Gravity waves: Physics Nobel

This year's Nobel prize in physics has gone to a very recent discovery by Rainer Weiss, Barry C. Barish, and Kip S. Thorne of the LIGO/VIRGO Collaboration, "for decisive contributions to the LIGO detector and the observation of gravitational waves".
Although scientists believed in the existence of gravitational waves for a long time, it was only recently (in 2015) that gravitational waves were directly observed.
Just like other waves (see box in the article on the Chemistry Nobel Prize), gravitational energy is also released in the form of waves which travel from the source and reach the detector. The obesrvation in 2015 came from a collision between two black holes which are exotic objects in our Universe. It took 1.3 billion years for the waves to arrive at the LIGO detector in the USA. The signal was very weak by the time it reached the Earth, but the superb LIGO detector was able to detect it, and so confirm Einstein's prediction of gravity waves made a 100 years ago.

The LIGO detector
The Laser Interferometer Gravitational-Wave Observatory (LIGO) is a collaborative project with over one thousand researchers from more than twenty countries. Just as waves in the ocean can interfere with one another and form interesting ripples that are visible to us, the gravity waves can also form ripples which can be observed. See the Fig. 
The LIGO detector, as the name implies, uses the interference between two laser light beams which are correlated in a special way called coherence. When a gravity wave passes through one of the beams, but not the other, the interference pattern changes and this is what is detected. The observed wave is shown in the figure. The interferometers could measure a change thousands of times smaller than an atomic nucleus, which is a really amazing achievement. It could do this because the perpendicular arms along which the laser light travels is 4 km long.
For more information, see
https://www.nobelprize.org/nobel_prizes/physics/laureates/2017/press.html
and www.ligo.org