“For this binary black hole system, it made a distinctive, rising ‘whoooop!’ sound.”
Matthew Evans, physicist at the Massachusetts Institute of Technology, on the frequency of the ‘chirps’ emitted by the black holes merging.
In 1916, Einstein predicted the existence of gravitational waves in his paper ‘Näherungsweise Integration der Feldgleichungen der Gravitation’. This was built on in the much more catchily named ‘Über Gravitationswellen’ in 1918, which described a formula expressing the energy of gravitational waves. The existence of gravitational waves was an integral part of his theory of relativity. Diverging from Newtonian physics, Einstein described these waves as ripples in space time caused by cataclysmic events (paraphrased from a fairly questionable translation from the original German).
Evidence of the existence of gravitational waves was previously found by astronomers Russell Hulse and Joseph Taylor in 1974. Earning them a Nobel Prize in 1993, the pair observed two pulsars exhibiting interesting behavior, losing energy and spiralling towards one another. Modelling the energy loss using Einstein’s equations of general relativity, they concluded that the energy loss was emitted as gravitational waves. Though this indicated the efficacy of the formula, this only indirectly indicated the existence of the waves.
On the 11
th of February 2016 it was announced that, on the 14
th of September the previous year, the recently upgraded Laser Interferometer Gravitational wave Observatory (LIGO) detected the gravitational waves produced by the collision of two black holes nearly 1.3 bn light years away. For the first time, direct observation supported the theory. Similar to light and other electromagnetic waves, gravitational waves exhibit red and blue shift which can give us information about the origin of the waves.
With the data collected and the maps we can form using gravitational wave detection, we can start to build a more complete picture of our universe and its history. We might even finally determine the initial conditions of time and space.
It only took 100 years, but we have now directly observed one of the fundamental properties of the universe predicted by the theory of relativity.
If you’re interested in the giant and very exciting interferometer used to detect the waves, check out
https://www.ligo.caltech.edu/page/ligos-ifo.
