60 Fun Facts About Physics

Roughly how fast does light travel through empty space?

Light travels at about 300,000 km per second through empty space, exactly 299,792,458 metres per second; since 1983 the metre has been defined from that speed.

Whose three laws of motion were first published in the Principia in 1687?

Isaac Newton set out the three laws in Philosophiae Naturalis Principia Mathematica, written in Latin and published in 1687, alongside universal gravitation.

Which SI unit, symbolised by the Greek letter omega, measures electrical resistance?

The ohm honours the German physicist Georg Ohm, whose 1827 law links voltage, current and resistance; one ohm passes one ampere under one volt.

What phenomenon makes the daytime sky look blue?

Rayleigh scattering by air molecules affects short blue wavelengths far more than long red ones, so scattered blue light fills the sky; the low Sun turns orange as its blue is scattered away.

At 20 °C, how fast does sound travel through air?

Sound moves at about 343 metres per second in air at 20 °C, roughly a kilometre every three seconds, which is why you count between lightning and thunder.

Absolute zero corresponds to which temperature on the Celsius scale?

Absolute zero is −273.15 °C, or 0 kelvin, the point to which an ideal gas's pressure would extrapolate to nothing; Johann Lambert had estimated about −270 °C in 1779.

Which SI unit of power is named after a Scottish inventor?

James Watt improved the steam engine, and Werner von Siemens proposed naming the unit after him. The absolute watt formally joined the SI in 1960.

Who received the very first Nobel Prize in Physics, in 1901?

Wilhelm Röntgen won the first physics Nobel in 1901 for discovering X-rays, known as Röntgen rays in German and other languages; he never patented them.

Ignoring air resistance, by roughly how much does a falling object's speed increase each second?

A falling object's speed grows by about 9.8 m/s every second; the figure is about 0.5% larger at the poles than at the Equator, so you weigh slightly more in Helsinki than in Singapore.

In the name of CERN's Large Hadron Collider, what is a hadron?

A hadron is a particle made of quarks bound by the strong force; the proton is the best-known example, and the LHC's 27 km ring near Geneva collides protons.

Which British physicist is credited with discovering the electron in 1897?

J. J. Thomson showed in 1897 that cathode rays were particles over a thousand times lighter than a hydrogen ion; his son George later won a Nobel for showing electrons diffract like waves.

Which SI unit is defined as one cycle or event per second?

It honours Heinrich Hertz, the first person to prove conclusively that electromagnetic waves exist. Like all units named after people, it is lower-case when written out in full.

In which year did the ATLAS and CMS experiments at CERN announce the discovery of the Higgs boson?

ATLAS and CMS announced the Higgs boson on 4 July 2012, nearly half a century after Peter Higgs and others proposed it in 1964; the particle weighed about 125 GeV.

In which year did Erwin Schrödinger describe his famous cat thought experiment?

Schrödinger published the cat paradox in 1935, the year of the EPR paper, after correspondence with Einstein; it was a critique of the Copenhagen interpretation, not an endorsement.

Whose principle says buoyant force equals the weight of fluid displaced?

Archimedes' principle, from the Greek mathematician of Syracuse in the third century BC, explains why steel ships float: the displaced water weighs as much as the ship.

Christian Doppler first proposed his famous effect in an 1842 treatise about the coloured light of what?

Doppler's 1842 paper was titled 'On the coloured light of the binary stars'; his idea that the effect explains star colours was wrong, but the effect itself was right.

Which SI unit of pressure is named after a French mathematician who experimented with barometers?

The pascal honours Blaise Pascal, who in 1648 had a barometer carried up the Puy de Dôme to show that air pressure falls with altitude; weather maps quote hectopascals.

Albert Einstein's Nobel Prize in Physics was awarded specifically for his work on which phenomenon?

The 1921 prize, announced in 1922, cited Einstein's law of the photoelectric effect; the committee judged relativity too controversial to reward.

Marie Curie won the 1903 Nobel Prize in Physics and a second Nobel in 1911 in which field?

Her 1911 Nobel was in Chemistry, for discovering radium and polonium; she was the first person to win Nobel Prizes in two different sciences.

The Planck constant links a photon's energy to which property of the light?

E = hν: a photon's energy is the Planck constant times its frequency, which is why ultraviolet photons carry more punch than red ones; since 2019 h is fixed at exactly 6.62607015 × 10⁻³⁴ J·s.

Which SI unit of energy is named after an English physicist born in 1818?

James Prescott Joule was a brewer's son who worked out how much mechanical work it takes to heat water. One of these units is the work done pushing with a force of one newton over one metre.

Which physicist led the first self-sustaining nuclear chain reaction at Chicago Pile-1 in 1942?

Enrico Fermi led the team that took Chicago Pile-1 critical on 2 December 1942 in a squash court under the west stands of Stagg Field, proving a controlled chain reaction possible.

Which particle did James Chadwick discover in 1932, earning him a Nobel Prize three years later?

His letter to Nature was titled 'Possible Existence of a Neutron' after only about two weeks of experiments. The discovery made it possible to create elements heavier than uranium.

In the acronym LASER, what does the letter S stand for?

The full phrase is light amplification by stimulated emission of radiation. Physicists have joked that LOSER, for light oscillation, would have been more accurate.

Superconductivity was discovered in 1911 in which metal, cooled to a few degrees above absolute zero?

Heike Kamerlingh Onnes saw the resistance of mercury vanish at about 4.2 K in 1911, having liquefied helium three years earlier; he won the 1913 Nobel Prize for low-temperature work.

Léon Foucault's famous pendulum of 1851 was the first simple, direct demonstration of what?

Foucault's pendulum, hung first at the Paris Observatory and then under the Panthéon's dome in 1851, swung in a slowly turning plane, showing the rotation of the Earth directly; he repeated the feat with a gyroscope in 1852.

Which of the four fundamental interactions is by far the weakest at the atomic scale?

Gravity is weaker than the other three by dozens of orders of magnitude: a fridge magnet lifting a paperclip beats the pull of the whole planet; it dominates at large scales only because it is always attractive.

Murray Gell-Mann took the word 'quark' from which novel?

The line 'Three quarks for Muster Mark' in James Joyce's Finnegans Wake appealed to Gell-Mann because he had proposed three such particles; George Zweig preferred the name 'aces'.

How many flavours of quark are there in the Standard Model?

There are six quark flavours: up, down, charm, strange, top and bottom; only up and down occur in ordinary matter, the rest appear briefly in accelerators and cosmic rays.

In which year did LIGO make the first direct detection of gravitational waves?

LIGO recorded GW150914 on 14 September 2015, the signal of two merging black holes; the detection was announced in February 2016.

What did radio astronomers Arno Penzias and Robert Wilson discover by accident in 1964?

The persistent hiss in their Holmdel, New Jersey horn antenna was the cosmic microwave background, the leftover glow of the Big Bang; it won them the 1978 Nobel Prize.

The 1887 Michelson–Morley experiment failed to detect Earth's motion through what?

The luminiferous aether was the supposed medium that light waved in, as sound does in air; the 1887 null result helped clear the way for Einstein's special relativity of 1905.

Which German physicist introduced the uncertainty principle in 1927?

Werner Heisenberg's 1927 paper used the word 'Ungenauigkeit', imprecision; the tidy modern inequality was proved by Earle Kennard later the same year.

Wolfgang Pauli postulated the neutrino in 1930 to rescue energy conservation in which process?

In beta decay the emitted electrons carried a spread of energies, as if some went missing, so Pauli proposed an invisible neutral particle; it took until 1956 to detect one.

At what temperature in Celsius do ice, liquid water and vapour coexist at the triple point?

It happens only at a very low pressure of about 611 pascals. Until 2019 this point was used to define the kelvin exactly.

What is engraved on Ludwig Boltzmann's tombstone in Vienna?

The inscription reads S = k log W. He died in 1906, before the atomic theory his statistical mechanics relied on had been fully accepted.

The Chandrasekhar limit, the maximum mass of a stable white dwarf, is roughly how many solar masses?

The limit is about 1.4 solar masses; above it electron degeneracy pressure can no longer hold a white dwarf up. Chandrasekhar derived it in 1930, aged 19, on the voyage to England.

The eerie blue glow in the water of a nuclear reactor pool is a classic example of which effect?

It appears when charged particles outrun light's speed in water. Pavel Cherenkov first detected it in 1934 and shared the 1958 Nobel Prize with Igor Tamm and Ilya Frank.

The first Bose–Einstein condensate, created in 1995 in Colorado, used a gas of which element's atoms?

Eric Cornell and Carl Wieman chilled about two thousand rubidium-87 atoms to 170 nanokelvins at JILA in Boulder; they shared the 2001 Nobel Prize with Wolfgang Ketterle.

From 1889 until May 2019, the kilogram was defined by what?

A metal prototype cylinder of platinum-iridium, kept at Sèvres near Paris, defined the kilogram; its copies drifted apart in mass, so from 2019 the kilogram has been fixed via the Planck constant.

Robert Millikan's 1909 oil drop experiment measured what?

Millikan and Harvey Fletcher balanced charged oil droplets between electrified plates and found every charge a multiple of one value, the charge of the electron; Millikan won the 1923 Nobel.

Which physicist adopted and popularised the term 'black hole' after a lecture in December 1967?

John Archibald Wheeler took up 'black hole' after an audience member suggested it at his December 1967 lecture, liking its 'advertising value'; he also coined 'a black hole has no hair'.

Which Nobel laureate reacted to the discovery of the muon with the quip 'Who ordered that?'

The muon turned out to be nothing more than a heavy electron with no role in holding nuclei together, which struck physicists as bafflingly pointless.

The fine-structure constant, which sets the strength of electromagnetism, is approximately equal to what?

The fine-structure constant is about 1/137, or 0.0072973525643; Arthur Eddington argued its reciprocal had to be exactly the integer 137, an idea regarded as numerology.

Henry Cavendish's 1797–98 torsion balance experiment was the first to give an accurate value for what?

Cavendish's torsion balance yielded the gravitational constant in all but name: he reported Earth's density as 5.4 times water, which implies G within about 1% of today's value.

The Geiger–Marsden gold foil experiments led Ernest Rutherford to propose that atoms have what?

Some alpha particles bounced back at more than 90 degrees, which Rutherford compared to firing a shell at tissue paper and having it come back. The nucleus is at least 10,000 times smaller than the atom.

Who coined the term 'Big Bang' during a BBC radio broadcast in 1949?

Fred Hoyle, a champion of the rival steady-state model, used 'Big Bang' on the BBC's Third Programme in 1949 to contrast it with his own theory; the name stuck anyway.

The first working transistor was built in 1947 at which laboratory?

At Bell Labs in Murray Hill, New Jersey, John Bardeen and Walter Brattain pressed two gold contacts onto a germanium crystal in December 1947; they shared the 1956 Nobel with William Shockley.

Per Hawking's 1974 theory, what does his namesake radiation eventually do to a black hole?

Hawking radiation makes it evaporate: a stellar-mass black hole would take far longer than the universe's age, but a small primordial one loses mass ever faster and ends in a burst.

Which chemist popularised the word 'photon' in a 1926 letter to the journal Nature?

Einstein had introduced the idea of light quanta in 1905, but it was two decades before the name caught on. Lewis is also known for the electron-dot diagrams named after him.

Whose equations, published in the 1860s, unified electricity, magnetism and optics?

James Clerk Maxwell showed in 1861-62 that electromagnetic waves travel at the speed of light and so must be light; Einstein kept Maxwell's portrait on his study wall beside Faraday's.

Sound cannot travel through which of the following?

Sound is a mechanical disturbance that needs a medium, so it cannot cross a vacuum, which is why space is silent; in steel it moves roughly 15 times faster than in air.

At roughly what angle is light returning from a raindrop most intense, forming the primary rainbow?

The primary bow sits at about 42° from the antisolar point, a turning angle where many light paths pile up; the 22° figure belongs to the ice-crystal halo around the Sun.

In which Dutch city did Simon Stevin drop lead balls from a church tower in 1586, before Galileo's Pisa test?

Stevin and Jan Cornets de Groot dropped the balls from the Nieuwe Kerk tower in Delft, about 10 metres, and heard them land together; Galileo's work later won the credit.

Who discovered radioactivity in 1896 while experimenting with uranium salts?

Henri Becquerel expected phosphorescent uranium salts to emit X-ray-like rays only after sunlight, then found they fogged photographic plates even in a dark drawer; he shared the 1903 Nobel with the Curies.

The word 'physics' ultimately derives from the Greek 'phúsis', meaning what?

Latin 'physica' meant 'study of nature', borrowed from the Greek 'phusikḗ' for natural science.

Which pre-Socratic philosopher proposed atomism, an idea confirmed roughly 2,000 years later?

Leucippus and his pupil Democritus argued matter was made of indivisible atoms; the pre-Socratics insisted every event had a natural cause.

Ibn al-Haytham's 'Book of Optics' replaced the Greek notion of vision emanating from the eye with what?

Ibn al-Haytham argued that vision happens when light rays from each point of an object enter the eye, and he tested reflection and refraction with controlled experiments, as Ptolemy had.

Between which years did Johannes Kepler determine his laws of planetary motion?

Kepler's laws date from 1609 and 1619: the first two appeared in Astronomia Nova, the third, the harmonic law, in Harmonices Mundi.

Which sixth-century Byzantine scholar challenged the dominant Aristotelian approach to science?

John Philoponus, a Christian scholar in Alexandria, attacked Aristotle's physics in the 500s, arguing a thrown body carries an impressed force, an idea later called impetus.