90 Fun Facts About Quantum Physics

Schrödinger's 1935 thought experiment has a Geiger counter release a hammer onto a flask of which poison?

Hydrocyanic acid in a small flask puts the cat's life at the mercy of one atom's random decay. Schrödinger called the case burlesque: he offered it as a critique of the theory, not as a serious proposal.

Albert Einstein's 1921 Nobel Prize in Physics cited which discovery, rather than his theory of relativity?

The photoelectric effect won because the Nobel committee still doubted relativity, so the citation pointedly avoided it. Einstein had already promised the prize money to his first wife Mileva in their 1919 divorce settlement.

Einstein's 1926 letter saying God does not play dice went to which pioneer of the wave function's statistical reading?

Max Born, whose probability rule the remark questioned, waited until 1954 for a Nobel Prize awarded 'especially for his statistical interpretation of the wavefunction'. The two men stayed friends and correspondents for life.

Which polymath, a Rosetta Stone decipherer, devised the two-slit experiment that shows light interfering like a wave?

Thomas Young's wave theory met scepticism in England because it contradicted Newton, yet his two-slit setup later showed even single electrons building up interference fringes.

Max Planck's 1900 idea that energy comes in discrete quanta was devised to fit the spectrum of what?

Black-body radiation from a heated cavity refused to match classical physics, which predicted infinite energy at high frequencies, the so-called ultraviolet catastrophe. Planck won the 1918 Nobel Prize for the discovery of energy quanta.

Heisenberg's 1927 uncertainty principle says which two properties of a particle cannot both be known precisely?

Position and momentum uncertainties multiply to at least ħ/2, so a particle pinned to a tiny region must carry a wildly uncertain velocity. This is a property of waves, not a flaw in instruments.

Which term, coined in jest by Benjamin Schumacher in 1995, names the basic unit of quantum information?

A qubit can sit in a superposition of 0 and 1 at once, which is why a few hundred of them could outrun any classical computer. Schumacher said the word came up in a conversation with William Wootters.

Niels Bohr's 1913 atom model derived the Rydberg formula for the spectral lines of which element?

Hydrogen's single electron made the model tractable: it explained Balmer's 1885 formula, a puzzle for nearly thirty years, yet it failed for atoms with more electrons. Bohr won the 1922 Nobel Prize.

Einstein derided which quantum effect, since confirmed by Bell tests, as 'spooky action at a distance'?

Entanglement links particles so that measuring one instantly fixes the other's result, yet nothing usable can be signalled that way, so relativity survives. Einstein thought so strange a link could not be the whole story.

Which QED pioneer dunked a clamped O-ring in ice water during the televised 1986 Challenger hearings?

Richard Feynman showed the rubber stayed stiff when cold, exposing why the booster seals failed on the freezing launch morning. He shared the 1965 Nobel Prize with Schwinger and Tomonaga for quantum electrodynamics.

Which chemist, a perennial Nobel nominee who never won, gave the light quantum the name 'photon' in 1926?

Gilbert Lewis was not the first to use the word, and his own idea of the photon was very different from Einstein's light quantum, yet physicists adopted his name for it anyway.

Which SI unit, long defined by a platinum–iridium cylinder near Paris, was redefined in 2019 via Planck's constant?

The kilogram was the last SI unit tied to a physical object, and the Paris prototype had drifted by tens of micrograms against its copies. A Kibble balance now realises it by weighing mass against electromagnetic force.

The 1922 Stern–Gerlach experiment, later read as the first sign of electron spin, split a beam of which metal's atoms in two?

Silver atoms split into two beams where classical physics predicted a smear; Stern and Gerlach credited the old Bohr–Sommerfeld theory, and only after spin was proposed in 1925 was the split traced to a single outer electron.

Which Austrian's 1925 exclusion principle bars two electrons in one atom from sharing all four quantum numbers?

Wolfgang Pauli's rule is why atoms have shells and chemistry has a periodic table, since electrons cannot all crowd into the lowest orbit. Colleagues joked that his mere presence broke laboratory equipment, the 'Pauli effect'.

Paul Dirac's 1928 equation implied which antiparticle, found by Carl Anderson in cosmic-ray tracks in 1932?

The positron is the electron's antimatter twin, and Anderson's discovery earned him the 1936 Nobel Prize at just 31. Hospital PET scanners now rely on positrons annihilating with electrons inside the body.

George Gamow's 1928 tunnelling theory explained which radioactive decay, whose particles a sheet of paper stops?

Alpha particles are helium nuclei trapped behind an energy barrier they could never classically climb, yet they leak out with a tiny probability on each bounce. The same theory explains half-lives from microseconds to billions of years.

Binnig and Rohrer invented the scanning tunnelling microscope in 1981 at which company's Zurich laboratory?

IBM's Zurich pair shared the 1986 Nobel Prize just five years after the invention. Company scientists later used the microscope to drag single xenon atoms into place, spelling out its three-letter name.

Which state of matter was first made in 1995 by chilling rubidium gas?

Bose–Einstein condensate forms when atoms merge into one quantum state, a 'superatom'; the Colorado team got there by cooling rubidium to under a millionth of a degree above absolute zero. Einstein had predicted it seven decades earlier.

Which company claimed 'quantum supremacy' in 2019 with a Sycamore chip it said outran any supercomputer?

Google's 200-second sampling task, it said, would take a supercomputer 10,000 years, though a rival argued its Summit machine could do it in 2.5 days. Physicist John Preskill had coined the phrase 'quantum supremacy' years earlier.

A 1926 rule of quantum mechanics sets a particle's probability density equal to what?

The square of the wave function's modulus is all experiment can ever see, so the phase stays invisible unless two paths interfere. Attempts to derive the rule from deeper principles remain contested; most textbooks take it as a postulate.

Which French physicist's 1924 doctoral thesis proposed that electrons, like light, behave as waves?

Louis de Broglie, later the 7th Duke of Broglie, won the 1929 Nobel Prize once electron diffraction confirmed his idea in 1927. A copy of the thesis had been sent to Einstein, who backed it from the start.

The 1927 Davisson-Germer experiment at Bell Labs saw electrons diffract like waves off a crystal of which metal?

Nickel gave the result by accident: after air leaked into the vacuum tube, heating the oxidised target grew big crystals whose neat planes produced the diffraction peaks. Davisson shared the 1937 Nobel Prize; Germer was left out.

The orthodox reading of quantum theory, shaped by Bohr and Heisenberg in the 1920s, is named for which city?

Copenhagen became the label only in 1955, when Heisenberg apparently coined it while criticising rival interpretations such as David Bohm's. There is still no agreed statement of what the interpretation actually says.

Whose 1957 Princeton thesis launched the many-worlds interpretation, though he gave up physics for Pentagon work?

Hugh Everett's branching universes were ignored for a decade, and he never returned to academia; his son is Mark Oliver Everett, frontman of the band Eels. His adviser John Wheeler had the thesis cut sharply before submission.

Which Austrian shared the 2022 Nobel Prize with Alain Aspect and John Clauser for Bell-inequality experiments?

Anton Zeilinger's Innsbruck team teleported the quantum state of a photon in 1997, and his group later teleported states 143 km through open air between two Canary Islands, a rehearsal for satellite links.

Bell's 1964 theorem showed which kind of theory, the sort Einstein hoped for, cannot match all quantum predictions?

Local hidden variables would let each particle carry a secret pre-set answer, but Bell showed such theories obey an inequality that experiments violate. Bell said the paradox was resolved 'in the way which Einstein would have liked least'.

Which Dutch physicist predicted in 1948 that two uncharged metal plates in a vacuum would pull towards each other?

Hendrik Casimir's force comes from vacuum fluctuations: fewer wavelengths fit between the plates than outside, so the outside pushes harder. It was first measured to within 5% of theory only in 1997.

Peter Shor's 1994 quantum algorithm threatens RSA encryption because it speeds up which mathematical task?

Factoring large integers is the hard problem RSA keys rest on, and Shor's method does it exponentially faster than any known classical approach. The first demonstration, in 2001, factored 15 into 3 × 5 on a seven-spin NMR machine.

Which 1996 quantum algorithm finds one entry among a million unsorted ones in about a thousand steps?

Grover's algorithm needs only about √N steps where a classical search needs N, a quadratic speed-up. It halves the effective length of symmetric encryption keys, so doubling their length is enough to stay safe.

Which cryogenic device cools superconducting quantum chips to about a hundredth of a degree above absolute zero?

Dilution refrigerators cool by diluting one helium isotope in another: helium-3 absorbs heat as it crosses into a helium-4-rich liquid, which makes the mixing chamber where that happens the coldest point in the machine.

Which formulation of quantum theory did Heisenberg devise in 1925 on Heligoland, where he fled to escape hay fever?

Matrix mechanics used arrays of numbers whose products depend on their order, and Heisenberg had no idea these were matrices until a Göttingen colleague recognised them. Schrödinger's wave version arrived months later and proved equivalent.

Quantum dots, the nanocrystals behind QLED televisions, glow in a colour fixed by which property of each dot?

Its size decides the colour: the smaller the dot, the bluer its light, while larger dots glow orange or red. The 2023 Nobel Prize in Chemistry went to the three scientists who discovered and made them.

Which process, predicted by Albert Einstein, supplies the 'SE' in the acronym LASER?

Stimulated emission lets one passing photon coax an excited atom into releasing an identical twin, so light amplifies in lockstep. Einstein's analysis, four decades before the first laser, introduced the coefficients still named after him.

Klaus von Klitzing's 1980 discovery, the quantum Hall effect, gave metrology an exact standard for which quantity?

Electrical resistance in the quantum Hall regime comes out as h/e², about 25,813 ohms, divided by an exact integer. Theorists had expected the steps to be only approximate, and the surprise earned von Klitzing the 1985 Nobel Prize.

Which Cardiff-born physicist predicted supercurrent tunnelling between superconductors at 22, winning a 1973 Nobel Prize?

Brian Josephson's junctions now sit inside superconducting quantum processors and in SQUID magnetometers sensitive enough to read brain signals. He later took up Transcendental Meditation and a project on mind and matter.

Which physicist calculated in 1974 that black holes should leak radiation and slowly evaporate?

Stephen Hawking titled his 1974 paper 'Black hole explosions?' because a black hole that keeps leaking radiation loses mass until it disappears in a final burst.

Roughly how long is the Planck length, the scale where quantum gravity is expected to take over?

10⁻³⁵ m is about 10²⁰ times smaller than a proton, and spacetime itself may dissolve into 'foam' at that scale. Planck built the unit from just three constants: G, c and his own h.

Particles with half-integer spin, which obey the exclusion principle, are named after which Italian physicist?

Enrico Fermi lent his name to fermions via Paul Dirac, who coined the word; electrons, protons and neutrons all belong to the club. Fermi also built the first nuclear reactor, under a Chicago football stand in 1942.

Charles Bennett and Gilles Brassard's BB84 protocol of 1984 was the first scheme for what?

Quantum key distribution began with BB84, which hides each key bit in a photon's polarisation, so an eavesdropper cannot measure it without leaving detectable errors.

Niels Bohr spent his last three decades in the honorary residence willed by J.C. Jacobsen, founder of which brewery?

Carlsberg's founder willed his own house as a home for a deserving man or woman of science, literature or art, and Bohr kept it until his death in 1962. The brewery's foundation also helped fund his institute.

Which Breaking Bad character borrows the surname of physicist Werner Heisenberg as an alias in the drug trade?

Walter White first uses the name Heisenberg when confronting the dealer Tuco Salamanca, and the alias becomes notorious across the Southwestern drug trade.

Max Planck's son Erwin was hanged in 1945 for his part in a failed plot to overthrow which leader?

Adolf Hitler ignored a letter in which Max Planck personally pleaded for his son's life after the 20 July 1944 bomb plot.

Which hospital imaging technique, based on the spin of atomic nuclei, dropped 'nuclear' from its original name?

An MRI scan began life as NMRI, short for nuclear magnetic resonance imaging, until the first word was cut to avoid negative associations.

Max Planck's professor Philipp von Jolly advised him against theoretical physics because he believed the field was what?

Almost complete was Jolly's verdict on physics, which he called a nearly fully matured science; Planck's quantum idea of 1900 then overturned it.

Before winning a Nobel Prize in Physics, Niels Bohr filled which role for the football club Akademisk Boldklub?

Goalkeeper Bohr played several matches for the club beside his brother Harald, a mathematician who went on to represent the national side at the 1908 London Olympics.

Which migratory bird appears to sense Earth's magnetic field through a quantum effect in a protein in its eye?

European robin experiments point to a compass built on the radical pair mechanism, and even very weak radio interference stops the birds orienting correctly.

Erwin Schrödinger's 1944 book on the physics of life inspired the two men who solved which molecule's structure?

DNA pioneers James Watson and Francis Crick both called What Is Life? formative; the book pictured heredity stored in an 'aperiodic crystal' years before the double helix.

Which attendee of the 1927 Solvay Conference on quantum theory was the only one with Nobel Prizes in two sciences?

Marie Curie had taken the physics prize in 1903 and the chemistry prize in 1911; seventeen of the 29 people in the room were or became Nobel laureates.

Quantum tunnelling lets nuclei fuse at temperatures too low for classical physics, allowing which objects to shine?

Stars have cores too cool for nuclei to climb the electric barrier that keeps them apart, so fusion happens only because some of them leak straight through it.

Which term describes a quantum system holding several states at once, as when Schrödinger's cat is both alive and dead?

Superposition is also what lets a quantum computer's basic unit hold 0 and 1 together, until a measurement leaves just one of the two.

Which English scientist argued in his 1704 book Opticks that light is made of tiny particles rather than waves?

Isaac Newton's 'corpuscles' fell out of favour in the early 1800s as evidence for light waves piled up, but quantum theory later brought the particle picture back.

Which kind of electromagnetic wave, given off by radioactive nuclei, carries the most energy in each individual photon?

Gamma rays sit at the high-frequency end of the spectrum, with wavelengths smaller than an atom, because a photon's energy rises in step with its frequency.

In atomic physics, a 'quantum jump' is an electron's abrupt move between two of which things inside an atom?

Energy levels in an atom are discrete, so an electron is never found in between them; everyday speech borrowed 'quantum leap' for a huge advance, though the real jump is minute.

Which dessert gives its name to the 1904 model of the atom that scattered electrons through a ball of positive charge?

Plum pudding was the popular nickname, with the electrons as raisins; the model fell in 1911 when the atom's positive charge was found packed into a tiny nucleus.

Which element, cooled to about 2 kelvin, becomes a superfluid that creeps up and over the walls of its container?

Helium in its superfluid form flows so freely that a thin film siphons itself up the wall of an open cup, over the rim and down the outside.

Which particle, announced at CERN in 2012, is the quantum of the field that gives elementary particles their mass?

Higgs boson hunters analysed more than 300 trillion proton collisions at CERN's giant collider before announcing the find on 4 July 2012.

Which proposed framework for quantum gravity swaps point-like particles for tiny vibrating one-dimensional filaments?

String theory treats each particle as a different note played by the same kind of filament, and one of those vibrations matches the graviton that would carry gravity.

The 'eigen' in the quantum terms eigenstate and eigenvalue is borrowed from which language's word for 'own'?

German eigen can also mean 'proper' or 'characteristic'; mathematicians adopted it in 1904 for the special values that became the possible results of a quantum measurement.

Niels Bohr built his 1913 quantum atom after working in Manchester under which New Zealand-born physicist?

Ernest Rutherford had just shown that an atom's mass sits in a tiny central nucleus, and Bohr's quantised orbits explained why the electrons circling it do not spiral inward.

The Solvay Conferences, where Einstein and Bohr debated quantum theory, have met since 1911 in which capital city?

Brussels hosts the institutes founded by Ernest Solvay, the Belgian industrialist who developed a new process for making soda ash.

Paul Dirac's equation for the electron is inscribed on a slate memorial to him unveiled in 1995 in which London church?

Westminster Abbey's dean at first refused the memorial, believing Dirac to be anti-Christian, and took five years to be persuaded.

Niels Bohr, on receiving the Order of the Elephant, chose which Chinese symbol for the coat of arms he designed himself?

Yin and yang stood for Bohr's view that rival pictures such as wave and particle are both needed, and his Latin motto declared that opposites are complementary.

Which word do physicists use for a wave function's sudden reduction to one definite outcome when a measurement is made?

Collapse is the odd process out in quantum theory: between measurements a wave function evolves smoothly under Schrödinger's equation, then seems to change all at once.

What name is given to an atom's condition of lowest possible energy, from which its electrons cannot drop any further?

Ground state energy is never quite nothing: a quantum system keeps a residual zero-point energy even at the coldest possible temperature.

Which Greek letter, shaped like a trident, is the standard symbol for the wave function in Schrödinger's equation?

Psi appears as lower-case ψ or capital Ψ, the two most common symbols physicists write for a wave function.

The word 'quantum', which Max Planck applied to packets of energy, comes from a Latin word meaning what?

How much is the sense of Latin quantus, and in the 17th century an English 'quantum' simply meant a portion, long before physics made it the smallest possible step.

Since 1967, the SI second has been defined by a quantum transition in the atoms of which metal?

Caesium atoms flip between two hyperfine states with microwaves that cycle exactly 9,192,631,770 times a second, the tick that atomic clocks count.

Superconductivity was discovered in 1911 when Heike Kamerlingh Onnes chilled which metal to about 4 kelvin?

Mercury, frozen solid at that temperature, abruptly stopped opposing the current; the exact date, 8 April 1911, was reconstructed only a century later from Onnes's notebook.

Which Nobel laureate treated the electron as a particle, decades before his son George won for showing its wave nature?

J.J. Thomson took the 1906 prize for his studies of electricity in gases; George shared the 1937 award for the diffraction of electrons by crystals.

Which storage technology writes data by tunnelling electrons onto a 'floating gate'?

Flash memory was invented by Fujio Masuoka at Toshiba in 1980; a colleague suggested the name because erasing a block reminded him of a camera flash.

Which instrument, pioneered by Ernst Ruska in the 1930s, beats light's resolution by using far shorter wavelengths?

Electron microscope beams can have wavelengths more than 100,000 times shorter than visible light, sharpening resolution from about 200 nanometres to about 0.1.

Which American, later a Nobel Peace Prize winner, used quantum mechanics in the 1930s to explain the chemical bond?

Linus Pauling took the 1954 chemistry prize for his research on the chemical bond and the 1962 peace prize for his activism, becoming the first person to win two unshared Nobels.

Murray Gell-Mann settled the spelling of 'quark' after meeting the word in which 1939 book by James Joyce?

Finnegans Wake gave Gell-Mann only the spelling, since he already had the sound in mind; George Zweig's rival name for the particle, 'ace', never caught on.

Which microwave forerunner of the laser was first built by Charles Townes's team at Columbia University in 1953?

Maser beams first came from a stream of energised ammonia molecules; the devices now keep time in atomic clocks and amplify faint signals for radio telescopes.

Erwin Schrödinger fled Nazi-ruled Austria and worked until 1955 at an advanced studies institute in which capital?

Dublin became his home after a personal invitation from Éamon de Valera, Ireland's Taoiseach, and he stayed at its newly founded institute until he retired.

George de Hevesy hid two gold Nobel medals from the Nazis at Niels Bohr's institute by dissolving them in what?

Aqua regia kept the gold of Max von Laue and James Franck safe as a solution on a laboratory shelf; after the war it was recovered and the medals were recast.

Which co-author of the BCS theory of superconductivity was the first person to win the Nobel Prize in Physics twice?

John Bardeen shared the 1972 prize for the theory of how some chilled metals carry current without loss, sixteen years after his first for an invention at Bell Labs.

Which American won a 1927 Nobel Prize for showing that X-rays scatter off electrons the way particles would?

Arthur Compton's result was a hard sell: light's wave nature was well demonstrated, and the idea that it also behaved as particles was not easily accepted.

What name is given to a quantum system's loss of wave-like behaviour through contact with its surroundings?

Decoherence is a central challenge for building quantum computers, whose calculations rely on quantum systems evolving in isolation from the environment.

Which 1997 Nobel laureate, honoured for trapping atoms with laser light, later served as US Secretary of Energy?

Steven Chu ran the Department of Energy under Barack Obama from 2009 to 2013, the first person appointed to the US Cabinet after winning a Nobel Prize.

Quantum states are described as vectors in which abstract mathematical structure, named after a Göttingen mathematician?

Hilbert space honours David Hilbert, though he did not coin the term himself; the same mathematics also underpins signal processing and the theory of heat flow.

Which Budapest-born mathematician gave quantum mechanics its first rigorous mathematical framework in a 1932 book?

John von Neumann is also known for game theory, and one chapter of the book made a deep analysis of what happens when a quantum system is measured.

Which American physicist, who popularised the term 'black hole', also coined 'wormhole' and 'quantum foam'?

John Wheeler pictured the fabric of the universe at the smallest scales as a chaotic froth of quantum fluctuations, hence the foam.

Which name did Paul Ehrenfest coin in 1911 for classical physics' prediction that hot objects emit infinite energy?

Ultraviolet catastrophe describes how the old formula misbehaves at high frequencies, where its predicted output grows without limit, something never observed in a real glowing cavity.

A 1999 experiment showed wave-like interference using which football-shaped molecules, each made of 60 carbon atoms?

Buckyballs behaved like waves despite being hefty cages of 60 atoms, and by 2019 the same had been shown for molecules of up to 2,000 atoms.

Which phenomenon, discovered in 1933, is the expulsion of a magnetic field from a metal as it turns superconducting?

The Meissner effect arises because lossless currents near the metal's surface generate an opposing field that exactly cancels the applied one inside.

Which acronym names the superconducting loops used as ultra-sensitive magnetometers to map activity in the brain?

SQUID stands for superconducting quantum interference device, and arrays of them pick up the minute magnetic fields produced by firing neurons.

The quantum effect in which constant observation freezes an unstable state is named after which Greek philosopher?

Zeno of Elea argued that an arrow in flight is motionless at every instant and so cannot be moving; an unstable atom observed without pause seems frozen in the same way.

The energy operator at the heart of Schrödinger's equation is named after which 19th-century Irish mathematician?

William Rowan Hamilton recast classical mechanics in a form built around a system's total energy, a framework that proved historically important to quantum physics.

Paul Dirac named the two halves of his notation for quantum states by splitting which ordinary English word in two?

Bracket splits into 'bra' and 'ket', matching the left and right angle marks that enclose a quantum state in Dirac's shorthand.