40 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, also called prussic acid, kills with a single whiff, so the cat's fate hangs on one atom's random decay. Schrödinger meant the setup as a mockery of superposition, not 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 'He does not play dice' of 1926 targeted which physicist's statistical reading of the wave function?

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

Which polymath, a Rosetta Stone decipherer, first demonstrated two-slit interference of light?

Thomas Young's fringes overturned Newton's particle view of light, and the same two-slit setup later showed single electrons interfering with themselves. By 1814 he had translated the stone's demotic text.

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; Bohr said 'everything became clear' once he saw Balmer's formula, yet his orbits failed for any atom with more electrons. He 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 no usable signal passes between them, so relativity survives. Einstein's German phrase was 'spukhafte Fernwirkung'.

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, nominated 41 times for a Nobel Prize without winning, coined the word 'photon' in 1926?

Gilbert Lewis, the Berkeley chemist behind electron-dot diagrams, named the light quantum two decades after Einstein's 1905 paper proposed it. His fruitless nominations remain one of the great Nobel controversies.

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, which revealed quantised spin, split a beam of which metal's atoms in two?

Silver was chosen because its lone outer electron gives the atom a clean magnetic moment, and the beam split into exactly two lines instead of smearing out. Otto Stern collected the 1943 Nobel Prize alone.

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, a remarkably short wait. The microscope reads a current that tunnels across a gap about one atom wide, mapping surfaces atom by atom.

The first Bose–Einstein condensate, made in Colorado in 1995, chilled which alkali metal to 170 nanokelvin?

Rubidium-87 atoms at 170 billionths of a degree above absolute zero collapsed into one giant quantum state, behaving like a single 'superatom'. Cornell, Wieman and Ketterle shared the 2001 Nobel Prize.

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. John Preskill coined the phrase 'quantum supremacy' in 2012.

The 1926 rule that won its author a 1954 Nobel Prize 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 aristocrat'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. His examiners were unsure enough to send the thesis to Einstein for an opinion.

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 the 1950s, when Heisenberg coined it while attacking 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 before he left 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 led the 1997 Innsbruck team that first teleported the quantum state of a photon, a feat the press promptly likened to Star Trek. His later experiments sent photon pairs 144 km between Canary Islands.

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.

Lov Grover's 1996 quantum search finds one item among N unsorted entries in roughly how many steps?

√N steps instead of N means a million-entry haystack takes about a thousand queries, a quadratic speed-up that also halves the effective strength of symmetric encryption keys. It is provably optimal for unstructured search.

Which cryogenic device, with no moving parts in its cold stage, mixes two helium isotopes to reach 2 millikelvin?

Dilution refrigerators are the gleaming chandelier towers seen in photos of quantum computers, with the chip hanging at the coldest bottom stage. Their cooling comes from the heat absorbed when helium-3 dissolves into helium-4.

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 alone decides the colour: dots 5–6 nanometres wide glow red or orange while 2–3 nanometre dots glow blue or green. The 2023 Nobel Prize in Chemistry went to the three scientists who discovered and made them.

Which process, predicted by Albert Einstein in 1917, 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 1917 analysis also 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, regardless of the sample's material or shape. Von Klitzing won the 1985 Nobel Prize for it.

Which Welsh 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's radiation is so faint that a black hole the mass of the Sun would take about 10⁶⁷ years to evaporate, far longer than the universe has existed. His 1974 paper was titled 'Black hole explosions?'.

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 in 1899 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.

The BB84 protocol, the first quantum cryptography scheme, is named for 1984, Gilles Brassard and which researcher?

Charles Bennett's scheme encodes key bits in photon polarisations so that any eavesdropper inevitably disturbs them and is detected. The first working prototype, built in 1989, sent keys across 32 centimetres of open air.

Niels Bohr lived from 1932 in the honorary residence willed by J.C. Jacobsen, founder of which Danish brewery?

Carlsberg's mansion went to the Dane with the most prominent contribution to science, literature or the arts, and Bohr kept it until his death in 1962. The brewery's foundation also helped fund his institute, opened in 1921.