{"id":187,"date":"2016-05-19T11:47:46","date_gmt":"2016-05-19T11:47:46","guid":{"rendered":"https:\/\/blogs.mathworks.com\/headlines\/?p=187"},"modified":"2020-02-26T18:18:04","modified_gmt":"2020-02-26T18:18:04","slug":"100-years-later-a-faint-chirp-proves-einstein-was-right","status":"publish","type":"post","link":"https:\/\/blogs.mathworks.com\/headlines\/2016\/05\/19\/100-years-later-a-faint-chirp-proves-einstein-was-right\/","title":{"rendered":"100 years later, a faint chirp proves Einstein was right"},"content":{"rendered":"

The New Yorker wrote an article called\u00a0Gravitational Waves Exist: The Inside Story of How Scientists Finally Found Them<\/a>.\u00a0The article describes how Professor Rainer Weiss<\/a>\u2019 idea to build a device sensitive enough to detect ripples in space-time became a\u00a0professional obsession and a quest that spanned a\u00a0half\u00a0century. This quest had a team of over 1000 scientists and engineers focused on the task by 2015. In September of last year, Professor Weiss\u2019 concept was validated when the device recorded a faint chirp and successfully detected gravitational waves.<\/p>\n

Weiss first published his idea for a laser interferometer gravitational-wave observatory (LIGO) in 1972. It called for a laser that is fired, split into 2 perpendicular beams, and then reconstructed to create a specific interference pattern.\u00a0But in 1972, much of the scientific community doubted the existence of both black holes and gravitational waves, making it a challenge to fund such an endeavor.<\/p>\n

September 2015, LIGO proves Einstein was right<\/strong><\/span><\/h2>\n

Albert Einstein predicted the existence of gravitational waves in\u00a01915\u00a0as part of the theory of general relativity. In 1916, he told Karl Schwartzchild, the discoverer of black holes, that gravitational waves did not exist. He would flip flop on the subject two more times.<\/p>\n

100 years later, Advanced LIGO\u00a0(aLIGO)\u00a0recorded the sound of two black holes colliding, providing the first direct evidence of gravitational waves. The corresponding research paper<\/a> was published in February of this year.<\/p>\n

\"simulation<\/a>

Image credit: The SXS (Simulating eXtreme Spacetimes) Project<\/p><\/div><\/p>\n

Two observatories<\/strong><\/span><\/h2>\n

Two observatories were built:\u00a0One in Washington State, and one in Louisiana. They are supported by the National Science Foundation and are operated by MIT<\/a> and Caltech<\/a>. Instead of looking into space, LIGO listens for proof of events that are beyond the limits of electromagnetic spectrum telescopes.<\/p>\n

\"\"<\/a>

Image credit: Caltech\/MIT\/LIGO Lab<\/p><\/div><\/p>\n

Initial LIGO ran from 2000 to 2010, and was known to be an experimental version. Over the last 5 years, the entire system was rebuilt to increase the sensitivity so that it could capture the existence of gravitational waves. The new system is known as aLIGO. After being operational for a mere 2 days, aLIGO\u00a0successfully detected gravitational waves. aLIGO\u00a0measured the expansion and contraction of space-time.<\/p>\n

\"\"<\/a>

Image credit: Wikipedia, Linearly polarized gravitational wave<\/p><\/div><\/p>\n

1 x 10-18<\/sup> meter\u00a0accuracy<\/strong><\/span><\/h2>\n

aLIGO\u2019s antennas are L-shaped vacuum chambers. Each arm is 4 km long and contains 9.5 million liters of empty space. There are mirrors hanging at the end of each arm, suspended by glass threads. The arms must be completely insulated from exterior noise and vibrations in order to maintain their accuracy.<\/p>\n

aLIGO can detect changes in one of the arms as small as an attometer, or 1 \u00d7 10\u221218<\/sup> meters. Basically,\u00a0aLIGO uses a\u00a0structure that would more than stretch\u00a0across\u00a0Manhattan to measure changes in space-time the size of 1\/10,000 the diameter of a proton.<\/p>\n

Even with this minute sensitivity, only massive events in the universe would be \u201cloud enough\u201d to be captured. On September 14th 2015, a signal was captured at the Livingston site.\u00a0Seven milliseconds later, the same signal hit the Hanford site.<\/p>\n

The chirp<\/strong><\/span><\/h2>\n

Detailed analysis showed that the \u201cchirp\u201d was caused when two black holes collided. One was 36 times as massive as the sun and the other was 29. Just before the collision, they were circling each other 250 times per second, causing a ringing sound. The ringing stopped when they combined to create a single black whole with the equivalent mass of 62 suns. This occurred in a fifth of a second 1.3 billion years ago.<\/p>\n

\"\"<\/a>

Image credit: Caltech\/MIT\/LIGO Lab<\/p><\/div><\/p>\n

The collision released 3 solar masses of energy. This energy took the form of gravitational waves. If it were visible light, \u201cit would be the equivalent to a billion trillion suns<\/a>\u201d. This immense amount of energy traveled 1.3 billion light years to eventually move the aLIGO mirrors only 4\/1000 diameter of a proton.<\/p>\n

LIGO research and MATLAB<\/strong><\/span><\/h2>\n

Over 1000 scientists and engineers are working on LIGO, with more researchers contributing during the decades of work that led up to the 2015 breakthrough. There are three main areas of mathematics\/simulations behind the LIGO breakthrough: simulation of the gravitational waves<\/a>, searching the obtained data<\/a> for matches to the numerical simulations, and the design of the physical system itself, including noise cancellation.<\/p>\n

Much of the research has focused on the accuracy needed to detect the distortion of space-time.\u00a0Here are\u00a0a number of articles relating to the use of MATLAB in the LIGO design:<\/p>\n