News & Comment

Bart Verberck reflects on measuring the speed of light, its role in metrology, and special relativity.

Understanding the muon’s magnetic moment holds the key for unlocking potential new physics, as Thomas Teubner shows.

October 23 is (unofficially) known by some chemists as Mole Day. Andrea Taroni attempts to get to grips with the concept of the mole itself, and the imminent change to its definition.

Solid angle is an ancient notion with modern relevance. A one-page primer by Ben Kravitz.

Richard Davis refreshes our memory on the venerable metre.

Hans-Georg Menzel walks us through the complex set of units characterizing radioactivity and ionizing radiation.

Tests of one of the most fundamental theories in physics reveal an issue with the size of the proton — or the Rydberg constant. Thomas Udem explains.

Michael Jentschel and Klaus Blaum explain why the most famous equation of physics needs checking — and how to do it.

Mark Keller explains how the elementary charge will soon be reinstated in metrology — and why it got sidelined in the first place.

How do you define colour? Nina Meinzer casts light on the vision it takes.

A nuclear clock could outperform atomic clocks, but its development has turned out to be a formidable task, writes Marianna Safronova.

Jay Hendricks tells about ongoing work to change the realization and dissemination of the pascal, which will lead to the elimination of mercury-barometer pressure standards.