Niels Bohr in the context of "Rutherford model"

Trinity College is a constituent college of the University of Cambridge. Founded in 1546 by King Henry VIII, Trinity is one of the largest Cambridge colleges, with the largest financial endowment of any college at Oxford or Cambridge. Trinity has some of the most distinctive architecture in Cambridge with its Great Court said to be the largest enclosed courtyard in Europe. Academically, Trinity performs exceptionally as measured by the Tompkins Table (the annual unofficial league table of Cambridge colleges), coming top from 2011 to 2017, and regaining the position in 2024.

Members of Trinity have been awarded 34 Nobel Prizes out of the 121 received by members of the University of Cambridge (more than any other Oxford or Cambridge college). Members of the college have received four Fields Medals, one Turing Award and one Abel Prize. Trinity alumni include Francis Bacon, six British prime ministers (the highest number of any Cambridge college), physicists Isaac Newton, James Clerk Maxwell, Ernest Rutherford and Niels Bohr, mathematicians Srinivasa Ramanujan and Charles Babbage, poets Lord Byron and Lord Tennyson, English jurist Edward Coke, writers Vladimir Nabokov and A. A. Milne, historians Lord Macaulay and G. M. Trevelyan, and philosophers Ludwig Wittgenstein and Bertrand Russell (who the college expelled before reaccepting). Two members of the British royal family have studied at Trinity and been awarded degrees: Prince William of Gloucester and Edinburgh, who gained an MA in 1790, and King Charles III, who was awarded a lower second class BA in 1970.

In atomic physics, the Bohr model or Rutherford–Bohr model is an obsolete model of the atom that incorporated some early quantum concepts. Developed from 1911 to 1918 by Niels Bohr and building on Ernest Rutherford's discover of the atom's nucleus, it supplanted the plum pudding model of J. J. Thomson only to be replaced by the quantum atomic model in the 1920s. It consists of a small, dense atomic nucleus surrounded by orbiting electrons. It is analogous to the structure of the Solar System, but with attraction provided by electrostatic force rather than gravity, and with the electron energies quantized (assuming only discrete values).

In the history of atomic physics, it followed, and ultimately replaced, several earlier models, including Joseph Larmor's Solar System model (1897), Jean Perrin's model (1901), the cubical model (1902), Hantaro Nagaoka's Saturnian model (1904), the plum pudding model (1904), Arthur Haas's quantum model (1910), the Rutherford model (1911), and John William Nicholson's nuclear quantum model (1912). The improvement over the 1911 Rutherford model mainly concerned the new quantum mechanical interpretation introduced by Haas and Nicholson, but forsaking any attempt to explain radiation according to classical physics.

Abraham Pais (/peɪs/; May 19, 1918 – July 28, 2000) was a Dutch-American physicist and science historian. Pais earned his Ph.D. from University of Utrecht just prior to a Nazi ban on Jewish participation in Dutch universities during World War II. When the Nazis began the forced relocation of Dutch Jews, he went into hiding, but was later arrested and saved only by the end of the war. He then served as an assistant to Niels Bohr in Denmark and was later a colleague of Albert Einstein at the Institute for Advanced Study in Princeton, New Jersey. Pais wrote books documenting the lives of these two great physicists and the contributions they and others made to modern physics. He was a physics professor at Rockefeller University until his retirement.

Ernest Rutherford, Baron Rutherford of Nelson (30 August 1871 – 19 October 1937), was a New Zealand physicist and chemist who was a pioneering researcher in both atomic and nuclear physics. He has been described as "the father of nuclear physics" and "the greatest experimentalist since Michael Faraday." In 1908, he was awarded the Nobel Prize in Chemistry "for his investigations into the disintegration of the elements, and the chemistry of radioactive substances." He was the first Oceanian Nobel laureate, and the first to perform Nobel-awarded work in Canada.

Rutherford's discoveries include the concept of radioactive half-life, the radioactive element radon, and the differentiation and naming of alpha and beta radiation. Together with Thomas Royds, Rutherford is credited with proving that alpha radiation is composed of helium nuclei. In 1911, he theorised that atoms have their charge concentrated in a very small nucleus. He arrived at this theory through his discovery and interpretation of Rutherford scattering during the gold foil experiment performed by Hans Geiger and Ernest Marsden. In 1912, he invited Niels Bohr to join his lab, leading to the Bohr model of the atom. In 1917, he performed the first artificially induced nuclear reaction by conducting experiments in which nitrogen nuclei were bombarded with alpha particles. These experiments led him to discover the emission of a subatomic particle that he initially called the "hydrogen atom", but later (more precisely) renamed the proton. He is also credited with developing the atomic numbering system alongside Henry Moseley. His other achievements include advancing the fields of radio communications and ultrasound technology.

The Bohr radius (⁠${\displaystyle a_{0}}$⁠) is a physical constant, approximately equal to the most probable distance between the nucleus and the electron in a hydrogen atom in its ground state. It is named after Niels Bohr, due to its role in the Bohr model of an atom. Its value is 5.29177210544(82)×10 m. The name "bohr" was also suggested for this unit.

In quantum mechanics, Schrödinger's cat is a thought experiment concerning quantum superposition. In the thought experiment, a hypothetical cat in a closed box may be considered to be simultaneously both alive and dead while it is unobserved, as a result of its fate being linked to a random subatomic event that may or may not occur. This experiment, viewed this way, is described as a paradox. This thought experiment was devised by physicist Erwin Schrödinger in 1935 in a discussion with Albert Einstein to illustrate what Schrödinger saw as the problems of Niels Bohr and Werner Heisenberg's philosophical views on quantum mechanics.

In Schrödinger's original formulation, a cat, a flask of poison, and a radioactive source are placed in a sealed box. If an internal radiation monitor such as a Geiger counter detects radioactivity (a single atom decaying), the flask is shattered, releasing the poison, which kills the cat. If no decaying atom triggers the monitor, the cat remains alive. Mathematically, the wave function that describes the contents of the box is a combination, or quantum superposition, of these two possibilities. Yet, when one looks in the box, one sees the cat either alive or dead, not both alive and dead. This poses the question of when exactly quantum superposition ends and reality resolves into one possibility or the other.

The Copenhagen interpretation is a collection of views about the meaning of quantum mechanics, stemming from the work of Niels Bohr, Werner Heisenberg, Max Born, and others. While "Copenhagen" refers to the city where Bohr and Heisenberg worked, the use as an "interpretation" was apparently coined by Heisenberg during the 1950s to refer to ideas developed in the 1925–1927 period, glossing over his disagreements with Bohr. Consequently, there is no definitive historical statement of what the interpretation entails.

Features common across versions of the Copenhagen interpretation include the idea that quantum mechanics is intrinsically indeterministic, with probabilities calculated using the Born rule, and the principle of complementarity, which states that objects have certain pairs of complementary properties that cannot all be observed or measured simultaneously. Moreover, the act of "observing" or "measuring" an object is irreversible, and no truth can be attributed to an object except according to the results of its measurement (that is, the Copenhagen interpretation rejects counterfactual definiteness). Copenhagen-type interpretations hold that quantum descriptions are objective, in that they are independent of physicists' personal beliefs and other arbitrary mental factors.

In physics, complementarity is a conceptual aspect of quantum mechanics that Niels Bohr regarded as an essential feature of the theory. The complementarity principle holds that certain pairs of complementary properties cannot all be observed or measured simultaneously. For example, position and momentum, frequency and lifetime, or optical phase and photon number. In contemporary terms, complementarity encompasses both the uncertainty principle and wave-particle duality.

Bohr considered one of the foundational truths of quantum mechanics to be the fact that setting up an experiment to measure one quantity of a pair, for instance the position of an electron, excludes the possibility of measuring the other, yet understanding both experiments is necessary to characterize the object under study. In Bohr's view, the behavior of atomic and subatomic objects cannot be separated from the measuring instruments that create the context in which the measured objects behave. Consequently, there is no "single picture" that unifies the results obtained in these different experimental contexts, and only the "totality of the phenomena" together can provide a completely informative description.