Measure the Gravitational Attraction of Two Spheres

Using the same idea, Planck's constant, but a completely different approach using atoms and how fast they recoil when you hit them with a photon. You can then measure the mass of an atom and kilograms. And this gives you another way of using Planck's Constant to get a kilogram.

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NIST Fellow William D. Phillips received the 1997 Nobel Prize in Physics “for development of methods to cool and trap atoms with laser light.” He shared the honor with Steven Chu and Claude Cohen-Tannoudji. Their work combined to create some of the most important technologies of modern atomic physics, which thousands of researchers worldwide employ today for a wide variety of applications. Today, he joins us to discuss time keeping throughout history and breakthroughs on the way to the best clocks ever made!

Phillips began his experiments with laser trapping and cooling shortly after he arrived in 1978 at the National Bureau of Standards (the agency that became NIST), with the intent of creating a more accurate atomic clock. Several of his innovations in the following years became landmarks in the field. These included a device using a laser along with a magnetic field to decelerate and cool an atomic beam (the “Zeeman slower”); demonstrating the first device that trapped electrically neutral atoms (a magnetic trap); and measuring a temperature far below that predicted by the accepted theory of laser cooling at the time (known as sub-Doppler cooling).