It is not often that people associate Albert Einstein with getting something wrong, yet even he made a mistake when he could not bring himself to believe in the existence of gravitational waves, as predicted by his own theory of general relativity. Luckily he was dissuaded from withholding his astonishing findings by a colleague, though he himself could not be convinced as to their existence for the next twenty years. For those unfamiliar with gravitational waves, they are minute ripples in the fabric of space and time caused by the acceleration of extremely heavy objects. A good example of the kind of phenomenon that can produce gravitational waves is a pair of black holes orbiting each other. These waves travel through space at the speed of light in a manner akin to the ripples that appear on a pond after you throw a stone into it.
Whilst the scientific community has been aware of their existence theoretically for over 70 years, the physical evidence for these waves was not found until their detection by the Laser Interferometer Gravitational-wave Observatory (LIGO) experiment in September 2015. This initial detection provided experimental evidence as to their existence, and opened the door to a whole new branch of astronomy. On the 1st June, the LIGO experiment announced a third such detection of the waves recorded in January. This new results has allowed for other aspects of Einstein’s theory to be put to the test. One such facet is whether gravitational waves have a dispersion relation; that is to say whether waves of different frequencies travel at different velocities. The evidence from this particular detection suggests they do not, once again perfectly matching the predictions of general relativity.
The gravitational waves from this month’s detection were generated from the collision of two black holes, 3 billion light years away – over twice as far away as the previous two detection’s sources. When they collided, they produced more energy than all of the stars in the universe shining at any one time, distorting the fabric of space and time around them. The LIGO team, which includes scientists from the University of Glasgow, are excited at the prospect of observing other events not detected by normal telescopes, and further understanding the dark corners of our universe.