From May until September I followed an astronomy course led by Servé Vaessen who gave this course for members of the astronomy club Galileo Zuid Limburg. The subjects were exoplanets, Solar systems and the life cycle of a stars. In the end he also discussed gravitational waves. On October 3th the professor discussed also gravitational waves. He hopes to be part of the team who will discover them. Yes, there is no proof yet they exist.
A century ago Albert Einstein predicted gravitational waves as part of his relativity theory. When 2 heavy objects in the universe (neutron stars or black holes) interact energy is released which cause changes in time and space. Like a droplet in the water a wave is created or ripples.
When such a wave reaches earth it might be detected by measuring changes in a given distance. There are now 3 places where this can be measured. One in Italy (Virgo) and 2 in the USA (Ligo).
In the future NASA and ESA will build and launch LISA which consists of 3 satellites at a set distance which will measure if a gravitational wave will change the distance between them.
I will follow this subject to see if they succeed. They expect to have proof in 2015 or 2016.