INTRODUCTION:
It's been an incredible period in science.
The speed of gravity is pretty much identical to the speed of light! Recently, for the first time ever, scientists were able to photograph a collision between two neutron stars. By conducting simultaneous optical and gravitational wave observations, they were able to accurately measure the speed of gravity.
THE EXPERIMENT
The landmark experiment shows that it travels at the speed of light, meaning that Einstein’s general theory of relativity has passed another test with flying colours.
Isaac Newton thought the influence of gravity was instantaneous, but Einstein assumed it travelled at the speed of light and built this into his 1915 general theory of relativity.
Light-speed gravity means that if the Sun suddenly disappeared from the centre of the Solar System, the Earth would remain in orbit for about 8.3 minutes – the time it takes light to travel from the Sun to the Earth. Then, suddenly feeling no gravity, Earth would shoot off into space in a straight line.
But the assumption of light-speed gravity has come under pressure from brane world theories, which suggest there are extra spatial dimensions rolled up very small. Gravity could take a short cut through these extra dimensions and so appear to travel faster than the speed of light – without violating the equations of general relativity.
But how can you measure the speed of gravity?
One way would be to detect gravitational waves, little ripples in space-time that propagate out from accelerating masses. But no one has yet managed to do this.
MEASURING THE SPEED OF GRAVITY
These two sets of data from the kilonova allowed scientists to compare the speed of the gamma-ray light to the speed of the gravitational waves, giving us a much clearer understanding of the speed of gravity than ever before. Previous measurements of gravitational waves had allowed scientists to narrow the range of possibles speeds of gravity to within 55 and 142 percent of c.
But this observation allowed them to narrow the difference between the speed of gravity and c further to within -3 x 10^-15 and 7 x 10^-16 of c — meaning the speed of gravity is practically the speed of light.
This scientific advancement has broad implications for fundamental physics and our understanding of the cosmos. Not least of all, determining the speed of gravity would help physicists debunk theories that contradict Einstein’s general relativity.
