In September, it detects a signal that looks likely to be from the collision between two black holes. 2015: LIGO upgraded againĪdvanced LIGO starts a new hunt for gravitational waves with four times the sensitivity of the original LIGO. But it looks like this was dust in our own galaxy spoofing the signal. The indirect signature of gravitational waves in the early universe was claimed by the BICEP2 experiment, looking at the cosmic microwave background. 2015: False alarm #3 for gravitational waves The new Advanced LIGO has finished installation and testing and is nearly ready to begin a new search. A major upgrade, called Advanced LIGO begins. 2010: Enhanced LIGO hunt endsĮnhanced LIGO fails to detect and gravitational waves. 2009: Enhanced LIGOĪn upgraded version called Enhanced LIGO starts new hunt for gravitational waves. The sensors then undergo an interim refit to improve sensitivity, called Enhanced LIGO. Wes Mountain/The Conversation, CC BY-ND 2005: LIGO hunt endsĪfter five searches, the first phase of LIGO ends with no detection of gravitational waves. It took a long time, but the construction of LIGO finally began in Hanford, Washington, and Livingston, Louisiana. 1987: Another false alarm for gravitational wavesĪ false alarm on direct detection from Joseph Weber (again) with claimed signal from the supernova SN 1987A using his torsion bar experiments, which consisted of large aluminium bars designed to vibrate when a large gravitational wave passed through it. US National Science Foundation funds construction of the Laser Interferometer Gravitational-Wave Observatory (LIGO). Since the 1980s, gravitational lensing has become a powerful probe of the distribution of mass in the universe. It turned out to be one quasar that appears as two separate images. The first extragalactic gravitational lens was discovered, when observers Dennis Walsh, Bob Carswell and Ray Weymann saw two identical quasi-stellar objects, or “quasars”. Wes Mountain/The Conversation, CC BY-ND 1979: First observation of a galactic gravitational lens This indicated that light was bending due to the sun’s mass. During a total solar eclipse in May 1919, stars near the sun were observed slightly out of position. Gravitational lensing is the bending of light around massive objects, such as a black hole, allowing us to view objects that lie behind it. 1919: First observation of gravitational lensing Josef Lense and Hans Thirring theorise that the rotation of a massive object in space would “drag” spacetime around with it. This process allowed for the development of the laser (light amplification by stimulated emission of radiation). In stimulated emission, an incoming photon interacts with the excited atom, causing it to move to a lower energy state, releasing photons that are in phase and have the same frequency and direction of travel as the incoming photon. In 1917, Einstein publishes a paper on the quantum theory of radiation indicating stimulated emission was possible.Įinstein proposed that an excited atom could return to a lower energy state by releasing energy in the form of photons in a process called spontaneous emission. Wes Mountain/The Conversation, CC BY-ND 1917: Einstein theorises stimulated emission
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