Measure for Measure

The assembly of the more than a million single parts of the ITER tokamak requires large-scale three-dimensional precision metrology. John Villanueva Jr gives us insights into the complexity of this project.

Wolfgang Pauli introduced the Bohr magneton as a fundamental unit of magnetic moment during an effort to find a quantum basis for magnetism, as Davide Castelvecchi recounts.

Giacomo Prando summarizes the troubled history of the radian, a unit with the odd property of appearing and disappearing seemingly at will in dimensional formulas.

When you start tearing a piece of aluminium foil apart, you create dislocations in the material. Suhas Eswarappa Prameela and Tim Weihs recount the story of the Burgers vector that is now an indispensable tool for describing dislocations.

As a unit for enzyme activity, the katal is enigmatic but struggles to find widespread acceptance. Soumitra Athavale tells its story.

The tool of choice to measure optical frequencies with extremely high precision is the optical frequency comb. Camille-Sophie Brès explains what makes this technique so powerful.

Watching the ocean’s ebb and flow may be soothing, but the history of the sverdrup unit for ocean flow is more turbulent. Tor Eldevik and Peter Mosby Haugan recount an oceanographic journey reaching high tide with Harald Ulrik Sverdrup and his unit.

Philip Lössl tells of mass spectrometry’s struggles to come to terms with terminology.

The note A tuned to 440 Hz only became the norm for musical performance in 1939 after decades of international and interdisciplinary disputes. Fanny Gribenski retraces this rocky path.

Working in a Mexican restaurant during his teenage years, Mark Buchanan discovered his love for jalapeños. Since then he has climbed higher and higher on the Scoville scale.

Tell Bartolo Luque and Fernando Ballesteros how far the Sun is from the Earth, and they will tell you the size of the Universe.

Continuously improving precision in length measurements increases understanding of our world and its phenomena, both at small and large scales, as Leo Gross reveals.

From determining the compound interest on borrowed money to gauging chances at the roulette wheel in Monte Carlo, Stefanie Reichert explains that there’s no way around Euler’s number.

Superconducting quantum interference devices can accurately measure temperatures even below 1 mK, but there’s more to them — as Thomas Schurig explains.

Imaginary numbers have a chequered history, and a sparse — if devoted — following. Abigail Klopper looks at why a concept as beautiful as i gets such a bad rap.

The way that we understand free space has varied wildly since our first conception of the vacuum. And how we measure the void has proven just as changeable, as Karl Jousten explains.

Bill Phillips celebrates a beautiful reformation of the metric system, by which scientists measure the physical world, coming into effect on World Metrology Day, 20 May 2019.

If you were ever puzzled about the fact that the detectors at the Large Hadron Collider record huge datasets despite the tiny probability of two protons colliding, this is for you. Steven Goldfarb and Katarina Anthony connect the dots.

In 2016, Peter Trueb computed 22.4 trillion digits of π. Ahead of π Day on 14 March, he reflects on the nature of π and its role in mathematics, science and philosophy.