In this course you will learn how LIGO detects gravitational waves. The basic idea behind the experiment is simple: that a passing gravitational wave will change the length of the arms in a laser interferometer, and as a result, it will create a changing amplitude in the interfering laser beams. However simple this idea is in concept, to put it into practice has required great care. New technologies have had to be created, and old ones have been refined. This was necessary in order to attain the highest precision measurements ever made in an experiment: a change in the length of each interferometer arm of only one part in 1021. After 40 years of design studies, technology development, prototyping and testing, construction of a suffieciently sensitive experiment was completed in 2015.
In the final stages of commissioning, even before the fi rst science runs had begun, the experiment met with success. On September 14, 2015, at 09:50:45 UTC, the LIGO experiment made the first-ever direct detection of gravitational waves (Abbott & et al., 2016).
No better way could have been conceived to mark the centenary of Einstein's General Theory of Relativity (Einstein, 1916), or his prediction of gravitational waves (Einstein, 1918).