60 Fun Facts About Physics

Roughly how fast does light travel through empty space?

The exact figure is 299,792,458 metres per second, and the metre itself is now defined from it. That works out to about one billion kilometres per hour.

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

The Principia's full title is Philosophiae Naturalis Principia Mathematica, and it also set out universal gravitation. It was written in Latin.

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

It honours the German physicist Georg Ohm, whose law links voltage, current and resistance. Omega was chosen because the letter O was easily confused with zero.

What phenomenon makes the daytime sky look blue?

Air molecules scatter short blue wavelengths far more than long red ones. The same effect leaves the low Sun looking orange at twilight once the blue has been scattered away.

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

That is roughly a kilometre every three seconds, which is why you count the seconds between lightning and thunder. In fresh water sound moves more than four times faster.

Absolute zero corresponds to which temperature on the Celsius scale?

It is the point where a gas's pressure and volume would extrapolate to nothing. In 1779 Johann Lambert had already estimated absolute cold at about −270 °C.

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?

He was honoured for discovering X-rays, which are still called Röntgen rays in many languages. He refused to patent the discovery.

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

The figure is not the same everywhere: it is about 0.5% larger at the poles than at the Equator, so you weigh very slightly more in Helsinki than in Singapore.

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

Protons and neutrons are the best-known hadrons. The 27 km ring near Geneva is the world's largest and highest-energy particle accelerator.

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

He measured the mass-to-charge ratio of cathode-ray 'corpuscles' and found them about 1,400 times lighter than a hydrogen ion. His son George later won a Nobel for showing electrons behave as 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?

The announcement came on 4 July, ending a search that had lasted about 40 years. The new particle weighed in at around 125 GeV.

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

It came out of a discussion with Albert Einstein and was meant as a critique of the Copenhagen view of quantum mechanics, not an endorsement of it.

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

The principle is the foundation of fluid mechanics and explains why steel ships float. It does not account for surface tension, which is what lets a needle rest on water.

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

He was trying to explain star colours, an application that turned out to be wrong, but the effect itself was right and now underpins everything from radar guns to medical ultrasound.

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

It has largely replaced pounds per square inch worldwide, though the United States still clings to psi. Weather maps usually quote it in hectopascals.

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

Relativity was still considered too controversial by the Nobel committee. He was awarded the 1921 prize a year late, in 1922.

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

She remains the only person to win Nobel Prizes in two different sciences. The 1911 award was for discovering radium and polonium.

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

That is why ultraviolet photons carry more punch than red ones. Since 2019 the constant has been 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?

The reactor was built under the stands of a disused football stadium at the University of Chicago. Ten days later its output was raised to a mighty 200 watts.

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 was studying resistance at cryogenic temperatures and watched it vanish completely. He won the 1913 Nobel Prize for his low-temperature work.

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

He hung it first at the Paris Observatory and then under the dome of the Panthéon. A year later he did the same job with a gyroscope.

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

A fridge magnet lifting a paperclip beats the pull of the entire planet. It only dominates at planetary scales because it is always attractive and reaches infinitely far.

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

The phrase 'Three quarks for Muster Mark' appealed to him because he had proposed three of the particles. His co-proposer George Zweig preferred the name 'aces'.

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

They are up, down, charm, strange, top and bottom. Only up and down are found 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?

The signal, GW150914, came from two merging black holes and was picked up on 14 September, but the announcement was held back until February 2016.

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

They were trying to eliminate a persistent hiss from a horn antenna in Holmdel, New Jersey. The leftover glow of the Big Bang won them the 1978 Nobel Prize.

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

Nineteenth-century physics assumed light needed a medium to wave in, just as sound needs air. The 'decidedly negative result' helped clear the way for special relativity.

Which German physicist introduced the uncertainty principle in 1927?

His original paper used the German word 'Ungenauigkeit', meaning imprecision. The tidy modern inequality was actually proved by Earle Kennard later the same year.

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

The energy of emitted electrons seemed to go missing, so Pauli proposed an invisible neutral particle carrying it away. It took until 1956 to actually 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?

Above it, electron degeneracy pressure can no longer hold the star up. Lev Landau computed a similar value in 1932 but did not apply it to white dwarfs.

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 atoms to 170 nanokelvins. They shared the 2001 Nobel Prize with Wolfgang Ketterle.

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

The International Prototype was kept near Paris, and its copies slowly drifted apart in mass. It is now defined from the Planck constant instead.

Robert Millikan's 1909 oil drop experiment measured what?

He and Harvey Fletcher watched charged oil droplets hover between electrified plates. Millikan later faced accusations of quietly discarding inconvenient data.

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

Someone in the audience reportedly suggested it, and he liked its brevity and 'advertising value'. He also coined the phrase '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?

Its exact value is about 0.0072973525643. Arthur Eddington once argued its reciprocal must be precisely the integer 137, an idea now regarded as numerology.

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

Cavendish reported his result as the density of the Earth, 5.4 g/cm³, which hinted at a dense iron core long before seismology confirmed it.

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?

Ironically, he was a champion of the rival steady-state model and used the phrase to contrast it with his own theory. It stuck anyway.

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

John Bardeen, Walter Brattain and William Shockley applied two gold contacts to a germanium crystal and got more power out than in. They shared the 1956 Nobel Prize.

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

The effect is absurdly slow for stellar-mass black holes, but a small primordial black hole would lose mass faster and faster and end in a burst of radiation.

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.

Which Scottish physicist's equations, published in the 1860s, unified electricity, magnetism and optics?

He realised in 1861 that electromagnetic waves and light were the same thing. Einstein kept his portrait on the wall alongside Faraday and Newton.

Sound cannot travel through which of the following?

Sound is a mechanical disturbance and needs a medium to carry it, which is why space is silent. In steel it moves almost 15 times faster than in air.

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

That angle is a turning point where many light paths pile up. The 22° figure belongs to a different phenomenon: the halo around the Sun caused by ice crystals.

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 showed the balls landed together, but the experiment was given less credit than Galileo's more substantial work.

Who discovered radioactivity in 1896 while experimenting with uranium salts?

He had expected phosphorescent minerals to give off X-ray-like radiation only after sitting in sunlight, then found the uranium glowed through photographic plates all by itself.

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?

Like Ptolemy, he used controlled experiments to verify the laws of reflection and refraction.

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

The same Scientific Revolution saw Galileo's telescopic astronomy and Newton's unification of motion and gravitation.

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

In the same century Isidore of Miletus compiled the works of Archimedes later copied in the Archimedes Palimpsest.