The 2017 Nobel Prize in physics was announced today, and as expected it was awarded to Rainer Weiss, Barry Barish, and Kip Thorne their work in developing the LIGO experiment that recently made the first detection of a gravitational wave. The experiment itself was an amazing piece of engineering, and its ability to detect and study gravitational waves is going to make it a very important tool in the future for understanding the Universe.

Just over a century ago Einstein published the general theory of relativity. Among its predictions was that space and time could be warped and curved, just like a sheet of fabric. And since it can be warped and curved, those distortions must also be able to propagate through spacetime from one region to another. These are called gravitational waves, and in our Universe they are generated by any mass or energy that moves or changes (with the exception of a spherical collapse, but that is an issue for another day).

Unfortunately they are also extremely weak, and until recently it was impossible to detect them. These are waves just like radio waves or light waves, but their interaction with other matter is several orders of magnitude weaker. A gravitational wave telescope would not work.

So how could scientist prove they exist, and use them to study the cosmos?

The answer was the Laser Interferometer Gravitational-Wave Observatory (LIGO). In the 1960s scientists in both Russia and the U.S. developed laser interferometers that could potentially detect gravitational waves. The idea was to split a single laser beam into two parts, and direct each part along a different perpendicular path. At the end of each path the laser beams are reflected back by mirrors, and then recombined into a single beam again. If the two paths are the same length, then the recombined beam is the same as the original one. However if a gravitational wave impacts the system, one path will be briefly elongated and then the recombined beam will show an interference pattern. It is through studying this interference pattern that the properties of the gravitational wave can be studied.

However it is a very difficult experiment to operate. The first interferometers were too small to detect the very weak gravitational signals from even the most violent, high energy sources in the Universe. Even a very large interferometer with paths measured in kilometers will suffer from signal noise caused by anything from leaky electronics nearby to passing trucks relatively far away from the experiment.

Then in the early 1980s scientists from MIT and Caltech united to build the LIGO experiment, a much larger and more precise version of the original interferometers. For over a decade they struggled to get funding for what was believed by many to be a longshot experiment, especially when compared with some of the more promising experiments in astrophysics and high energy particle physics that were competing for the some research money.  Finally in 1994 the U.S. government approved the project and gave them a $395 million budget, making it the largest project funded by the NSF up to that point. 

LIGO started collecting data in 2002, and began sifting through the data. To assist with this monumental task, researchers set up the Einstein@Home project and the GravitySpy project to allow volunteers from around the world to process the signals (both of which I am proud to say I participated in). 

Then on September 14, 2015, after thirty years of effort, the project finally paid off. A gravitational wave was detected, which was believe to have been generated by the collision of two black holes, each approximately thirty times the mass of our own Sun, which occurred approximately 1.3 billion lightyears away. Then on December 26, 2015 the LIGO team detected a second black hole collision, confirming their earlier detection. Two more detections were made on January 4 and August 14 of this year, with the last one being the first event to be detected in three different detectors.

And so it was no surprise to anyone that the Nobel Prize committee has selected the pioneers behind the LIGO experiment to receive the 2017 Nobel Prize in Physics. Congratulations to the winners, and to all of the people who made this experiment a reality. They have earned it!