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 engineering. 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 In archaeology a posthole or post-hole is a cut feature used to hold a surface timber or stone. They are usually much deeper than they are wide; however, truncation may not make this apparent. Although the remains of the timber may survive, most ...

s made for securing an object, are usually made through the process of

digging Digging, also referred to as excavation, is the process of using some implement such as claws, hands, manual tools or heavy equipment, to remove material from a solid surface, usually soil, sand or rock on the surface of Earth. Digging is actu ...

. Unintentional holes in an object are often a sign of

damage Damage is any change in a thing, often a physical object, that degrades it away from its initial state. It can broadly be defined as "changes introduced into a system that adversely affect its current or future performance".Farrar, C.R., Sohn, H., ...

. 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 locally also known as ''vrtače'' and shakeholes, and to openi ...

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 which is the lack of an electron at a position where one could exist in an atom or atomic lattice. Since in a normal atom or ...

, which is a position in an

atom Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons. Every solid, liquid, gas, ...

or atomic lattice where an

electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no ...

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 ob ...

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

sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

. The deepest hole on Earth is the man-made

Kola Superdeep Borehole The Kola Superdeep Borehole (russian: Кольская сверхглубокая скважина, translit=Kol'skaya sverkhglubokaya skvazhina) SG-3 is the result of a scientific drilling project of the Soviet Union in the Pechengsky District ...

, 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

In mathematics, holes are examined in a number of ways. One of these is in

homology Homology may refer to: Sciences Biology *Homology (biology), any characteristic of biological organisms that is derived from a common ancestor * Sequence homology, biological homology between DNA, RNA, or protein sequences *Homologous chrom ...

, 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 geometrical space in which closeness is defined but cannot necessarily be measured by a numeric distance. More specifically, a topological space is a set whose elements are called po ...

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 invariants that classify topological spaces up to homeomorphism, though usually most classify ...

, and homology was originally a rigorous mathematical method for defining and categorizing holes in a mathematical object called a manifold. 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: 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 () is a geometrical object that is a three-dimensional analogue to a two-dimensional circle. A sphere is the set of points that are all at the same distance from a given point in three-dimensional space.. That given point is th ...

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 ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

of a connected,

orientable In mathematics, orientability is a property of some topological spaces such as real vector spaces, Euclidean spaces, surfaces, and more generally manifolds that allows a consistent definition of "clockwise" and "counterclockwise". A space i ...

is an

integer An integer is the number zero (), a positive natural number (, , , etc.) or a negative integer with a minus sign ( −1, −2, −3, etc.). The negative numbers are the additive inverses of the corresponding positive numbers. In the languag ...

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 manifold 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 particles in "ordinary" matter. Antimatter occurs in natural processes like cosmic ray collisions and some types of radioac ...

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 positrons (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 transistors 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, Gramicidin A, a Peptide, polypeptide with a helical shape, has been described as a portable hole. When it forms a Dimer (chemistry), dimer, it can embed itself in Lipid bilayer, cellular bilayer membranes and form a hole through which water molecules can pass.

Blind and through

In engineering, machining, and Machine tools, 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 reamer, reamed, drilled, or Milling machine, 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. Tap and die, 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 Screw thread, 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 Taps and Dies, tapping, especially with bottom taps # Threading (manufacturing)#Single-point threading, 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 (manufacturing), 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, Numerical control, 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 (CNC) moves a milling cutter in the correct helical path for a given thread, milling the thread. At least two U.S. tool manufacturers have manufactured tools for Threading (manufacturing)#Thread milling, 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 preventers. 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, a mounting scheme involving the use of lead (electronics), leads on the components that are inserted into holes drilled in printed circuit boards (PCB) and soldering, 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 or a very thin layer of metal. Similar holes made by other means are also often called pinholes. Pinholes may be intentionally made for various reasons. For example, in optics pinhole (optics), pinholes are used as apertures to select certain rays of light. This is used in pinhole cameras to form an image without the use of a lens (optics), lens. Pinholes on produce 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 Insulator (electricity), insulator layer coating the circuit can cause the circuit to fail. Therefore, "[t]o 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_(perception) , 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 basis.

In Culture and as a Metaphor

An example of the use of holes in popular culture can be found in the Beatles lyric from the song, "A Day in the Life", from their 1967 album ''Sgt. Pepper's Lonely Hearts Club Band'': The reference to A Day in the Life#"4,000 holes", 4,000 holes was written by John Lennon, 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 games 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, as in the case of the Japanese concept of Ma_(negative_space), 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 holes. 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 symbol for HOLE, U+1F573, was approved in 2014 as part of the Miscellaneous Symbols and Pictographs 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. 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 view of an electronic circuit board showing component lead holes (gold-plated) with through-hole plating. Ovation guitar sound holes horizontal.jpg, Sound holes precisely carved into the surface of a guitar can facilitate a desired sound. Well, if you know of a better 'ole, go to it.jpg, First World War cartoon ''Well, if you knows of a better 'ole, go to it'' by Bruce Bairnsfather, 1915. Hole in berlin wall.jpg, A hole in the Berlin wall, 2019. Single-hole-punch.jpg, A Hole punch, handheld hole punch, used to make holes in paper and similar materials.

References

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