Synopsis: Quantum Bending of Light

Theorists calculate how quantum gravity effects could alter the bending of light induced by massive objects.
Synopsis figure
NASA

Light traveling close to an object gets deflected from its path because of the pull of gravity. For a massive object like the Sun, this deflection is measurable: The best measurements to date show that the gravitational pull of the Sun deflects light by 0.00049º—in line with the predictions of general relativity. Now Niels Bjerrum-Bohr, at the Niels Bohr Institute in Denmark, and colleagues have calculated how this deflection would be altered when gravity is described as a quantum field.

The authors describe gravity using an effective-field theory—a low-energy approximation of a possible underlying quantum-field theory of gravity. This allowed them to compute how photons couple to gravitational effects, formulating an analytical solution to the problem of light deflection by a heavy object like the Sun or a Schwarzschild black hole. While their predicted quantum correction is too small to be measured experimentally (the effect of gravity is 80 orders of magnitude bigger), they show that quantum effects do cause a difference. This difference arises from the fact that massless particles like photons are no longer confined to traveling exactly on geodesics (in general relativity, the straight lines modified by spacetime curvature along which any free-falling particle moves). In particular, they are predicted to bend differently depending on their spin. These departures from the behavior predicted by general relativity amount to a deviation from Einstein’s equivalence principle. The computational framework presented by the authors provides a simple way to evaluate the possible effects of quantum gravity on light bending and other cosmological phenomena.

This research is published in Physical Review Letters

–Katherine Wright


Features

More Features »

Announcements

More Announcements »

Subject Areas

GravitationQuantum Physics

Previous Synopsis

Next Synopsis

Superconductivity

Vortices Queue Up in a Nanowire

Read More »

Related Articles

Synopsis: Neutron Test for Newton’s Gravity
Gravitation

Synopsis: Neutron Test for Newton’s Gravity

Experiments with neutrons search for violations of gravity’s inverse square law at subnanometer distances. Read More »

Viewpoint: Moiré Effect Could Enhance Neutron Interferometry
Gravitation

Viewpoint: Moiré Effect Could Enhance Neutron Interferometry

A new and more flexible neutron interferometer design relies on the moiré effect, in which two periodic patterns are combined to give a longer-period pattern. Read More »

Synopsis: Quantum Simulators Tackle Energy Transfer
Quantum Information

Synopsis: Quantum Simulators Tackle Energy Transfer

A quantum simulator made of two trapped-ion qubits can model quantum effects occurring during energy-transfer processes in molecules. Read More »

More Articles