Synopsis: Pinpointing Planck’s Constant with GPS

Using the orbiting network of GPS satellites, researchers have placed new limits on how much Planck’s constant varies with respect to relativistic changes.

GPS is helping drivers find their way and parents track their kids and pets. But now a pair of researchers—reporting in Physical Review Letters—has used the same technology to put new limits on variations in Planck’s constant.

Certain theories allow physical constants, such as the speed of light or the gravitational constant, to vary, and some astronomical observations have been interpreted as suggesting the electromagnetic coupling was different in the past. Testing these hypotheses often requires sophisticated instruments. But James Kentosh and Makan Mohageg of California State University, Northridge, have found a way to use the ubiquitous global positioning system, or GPS, to evaluate the constancy of Planck’s constant, h.

GPS relies on atomic clocks, which are sensitive to Planck’s constant through their ticking frequency, f=E/h, where E is the energy of a specific atomic transition. For a clock orbiting in one of the 32 GPS satellites, this frequency can shift with respect to ground-based clocks because of well-known relativistic effects. The GPS system keeps track of this frequency drift and broadcasts a clock correction with its signal.

Kentosh and Mohageg looked through a year’s worth of GPS data and found that the corrections depended in an unexpected way on a satellite’s distance above the Earth. This small discrepancy could be due to atmospheric effects or random errors, but it could also arise from a position-dependent Planck’s constant. Assuming the latter, the authors derive an upper limit on Planck variation. – Michael Schirber


Features

More Features »

Announcements

More Announcements »

Subject Areas

Gravitation

Previous Synopsis

Atomic and Molecular Physics

Mapping the Topology of a Cold World

Read More »

Next Synopsis

Related Articles

Synopsis: Searching for Neutron Star Gravitational Waves
Astrophysics

Synopsis: Searching for Neutron Star Gravitational Waves

The first run of LIGO and Virgo’s gravitational-wave search shows no evidence of spinning asymmetric neutron stars, but recent upgrades could make the detection possible. Read More »

Viewpoint: Spinning Black Holes May Grow Hair
Gravitation

Viewpoint: Spinning Black Holes May Grow Hair

A spinning black hole may lose up to 9% of its mass by spontaneously growing “hair” in the form of excitations of a hypothetical particle field with a tiny mass. Read More »

Synopsis: LIGO’s Black Hole Got the Boot
Astrophysics

Synopsis: LIGO’s Black Hole Got the Boot

An analysis of data from LIGO’s second gravitational-wave event indicates that a supernova can impart a strong kick to the black hole it creates. Read More »

More Articles