to the maximum weight that atmospheric pressure could support. Some people believe that although Torricelli's experiment was crucial, it was Blaise Pascal's experiments that proved the top space really contained vacuum. Blaise Pascal (blɛz paskal (June 19 1623 &ndash August 19 1662 was a French Mathematician, Physicist, and religious Philosopher

In 1654, Otto von Guericke invented the first vacuum pump and conducted his famous Magdeburg hemispheres experiment, showing that teams of horses could not separate two hemispheres from which the air had been evacuated. Otto von Guericke (originally spelled Gericke ˈgeːʁɪkə ( November 20, 1602 &ndash May 11, 1686 ( Julian calendar) The Magdeburg hemispheres were a pair of large copper hemispheres with mating rims Robert Boyle improved Guericke's design and conducted experiments on the properties of vacuum. Robert Boyle was a Natural philosopher, chemist physicist inventor and early Gentleman scientist, noted for his work in Physics and Chemistry Robert Hooke also helped Boyle produce an air pump which helped to produce the vacuum. Robert Hooke, FRS (18 July 1635 – 3 March 1703 was an English Natural philosopher and Polymath who played an important role in the The study of vacuum then lapsed until 1855, when Heinrich Geissler invented the mercury displacement pump and achieved a record vacuum of about 10 Pa (0. Year 1855 ( MDCCCLV) was a Common year starting on Monday (link will display the full calendar of the Gregorian Calendar (or a Common year Johann Heinrich Wilhelm Geißler ( May 26 1814 - January 24 1879) was a German Physicist and inventor of the Geissler tube 1 Torr). The torr (symbol Torr) is a non- SI unit of Pressure defined as 1/760 of an atmosphere. A number of electrical properties become observable at this vacuum level, and this renewed interest in vacuum. This, in turn, led to the development of the vacuum tube. This article is about the electronic device not an evacuated pipe used for experiments in Free-fall.

While outer space has been likened to a vacuum, early theories of the nature of light relied upon the existence of an invisible, aetherial medium which would convey waves of light (Isaac Newton relied on this idea to explain refraction and radiated heat). Light, or visible light, is Electromagnetic radiation of a Wavelength that is visible to the Human eye (about 400–700 Sir Isaac Newton, FRS (ˈnjuːtən 4 January 1643 31 March 1727) Biography Early years See also Isaac Newton's early life and achievements Refraction is the change in direction of a Wave due to a change in its Speed. ^[13] This evolved into the luminiferous aether of the 19th century, but the idea was known to have significant shortcomings - specifically that if the Earth were moving through a material medium, the medium would have to be both extremely tenuous (because the Earth is not detectably slowed in its orbit), and extremely rigid (because vibrations propagate so rapidly). In the late 19th century " luminiferous aether " (or " ether " meaning light-bearing aether, was the term used to describe a medium for the propagation An 1891 article by William Crookes noted: "the [freeing of] occluded gases into the vacuum of space". Year 1891 ( MDCCCXCI) was a Common year starting on Thursday (link will display the full calendar of the Gregorian calendar (or a Common Sir William Crookes, OM, FRS (17 June 1832 – 4 April 1919 was an English Chemist and Physicist. ^[14] Even up until 1912, astronomer Henry Pickering commented: "While the interstellar absorbing medium may be simply the ether, [it] is characteristic of a gas, and free gaseous molecules are certainly there". Year 1912 ( MCMXII) was a Leap year starting on Monday (link will display the full calendar of the Gregorian calendar (or a Leap year starting Historically Astronomy was more concerned with the classification and description of phenomena in the sky while Astrophysics attempted to explain these phenomena William Henry Pickering ( February 15, 1858 &ndash January 17, 1938) was an American Astronomer, brother of Edward ^[15]

In 1887, the Michelson-Morley experiment, using an interferometer to attempt to detect the change in the speed of light caused by the Earth moving with respect to the aether, was a famous null result, showing that there really was no static, pervasive medium throughout space and through which the Earth moved as though through a wind. Year 1887 ( MDCCCLXXXVII) was a Common year starting on Saturday (link will display the full calendar of the Gregorian calendar (or a Common The Michelson–Morley experiment, one of the most important and famous experiments in the History of physics, was performed in 1887 by Albert Michelson and Interferometry is the technique of using the pattern of Interference created by the superposition of two or more Waves to diagnose the properties of EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 While there is therefore no aether, and no such entity is required for the propagation of light, space between the stars is not completely empty. Besides the various particles which comprise cosmic radiation, there is a cosmic background of photonic radiation (light), including the thermal background at about 2. For the 1962 Bruce Conner film see Cosmic Ray (film Cosmic rays are energetic particles originating from space that impinge on In Physics, the photon is the Elementary particle responsible for electromagnetic phenomena 7 K, seen as a relic of the Big Bang. The Big Bang is the cosmological model of the Universe that is best supported by all lines of scientific evidence and Observation. None of these findings affect the outcome of the Michelson-Morley experiment to any significant degree.

Einstein argued that physical objects are not located in space, but rather have a spatial extent. Seen this way, the concept of empty space loses its meaning. ^[16] Rather, space is an abstraction, based on the relationships between local objects. Nevertheless, the general theory of relativity admits a pervasive gravitational field, which, in Einstein's words^[17], may be regarded as an "aether", with properties varying from one location to another. General relativity or the general theory of relativity is the geometric theory of Gravitation published by Albert Einstein in 1916 One must take care, though, to not ascribe to it material properties such as velocity and so on.

In 1930, Paul Dirac proposed a model of vacuum as an infinite sea of particles possessing negative energy, called the Dirac sea. The Dirac sea is a theoretical model of the Vacuum as an infinite sea of particles possessing Negative energy. This theory helped refine the predictions of his earlier formulated Dirac equation, and successfully predicted the existence of the positron, discovered two years later in 1932. In Physics, the Dirac equation is a relativistic quantum mechanical wave equation formulated by British physicist Paul Dirac in 1928 and provides The positrons or antielectron is the Antiparticle or the Antimatter counterpart of the Electron. Year 1932 ( MCMXXXII) was a Leap year starting on Friday of the Gregorian calendar. Despite this early success, the idea was soon abandoned in favour of the more elegant quantum field theory. In quantum field theory (QFT the forces between particles are mediated by other particles

The development of quantum mechanics has complicated the modern interpretation of vacuum by requiring indeterminacy. Quantum mechanics is the study of mechanical systems whose dimensions are close to the Atomic scale such as Molecules Atoms Electrons Quantum indeterminacy is the apparent necessary incompleteness in the description of a Physical system, that has become one of the characteristics of the standard Niels Bohr and Werner Heisenberg's uncertainty principle and Copenhagen interpretation, formulated in 1927, predict a fundamental uncertainty in the instantaneous measurability of the position and momentum of any particle, and which, not unlike the gravitational field, questions the emptiness of space between particles. Niels Henrik David Bohr (nels ˈb̥oɐ̯ˀ in Danish 7 October 1885 – 18 November 1962 was a Danish Physicist who made fundamental contributions to understanding Werner Heisenberg (5 December 1901 in Würzburg &ndash1 February 1976 in Munich) was a German theoretical physicist best known for enunciating the In Quantum physics, the Heisenberg uncertainty principle states that locating a particle in a small region of space makes the Momentum of the particle uncertain The Copenhagen interpretation is an interpretation of Quantum mechanics. Year 1927 ( MCMXXVII) was a Common year starting on Saturday (link will display full calendar of the Gregorian calendar. In Classical mechanics, momentum ( pl momenta SI unit kg · m/s, or equivalently N · s) is the product In the late 20th century, this principle was understood to also predict a fundamental uncertainty in the number of particles in a region of space, leading to predictions of virtual particles arising spontaneously out of the void. In Physics, a virtual particle is a particle that exists for a limited time and space introducing uncertainty in their energy and momentum due to the Heisenberg Uncertainty In other words, there is a lower bound on the vacuum, dictated by the lowest possible energy state of the quantized fields in any region of space.

Quantum-mechanical definition

For more details on this topic, see vacuum state. In Quantum field theory, the vacuum state (also called the vacuum) is the Quantum state with the lowest possible Energy.

In quantum mechanics, the vacuum is defined as the state (i. e. solution to the equations of the theory) with the lowest energy. To first approximation, this is simply a state with no particles, hence the name.

Even an ideal vacuum, thought of as the complete absence of anything, will not in practice remain empty. Consider a vacuum chamber that has been completely evacuated, so that the (classical) particle concentration is zero. The walls of the chamber will emit light in the form of black body radiation. The Electromagnetic radiation emitted by a Black body. You may also be looking for Incandescence, the radiation from a body This light carries momentum, so the vacuum does have a radiation pressure. This limitation applies even to the vacuum of interstellar space. Even if a region of space contains no particles, the Cosmic Microwave Background fills the entire universe with black body radiation.

An ideal vacuum cannot exist even inside of a molecule. Each atom in the molecule exists as a probability function of space, which has a certain non-zero value everywhere in a given volume. Thus, even "between" the atoms there is a certain probability of finding a particle, so the space cannot be said to be a vacuum.

More fundamentally, quantum mechanics predicts that vacuum energy will be different from its naive, classical value. Quantum mechanics is the study of mechanical systems whose dimensions are close to the Atomic scale such as Molecules Atoms Electrons Vacuum energy is an underlying background Energy that exists in Space even when devoid of Matter (known as Free space) The quantum correction to the energy is called the zero-point energy and consists of energies of virtual particles that have a brief existence. In Physics, the zero-point energy is the lowest possible Energy that a Quantum mechanical Physical system may possess and is the energy of the In Physics, a virtual particle is a particle that exists for a limited time and space introducing uncertainty in their energy and momentum due to the Heisenberg Uncertainty This is called vacuum fluctuation. In Physics, a virtual particle is a particle that exists for a limited time and space introducing uncertainty in their energy and momentum due to the Heisenberg Uncertainty Vacuum fluctuations may also be related to the so-called cosmological constant in cosmology. In Physical cosmology, the cosmological constant (usually denoted by the Greek capital letter Lambda: Λ was proposed by Albert Einstein as a modification Physical cosmology, as a branch of Astronomy, is the study of the large-scale structure of the Universe and is concerned with fundamental questions about its The best evidence for vacuum fluctuations is the Casimir effect and the Lamb shift. In Physics, the Casimir effect and the Casimir-Polder force are physical forces arising from a quantized field. In Physics, the Lamb shift, named after Willis Lamb (1913-2008 is a small difference in Energy between two Energy levels ^2S_{1/2} ^[11]

In quantum field theory and string theory, the term "vacuum" is used to represent the ground state in the Hilbert space, that is, the state with the lowest possible energy. In quantum field theory (QFT the forces between particles are mediated by other particles String theory is a still-developing scientific approach to Theoretical physics, whose original building blocks are one-dimensional extended objects called strings In Quantum mechanics, a stationary state is an Eigenstate of a Hamiltonian, or in other words a state of definite energy This article assumes some familiarity with Analytic geometry and the concept of a limit. In free (non-interacting) quantum field theories, this state is analogous to the ground state of a quantum harmonic oscillator. The quantum harmonic oscillator is the quantum mechanical analogue of the classical harmonic oscillator. If the theory is obtained by quantization of a classical theory, each stationary point of the energy in the configuration space gives rise to a single vacuum. In Mathematics, particularly in Calculus, a stationary point is an input to a function where the Derivative is zero (equivalently the "Configuration space" may also refer to PCI Configuration Space. String theory is believed to have a huge number of vacua - the so-called string theory landscape. String theory is a still-developing scientific approach to Theoretical physics, whose original building blocks are one-dimensional extended objects called strings The string theory landscape or anthropic landscape refers to the large number of possible false vacua in String theory.

Pumping

The manual water pump draws water up from a well by creating a vacuum that water rushes in to fill. In a sense, it acts to evacuate the well, although the high leakage rate of dirt prevents a high quality vacuum from being maintained for any length of time.

Main article: Vacuum pump

Fluids cannot be pulled, so it is technically impossible to create a vacuum by suction. A vacuum pump is a device that removes gas molecules from a sealed volume in order to leave behind a partial Vacuum. Suction can spread and dilute a vacuum by letting a higher pressure push fluids into it, but the vacuum has to be created first before suction can occur. The easiest way to create an artificial vacuum is to expand the volume of a container. For example, the diaphragm muscle expands the chest cavity, which causes the volume of the lungs to increase. For other types of diaphragm see Diaphragm. In the Anatomy of Mammals the thoracic diaphragm is a sheet of Muscle This expansion reduces the pressure and creates a partial vacuum, which is soon filled by air pushed in by atmospheric pressure.

To continue evacuating a chamber indefinitely without requiring infinite growth, a compartment of the vacuum can be repeatedly closed off, exhausted, and expanded again. This is the principle behind positive displacement pumps, like the manual water pump for example. A vacuum pump is a device that removes gas molecules from a sealed volume in order to leave behind a partial Vacuum. Inside the pump, a mechanism expands a small sealed cavity to create a vacuum. Because of the pressure differential, some fluid from the chamber (or the well, in our example) is pushed into the pump's small cavity. The pump's cavity is then sealed from the chamber, opened to the atmosphere, and squeezed back to a minute size.

A cutaway view of a turbomolecular pump, a momentum transfer pump used to achieve high vacuum

The above explanation is merely a simple introduction to vacuum pumping, and is not representative of the entire range of pumps in use. A turbomolecular pump is a type of Vacuum pump, superficially similar to a Turbopump, used to obtain and maintain high Vacuum. Many variations of the positive displacement pump have been developed, and many other pump designs rely on fundamentally different principles. Momentum transfer pumps, which bear some similarities to dynamic pumps used at higher pressures, can achieve much higher quality vacuums than positive displacement pumps. A vacuum pump is a device that removes gas molecules from a sealed volume in order to leave behind a partial Vacuum. Entrapment pumps can capture gases in a solid or absorbed state, often with no moving parts, no seals and no vibration. A vacuum pump is a device that removes gas molecules from a sealed volume in order to leave behind a partial Vacuum. None of these pumps are universal; each type has important performance limitations. They all share a difficulty in pumping low molecular weight gases, especially hydrogen, helium, and neon. Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical Neon (ˈniːɒn is the Chemical element that has the symbol Ne and Atomic number 10

The lowest pressure that can be attained in a system is also dependent on many things other than the nature of the pumps. Multiple pumps may be connected in series, called stages, to achieve higher vacuums. The choice of seals, chamber geometry, materials, and pump-down procedures will all have an impact. Collectively, these are called vacuum technique. And sometimes, the final pressure is not the only relevant characteristic. Pumping systems differ in oil contamination, vibration, preferential pumping of certain gases, pump-down speeds, intermittent duty cycle, reliability, or tolerance to high leakage rates.

In ultra high vacuum systems, some very odd leakage paths and outgassing sources must be considered. Ultra high vacuum (UHV is the Vacuum regime characterised by Pressures lower than about 10−7 pascal or 100 nanopascals (~10−9 The water absorption of aluminium and palladium becomes an unacceptable source of outgassing, and even the adsorptivity of hard metals such as stainless steel or titanium must be considered. WikipediaNaming Palladium (pronounced \pəˈleɪdiəm\ is a rare and lustrous silvery-white metal that was discovered in 1803 by William Hyde Wollaston, who named it palladium after the Titanium (taɪˈteɪniəm is a Chemical element with the symbol Ti and Atomic number 22 Some oils and greases will boil off in extreme vacuums. The permeability of the metallic chamber walls may have to be considered, and the grain direction of the metallic flanges should be parallel to the flange face.

The lowest pressures currently achievable in laboratory are about 10^-13 Torr. The torr (symbol Torr) is a non- SI unit of Pressure defined as 1/760 of an atmosphere. ^[18] However, pressures as low as 5×10^-17 Torr have been indirectly measured in a 4 K cryogenic vacuum system. The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic ^[19]

Outgassing

Main article: Outgassing

Evaporation and sublimation into a vacuum is called outgassing. Outgassing (sometimes called offgassing, particularly when in reference to indoor Air quality is the slow release of a Gas that was trapped Evaporation is the process by which Molecules in a Liquid state (e Sublimation of an element or compound is a transition from the Solid to Gas phase with no intermediate liquid stage Outgassing (sometimes called offgassing, particularly when in reference to indoor Air quality is the slow release of a Gas that was trapped All materials, solid or liquid, have a small vapour pressure, and their outgassing becomes important when the vacuum pressure falls below this vapour pressure. Vapor pressure (also known as equilibrium vapor pressure or saturation vapor pressure) is the Pressure of a Vapor in equilibrium In man-made systems, outgassing has the same effect as a leak and can limit the achievable vacuum. Outgassing products may condense on nearby colder surfaces, which can be troublesome if they obscure optical instruments or react with other materials. This is of great concern to space missions, where an obscured telescope or solar cell can ruin an expensive mission.

The most prevalent outgassing product in man-made vacuum systems is water absorbed by chamber materials. It can be reduced by desiccating or baking the chamber, and removing absorbent materials. Outgassed water can condense in the oil of rotary vane pumps and reduce their net speed drastically if gas ballasting is not used. A rotary vane pump is a positive-displacement Pump that consists of vanes mounted to a rotor that rotates inside of a cavity High vacuum systems must be clean and free of organic matter to minimize outgassing.

Ultra-high vacuum systems are usually baked, preferably under vacuum, to temporarily raise the vapour pressure of all outgassing materials and boil them off. Once the bulk of the outgassing materials are boiled off and evacuated, the system may be cooled to lower vapour pressures and minimize residual outgassing during actual operation. Some systems are cooled well below room temperature by liquid nitrogen to shut down residual outgassing and simultaneously cryopump the system. Liquid nitrogen (liquid density at the Triple point is 0707 g/mL is the liquid produced industrially in large quantities by Fractional distillation of A cryopump is a Vacuum pump that traps Gases and Vapours by condensing them on a cold surface

Quality

The quality of a vacuum is indicated by the amount of matter remaining in the system, so that a high quality vacuum is one with very little matter left in it. Vacuum is primarily measured by its absolute pressure, but a complete characterization requires further parameters, such as temperature and chemical composition. Pressure (symbol 'p' is the force per unit Area applied to an object in a direction perpendicular to the surface Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature One of the most important parameters is the mean free path (MFP) of residual gases, which indicates the average distance that molecules will travel between collisions with each other. In Physics the mean free path of a particle is the average distance covered by a particle ( Photon, Atom or Molecule) between subsequent impacts As the gas density decreases, the MFP increases, and when the MFP is longer than the chamber, pump, spacecraft, or other objects present, the continuum assumptions of fluid mechanics do not apply. Fluid mechanics is the study of how Fluids move and the Forces on them This vacuum state is called high vacuum, and the study of fluid flows in this regime is called particle gas dynamics. The MFP of air at atmospheric pressure is very short, 70 nm, but at 100 mPa (~1×10^-3 Torr) the MFP of room temperature air is roughly 100 mm, which is on the order of everyday objects such as vacuum tubes. A nanometre ( American spelling: nanometer, symbol nm) ( Greek: νάνος nanos dwarf; μετρώ metrό count) is a This article is about the electronic device not an evacuated pipe used for experiments in Free-fall. The Crookes radiometer turns when the MFP is larger than the size of the vanes. The Crookes radiometer, also known as the light mill, consists of an airtight glass bulb containing a partial Vacuum.

Vacuum quality is subdivided into ranges according to the technology required to achieve it or measure it. These ranges do not have universally agreed definitions, but a typical distribution is as follows:^[20][21]

• Atmospheric pressure is variable but standardized at 101. Ultra high vacuum (UHV is the Vacuum regime characterised by Pressures lower than about 10−7 pascal or 100 nanopascals (~10−9 Outer space, often simply called space, comprises the relatively empty regions of the Universe outside the escape velocities of Celestial bodies. In Classical physics, free space is a concept of Electromagnetic theory, corresponding to a theoretically "perfect" Vacuum, and sometimes 325 kPa (760 Torr)
• Low vacuum, also called rough vacuum or coarse vacuum, is vacuum that can be achieved or measured with rudimentary equipment such as a vacuum cleaner and a liquid column manometer. A vacuum cleaner (in colloquial British English also hoover) is a device that uses an air Pump to create a partial Vacuum to Suck Many techniques have been developed for the measurement of Pressure and Vacuum.
• Medium vacuum is vacuum that can be achieved with a single pump, but is too low to measure with a liquid or mechanical manometer. It can be measured with a McLeod gauge, thermal gauge or a capacitive gauge.
• High vacuum is vacuum where the MFP of residual gases is longer than the size of the chamber or of the object under test. In Physics the mean free path of a particle is the average distance covered by a particle ( Photon, Atom or Molecule) between subsequent impacts High vacuum usually requires multi-stage pumping and ion gauge measurement. Some texts differentiate between high vacuum and very high vacuum.
• Ultra high vacuum requires baking the chamber to remove trace gases, and other special procedures. British and German standards define ultra high vacuum as pressures below 10^-6 Pa (10^-8 Torr). ^[22][23]
• Deep space is generally much more empty than any artificial vacuum that we can create. It may or may not meet the definition of high vacuum above, depending on what region of space and astronomical bodies are being considered. For example, the MFP of interplanetary space is smaller than the size of the solar system, but larger than small planets and moons. As a result, solar winds exhibit continuum flow on the scale of the solar system, but must be considered as a bombardment of particles with respect to the Earth and Moon.
• Perfect vacuum is an ideal state that cannot be obtained in a laboratory, nor can it be found in outer space. A laboratory (informally lab) is a facility that provides controlled conditions in which scientific Research, Experiments and

Examples

Measurement

Main article: Pressure measurement

Vacuum is measured in units of pressure. Outer space, often simply called space, comprises the relatively empty regions of the Universe outside the escape velocities of Celestial bodies. Intergalactic space is the physical space between galaxies. Generally free of dust and debris intergalactic space is very close to a total Vacuum. Many techniques have been developed for the measurement of Pressure and Vacuum. Pressure (symbol 'p' is the force per unit Area applied to an object in a direction perpendicular to the surface The SI unit of pressure is the pascal (symbol Pa), but vacuum is usually measured in torrs (symbol Torr), named for Torricelli, an early Italian physicist (1608 - 1647). The torr (symbol Torr) is a non- SI unit of Pressure defined as 1/760 of an atmosphere. A torr is equal to the displacement of a millimeter of mercury (mmHg) in a manometer with 1 torr equaling 133. The torr (symbol Torr) is a non- SI unit of Pressure defined as 1/760 of an atmosphere. Many techniques have been developed for the measurement of Pressure and Vacuum. 3223684 pascals above absolute zero pressure. Vacuum is often also measured using inches of mercury on the barometric scale or as a percentage of atmospheric pressure in bars or atmospheres. Inches of mercury, inHg or "Hg is a measuring unit for Pressure. History The first barometer is thought to have been built unintentionally by Gasparo Berti, sometime between 1640 and 1643 The bar (symbol bar) decibar (symbol dbar) and the millibar (symbol mbar, also mb are units of Pressure. The Standard atmosphere is an international reference pressure defined as 101325 Pa and formerly used as unit of Pressure (symbol atm Low vacuum is often measured in inches of mercury (inHg), millimeters of mercury (mmHg) or kilopascals (kPa) below atmospheric pressure. Inches of mercury, inHg or "Hg is a measuring unit for Pressure. The torr (symbol Torr) is a non- SI unit of Pressure defined as 1/760 of an atmosphere. "Below atmospheric" means that the absolute pressure is equal to the current atmospheric pressure (e. g. 29. 92 inHg) minus the vacuum pressure in the same units. Thus a vacuum of 26 inHg is equivalent to an absolute pressure of 4 inHg (29. 92 inHg - 26 inHg).

A glass McLeod gauge, drained of mercury

Many devices are used to measure the pressure in a vacuum, depending on what range of vacuum is needed. ^[26]

Hydrostatic gauges (such as the mercury column manometer) consist of a vertical column of liquid in a tube whose ends are exposed to different pressures. Many techniques have been developed for the measurement of Pressure and Vacuum. The column will rise or fall until its weight is in equilibrium with the pressure differential between the two ends of the tube. The simplest design is a closed-end U-shaped tube, one side of which is connected to the region of interest. Any fluid can be used, but mercury is preferred for its high density and low vapour pressure. Mercury (ˈmɜrkjʊri also called quicksilver or hydrargyrum, is a Chemical element with the symbol Hg ( Latinized hydrargyrum Simple hydrostatic gauges can measure pressures ranging from 1 Torr (100 Pa) to above atmospheric. An important variation is the McLeod gauge which isolates a known volume of vacuum and compresses it to multiply the height variation of the liquid column. A McLeod gauge is a scientific instrument to measure very low Pressures down to 10-7 Torr. The McLeod gauge can measure vacuums as high as 10⁻⁶ Torr (0. 1 mPa), which is the lowest direct measurement of pressure that is possible with current technology. Other vacuum gauges can measure lower pressures, but only indirectly by measurement of other pressure-controlled properties. These indirect measurements must be calibrated via a direct measurement, most commonly a McLeod gauge. ^[27]

Mechanical or elastic gauges depend on a Bourdon tube, diaphragm, or capsule, usually made of metal, which will change shape in response to the pressure of the region in question. A variation on this idea is the capacitance manometer, in which the diaphragm makes up a part of a capacitor. A change in pressure leads to the flexure of the diaphragm, which results in a change in capacitance. These gauges are effective from 10⁻³ Torr to 10⁻⁴ Torr.

Thermal conductivity gauges rely on the fact that the ability of a gas to conduct heat decreases with pressure. In this type of gauge, a wire filament is heated by running current through it. A thermocouple or Resistance Temperature Detector (RTD) can then be used to measure the temperature of the filament. In Electrical engineering and industry thermocouples are a widely used type of temperature sensor and can also be used as a means to convert thermal Potential Resistance thermometers, also called resistance temperature detectors ( RTD s are Temperature Sensors that exploit the predictable change in This temperature is dependent on the rate at which the filament loses heat to the surrounding gas, and therefore on the thermal conductivity. A common variant is the Pirani gauge which uses a single platimum filament as both the heated element and RTD. The Pirani gauge is a robust Thermal conductivity gauge used for the measurement of the pressures in vacuum systems These gauges are accurate from 10 Torr to 10⁻³ Torr, but they are sensitive to the chemical composition of the gases being measured.

Ion gauges are used in ultrahigh vacuum. Many techniques have been developed for the measurement of Pressure and Vacuum. They come in two types: hot cathode and cold cathode. In the hot cathode version an electrically heated filament produces an electron beam. The hot filament Ionization gauge, sometimes called a hot filament gauge or hot cathode gauge, is the most widely used vacuum (negative pressure measuring The electrons travel through the gauge and ionize gas molecules around them. The resulting ions are collected at a negative electrode. The current depends on the number of ions, which depends on the pressure in the gauge. Hot cathode gauges are accurate from 10⁻³ Torr to 10⁻¹⁰ Torr. The principle behind cold cathode version is the same, except that electrons are produced in a discharge created by a high voltage electrical discharge. A cold cathode is an element used within some Nixie tubes Gas discharge lamps Gas filled tubes and Vacuum tubes Cold cathodes do not Cold cathode gauges are accurate from 10⁻² Torr to 10⁻⁹ Torr. Ionization gauge calibration is very sensitive to construction geometry, chemical composition of gases being measured, corrosion and surface deposits. Their calibration can be invalidated by activation at atmospheric pressure or low vacuum. The composition of gases at high vacuums will usually be unpredictable, so a mass spectrometer must be used in conjunction with the ionization gauge for accurate measurement. ^[28]

Properties

As a vacuum approaches perfection, several properties of space approach non-zero values. The ideal values which would be attained in an ideal vacuum are called free space constants. Some common ones are as follows:

• The speed of light c approaches the speed of light in vacuum c₀ 299,792,458 m/s, but is always slower
• Index of refraction n approaches 1. The refractive index (or index of Refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves is reduced inside the medium 0, but is always higher
• Electric permittivity (ε) approaches the electric constant ε₀ ≈ 8. Permittivity is a Physical quantity that describes how an Electric field affects and is affected by a Dielectric medium and is determined by the ability Vacuum permittivity, referred to by international standards organizations as the electric constant, and denoted by the symbol ε0 is a fundamental Physical 8541878176x10^-12 farads per meter (F/m). This is about the capacitance unit of measure For the charge unit see Faraday (unit. The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International
• Magnetic permeability (μ) approaches the magnetic constant μ₀ 4π×10⁻⁷ N/A². In Electromagnetism, permeability is the degree of Magnetization of a material that responds linearly to an applied Magnetic field. The vacuum permeability, referred to by international standards organizations as the magnetic constant, and denoted by the symbol μ 0 (also
• Characteristic impedance (η) approaches the characteristic impedance of vacuum Z₀ ≈ 376. The characteristic impedance or surge impedance of a uniform Transmission line, usually written Z_0 is the ratio of the amplitudes of a single Impedance of Free Space (also known as Z_0 is a Canadian IDM and Electronica group 73 Ω.

Notes

See also

• Vacuum state
• Vacuum energy
• QCD vacuum
• Zero-point field
• Zero-point energy
• Free space
• Decay of the vacuum (Pair production)
• Helium mass spectrometer - technical instrumentation to detect a vacuum leak
• Engine vacuum
• Mean free path
• Negative pressure
• Rarefaction - reduction of a medium's density
• Suction - creation of a partial vacuum
• Ultra high vacuum
• Vacuum cementing - natural process of solidifying homogenous "dust" in vacuum
• Vacuum engineering
• Vacuum angle
• Vacuum flange
• Vacuum deposition - process of depositing atoms and molecules in a sub-atmospheric pressure environment
• Joining materials
• Vacuum tube

External links

• The Foundations of Vacuum Coating Technology
• American Vacuum Society
• Journal of Vacuum Science and Technology A
• Journal of Vacuum Science and Technology B
• FAQ on explosive decompression and vacuum exposure. In Quantum field theory, the vacuum state (also called the vacuum) is the Quantum state with the lowest possible Energy. Vacuum energy is an underlying background Energy that exists in Space even when devoid of Matter (known as Free space) The QCD vacuum is the Vacuum state of Quantum chromodynamics (QCD In Quantum field theory, the zero-point field is the lowest energy state of a field, i In Physics, the zero-point energy is the lowest possible Energy that a Quantum mechanical Physical system may possess and is the energy of the In Classical physics, free space is a concept of Electromagnetic theory, corresponding to a theoretically "perfect" Vacuum, and sometimes See also Electron-positron annihilation Meitner–Hupfeld effect Pair instability supernova See also Electron-positron annihilation Meitner–Hupfeld effect Pair instability supernova A helium mass spectrometer is an instrument commonly used to detect and locate small leaks Manifold vacuum, or engine Vacuum in an internal combustion engine is the difference in air pressure between the engine's intake manifold and In Physics the mean free path of a particle is the average distance covered by a particle ( Photon, Atom or Molecule) between subsequent impacts Rarefaction is the reduction of a medium's density or the opposite of compression. Suction is the flow of a fluid into a partial Vacuum, or region of low pressure Ultra high vacuum (UHV is the Vacuum regime characterised by Pressures lower than about 10−7 pascal or 100 nanopascals (~10−9 Vacuum cementing or vacuum welding is the natural process of solidifying small objects in a hard Vacuum. Vacuum engineering deals with technological processes and equipment that use Vacuum to achieve better results than those run under atmospheric Pressure. In quantum gauge theories, in the Hamiltonian formulation the Wave function is a Functional of the gauge Connection A and matter fields φ A vacuum flange is a Flange at the end of a Tube used to connect Vacuum chambers tubing and Vacuum pumps to each other Vacuum deposition or vacuum coating is a family of processes used to deposit layers atom-by-atom or molecule-by-molecule at sub- Atmospheric pressure ( Vacuum Brazing is a joining process whereby a Filler metal or Alloy is heated to melting temperature above - or by the traditional definition in the United States This article is about the electronic device not an evacuated pipe used for experiments in Free-fall.
• Discussion of the effects on humans of exposure to hard vacuum.
• Vacuum Energy in High Energy Physics
• Vacuum, Production of Space
• VIDEO on the nature of vacuum by Canadian astrophysicist Doctor P
• "Much Ado About Nothing" by Professor John D. Barrow, Gresham College