metrology

Humanity’s desire to measure time more and more accurately has been a driving force in technological development, and improved clocks and the innovations behind them have repeatedly delivered unexpected applications and scientific discoveries. For instance, when sailors needed high precision timekeeping to better navigate the open seas, it motivated the development of mechanical clocks. And in turn, more accurate clocks allowed better measurements in astronomy and physics. Now, clocks are inescapable parts of daily life, but the demands of GPS, space navigation and other applications are still motivating scientists to push timekeeping to new extremes.

Next year, scientists expect to change the way we define the basic units with which we measure our universe. An article by scientists at the National Institute of Standards and Technology (NIST) written for teachers will help ensure high school physics students are hip to the news.The brief, six-page article, which appears in this month’s issue of The Physics Teacher, is designed to be a resource for teachers who are introducing the International System of Units (SI) into their classrooms. The SI, as the modern form of the metric system, has seven fundamental units, including the meter and the second. It is expected that in 2018, for the first time in history, all seven of these units will be defined in terms of fundamental constants of the universe such as the speed of light or the charge of a single electron. Only recently were all the relevant fundamental constants known with sufficient certainty to make such a redefinition possible, and the authors are eager to help students realize the change’s importance.

When is a traffic jam not a traffic jam? When it's a quantum traffic jam, of course. Only in quantum physics can traffic be standing still and moving at the same time. A new theoretical paper from scientists at the National Institute of Standards and Technology (NIST) and the University of Maryland suggests that intentionally creating just such a traffic jam out of a ring of several thousand ultracold atoms could enable precise measurements of motion. If implemented with the right experimental setup, the atoms could provide a measurement of gravity, possibly even at distances as short as 10 micrometers—about a tenth of a human hair's width.