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Related Concept Videos

Equation of Motion: Center of Mass01:14

Equation of Motion: Center of Mass

The equation of motion for a single particle can be expanded to encompass a system of particles consisting of n particles. For any arbitrarily chosen particle within this system, the net force acting upon it is the aggregate of both internal and external forces. Extending this principle to all particles within the system results in the equation of motion for the entire assembly.
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Updated: May 15, 2026

Preparing an Isotopically Pure 229Th Ion Beam for Studies of 229mTh
10:42

Preparing an Isotopically Pure 229Th Ion Beam for Studies of 229mTh

Published on: May 3, 2019

A clock directly linking time to a particle's mass.

Shau-Yu Lan1, Pei-Chen Kuan, Brian Estey

  • 1Department of Physics, University of California-Berkeley, CA 94720, USA.

Science (New York, N.Y.)
|January 12, 2013
PubMed
Summary
This summary is machine-generated.

Scientists developed a new clock linking time and mass using quantum mechanics. This breakthrough enables precise microscopic mass measurements and redefines the second, impacting fundamental physics and SI units.

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Last Updated: May 15, 2026

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Area of Science:

  • Quantum Physics
  • Metrology
  • Atomic Physics

Background:

  • Timekeeping historically relies on oscillating systems, from celestial bodies to atomic transitions.
  • Relativity and quantum mechanics link a particle's mass (m) to its Compton frequency (ω(0) = mc²/ħ).
  • A clock based on Compton frequency could offer high-precision mass measurements and a fundamental time definition.

Purpose of the Study:

  • To demonstrate a clock directly referencing the Compton frequency (ω(0)).
  • To establish a link between fundamental constants of time and mass.
  • To enable high-precision measurements of microscopic masses.

Main Methods:

  • Utilizing an optical frequency comb to self-reference a Ramsey-Bordé atom interferometer.
  • Synchronizing an oscillator to a subharmonic of the Compton frequency (ω(0)).
  • Directly measuring microscopic masses with high accuracy.

Main Results:

  • Successfully demonstrated a clock based on the Compton frequency of a particle.
  • Achieved a mass measurement accuracy of 4 × 10⁻⁹.
  • Provided a direct experimental link between time and mass.

Conclusions:

  • The developed clock enables fundamental definitions of time and precise mass measurements.
  • This technology supports the proposed revision of SI units.
  • Integration with projects like Avogadro can yield calibrated kilograms.