title: Electromagnetic radiation

text: Electromagnetic waves are emitted by electrically charged particles undergoing acceleration, and these waves can subsequently interact with other charged particles, exerting force on them. EM waves carry energy, momentum and angular momentum away from their source particle and can impart those quantities to matter with which they interact. Electromagnetic radiation is associated with those EM waves that are free to propagate themselves ("radiate") without the continuing influence of the moving charges that produced them, because they have achieved sufficient distance from those charges. Thus, EMR is sometimes referred to as the far field. In this language, the near field refers to EM fields near the charges and current that directly produced them, specifically electromagnetic induction and electrostatic induction phenomena.


title: Electromagnetic radiation

text: In quantum mechanics, an alternate way of viewing EMR is that it consists of photons, uncharged elementary particles with zero rest mass which are the quanta of the electromagnetic field, responsible for all electromagnetic interactions. Quantum electrodynamics is the theory of how EMR interacts with matter on an atomic level. Quantum effects provide additional sources of EMR, such as the transition of electrons to lower energy levels in an atom and black-body radiation. The energy of an individual photon is quantized and is greater for photons of higher frequency. This relationship is given by Planck's equation "E" = "hf", where "E" is the energy per photon, "f" is the frequency of the photon, and "h" is Planck's constant. A single gamma ray photon, for example, might carry ~100,000 times the energy of a single photon of visible light.


title: Electromagnetic radiation

text: The effects of EMR upon chemical compounds and biological organisms depend both upon the radiation's power and its frequency. EMR of visible or lower frequencies (i.e., visible light, infrared, microwaves, and radio waves) is called "non-ionizing radiation", because its photons do not individually have enough energy to ionize atoms or molecules, or break chemical bonds. The effects of these radiations on chemical systems and living tissue are caused primarily by heating effects from the combined energy transfer of many photons. In contrast, high frequency ultraviolet, X-rays and gamma rays are called "ionizing radiation", since individual photons of such high frequency have enough energy to ionize molecules or break chemical bonds. These radiations have the ability to cause chemical reactions and damage living cells beyond that resulting from simple heating, and can be a health hazard.


title: Electromagnetic radiation

text: James Clerk Maxwell derived a wave form of the electric and magnetic equations, thus uncovering the wave-like nature of electric and magnetic fields and their symmetry. Because the speed of EM waves predicted by the wave equation coincided with the measured speed of light, Maxwell concluded that light itself is an EM wave. Maxwell's equations were confirmed by Heinrich Hertz through experiments with radio waves.


title: Electromagnetic radiation

text: Maxwell's equations established that some charges and currents ("sources") produce a local type of electromagnetic field near them that does "not" have the behaviour of EMR. Currents directly produce a magnetic field, but it is of a magnetic dipole type that dies out with distance from the current. In a similar manner, moving charges pushed apart in a conductor by a changing electrical potential (such as in an antenna) produce an electric dipole type electrical field, but this also declines with distance. These fields make up the near-field near the EMR source. Neither of these behaviours are responsible for EM radiation. Instead, they cause electromagnetic field behaviour that only efficiently transfers power to a receiver very close to the source, such as the magnetic induction inside a transformer, or the feedback behaviour that happens close to the coil of a metal detector. Typically, near-fields have a powerful effect on their own sources, causing an increased "load" (decreased electrical reactance) in the source or transmitter, whenever energy is withdrawn from the EM field by a receiver. Otherwise, these fields do not "propagate" freely out into space, carrying their energy away without distance-limit, but rather oscillate, returning their energy to the transmitter if it is not received by a receiver.


title: Electromagnetic radiation

text: By contrast, the EM far-field is composed of "radiation" that is free of the transmitter in the sense that (unlike the case in an electrical transformer) the transmitter requires the same power to send these changes in the fields out, whether the signal is immediately picked up or not. This distant part of the electromagnetic field "is" "electromagnetic radiation" (also called the far-field). The far-fields propagate (radiate) without allowing the transmitter to affect them. This causes them to be independent in the sense that their existence and their energy, after they have left the transmitter, is completely independent of both transmitter and receiver. Due to conservation of energy, the amount of power passing through any spherical surface drawn around the source is the same. Because such a surface has an area proportional to the square of its distance from the source, the power density of EM radiation always decreases with the inverse square of the distance from the source; this is called the inverse-square law. This is in contrast to dipole parts of the EM field close to the source (the near-field), which vary in power according to an inverse cube power law, and thus do "not" transport a conserved amount of energy over distances, but instead fade with distance, with its energy (as noted) rapidly returning to the transmitter or absorbed by a nearby receiver (such as a transformer secondary coil).


title: Electromagnetic radiation

text: The far-field (EMR) depends on a different mechanism for its production than the near-field, and upon different terms in Maxwell's equations. Whereas the magnetic part of the near-field is due to currents in the source, the magnetic field in EMR is due only to the local change in the electric field. In a similar way, while the electric field in the near-field is due directly to the charges and charge-separation in the source, the electric field in EMR is due to a change in the local magnetic field. Both processes for producing electric and magnetic EMR fields have a different dependence on distance than do near-field dipole electric and magnetic fields. That is why the EMR type of EM field becomes dominant in power "far" from sources. The term "far from sources" refers to how far from the source (moving at the speed of light) any portion of the outward-moving EM field is located, by the time that source currents are changed by the varying source potential, and the source has therefore begun to generate an outwardly moving EM field of a different phase.


title: Electromagnetic radiation

text: A more compact view of EMR is that the far-field that composes EMR is generally that part of the EM field that has traveled sufficient distance from the source, that it has become completely disconnected from any feedback to the charges and currents that were originally responsible for it. Now independent of the source charges, the EM field, as it moves farther away, is dependent only upon the accelerations of the charges that produced it. It no longer has a strong connection to the direct fields of the charges, or to the velocity of the charges (currents).


title: Electromagnetic radiation

text: In the Liénard–Wiechert potential formulation of the electric and magnetic fields due to motion of a single particle (according to Maxwell's equations), the terms associated with acceleration of the particle are those that are responsible for the part of the field that is regarded as electromagnetic radiation. By contrast, the term associated with the changing static electric field of the particle and the magnetic term that results from the particle's uniform velocity, are both associated with the electromagnetic near-field, and do not comprise EM radiation.


title: Electromagnetic radiation

text: Electrodynamics is the physics of electromagnetic radiation, and electromagnetism is the physical phenomenon associated with the theory of electrodynamics. Electric and magnetic fields obey the properties of superposition. Thus, a field due to any particular particle or time-varying electric or magnetic field contributes to the fields present in the same space due to other causes. Further, as they are vector fields, all magnetic and electric field vectors add together according to vector addition. For example, in optics two or more coherent light waves may interact and by constructive or destructive interference yield a resultant irradiance deviating from the sum of the component irradiances of the individual light waves.


title: Electromagnetic radiation

text: The electromagnetic fields of light are not affected by traveling through static electric or magnetic fields in a linear medium such as a vacuum. However, in nonlinear media, such as some crystals, interactions can occur between light and static electric and magnetic fields—these interactions include the Faraday effect and the Kerr effect.


title: Electromagnetic radiation

text: In refraction, a wave crossing from one medium to another of different density alters its speed and direction upon entering the new medium. The ratio of the refractive indices of the media determines the degree of refraction, and is summarized by Snell's law. Light of composite wavelengths (natural sunlight) disperses into a visible spectrum passing through a prism, because of the wavelength-dependent refractive index of the prism material (dispersion); that is, each component wave within the composite light is bent a different amount.


title: Electromagnetic radiation

text: EM radiation exhibits both wave properties and particle properties at the same time (see wave-particle duality). Both wave and particle characteristics have been confirmed in many experiments. Wave characteristics are more apparent when EM radiation is measured over relatively large timescales and over large distances while particle characteristics are more evident when measuring small timescales and distances. For example, when electromagnetic radiation is absorbed by matter, particle-like properties will be more obvious when the average number of photons in the cube of the relevant wavelength is much smaller than 1. It is not so difficult to experimentally observe non-uniform deposition of energy when light is absorbed, however this alone is not evidence of "particulate" behavior. Rather, it reflects the quantum nature of "matter". Demonstrating that the light itself is quantized, not merely its interaction with matter, is a more subtle affair.


title: Electromagnetic radiation

text: Some experiments display both the wave and particle natures of electromagnetic waves, such as the self-interference of a single photon. When a single photon is sent through an interferometer, it passes through both paths, interfering with itself, as waves do, yet is detected by a photomultiplier or other sensitive detector only once.


title: Electromagnetic radiation

text: A quantum theory of the interaction between electromagnetic radiation and matter such as electrons is described by the theory of quantum electrodynamics.


title: Electromagnetic radiation

text: Electromagnetic waves can be polarized, reflected, refracted, diffracted or interfere with each other.


title: Electromagnetic radiation

text: In homogeneous, isotropic media, electromagnetic radiation is a transverse wave, meaning that its oscillations are perpendicular to the direction of energy transfer and travel. It comes from the following equations:formula_1These equations predicate that any electromagnetic wave must be a transverse wave, where the electric field and the magnetic field are both perpendicular to the direction of wave propagation.


title: Electromagnetic radiation

text: The electric and magnetic parts of the field in an electromagnetic wave stand in a fixed ratio of strengths to satisfy the two Maxwell equations that specify how one is produced from the other. In dissipation-less (lossless) media, these E and B fields are also in phase, with both reaching maxima and minima at the same points in space (see illustrations). A common misconception is that the E and B fields in electromagnetic radiation are out of phase because a change in one produces the other, and this would produce a phase difference between them as sinusoidal functions (as indeed happens in electromagnetic induction, and in the near-field close to antennas). However, in the far-field EM radiation which is described by the two source-free Maxwell curl operator equations, a more correct description is that a time-change in one type of field is proportional to a space-change in the other. These derivatives require that the E and B fields in EMR are in-phase (see mathematics section below).


title: Electromagnetic radiation

text: An important aspect of light's nature is its frequency. The frequency of a wave is its rate of oscillation and is measured in hertz, the SI unit of frequency, where one hertz is equal to one oscillation per second. Light usually has multiple frequencies that sum to form the resultant wave. Different frequencies undergo different angles of refraction, a phenomenon known as dispersion.


title: Electromagnetic radiation

text: A monochromatic wave (a wave of a single frequency) consists of successive troughs and crests, and the distance between two adjacent crests or troughs is called the wavelength. Waves of the electromagnetic spectrum vary in size, from very long radio waves longer than a continent to very short gamma rays smaller than atom nuclei. Frequency is inversely proportional to wavelength, according to the equation:


title: Electromagnetic radiation

text: where "v" is the speed of the wave ("c" in a vacuum or less in other media), "f" is the frequency and λ is the wavelength. As waves cross boundaries between different media, their speeds change but their frequencies remain constant.


title: Electromagnetic radiation

text: Electromagnetic waves in free space must be solutions of Maxwell's electromagnetic wave equation. Two main classes of solutions are known, namely plane waves and spherical waves. The plane waves may be viewed as the limiting case of spherical waves at a very large (ideally infinite) distance from the source. Both types of waves can have a waveform which is an arbitrary time function (so long as it is sufficiently differentiable to conform to the wave equation). As with any time function, this can be decomposed by means of Fourier analysis into its frequency spectrum, or individual sinusoidal components, each of which contains a single frequency, amplitude and phase. Such a component wave is said to be "monochromatic". A monochromatic electromagnetic wave can be characterized by its frequency or wavelength, its peak amplitude, its phase relative to some reference phase, its direction of propagation, and its polarization.


title: Electromagnetic radiation

text: Interference is the superposition of two or more waves resulting in a new wave pattern. If the fields have components in the same direction, they constructively interfere, while opposite directions cause destructive interference. An example of interference caused by EMR is electromagnetic interference (EMI) or as it is more commonly known as, radio-frequency interference (RFI). Additionally, multiple polarization signals can be combined (i.e. interfered) to form new states of polarization, which is known as parallel polarization state generation.


title: Electromagnetic radiation

text: An anomaly arose in the late 19th century involving a contradiction between the wave theory of light and measurements of the electromagnetic spectra that were being emitted by thermal radiators known as black bodies. Physicists struggled with this problem unsuccessfully for many years. It later became known as the ultraviolet catastrophe. In 1900, Max Planck developed a new theory of black-body radiation that explained the observed spectrum. Planck's theory was based on the idea that black bodies emit light (and other electromagnetic radiation) only as discrete bundles or packets of energy. These packets were called quanta. In 1905, Albert Einstein proposed that light quanta be regarded as real particles. Later the particle of light was given the name photon, to correspond with other particles being described around this time, such as the electron and proton. A photon has an energy, "E", proportional to its frequency, "f", by


title: Electromagnetic radiation

text: where "h" is Planck's constant, formula_4 is the wavelength and "c" is the speed of light. This is sometimes known as the Planck–Einstein equation. In quantum theory (see first quantization) the energy of the photons is thus directly proportional to the frequency of the EMR wave.


title: Electromagnetic radiation

text: Likewise, the momentum "p" of a photon is also proportional to its frequency and inversely proportional to its wavelength:


title: Electromagnetic radiation

text: The source of Einstein's proposal that light was composed of particles (or could act as particles in some circumstances) was an experimental anomaly not explained by the wave theory: the photoelectric effect, in which light striking a metal surface ejected electrons from the surface, causing an electric current to flow across an applied voltage. Experimental measurements demonstrated that the energy of individual ejected electrons was proportional to the "frequency", rather than the "intensity", of the light. Furthermore, below a certain minimum frequency, which depended on the particular metal, no current would flow regardless of the intensity. These observations appeared to contradict the wave theory, and for years physicists tried in vain to find an explanation. In 1905, Einstein explained this puzzle by resurrecting the particle theory of light to explain the observed effect. Because of the preponderance of evidence in favor of the wave theory, however, Einstein's ideas were met initially with great skepticism among established physicists. Eventually Einstein's explanation was accepted as new particle-like behavior of light was observed, such as the Compton effect.


title: Electromagnetic radiation

text: As a photon is absorbed by an atom, it excites the atom, elevating an electron to a higher energy level (one that is on average farther from the nucleus). When an electron in an excited molecule or atom descends to a lower energy level, it emits a photon of light at a frequency corresponding to the energy difference. Since the energy levels of electrons in atoms are discrete, each element and each molecule emits and absorbs its own characteristic frequencies. Immediate photon emission is called fluorescence, a type of photoluminescence. An example is visible light emitted from fluorescent paints, in response to ultraviolet (blacklight). Many other fluorescent emissions are known in spectral bands other than visible light. Delayed emission is called phosphorescence.


title: Electromagnetic radiation

text: The modern theory that explains the nature of light includes the notion of wave–particle duality. More generally, the theory states that everything has both a particle nature and a wave nature, and various experiments can be done to bring out one or the other. The particle nature is more easily discerned using an object with a large mass. A bold proposition by Louis de Broglie in 1924 led the scientific community to realize that matter (e.g. electrons) also exhibits wave–particle duality.


title: Electromagnetic radiation

text: Together, wave and particle effects fully explain the emission and absorption spectra of EM radiation. The matter-composition of the medium through which the light travels determines the nature of the absorption and emission spectrum. These bands correspond to the allowed energy levels in the atoms. Dark bands in the absorption spectrum are due to the atoms in an intervening medium between source and observer. The atoms absorb certain frequencies of the light between emitter and detector/eye, then emit them in all directions. A dark band appears to the detector, due to the radiation scattered out of the beam. For instance, dark bands in the light emitted by a distant star are due to the atoms in the star's atmosphere. A similar phenomenon occurs for emission, which is seen when an emitting gas glows due to excitation of the atoms from any mechanism, including heat. As electrons descend to lower energy levels, a spectrum is emitted that represents the jumps between the energy levels of the electrons, but lines are seen because again emission happens only at particular energies after excitation. An example is the emission spectrum of nebulae. Rapidly moving electrons are most sharply accelerated when they encounter a region of force, so they are responsible for producing much of the highest frequency electromagnetic radiation observed in nature.


title: Electromagnetic radiation

text: These phenomena can aid various chemical determinations for the composition of gases lit from behind (absorption spectra) and for glowing gases (emission spectra). Spectroscopy (for example) determines what chemical elements comprise a particular star. Spectroscopy is also used in the determination of the distance of a star, using the red shift.


title: Electromagnetic radiation

text: When any wire (or other conducting object such as an antenna) conducts alternating current, electromagnetic radiation is propagated at the same frequency as the current. In many such situations it is possible to identify an electrical dipole moment that arises from separation of charges due to the exciting electrical potential, and this dipole moment oscillates in time, as the charges move back and forth. This oscillation at a given frequency gives rise to changing electric and magnetic fields, which then set the electromagnetic radiation in motion.


title: Electromagnetic radiation

text: At the quantum level, electromagnetic radiation is produced when the wavepacket of a charged particle oscillates or otherwise accelerates. Charged particles in a stationary state do not move, but a superposition of such states may result in a transition state that has an electric dipole moment that oscillates in time. This oscillating dipole moment is responsible for the phenomenon of radiative transition between quantum states of a charged particle. Such states occur (for example) in atoms when photons are radiated as the atom shifts from one stationary state to another.


title: Electromagnetic radiation

text: As a wave, light is characterized by a velocity (the speed of light), wavelength, and frequency. As particles, light is a stream of photons. Each has an energy related to the frequency of the wave given by Planck's relation "E = hf", where "E" is the energy of the photon, "h" is Planck's constant, 6.626 × 10 J·s, and "f" is the frequency of the wave.


title: Electromagnetic radiation

text: One rule is obeyed regardless of circumstances: EM radiation in a vacuum travels at the speed of light, "relative to the observer", regardless of the observer's velocity.


title: Electromagnetic radiation

text: In a medium (other than vacuum), velocity factor or refractive index are considered, depending on frequency and application. Both of these are ratios of the speed in a medium to speed in a vacuum.


title: Electromagnetic radiation

text: By the late nineteenth century, various experimental anomalies could not be explained by the simple wave theory. One of these anomalies involved a controversy over the speed of light. The speed of light and other EMR predicted by Maxwell's equations did not appear unless the equations were modified in a way first suggested by FitzGerald and Lorentz (see history of special relativity), or else otherwise that speed would depend on the speed of observer relative to the "medium" (called luminiferous aether) which supposedly "carried" the electromagnetic wave (in a manner analogous to the way air carries sound waves). Experiments failed to find any observer effect. In 1905, Einstein proposed that space and time appeared to be velocity-changeable entities for light propagation and all other processes and laws. These changes accounted for the constancy of the speed of light and all electromagnetic radiation, from the viewpoints of all observers—even those in relative motion.


title: Electromagnetic radiation

text: Electromagnetic radiation of wavelengths other than those of visible light were discovered in the early 19th century. The discovery of infrared radiation is ascribed to astronomer William Herschel, who published his results in 1800 before the Royal Society of London. Herschel used a glass prism to refract light from the Sun and detected invisible rays that caused heating beyond the red part of the spectrum, through an increase in the temperature recorded with a thermometer. These "calorific rays" were later termed infrared.


title: Electromagnetic radiation

text: In 1801, German physicist Johann Wilhelm Ritter discovered ultraviolet in an experiment similar to Herschel's, using sunlight and a glass prism. Ritter noted that invisible rays near the violet edge of a solar spectrum dispersed by a triangular prism darkened silver chloride preparations more quickly than did the nearby violet light. Ritter's experiments were an early precursor to what would become photography. Ritter noted that the ultraviolet rays (which at first were called "chemical rays") were capable of causing chemical reactions.


title: Electromagnetic radiation

text: In 1862–64 James Clerk Maxwell developed equations for the electromagnetic field which suggested that waves in the field would travel with a speed that was very close to the known speed of light. Maxwell therefore suggested that visible light (as well as invisible infrared and ultraviolet rays by inference) all consisted of propagating disturbances (or radiation) in the electromagnetic field. Radio waves were first produced deliberately by Heinrich Hertz in 1887, using electrical circuits calculated to produce oscillations at a much lower frequency than that of visible light, following recipes for producing oscillating charges and currents suggested by Maxwell's equations. Hertz also developed ways to detect these waves, and produced and characterized what were later termed radio waves and microwaves.


title: Electromagnetic radiation

text: Wilhelm Röntgen discovered and named X-rays. After experimenting with high voltages applied to an evacuated tube on 8 November 1895, he noticed a fluorescence on a nearby plate of coated glass. In one month, he discovered X-rays' main properties.


title: Electromagnetic radiation

text: The last portion of the EM spectrum to be discovered was associated with radioactivity. Henri Becquerel found that uranium salts caused fogging of an unexposed photographic plate through a covering paper in a manner similar to X-rays, and Marie Curie discovered that only certain elements gave off these rays of energy, soon discovering the intense radiation of radium. The radiation from pitchblende was differentiated into alpha rays (alpha particles) and beta rays (beta particles) by Ernest Rutherford through simple experimentation in 1899, but these proved to be charged particulate types of radiation. However, in 1900 the French scientist Paul Villard discovered a third neutrally charged and especially penetrating type of radiation from radium, and after he described it, Rutherford realized it must be yet a third type of radiation, which in 1903 Rutherford named gamma rays. In 1910 British physicist William Henry Bragg demonstrated that gamma rays are electromagnetic radiation, not particles, and in 1914 Rutherford and Edward Andrade measured their wavelengths, finding that they were similar to X-rays but with shorter wavelengths and higher frequency, although a 'cross-over' between X and gamma rays makes it possible to have X-rays with a higher energy (and hence shorter wavelength) than gamma rays and vice versa. The origin of the ray differentiates them, gamma rays tend to be natural phenomena originating from the unstable nucleus of an atom and X-rays are electrically generated (and hence man-made) unless they are as a result of bremsstrahlung X-radiation caused by the interaction of fast moving particles (such as beta particles) colliding with certain materials, usually of higher atomic numbers.


title: Electromagnetic radiation

text: EM radiation (the designation 'radiation' excludes static electric and magnetic and near fields) is classified by wavelength into radio, microwave, infrared, visible, ultraviolet, X-rays and gamma rays. Arbitrary electromagnetic waves can be expressed by Fourier analysis in terms of sinusoidal monochromatic waves, which in turn can each be classified into these regions of the EMR spectrum.


title: Electromagnetic radiation

text: For certain classes of EM waves, the waveform is most usefully treated as "random", and then spectral analysis must be done by slightly different mathematical techniques appropriate to random or stochastic processes. In such cases, the individual frequency components are represented in terms of their "power" content, and the phase information is not preserved. Such a representation is called the power spectral density of the random process. Random electromagnetic radiation requiring this kind of analysis is, for example, encountered in the interior of stars, and in certain other very wideband forms of radiation such as the Zero point wave field of the electromagnetic vacuum.


title: Electromagnetic radiation

text: The behavior of EM radiation and its interaction with matter depends on its frequency, and changes qualitatively as the frequency changes. Lower frequencies have longer wavelengths, and higher frequencies have shorter wavelengths, and are associated with photons of higher energy. There is no fundamental limit known to these wavelengths or energies, at either end of the spectrum, although photons with energies near the Planck energy or exceeding it (far too high to have ever been observed) will require new physical theories to describe.


title: Electromagnetic radiation

text: When radio waves impinge upon a conductor, they couple to the conductor, travel along it and induce an electric current on the conductor surface by moving the electrons of the conducting material in correlated bunches of charge. Such effects can cover macroscopic distances in conductors (such as radio antennas), since the wavelength of radiowaves is long.


title: Electromagnetic radiation

text: Electromagnetic radiation phenomena with wavelengths ranging from as long as one meter to as short as one millimeter are called microwaves; with frequencies between 300 MHz (0.3 GHz) and 300 GHz.


title: Electromagnetic radiation

text: At radio and microwave frequencies, EMR interacts with matter largely as a bulk collection of charges which are spread out over large numbers of affected atoms. In electrical conductors, such induced bulk movement of charges (electric currents) results in absorption of the EMR, or else separations of charges that cause generation of new EMR (effective reflection of the EMR). An example is absorption or emission of radio waves by antennas, or absorption of microwaves by water or other molecules with an electric dipole moment, as for example inside a microwave oven. These interactions produce either electric currents or heat, or both.


title: Electromagnetic radiation

text: Like radio and microwave, infrared (IR) also is reflected by metals (and also most EMR, well into the ultraviolet range). However, unlike lower-frequency radio and microwave radiation, Infrared EMR commonly interacts with dipoles present in single molecules, which change as atoms vibrate at the ends of a single chemical bond. It is consequently absorbed by a wide range of substances, causing them to increase in temperature as the vibrations dissipate as heat. The same process, run in reverse, causes bulk substances to radiate in the infrared spontaneously (see thermal radiation section below).


title: Electromagnetic radiation

text: Infrared radiation is divided into spectral subregions. While different subdivision schemes exist, the spectrum is commonly divided as near-infrared (0.75–1.4 μm), short-wavelength infrared (1.4–3 μm), mid-wavelength infrared (3–8 μm), long-wavelength infrared (8–15 μm) and far infrared (15–1000 μm).


title: Electromagnetic radiation

text: Natural sources produce EM radiation across the spectrum. EM radiation with a wavelength between approximately 400 nm and 700 nm is directly detected by the human eye and perceived as visible light. Other wavelengths, especially nearby infrared (longer than 700 nm) and ultraviolet (shorter than 400 nm) are also sometimes referred to as light.


title: Electromagnetic radiation

text: As frequency increases into the visible range, photons have enough energy to change the bond structure of some individual molecules. It is not a coincidence that this happens in the visible range, as the mechanism of vision involves the change in bonding of a single molecule, retinal, which absorbs a single photon. The change in retinal causes a change in the shape of the rhodopsin protein it is contained in, which starts the biochemical process that causes the retina of the human eye to sense the light.


title: Electromagnetic radiation

text: Photosynthesis becomes possible in this range as well, for the same reason. A single molecule of chlorophyll is excited by a single photon. In plant tissues that conduct photosynthesis, carotenoids act to quench electronically excited chlorophyll produced by visible light in a process called non-photochemical quenching, to prevent reactions that would otherwise interfere with photosynthesis at high light levels.


title: Electromagnetic radiation

text: Animals that detect infrared make use of small packets of water that change temperature, in an essentially thermal process that involves many photons.


title: Electromagnetic radiation

text: Infrared, microwaves and radio waves are known to damage molecules and biological tissue only by bulk heating, not excitation from single photons of the radiation.


title: Electromagnetic radiation

text: Visible light is able to affect only a tiny percentage of all molecules. Usually not in a permanent or damaging way, rather the photon excites an electron which then emits another photon when returning to its original position. This is the source of color produced by most dyes. Retinal is an exception. When a photon is absorbed, the retinal permanently changes structure from cis to trans, and requires a protein to convert it back, i.e. reset it to be able to function as a light detector again.


title: Electromagnetic radiation

text: Limited evidence indicate that some reactive oxygen species are created by visible light in skin, and that these may have some role in photoaging, in the same manner as ultraviolet A.


title: Electromagnetic radiation

text: As frequency increases into the ultraviolet, photons now carry enough energy (about three electron volts or more) to excite certain doubly bonded molecules into permanent chemical rearrangement. In DNA, this causes lasting damage. DNA is also indirectly damaged by reactive oxygen species produced by ultraviolet A (UVA), which has energy too low to damage DNA directly. This is why ultraviolet at all wavelengths can damage DNA, and is capable of causing cancer, and (for UVB) skin burns (sunburn) that are far worse than would be produced by simple heating (temperature increase) effects. This property of causing molecular damage that is out of proportion to heating effects, is characteristic of all EMR with frequencies at the visible light range and above. These properties of high-frequency EMR are due to quantum effects that permanently damage materials and tissues at the molecular level.


title: Electromagnetic radiation

text: At the higher end of the ultraviolet range, the energy of photons becomes large enough to impart enough energy to electrons to cause them to be liberated from the atom, in a process called photoionisation. The energy required for this is always larger than about 10 electron volt (eV) corresponding with wavelengths smaller than 124 nm (some sources suggest a more realistic cutoff of 33 eV, which is the energy required to ionize water). This high end of the ultraviolet spectrum with energies in the approximate ionization range, is sometimes called "extreme UV." Ionizing UV is strongly filtered by the Earth's atmosphere.


title: Electromagnetic radiation

text: Electromagnetic radiation composed of photons that carry minimum-ionization energy, or more, (which includes the entire spectrum with shorter wavelengths), is therefore termed ionizing radiation. (Many other kinds of ionizing radiation are made of non-EM particles). Electromagnetic-type ionizing radiation extends from the extreme ultraviolet to all higher frequencies and shorter wavelengths, which means that all X-rays and gamma rays qualify. These are capable of the most severe types of molecular damage, which can happen in biology to any type of biomolecule, including mutation and cancer, and often at great depths below the skin, since the higher end of the X-ray spectrum, and all of the gamma ray spectrum, penetrate matter.


title: Electromagnetic radiation

text: Most UV and X-rays are blocked by absorption first from molecular nitrogen, and then (for wavelengths in the upper UV) from the electronic excitation of dioxygen and finally ozone at the mid-range of UV. Only 30% of the Sun's ultraviolet light reaches the ground, and almost all of this is well transmitted.


title: Electromagnetic radiation

text: Visible light is well transmitted in air, as it is not energetic enough to excite nitrogen, oxygen, or ozone, but too energetic to excite molecular vibrational frequencies of water vapor.


title: Electromagnetic radiation

text: Absorption bands in the infrared are due to modes of vibrational excitation in water vapor. However, at energies too low to excite water vapor, the atmosphere becomes transparent again, allowing free transmission of most microwave and radio waves.


title: Electromagnetic radiation

text: Finally, at radio wavelengths longer than 10 m or so (about 30 MHz), the air in the lower atmosphere remains transparent to radio, but plasma in certain layers of the ionosphere begins to interact with radio waves (see skywave). This property allows some longer wavelengths (100 m or 3 MHz) to be reflected and results in shortwave radio beyond line-of-sight. However, certain ionospheric effects begin to block incoming radiowaves from space, when their frequency is less than about 10 MHz (wavelength longer than about 30 m).


title: Electromagnetic radiation

text: The basic structure of matter involves charged particles bound together. When electromagnetic radiation impinges on matter, it causes the charged particles to oscillate and gain energy. The ultimate fate of this energy depends on the context. It could be immediately re-radiated and appear as scattered, reflected, or transmitted radiation. It may get dissipated into other microscopic motions within the matter, coming to thermal equilibrium and manifesting itself as thermal energy, or even kinetic energy, in the material. With a few exceptions related to high-energy photons (such as fluorescence, harmonic generation, photochemical reactions, the photovoltaic effect for ionizing radiations at far ultraviolet, X-ray and gamma radiation), absorbed electromagnetic radiation simply deposits its energy by heating the material. This happens for infrared, microwave and radio wave radiation. Intense radio waves can thermally burn living tissue and can cook food. In addition to infrared lasers, sufficiently intense visible and ultraviolet lasers can easily set paper afire.


title: Electromagnetic radiation

text: Ionizing radiation creates high-speed electrons in a material and breaks chemical bonds, but after these electrons collide many times with other atoms eventually most of the energy becomes thermal energy all in a tiny fraction of a second. This process makes ionizing radiation far more dangerous per unit of energy than non-ionizing radiation. This caveat also applies to UV, even though almost all of it is not ionizing, because UV can damage molecules due to electronic excitation, which is far greater per unit energy than heating effects.


title: Electromagnetic radiation

text: Infrared radiation in the spectral distribution of a black body is usually considered a form of heat, since it has an equivalent temperature and is associated with an entropy change per unit of thermal energy. However, "heat" is a technical term in physics and thermodynamics and is often confused with thermal energy. Any type of electromagnetic energy can be transformed into thermal energy in interaction with matter. Thus, "any" electromagnetic radiation can "heat" (in the sense of increase the thermal energy temperature of) a material, when it is absorbed.


title: Electromagnetic radiation

text: The inverse or time-reversed process of absorption is thermal radiation. Much of the thermal energy in matter consists of random motion of charged particles, and this energy can be radiated away from the matter. The resulting radiation may subsequently be absorbed by another piece of matter, with the deposited energy heating the material.


title: Electromagnetic radiation

text: The electromagnetic radiation in an opaque cavity at thermal equilibrium is effectively a form of thermal energy, having maximum radiation entropy.


title: Electromagnetic radiation

text: Bioelectromagnetics is the study of the interactions and effects of EM radiation on living organisms. The effects of electromagnetic radiation upon living cells, including those in humans, depends upon the radiation's power and frequency. For low-frequency radiation (radio waves to visible light) the best-understood effects are those due to radiation power alone, acting through heating when radiation is absorbed. For these thermal effects, frequency is important as it affects the intensity of the radiation and penetration into the organism (for example, microwaves penetrate better than infrared). It is widely accepted that low frequency fields that are too weak to cause significant heating could not possibly have any biological effect.


title: Electromagnetic radiation

text: Despite the commonly accepted results, some research has been conducted to show that weaker "non-thermal" electromagnetic fields (including weak ELF magnetic fields, although the latter does not strictly qualify as EM radiation) and modulated RF and microwave fields have biological effects. Fundamental mechanisms of the interaction between biological material and electromagnetic fields at non-thermal levels are not fully understood.


title: Electromagnetic radiation

text: The World Health Organization has classified radio frequency electromagnetic radiation as Group 2B – possibly carcinogenic. This group contains possible carcinogens such as lead, DDT, and styrene. For example, epidemiological studies looking for a relationship between cell phone use and brain cancer development have been largely inconclusive, save to demonstrate that the effect, if it exists, cannot be a large one.


title: Electromagnetic radiation

text: At higher frequencies (visible and beyond), the effects of individual photons begin to become important, as these now have enough energy individually to directly or indirectly damage biological molecules. All UV frequencies have been classed as Group 1 carcinogens by the World Health Organization. Ultraviolet radiation from sun exposure is the primary cause of skin cancer.


title: Electromagnetic radiation

text: Thus, at UV frequencies and higher (and probably somewhat also in the visible range), electromagnetic radiation does more damage to biological systems than simple heating predicts. This is most obvious in the "far" (or "extreme") ultraviolet. UV, with X-ray and gamma radiation, are referred to as ionizing radiation due to the ability of photons of this radiation to produce ions and free radicals in materials (including living tissue). Since such radiation can severely damage life at energy levels that produce little heating, it is considered far more dangerous (in terms of damage-produced per unit of energy, or power) than the rest of the electromagnetic spectrum.


title: Electromagnetic radiation

text: The heat ray is an application of EMR that makes use of microwave frequencies to create an unpleasant heating effect in the upper layer of the skin. A publicly known heat ray weapon called the Active Denial System was developed by the US military as an experimental weapon to deny the enemy access to an area. A death ray is a theoretical weapon that delivers heat ray based on electromagnetic energy at levels that are capable of injuring human tissue. An inventor of a death ray, Harry Grindell Matthews, claimed to have lost sight in his left eye while working on his death ray weapon based on a microwave magnetron from the 1920s (a normal microwave oven creates a tissue damaging cooking effect inside the oven at around 2 kV/m).


title: Electromagnetic radiation

text: Electromagnetic waves are predicted by the classical laws of electricity and magnetism, known as Maxwell's equations. There are nontrivial solutions of the homogeneous Maxwell's equations (without charges or currents), describing "waves" of changing electric and magnetic fields. Beginning with Maxwell's equations in free space:


title: Electromagnetic radiation

text: useful solutions can be derived with the following vector identity, valid for all vectors formula_16 in some vector field:


title: Electromagnetic radiation

text: Evaluating the right hand side of () by exchanging the sequence of derivations and inserting the fourth yields:


title: Electromagnetic radiation

text: Combining () and () again, gives a vector-valued differential equation for the electric field, solving the homogeneous Maxwell equations:


title: Electromagnetic radiation

text: Taking the curl of the fourth Maxwell equation () results in a similar differential equation for a magnetic field solving the homogeneous Maxwell equations:


title: Electromagnetic radiation

text: Both differential equations have the form of the general wave equation for waves propagating with speed formula_18 where formula_19 is a function of time and location, which gives the amplitude of the wave at some time at a certain location:


title: Electromagnetic radiation

text: formula_20 is a unit vector in the direction of propagation, and formula_21 is a position vector. formula_22 is a generic solution to the wave equation. In other words,


title: Electromagnetic radiation

text: which implies that the electric field is orthogonal to the direction the wave propagates. The second of Maxwell's equations yields the magnetic field, namely,


title: Electromagnetic radiation

text: The electric and magnetic field waves in the far-field travel at the speed of light. They have a special restricted orientation and proportional magnitudes, formula_30, which can be seen immediately from the Poynting vector. The electric field, magnetic field, and direction of wave propagation are all orthogonal, and the wave propagates in the same direction as formula_31. Also, E and B far-fields in free space, which as wave solutions depend primarily on these two Maxwell equations, are in-phase with each other. This is guaranteed since the generic wave solution is first order in both space and time, and the curl operator on one side of these equations results in first-order spatial derivatives of the wave solution, while the time-derivative on the other side of the equations, which gives the other field, is first-order in time, resulting in the same phase shift for both fields in each mathematical operation.


title: Electromagnetic radiation

text: From the viewpoint of an electromagnetic wave traveling forward, the electric field might be oscillating up and down, while the magnetic field oscillates right and left. This picture can be rotated with the electric field oscillating right and left and the magnetic field oscillating down and up. This is a different solution that is traveling in the same direction. This arbitrariness in the orientation with respect to propagation direction is known as polarization. On a quantum level, it is described as photon polarization. The direction of the polarization is defined as the direction of the electric field.


title: Electromagnetic radiation

text: More general forms of the second-order wave equations given above are available, allowing for both non-vacuum propagation media and sources. Many competing derivations exist, all with varying levels of approximation and intended applications. One very general example is a form of the electric field equation, which was factorized into a pair of explicitly directional wave equations, and then efficiently reduced into a single uni-directional wave equation by means of a simple slow-evolution approximation.


title: 2022 Texas gubernatorial election

text: The 2022 Texas gubernatorial election took place on November 8, 2022, to elect the governor of Texas. Incumbent Republican Governor Greg Abbott defeated the Democratic nominee and former U.S. Representative Beto O'Rourke to win reelection to a third term. All statewide elected offices are currently held by Republicans. In his previous gubernatorial race in 2018, Abbott won with 55.8% of the vote.


title: 2022 Texas gubernatorial election

text: The Democratic and Republican primaries were held on March 1, 2022. O'Rourke and Abbott won outright majorities in their respective primaries, and therefore did not participate in the May 24 runoffs.


title: 2022 Texas gubernatorial election

text: Texas has not voted for a Democratic candidate for governor since Ann Richards in 1990. Additionally, Abbott had a strong approval rating on election day, with 55% of voters approving to 45% disapproving. Beto O'Rourke, who gained national attention in 2018 for his unusually close and competitive campaign against Senator Ted Cruz, was widely viewed as a rising star in the Texas Democratic Party and potential challenger for Abbott, but a failed run for President of the United States in 2020 prompted criticisms of opportunism, via Republican attempts to brand him as anti-law enforcement and his former comments on guns.


title: 2022 Texas gubernatorial election

text: Abbott won re-election by 10.9%, which is a margin slightly smaller than his 13.3% in 2018 in spite of a much redder national climate in 2022, making this the closest gubernatorial election in Texas since 2006, and the closest election of Abbott's entire political career since his first race for the Texas Supreme Court in 1998. Beto O'Rourke, meanwhile, performed 8.3% worse than his 2018 Senate run, but "did" still win the highest share for a Democratic gubernatorial candidate since Ann Richards received 45.88% in her unsuccessful reelection bid against George W. Bush in 1994. Abbott's raw vote total was less than his 4.65 million in 2018, while O'Rourke set a record of most raw votes for a Texas Democratic gubernatorial candidate at around 3.55 million, but was also less than his 4.04 million vote total in the 2018 Senate race.


title: 2022 Texas gubernatorial election

text: Abbott carried 235 out of 254 counties in his re-election victory, flipping the heavily Hispanic counties of Culberson and Zapata and becoming the first Republican gubernatorial candidate to win the latter in the state's history (though Zapata had voted Republican in the 2020 presidential election), while O'Rourke became the first Democratic gubernatorial candidate to win the county of Fort Bend since 1974. O'Rourke outperformed Joe Biden two years prior among Latino voters though his performance with them was still worse than past nominees because Joe Biden had a 58% disapproval rating in Texas on election day.


title: 2022 Texas gubernatorial election

text: On June 4, 2021, Texas Republican Party chairman Allen West announced his resignation as party chair. West criticized Gov. Greg Abbott's handling of the COVID-19 pandemic in Texas. The history of conflict between West and Abbott included a lawsuit by West and other Republicans challenging Abbott's extension of the early voting period in 2020, as well as a protest outside the Governor's Mansion over pandemic-related shutdowns as well as mask mandates. On July 4, 2021, West announced that he would challenge Abbott in the 2022 gubernatorial primary. Both West and fellow gubernatorial candidate Don Huffines were considered more conservative than Abbott. On March 1, 2022, Abbott won the Republican primary by a much smaller margin than in 2018.


title: 2022 Texas gubernatorial election

text: While Texas Democrats hoped for Beto O'Rourke to achieve an upset over the incumbent Greg Abbott, one did not materialize. Abbott won by about 10.9 points, a margin slightly larger than aggregate polling, but virtually in line with the last poll conducted. He won the vast majority of counties, mostly rural, and by significantly wide margins. 34 counties, in particular, gave Abbott over 90% of the vote, the most by any Texas Republican gubernatorial candidate, and the most for any candidate since Democrat Allan Shivers' 1954 re-election.


title: 2022 Texas gubernatorial election

text: He won several mid-sized metro areas which include Corpus Christi along the coastal bend; Beaumont–Port Arthur, Tyler and Longview in East Texas; Lubbock and Midland-Odessa in West Texas; and Amarillo in the Panhandle. Abbott also did well in the suburbs of the Texas Triangle, winning Brazoria, Galveston, and Montgomery counties around Houston; Comal and Guadalupe around San Antonio; Collin, Denton, Ellis, Kaufman, Rockwall, and Tarrant in the Dallas-Fort Worth metroplex; and Williamson in Greater Austin. In DFW and Austin specifically, Republican strength has collapsed much faster in these metros than anywhere else in Texas, with Abbott carrying Collin, Denton, Tarrant, and Williamson by 10.07%, 12.81%, 4.11%, and 0.62% respectively, down from his margins of 19.48%, 20.60%, 10.64%, and 10.71% from 2018.


title: 2022 Texas gubernatorial election

text: O'Rourke, despite his loss, did best in Texas's urban centers. He carried Travis, home to the state capital Austin (72.6% - 25.9%), his best performance in the state; El Paso, his home county, 63.4% - 35%; Dallas (62.8% - 35.9%); Bexar (57.5% - 41.1%); and Harris (54% - 44.5%). He also carried Hays, a rapidly growing county south of Austin which contains San Marcos and Texas State University, by 54.5% - 43.7%. Despite improving on 2018 nominee Lupe Valdez's margins in these counties, he did worse in all of them compared to his Senate campaign in 2018, and, excluding Travis and Hays, worse than Joe Biden in the 2020 presidential race but that is chiefly because Greg Abbott is much more popular than Donald Trump in the state. The only county O'Rourke flipped was suburban Fort Bend outside Houston, which voted for Abbott by 0.2% in 2018, but voted for O'Rourke by 4.68% in this election.


title: 2022 Texas gubernatorial election

text: Outside the Texas Triangle and Trans Pecos, the only other area O'Rourke won was the heavily Hispanic Rio Grande Valley along the U.S. border with Mexico, but his performance was worse than Valdez's and his own from 2018, which continued the trend of rural Hispanic voters away from the Democrats towards Republicans, but did slightly outperform Biden from 2020. Counties that voted for Biden by single digits like Duval (2.61%), Starr (5%), and Maverick (9.45%); voted for O'Rourke 11.02%, 17.85%, and 17.68% respectively. Despite this improvement from the 2020 presidential race, Abbott flipped two heavily Hispanic counties, Zapata and Culberson (in the Trans Pecos).


title: 2022 Texas gubernatorial election

text: Exit polls according to NBC News showed Abbott winning male (58% - 41%) and female voters (51% - 48%), whites (66% - 33%), voters over 45 (60% - 39%), college graduates (52% - 47%) and non-college graduates (56% - 43%), and voters who denied the results of the 2020 presidential election (94% - 5%). O'Rourke won black voters (84% - 15%), Latinos (57% - 40%), Asians (52% - 48%), voters between 18-44 (54% - 44%), Independents (49%-47%) and moderates (60% - 38%).


title: 2022 Texas gubernatorial election

text: Fox News Voter Analysis exit polls showed Abbott winning male (59%-39%) and female voters (51%-48%); whites (68%-30%); voters over 45 (61%-37%); college graduates (54%-44%), non-college graduates (56%-43%) and other minorities (53%-42%); white men (70%-28%); white women (67%-32%). O'Rourke won African Americans (81%-18%), Latinos (56%-42%); African American men (76%-24%); African American women (85%-13%) and Latina women (61%-37%). O'Rourke also won Latino men (55%-45%). Fox News Voter Analysis


title: The Doctor (Doctor Who)

text: The Doctor is the title character in the long-running BBC science fiction television programme "Doctor Who". Since the show's inception in 1963, the character has been portrayed by thirteen lead actors. In the programme, "the Doctor" is the alias assumed by a millennia-old humanoid alien, a Time Lord who travels through space and time in the TARDIS, frequently with companions. The transition to each succeeding actor is explained within the show's narrative through the plot device of "regeneration", a biological function of the Time Lord race that allows a change of cellular structure and appearance with recovery following a fatal injury.


title: The Doctor (Doctor Who)

text: A number of other actors have played the character in stage and audio plays, as well as in various film and television productions. The Doctor has been well-received by the public, with an enduring popularity leading "The Daily Telegraph" to dub the character "Britain's favourite alien", while abroad the character has come to be seen as a British cultural icon. The Doctor has also been featured in films and a vast range of spin-off novels, audio dramas and comic strips.


title: The Doctor (Doctor Who)

text: Returning for the 60th anniversary, David Tennant is now portraying the Fourteenth Doctor, having previously played the Tenth Doctor from 2005-2010, succeeding Jodie Whitaker at the end of "The Power of the Doctor". Ncuti Gatwa is scheduled to take over as the Fifteenth Doctor from 2023.


title: The Doctor (Doctor Who)

text: Within the fictional narrative, the Doctor is a Time Lord who travels through time and space in a stolen dimensionally transcendental – "bigger on the inside" – time machine: the TARDIS (Time And Relative Dimension(s) In Space) which takes the exterior form of a 1963 police telephone call box, and retains the appearance throughout the programme. Human companions accompany the Doctor through their adventures who serve as audience surrogate characters to ask questions which allow the Doctor to provide relevant exposition.


title: The Doctor (Doctor Who)

text: "Doctor" is a self-selected alias. In later episodes of the revived programme, specifically under show runner Steven Moffat, the story arcs surrounding events in the Doctor's future implied serious consequences in the event of the Doctor's true name being spoken, with the nature of these finally revealed in "The Time of the Doctor". Spin-off media offer the explanation that the Doctor's true name is unpronounceable by humans. In "The Name of the Doctor", the Eleventh Doctor tells companion Clara Oswald that the name "Doctor" is essentially a promise he made. The promise itself is revealed in "The Day of the Doctor": "Never cruel nor cowardly. Never give up. Never give in."


title: The Doctor (Doctor Who)

text: The Doctor was originally known as the Timeless Child, as revealed in "The Timeless Children" (2020). This episode substantially retconned the Doctor's history, as they had previously been said to be a high-born Time Lord whose incarnation played by William Hartnell in the show was born on Gallifrey. In the Doctor's revised and expanded origin story, a native Gallifreyan Shobogan scientist and explorer named Tecteun discovered the child as a young girl next to a portal to another reality. Tecteun adopted her as her own and discovered that the Child had a capacity to regenerate her body indefinitely. After much study, Tecteun genetically incorporated this ability into some of the Shobogan race, who became the basis for the formation of the elite Time Lords, although their regenerations were forcibly limited to twelve. After many regenerations, Tecteun inducted the Timeless Child into a clandestine operative group within the Time Lords known as the Division. The secrecy of the Division required Tecteun to eventually wipe all of the Timeless Child's memories up to that point and leave them, reduced in age to a child once again, in Gallifreyan society. This is where the Doctor's memories begin, with his boyhood as the First Doctor.


title: The Doctor (Doctor Who)

text: The First Doctor's childhood on Gallifrey has been little described in the series. In "Hell Bent" the Doctor recalled his origins as a high-born Gallifreyan. In "The Time Monster", the Doctor says he grew up in a house on a mountainside and talks about a hermit who lived under a tree behind the house and inspired the Doctor when he was depressed. He is later reunited with this former mentor, now on Earth posing as the abbot K'anpo Rimpoche, in "Planet of the Spiders". In "The Girl in the Fireplace", according to Madame de Pompadour who psychically linked with the Doctor's memories, the Doctor experienced a very lonely childhood. An elderly woman on Gallifrey died and was shrouded in veils and surrounded by flies, giving the Doctor recurring nightmares, which the confession dial in "Heaven Sent" would later visualise to torment him. In "Listen", it is revealed the Doctor as a child often slept alone in a barn in the Drylands (a desert region outside the city capital), was withdrawn from other children, and was cared for by guardian figures who privately doubted the child's ability as an eventual Time Lord. Through the dialogue, it is suggested that several Gallifreyan children were pressured into joining the army, a path which did not sit right with the Doctor's pacifist beliefs, and as a result he wished to enroll into the Time Lord Academy instead.


title: The Doctor (Doctor Who)

text: The classic programme refers to his time at the Academy and his affiliation with the notoriously devious Prydonian chapter of Time Lords. In "The Sound of Drums", the Doctor describes an Academy initiation where, at the age of 8, Gallifreyan children were taken from their families and made to look into the Untempered Schism, a gap in the fabric of reality, to view the Time Vortex. According to the Doctor, when regarding the effects of the initiation on participants: "Some would be inspired, some would run away and some would go mad (as he suggests happened to his nemesis, the Master)." When asked to which group he belonged, he replied, "Oh, the ones that ran away; I never stopped!". The Doctor was taught by future Lord President Borusa and Azmael, where he met Drax, with whom he attended a Tech course as part of the class of '92. In "the Armageddon Factor", it is revealed that the Doctor scraped through the Academy with 51% on his second attempt. In "The Time Meddler", it is said that the Doctor was fifty years before the Meddling Monk. In "Time and the Rani", the Doctor claims to have attended university alongside the Rani, specialising in thermodynamics.


title: The Doctor (Doctor Who)

text: At the academy, he met his childhood friend the Master and the pair grew up together. In "The End of Time", the Master recollects their childhood together where they would run all day across his father's field, described as 'pastures of red grass stretching far across the slopes of Mount Perdition' and the boys would call up at the sky. In "World Enough and Time", the Doctor claims that they both made a special pact where together they would visit every star in the universe; however, The Master was 'too busy burning them'. In "Hell Bent", one day at the Academy, the Doctor found himself lost inside the Cloisters (an area located deep beneath the citadel) and spent four days inside. He was contacted by a Wraith who told him about the prophecy of a legendary creature known as 'the Hybrid', prophesied to have been crossbred from two warrior races that would stand in the ruins of Gallifrey, unravel the Web of Time and burn a billion hearts to heal its own. The Wraiths then revealed to him the secret passage leading to another side of the city. The last anyone heard from him was that he apparently stole the moon and the President's wife; however, this was revealed to have been a lie spread about by the Shobogans when in reality it was the President's daughter and he lost the moon. This event had a massive impact on the Doctor, who theorized that he himself was possibly the Hybrid. The Doctor decided to leave Gallifrey out of fear.


title: The Doctor (Doctor Who)

text: The Doctor chose to steal a faulty Type 40 TARDIS in order to explore the universe. In "The Doctor's Wife" it is revealed that when the Doctor was young, he first saw the Tardis in a museum, where after stroking her console he commented that she was the most beautiful thing he had ever known. In "The Shakespeare Code", the Doctor once took a driving test to pilot the Tardis and failed. In Amy's Choice, the Doctor mentions that he threw the instruction manual in a supernova because he disagreed with it. In "The Name of the Doctor" the Tardis was later relocated in a repair shop which the Doctor managed to seize alongside his granddaughter Susan. In "The Doctor's Wife", Idris mentions that the Doctor had been travelling in the Tardis for 700 years, which indicates that he would have been 200 years old when he first borrowed her. In "Twice Upon a Time" it is revealed that the Doctor also left to investigate the mystery of why good prevails in a universe where evil would seem to have so many advantages. It would be after his encounter with his twelfth incarnation that the Doctor realized his actions made the difference in the balance between good and evil, stating "The universe generally fails to be a fairy tale, but that's where we come in."


title: The Doctor (Doctor Who)

text: In other media, more has been revealed of the Doctor's early life. In the Past Doctor Adventures novel "Divided Loyalties", the Doctor recalls his Academy years in a dream induced by the Celestial Toymaker. According to this, he was a member of an organisation called the Deca, ten brilliant Academy students campaigning for increased Time Lord intervention, alongside Mortimus (the Meddling Monk), Ushas (the Rani), Koschei (the Master), Magnus (the War Chief), Drax, a spy named Vansell, Millennia, Rallon and Jelpax. With this group, he learns about the Celestial Toymaker and travels to his realm in a type 18 TARDIS with Deca members Rallon and Millennia, who are killed. This leads to the Doctor's expulsion from the Academy, condemned to five hundred years in Records and Traffic Control. In "The Quantum Archangel", it is revealed the Doctor studied cosmic science alongside the Master, taught by Cardinal Sendok. In the Virgin Missing Adventures novel "Goth Opera", it is said the Doctor was a frequent prankster while at the Academy, introducing cats into Gallifrey's ecosystem with his friend Ruath and electrifying a "perigosto stick" belonging to his teacher, Borusa.


title: The Doctor (Doctor Who)

text: Feeling that too much of the Doctor's backstory had been revealed by the Seventh Doctor's era, writers Andrew Cartmel, Ben Aaronovitch and Marc Platt developed a new direction for the series. Cartmel wished to restore the character's "awe, mystery and strength" and make him "once again more than a mere chump of a Time Lord" – an idea the media dubbed the "Cartmel Masterplan". Under Cartmel, the show foreshadowed this concept; however, its 1989 cancellation meant that it was never realised onscreen. The proposed backstory was fully explored in Platt's 1997 novel "Lungbarrow", where the Doctor is revealed as "the Other", a mysterious figure in Gallifreyan lore who co-founded Time Lord society with Rassilon and Omega. After a curse renders Gallifrey sterile, the Other devises biotechnological looms to "weave" new Time Lords; his granddaughter Susan is Gallifrey's last natural child. To escape a civil war with Rassilon, the Other throws himself into the loom system, where he is disintegrated and later woven into the Doctor.


title: The Doctor (Doctor Who)

text: References to the Doctor's family are rare in the programme. During the first two seasons, he travelled with his granddaughter, Susan Foreman, who has since been referred to occasionally and who returned in "The Five Doctors". In "The Tomb of the Cybermen" when asked about his family, the Second Doctor says his memories of them are alive when he wants them to be otherwise they sleep in his mind and he forgets. In "The Curse of Fenric," when asked if he has family, the Seventh Doctor replies that he does not know. In the 1996 television movie, the Eighth Doctor remarks that he is half-human on his mother's side, and recalls watching a meteor storm with his father on Gallifrey. The revived series never addresses a human mother again and at times even contradicted this remark: The half-human clone of the Tenth Doctor is initially disgusted to be half-human ("Journey's End") and the Twelfth Doctor rejects that he could be a hybrid of human and Time Lord ("Hell Bent"). Furthermore, an unnamed Time Lady appearing throughout The End of Time which the Tenth Doctor appears to recognize towards the end of the story was intended to be the Doctor's mother. The Doctor mentions having had a brother in "Smith and Jones", and sisters in "Arachnids in the UK". In "It Takes You Away", the Doctor claims that she had seven grandmothers. Later in the same scene, she mentions that her favourite grandmother, Granny 5, alleged Granny 2 was "a secret agent for the Zygons".


title: The Doctor (Doctor Who)

text: Throughout the revival, the Doctor routinely attempts to change the topic when questioned about being a parent or his family life, as in "Fear Her", "The Beast Below" and "A Good Man Goes to War". In "The Empty Child", a hospital doctor named Dr. Constantine says to him, "Before this war began, I was a father and a grandfather. Now I'm neither. But I'm still a doctor." The Ninth Doctor's reply is, "Yeah. I know the feeling." In "The Doctor's Daughter", when discussing the topic of parenthood, the Tenth Doctor confirms that he had at one point been a father and that he lost his children 'a long time ago', saying 'When they died that part of me died with them'; the nature of their deaths, however, has never been explained, as it is suggested that whatever happened to his family is very painful for the Doctor to talk about. In "The Woman Who Fell to Earth" when the Thirteenth Doctor is questioned how she copes with the loss of her family, she states that she carries the memories of them with her and thus makes them a part of who she is, saying "even though they're gone from the world ... they're never gone from me."


title: The Doctor (Doctor Who)

text: In "The End of Time", a mysterious individual, referred to only in the credits as "The Woman", appears unexpectedly to Wilfred Mott throughout both episodes. She is later revealed to be a dissident Time Lady, who opposed the Time Lord High Council's plan to escape the Time War. When she reveals her face to the Doctor, his reaction indicates that he recognises her. Julie Gardner, in the episode's commentary, states that while some have speculated that the Time Lady is the Doctor's mother, neither she nor Russell T. Davies is willing to comment on her identity. When later asked by Wilfred who she was, the Doctor evades answering the question, making their connection unclear. In "Doctor Who: The Writer's Tale – The Final Chapter", Russell T Davies states that he created the character to be the Doctor's mother and this is what actress Claire Bloom was told when she was cast.


title: The Doctor (Doctor Who)

text: In spin-off media, several individuals related to the Doctor have made appearances, and do not appear in the television series, such as his grandchildren John and Gillian, who appeared alongside the First and Second Doctors in comics and annuals. Two different, conflicting accounts exist on the descendants of Susan after leaving the Doctor. In the audio play "An Earthly Child", it is revealed that Susan has had a half-human child, Alex Campbell, the Doctor's great-grandson. Alternatively, in the novel "Legacy of the Daleks", Susan and her husband David adopt three children whom they name David Campbell Jr, Ian and Barbara; named after David himself, Ian Chesterton and Barbara Wright, respectively. Irving Braxiatel, a character first introduced in the novel "Theatre of War", was initially hinted at, and later confirmed to be, the Doctor's biological older brother. He has since become a recurring character, especially within the Big Finish spin-off audio series "Gallifrey" and "Bernice Summerfield".


title: The Doctor (Doctor Who)

text: In the novel "Father Time," the Eighth Doctor, during his hundred-year exile on Earth, found an orphaned Time Lord girl named Miranda whom he adopted and raised until she was 16. In the novel "Sometime Never...", she returned to the Doctor with her daughter Zezanne. She was also the central character in a three-issue comic book series published by Comeuppance Comics in 2003. Author Lance Parkin, who devised the character of Miranda, has hinted that her real father is a future incarnation of the Doctor which, if so, would make Zezanne the Doctor's biological granddaughter as well. The Virgin New Adventures novel "Lungbarrow" presents an alternative take on the Doctor's origins, suggesting that Time Lords are "loomed" in large batches of "cousins" and not produced via sexual reproduction. "Lungbarrow" portrays the Doctor as one of 45 cousins grown from his house's genetic loom as an adult. By contrast, the TV programme has shown Time Lords as children and stated that Time Lords can have sexual relationships.


title: The Doctor (Doctor Who)

text: The Doctor is assumed to be or to have been married to Susan's grandmother, including by head writer Steven Moffat. In "Blink", the Doctor mentioned that he was rubbish at his own wedding. In The Virgin New Adventures novel "Cold Fusion", a Time Lord lady named Patience who was the widow of Omega, one of the founding-fathers of Gallifreyan society who fell into an anti-matter universe. Patience later met and married the Doctor and together they had thirteen children. Once their first-born son announced the arrival of a baby, the family was targeted by the Lord President, as the child was to be conceived naturally and only the Loom-born could inherit the Legacy of Rassilon; as a result, the Doctor's children were systemically culled. The Doctor managed to help Patience escape through the use of the Machine, a prototype TARDIS, after assuring that her daughter-in-law had given birth to a girl named Susan and promised that he would keep the child safely away from Gallifrey.


title: The Doctor (Doctor Who)

text: In "The Wedding of River Song", he marries a recurring companion and love interest River Song. Comments by both River and the Doctor in the seventh series, particularly in "The Angels Take Manhattan", confirmed that they were married; in "The Name of the Doctor", the Doctor refers to her as his "wife" after seeing a grave stone with her name on it, after initially answering "yes" when Clara asks if she was an "ex".


title: The Doctor (Doctor Who)

text: In "The End of Time", the Tenth Doctor mentions marrying Queen Elizabeth I and implies that they had sex, stating: "her nickname [the Virgin Queen] is no longer...". The joke continues in "The Beast Below", featuring future British monarch Queen Elizabeth X or Liz Ten, and the marriage is finally shown in "The Day of the Doctor" during an adventure with Zygons. In the 2010 Christmas special, "A Christmas Carol", the Eleventh Doctor accidentally marries Marilyn Monroe but later questions the authenticity of the chapel in which they were married. Steven Moffat did not consider the marriages to Elizabeth I and Marilyn Monroe to count when questioned on how many wives the Doctor had had, remarking that he was married to Susan's grandmother and River Song.


title: The Doctor (Doctor Who)

text: An adventurous scientist, the Doctor usually solves problems with his wits rather than with force. With the exception of his sonic screwdriver (which cannot kill, wound or maim), the Doctor detests weapons and uses violence only as a last resort. According to the alien villain Chedaki in the episode "The Android Invasion," "his entire history is one of opposition to conquest."


title: The Doctor (Doctor Who)

text: As a time traveller, the Doctor has been present at, or directly involved in, countless major historical events on the planet Earth and elsewhere – sometimes more than once. In the 2005 series premiere, "Rose", it is revealed that the Ninth Doctor was instrumental in preventing a family from boarding the "Titanic" prior to her fateful voyage. In "The End of the World", the Doctor recalls having been on board and surviving the "Titanic's" sinking to find himself "clinging to an iceberg". The Fourth Doctor mentioned this event in "Robot" and "The Invasion of Time", where he insists that the sinking was not his fault; the Seventh Doctor became involved in the sinking when tracking an alien entity in the novel "The Left-Handed Hummingbird". The Doctor has also encountered many of Earth's historical figures.


title: The Doctor (Doctor Who)

text: It is his tendency for becoming "involved" with the universe – in direct violation of official Time Lord policy – that has caused the Doctor to be labelled a renegade by the Time Lords as stated in "The War Games." However, the Doctor's actions are largely tolerated as he saved Gallifrey and the universe several times. The Time Lords are partial to sending him on missions when deniability or expendability is needed, implied to have begun after his capture during "The War Games" and witnessed further in later stories, the Time Lords directing the Doctor and/or the TARDIS to specific locations in "Colony in Space", "The Curse of Peladon", "The Mutants", "Genesis of the Daleks", "The Brain of Morbius" and "Attack of the Cybermen". The Doctor's standing in Time Lord society has waxed and waned over the years, from being a hunted man who was eventually punished with a forced regeneration and an exile sentence on Earth, to being appointed Lord President of the High Council. He does not assume the office for very long, fleeing Gallifrey after his appointment rather than accepting the limitations on his freedom that the role would place on him ("The Five Doctors"), and is eventually deposed "in absentia" ("The Trial of a Time Lord"). By the time of his twelfth incarnation, he is regarded by many Gallifreyans as a war hero, "the man who won the Time War" ("Hell Bent").


title: The Doctor (Doctor Who)

text: In the first series of the 2005 revival, writer Russell T Davies introduced the concept of the Time War to streamline the Doctor's backstory for new viewers of the show. It was a war across all of time and space which ended when the Doctor presumably destroyed both the Time Lords and the Daleks. The Doctor's remorse for his actions in his Ninth, Tenth and Eleventh incarnations is a key part of his characterisation throughout the revival. The Time War happened between the 1996 television movie and 2005 opening episode "Rose" according to the show's internal chronology, although the events of past serials such as "Genesis of the Daleks" have been retroactively attributed to the Time War. It was never shown on-screen until "The End of Time", which was both Davies' last story as head writer and producer and David Tennant's last regular story as the Tenth Doctor. This episode featured brief views of Gallifrey and the Time Lords on the last day of the Time War.


title: The Doctor (Doctor Who)

text: The 2013 mini-episode "The Night of the Doctor", released as a prelude to the 50th anniversary special, featured Paul McGann reprising his role as the Eighth Doctor and was set during the Last Great Time War, albeit much earlier than during "The End of Time". The mini-episode presented him as a conscientious objector to the war who regenerated under controlled circumstances into the War Doctor (John Hurt), a previously unseen incarnation created retroactively by Davies' successor as head writer, Steven Moffat, for the 50th anniversary special "The Day of the Doctor". The Tenth and Eleventh Doctors explained that Hurt's regeneration was not the Doctor because his actions during the Time War were a betrayal of the promise that name symbolized. "The Day of the Doctor" revisited the last day of the Time War after "The End of Time "and revealed that the interference of the future Doctors and future companion Clara Oswald caused the War Doctor to change his plan at the last moment. Ultimately, Gallifrey was hidden in a parallel dimension and the Daleks destroyed themselves in the ensuing crossfire; to all observers, it appeared as though the two races had been annihilated together. The unsynchronized timestreams caused the War Doctor to forget the specifics of his actions at this time. The Doctor remembered committing the apparent genocide during the lives of his ninth, tenth and eleventh incarnations up until the time of the Eleventh Doctor's present.


title: The Doctor (Doctor Who)

text: The character of the Doctor was created by BBC Head of Drama, Sydney Newman. The first format document for the programme that was to become "Doctor Who" – then provisionally titled "The Troubleshooters" – was written in March 1963 by C. E. Webber, a staff writer who had been brought in to help develop the project. Webber's document contained a main character described as "The maturer man, 35–40, with some 'character twist.' " Newman was not keen on this idea and – along with several other changes to Webber's initial format – created an alternative lead character named Dr Who, a crotchety older man piloting a stolen time machine, on the run from his own far-future world. No written record of Newman's conveyance of these ideas – believed to have taken place in April 1963 – exists, and the character of Dr Who first begins appearing in existing documentation from May of that year. It is possible that series co-creator Donald Wilson may have named the character; in a 1971 interview Wilson claimed to have come up with the series' title, and when this claim was put to Newman he did not dispute it.


title: The Doctor (Doctor Who)

text: The character was first portrayed by William Hartnell in 1963. At the programme's beginning, nothing at all is known of the Doctor: not even his name, the actual form of which remains a mystery. In the first serial, "An Unearthly Child," two teachers from Coal Hill School in London, Barbara Wright and Ian Chesterton, become intrigued by one of their pupils, Susan Foreman, who exhibits high intelligence and unusually advanced knowledge. Trailing her to a junkyard at 76 Totter's Lane, they encounter a strange old man and hear Susan's voice coming from inside what appears to be a police box. Pushing their way inside, the two find that the exterior is camouflage for the dimensionally transcendental interior of the TARDIS. The old man, whom Susan calls "Grandfather", kidnaps Barbara and Ian to prevent them from telling anyone about the existence of the TARDIS, taking them on an adventure in time and space. The first Doctor, says cultural scholar John Paul Green, "explicitly positioned the Doctor as grandfather to his companion Susan." He wore long white hair and Edwardian costume, reflecting, Green says, a "definite sense of Englishness".


title: The Doctor (Doctor Who)

text: When Hartnell left the programme after three years due to ill health, the role was handed over to character actor Patrick Troughton. , official television productions have depicted fourteen distinct incarnations of the Doctor. The longest-lasting on-screen incarnation is the Fourth Doctor, played by Tom Baker for seven years. Within the narrative, these changes were explained as regeneration, a biological process which heals a Time Lord when their incarnation is about to die. Consequently, the Time Lord is given a wholly new body. In "The Deadly Assassin", the concept of a regeneration limit is introduced, giving Time Lords a fixed number of twelve regenerations, meaning that every Time Lord had a total of thirteen incarnations including the original. The plot of "The Time of the Doctor" involves the Doctor receiving a new cycle of regenerations from the Time Lords before his expected demise, triggering the regeneration into the Twelfth Doctor, played by Peter Capaldi.


title: The Doctor (Doctor Who)

text: The origins of the programme were explored in the docudrama "An Adventure in Space and Time" as part of the 50th-anniversary celebrations of "Doctor Who", which starred David Bradley as William Hartnell.


title: The Doctor (Doctor Who)

text: Although Time Lords resemble humans, their physiology differs in key respects. Like other members of their race, the Doctor has two hearts (binary vascular system), a "respiratory bypass system" that allows the Doctor to go without air, an internal body temperature of 15–16 °C (60 °F) and occasionally exhibits a super-human level of stamina and the ability to absorb, withstand and expel large amounts of certain types of radiation (the Tenth Doctor stated they used to play with Röntgen bricks in the nursery, after absorbing the radiation from an x-ray of significantly magnified power). This ability would seem to have limitations which have yet to be fully explained, as the Doctor "is" harmed by radiation in "The Daleks", "Planet of the Spiders" and "The End of Time". The Doctor has withstood, with minimal damage, exposure to electricity deadly enough to kill a human ("Terror of the Zygons", "Genesis of the Daleks", "Aliens of London", "The Christmas Invasion", "The Idiot's Lantern", "Evolution of the Daleks" and spin-off audio "Spare Parts"). Certain stories imply that the Time Lord is resistant to cold temperatures ("42"). To counter extreme trauma, such as exposure to the poisonous fungus in "The Seeds of Death" and after being shot in "Spearhead from Space", the Doctor can go into a self-induced coma until they recover. The Doctor's hypersensitive body and senses enable them to detect anomalies humans cannot, such as identifying alien species, blood type or chemical composition by taste and determining location or time period by sniffing the air. In "The Unicorn and the Wasp" (2008) he was able to sense the changes in his body's enzymes (i.e. cyanide poisoning) and expel the cyanide from his body by ingesting a concoction of ginger beer, protein foods and salts.


title: The Doctor (Doctor Who)

text: The Doctor has shown a resistance to temporal effects and has demonstrated telepathic ability, both the ability to mentally connect to other incarnations of themselves they have encountered ("The Five Doctors"), and an ability to enter into the memories of other individuals ("The Girl in the Fireplace"). The Doctor can apparently reverse this process, sharing their memory with another, as shown in "The Lodger". Some humans can enter the Doctor's memories after the Doctor enters theirs, as demonstrated by Madame de Pompadour (much to the Doctor's surprise) in "The Girl in the Fireplace", when she explains, "A door, once opened, may be stepped through in either direction." In "The Fires of Pompeii", the Doctor reveals that he is able to perceive the fabric of time, discerning "fixed points" and "points in flux" – moments when history must remain as it was originally versus moments when he can change or influence the original course of events, as well as all past, present and possible future events. However, in "Kill the Moon", the Twelfth Doctor claims that there are "grey areas", points in time for which he cannot see the outcome. Like many other alien species in the programme, the Doctor is able to sense when their own species is within proximity through an inherent telepathic connection.


title: The Doctor (Doctor Who)

text: The Doctor exhibits some weaknesses uncommon to humans. For example, according to "The Mind of Evil" (1971), a tablet of aspirin could kill him. In "Cold Blood", a process meant to decontaminate him of bacteria from the surface of Earth causes him intense pain, and he says it could have killed him if allowed to proceed to completion. In the Eighth Doctor Adventures novel "The Adventuress of Henrietta Street", the Doctor's second heart was surgically removed, resulting in the loss of his abilities to metabolise drugs and go without air; these are restored when he begins to grow a new heart after his old one 'dies' ("Camera Obscura").


title: The Doctor (Doctor Who)

text: In his final serial, the Second Doctor states that Time Lords can live forever, "barring accidents." When "accidents" do occur, Time Lords can usually regenerate into a new body. It is stated in "The Deadly Assassin" that Time Lords can only regenerate a total of twelve times, giving a theoretical final total of thirteen incarnations. However, The Doctor has a natural ability to regenerate an infinite number of times. It is possible to exceed this limit: in "The Five Doctors" the Time Lords offer the Master, who is inhabiting a Trakenite body after exhausting his original twelve regenerations, a new regeneration cycle as a reward for his help and cooperation, and at some point, during the Time War they resurrected him, with his new body having at least one regeneration of its own. Regeneration is apparently optional, as in "Last of the Time Lords" the Master refuses to regenerate despite the Tenth Doctor's pleading. In addition, there are ways of killing a Time Lord that do not permit regeneration; for example, more than once it has been implied that stopping both the Doctor's hearts simultaneously would accomplish this (as demonstrated in the Eleventh Doctor story "The Impossible Astronaut"). The Chancellery Guard (Gallifrey's equivalent of a police force) are armed with stasers, weapons capable of suppressing regeneration. In "Death of the Doctor", a serial from spin-off programme "The Sarah Jane Adventures", the Eleventh Doctor flippantly responds to Clyde Langer that he can regenerate "507" times; writer Russell T. Davies intended this line as a joke. Due to the retroactive creation of a numberless War Doctor and the Tenth Doctor's aborted regeneration in "The Stolen Earth"/"Journey's End", the Eleventh Doctor was the final incarnation in his natural cycle. The Time Lords used a crack in the universe to give him a new cycle consisting of an unknown number of regenerations in "The Time of the Doctor", triggering the regeneration into the Twelfth Doctor (Peter Capaldi). The Twelfth Doctor later claims to be uncertain he "won't keep regenerating forever" ("Kill the Moon"), and even Rassilon, the president of the Time Lords, expresses uncertainty about how many regenerations the Doctor has available to him.


title: The Doctor (Doctor Who)

text: Other skills include his mental communication with other Time Lords, in some cases over a galaxy's distance. His skill with hypnosis requires only a glance into the eyes to put the subject under a trance. The Doctor can read an entire book cover to cover in a second by thumb-flipping the pages before his eyes ("City of Death", "Rose", "The Time of Angels"). Though medical skills he shows early in the programme are rudimentary, by "Remembrance of the Daleks" he can perform sophisticated medical diagnoses merely by touching someone's ear. He is an excellent cricket player ("Black Orchid") and in "The Lodger" he proves to be a prodigiously talented footballer despite unfamiliarity with some of the game's basic rules. Though reluctant to engage in combat against living opponents, this is not for lack of skill; the Doctor is conversant with both real and fictitious styles of unarmed combat (most obviously the "Venusian Aikido" practised by the Third Doctor), has won several sword fights against skilled opponents, and is able to make extremely difficult shots with firearms and, in "The Face of Evil", with a crossbow. Thanks to exposure to many of history's greatest experts, including those from the future, the Doctor is a talented boxer, musician, organist, scientist and singer (able to shatter windows with his voice), and has a PhD in cheesemaking ("The God Complex").


title: The Doctor (Doctor Who)

text: In the first episode, Barbara addresses the Doctor as "Doctor Foreman", as this is the surname the Doctor's granddaughter Susan goes by, and the junkyard in which they find him bears the sign "I.M. Foreman". When addressed by Ian with this name, the Doctor responds, "Eh? Doctor who? What's he talking about?" Later, when Ian realises that "Foreman" is not the Doctor's name, Ian asks Barbara, "Who is he? Doctor who?" In an ultimately unused idea from documents written at the programme's inception, Barbara and Ian would have subsequently referred to the Doctor as "Doctor Who", given their not knowing his name.


title: The Doctor (Doctor Who)

text: Throughout both the classic and revived programme, a running joke is that when the Doctor is introduced as just the Doctor, characters reply "Doctor who?" Another variation is "Doctor what?"


title: The Doctor (Doctor Who)

text: The story arc running throughout the tenure of the Eleventh Doctor involved the oldest question in the universe, revealed in "The Wedding of River Song" to be "Doctor who?", giving the phrase in-universe significance. In "The Name of the Doctor", the Doctor's real name was revealed to be the password used to enter the Doctor's tomb following his death on the planet Trenzalore. The story arc was resolved in "The Time of the Doctor", wherein it was revealed that the question had been projected by the Time Lords across all of time and space through a "crack in the skin of the universe" as a means of contacting the Doctor and seeing whether it was safe to leave the parallel universe in which their planet, Gallifrey, had been left following the events of "The Day of the Doctor". This arc was penned by Steven Moffat, who has been exploring the significance of the Doctor's name in his episodes since 2006's "The Girl in the Fireplace", in which historical figure Madame de Pompadour reads the Doctor's mind and remarks, "Doctor who? It's more than just a secret, isn't it?" According to the in-vision commentary on the DVD release, David Tennant had to inform actress Sophia Myles (who played Madame de Pompadour) that she was not, in fact, revealing the Doctor's surname as she believed was the intent of the dialogue. The 2011 mid-series finale "A Good Man Goes to War", also written by Moffat, suggested through the character of River Song that the Doctor's travels had influenced the etymology of the word "doctor", perverting its meaning on some worlds from "wise man" or "healer" to "great warrior". In "The End of Time" (2009–2010) it is mentioned that after he smote a demon in the 13th century, the residents of a convent called the Doctor the "sainted physician".


title: The Doctor (Doctor Who)

text: The anonymity of the Doctor is the theme of series 7 of the revived programme. After faking his death, the Doctor erases himself from the various databases of the universe. In "Asylum of the Daleks", a "time splinter" of future companion Clara Oswald using the name Oswin wipes all knowledge of the Doctor from the Daleks' collective memory. This knowledge is regained when the Daleks conquer the Church of the Silence in "The Time of the Doctor" (2013). The Doctor is not present on Solomon's database in "Dinosaurs on a Spaceship" and holds a conversation about his newfound anonymity in "The Angels Take Manhattan" with River Song. In "Nightmare in Silver", the collective consciousness of the Cybermen informs the Doctor that he could be reconstructed from the "hole" – the missing records – that he has left behind, a mistake which the Doctor intends to rectify.


title: The Doctor (Doctor Who)

text: Few individuals are said to know the Doctor's true name. River Song whispered something to the Tenth Doctor to make him trust her during "Silence in the Library"/"Forest of the Dead", confirmed to have been his name towards the end of "Forest of the Dead". The events of "The Time of the Doctor" make it clear that his people, the Time Lords, know his true name, despite referring to him by his chosen alias as "the Doctor", even in formal settings such as court.


title: The Doctor (Doctor Who)

text: Despite the common belief amongst some areas of the fanbase that the Doctor should never be referred to by the name of the series, "Doctor Who" is actually fairly often used as the character's name, most frequently in the spin-off material of the 1960s and 1970s, but occasionally also in the TV series itself. For example, in "The Gunfighters" the Doctor assumes the name of Doctor Caligari and subsequently responds to the question "Doctor who?" with "yes, quite right". In the serial "The War Machines", the computer WOTAN commands that "Doctor Who is required", and his human agents also use the name. The Third Doctor's car, dubbed "Bessie", carried the plate WHO 1, the only ongoing reference to the "Doctor Who" enigma in the original programme. The Third Doctor later drove an outlandish vehicle called the "Whomobile" in publicity materials, but it is never referred to as such in the programme, being simply known as "the Doctor's car" or "my car", as the Doctor puts it. The name "Doctor Who" is used in the title of the serial "Doctor Who and the Silurians", but this was a captioning error rather than an in-story mention. The only other time this occurs is in the title of episode five of "The Chase", which is titled "The Death of Doctor Who". In "World Enough and Time" (2017), the Doctor's old friend and archenemy the Master (as Missy) insists that the Doctor's real name is in fact Doctor Who, and that he chose it himself, though he tries to reassure his companion that she is joking, although later in the episode self-identifies by that name.