A hole is an opening in or through a particular medium, usually a

solid Solid is a state of matter where molecules are closely packed and can not slide past each other. Solids resist compression, expansion, or external forces that would alter its shape, with the degree to which they are resisted dependent upon the ...

body. Holes occur through natural and artificial processes, and may be useful for various purposes, or may represent a problem needing to be addressed in many fields of

engineering Engineering is the practice of using natural science, mathematics, and the engineering design process to Problem solving#Engineering, solve problems within technology, increase efficiency and productivity, and improve Systems engineering, s ...

. Depending on the material and the placement, a hole may be an indentation in a

surface A surface, as the term is most generally used, is the outermost or uppermost layer of a physical object or space. It is the portion or region of the object that can first be perceived by an observer using the senses of sight and touch, and is ...

(such as a hole in the ground), or may pass completely through that surface (such as a hole created by a hole puncher in a piece of paper).

Types

Holes can occur for a number of reasons, including natural processes and intentional actions by humans or animals. Holes in the ground that are made intentionally, such as holes made while searching for food, for replanting trees, or

posthole This page is a glossary of archaeology, the study of the human past from material remains. A B C D E F ...

s made for securing an object, are usually made through the process of digging. Unintentional holes in an object are often a sign of damage. Potholes and

sinkhole A sinkhole is a depression or hole in the ground caused by some form of collapse of the surface layer. The term is sometimes used to refer to doline, enclosed depressions that are also known as shakeholes, and to openings where surface water ...

s can damage human settlements. Holes can occur in a wide variety of materials, and at a wide range of scales. The smallest holes observable by humans include pinholes and

perforation A perforation is a small hole in a thin material or web. There is usually more than one perforation in an organized fashion, where all of the holes collectively are called a ''perforation''. The process of creating perforations is called perfor ...

s, but the smallest phenomenon described as a hole is an

electron hole In physics, chemistry, and electronic engineering, an electron hole (often simply called a hole) is a quasiparticle denoting the lack of an electron at a position where one could exist in an atom or crystal structure, atomic lattice. Since in ...

, which is a position in an

atom Atoms are the basic particles of the chemical elements. An atom consists of a atomic nucleus, nucleus of protons and generally neutrons, surrounded by an electromagnetically bound swarm of electrons. The chemical elements are distinguished fr ...

or atomic lattice where an

electron The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...

is missing. The largest phenomenon described as a hole is a

supermassive black hole A supermassive black hole (SMBH or sometimes SBH) is the largest type of black hole, with its mass being on the order of hundreds of thousands, or millions to billions, of times the mass of the Sun (). Black holes are a class of astronomical ...

, an astronomical object which can be billions of times more massive than Earth's

sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

. The deepest hole on Earth is the man-made

Kola Superdeep Borehole The Kola Superdeep Borehole SG-3 () is the deepest human-made hole on Earth (since 1979), which attained maximum true vertical depth of in 1989. It is the result of a scientific drilling effort to penetrate as deeply as possible into the ...

, with a true vertical drill-depth of more than 7.5 miles (12 kilometers), which is only a fraction of the nearly 4,000 mile (6,400 kilometer) distance to the center of the Earth.

In mathematics

mathematics Mathematics is a field of study that discovers and organizes methods, Mathematical theory, theories and theorems that are developed and Mathematical proof, proved for the needs of empirical sciences and mathematics itself. There are many ar ...

, holes are examined in a number of ways. One of these is in homology, which is a general way of associating certain algebraic objects to other mathematical objects such as

topological space In mathematics, a topological space is, roughly speaking, a Geometry, geometrical space in which Closeness (mathematics), closeness is defined but cannot necessarily be measured by a numeric Distance (mathematics), distance. More specifically, a to ...

s. Homology groups were originally defined in

algebraic topology Algebraic topology is a branch of mathematics that uses tools from abstract algebra to study topological spaces. The basic goal is to find algebraic invariant (mathematics), invariants that classification theorem, classify topological spaces up t ...

, and homology was originally a rigorous mathematical method for defining and categorizing holes in a mathematical object called a

manifold In mathematics, a manifold is a topological space that locally resembles Euclidean space near each point. More precisely, an n-dimensional manifold, or ''n-manifold'' for short, is a topological space with the property that each point has a N ...

. The initial motivation for defining homology groups was the observation that two shapes can be distinguished by examining their holes. For instance, a circle is not a disk because the circle has a hole through it while the disk is solid, and the ordinary sphere is not a circle because the sphere encloses a two-dimensional hole while the circle encloses a one-dimensional hole. Because a hole is immaterial, it is not immediately obvious how to define one or distinguish it from others. Another is the notion of

homotopy group In mathematics, homotopy groups are used in algebraic topology to classify topological spaces. The first and simplest homotopy group is the fundamental group, denoted \pi_1(X), which records information about loops in a space. Intuitively, homo ...

: these are invariants of a topological space that, when non-trivial (one also says in this case that the space is not

k-connected In algebraic topology, homotopical connectivity is a property describing a topological space based on the dimension of its holes. In general, low homotopical connectivity indicates that the space has at least one low-dimensional hole. The concep ...

), detect the presence of "holes" in the sense that the space contains a

sphere A sphere (from Ancient Greek, Greek , ) is a surface (mathematics), surface analogous to the circle, a curve. In solid geometry, a sphere is the Locus (mathematics), set of points that are all at the same distance from a given point in three ...

that cannot be contracted to a point. The term of hole is often used informally when discussing these objects. For surfaces a notion closer to the intuitive meaning exists: the

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of a connected, orientable

is an

integer An integer is the number zero (0), a positive natural number (1, 2, 3, ...), or the negation of a positive natural number (−1, −2, −3, ...). The negations or additive inverses of the positive natural numbers are referred to as negative in ...

representing the maximum number of cuttings along non-intersecting closed simple

curve In mathematics, a curve (also called a curved line in older texts) is an object similar to a line, but that does not have to be straight. Intuitively, a curve may be thought of as the trace left by a moving point. This is the definition that ...

s without rendering the resultant

disconnected. In layman's terms, it is exactly the number of "holes" the surface has, when represented as a submanifold in 3-space.

In physics

In physics,

antimatter In modern physics, antimatter is defined as matter composed of the antiparticles (or "partners") of the corresponding subatomic particle, particles in "ordinary" matter, and can be thought of as matter with reversed charge and parity, or go ...

is pervasively described as a hole, a location that, when brought together with ordinary matter to fill the hole, results in both the hole and the matter cancelling each-other out. This is analogous to patching a pothole with asphalt, or filling a bubble below the surface of water with an equal amount of water to cancel it out. The most direct example is the

; a fairly general theoretical description is provided by the Dirac sea, which treats

positron The positron or antielectron is the particle with an electric charge of +1''elementary charge, e'', a Spin (physics), spin of 1/2 (the same as the electron), and the same Electron rest mass, mass as an electron. It is the antiparticle (antimatt ...

s (or anti-particles in general) as holes. Holes provide one of the two primary forms of conduction in a semi-conductor, that is, the material from which

transistor A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch electrical signals and electric power, power. It is one of the basic building blocks of modern electronics. It is composed of semicondu ...

s are made; without holes, current could not flow, and transistors turn on and off by enabling or disabling the creation of holes.

In biology

Animal bodies tend to contain specialized holes which serve various biological functions, such as the intake of oxygen or food, the excretion of waste, and the intake or expulsion of other fluids for reproductive purposes. In some simple animals, a single hole serves all of these purposes. The formation of holes is a significant event in the development of an animal: Gramicidin A, a

polypeptide Peptides are short chains of amino acids linked by peptide bonds. A polypeptide is a longer, continuous, unbranched peptide chain. Polypeptides that have a molecular mass of 10,000 Da or more are called proteins. Chains of fewer than twenty ...

with a helical shape, has been described as a portable hole. When it forms a dimer, it can embed itself in cellular bilayer membranes and form a hole through which water molecules can pass.

Blind and through

machining Machining is a manufacturing process where a desired shape or part is created using the controlled removal of material, most often metal, from a larger piece of raw material by cutting. Machining is a form of subtractive manufacturing, which util ...

, and tooling, a hole may be a blind hole or a through hole (also called a thru-hole or clearance hole). A blind hole is a hole that is reamed,

drill A drill is a tool used for making round holes or driving fasteners. It is fitted with a drill bit for making holes, or a screwdriver bit for securing fasteners. Historically, they were powered by hand, and later mains power, but cordless b ...

ed, or milled to a specified depth without breaking through to the other side of the workpiece. A through hole is a hole that is made to go completely through the material of an object. In other words, a through hole is a hole that goes all the way through something. Taps used for through holes are generally tapered since it will tap faster and the chips will be released when the tap exits the hole. The etymology of the ''blind'' hole is that it is not possible to see through it. It may also refer to any feature that is taken to a specific depth, more specifically referring to internally threaded hole (tapped holes). Not considering the drill point, the depth of the blind hole, conventionally, may be slightly deeper than that of the threaded depth. There are three accepted methods of threading blind holes: # Conventional

tapping Tapping is a playing technique that can be used on any stringed instrument, but which is most commonly used on guitar. The technique involves a string being fretted and set into vibration as part of a single motion. This is in contrast to stand ...

, especially with bottom taps # Single-point threading, where the workpiece is rotated, and a pointed cutting tool is fed into the workpiece at the same rate as the pitch of the internal thread. Single-pointing inside a blind hole, like boring inside one, is inherently more challenging than doing so in a through hole. This was especially true in the era when manual machining was the only method of control. Today, CNC makes these tasks less stressful, but nevertheless still more challenging than with through holes. # Helical interpolation, where the workpiece remains stationary and

Computer Numerical Control Computer numerical control (CNC) or CNC machining is the Automation, automated control of machine tools by a computer. It is an evolution of numerical control (NC), where machine tools are directly managed by data storage media such as punched ...

(CNC) moves a

milling cutter Milling cutters are cutting tools typically used in milling machines or machining centres to perform milling operations (and occasionally in other machine tools). They remove material by their movement within the machine (e.g., a ball nose mill) ...

in the correct helical path for a given thread, milling the thread. At least two U.S. tool manufacturers have manufactured tools for thread milling in blind holes: Ingersoll Cutting Tools of Rockford, Illinois, and Tooling Systems of Houston, Texas, who introduced the Thread Mill in 1977, a device that milled large internal threads in the blind holes of oil well

blowout preventer A blowout preventer (BOP) (pronounced B-O-P) is a specialized valve or similar mechanical device, used to seal, control and monitor oil well, oil and gas wells to prevent Blowout (well drilling), blowouts, the uncontrolled release of crude oil ...

s. Today many CNC milling machines can run such a thread milling cycle (see a video of such a cut in the "External links" section). One use of through holes in electronics is with

through-hole technology In electronics, through-hole technology (also spelled "thru-hole") is a manufacturing scheme in which leads on the components are inserted through holes drilled in printed circuit boards (PCB) and soldered to pads on the opposite side, eithe ...

, a mounting scheme involving the use of

lead Lead () is a chemical element; it has Chemical symbol, symbol Pb (from Latin ) and atomic number 82. It is a Heavy metal (elements), heavy metal that is density, denser than most common materials. Lead is Mohs scale, soft and Ductility, malleabl ...

s on the components that are inserted into holes drilled in

printed circuit board A printed circuit board (PCB), also called printed wiring board (PWB), is a Lamination, laminated sandwich structure of electrical conduction, conductive and Insulator (electricity), insulating layers, each with a pattern of traces, planes ...

s (PCB) and soldered to pads on the opposite side either by manual assembly (hand placement) or by the use of automated insertion mount machines.

Pinholes

A pinhole is a small hole, usually made by pressing a thin, pointed object such as a pin through an easily penetrated material such as a

fabric Textile is an umbrella term that includes various fiber-based materials, including fibers, yarns, filaments, threads, and different types of fabric. At first, the word "textiles" only referred to woven fabrics. However, weaving is no ...

or a very thin layer of

metal A metal () is a material that, when polished or fractured, shows a lustrous appearance, and conducts electrical resistivity and conductivity, electricity and thermal conductivity, heat relatively well. These properties are all associated wit ...

. Similar holes made by other means are also often called pinholes. Pinholes may be intentionally made for various reasons. For example, in

optics Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of optical instruments, instruments that use or Photodetector, detect it. Optics usually describes t ...

pinhole A hole is an opening in or through a particular medium, usually a solid body. Holes occur through natural and artificial processes, and may be useful for various purposes, or may represent a problem needing to be addressed in many fields of e ...

s are used as

aperture In optics, the aperture of an optical system (including a system consisting of a single lens) is the hole or opening that primarily limits light propagated through the system. More specifically, the entrance pupil as the front side image o ...

s to select certain rays of light. This is used in

pinhole camera A pinhole camera is a simple camera without a lens but with a tiny aperture (the so-called ''Pinhole (optics), pinhole'')—effectively a light-proof box with a small hole in one side. Light from a scene passes through the aperture and projects a ...

s to form an image without the use of a

lens A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements'') ...

. Pinholes on

produce In American English, produce generally refers to wikt:fresh, fresh List of culinary fruits, fruits and Vegetable, vegetables intended to be Eating, eaten by humans, although other food products such as Dairy product, dairy products or Nut (foo ...

packaging have been used to control the atmosphere and relative humidity within the packaging. In many fields, pinholes are a harmful side effect of manufacturing processes. For example, in the assembly of microcircuits, pinholes in the

dielectric In electromagnetism, a dielectric (or dielectric medium) is an Insulator (electricity), electrical insulator that can be Polarisability, polarised by an applied electric field. When a dielectric material is placed in an electric field, electric ...

insulator layer coating the circuit can cause the circuit to fail. Therefore, " avoid pinholes that might protrude through the entire thickness of the dielectric layer, it is a common practice to screen several layers of dielectric with drying and firing after each screening", thereby preventing the pinholes from becoming continuous.

Philosophy and psychology

It has been noted that holes occupy an unusual ontological position in philosophy, as people tend to refer to them as tangible and countable objects, when in fact they are the absence of something in another object. In the study of visual perception, a hole is a special case of figure-ground, because the ground region is entirely surrounded by the figure. For a region to be perceived as a visual hole three factors are important: depth factors indicating that the enclosed region lies behind; grouping between the enclosed region and the surround; and figural factors (for example symmetry, convexity, or familiarity) that lead to the perception of a figure rather than a hole. There is a debate on whether holes are special and whether they are perceived as having their own shape. They may be special in some cases, but not in the ownership of the contours. Some people have an aversion to the sight of irregular patterns or clusters of small holes, a condition called trypophobia. Researchers hypothesize that this is the result of a biological revulsion that associates trypophobic shapes with danger or disease, and may therefore have an

evolutionary Evolution is the change in the heritable characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, resulting in certa ...

basis.

In culture and as a metaphor

An example of the use of holes in popular culture can be found in the

Beatles The Beatles were an English Rock music, rock band formed in Liverpool in 1960. The core lineup of the band comprised John Lennon, Paul McCartney, George Harrison and Ringo Starr. They are widely regarded as the Cultural impact of the Beatle ...

lyric from the song, " A Day in the Life", from their 1967 album ''

Sgt. Pepper's Lonely Hearts Club Band ''Sgt. Pepper's Lonely Hearts Club Band'' (often referred to simply as ''Sgt. Pepper'') is the eighth studio album by the English rock band the Beatles. Released on 26May 1967, ''Sgt. Pepper'' is regarded by musicologists as an early concept ...

'': The reference to 4,000 holes was written by

John Lennon John Winston Ono Lennon (born John Winston Lennon; 9 October 19408 December 1980) was an English singer-songwriter, musician and activist. He gained global fame as the founder, co-lead vocalist and rhythm guitarist of the Beatles. Lennon's ...

, and inspired by a ''Far & Near'' news brief from the same 17 January edition of the ''Daily Mail'', which had also provided inspiration for previous verses of the song. Under the headline "The holes in our roads", the brief stated: "There are 4,000 holes in the road in Blackburn, Lancashire, or one twenty-sixth of a hole per person, according to a council survey. If Blackburn is typical, there are two million holes in Britain's roads and 300,000 in London". Holes have also been described as ontological parasites because they can only exist as aspects of another object. The psychological concept of a hole as a physical object is taken to its logical extreme in the fictional concept of a portable hole, exemplified in

role-playing game A role-playing game (sometimes spelled roleplaying game, or abbreviated as RPG) is a game in which players assume the roles of player character, characters in a fictional Setting (narrative), setting. Players take responsibility for acting out ...

s and characterized as a "hole" that a person can carry with them, keep things in, and enter themselves as needed. In art holes are sometimes referred to as

negative space In art and design, negative space or negative volume is the empty space around and between the subject(s) of an image. In graphic design this is known as white space. Negative space may be most evident when the space around a subject, not th ...

, as in the case of the Japanese concept of Ma. Holes can also be referenced metaphorically as existing in non-tangible things. For example, a person who provides an account of an event that lacks important details can be said to have "holes in their story", and a fictional work with unexplained narrative elements can be said to have

plot hole In fiction, a plot hole, plothole, or plot error is an inconsistency in a storyline that goes against the flow of logic established by the story's plot. Plot holes are usually created unintentionally, often as a result of editing or the writers ...

s. A person who has suffered loss is often referred to as having a "hole in their heart". The concept of a "God-shaped hole" occurs in religious discourse:

Unicode

The

Unicode Unicode or ''The Unicode Standard'' or TUS is a character encoding standard maintained by the Unicode Consortium designed to support the use of text in all of the world's writing systems that can be digitized. Version 16.0 defines 154,998 Char ...

symbol for HOLE, U+1F573, was approved in 2014 as part of the

Miscellaneous Symbols and Pictographs Miscellaneous Symbols and Pictographs is a Unicode block containing meteorological and astronomical symbols, emoji characters largely for compatibility with Japanese telephone carriers' implementations of Shift JIS, and characters originally from ...

chart in Unicode 7.0, and was part of Emoji 1.0, published in 2015. As pictorial representations for emoji are platform-dependent, Emojipedia shows images of the hole symbol as depicted on various platforms.

Gallery

LiščíNoraVsž1.JPG, Hole in the ground dug by a fox as its burrow. Bangalay-bird-hollow.jpg, Hole in a Eucalyptus tree used as a nest by Lorikeets. Two Arecaceae in the fields viewed through a hole in a tree trunk in Laos at sunrise.jpg, Trees visible through a large hole in a tree trunk in Laos. Trees and clouds with a hole, Karawanks, Slovenia.jpg, Hole in a cloud over Karawanks, Slovenia. 靴下にデカい穴があいてた.jpg, Sock with a hole in it, through which the

foot The foot (: feet) is an anatomical structure found in many vertebrates. It is the terminal portion of a limb which bears weight and allows locomotion. In many animals with feet, the foot is an organ at the terminal part of the leg made up o ...

is visible. BH LMC.png, Simulated view of a black hole in front of the Large Magellanic Cloud. Black hole - Messier 87 crop max res.jpg, First image of a black hole by the Event Horizon Telescope. Plated-through_holes_on_an_electronic_circuit_board.jpg,

Close-up A close-up or closeup in filmmaking, television production A television show, TV program (), or simply a TV show, is the general reference to any content produced for viewing on a television set that is broadcast via over-the-air, s ...

view of a

showing component lead holes (gold-plated) with through-hole plating (

Through-hole technology In electronics, through-hole technology (also spelled "thru-hole") is a manufacturing scheme in which leads on the components are inserted through holes drilled in printed circuit boards (PCB) and soldered to pads on the opposite side, eithe ...

). Ovation guitar sound holes horizontal.jpg, Sound holes precisely carved into the surface of a

guitar The guitar is a stringed musical instrument that is usually fretted (with Fretless guitar, some exceptions) and typically has six or Twelve-string guitar, twelve strings. It is usually held flat against the player's body and played by strumming ...

can facilitate a desired sound. Well, if you know of a better 'ole, go to it.jpg,

First World War World War I or the First World War (28 July 1914 – 11 November 1918), also known as the Great War, was a World war, global conflict between two coalitions: the Allies of World War I, Allies (or Entente) and the Central Powers. Fighting to ...

cartoon ''Well, if you knows of a better 'ole, go to it'' by

Bruce Bairnsfather Captain Charles Bruce Bairnsfather (9 July 188729 September 1959) was a prominent British humour, humorist and cartoonist. His best-known cartoon character is Old Bill (comics), Old Bill. Bill and his pals Bert and Alf featured in Bairnsfather's ...

, 1915. Hole in berlin wall.jpg, A hole in the

Berlin Wall The Berlin Wall (, ) was a guarded concrete Separation barrier, barrier that encircled West Berlin from 1961 to 1989, separating it from East Berlin and the East Germany, German Democratic Republic (GDR; East Germany). Construction of the B ...

, 2019. Single-hole-punch.jpg, A handheld hole punch, used to make holes in paper and similar materials.

References

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, location=Cambridge , isbn=978-0-52137095-0 , edition=2nd , author-last1=Horowitz , author-first1=Paul , author-last2=Hill , author-first2=Winfield , url-access=registration , url=https://archive.org/details/artofelectronics00horo What is a Pinhole Camera?
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LIFE Life, also known as biota, refers to matter that has biological processes, such as Cell signaling, signaling and self-sustaining processes. It is defined descriptively by the capacity for homeostasis, Structure#Biological, organisation, met ...

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