{"id":12466,"date":"2017-11-18T17:04:16","date_gmt":"2017-11-18T09:04:16","guid":{"rendered":"http:\/\/stuif.com\/blog\/?p=12466"},"modified":"2018-01-08T21:57:32","modified_gmt":"2018-01-08T13:57:32","slug":"physics-nobel-prize-2017","status":"publish","type":"post","link":"https:\/\/stuif.com\/blog\/?p=12466","title":{"rendered":"Physics Nobel Prize 2017"},"content":{"rendered":"

Last month\u00a0\u00a0the Nobel Prize for Physics<\/a> has been awarded to three American physicists for their\u00a0” decisive contributions to the LIGO detector and the observation of gravitational waves”<\/em><\/span><\/p>\n

Here they are, from left to right Rainer Weiss<\/a>\u00a0(85),\u00a0Barry Barish<\/a> (81),\u00a0Kip Thorne<\/a>\u00a0(77) .<\/p>\n

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All are retired professors and quite old, not unusual for Nobel Prize winners…:-; More\u00a0unusual is that this Nobel Prize has been awarded for\u00a0the observation of gravitational waves in September 2015, only two years ago<\/span>! The time between a discovery and the Nobel Prize\u00a0is often 10-20 years and tends to increase<\/a><\/p>\n

In this case the physics community was\u00a0pretty sure\u00a0that the Nobel Prize would go to\u00a0\u00a0LIGO, the\u00a0L<\/span>aser I<\/span>nterferometer G<\/span>ravitational-Wave O<\/span>bservatory, where the gravitational waves were observed.\u00a0Problem is that a Nobel Prize (with the exception of the Peace Prize)\u00a0can not be awarded to an organisation but only to a maximum of three individuals (and never posthumously). And the article in Physical Review Letters<\/a>, where the discovery was published in February 2016, has more than 1000(!) authors. Here is\u00a0the beginning\u00a0of the author list<\/p>\n

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In this blog I will explain why these three people were selected. But first I must tell a bit more about gravitational waves, and why physicists are so excited that they have been observed.<\/p>\n

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In 1687 Newton publishes his\u00a0 masterwork “Principia”<\/a> in which he presents\u00a0the three laws\u00a0of motion<\/a> \u00a0and the universal law of gravitation<\/a>.<\/p>\n

Motion takes place in 3-dimensional space as a function of time. Both space and time are absolute concepts, independent of each other.<\/p>\n

Newtonian mechanics<\/a> works extremely well, but there is one disturbing fact, the speed of light c in vacuum turns out to be\u00a0always<\/strong> the same, no matter how fast the light source is moving itself.\u00a0Einstein\u00a0 “solved” the problem in 1905 by accepting\u00a0the constancy of c as a fact, which resulted in\u00a0 his <\/span>Theory of Special Relativity<\/a>\u00a0(TSR)<\/p>\n

But it came at a price! Space and time are no longer absolute and independent in this theory, together the three dimensions of space and the\u00a0single dimension of time form a 4-dimensional continuum, called\u00a0spacetime<\/a> .<\/p>\n

Gravitation doesn’t play a role in the TSR, but in 1916 \u00a0Einstein publishes his Theory of General\u00a0 Relativity<\/a> (TGR).\u00a0In this theory gravitation is described as a curvature of\u00a0 spacetime. A massive object like the\u00a0Sun curves the spacetime in its surroundings and a planet like Earth just “follows” this curvature.<\/p>\n

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A consequence of this theory is that\u00a0even light would follow this curved spacetime and will be deflected when it passes close to the Sun. This prediction was successfully confirmed only a few years later. During a solar eclipse the stars near the Sun became visible and their position was shifted in complete agreement with the TGR. It was front page news<\/a> and made Einstein world famous.<\/p>\n

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Another prediction of the TGR\u00a0was that (accelerated) motion of massive objects could produce waves and ripples in this fabric of spacetime. Mind you, in spacetime\u00a0itself ! However, these waves and ripples were estimated to be\u00a0very small, maybe only measurable\u00a0if\u00a0 those objects were extremely massive.<\/p>\n

For example, two black holes or neutron stars, orbiting each other.<\/span><\/p>\n

Here is an\u00a0artist impression of the gravitational waves caused by two orbiting black holes. I have hesitated to include this image, because I find it very confusing, suggesting that the\u00a0cells of the spacetime fabric are moving up and down, whereas the cells themselves are changing shape, stretching and contracting. But the image comes from LIGO, so who am I…:-)?<\/p>\n

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After this long(?) introduction it is time to go back to LIGO and the three Nobel Prize winners.<\/p>\n

LIGO has a long and complicated history<\/a>, starting in the 1960!\u00a0\u00a0Here are some important dates. The names of the three Nobel Prize winners in blue.
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In 1968<\/span>, almost 50 (!) years ago, Kip Thorne<\/span> (Caltech) did calculations about\u00a0the gravitational waves of black holes. Which, by the way, had not yet been discovered at that time, but their existence followed from the TGR! He came to the conclusion that detection should be possible. Also in the 1960s, Rainer Weis<\/span> (MIT) proposed to use interferometry<\/a> to detect the incredibly small variations in the fabric of spacetime.\u00a0See below for\u00a0more about interferometry.<\/p>\n

In 1980<\/span>, under pressure of the American National Science Foundation (NSF) , MIT and Caltech joined forces in\u00a0the LIGO project. But progress was slow and funding not easy.<\/p>\n

In 1994<\/span>,\u00a0Barry Barish<\/span> (Caltech) was appointed director of the project. He was a good organiser, proposed to build the LIGO detector in two phases. This proposal was approved by NSF and got a budget of\u00a0 USD 395 million,\u00a0\u00a0the largest project in NSF history!<\/p>\n

In 2002<\/span>, the first phase of LIGO became operational, but no gravitational waves were detected.<\/p>\n

In 2004<\/span>, funding and groundwork started for the second phase, “Enhanced LIGO”, four times more sensitive than the first phase.<\/p>\n

In September 2015<\/span>, after a\u00a05 year overhaul of USD 200\u00a0million was completed, Enhanced Ligo started operating.<\/p>\n

Within days<\/strong><\/span>, on 14 September at 9:50:45 UTC<\/span>,\u00a0 Enhanced LIGO detected gravitational waves for the first time in history.
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So, what is\u00a0an interferometer? Here is a sketch of the LIGO interferometer<\/p>\n

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And\u00a0who could better explain how it works than Rainer Weis himself?<\/p>\n