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text large_stringlengths 1 3.58k	length int64 1 3.58k	page_title large_stringlengths 3 128	url large_stringlengths 33 158	text_id int64 0 102k	paragraph_idx int64 0 509	year int64 2.02k 2.02k	month int64 8 8	day int64 10 10	minute int64 30 54	second int64 0 59
While modelling atoms in isolation may not seem realistic, if one considers atoms in a gas or plasma then the time-scales for atom-atom interactions are huge in comparison to the atomic processes that are generally considered. This means that the individual atoms can be treated as if each were in isolation, as the vast...	519	Atomic_physics	https://en.wikipedia.org/wiki/Atomic_physics	200	4	2,024	8	10	30	58
Electrons form notional shells around the nucleus. These are normally in a ground state but can be excited by the absorption of energy from light (photons), magnetic fields, or interaction with a colliding particle (typically ions or other electrons).	251	Atomic_physics	https://en.wikipedia.org/wiki/Atomic_physics	201	5	2,024	8	10	30	58
Electrons that populate a shell are said to be in a bound state. The energy necessary to remove an electron from its shell (taking it to infinity) is called the binding energy. Any quantity of energy absorbed by the electron in excess of this amount is converted to kinetic energy according to the conservation of energy...	383	Atomic_physics	https://en.wikipedia.org/wiki/Atomic_physics	202	6	2,024	8	10	30	58
If the electron absorbs a quantity of energy less than the binding energy, it will be transferred to an excited state. After a certain time, the electron in an excited state will "jump" (undergo a transition) to a lower state. In a neutral atom, the system will emit a photon of the difference in energy, since energy is...	331	Atomic_physics	https://en.wikipedia.org/wiki/Atomic_physics	203	7	2,024	8	10	30	58
If an inner electron has absorbed more than the binding energy (so that the atom ionizes), then a more outer electron may undergo a transition to fill the inner orbital. In this case, a visible photon or a characteristic X-ray is emitted, or a phenomenon known as the Auger effect may take place, where the released ener...	478	Atomic_physics	https://en.wikipedia.org/wiki/Atomic_physics	204	8	2,024	8	10	30	58
There are rather strict selection rules as to the electronic configurations that can be reached by excitation by light — however, there are no such rules for excitation by collision processes.	192	Atomic_physics	https://en.wikipedia.org/wiki/Atomic_physics	205	9	2,024	8	10	30	58
One of the earliest steps towards atomic physics was the recognition that matter was composed of atoms. It forms a part of the texts written in 6th century BC to 2nd century BC, such as those of Democritus or Vaiśeṣika Sūtra written by Kaṇāda. This theory was later developed in the modern sense of the basic unit of a c...	633	Atomic_physics	https://en.wikipedia.org/wiki/Atomic_physics	206	10	2,024	8	10	30	58
The true beginning of atomic physics is marked by the discovery of spectral lines and attempts to describe the phenomenon, most notably by Joseph von Fraunhofer. The study of these lines led to the Bohr atom model and to the birth of quantum mechanics. In seeking to explain atomic spectra, an entirely new mathematical ...	589	Atomic_physics	https://en.wikipedia.org/wiki/Atomic_physics	207	11	2,024	8	10	30	58
Since the Second World War, both theoretical and experimental fields have advanced at a rapid pace. This can be attributed to progress in computing technology, which has allowed larger and more sophisticated models of atomic structure and associated collision processes. Similar technological advances in accelerators, d...	407	Atomic_physics	https://en.wikipedia.org/wiki/Atomic_physics	208	12	2,024	8	10	30	58
Alpha decay or α-decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus) and thereby transforms or "decays" into a different atomic nucleus, with a mass number that is reduced by four and an atomic number that is reduced by two. An alpha particle is identical to the nucl...	488	Alpha_decay	https://en.wikipedia.org/wiki/Alpha_decay	209	0	2,024	8	10	30	58
While alpha particles have a charge +2 e, this is not usually shown because a nuclear equation describes a nuclear reaction without considering the electrons – a convention that does not imply that the nuclei necessarily occur in neutral atoms.	244	Alpha_decay	https://en.wikipedia.org/wiki/Alpha_decay	210	1	2,024	8	10	30	58
Alpha decay typically occurs in the heaviest nuclides. Theoretically, it can occur only in nuclei somewhat heavier than nickel (element 28), where the overall binding energy per nucleon is no longer a maximum and the nuclides are therefore unstable toward spontaneous fission-type processes. In practice, this mode of de...	548	Alpha_decay	https://en.wikipedia.org/wiki/Alpha_decay	211	2	2,024	8	10	30	58
Alpha decay is by far the most common form of cluster decay, where the parent atom ejects a defined daughter collection of nucleons, leaving another defined product behind. It is the most common form because of the combined extremely high nuclear binding energy and relatively small mass of the alpha particle. Like othe...	515	Alpha_decay	https://en.wikipedia.org/wiki/Alpha_decay	212	3	2,024	8	10	30	58
Alpha particles have a typical kinetic energy of 5 MeV (or ≈ 0.13% of their total energy, 110 TJ/kg) and have a speed of about 15,000,000 m/s, or 5% of the speed of light. There is surprisingly small variation around this energy, due to the strong dependence of the half-life of this process on the energy produced. Beca...	565	Alpha_decay	https://en.wikipedia.org/wiki/Alpha_decay	213	4	2,024	8	10	30	58
Approximately 99% of the helium produced on Earth is the result of the alpha decay of underground deposits of minerals containing uranium or thorium. The helium is brought to the surface as a by-product of natural gas production.	229	Alpha_decay	https://en.wikipedia.org/wiki/Alpha_decay	214	5	2,024	8	10	30	58
Alpha particles were first described in the investigations of radioactivity by Ernest Rutherford in 1899, and by 1907 they were identified as He ions. By 1928, George Gamow had solved the theory of alpha decay via tunneling. The alpha particle is trapped inside the nucleus by an attractive nuclear potential well and a ...	871	Alpha_decay	https://en.wikipedia.org/wiki/Alpha_decay	215	6	2,024	8	10	30	58
The nuclear force holding an atomic nucleus together is very strong, in general much stronger than the repulsive electromagnetic forces between the protons. However, the nuclear force is also short-range, dropping quickly in strength beyond about 3 femtometers, while the electromagnetic force has an unlimited range. Th...	888	Alpha_decay	https://en.wikipedia.org/wiki/Alpha_decay	216	7	2,024	8	10	30	58
One curiosity is why alpha particles, helium nuclei, should be preferentially emitted as opposed to other particles like a single proton or neutron or other atomic nuclei. Part of the reason is the high binding energy of the alpha particle, which means that its mass is less than the sum of the masses of two free proton...	1,761	Alpha_decay	https://en.wikipedia.org/wiki/Alpha_decay	217	8	2,024	8	10	30	58
These disintegration energies, however, are substantially smaller than the repulsive potential barrier created by the interplay between the strong nuclear and the electromagnetic force, which prevents the alpha particle from escaping. The energy needed to bring an alpha particle from infinity to a point near the nucleu...	739	Alpha_decay	https://en.wikipedia.org/wiki/Alpha_decay	218	9	2,024	8	10	30	58
Quantum mechanics, however, allows the alpha particle to escape via quantum tunneling. The quantum tunneling theory of alpha decay, independently developed by George Gamow and by Ronald Wilfred Gurney and Edward Condon in 1928, was hailed as a very striking confirmation of quantum theory. Essentially, the alpha particl...	519	Alpha_decay	https://en.wikipedia.org/wiki/Alpha_decay	219	10	2,024	8	10	30	58
It has hitherto been necessary to postulate some special arbitrary 'instability' of the nucleus, but in the following note, it is pointed out that disintegration is a natural consequence of the laws of quantum mechanics without any special hypothesis... Much has been written of the explosive violence with which the α-p...	475	Alpha_decay	https://en.wikipedia.org/wiki/Alpha_decay	220	11	2,024	8	10	30	58
The theory supposes that the alpha particle can be considered an independent particle within a nucleus, that is in constant motion but held within the nucleus by strong interaction. At each collision with the repulsive potential barrier of the electromagnetic force, there is a small non-zero probability that it will tu...	779	Alpha_decay	https://en.wikipedia.org/wiki/Alpha_decay	221	12	2,024	8	10	30	58
The isotopes in beta-decay stable isobars that are also stable with regards to double beta decay with mass number A = 5, A = 8, 143 ≤ A ≤ 155, 160 ≤ A ≤ 162, and A ≥ 165 are theorized to undergo alpha decay. All other mass numbers (isobars) have exactly one theoretically stable nuclide. Those with mass 5 decay to heliu...	623	Alpha_decay	https://en.wikipedia.org/wiki/Alpha_decay	222	13	2,024	8	10	30	58
Working out the details of the theory leads to an equation relating the half-life of a radioisotope to the decay energy of its alpha particles, a theoretical derivation of the empirical Geiger–Nuttall law.	205	Alpha_decay	https://en.wikipedia.org/wiki/Alpha_decay	223	14	2,024	8	10	30	58
Americium-241, an alpha emitter, is used in smoke detectors. The alpha particles ionize air in an open ion chamber and a small current flows through the ionized air. Smoke particles from the fire that enter the chamber reduce the current, triggering the smoke detector's alarm.	277	Alpha_decay	https://en.wikipedia.org/wiki/Alpha_decay	224	15	2,024	8	10	30	58
Radium-223 is also an alpha emitter. It is used in the treatment of skeletal metastases (cancers in the bones).	111	Alpha_decay	https://en.wikipedia.org/wiki/Alpha_decay	225	16	2,024	8	10	30	58
Alpha decay can provide a safe power source for radioisotope thermoelectric generators used for space probes and were used for artificial heart pacemakers. Alpha decay is much more easily shielded against than other forms of radioactive decay.	243	Alpha_decay	https://en.wikipedia.org/wiki/Alpha_decay	226	17	2,024	8	10	30	58
Static eliminators typically use polonium-210, an alpha emitter, to ionize the air, allowing the "static cling" to dissipate more rapidly.	138	Alpha_decay	https://en.wikipedia.org/wiki/Alpha_decay	227	18	2,024	8	10	30	58
Highly charged and heavy, alpha particles lose their several MeV of energy within a small volume of material, along with a very short mean free path. This increases the chance of double-strand breaks to the DNA in cases of internal contamination, when ingested, inhaled, injected or introduced through the skin. Otherwis...	670	Alpha_decay	https://en.wikipedia.org/wiki/Alpha_decay	228	19	2,024	8	10	30	58
Relative biological effectiveness (RBE) quantifies the ability of radiation to cause certain biological effects, notably either cancer or cell-death, for equivalent radiation exposure. Alpha radiation has a high linear energy transfer (LET) coefficient, which is about one ionization of a molecule/atom for every angstro...	545	Alpha_decay	https://en.wikipedia.org/wiki/Alpha_decay	229	20	2,024	8	10	30	58
However, the recoil of the parent nucleus (alpha recoil) gives it a significant amount of energy, which also causes ionization damage (see ionizing radiation). This energy is roughly the weight of the alpha (4 Da) divided by the weight of the parent (typically about 200 Da) times the total energy of the alpha. By some ...	726	Alpha_decay	https://en.wikipedia.org/wiki/Alpha_decay	230	21	2,024	8	10	30	58
The largest natural contributor to public radiation dose is radon, a naturally occurring, radioactive gas found in soil and rock. If the gas is inhaled, some of the radon particles may attach to the inner lining of the lung. These particles continue to decay, emitting alpha particles, which can damage cells in the lung...	838	Alpha_decay	https://en.wikipedia.org/wiki/Alpha_decay	231	22	2,024	8	10	30	58
The Russian defector Alexander Litvinenko 's 2006 murder by radiation poisoning is thought to have been carried out with polonium-210, an alpha emitter.	152	Alpha_decay	https://en.wikipedia.org/wiki/Alpha_decay	232	23	2,024	8	10	30	58
Onia	4	Antiparticle	https://en.wikipedia.org/wiki/Antiparticle	233	0	2,024	8	10	30	58
In particle physics, every type of particle of "ordinary" matter (as opposed to antimatter) is associated with an antiparticle with the same mass but with opposite physical charges (such as electric charge). For example, the antiparticle of the electron is the positron (also known as an antielectron). While the electro...	540	Antiparticle	https://en.wikipedia.org/wiki/Antiparticle	234	1	2,024	8	10	30	58
Some particles, such as the photon, are their own antiparticle. Otherwise, for each pair of antiparticle partners, one is designated as the normal particle (the one that occurs in matter usually interacted with in daily life). The other (usually given the prefix "anti-") is designated the antiparticle.	303	Antiparticle	https://en.wikipedia.org/wiki/Antiparticle	235	2	2,024	8	10	30	58
Particle–antiparticle pairs can annihilate each other, producing photons ; since the charges of the particle and antiparticle are opposite, total charge is conserved. For example, the positrons produced in natural radioactive decay quickly annihilate themselves with electrons, producing pairs of gamma rays, a process e...	361	Antiparticle	https://en.wikipedia.org/wiki/Antiparticle	236	3	2,024	8	10	30	58
The laws of nature are very nearly symmetrical with respect to particles and antiparticles. For example, an antiproton and a positron can form an antihydrogen atom, which is believed to have the same properties as a hydrogen atom. This leads to the question of why the formation of matter after the Big Bang resulted in ...	815	Antiparticle	https://en.wikipedia.org/wiki/Antiparticle	237	4	2,024	8	10	30	58
Because charge is conserved, it is not possible to create an antiparticle without either destroying another particle of the same charge (as is for instance the case when antiparticles are produced naturally via beta decay or the collision of cosmic rays with Earth's atmosphere), or by the simultaneous creation of both ...	454	Antiparticle	https://en.wikipedia.org/wiki/Antiparticle	238	5	2,024	8	10	30	58
Particles and their antiparticles have equal and opposite charges, so that an uncharged particle also gives rise to an uncharged antiparticle. In many cases, the antiparticle and the particle coincide: pairs of photons, Z bosons, π mesons, and hypothetical gravitons and some hypothetical WIMPs all self-annihilate. Howe...	456	Antiparticle	https://en.wikipedia.org/wiki/Antiparticle	239	6	2,024	8	10	30	58
In 1932, soon after the prediction of positrons by Paul Dirac, Carl D. Anderson found that cosmic-ray collisions produced these particles in a cloud chamber – a particle detector in which moving electrons (or positrons) leave behind trails as they move through the gas. The electric charge-to-mass ratio of a particle ca...	854	Antiparticle	https://en.wikipedia.org/wiki/Antiparticle	240	7	2,024	8	10	30	58
The antiproton and antineutron were found by Emilio Segrè and Owen Chamberlain in 1955 at the University of California, Berkeley. Since then, the antiparticles of many other subatomic particles have been created in particle accelerator experiments. In recent years, complete atoms of antimatter have been assembled out o...	384	Antiparticle	https://en.wikipedia.org/wiki/Antiparticle	241	8	2,024	8	10	30	58
... the development of quantum field theory made the interpretation of antiparticles as holes unnecessary, even though it lingers on in many textbooks.	151	Antiparticle	https://en.wikipedia.org/wiki/Antiparticle	242	9	2,024	8	10	30	58
Steven Weinberg	15	Antiparticle	https://en.wikipedia.org/wiki/Antiparticle	243	10	2,024	8	10	30	58
Solutions of the Dirac equation contain negative energy quantum states. As a result, an electron could always radiate energy and fall into a negative energy state. Even worse, it could keep radiating infinite amounts of energy because there were infinitely many negative energy states available. To prevent this unphysic...	1,090	Antiparticle	https://en.wikipedia.org/wiki/Antiparticle	244	11	2,024	8	10	30	58
This picture implied an infinite negative charge for the universe – a problem of which Dirac was aware. Dirac tried to argue that we would perceive this as the normal state of zero charge. Another difficulty was the difference in masses of the electron and the proton. Dirac tried to argue that this was due to the elect...	904	Antiparticle	https://en.wikipedia.org/wiki/Antiparticle	245	12	2,024	8	10	30	58
Within Dirac's theory, the problem of infinite charge of the universe remains. Some bosons also have antiparticles, but since bosons do not obey the Pauli exclusion principle (only fermions do), hole theory does not work for them. A unified interpretation of antiparticles is now available in quantum field theory, which...	476	Antiparticle	https://en.wikipedia.org/wiki/Antiparticle	246	13	2,024	8	10	30	58
If a particle and antiparticle are in the appropriate quantum states, then they can annihilate each other and produce other particles. Reactions such as e + e → γ γ (the two-photon annihilation of an electron-positron pair) are an example. The single-photon annihilation of an electron-positron pair, e + e → γ, cannot o...	1,250	Antiparticle	https://en.wikipedia.org/wiki/Antiparticle	247	14	2,024	8	10	30	58
Quantum states of a particle and an antiparticle are interchanged by the combined application of charge conjugation C , parity P and time reversal T . C and P are linear, unitary operators, T is antilinear and antiunitary, ⟨ ⟨ Ψ Ψ \| T Φ Φ ⟩ ⟩ = ⟨ ⟨ Φ Φ \| T − − 1 Ψ Ψ ⟩ ⟩ . If \| p , σ σ , n ⟩ ⟩ denotes the quantum state ...	419	Antiparticle	https://en.wikipedia.org/wiki/Antiparticle	248	15	2,024	8	10	30	58
where n c denotes the charge conjugate state, that is, the antiparticle. In particular a massive particle and its antiparticle transform under the same irreducible representation of the Poincaré group which means the antiparticle has the same mass and the same spin.	266	Antiparticle	https://en.wikipedia.org/wiki/Antiparticle	249	16	2,024	8	10	30	58
If C , P and T can be defined separately on the particles and antiparticles, then	81	Antiparticle	https://en.wikipedia.org/wiki/Antiparticle	250	17	2,024	8	10	30	58
where the proportionality sign indicates that there might be a phase on the right hand side.	92	Antiparticle	https://en.wikipedia.org/wiki/Antiparticle	251	18	2,024	8	10	30	58
As C P T anticommutes with the charges, C P T Q = − − Q C P T , particle and antiparticle have opposite electric charges q and -q.	130	Antiparticle	https://en.wikipedia.org/wiki/Antiparticle	252	19	2,024	8	10	30	58
One may try to quantize an electron field without mixing the annihilation and creation operators by writing	107	Antiparticle	https://en.wikipedia.org/wiki/Antiparticle	253	20	2,024	8	10	30	58
where we use the symbol k to denote the quantum numbers p and σ of the previous section and the sign of the energy, E(k), and a k denotes the corresponding annihilation operators. Of course, since we are dealing with fermions, we have to have the operators satisfy canonical anti-commutation relations. However, if one n...	350	Antiparticle	https://en.wikipedia.org/wiki/Antiparticle	254	21	2,024	8	10	30	58
then one sees immediately that the expectation value of H need not be positive. This is because E(k) can have any sign whatsoever, and the combination of creation and annihilation operators has expectation value 1 or 0.	219	Antiparticle	https://en.wikipedia.org/wiki/Antiparticle	255	22	2,024	8	10	30	58
So one has to introduce the charge conjugate antiparticle field, with its own creation and annihilation operators satisfying the relations	138	Antiparticle	https://en.wikipedia.org/wiki/Antiparticle	256	23	2,024	8	10	30	58
where k has the same p, and opposite σ and sign of the energy. Then one can rewrite the field in the form	105	Antiparticle	https://en.wikipedia.org/wiki/Antiparticle	257	24	2,024	8	10	30	58
where the first sum is over positive energy states and the second over those of negative energy. The energy becomes	115	Antiparticle	https://en.wikipedia.org/wiki/Antiparticle	258	25	2,024	8	10	30	58
where E 0 is an infinite negative constant. The vacuum state is defined as the state with no particle or antiparticle, i.e., a k \| 0 ⟩ ⟩ = 0 and b k \| 0 ⟩ ⟩ = 0 . Then the energy of the vacuum is exactly E 0. Since all energies are measured relative to the vacuum, H is positive definite. Analysis of the properties of a...	452	Antiparticle	https://en.wikipedia.org/wiki/Antiparticle	259	26	2,024	8	10	30	58
This approach is due to Vladimir Fock, Wendell Furry and Robert Oppenheimer. If one quantizes a real scalar field, then one finds that there is only one kind of annihilation operator; therefore, real scalar fields describe neutral bosons. Since complex scalar fields admit two different kinds of annihilation operators, ...	390	Antiparticle	https://en.wikipedia.org/wiki/Antiparticle	260	27	2,024	8	10	30	58
By considering the propagation of the negative energy modes of the electron field backward in time, Ernst Stückelberg reached a pictorial understanding of the fact that the particle and antiparticle have equal mass m and spin J but opposite charges q. This allowed him to rewrite perturbation theory precisely in the for...	795	Antiparticle	https://en.wikipedia.org/wiki/Antiparticle	261	28	2,024	8	10	30	58
Since this picture was first developed by Stückelberg, and acquired its modern form in Feynman's work, it is called the Feynman–Stückelberg interpretation of antiparticles to honor both scientists.	197	Antiparticle	https://en.wikipedia.org/wiki/Antiparticle	262	29	2,024	8	10	30	58
Ḥasan Ibn al-Haytham (Latinized as Alhazen ; / æ l ˈ h æ z ən / ; full name Abū ʿAlī al-Ḥasan ibn al-Ḥasan ibn al-Haytham أبو علي، الحسن بن الحسن بن الهيثم ; c. 965 – c. 1040) was a medieval mathematician, astronomer, and physicist of the Islamic Golden Age from present-day Iraq. Referred to as "the father of modern op...	733	Ibn_al-Haytham	https://en.wikipedia.org/wiki/Ibn_al-Haytham	263	0	2,024	8	10	30	59
Ibn al-Haytham was the first to correctly explain the theory of vision, and to argue that vision occurs in the brain, pointing to observations that it is subjective and affected by personal experience. He also stated the principle of least time for refraction which would later become the Fermat's principle. He made maj...	827	Ibn_al-Haytham	https://en.wikipedia.org/wiki/Ibn_al-Haytham	264	1	2,024	8	10	30	59
Born in Basra, he spent most of his productive period in the Fatimid capital of Cairo and earned his living authoring various treatises and tutoring members of the nobilities. Ibn al-Haytham is sometimes given the byname al-Baṣrī after his birthplace, or al-Miṣrī ("the Egyptian"). Al-Haytham was dubbed the "Second Ptol...	457	Ibn_al-Haytham	https://en.wikipedia.org/wiki/Ibn_al-Haytham	265	2	2,024	8	10	30	59
Ibn al-Haytham (Alhazen) was born c. 965 to a family of Arab or Persian origin in Basra, Iraq, which was at the time part of the Buyid emirate. His initial influences were in the study of religion and service to the community. At the time, society had a number of conflicting views of religion that he ultimately sought ...	606	Ibn_al-Haytham	https://en.wikipedia.org/wiki/Ibn_al-Haytham	266	3	2,024	8	10	30	59
Upon his return to Cairo, he was given an administrative post. After he proved unable to fulfill this task as well, he contracted the ire of the caliph al-Hakim, and is said to have been forced into hiding until the caliph's death in 1021, after which his confiscated possessions were returned to him. Legend has it that...	791	Ibn_al-Haytham	https://en.wikipedia.org/wiki/Ibn_al-Haytham	267	4	2,024	8	10	30	59
Among his students were Sorkhab (Sohrab), a Persian from Semnan, and Abu al-Wafa Mubashir ibn Fatek, an Egyptian prince.	120	Ibn_al-Haytham	https://en.wikipedia.org/wiki/Ibn_al-Haytham	268	5	2,024	8	10	30	59
Alhazen's most famous work is his seven-volume treatise on optics Kitab al-Manazir (Book of Optics), written from 1011 to 1021. In it, Ibn al-Haytham was the first to explain that vision occurs when light reflects from an object and then passes to one's eyes, and to argue that vision occurs in the brain, pointing to ob...	389	Ibn_al-Haytham	https://en.wikipedia.org/wiki/Ibn_al-Haytham	269	6	2,024	8	10	30	59
Optics was translated into Latin by an unknown scholar at the end of the 12th century or the beginning of the 13th century.	123	Ibn_al-Haytham	https://en.wikipedia.org/wiki/Ibn_al-Haytham	270	7	2,024	8	10	30	59
This work enjoyed a great reputation during the Middle Ages. The Latin version of De aspectibus was translated at the end of the 14th century into Italian vernacular, under the title De li aspecti.	197	Ibn_al-Haytham	https://en.wikipedia.org/wiki/Ibn_al-Haytham	271	8	2,024	8	10	30	59
It was printed by Friedrich Risner in 1572, with the title Opticae thesaurus: Alhazeni Arabis libri septem, nuncprimum editi; Eiusdem liber De Crepusculis et nubium ascensionibus (English: Treasury of Optics: seven books by the Arab Alhazen, first edition; by the same, on twilight and the height of clouds). Risner is a...	755	Ibn_al-Haytham	https://en.wikipedia.org/wiki/Ibn_al-Haytham	272	9	2,024	8	10	30	59
Two major theories on vision prevailed in classical antiquity. The first theory, the emission theory, was supported by such thinkers as Euclid and Ptolemy, who believed that sight worked by the eye emitting rays of light. The second theory, the intromission theory supported by Aristotle and his followers, had physical ...	1,290	Ibn_al-Haytham	https://en.wikipedia.org/wiki/Ibn_al-Haytham	273	10	2,024	8	10	30	59
What Alhazen needed was for each point on an object to correspond to one point only on the eye. He attempted to resolve this by asserting that the eye would only perceive perpendicular rays from the object—for any one point on the eye, only the ray that reached it directly, without being refracted by any other part of ...	1,958	Ibn_al-Haytham	https://en.wikipedia.org/wiki/Ibn_al-Haytham	274	11	2,024	8	10	30	59
Alhazen showed through experiment that light travels in straight lines, and carried out various experiments with lenses, mirrors, refraction, and reflection. His analyses of reflection and refraction considered the vertical and horizontal components of light rays separately.	275	Ibn_al-Haytham	https://en.wikipedia.org/wiki/Ibn_al-Haytham	275	12	2,024	8	10	30	59
Alhazen studied the process of sight, the structure of the eye, image formation in the eye, and the visual system. Ian P. Howard argued in a 1996 Perception article that Alhazen should be credited with many discoveries and theories previously attributed to Western Europeans writing centuries later. For example, he desc...	1,073	Ibn_al-Haytham	https://en.wikipedia.org/wiki/Ibn_al-Haytham	276	13	2,024	8	10	30	59
In a more detailed account of Ibn al-Haytham's contribution to the study of binocular vision based on Lejeune and Sabra, Raynaud showed that the concepts of correspondence, homonymous and crossed diplopia were in place in Ibn al-Haytham's optics. But contrary to Howard, he explained why Ibn al-Haytham did not give the ...	699	Ibn_al-Haytham	https://en.wikipedia.org/wiki/Ibn_al-Haytham	277	14	2,024	8	10	30	59
Alhazen's most original contribution was that, after describing how he thought the eye was anatomically constructed, he went on to consider how this anatomy would behave functionally as an optical system. His understanding of pinhole projection from his experiments appears to have influenced his consideration of image ...	776	Ibn_al-Haytham	https://en.wikipedia.org/wiki/Ibn_al-Haytham	278	15	2,024	8	10	30	59
Alhazen's synthesis of light and vision adhered to the Aristotelian scheme, exhaustively describing the process of vision in a logical, complete fashion.	153	Ibn_al-Haytham	https://en.wikipedia.org/wiki/Ibn_al-Haytham	279	16	2,024	8	10	30	59
His research in catoptrics (the study of optical systems using mirrors) was centred on spherical and parabolic mirrors and spherical aberration. He made the observation that the ratio between the angle of incidence and refraction does not remain constant, and investigated the magnifying power of a lens.	304	Ibn_al-Haytham	https://en.wikipedia.org/wiki/Ibn_al-Haytham	280	17	2,024	8	10	30	59
Alhazen was the first physicist to give complete statement of the law of reflection. He was first to state that the incident ray, the reflected ray, and the normal to the surface all lie in a same plane perpendicular to reflecting plane.	237	Ibn_al-Haytham	https://en.wikipedia.org/wiki/Ibn_al-Haytham	281	18	2,024	8	10	30	59
His work on catoptrics in Book V of the Book of Optics contains a discussion of what is now known as Alhazen's problem, first formulated by Ptolemy in 150 AD. It comprises drawing lines from two points in the plane of a circle meeting at a point on the circumference and making equal angles with the normal at that point...	2,141	Ibn_al-Haytham	https://en.wikipedia.org/wiki/Ibn_al-Haytham	282	19	2,024	8	10	30	59
The camera obscura was known to the ancient Chinese, and was described by the Han Chinese polymath Shen Kuo in his scientific book Dream Pool Essays, published in the year 1088 C.E. Aristotle had discussed the basic principle behind it in his Problems, but Alhazen's work contained the first clear description of camera ...	362	Ibn_al-Haytham	https://en.wikipedia.org/wiki/Ibn_al-Haytham	283	20	2,024	8	10	30	59
Ibn al-Haytham used a camera obscura mainly to observe a partial solar eclipse. In his essay, Ibn al-Haytham writes that he observed the sickle-like shape of the sun at the time of an eclipse. The introduction reads as follows: "The image of the sun at the time of the eclipse, unless it is total, demonstrates that when...	449	Ibn_al-Haytham	https://en.wikipedia.org/wiki/Ibn_al-Haytham	284	21	2,024	8	10	30	59
It is admitted that his findings solidified the importance in the history of the camera obscura but this treatise is important in many other respects.	150	Ibn_al-Haytham	https://en.wikipedia.org/wiki/Ibn_al-Haytham	285	22	2,024	8	10	30	59
Ancient optics and medieval optics were divided into optics and burning mirrors. Optics proper mainly focused on the study of vision, while burning mirrors focused on the properties of light and luminous rays. On the shape of the eclipse is probably one of the first attempts made by Ibn al-Haytham to articulate these t...	332	Ibn_al-Haytham	https://en.wikipedia.org/wiki/Ibn_al-Haytham	286	23	2,024	8	10	30	59
Very often Ibn al-Haytham's discoveries benefited from the intersection of mathematical and experimental contributions. This is the case with On the shape of the eclipse. Besides the fact that this treatise allowed more people to study partial eclipses of the sun, it especially allowed to better understand how the came...	630	Ibn_al-Haytham	https://en.wikipedia.org/wiki/Ibn_al-Haytham	287	24	2,024	8	10	30	59
In his work he explains the inversion of the image in the camera obscura, the fact that the image is similar to the source when the hole is small, but also the fact that the image can differ from the source when the hole is large. All these results are produced by using a point analysis of the image.	301	Ibn_al-Haytham	https://en.wikipedia.org/wiki/Ibn_al-Haytham	288	25	2,024	8	10	30	59
In the seventh tract of his book of optics, Alhazen described an apparatus for experimenting with various cases of refraction, in order to investigate the relations between the angle of incidence, the angle of refraction and the angle of deflection. This apparatus was a modified version of an apparatus used by Ptolemy ...	340	Ibn_al-Haytham	https://en.wikipedia.org/wiki/Ibn_al-Haytham	289	26	2,024	8	10	30	59
Alhazen basically states the concept of unconscious inference in his discussion of colour before adding that the inferential step between sensing colour and differentiating it is shorter than the time taken between sensing and any other visible characteristic (aside from light), and that "time is so short as not to be ...	529	Ibn_al-Haytham	https://en.wikipedia.org/wiki/Ibn_al-Haytham	290	27	2,024	8	10	30	59
the sentient organ does not sense the forms that reach it from the visible objects until after it has been affected by these forms; thus it does not sense color as color or light as light until after it has been affected by the form of color or light. Now the affectation received by the sentient organ from the form of ...	867	Ibn_al-Haytham	https://en.wikipedia.org/wiki/Ibn_al-Haytham	291	28	2,024	8	10	30	59
Alhazen explained color constancy by observing that the light reflected from an object is modified by the object's color. He explained that the quality of the light and the color of the object are mixed, and the visual system separates light and color. In Book II, Chapter 3 he writes:	285	Ibn_al-Haytham	https://en.wikipedia.org/wiki/Ibn_al-Haytham	292	29	2,024	8	10	30	59
Again the light does not travel from the colored object to the eye unaccompanied by the color, nor does the form of the color pass from the colored object to the eye unaccompanied by the light. Neither the form of the light nor that of the color existing in the colored object can pass except as mingled together and the...	548	Ibn_al-Haytham	https://en.wikipedia.org/wiki/Ibn_al-Haytham	293	30	2,024	8	10	30	59
The Kitab al-Manazir (Book of Optics) describes several experimental observations that Alhazen made and how he used his results to explain certain optical phenomena using mechanical analogies. He conducted experiments with projectiles and concluded that only the impact of perpendicular projectiles on surfaces was force...	1,130	Ibn_al-Haytham	https://en.wikipedia.org/wiki/Ibn_al-Haytham	294	31	2,024	8	10	30	59
Sudanese psychologist Omar Khaleefa has argued that Alhazen should be considered the founder of experimental psychology, for his pioneering work on the psychology of visual perception and optical illusions. Khaleefa has also argued that Alhazen should also be considered the "founder of psychophysics ", a sub-discipline...	526	Ibn_al-Haytham	https://en.wikipedia.org/wiki/Ibn_al-Haytham	295	32	2,024	8	10	30	59
Alhazen offered an explanation of the Moon illusion, an illusion that played an important role in the scientific tradition of medieval Europe. Many authors repeated explanations that attempted to solve the problem of the Moon appearing larger near the horizon than it does when higher up in the sky. Alhazen argued again...	1,591	Ibn_al-Haytham	https://en.wikipedia.org/wiki/Ibn_al-Haytham	296	33	2,024	8	10	30	59
Therefore, the seeker after the truth is not one who studies the writings of the ancients and, following his natural disposition, puts his trust in them, but rather the one who suspects his faith in them and questions what he gathers from them, the one who submits to argument and demonstration, and not to the sayings o...	732	Ibn_al-Haytham	https://en.wikipedia.org/wiki/Ibn_al-Haytham	297	34	2,024	8	10	30	59
An aspect associated with Alhazen's optical research is related to systemic and methodological reliance on experimentation (i'tibar)(Arabic: اختبار) and controlled testing in his scientific inquiries. Moreover, his experimental directives rested on combining classical physics (ilm tabi'i) with mathematics (ta'alim ; ge...	678	Ibn_al-Haytham	https://en.wikipedia.org/wiki/Ibn_al-Haytham	298	35	2,024	8	10	30	59
According to Matthias Schramm, Alhazen "was the first to make a systematic use of the method of varying the experimental conditions in a constant and uniform manner, in an experiment showing that the intensity of the light-spot formed by the projection of the moonlight through two small apertures onto a screen diminish...	1,093	Ibn_al-Haytham	https://en.wikipedia.org/wiki/Ibn_al-Haytham	299	36	2,024	8	10	30	59

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