40 Fun Facts About Special Relativity

Albert Einstein held a day job at what kind of workplace when he published special relativity in 1905?

A patent office in Switzerland employed Einstein as an assistant examiner. The inventions that crossed his desk there included a gravel sorter and an electric typewriter.

Which navigation technology would drift by over 10 kilometres a day if its clocks ignored the effects of relativity?

GPS satellite clocks run about 38 microseconds a day fast: their speed slows them, but their height above Earth speeds them up by more. The system is built to correct for it.

In which classic film do astronauts on a near-light-speed voyage land some two thousand years after their launch?

Planet of the Apes has the ship's chronometer read 3978 as the crew abandon it, about two millennia after their 1972 departure. Relativity lets a fast traveller skip ahead like that.

Which metal owes its colour to relativity, because its innermost electrons move at over half the speed of light?

Gold would be silvery like most other metals if relativity did not apply. Its innermost electrons travel at about 58% of light speed.

Albert Einstein won the 1921 Nobel Prize in Physics for explaining what, rather than for relativity?

The photoelectric effect is named in his Nobel citation, and relativity is not. The 1921 prize was actually awarded a year late, in 1922.

Which particles seemed to outrun light between CERN and Italy in 2011, a result later traced to a loose cable?

Neutrinos sent from CERN to the Gran Sasso lab appeared to arrive too early. A fibre cable that was not fully screwed in had skewed the timing, and two of the experiment's leaders resigned.

Which Italian scientist argued in 1632 that a passenger on a smoothly sailing ship has no sense of its motion?

Galileo Galilei used the ship to answer critics who said a moving Earth would be felt. Einstein later stretched the same principle to cover light as well as mechanics.

Albert Einstein imagined lightning hitting both ends of which moving vehicle to show that simultaneity is relative?

A train passing a platform is the setting: a bystander sees both bolts strike at once, while for a passenger in the middle carriage the front bolt strikes first. Neither is wrong.

Which equation of Albert Einstein's from 1905 shows that a little matter holds an enormous amount of energy?

E = mc² multiplies mass by the speed of light squared, a huge number. It came from a short follow-up paper whose title asked whether a body's inertia depends on its energy content.

Which effect of relativity makes astronauts on the International Space Station age slightly less than people on Earth?

Time dilation trims about 5 milliseconds off an astronaut's ageing during six months in orbit at 7.7 km per second. A faster ship would widen the gap.

Which invisible medium, once thought to fill space and carry light waves, did special relativity show was not needed?

The aether was the light-bearing medium that physicists assumed light waves must travel through. Experiments in the 1880s failed to find any sign of Earth moving through it.

What name did the physicist Gerald Feinberg coin in 1967 for hypothetical particles that always move faster than light?

Tachyons have never been detected. Physicists expect they cannot exist, because a faster-than-light particle could be used to send signals into the past.

Which force does special relativity leave out, the one Albert Einstein's general theory went on to explain?

Gravity is absent from the 1905 theory, which deals with observers moving steadily in straight lines. Einstein needed about another decade to extend relativity to cover it.

Which 1887 experiment in Cleveland found light's speed unaffected by Earth's motion, a famous 'failed' result?

Michelson–Morley has been called the most famous failed experiment in history, because it detected nothing. The pair then turned their technique to making light a standard of length.

Which short-lived cosmic-ray particles reach the ground only because their speed stretches their lifetimes?

Muons made high in the atmosphere last about two millionths of a second at rest. At 98% of light speed their lifetime is about five times longer, so many survive the trip down.

Which former teacher of Albert Einstein recast special relativity in 1908 as the geometry of four dimensions?

Hermann Minkowski taught Einstein at the Zurich Polytechnic. He argued that space and time are not separate things but parts of a single four-dimensional whole.

Which Dutch Nobel laureate is named in the equations that convert measurements between moving observers?

Hendrik Lorentz derived the transformations before Einstein showed what they meant, and they were named after him in 1905. His 1902 Nobel Prize was for explaining the Zeeman effect.

Which British physicist united relativity and quantum mechanics in a 1928 equation that predicted antimatter?

Paul Dirac found that his equation implied a mirror-image partner for the electron. Carl Anderson observed that particle, the positron, in 1932, and Dirac shared the Nobel Prize a year later.

Which Greek letter stands for the factor by which time slows, equal to one at rest and soaring near light speed?

Gamma also sets how much a moving object's length and energy change. The jets behind long bursts of cosmic radiation are thought to start with a value above 100.

Whose 1860s equations, which give light one fixed speed, clashed with the old rules of relative motion?

James Clerk Maxwell showed that electric waves cross space at the speed of light. Einstein later ranked his work as the most profound and fruitful in physics since Newton.

Which CERN machine pushes protons to 99.999999% of light speed, where they carry thousands of times their rest energy?

Large Hadron Collider protons end up only about 11 km/h slower than light itself. Adding more energy barely raises their speed, just as relativity predicts.

Joseph Hafele and Richard Keating tested relativity in 1971 by flying what around the world on airliners?

Atomic clocks flown east and then west were compared with ones left behind at the US Naval Observatory. The four travelling clocks went as ordinary passengers on commercial flights.

Since 1983, which SI unit has been defined using the speed of light and a fixed fraction of a second?

Metre lengths were once set by a platinum-iridium bar kept near Paris. Tying the unit to light instead made the speed of light exact by definition, with nothing left to measure.

Which Serbian classmate, the only woman in Einstein's course at Zurich Polytechnic, was his wife in 1905?

Mileva Marić was married to Einstein from 1903 to 1919. Historians still disagree over whether she contributed to his 1905 papers, though many argue that she did not.

In which Swiss city was Albert Einstein living when he wrote his 1905 paper on special relativity?

Bern's Einsteinhaus, at Kramgasse 49, preserves the second-floor flat that Einstein rented from 1903 to 1905. It has been restored in the style of the period and is open to visitors.

Which French mathematician named the principle of relativity in 1904, a year before Einstein's theory appeared?

Henri Poincaré said that no physical experiment can tell uniform motion from rest. A conjecture of his about shapes stayed unproven for almost a century.

Which particle has no rest mass, the property that lets it travel at the fastest speed relativity allows?

Photon speed is not a choice: a massless particle can only ever move at the speed of light in a vacuum. Anything with mass can approach that speed but never reach it.

Which blue glow in nuclear reactor pools is made by particles outrunning the slowed speed of light in water?

Cherenkov radiation breaks no rule, because only light's speed in a vacuum is the limit. Pavel Cherenkov shared the 1958 Nobel Prize for being the first to detect it.

Lise Meitner used Einstein's mass–energy formula in 1938 to explain the energy released by which newly found process?

Nuclear fission made sense on a winter walk with her nephew Otto Frisch. The pieces of a split uranium nucleus weigh a little less than the original, and the missing mass becomes energy.

Light in a vacuum covers roughly what distance each second, the speed limit at the heart of special relativity?

300,000 km is a rounding of 299,792 km, a figure now fixed by definition. Even at that pace, sunlight needs more than eight minutes to reach Earth.

Which rock band's song '39 follows astronauts who return from a one-year voyage to find a century has passed?

Queen guitarist Brian May wrote and sang it, inspired by his studies in astrophysics. It is the fifth track on the album A Night at the Opera.

Relativity supplies most of the voltage in an ordinary car battery through its effect on which heavy metal?

Lead would behave much like tin if relativity did not apply, and a tin battery would not work. Calculations credit relativistic effects with about 10 of a car battery's 12 volts.

According to special relativity, which familiar force can turn into an electric one when the observer's motion changes?

Magnetism and electricity are two views of one thing. Whether an observer sees a magnetic effect or an electric one depends on that observer's frame of reference.

Albert Einstein's 1905 run of four landmark papers shares which Latin label with Isaac Newton's work of 1665–1666?

Annus mirabilis means miraculous year. Einstein was 26 and Newton only 23 when each produced the burst of work that earned the name.

Einstein's 1905 paper introducing special relativity carried the modest title 'On the Electrodynamics of' what?

Moving Bodies completed the title of a paper that contains no direct references to other papers. It was the third of the four he published that year.

Which German physicist, later a Nobel laureate, became the first to defend Einstein's special relativity in public?

Max Planck saw the theory's importance at once, and his influence got it widely accepted in Germany. He also set two of his own students to work on it.

Which Irish physicist proposed in 1889 that moving objects shrink along their line of travel, years before Einstein?

George FitzGerald put the idea in a short letter to the journal Science, where it went largely unnoticed for years. His uncle coined the word electron.

Which engineer friend did Albert Einstein thank in the closing lines of his 1905 paper on special relativity?

Michele Besso was, in Einstein's words, the best sounding board in Europe for scientific ideas. He also introduced Einstein to the writings of the sceptical physicist Ernst Mach.

Which Joe Haldeman novel follows soldiers who age a few years fighting in deep space while centuries pass at home?

The Forever War grew out of Haldeman's own service in Vietnam. Its soldiers' lost centuries are often read as the alienation of troops coming home to a changed country.

Which Danish astronomer first showed that light takes time to travel, by timing eclipses of Jupiter's moon Io?

Ole Rømer made the discovery in 1676 while working at the Royal Observatory in Paris. He deduced that light takes 22 minutes to cross Earth's orbit; the modern figure is under 17.