The graphic above represents two stars circling each other, their gravity ensuring that they will end each other’s existence in a collision that will release three times the mass of our Sun in a few seconds.
LIGO (the Laser Interferometer Gravitational-Wave Observatory) announced this week that it had detected the gravity waves of such a collision. Einstein predicted the existence of gravity waves in 1915 but until this week they had never been observed.
Gravity waves occur when the mass of two objects combine. The resulting entity has less mass and therefore “sits” on the fabric of space-time differently. The space-time fabric adjusts to the lesser mass and the adjustment ripples out from the new object through the fabric. The folds in the graphic represent those ripples.
LIGO’s detection mechanism is based on the fact that changes in the space-time fabric will affect the distance between objects. If those objects are mirrors then light will take longer to move between those two mirrors than it usually would.
Scientific America has a great description of LIGO’s process: