by Lisa Zyga
Artist’s illustration of two merging neutron stars. Credit: NSF/LIGO/Sonoma State University/A. Simonnet
(Phys.org)—Recent gravitational wave detections have allowed physicists to confirm with greater and greater precision what Einstein predicted over 100 years ago in the theory of general relativity: that gravity does not act instantaneously as Newton thought, but instead propagates at the speed of light.
On the other hand, when a source emits only gravitational waves, scientists must detect the same signal in multiple Earth-based detectors and measure the (very slight) difference in arrival times. The scientists of the PRL paper did this by comparing signals detected by two LIGO detectors located 1800 miles apart: one in Hanford, Washington, and the other in Livingston, Louisiana.
As the physicists explain, it's possible to greatly improve the bounds on the speed of gravity using sources that emit only gravitational waves. For example, using four detectors located at different places on Earth, with five gravitational wave events for comparison, the constraints could improve to within 1% of the speed of light. But they could still not reach the degree of precision of experiments that have access to both gravity and light.
Overall, bounding the speed of light has many significant implications for fundamental physics and cosmology. One of the biggest implications is that the tight bounds provide a more precise test of general relativity and rule out proposed alternatives to general relativity.
"Many alternative theories of gravity, including some that have been invoked to explain the accelerated expansion of the Universe, predict that the speed of gravity is different from the speed of light," Cornish said. "Several of those theories have now been ruled out, thereby restricting the ways in which Einstein's theory can sensibly be modified, and making dark energy a more likely explanation for the accelerated expansion."
Explore further: Stronger tests of Einstein's theory of general relativity with binary neutron stars
More information: Neil Cornish, Diego Blas, and Germano Nardini. "Bounding the Speed of Gravity with Gravitational Wave Observations." Physical Review Letters. DOI: 10.1103/PhysRevLett.119.161102
B.P. Abbott, et al. (LIGO Scientific Collaboration and Virgo Collaboration, Fermi Gamma-ray Burst Monitor, and INTEGRAL.) "Gravitational Waves and Gamma-Rays from a Binary Neutron Star Merger: GW170817 and GRB 170817A." The Astrophysical Journal Letters. DOI: 10.3847/2041-8213/aa920c
Journal reference: Physical Review Letters
Astrophysical Journal Letters
Artist’s illustration of two merging neutron stars. Credit: NSF/LIGO/Sonoma State University/A. Simonnet
(Phys.org)—Recent gravitational wave detections have allowed physicists to confirm with greater and greater precision what Einstein predicted over 100 years ago in the theory of general relativity: that gravity does not act instantaneously as Newton thought, but instead propagates at the speed of light.
On the other hand, when a source emits only gravitational waves, scientists must detect the same signal in multiple Earth-based detectors and measure the (very slight) difference in arrival times. The scientists of the PRL paper did this by comparing signals detected by two LIGO detectors located 1800 miles apart: one in Hanford, Washington, and the other in Livingston, Louisiana.
As the physicists explain, it's possible to greatly improve the bounds on the speed of gravity using sources that emit only gravitational waves. For example, using four detectors located at different places on Earth, with five gravitational wave events for comparison, the constraints could improve to within 1% of the speed of light. But they could still not reach the degree of precision of experiments that have access to both gravity and light.
Overall, bounding the speed of light has many significant implications for fundamental physics and cosmology. One of the biggest implications is that the tight bounds provide a more precise test of general relativity and rule out proposed alternatives to general relativity.
"Many alternative theories of gravity, including some that have been invoked to explain the accelerated expansion of the Universe, predict that the speed of gravity is different from the speed of light," Cornish said. "Several of those theories have now been ruled out, thereby restricting the ways in which Einstein's theory can sensibly be modified, and making dark energy a more likely explanation for the accelerated expansion."
Explore further: Stronger tests of Einstein's theory of general relativity with binary neutron starsMore information: Neil Cornish, Diego Blas, and Germano Nardini. "Bounding the Speed of Gravity with Gravitational Wave Observations." Physical Review Letters. DOI: 10.1103/PhysRevLett.119.161102
B.P. Abbott, et al. (LIGO Scientific Collaboration and Virgo Collaboration, Fermi Gamma-ray Burst Monitor, and INTEGRAL.) "Gravitational Waves and Gamma-Rays from a Binary Neutron Star Merger: GW170817 and GRB 170817A." The Astrophysical Journal Letters. DOI: 10.3847/2041-8213/aa920c
Journal reference: Physical Review Letters
Astrophysical Journal Letters
