"This colloquium approximately marks the six year anniversary of the detection of gravitational waves by LIGO in September 2015. Over the last six years we have detected dozens of gravitational wave sources. So far all sources are believed to be the merger of two neutron stars or black holes. I will discuss what we have learned from these gravitational wave sources, but I will also describe key null results where the non-observation of gravitational waves has been enlightening. I hope to convince you that gravitational waves observations are already a powerful probe of the hidden universe, but I will also describe plans to further improve observing capabilities with new instrumentation in the coming years."