Gravitational Waves are, in their most basic sense, ripples in spacetime. Einstein's theory of general relativity predicted them over a century ago and they are generated by the acceleration (or, indeed, deceleration) of massive objects in the cosmos. If a star explodes as a supernova, gravitational waves carry energy away from the detonation at the speed of light. If two black holes collide, they will cause these ripples in spacetime to propagate like ripples across the surface of a pond. If two neutron stars orbit each other very closely, energy is carried away from the system by - you guessed it - gravitational waves. If we could detect and observe these waves, a new era of gravitational wave astronomy may be possible, allowing us to differentiate between gravitational wave signatures and work out which phenomenon is generating them. For example, a sudden pulse of gravitational waves may indicate they came from a supernova explosion, whereas a continuous oscillating signal may indicate two closely-orbiting black holes before merging.
ANALYSIS: Advanced LIGO Resumes Quest for Gravitational Waves
So far, gravitational waves are theoretical, even though strong indirect evidence for their existence is known. Interestingly, as gravitational waves propagate through spacetime, they will physically warp the "fabric" of space, very slightly shrinking or expanding the space between two objects. The effect is minuscule, but using laser interferometers - such as the Laser Interferometer Gravitational-Wave Observatory, or LIGO, that measures the tiniest perturbations in lasers reflected along 2.5 mile-long L-shaped vacuum tunnels - the propagation of gravitational waves through our planet may be detected. In the case of LIGO, there are 2 stations located on opposite sides of the US separated nearly 2,000 miles. If a gravitational wave signal is real, its signature will be observed at both locations; if it's a false positive (i.e. a truck driving past) only one station will detect it. Though LIGO started operations in 2002, it has yet to detect gravitational waves, but in September 2015, the system was upgraded to Advanced LIGO and hopes are high that, finally, physicists may have some good news for us on Thursday.