general relativity
https://plus.maths.org/content/taxonomy/term/478
enWhat is time?
https://plus.maths.org/content/what-time-0
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Marianne Freiberger </div>
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Everyone knows what time is. We can practically feel it ticking away,
marching on in the same direction with horrifying regularity. Time has
enslaved the Western world and become our most precious commodity. Turn it
over to the physicists however, and it begins to
morph, twist and even crumble away. So what is
time exactly? </div>
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<p><em>In the latest poll of our <a href="https://plus.maths.org/content/science-fiction-science-fact-reports-frontiers-physics">Science fiction, science fact project</a> you told us that you wanted to know what time is. Here is an answer, based on an interview with <a href="http://cosmos.asu.edu/">Paul Davies</a>, a theoretical physicist and cosmologist at
Arizona State University and Director of <a
href="http://beyond.asu.edu/">BEYOND: Centre for Fundamental Concepts
in Science</a>.<p><a href="https://plus.maths.org/content/what-time-0" target="_blank">read more</a></p>https://plus.maths.org/content/what-time-0#commentsFrontiers of physicsmathematical realityentropygeneral relativitygravityquantum mechanicsrelativityspecial relativitythermodynamicstimetime dilationTue, 23 Aug 2011 15:25:34 +0000mf3445524 at https://plus.maths.org/contentWhat is time: The podcast
https://plus.maths.org/content/science-fiction-science-fact-what-time
<div class="rightimage" style="width: 280px;"><img src="/issue36/features/davies/pauldavies.jpg" width="280" height="210" alt="Paul Davies"/><p>Paul Davies</p></div><p>As part of our joint project with <a href="http://www.fqxi.org/community">FQXi</a> called <a href="https://plus.maths.org/content/science-fiction-science-fact-reports-frontiers-physics">Science fiction, science fact</a>, we asked you what question on the frontiers of physics you'd like to have answered. The question that topped our first poll was 'What is time?'. </p><p><a href='http://plus.maths.org/content/sites/plus.maths.org/files/podcast/davies_final.mp3'>Listen to "What is time?"</a></p><p><a href="https://plus.maths.org/content/science-fiction-science-fact-what-time" target="_blank">read more</a></p>https://plus.maths.org/content/science-fiction-science-fact-what-time#commentsFrontiers of physicsmathematical realitygeneral relativitygravityquantum mechanicsrelativityspecial relativitytimetime dilationtime travelTue, 23 Aug 2011 15:02:44 +0000mf3445536 at https://plus.maths.org/contentCelebrating general relativity
https://plus.maths.org/content/celebrating-general-relativity
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<p>A hundred years ago, on 25 November 1915, Einstein first presented his general theory of relativity. We explore this famous theory and what it says about the world we live in.</p>
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<div style="float: left; max-width: 550px;"><p>A hundred years ago, on 25 November 1915, Einstein
presented his general theory of relativity to the world. But what exactly is this famous theory and what does it say about the world we live in? To celebrate the centenary of general relativity we bring you a collection of articles, videos and podcasts exploring the theory, Einstein's struggle to find it, and some interesting consequences.</p><p><a href="https://plus.maths.org/content/celebrating-general-relativity" target="_blank">read more</a></p>https://plus.maths.org/content/celebrating-general-relativity#commentsblack holeEinsteinFP-carouselgeneral relativitygravitational wavehistory of mathematicsrelativityMon, 16 Nov 2015 13:26:20 +0000mf3446456 at https://plus.maths.org/contentWhat is a black hole – mathematically?
https://plus.maths.org/content/what-black-hole-part-2
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The Plus team </div>
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<p>Pau Figueras explains how Einstein's theories predicted the existence of black holes, and how to describe them mathematically.</p>
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<p><EM>We asked cosmologist <a href="http://www.damtp.cam.ac.uk/people/p.figueras/">Pau Figueras</a> everything you've ever wanted to know about black holes. In the <a href="https://plus.maths.org/content/what-black-hole">other part of the interview</a> he explained what black holes are, physically, and how we hope to observe them. In this second part of the interview, he explains how Einstein's theories predict their existence, and how to describe them mathematically.</em></p>
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<strong>How were black holes first predicted?</strong>
</p><p><a href="https://plus.maths.org/content/what-black-hole-part-2" target="_blank">read more</a></p>https://plus.maths.org/content/what-black-hole-part-2#commentsblack holeEinsteingeneral relativityUniversity of CambridgevideoFri, 13 Nov 2015 16:24:38 +0000Rachel6451 at https://plus.maths.org/contentWhat is a black hole – mathematically?
https://plus.maths.org/content/what-black-hole-mathematically
<div class="rightimage" style="width: 300px;"><img src="/sites/plus.maths.org/files/articles/2012/mtheory/blackhole.png" alt="Black hole" width="300" height="240" /><p>Simulated view of a black hole. Image: Alain Riazuelo.</p></div>
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We asked cosmologist Pau Figueras everything we’ve ever wanted to know about black holes. In this podcast he explains how you describe black holes mathematically, and how they were predicted by Einstein’s theories.
</p><p><a href='https://plus.maths.org/content/sites/plus.maths.org/files/podcast/pluspodcastnov15-blackholes2.mp3'>Listen to our interview with Pau Figueras</a></p><p><a href="https://plus.maths.org/content/what-black-hole-mathematically" target="_blank">read more</a></p>https://plus.maths.org/content/what-black-hole-mathematically#commentsblack holegeneral relativityrelativityUniversity of CambridgeFri, 13 Nov 2015 14:13:44 +0000Rachel6466 at https://plus.maths.org/contentWhat is a black hole – physically?
https://plus.maths.org/content/what-black-hole
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The Plus team </div>
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<img class="imagefield imagefield-field_abs_img" width="100" height="100" alt="" src="https://plus.maths.org/content/sites/plus.maths.org/files/abstractpics/5/21_jan_2016_-_1202/blackhole_icon.jpg?1453377739" /> </div>
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<p>Small, dark, and very hard to see. This and far more indepth answers to every question you ever wanted to ask about black holes.</p>
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<p><EM>We asked cosmologist <a href="http://www.damtp.cam.ac.uk/people/p.figueras/">Pau Figueras</a> everything you've ever wanted to know about black holes. In this, the first part of the interview, he explained what black holes are, physically, and how we hope to observe them. You can also read the <a href="https://plus.maths.org/content/what-black-hole-part-2">second part of the interview</a> where Pau explains how black holes were predicted, and how the maths of black holes makes them particularly simple to describe.</em></p>
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<strong>What is a black hole?</strong>
</p><p><a href="https://plus.maths.org/content/what-black-hole" target="_blank">read more</a></p>https://plus.maths.org/content/what-black-hole#commentsblack holeEinsteinFP-carouselgeneral relativityUniversity of CambridgevideoFri, 13 Nov 2015 14:12:11 +0000Rachel6449 at https://plus.maths.org/contentWhat is a black hole – physically?
https://plus.maths.org/content/what-black-hole-physically
<div class="rightimage" style="max-width: 350px;"><img src="https://plus.maths.org/content/sites/plus.maths.org/files/articles/2015/Tong/blackhole.jpg" alt="Curved space-time" width="350" height="222" />
<p>An artist's impression of a black hole. Image: Robert Hurt, <a href="http://www.nasa.gov">NASA</a>/<a href="http://www.jpl.nasa.gov">JPL-Caltech</a>.</p>
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We asked cosmologist Pau Figueras everything we’ve ever wanted to know about black holes. In this podcast he explains what black holes are, physically, and how we hope to observe them.
</p><p><a href='https://plus.maths.org/content/sites/plus.maths.org/files/podcast/pluspodcastnov15-blackholes1.mp3'>Listen to our interview with Pau Figueras</a></p><p><a href="https://plus.maths.org/content/what-black-hole-physically" target="_blank">read more</a></p>https://plus.maths.org/content/what-black-hole-physically#commentsblack holegeneral relativityrelativityUniversity of CambridgeFri, 13 Nov 2015 14:00:08 +0000Rachel6465 at https://plus.maths.org/contentPhysics in a minute: What's the problem with quantum gravity?
https://plus.maths.org/content/physics-minute-whats-problem-quantum-gravity
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<p>At the heart of modern physics lurks a terrible puzzle: the two main theories that describe the world we live in just won't fit together.</p>
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<p>At the heart of modern physics lurks a terrible puzzle: the
two main theories that describe the world we live in just won't fit
together.</p>
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<p> The force of gravity is
described by Einstein's general theory of relativity (which celebrates
its 100th birthday this year). General relativity says that space and
time can be curved by massive objects.</p><p><a href="https://plus.maths.org/content/physics-minute-whats-problem-quantum-gravity" target="_blank">read more</a></p>https://plus.maths.org/content/physics-minute-whats-problem-quantum-gravity#commentsgeneral relativityquantum gravityquantum mechanicsquantum uncertaintyrelativityThu, 29 Oct 2015 11:21:39 +0000mf3446457 at https://plus.maths.org/contentWhat is general relativity?
https://plus.maths.org/content/what-general-relativity
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David Tong (with the Plus team) </div>
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<p>To celebrate the centenary of the general theory of relativity we asked physicist David Tong to explain the theory and the equation that expresses it. Watch the video or read the article!</p>
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<p><em>When physicists talk about Einstein's equation they don't
usually mean the famous <em>E=mc<sup>2</sup></em>, but another
formula, which encapsulates the celebrated general theory of
relativity. Einstein published that theory a hundred years ago, in
1915. To celebrate its centenary we asked physicist <a href="http://www.damtp.cam.ac.uk/user/tong/">David Tong</a> of the
University of Cambridge to explain what general relativity is and how
Einstein's equation expresses it. You can watch his explanation in the video
below, or read on.</em></p><p><a href="https://plus.maths.org/content/what-general-relativity" target="_blank">read more</a></p>https://plus.maths.org/content/what-general-relativity#commentsEinsteingeneral relativityhistory of mathematicsrelativityUniversity of CambridgevideoFri, 12 Jun 2015 10:17:46 +0000mf3446375 at https://plus.maths.org/contentEinstein and relativity: Part I
https://plus.maths.org/content/einstein-relativity
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David Tong </div>
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<img class="imagefield imagefield-field_abs_img" width="100" height="100" alt="" src="https://plus.maths.org/content/sites/plus.maths.org/files/abstractpics/5/5_may_2015_-_1456/icon_einstein.jpg?1430834214" /> </div>
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<p>Read about the rocky road to one of Einstein's greatest achievements: the general theory of relativity, which celebrates its centenary this year.</p>
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<p><em>This article is an abridged version of a talk David Tong gave at the Southbank Centre in London in 2013. You can listen to a sound recording of the talk on <a href="https://soundcloud.com/southbankcentre/david-tong-on-einsteins-theory/">Soundcloud</a>, or watch a video of a very similar talk, aimed at 16 to 17 year-olds, <a href="https://plus.maths.org/content/stories-einstein">here</a>.</em></p>
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<p>2015 is a special year for physics. It is the 100th
anniversary of Albert Einstein's greatest achievement: the <em>general theory of relativity</em>. </p><p><a href="https://plus.maths.org/content/einstein-relativity" target="_blank">read more</a></p>https://plus.maths.org/content/einstein-relativity#commentscreativityEinsteinFP-carouselgeneral relativityhistory of mathematicsrelativityspecial relativityUniversity of CambridgeThu, 04 Jun 2015 15:56:07 +0000mf3446360 at https://plus.maths.org/contentEinstein and relativity: Part II
https://plus.maths.org/content/einstein-and-relativity-part-ii
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David Tong </div>
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<img class="imagefield imagefield-field_abs_img" width="100" height="100" alt="" src="https://plus.maths.org/content/sites/plus.maths.org/files/abstractpics/5/4_jun_2015_-_1621/galaxies_icon.png?1433431315" /> </div>
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<p>General relativity, Einstein's rise to international stardom, and his legacy.</p>
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<p><em>To read about Einstein's motivation for the general theory of relativity and his struggle to formulate it, read the <a href="https://plus.maths.org/content/einstein-relativity">first part</a> of this article.</em></p>
<h3>General relativity</h3>
<p>Einstein's theory changed our understanding of space and time. Before Einstein people thought of space as stage on which the laws of physics play out. We could throw in some stars or some planets and they would move around on this stage.</p><p><a href="https://plus.maths.org/content/einstein-and-relativity-part-ii" target="_blank">read more</a></p>https://plus.maths.org/content/einstein-and-relativity-part-ii#commentscreativityEinsteingeneral relativityhistory of mathematicsrelativityUniversity of CambridgeThu, 04 Jun 2015 15:15:38 +0000mf3446374 at https://plus.maths.org/contentProblems of gravity
https://plus.maths.org/content/problems-gravity
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Marianne Freiberger </div>
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<img class="imagefield imagefield-field_abs_img" width="100" height="100" alt="" src="https://plus.maths.org/content/sites/plus.maths.org/files/abstractpics/5/18_jul_2014_-_1240/icon.jpg?1405683602" /> </div>
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<p>Why (some) physicists want to modify Einstein's general theory of relativity.</p>
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<p>Albert Einstein is an icon and for good reason. His general
theory of relativity, which describes the force of gravity, was an
intellectual tour de force. Not only were his ideas entirely new, they have also stood the test of
time.
Despite this success, some physicists are doing what many would consider sacrilege: they are tinkering with the theory, producing modified versions of it. But why? </p><p><a href="https://plus.maths.org/content/problems-gravity" target="_blank">read more</a></p>https://plus.maths.org/content/problems-gravity#commentsEinsteingeneral relativitygravityphilosophy of cosmologyrelativitysymmetryWed, 23 Jul 2014 09:01:32 +0000mf3446099 at https://plus.maths.org/contentWhat is cosmology?
https://plus.maths.org/content/what-cosmology
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David J. Mulryne </div>
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<p>How big is the Universe? Where did it come from and where is it going? Why is it the way it is? These are just some of the questions cosmologists study.</p>
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<div class="rightimage" style="width: 250px;"><img src="https://plus.maths.org/content/sites/plus.maths.org/files/packages/2013/QM/qmlogo_0.jpg" width="250" height="62" alt="QM logo"/></div><p><em>This article is part of the <a href="https://plus.maths.org/content/researching-unknown">Researching the unknown project</a>, a collaboration with researchers from <a href="http://ph.qmul.ac.uk/">Queen Mary University of London</a>, bringing you the latest research on the forefront of physics. Click <a href="https://plus.maths.org/content/researching-unknown">here</a> to read more articles from the project.</em></p><p><a href="https://plus.maths.org/content/what-cosmology" target="_blank">read more</a></p>https://plus.maths.org/content/what-cosmology#commentscosmologydark energydark mattergeneral relativityrelativityThu, 20 Mar 2014 10:50:06 +0000mf3446050 at https://plus.maths.org/contentA matter of gravity
https://plus.maths.org/content/matter-gravity
<div class="rightimage" style="width: 350px;"><img src="https://plus.maths.org/content/sites/plus.maths.org/files/blog/022014/snowboarder_in_halfpipe.jpg" alt="Snowboarder" width="350" height="233" />
<p>Snowboarders are vulnerable to gravity. Image: <a href="http://commons.wikimedia.org/wiki/File:Snowboarder_in_halfpipe.jpg">Picswiss.ch</a>.</p><p><a href="https://plus.maths.org/content/matter-gravity" target="_blank">read more</a></p>https://plus.maths.org/content/matter-gravity#commentsgeneral relativitygravitational wavegravitational wave detectorgravityinverse square lawspecial relativityThu, 27 Feb 2014 15:58:39 +0000mf3446051 at https://plus.maths.org/contentWhat is space?
https://plus.maths.org/content/what-space
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Marianne Freiberger </div>
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<p>Space is the stage on which physics happens. It's unaffected by what happens in it and it would still be there if everything in it disappeared. This is how we learn to think about space at school. But the idea is as novel as it is out-dated.</p>
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<p><em>In the latest poll of our <a href="https://plus.maths.org/content/science-fiction-science-fact-reports-frontiers-physics">Science fiction, science fact project</a> you told us that you wanted to know an answer to this question. So we went to speak to Francesca Vidotto and George Ellis to find out. Click <a href="https://plus.maths.org/content/science-fiction-science-fact-what-space">here</a> to see other articles exploring this question.</em></p><p><a href="https://plus.maths.org/content/what-space" target="_blank">read more</a></p>https://plus.maths.org/content/what-space#commentsFrontiers of physicsmathematical realityblack holecurvature of spacegeneral relativitygravityPlanck unitquantum gravityquantum mechanicsquantum physicsrelativityspacetimeTue, 16 Apr 2013 14:08:03 +0000mf3445881 at https://plus.maths.org/content