A surfer’s guide to gravitational waves

HEY Einstein, surf’s up! Researchers from the BICEP2 telescope in Antarctica have announced the detection of primordial gravitational waves, ripples in space-time predicted by the iconic physicist. The discovery should help us piece together the exact sequence of events in our universe’s birth, as well as a collection of other cosmic puzzles (see main story). But what exactly is a ripple in space-time? COSMIC CRASHES Albert Einstein compared the universe’s shape to a single fabric, hewn from space and time. According  to his theory of general relativity, the force of gravity is the result of curvature in space-time: gravitational waves are ripples in it. The ripples are produced by accelerating objects, such as two massive stars spinning around each other. Colliding black holes and stars create modern-day gravitational waves. Cosmologists also believe the big bang itself produced primordial waves that still reverberate through space-time. It is these ripples, dating back to a fraction of a second after the birth of the universe, that the BICEP2 researchers have detected. But they are not the first people to show indirect signals of gravitational waves. In 1974, astronomers Russell Hulse and Joseph Taylor detected a binary pulsar, a pair of dead stars emitting pulses of radio waves. Hulse and Taylor realised that the two pulsars were losing energy and slowly spiralling towards each other in a  way that is consistent with Einstein’s equations of general relativity: the missing energy is thought to be emitted as gravitational waves The finding earned the pair the Nobel prize for physics in 1993. But with only indirect signs of modern and primordial waves, physicists still hope to surf a passing gravitational wave, which would amount to the first direct detection. Experiments like LIGO, which is spread over two sites in Washington state and Louisiana in the US, and VIRGO, in Cascina, Italy, look for high-frequency waves caused by modern-day black hole mergers or exploding stars. These should cause slight but measurable disturbances on Earth. Detectors in space, meanwhile, can find lower frequency waves – next year the European Space Agency plans to launch LISA Pathfinder, a test mission that will lead to a trio of  spacecraft in 2034 intended to hunt for gravitational waves emitted by black holes.  Jacob Aron