6 Amazing Facts About Gravitational Waves and LIGO

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Please refer to the appropriate style manual or other sources if you have any questions. </div> <div class="label mt-20 mb-10">Select Citation Style</div> <select class="js-citation-format-select form-select"> <option selected value="mla">MLA</option> <option value="apa">APA</option> <option value="chicago">Chicago Manual of Style</option> </select> <div class="citation font-serif border rounded p-15 mt-20" data-authors="Erik Gregersen" data-title="6 Amazing Facts About Gravitational Waves and LIGO" data-published-date="10 Feb. 2016" data-url="https://www.britannica.com/list/6-amazing-facts-about-gravitational-waves-and-ligo" > <div class="citation-text"></div> </div> <button class="js-copy-citation-button mt-20 btn btn-xs btn-outline-blue border shadow-sm pr-10" > <em class="material-icons md-icon ml-n10 my-n5 mr-5" data-icon="file_copy"></em> <span class="js-citation-status-text">Copy Citation</span> </button> </div> </div> </div> <div> <button class="js-share-modal-button js-modal gtm-topic-tool btn btn-xs btn-outline-blue border shadow-sm pr-10" data-modal=".md-share-modal"> <em class="material-icons md-icon ml-n10 my-n5 mr-5" data-icon="share"></em> Share </button> <div class="md-share-modal size-lg d-none qa-share-modal"> <div class="md-modal-body"> <div class="h2 font-serif d-flex align-items-center pb-15 border-bottom"> <em class="material-icons text-blue mr-10" data-icon="share"></em> Share </div> <div class="label my-20">Share to social media</div> <div class="md-social-toolbar-circle d-flex align-items-start inverted" data-value="share" title="6 Amazing Facts About Gravitational Waves and LIGO" data-url="https://www.britannica.com/list/6-amazing-facts-about-gravitational-waves-and-ligo" > <a class="social-icon facebook justify-content-center d-flex align-items-center align-self-center" data-provider="facebook" href="https://www.facebook.com/BRITANNICA/" target="_blank" rel="noopener"><span>Facebook</span></a> <a class="social-icon x justify-content-center d-flex align-items-center align-self-center" data-provider="x" href="https://x.com/britannica" target="_blank" rel="noopener"><span>X</span></a> </div> <div class="label pt-20 mt-20 mb-5 border-top">URL</div> <a class="font-serif text-truncate d-inline-block" href="https://www.britannica.com/list/6-amazing-facts-about-gravitational-waves-and-ligo">https://www.britannica.com/list/6-amazing-facts-about-gravitational-waves-and-ligo</a> </div> </div> </div> </div> <div class="md-byline module-spacing font-14"> <div class="font-serif font-12"> <span class="written-by text-gray-700"> Written by </span> <div class="editor-popover popover p-0"> <a class="d-block p-20 gtm-byline font-12 byline-contributor" href="/editor/Erik-Gregersen/6723" > <div class="editor-title font-16 font-weight-bold">Erik Gregersen</div> <div class="editor-description font-12 font-serif mt-5 clamp-description text-black">Erik Gregersen is a senior editor at Encyclopaedia Britannica, specializing in the physical sciences and technology. Before joining Britannica in 2007, he worked at the University of Chicago Press on the...</div> </a> <div data-popper-arrow></div> </div> <span class="btn btn-link editor-link p-0 qa-byline-link gtm-byline font-12 byline-contributor text-decoration-underline"> Erik Gregersen</span></div> <div class="font-serif font-12 text-gray-700"> <span class="qa-fact-checked-by">Fact-checked by</span> <div class="editor-popover popover p-0"> <a class="d-block p-20 font-12" href="/editor/The-Editors-of-Encyclopaedia-Britannica/4419" > <div class="editor-title font-16 font-weight-bold">The Editors of Encyclopaedia Britannica</div> <div class="editor-description font-12 font-serif mt-5 text-black">Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree. They write new content and verify and edit content received from contributors.</div> </a> <div data-popper-arrow></div> </div> <span class="btn btn-link editor-link p-0 qa-byline-link font-12 "> The Editors of Encyclopaedia Britannica</span></div></div> </div> <article class="topic-content content"><div class="topic-paragraph font-serif md-list-intro pt-15 pb-20"><figure class="md-assembly md-feature-assembly print-false" data-type="1" data-descid="1"><div class="md-assembly-wrapper card-media " data-type="image"><a href="https://cdn.britannica.com/20/188520-131-FA4C1A43/Laser-Interferometer-Gravitational-Wave-Observatory-Hanford-Washington-installations.jpg" target="_blank" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center " data-href="*0"><img src="https://cdn.britannica.com/20/188520-131-FA4C1A43/Laser-Interferometer-Gravitational-Wave-Observatory-Hanford-Washington-installations.jpg?w=1000" alt="The LIGO Laboratory operates two detector sites, one near Hanford in eastern Washington, and another near Livingston, Louisiana. This photo shows the Hanford detector site." data-width="900" data-height="675" loading="eager"><button class="magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10" aria-label="Zoom in"><em class="material-icons link-blue" data-icon="zoom_in"></em></button></a></div><figcaption class=""><div class="md-assembly-caption text-muted font-14 font-serif "><span></span></div><cite class="credit d-block mt-5">Caltech/MIT/LIGO Lab</cite></figcaption></figure><p class="topic-paragraph">Nearly everything we know about the universe comes from <a href="https://www.britannica.com/science/electromagnetic-radiation" class="md-crosslink " data-show-preview="true">electromagnetic radiation</a>—that is, light. Astronomy began with visible light and then expanded to the rest of the electromagnetic spectrum. By using the spectrum, from the short wavelengths of <a href="https://www.britannica.com/science/gamma-ray" class="md-crosslink " data-show-preview="true">gamma rays</a> to the long wavelengths of <a href="https://www.britannica.com/science/radio-wave" class="md-crosslink " data-show-preview="true">radio waves</a>, astronomers have discovered strange and wondrous things. Now a new form of astronomy, <a href="https://www.britannica.com/science/gravitational-wave" class="md-crosslink " data-show-preview="true">gravitational-wave</a> astronomy, has come. It watches not light but movements in <a href="https://www.britannica.com/science/space-time" class="md-crosslink " data-show-preview="true">space-time</a>. Along with the new astronomy has come a new kind of observatory, the <a href="https://www.britannica.com/topic/Laser-Interferometer-Gravitational-wave-Observatory" class="md-crosslink " data-show-preview="true">Laser Interferometer Gravitational-Wave Observatory (LIGO)</a>.</p><span class="MOD"></span></div><ul class="md-list-order-reverse md-mendel-list" style="counter-reset: item 7"><li><h2>Gravitational Waves Are Ripples in Space-Time</h2><div><p class="topic-paragraph">According to Albert Einstein’s theory of <a href="https://www.britannica.com/science/general-relativity" class="md-crosslink " data-show-preview="true">general relativity</a>, gravity is not a force reaching out through the universe. It’s a bending of space-time. When an object accelerates, it distorts the space-time around it, and that distortion travels away from the source at the speed of light.</p><span class="MOD"></span></div><span class="LIST-ITEM-1"></span></li><li><h2>Gravitational Waves Come from Really Heavy Objects </h2><div><p class="topic-paragraph">So how massive an object are we talking about? The first proof that gravitational waves actually exist came from a binary <a href="https://www.britannica.com/science/pulsar" class="md-crosslink " data-show-preview="true">pulsar</a>—two neutron stars, each about the mass of the Sun, that orbit each other. The pulsars’ orbit is gradually shrinking, so the pulsars are losing energy. That energy is exactly the amount that general relativity predicts that the pulsars would give off in gravitational waves.</p><span class="MOD"></span></div><span class="LIST-ITEM-2"></span></li><li><h2>The Effect of Gravitational Waves Is Very, Very Small </h2><div><p class="topic-paragraph">Since gravitational waves are a ripple in space-time, they cause the distance between two points to change ever so slightly. How slightly? LIGO must be able to measure distances as small as 10<sup>−19</sup> meter. The <a href="https://www.britannica.com/science/proton-subatomic-particle" class="md-crosslink " data-show-preview="true">proton</a> has a radius of about 0.85 × 10<sup>−15</sup> meter, or 10,000 times larger.</p><span class="MOD"></span></div><span class="LIST-ITEM-3"></span></li><li><h2>Measuring Gravitational Waves Is Tricky</h2><div><p class="topic-paragraph">To detect a change in distance much smaller than the proton requires great precision. Each LIGO installation is a laser <a href="https://www.britannica.com/technology/optical-interferometer" class="md-crosslink " data-show-preview="true">interferometer</a> made up of two underground pipes, each 1.3 meters (4.3 feet) wide and 4 km (2.5 miles) long, set in an L-shape. The inside of the pipes is a vacuum. When a gravitational wave passes through LIGO, one arm of the instrument gets longer and the other gets shorter. A laser beam is split in half, sent down the two pipes, reflected back, and then recombined so the two beams cancel each other out in destructive interference if there is no gravitational wave. If there <em>is</em> a gravitational wave, the beams won’t cancel each other out. A 4-km long beam is still not enough to detect a gravitational wave, so the beams are bounced back and forth about 400 times so the light travels a distance of 1,600 km (1,000 miles).</p><span class="MOD"></span></div><span class="LIST-ITEM-4"></span></li><li><h2>LIGO Is Very Sensitive </h2><div><p class="topic-paragraph">LIGO detects such a small change in distance that it can detect a lot of other vibrations too. For example, the speed limit at LIGO is 16 km (10 miles) per hour to minimize vibrations from nearby cars. One source of noise is gravity gradient noise, which is the minute change in Earth’s gravitational field when a vibration passes through the ground near the mirrors. The mirrors that reflect the light weigh 40 kg (88 pounds) and hang by silica fibers in a complex suspension system. To make sure that LIGO does detect gravitational waves and not just passing cars, there are two LIGO installations—one in Livingston, Louisiana, and the other in Hanford, Washington. A gravitational wave would show up at both installations.</p><span class="MOD"></span></div><span class="LIST-ITEM-5"></span></li><li><h2>Gravitational-Wave Astronomy Can See an Entirely New Side of the Universe</h2><div><p class="topic-paragraph">If supermassive <a href="https://www.britannica.com/science/black-hole" class="md-crosslink " data-show-preview="true">black holes</a> (black holes one million times more massive than the Sun) merged in a distant galaxy, LIGO could observe it. Scientists also expect that if a neutron star is slightly nonspherical, the gravitational waves could be observed and thus reveal much about the star’s structure. Every time astronomers have been able to look at the universe in a new way, they’ve always observed something unexpected, and gravitational-wave astronomy will likely show something not yet thought of. </p><span class="MOD"></span></div><span class="LIST-ITEM-6"></span></li></ul><span class="AM-END-OF-ARTICLE am-inline"></span></article> </div> </div> </div> <aside class="cm-rightrail d-none d-md-block ad-rail"></aside> </div> </div> </div> <div class="grid gx-0"> <div class="col"> <div class="md-loading hidden display-4 font-weight-normal"></div> <div class="text-center my-20 mb-100"> <button class="md-infinite-load-next btn btn-blue" data-value="next-page">Load More</button> </div> </div> <div class="col-md-da-320 hidden-xs"> </div> </div></div> </div> </main> <div id="md-footer"></div> <noscript><iframe src="//www.googletagmanager.com/ns.html?id=GTM-5W6NC8" height="0" width="0" style="display:none;visibility:hidden"></iframe></noscript> <script type="text/javascript" id="_informizely_script_tag"> var IzWidget = IzWidget || {}; (function (d) { var scriptElement = d.createElement('script'); scriptElement.type = 'text/javascript'; scriptElement.async = true; scriptElement.src = "https://insitez.blob.core.windows.net/site/f780f33e-a610-4ac2-af81-3eb184037547.js"; var node = d.getElementById('_informizely_script_tag'); node.parentNode.insertBefore(scriptElement, node); } )(document); </script>  <script> window.ap3c = window.ap3c || {}; var ap3c = window.ap3c; ap3c.cmd = ap3c.cmd || []; ap3c.cmd.push(function() { ap3c.init('ZO4siT4cLwnykPnzZWJtd3Byb2Q', 'https://engage.email.britannica.com/'); ap3c.track({v: 0}); }); ap3c.activity = function(act) { ap3c.act = (ap3c.act || []); ap3c.act.push(act); }; var s, t; s = document.createElement('script'); s.type = 'text/javascript'; s.src = "https://engage.email.britannica.com/app.js"; t = document.getElementsByTagName('script')[0]; t.parentNode.insertBefore(s, t); </script> <script class="marketing-page-info" type="application/json"> {"pageType":"List","templateName":null,"pageNumber":1,"pagesTotal":11,"pageId":5451,"pageLength":null,"initialLoad":true,"lastPageOfScroll":false} </script> <script class="marketing-content-info" type="application/json"> [] </script> <script src="https://cdn.britannica.com/mendel-resources/3-130/js/libs/jquery-3.5.0.min.js?v=3.130.14"></script> <script type="text/javascript" data-type="Init Mendel Code Splitting"> (function() { $.ajax({ dataType: 'script', cache: true, url: 'https://cdn.britannica.com/mendel-resources/3-130/dist/list-page.js?v=3.130.14' }); })(); </script> <script class="analytics-metadata" type="application/json"> {"leg":"C","adLeg":"C","userType":"ANONYMOUS","pageType":"List","pageSubtype":null,"articleTemplateType":null,"gisted":false,"pageNumber":1,"hasSummarizeButton":false,"hasAskButton":false} </script> <script type="text/javascript"> EBStat={accountId:-1,hostnameOverride:'webstats.eb.com',domain:'www.britannica.com', json:''}; </script> <script type="text/javascript"> ( function() { $.ajax( { dataType: 'script', cache: true, url: '//www.britannica.com/webstats/mendelstats.js?v=1' } ) .done( function() { try {writeStat(null,EBStat);} catch(err){} } ); })(); </script> <div id="bc-fixed-dialogue"></div> </body> </html>

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6 Amazing Facts About Gravitational Waves and LIGO | Britannica