Over 100 years ago, Albert Einstein published his general theory of relativity, laying the foundation for our modern view of gravity. Einstein proposed that massive objects can warp the fabric of space-time, with the heaviest, densest objects, such as stars and black holes, creating deep “gravity wells” in the fabric. And much like a donated penny rolls along a curved path when it’s dropped into a charity well, Einstein realized that when light passes through a gravity well, the photons' paths likewise get deformed.
But that’s far from all that Einstein’s theory predicted. It also suggested that when two very massive objects spiral toward each other before colliding, their individual gravity wells interact. And as two whirlpools rotating around each other in an ocean would send out strong ripples in the water, two inspiraling cosmic objects send out ripples across space-time — known as gravitational waves.
Despite Einstein’s prediction of the existence of gravitational waves, it wasn’t until 1974 — nearly 20 years after his death — that two astronomers using the Arecibo Observatory in Puerto Rico found the first indirect evidence of gravitational waves. But It was another four decades before scientists found direct proof of them. On September 14, 2015, the Laser Interferometer Gravitational-wave Observatory (LIGO) detectors in Hanford, Washington, and Livingston, Louisiana, both captured the telltale “chirp” of gravitational-waves, generated when two black holes collided some 1.3 billion light-years away.
With this first detection of gravitational waves, astronomers proved the existence of an entirely new tool that they could use to explore the cosmos, ushering in an era of multi-messenger astronomy that will help them answer the biggest lingering questions in astrophysics and cosmology.
