tag:theconversation.com,2011:/au/topics/gravity-waves-1428/articles
Gravity waves – The Conversation
2017-08-08T00:57:14Z
tag:theconversation.com,2011:article/80636
2017-08-08T00:57:14Z
2017-08-08T00:57:14Z
Scientist at work: Why this meteorologist is eager for an eclipse
<figure><img src="https://images.theconversation.com/files/181075/original/file-20170804-27483-1h1khg2.jpg?ixlib=rb-1.1.0&rect=209%2C0%2C1622%2C1072&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Hiscox and students practice for the big day with a weather balloon.</span> <span class="attribution"><span class="source">Joshua Burrack</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>By all accounts a total solar eclipse is a life-changing event. I wouldn’t know, I’ve never seen one. Fortunately for me and millions across the U.S., that will change this summer.</p>
<p>I’m not really an eclipse expert, even though I can’t wait for August 21. I’m actually a meteorologist, and a fairly specialized one at that. Six months ago, I didn’t know the difference between an umbra and penumbra. What I did know is that the sun provides energy for everything that happens on our planet, and that the daily cycle of sun rising and setting is a key component of what happens in the atmosphere, and how air circulates locally and globally. </p>
<p>So why is someone who worries about subsecond- and submeter-scale winds interested in this astronomical-scale event? Because any change in incoming sun – such as the complete blackout during a total solar eclipse – will affect the energy received by the land, and in turn the energy transferred back to the atmosphere. And because the total eclipse period is short, those changes will be small. It’s both an exciting event and an interesting challenge: a scientist’s dream.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/181116/original/file-20170806-10088-1o0whzd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/181116/original/file-20170806-10088-1o0whzd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/181116/original/file-20170806-10088-1o0whzd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=408&fit=crop&dpr=1 600w, https://images.theconversation.com/files/181116/original/file-20170806-10088-1o0whzd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=408&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/181116/original/file-20170806-10088-1o0whzd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=408&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/181116/original/file-20170806-10088-1o0whzd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=513&fit=crop&dpr=1 754w, https://images.theconversation.com/files/181116/original/file-20170806-10088-1o0whzd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=513&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/181116/original/file-20170806-10088-1o0whzd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=513&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The mini-night caused by the moon blacking out the sun during the day is an opportunity to investigate many scientific questions.</span>
<span class="attribution"><a class="source" href="http://www.apimages.com/metadata/Index/Russia-Europe-Solar-Eclipse/44d1094c93774d39a3324d19adb5efee/1/0">AP Photo/Dmitry Lovetsky</a></span>
</figcaption>
</figure>
<p>Coupled with advances in observational techniques, every eclipse offers a new chance to prove meteorological theories. This one even more so because coordination across the entire length of the continental United States almost guarantees that someone will have ideal observing conditions. We’re prepping our weather balloons and weather stations to take advantage of that opportunity – to see exactly what a short blackout does to atmospheric motion.</p>
<h2>Meteorology all goes back to the sun</h2>
<p>From how <a href="https://www.epa.gov/ozone-pollution">pollutants are formed and transported</a>, to how plants exchange carbon using photosynthesis, to what direction the wind blows, daytime processes are <a href="https://doi.org/10.1175/JAS3654.1">different from nighttime processes</a>. Without energy input from the sun, the lower atmosphere slowly flips itself at night. </p>
<p>During the day, it’s warm near the ground and cooler up above; at night it’s just the opposite. This “stable” (warmer over cooler) air inhibits vertical motion of the air and anything suspended in it. So <a href="https://doi.org/10.1191/0309133305pp442ra">pollutants can stay closer to the ground</a>, <a href="https://doi.org/10.1175/1520-0469(2001)058%3C1409:FADONB%3E2.0.CO;2">clouds form differently</a>, <a href="https://doi.org/10.1175/1520-0469(1967)024%3C0029:KWITEA%3E2.0.CO;2">air flows faster down valleys</a> and at the coasts <a href="http://www.srh.noaa.gov/jetstream/ocean/seabreeze.html">wind blows offshore instead of on</a>. </p>
<p>While those generalities are known, the nuances and timings aren’t fully understood, and thus they are not completely predictable. That’s my sphere of science – turbulence. I’m interested in the atmospheric changes in short times and small spaces that can eventually influence the larger “weather” most people are familiar with.</p>
<p>The total solar eclipse is a mini-night experience, so we will use it as a natural experiment. Is a brief period without solar radiation enough to cause detectable changes in turbulence and stability, or is it the slower interactions of land and atmosphere over a whole night that are required? We’ll take what we find and use it to think about normal non-eclipse conditions.</p>
<h2>Head in the sky</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/181066/original/file-20170804-6948-1y2u1lq.gif?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/181066/original/file-20170804-6948-1y2u1lq.gif?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/181066/original/file-20170804-6948-1y2u1lq.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=329&fit=crop&dpr=1 600w, https://images.theconversation.com/files/181066/original/file-20170804-6948-1y2u1lq.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=329&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/181066/original/file-20170804-6948-1y2u1lq.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=329&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/181066/original/file-20170804-6948-1y2u1lq.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=413&fit=crop&dpr=1 754w, https://images.theconversation.com/files/181066/original/file-20170804-6948-1y2u1lq.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=413&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/181066/original/file-20170804-6948-1y2u1lq.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=413&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The troposphere is the part of the atmosphere closest to Earth’s surface and includes the air we breathe.</span>
<span class="attribution"><a class="source" href="https://www.giss.nasa.gov/research/features/201210_shindell/">NASA ESPO/INTEX-NA Educational Outreach</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>By launching a series of weather balloons before, during and after the eclipse we will see the evolution of winds and temperatures above the Earth’s surface over time. The instrument packages attached to the balloons take measurements from about 100 meters above the surface up through the lower atmosphere, troposphere and lower stratosphere, eventually reaching nearly 20 kilometers. Scientists are coordinating all across the eclipse’s path, and will conduct this same experiment at <a href="http://eclipse.montana.edu/">several sites</a> across the country.</p>
<p>At our site in South Carolina, we are focusing on the question of whether a total eclipse can generate internal atmospheric <a href="http://glossary.ametsoc.org/wiki/Gravity_wave">gravity waves</a>: parcels of air moving together as chunks trying to regain an equilibrium in temperature and density. (These are different from the <a href="https://theconversation.com/gravitational-waves-discovered-top-scientists-respond-53956">gravitational waves</a> that result when black holes collide.) Sometimes gravity waves are visible in clouds. During previous eclipses <a href="https://doi.org/10.1098/rsta.2015.0222">there has been promising evidence</a> of gravity wave activity, but not enough data from enough locations to fully understand them.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/181044/original/file-20170804-10658-igira4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/181044/original/file-20170804-10658-igira4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/181044/original/file-20170804-10658-igira4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=462&fit=crop&dpr=1 600w, https://images.theconversation.com/files/181044/original/file-20170804-10658-igira4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=462&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/181044/original/file-20170804-10658-igira4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=462&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/181044/original/file-20170804-10658-igira4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=580&fit=crop&dpr=1 754w, https://images.theconversation.com/files/181044/original/file-20170804-10658-igira4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=580&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/181044/original/file-20170804-10658-igira4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=580&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The pattern of atmospheric gravity waves is visible in this satellite image of double, overlapping arcs of clouds over the Indian Ocean.</span>
<span class="attribution"><a class="source" href="https://visibleearth.nasa.gov/view.php?id=69463">Jacques Descloitres, MODIS Rapid Response Team, NASA/GSFC</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>The vertical profiles of temperature, relative humidity, wind speed and wind direction we collect will be used to answer a number of other scientific questions as well. First, we’ll add to the sparse database of eclipse-induced temperature changes and provide quantitative measures of how strong the temperature change is and how long the lag between the total blackness at solar minimum and the temperature minimum is.</p>
<p>We will also be able to see if the cooling when the sun disappears and sudden rewarming when it returns propagates vertically and, if so, how far above the Earth’s surface it goes. In terms of wind, questions to be answered center around changes in wind speed and turbulence intensity. We believe we will see a reduction of both, which provides further explanation for the eerie “<a href="https://phys.org/news/2016-08-mystery-eclipse-years.html">eclipse wind</a>” so often cited by human observers.</p>
<p>This more comprehensive examination of the troposphere and stratosphere in time and space will help inform our modeling and prediction of regional weather and climate.</p>
<h2>Feet on the ground</h2>
<p>But what if the changes are smaller? A helium-filled balloon leaves the ground quickly – ideally at five meters per second – and the first reliable measurement is almost 100 meters above the ground. A lot can happen in 100 meters.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/181067/original/file-20170804-2386-s32kso.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/181067/original/file-20170804-2386-s32kso.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/181067/original/file-20170804-2386-s32kso.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/181067/original/file-20170804-2386-s32kso.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/181067/original/file-20170804-2386-s32kso.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/181067/original/file-20170804-2386-s32kso.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/181067/original/file-20170804-2386-s32kso.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/181067/original/file-20170804-2386-s32kso.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Postdoc Alexandria McCombs and graduate students Mayra Roman-Rivera and Peter Tereskiewicz work on installing meteorological instruments in preparation for the eclipse experiment.</span>
<span class="attribution"><span class="source">Ian Giammanco, Insurance Institute for Business & Home Safety,DisasterSafety.org</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>To fill in that gap, at our site in South Carolina, we are adding other measurements. We’ve erected a small tower with fine thermocouples every half-meter from the ground up. These thin wires can detect temperature changes over 0.1-second time periods and will help us see if the darkness causes a very shallow layer of cooler air to start to grow under the typical daytime warmth. </p>
<p>The tower will also house two sonic anemometers – sensors that use disruption in a sound pulse to measure the wind speed in three dimensions at very fast rates – to see if a <a href="http://glossary.ametsoc.org/wiki/Wind_shear">wind shear</a> develops near ground level.</p>
<p>An infrared gas analyzer will record carbon fluxes throughout the eclipse period to see if there is any detectable change in plant respiration. Remember, they “breathe” in carbon dioxide. <a href="http://sciencing.com/animals-reaction-solar-eclipse-3503.html">Some animals interpret an eclipse as night</a> – do the plants?</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/181069/original/file-20170804-2386-e2v3uh.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/181069/original/file-20170804-2386-e2v3uh.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/181069/original/file-20170804-2386-e2v3uh.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/181069/original/file-20170804-2386-e2v3uh.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/181069/original/file-20170804-2386-e2v3uh.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/181069/original/file-20170804-2386-e2v3uh.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/181069/original/file-20170804-2386-e2v3uh.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/181069/original/file-20170804-2386-e2v3uh.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The USC backscatter lidar at a recent field deployment in New Zealand.</span>
<span class="attribution"><span class="source">April Hiscox</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Finally, we’ll also deploy a lidar system. That’s like a radar, but with a laser that will point upward. This is to see if there are any changes in the depth of the boundary layer – a transition point between where the atmosphere is affected by the Earth’s surface to the free troposphere above.</p>
<p>And we’re going to do all of this in just two minutes and 36 seconds. A tiny window for a big impact.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/181070/original/file-20170804-7490-3b1kae.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/181070/original/file-20170804-7490-3b1kae.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/181070/original/file-20170804-7490-3b1kae.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/181070/original/file-20170804-7490-3b1kae.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/181070/original/file-20170804-7490-3b1kae.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/181070/original/file-20170804-7490-3b1kae.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/181070/original/file-20170804-7490-3b1kae.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/181070/original/file-20170804-7490-3b1kae.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A practice weather balloon soars above the USC campus.</span>
<span class="attribution"><span class="source">Patrick Remson</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Collating the data to flesh out the theory</h2>
<p>A total solar eclipse is often referred to as a meteorological playground, and that is just how it feels. We’re taking out all our scientific toys to see what we can find. Eclipse events are relatively rare; meteorologists like me take what we know about the interactions between land and air to think logically about what will happen during an eclipse. But until we see it, put an equation on it and predict the next one, it still falls into the realm of theory, not reliably predictable weather. </p>
<p>I feel like a kid again – the eclipse has forced me to think about meteorology in a new and different way – just like looking at the world while hanging upside down from monkey bars.</p><img src="https://counter.theconversation.com/content/80636/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>April Hiscox receives funding for eclipse related research from South Carolina Space Grant and The University of South Carolina Office of Research. </span></em></p>
Meteorology researchers across the country are prepping experiments for the mini-night the eclipse will bring on August 21 – two minutes and 36 seconds without the sun in the middle of the day.
April Hiscox, Associate Professor of Geography, University of South Carolina
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/72743
2017-02-10T04:17:15Z
2017-02-10T04:17:15Z
Black holes are even stranger than you can imagine
<figure><img src="https://images.theconversation.com/files/156285/original/image-20170210-8637-o4kx0u.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An artist's impression of a Sun-like star close to a rapidly spinning supermassive black hole, with a mass of about 100 million times the mass of our Sun.</span> <span class="attribution"><a class="source" href="https://www.spacetelescope.org/images/heic1622a/">ESA/Hubble, ESO, M. Kornmesser</a></span></figcaption></figure><p>Our love of black holes continues to grow as our knowledge of these celestial bodies expands. The latest news is the discovery of a rare <a href="http://www.abc.net.au/news/2017-02-09/middleweight-black-hole-found-in-space-qld-scientist-says/8253468">“middleweight” black hole</a>, a <a href="https://www.scientificamerican.com/article/intermediate-black-hole/">relative newcomer</a> to the black hole family. </p>
<p>We already knew that some black holes are just a few times the mass of our Sun, while others are more than a billion times as massive. But others with intermediate masses, such as the one 2,200 times the mass of our Sun recently discovered in the star cluster 47 Tucanae, are surprisingly elusive.</p>
<p>So what is it about black holes, these gravitational prisons that trap anything that gets too close to them, that captures the imagination of people of all ages and professions?</p>
<h2>‘Dark stars’</h2>
<p>As far back as 1783, within the framework of Newtonian dynamics, the concept of “dark stars” with sufficiently high density that not even light can escape their gravitational pull <a href="https://www.aps.org/publications/apsnews/200911/physicshistory.cfm">had been advanced</a> by the English philosopher and mathematician John Michell.</p>
<p>Almost immediately after Albert Einstein presented his theory of general relativity in 1915, which supplanted Newton’s description of our Universe and revealed how space and time are intimately linked, fellow German Karl Schwarzschild and Dutchman Johannes Droste independently derived the new equations for a spherical or point mass.</p>
<p>Although at the time the issue was still something of a mathematical curiosity, over the ensuing quarter of a century nuclear physicists realised that sufficiently massive stars would collapse under their own weight to become these previously theorised black holes.</p>
<p>Their existence was eventually confirmed by astronomers using powerful telescopes, and more recently colliding black holes were the source of the <a href="https://theconversation.com/au/topics/gravitational-waves-9473">gravitational waves</a> detected with the LIGO instrumentation in the United States.</p>
<h2>A dense object</h2>
<p>The densities of such objects is mind-boggling. If our Sun were to become a black hole, it would need to collapse from its current size of 1.4 million km across to a diameter of less than 6km. Its average density within this “Schwarzschild radius” would be nearly 20 billion tonnes per cubic centimetre.</p>
<p>The increasing strength and pull of gravity as you get closer to a black hole can be dramatic.</p>
<p>On Earth, the strength of the gravitational pull holding you to its surface is roughly the same at your feet as it is at your head, which is a little bit farther away from the planet.</p>
<p>But near some black holes, the difference in gravitational pull from head to toe is so great that you would be pulled apart and stretched out on an atomic level, in a process referred to as <a href="https://en.oxforddictionaries.com/definition/spaghettification">spaghettification</a>.</p>
<p>In 1958, the American physicist David Finkelstein was the first to realise the true nature of what has come to be called the “<a href="http://astronomy.swin.edu.au/cosmos/E/Event+Horizon">event horizon</a>” of a black hole. He described this boundary around a black hole as the perfect unidirectional membrane.</p>
<p>It’s an intangible surface encapsulating a sphere of no return. Once inside this sphere, the gravitational pull of the black hole is too great to escape – even for light.</p>
<p>In 1963, the New Zealand mathematician Roy Kerr solved the equations for the more realistic rotating black holes. These yielded closed time-like curves that permitted movement backwards through time. </p>
<p>While such strange solutions to the equations of general relativity first appeared in the 1949 work of Austrian-American logician Kurt Gödel, it is commonly thought that they must be a mathematical artefact yet to be explained away.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/FZENB1pCPe8?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">A video simulation of two black holes merging.</span></figcaption>
</figure>
<h2>Black and white holes</h2>
<p>In 1964, two Americans, the writer Ann Ewing and the theoretical physicist John Wheeler, introduced the term “black hole”. Subsequently, in 1965, the Russian theoretical astrophysicist Igor Novikov introduced the term “white hole” to describe the hypothetical opposite of a black hole.</p>
<p>The argument was that if matter falls into a black hole, then perhaps it is spewed out into our universe from a white hole.</p>
<p>This idea is partly rooted in the mathematical concept known as an Einstein-Rosen bridge. Discovered (mathematically) in 1916 by the Austrian physicist Ludwig Flamm, and re-introduced in 1935 by Einstein and the American-Israeli physicist Nathan Rosen, it was later termed a “wormhole” by Wheeler. </p>
<p>In 1962, Wheeler and the American physicist Robert Fuller explained why such wormholes would be unstable for transporting even a single photon across the same universe. </p>
<h2>Fact and fiction</h2>
<p>Not surprisingly, the idea of entering a (black hole) portal and re-emerging somewhere else in the universe – in space and/or time – has spawned countless science fiction stories, including <a href="http://www.imdb.com/title/tt0772457/">Doctor Who</a>, <a href="http://www.imdb.com/title/tt0118480/">Stargate</a>, <a href="http://www.imdb.com/title/tt1119644/">Fringe</a>, <a href="http://www.imdb.com/title/tt0187636/">Farscape</a> and Disney’s <a href="http://www.imdb.com/title/tt0078869/">Black Hole</a>.</p>
<p>Ongoing productions can simply claim that their characters are travelling to a different or a parallel universe to our own. While it appears to be mathematically feasible, there is of course no physical evidence to support the existences of such universes.</p>
<p>But this is not to say that time travel, at least in a limited sense, is not real. When travelling at great speed, or perhaps falling into a black hole, the passage of time does slow down relative to that experienced by stationary observers. </p>
<p>Clocks flown quickly around the world have demonstrated this, displaying time lags in accordance with Einstein’s theory of special relativity.</p>
<p>The 2014 movie <a href="http://www.imdb.com/title/tt0816692/">Interstellar</a> played on this effect around a black hole, thereby creating a sense of travelling forward in time for astronaut Cooper (played by Matthew McConaughey).</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/2LqzF5WauAw?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>Despite the strangely endearing name, the phrase “black hole” is perhaps somewhat misleading. It implies a hole in space-time through which matter will fall, as opposed to matter falling onto an incredibly dense object.</p>
<p>What actually exists within a black hole’s event horizon is hotly debated. Attempts to understand this include the “<a href="https://www.wired.com/2015/06/fuzzball-fix-black-hole-paradox/">fuzzball</a>” picture from string theory, or descriptions of black holes in quantum gravity theories known as “spin foam networks” or “loop quantum gravity”.</p>
<p>One thing that does seem certain is that black holes will continue to intrigue and fascinate us for some time yet.</p><img src="https://counter.theconversation.com/content/72743/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Alister Graham receives funding from The Australian Research Council. </span></em></p>
The discovery of a new black hole adds to our understanding of these celestial objects that fascinate in both fact and fiction.
Alister Graham, Professor of Astronomy, Swinburne University of Technology
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/71347
2017-01-16T16:02:39Z
2017-01-16T16:02:39Z
Astronomers spot strange, bow-like structure in Venus’ atmosphere
<figure><img src="https://images.theconversation.com/files/152848/original/image-20170116-8769-qypmxh.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Strange shape in Venus' atmosphere.</span> <span class="attribution"><span class="source">©Planet-C</span></span></figcaption></figure><p>Venus is known both as the “<a href="https://theconversation.com/venus-calling-lets-return-to-the-planet-of-love-7598">planet of love</a>” and the Earth’s “evil twin”. And although research suggests its environment <a href="https://www.theguardian.com/science/gallery/2007/nov/29/venus.express">is more hellish than romantic</a>, there’s actually a lot we don’t know about our celestial neighbour. Now Japanese scientists have made a surprising discovery: an enormous, bow-shaped feature in the planet’s cloud region which seems fixed to the slowly rotating planet. Clouds around it, on the other hand, whizz by at about 100 metres per second. So what is it?</p>
<p>Venus is almost as large as Earth but orbits closer to the sun. A spacecraft approaching the planet would see chevron-shaped structures in the clouds, due to the rapid “super-rotation” of its thick atmosphere well above the surface. </p>
<p>Before the space age, it was thought that Venus would be somewhat similar to Earth. Indeed, the expectation in science fiction was that the planet may support life, with thick vegetation under water-rich clouds. But spacecraft have shown us that Venus is lifeless and very different to our own planet – and the clouds are sulphuric acid. It has the hottest planetary surface in the solar system (720 Kelvin or 447°C – hot enough to melt lead), a thick atmosphere (92 times Earth’s atmospheric pressure) and no protective magnetic field. Its rotation is slow – and the wrong way around (243 Earth days) – and it has hurricane force winds and strange vortices near the poles.</p>
<p>Although early Venus may have had some surface water, this gradually evaporated into the atmosphere due to the close distance to the sun. This led to a greenhouse effect in which the atmosphere got thicker, the surface got hotter, more water evaporated into the atmosphere and so forth. The water broke up in the high atmosphere rather than condensing onto the warm surface as oceans. Unlike Earth, carbon dioxide in the atmosphere could not be dissolved into the oceans, settling on the ocean floor as carbonates and cycled as carbon dioxide gas by volcanism. Instead, volcanism continued pumping gases into the atmosphere, building up the atmospheric pressure. The atmosphere of Venus now is principally carbon dioxide, which is the reason the surface is extremely hot.</p>
<p>The early missions, including <a href="http://www.jpl.nasa.gov/jplhistory/mission/venus-t.php">Mariner</a>, <a href="http://www.russianspaceweb.com/spacecraft_planetary_venus.html">Venera</a> and <a href="https://www.nasa.gov/mission_pages/pioneer-venus/">Pioneer Venus</a> determined the composition of the clouds and measured the atmospheric structure. The Russian Venera landers, the only craft so far to have landed in the harsh Venus environment, showed images of lava plains and volcanic terrain. Later the <a href="http://www2.jpl.nasa.gov/magellan/">Magellan mission</a>, which used radar to peer under the clouds, allowed mapping of the volcanoes and lava channels in detail – revealing a young surface with relatively few craters. This shows that the planet was resurfaced by volcanic activity about 500m years ago. More recently, <a href="http://sci.esa.int/venus-express/">Venus Express</a> has shown possible signs of some volcanism <a href="http://adsabs.harvard.edu/full/1988LPSC...18..659W">within the last 100 to 10,000 years</a>.</p>
<p>The super-rotation of Venus’ atmosphere makes it very different from Earth. At the cloud level of 50-65km, where the atmospheric pressure varies between the Earth’s surface pressure to 10% of that, the speed of rotation is up to 100m/s – about 60 times the speed of the planet’s rotation. This is higher than a hurricane force on Earth. By contrast, Earth’s fastest winds are only about 10-20% of the planet’s rotation speed. Although the super-rotation is not fully understood, Pioneer Venus showed that the high speed <a href="http://sci.esa.int/venus-express/43391-a-3d-view-of-variable-winds-in-venus-s-cloud-layers/">reduces through the lower atmosphere</a>, eventually rotating with the planet at the surface.</p>
<h2>Perplexing planet</h2>
<p>Enter the Japanese spacecraft Akatsuki, which was launched on May 20, 2010. The spacecraft is designed to study the structure and activity of the Venus atmosphere. After a <a href="http://www.space.com/10450-collision-japanese-probe-venus.html">difficult journey</a> , it was successfully inserted into orbit at the second attempt in 2015. This, along with the first few results, were a huge achievement. </p>
<p>The new study reporting the discovery of the bow-shaped structure, <a href="http://nature.com/articles/doi:10.1038/ngeo2873">just published in Nature Geoscience</a>, is the most recent result of the mission. The wave was caught by Akatsuki’s imaging instruments – looking in the infrared and ultraviolet parts of the <a href="https://theconversation.com/explainer-what-is-the-electromagnetic-spectrum-8046">electromagnetic spectrum</a>. The astronomers analysing the data noted that the structure extended 10,000 km through the Venus cloud tops and persisted for a few days, then suddenly disappeared.</p>
<p>Remarkably, the shape seems tied to the slowly rotating terrain below, particularly a high region called <a href="http://www.jpl.nasa.gov/news/news.php?feature=5642">Aphrodite Terra</a>, which is up to 5km high and the size of Africa near the equator. The structure persists in the rapidly moving, super-rotating winds at the cloud level. This is a bit like the flow of water flow around a submerged stone in a stream.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/152847/original/image-20170116-8797-13okxfw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/152847/original/image-20170116-8797-13okxfw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/152847/original/image-20170116-8797-13okxfw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/152847/original/image-20170116-8797-13okxfw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/152847/original/image-20170116-8797-13okxfw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/152847/original/image-20170116-8797-13okxfw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/152847/original/image-20170116-8797-13okxfw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Clouds caused by gravity waves within meteorological disturbance.</span>
<span class="attribution"><span class="source">Glen Talbot</span></span>
</figcaption>
</figure>
<p>The researchers suggest that a stationary “gravity wave” (which is different from a <a href="https://theconversation.com/uk/topics/gravitational-waves-9473">gravitational wave</a>) in the atmosphere might cause the effect. Gravity waves are generated at the boundary between the atmosphere and a surface, or between horizontal layers in the atmosphere, when the force of gravity opposes buoyancy (ability to float). An example on Earth is the wind waves on the sea – just between the atmosphere and the ocean. There are also gravity waves over mountainous terrain, which form when air ripples move over a bumpy surface. Gravity waves on a larger scale can also be seen in the upper atmosphere between different layers.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/152864/original/image-20170116-27894-1ee8i89.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/152864/original/image-20170116-27894-1ee8i89.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=426&fit=crop&dpr=1 600w, https://images.theconversation.com/files/152864/original/image-20170116-27894-1ee8i89.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=426&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/152864/original/image-20170116-27894-1ee8i89.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=426&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/152864/original/image-20170116-27894-1ee8i89.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=536&fit=crop&dpr=1 754w, https://images.theconversation.com/files/152864/original/image-20170116-27894-1ee8i89.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=536&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/152864/original/image-20170116-27894-1ee8i89.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=536&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Gravity waves seen by Venus Express.</span>
<span class="attribution"><span class="source">nasa.</span></span>
</figcaption>
</figure>
<p>Although smaller scale gravity waves <a href="http://sci.esa.int/venus-express/58088-gravity-waves-on-venus/">have been seen</a> near to ground level on Venus before, the scale of this new feature seems to be extremely large, probably the largest in the solar system. In fact it is unclear whether it is even possible for gravity waves to cause such a big effect. </p>
<p>The discovery illustrates that, although we can explain some of the features of the thick, fast Venus atmosphere, it appears that low-altitude atmospheric dynamics are not fully understood yet. But we are slowly uncovering the planet’s secrets and the latest study is certainly making waves.</p><img src="https://counter.theconversation.com/content/71347/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Andrew Coates receives funding from STFC and UKSA. </span></em></p>
Enormous odd feature presents puzzle for scientists.
Andrew Coates, Professor of Physics, Deputy Director (Solar System) at the Mullard Space Science Laboratory, UCL
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/54521
2016-02-11T16:48:11Z
2016-02-11T16:48:11Z
Gravitational waves discovered: scientists explain why it is such a big deal
<figure><img src="https://images.theconversation.com/files/111023/original/image-20160210-12137-1of6m0m.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Historic beauty.</span> <span class="attribution"><span class="source">NASA/ESA/wikipedia commons</span></span></figcaption></figure><p>It’s one of the biggest scientific discoveries of modern times. Scientists at the Laser Interferometer Gravitational-Wave Observatory (LIGO) announced that they had <a href="http://theconversation.com/explainer-gravitational-waves-and-why-their-discovery-is-such-a-big-deal-53239">detected gravitational waves</a> for the first time. </p>
<p><a href="https://theconversation.com/explainer-gravity-5256">For decades</a>, physicists have been trying to prove the existence of the elusive waves, first proposed by Albert Einstein a century ago. They even thought they’d finally <a href="https://www.cfa.harvard.edu/news/2014-05">found them two years ago</a> – only to be left deflated once they realised the signals detected by the BICEP2 telescope were <a href="https://theconversation.com/bicep2-gravity-wave-finding-clouded-by-interstellar-dust-32048">actually due to cosmic dust</a>. This time though, it does look like they’ve done it. </p>
<p>But isn’t gravity a force that keeps us grounded? How can it be waves? Why are scientists making such a big deal out of this?</p>
<p>The answers to these questions are mindblowing and go to the very core of our understanding of what constitutes space and time. Here’s why:</p>
<p><strong><a href="http://theconversation.com/explainer-gravitational-waves-and-why-their-discovery-is-such-a-big-deal-53239">A simple analogy to understand gravitational waves and why they matter</a></strong> Drop a ball while you’re standing on a trampoline and it’ll roll to your feet. The same logic explains space-time. </p>
<p><strong><a href="https://theconversation.com/gravitational-waves-found-how-we-proved-the-power-of-the-dark-side-54589">How we made the discovery: the inside story</a></strong>. Martin Hendry tells the story about how a consortium of UK institutions, led by the University of Glasgow, played a key role developing, constructing and installing the sensitive mirror suspensions at the heart of the LIGO detectors that were crucial to the detection. </p>
<p><strong><a href="https://theconversation.com/hunting-for-gravitational-waves-how-does-an-experiment-at-ligo-actually-work-54510">How does the LIGO experiment actually work? Find out from a team member</a></strong>
It took a marvel of engineering and physics to detect them. Yes, that involves lasers.</p>
<p><strong><a href="https://theconversation.com/lisa-pathfinder-will-pave-the-way-for-us-to-see-black-holes-for-the-first-time-51374">The discovery can help us “sense” the universe in a new way – here’s how</a></strong>
We’ve been looking at the universe by detecting a broad range of electromagnetic waves. Detecting gravitational waves is an entirely new way of comprehending space that can help us “see” black holes and other violent events.</p>
<p><strong><a href="http://theconversation.com/gravitational-waves-found-how-we-proved-the-power-of-the-dark-side-54589">What happens when LIGO texts you it’s detected one of Einstein’s predicted gravitational waves?</a></strong> More LIGO inside news from Chad Hanna, assistant Professor of Physics, Pennsylvania State University.</p>
<p><strong><a href="http://theconversation.com/gravitational-waves-discovered-the-universe-has-spoken-54237">Gravitational waves discovered: the universe has spoken</a></strong> David Blair, the director of the Australian International Gravitational Research Centre, gives us his take of the discovery and argues it provides an opportunity and responsibility for educating the public. </p>
<p><strong><a href="https://theconversation.com/five-myths-about-gravitational-waves-46493">Debunking some myths about gravitational waves you’ll probably come across soon</a></strong>
The waves don’t come from the early universe nor do they “prove” the Big Bang.</p>
<p><strong><a href="https://theconversation.com/explainer-gravity-5256">Explaining space-time and gravitational waves to 11-year-olds</a></strong>
This scientist has been teaching primary school students about space-time, explaining how gravity is a consequence of time being warped by matter. Sounds complicated? Don’t worry, he knows what he’s talking about.</p>
<p><strong><a href="http://theconversation.com/gravitational-waves-discovered-top-scientists-respond-53956">For the adventurous: everything you’d want to know about gravitational waves</a></strong>
If you’ve got the basics covered, this is the complete overview you need from a range of experts commenting on the announcement.</p><img src="https://counter.theconversation.com/content/54521/count.gif" alt="The Conversation" width="1" height="1" />
All this time we were only observing some of gravity’s most superficial effects. This discovery changes everything.
Khalil A. Cassimally, Head of Audience Insights, The Conversation International
Miriam Frankel, Senior Science Editor
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/35163
2014-12-29T19:13:17Z
2014-12-29T19:13:17Z
From comet chasing to gravity waves: 2014 in six science stories
<figure><img src="https://images.theconversation.com/files/66540/original/image-20141208-20492-ksgibl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">2014: the year crystallography went mainstream.</span> <span class="attribution"><a class="source" href="http://commons.wikimedia.org/wiki/File:CSIRO_ScienceImage_296_Protein_Crystals_Use_in_XRay_Crystallography.jpg">CSIRO</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>’Tis the season for listicles rounding up the stories of the year. So with, the authority vested in me, here is a selection of six top, bottom and forgotten science stories of 2014.</p>
<h2>Bounciest landing</h2>
<p>The Rosetta drama reached fever pitch in November with the descent of Philae to the surface of a comet. But let’s not forget the slow build to the plot, starting with a launch back in 2004 setting <a href="https://theconversation.com/uk/topics/rosetta">Rosetta</a> on a path that involved four gravitational “slingshots” around Earth and Mars, three orbits of the Sun, two close encounters with asteroids and a rendezvous with 67P/Churyumov–Gerasimenko in August. Chasing down the four kilometre-wide comet travelling at 135,000 km/hr and then touching down on its surface was a staggering feet of precision, roughly equivalent to a marksman hitting a bulls-eye on a one metre target from a million kilometres away (three times the distance from the Earth to the Moon).</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/66537/original/image-20141208-20498-1u6ripd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/66537/original/image-20141208-20498-1u6ripd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/66537/original/image-20141208-20498-1u6ripd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=351&fit=crop&dpr=1 600w, https://images.theconversation.com/files/66537/original/image-20141208-20498-1u6ripd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=351&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/66537/original/image-20141208-20498-1u6ripd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=351&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/66537/original/image-20141208-20498-1u6ripd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=441&fit=crop&dpr=1 754w, https://images.theconversation.com/files/66537/original/image-20141208-20498-1u6ripd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=441&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/66537/original/image-20141208-20498-1u6ripd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=441&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Philae hangs on … just.</span>
<span class="attribution"><a class="source" href="http://www.esa.int/spaceinimages/Images/2014/11/Welcome_to_a_comet">ESA</a></span>
</figcaption>
</figure>
<p>Be prepared for a potential 2015 sequel which may see the hibernating Philae awaken as its ride approaches the Sun and the little probe’s solar panels eke enough power out of the rays to spring back to life.</p>
<h2>Best quiet achiever</h2>
<p>The year 2014 was observed, by the UN, as an <a href="http://www.un.org/en/events/observances/years.shtml">international year</a> for small island developing states, family farming and of crystallography. <a href="https://theconversation.com/explainer-what-is-x-ray-crystallography-22143">Crystallography</a> wins out. It is a technique that usually gets little mainstream attention despite its importance to chemistry, physics and biology. Its implementation has led to no less than 27 Nobel prizes, not to mention the <a href="https://theconversation.com/the-little-known-science-that-improved-everything-around-us-22452">development of countless</a> medical advances, technological discoveries and engineering innovations. </p>
<p>And so 2014 saw an <a href="http://richannel.org/celebrating-crystallography">effort</a> from <a href="http://www.nature.com/news/specials/crystallography-1.14540">major</a> science and <a href="http://www.theguardian.com/science/occams-corner/2014/jan/14/dorothy-hodgkin-year-of-crystallography">media</a> <a href="http://science.time.com/2014/01/09/crystallography-100-years/">outlets</a> to highlight the importance of the 100 year old technique to today’s world.</p>
<h2>Biggest story</h2>
<p>The <a href="https://theconversation.com/uk/topics/ebola">Ebola</a> epidemic started in Guéckédou in Guinea, where a <a href="edition.cnn.com/2014/10/28/health/ebola-patient-zero/index.html?iid=article_sidebar">two-year-old girl</a> who died in late 2013, is believed to be the first case. In March the <a href="http://www.cdc.gov/">CDC</a> announced <a href="http://edition.cnn.com/2014/04/11/health/ebola-fast-facts/">the outbreak</a> and since then the virus and the resting hemorrhagic fever has dominated the science news. By the <a href="http://www.economist.com/blogs/graphicdetail/2014/12/ebola-graphics">end of November</a>
more than 17,000 people had been infected resulting in more than 6,000 deaths. </p>
<p>The ramifications could be felt worldwide, with <a href="http://www.bbc.co.uk/news/health-29549722">health screening</a> at international airports, <a href="http://www.theguardian.com/us-news/2014/dec/02/us-ebola-treatment-hospital">western hospitals prepping</a> to handle Ebola victims, <a href="http://www.telegraph.co.uk/news/worldnews/ebola/11202797/American-Ebola-nurse-wins-court-battle-to-avoid-quarantine-order.html">court rulings</a> on the quarantine of infected health workers and <a href="http://www.bbc.co.uk/news/health-28663217">unprecedented circumvention of drug trials</a> in an attempt to rush experimental drugs and vaccines into use.</p>
<h2>Quickest u-turn</h2>
<p>In 1916 Einstein predicted the existence of waves and a corresponding particle, the graviton, that are responsible for gravity. But almost a century later and despite a plethora of massive experiments, direct evidence of either the waves or particles is sorely lacking. Without this evidence the two dominating pillars of physics, general relativity and quantum mechanics, remain at odds.</p>
<p>So in March the science world was aflutter with the news of the <a href="http://www.theguardian.com/science/2014/mar/17/primordial-gravitational-wave-discovery-physics-bicep">discovery</a> of these allusive gravitational waves. The BICEP2 telescope in the heart of Antarctica peering into the distant Universe and back to the afterglow of the Big Bang found tantalising signs of the long sought gravity waves.</p>
<p>Before the talk of <a href="http://www.theguardian.com/science/2014/mar/21/gravitational-waves-nobel-prize-inflation">Nobel prizes</a> could die down, the evidence <a href="http://physicsworld.com/cws/article/news/2014/sep/22/bicep2-gravitational-wave-result-bites-the-dust-thanks-to-new-planck-data">disappeared in a cloud of dust</a>. The data that looked so promising turned out to be the result of fine matter scattered throughout our galaxy.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/66533/original/image-20141208-20507-zfqpid.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/66533/original/image-20141208-20507-zfqpid.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/66533/original/image-20141208-20507-zfqpid.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/66533/original/image-20141208-20507-zfqpid.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/66533/original/image-20141208-20507-zfqpid.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/66533/original/image-20141208-20507-zfqpid.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/66533/original/image-20141208-20507-zfqpid.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/66533/original/image-20141208-20507-zfqpid.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">BICEP2 flexes at the South Pole.</span>
<span class="attribution"><a class="source" href="http://en.wikipedia.org/wiki/BICEP_and_Keck_Array#mediaviewer/File:South_pole_spt_dsl.jpg">Amble</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>But in science there is no shame in a u-turn. Theories and interpretations are adapted in the face of evidence. And so the hunt for the source of gravity continues.</p>
<h2>Most overlooked innovation</h2>
<p>In the decade that Rosetta was homing in on its target, research into a far less dramatic topic was gaining traction.</p>
<p><a href="http://www.nature.com/articles/504S1a.epdf?shared_access_token=WMGAb3ONLaX--bfGK-8EGtRgN0jAjWel9jnR3ZoTv0NYaB9RDJcu38wBR5pnw6QRFGDQdXK7XdS3I0siGEr0-DRJ5W0NXUI6g2n2ccND_QBIgx75tyg8dJQsg_RxKBSI1Lg7ZAgG3i1P7K41yO71cfuBg7ZsXMQRIUHPLLi9Tn1nLK0fB4sa8oBVA1h9rxZzdiHH-kfgOcOJiq4b7gzb5Q%3D%3D">Cancer immunotherapy</a> went mainstream this year. It may not have had the same media coverage as space science and medical epidemics, but its likely to have a greater impact on many of our lives.</p>
<p>The therapy exploits subtle differences between the surface proteins on cancer and normal cells, then persuades our own immune system to recognise these differences and attack the cancer cells.</p>
<p>The fruits of this research ripened in 2014, with <a href="http://www.tandfonline.com/doi/abs/10.4161/onci.27048#.VIRLFGSsX9c">trials</a> <a href="http://www.cancer.org/treatment/treatmentsandsideeffects/treatmenttypes/immunotherapy/immunotherapy-whats-new-immuno-res">underway</a> and promising successes reported in top the journal <a href="http://www.sciencemag.org/content/344/6184/641">Science</a> and Nature Cancer reviews published <a href="http://www.nature.com/search/executeSearch?pub-date-mode=exact&sp-q-3=&sp-q-2=&siteCode=nrc&sp-q-9%5BNRC%5D=1&sp-c=25&shunter=1416997528296&sp-advanced=true&sp-q=immunotherapy&sp-p=all&sp-s=&sp-date-range=0&sp-q-10=&sp-q-11=&sp-q-12=2014&sp-start-month=&sp-start-year=&sp-end-month=&sp-end-year=">24 articles</a> on the subject.</p>
<h2>Losses</h2>
<p>The year saw the passing of some truly great and <a href="http://www.telegraph.co.uk/news/obituaries/science-obituaries/">influential scientists</a>. To name three:</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/66532/original/image-20141208-20504-1v4if3w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/66532/original/image-20141208-20504-1v4if3w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/66532/original/image-20141208-20504-1v4if3w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=725&fit=crop&dpr=1 600w, https://images.theconversation.com/files/66532/original/image-20141208-20504-1v4if3w.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=725&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/66532/original/image-20141208-20504-1v4if3w.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=725&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/66532/original/image-20141208-20504-1v4if3w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=911&fit=crop&dpr=1 754w, https://images.theconversation.com/files/66532/original/image-20141208-20504-1v4if3w.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=911&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/66532/original/image-20141208-20504-1v4if3w.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=911&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Chemistry pioneer Stephanie Kwolek.</span>
<span class="attribution"><a class="source" href="http://en.wikipedia.org/wiki/Stephanie_Kwolek#mediaviewer/File:Stephanie_Kwolek_at_Spinning_Elements_by_Harry_Kalish.TIF">Chemical Heritage Foundation</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Chemist <a href="http://www.telegraph.co.uk/news/obituaries/10923157/Stephanie-Kwolek-obituary.html">Stephanie Kowlek</a> was most well known for her work on a compound beloved by soldiers and cyclists alike. For she invented the kevlar used in bullet-proof vests and puncture-resistant tires. Kowlek’s chemical was patented by Dupont for whom she served for 40 years.</p>
<p><a href="http://blogs.scientificamerican.com/cross-check/2014/05/22/my-testy-encounter-with-the-late-great-gerald-edelman/">Gerald Edelman</a> received a Nobel prize for discovering the structure of antibodies. His work resolved questions about how our bodies deal with invaders. An understanding on which cancer immunotherapy now hangs. He passed away in May aged 84.</p>
<p><a href="http://www.theguardian.com/science/2014/sep/14/dame-julia-polak">Julia Polak</a> was a pioneer in stem cell and tissue engineering. Her own need for a lung transplant triggered her desire to research growing artificial implants. She died aged 75, almost 20 years after her transplant.</p>
<p>Their achievements, of course, live on. So here’s looking forward to a <a href="http://www.light2015.org/Home.html">bright 2015</a>.</p><img src="https://counter.theconversation.com/content/35163/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Mark Lorch does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>
’Tis the season for listicles rounding up the stories of the year. So with, the authority vested in me, here is a selection of six top, bottom and forgotten science stories of 2014. Bounciest landing The…
Mark Lorch, Senior Lecturer in Biological Chemistry, University of Hull
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/22336
2014-02-23T19:29:33Z
2014-02-23T19:29:33Z
An end in sight in the long search for gravity waves
<figure><img src="https://images.theconversation.com/files/42119/original/dxybw6ts-1392940790.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">We know gravity waves exist but just haven't detected any... yet.</span> <span class="attribution"><span class="source">www.shutterstock.com</span></span></figcaption></figure><p>Our unfolding understanding of the universe is marked by epic searches and we are now on the brink of discovering something that has escaped detection for many years.</p>
<p>The search for gravity waves has been a <a href="https://theconversation.com/gravity-waves-scientists-wave-back-squeezing-light-beyond-quantum-limit-3342">century long epic</a>. They are a prediction of Einstein’s <a href="https://theconversation.com/explainer-einsteins-theory-of-general-relativity-3481">General Theory of Relativity</a> but for years physicists argued about their theoretical existence.</p>
<p>By 1957 physicists had proved that they must carry energy and cause vibrations. But it was also apparent that waves carrying a million times more energy than sunlight would make vibrations smaller than an atomic nucleus.</p>
<p>Building detectors seemed a daunting task but in the 1960s a maverick physicist <a href="http://physicsworld.com/cws/article/news/2000/oct/10/joseph-weber-1919-to-2000">Joseph Weber</a>, at the University of Maryland, began to design the first detectors. By 1969 he claimed success!</p>
<p>There was excitement and consternation. How could such vast amounts of energy be reconciled with our understanding of stars and galaxies? A scientific gold rush began.</p>
<p>Within two years, ten new detectors had been built in major labs across the planet. But nothing was detected.</p>
<h2>Going to need a better detector</h2>
<p>Some physicists gave up on the field but for the next 40 years a growing group of physicists set about trying to build vastly better detectors.</p>
<p>By the 1980s a worldwide collaboration to build five detectors, called cryogenic resonant bars, was underway, with one detector called NIOBE located at the University of Western Australia.</p>
<p>These were huge metal bars cooled to near <a href="http://physics.about.com/od/glossary/g/absolutezero.htm">absolute zero</a>. They used superconducting sensors that could detect a million times smaller vibration energy than those of Weber.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/42145/original/qtjfj7wx-1392949481.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/42145/original/qtjfj7wx-1392949481.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/42145/original/qtjfj7wx-1392949481.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=300&fit=crop&dpr=1 600w, https://images.theconversation.com/files/42145/original/qtjfj7wx-1392949481.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=300&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/42145/original/qtjfj7wx-1392949481.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=300&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/42145/original/qtjfj7wx-1392949481.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=377&fit=crop&dpr=1 754w, https://images.theconversation.com/files/42145/original/qtjfj7wx-1392949481.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=377&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/42145/original/qtjfj7wx-1392949481.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=377&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Gravity waves caused by two rotating black holes.</span>
<span class="attribution"><a class="source" href="http://spaceplace.nasa.gov/lisa-g-waves/en/">Nasa</a></span>
</figcaption>
</figure>
<p>They operated throughout much of the 1990s. If a pair of black holes had collided in our galaxy, or a new black hole had formed, it would have been heard as a gentle ping in the cold bars… but all remained quiet.</p>
<p>What the cryogenic detectors did achieve was an understanding of how quantum physics affects measurement, even of tonne-scale objects. The detectors forced us to come to grips with a new approach to measurement. Today this has grown into a major research field called macroscopic quantum mechanics.</p>
<p>But the null results did not mean the end. It meant that we had to look further into the universe. A black hole collision may be rare in one galaxy but it could be a frequent occurrence if you could listen in to a million galaxies.</p>
<h2>Laser beams will help</h2>
<p>A new technology was needed to stretch the sensitivity enormously, and by the year 2000 this was available: a method called laser interferometry.</p>
<p>The idea was to use laser beams to measure tiny vibrations in the distance between widely spaced mirrors. The bigger the distance the bigger the vibration! And an L-shape could double the signal and cancel out the noise from the laser.</p>
<p>Several teams of physicists including a team at the Australian National University had spent many years researching the technology. Laser beam measurements allowed very large spacing and so new detectors up to 4km in size were designed and constructed in the US, Europe and Japan.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/42144/original/twnkxfbh-1392948957.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/42144/original/twnkxfbh-1392948957.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/42144/original/twnkxfbh-1392948957.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=402&fit=crop&dpr=1 600w, https://images.theconversation.com/files/42144/original/twnkxfbh-1392948957.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=402&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/42144/original/twnkxfbh-1392948957.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=402&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/42144/original/twnkxfbh-1392948957.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=505&fit=crop&dpr=1 754w, https://images.theconversation.com/files/42144/original/twnkxfbh-1392948957.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=505&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/42144/original/twnkxfbh-1392948957.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=505&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The gravity wave facility at Gingin.</span>
<span class="attribution"><a class="source" href="http://www.gravity.uwa.edu.au/">Australian International Gravitational Research Centre.</a></span>
</figcaption>
</figure>
<p>The <a href="http://www.anu.edu.au/physics/ACIGA/">Australian Consortium for Gravitational Astronomy</a> built a research centre on a huge site at Gingin, just north of Perth, in Western Australia, that was reserved for the future southern hemisphere gravitational wave detector.</p>
<p>The world would need this so that triangulation could be used to locate signals.</p>
<h2>Latest detectors</h2>
<p>The new detectors were proposed in two stages. Because they involved formidable technological challenges, the first detectors would have the modest aim of proving that the laser technology could be implemented on a 4km scale, but using relatively low intensity laser light that would mean only a few per cent chance of detecting any signals.</p>
<p>The detectors were housed inside the world’s largest vacuum system, the mirrors had to be 100 times more perfect than a telescope mirror, seismic vibrations had to be largely eliminated, and the laser light had to be the purest light ever created.</p>
<p>A second stage would be a complete rebuild with bigger mirrors, much more laser power and even better vibration control. The second stage would have a sensitivity where coalescing pairs of neutron stars merging to form black holes, would be detectable about 20 to 40 times per year.</p>
<p>Australia has been closely involved with both stages of the US project. CSIRO was commissioned to polish the <a href="http://www.csiro.au/Organisation-Structure/Flagships/Future-Manufacturing-Flagship/Agile-Manufacturing/Intelligent-Manufacturing-Technologies/Gravity-wave-detection.aspx">enormously precise mirrors</a> that were the heart of the first stage detectors.</p>
<h2>A gathering of minds</h2>
<p>The Australian Consortium gathered at Gingin earlier this year to plan a new national project.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/42120/original/vtqny9wn-1392940821.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/42120/original/vtqny9wn-1392940821.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/42120/original/vtqny9wn-1392940821.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/42120/original/vtqny9wn-1392940821.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/42120/original/vtqny9wn-1392940821.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/42120/original/vtqny9wn-1392940821.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/42120/original/vtqny9wn-1392940821.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/42120/original/vtqny9wn-1392940821.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Students at work in the labs at Gingin.</span>
<span class="attribution"><span class="source">University of WA</span></span>
</figcaption>
</figure>
<p>Part of that project focusses on an 80 meter scale laser research facility – a sort of mini gravity wave detector – the consortium has developed at the site. Experiments are looking at the physics of the new detectors and especially the forces exerted by laser light.</p>
<p>The team has discovered several new phenomena including one that involves laser photons bouncing off particles of sound called <a href="http://physics.about.com/od/physicsmtop/g/phonon.htm">phonons</a>. This phenomenon turns out to be very useful as it allows new diagnostic tools to prevent instabilities in the new detectors.</p>
<p>The light forces can also be used to make “optical rods” – think of a Star Wars light sabre! These devices can capture more gravitational wave energy – opening up a whole range of future possibilities from useful gadgets to new gravitational wave detectors.</p>
<h2>Final stages of discovery</h2>
<p>The first stage detectors achieved their target sensitivity in 2006 and, as expected, they detected no signals. You would know if they had!</p>
<p>The second stage detectors are expected to begin operating next year. The Australian team is readying itself because the new detectors change the whole game.</p>
<p>For the first time we have firm predictions: both the strength and the number of signals. No longer are we hoping for rare and unknown events.</p>
<p>We will be monitoring a significant volume of the universe and for the first time we can be confident that we will “listen” to the coalescence of binary neutron star systems and the formation of black holes.</p>
<p>Once these detectors reach full sensitivity we should hear signals almost once a week. Exactly when we will reach this point, no one knows. We have to learn how to operate the vast and complex machines.</p>
<p>If you want to place bets on the date of first detection of some gravity wave then some physicists would bet on 2016, probably the majority would bet 2017. A few pessimists would say that we will discover unexpected problems that might take a few years to solve.</p><img src="https://counter.theconversation.com/content/22336/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Blair receives funding from the Australian Research Council, is a member of the Australian Consortium for Gravitational Astronomy and is a member of the LIGO Scientific Collaboration.</span></em></p>
Our unfolding understanding of the universe is marked by epic searches and we are now on the brink of discovering something that has escaped detection for many years. The search for gravity waves has been…
David Blair, Director, Australian International Gravitational Research Centre, The University of Western Australia
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/7314
2012-06-05T04:03:35Z
2012-06-05T04:03:35Z
Rippling space-time: what science could do with Einstein’s gravitational waves
<figure><img src="https://images.theconversation.com/files/11388/original/xnkp4246-1338863629.jpg?ixlib=rb-1.1.0&rect=0%2C64%2C1024%2C547&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The search for gravitational waves is far more than just a novelty.</span> <span class="attribution"><span class="source">msmail</span></span></figcaption></figure><p>In my <a href="https://theconversation.com/rippling-space-time-how-to-catch-einsteins-gravitational-waves-7058">previous article</a> we discussed the “who, what, when, where and how” of the worldwide gravitational wave detection effort. The observant observer will have noticed we’re still missing the “why”.</p>
<p>Why bother spending hundreds of millions of dollars to detect extraordinarily tiny ripples in space that have come from the furthest corners of the universe? Why bother directly detecting these waves when we’ve already inferred their existence? Why bother verifying Einstein’s <a href="https://theconversation.com/explainer-einsteins-theory-of-general-relativity-3481">theory of gravity</a> when we <a href="http://news.nationalgeographic.com/news/2011/05/110505-einstein-theories-confirmed-gravity-probe-nasa-space-science/">know it’s right</a>?</p>
<p>These are all reasonable questions. But not only do they have reasonable answers, they have answers that will undeniably have far-reaching implications for the way we perceive the universe.</p>
<h2>Not because they are easy …</h2>
<p>Of course a first answer to the “why bother” questions is: <a href="http://www.thisdayinquotes.com/2010/03/george-mallory-coins-because-its-there.html">“because it’s there”</a>. </p>
<p>Attempting to understand the basic workings of the universe is a pure endeavour, and gravitational wave science is just one part of this. Moreover, the actual detection of gravitational waves presents one of the greatest technical challenges ever attempted. In and of itself this can provide significant impetus. </p>
<p>Then there are the pragmatic among us who want spin-off technologies. Science for science’s sake undoubtedly spawns technology, and <a href="http://www.aigo.org.au/industry.php">gravitational wave science will be no different</a>. The detection effort is already enhancing various fields of research including optics, lasers, <a href="http://www.analog.com/en/content/beginners_guide_to_dsp/fca.html">digital signal processing</a> and <a href="http://en.wikipedia.org/wiki/Data_visualization">data visualisation</a>.</p>
<p>Gravitational waves themselves may even be the technological spin-off – some have proposed using them for new communication methods with “<a href="http://www.drrobertbaker.com/docs/com%20study%20composite%20.pdf">very low probability of intercept</a>”. </p>
<p>The idea that sufficiently advanced civilisations may already be using this technology <a href="http://ia600501.us.archive.org/18/items/nasa_techdoc_19740003098/19740003098.pdf">has not been lost on NASA</a>.</p>
<p>But there is also pure science to be done – and for me, that is the truly exciting part.</p>
<figure><a href="http://upload.wikimedia.org/wikipedia/commons/b/b8/Wavy.gif"><img width="440" alt="Gravity waves" src="http://upload.wikimedia.org/wikipedia/commons/b/b8/Wavy.gif"></a><figcaption>Ripples in spacetime are generated by fast-orbiting stars (such as neutron stars, white dwarfs and black holes.) <span>NASA</span></figcaption> </figure>
<h2>Gravitational waves are the apparatus</h2>
<p>Let’s jump forward five years to imagine a scenario. <a href="http://default.media.ipcdigital.co.uk/11140%7C000015353%7Cfd60_One-Direction-21.jpg">One Direction</a> have lost their way and Australia’s Got Talent still hasn’t found any of the aforementioned talent. But the <a href="http://www.ligo.org/">LIGO Scientific Collaboration</a> has successfully detected a gravitational wave signal and the American physicist <a href="http://en.wikipedia.org/wiki/Kip_Thorne">Kip Thorne</a> is preparing his Nobel Prize acceptance speech. Gravitational waves are being detected on a weekly, even daily basis. </p>
<p>It’s now time to do some <em>real</em> science. It’s time to probe the physics of the universe using gravitational waves as the apparatus.</p>
<p>As a first port of call, we can test the accuracy with which <a href="https://theconversation.com/explainer-gravity-5256">Einstein’s theory of general relativity</a> actually describes gravity. </p>
<p>Contrary to popular belief, there are numerous <a href="http://en.wikipedia.org/wiki/Alternatives_to_general_relativity">alternative theories of gravity</a> in the <a href="http://relativity.livingreviews.org/Articles/lrr-2006-3/">mainstream scientific literature</a> (there are also <em>many</em> crackpot theories that are <em>not</em> in the mainstream literature). </p>
<p>Many of these aim to recast the issue of <a href="https://theconversation.com/adventures-in-the-dark-side-of-cosmology-1455">dark matter and dark energy</a> as a problem with our understanding of gravity itself.</p>
<p>But as with any good scientific theory, Einstein’s version of gravity makes unique predictions. And these can be rigorously tested using gravitational waves.</p>
<h2>Testing Einstein</h2>
<p>Take, for example, the orientation of the gravitational waves oscillations, known as their <a href="http://en.wikipedia.org/wiki/Polarization_(waves)">polarisation</a>. General relativity postulates that only two polarisations of gravitational waves exist – so-called <a href="http://en.wikipedia.org/wiki/File:GravitationalWave_PlusPolarization.gif">“plus”</a> and <a href="http://en.wikipedia.org/wiki/File:GravitationalWave_CrossPolarization.gif">“cross”</a> polarisations. </p>
<p>Interestingly, almost all <em>reputable</em> alternatives to Einstein’s gravity postulate the existence of gravitational waves – but almost all of those say there should be somewhere between three and six polarisations.</p>
<p>These include the plus and cross polarisations that relativity proposes. But if you find any of the other polarisations, you’ve proven Einstein wrong!</p>
<p>Another particularly beautiful example relates to <a href="https://theconversation.com/scary-monsters-and-supermassive-black-holes-4661">black holes</a>. According to Einstein’s theory, black holes are incredibly simple beasts. In fact, an astrophysical black hole is completely characterised by <em>only</em> its mass and its rotation rate. This is known as the <a href="http://en.wikipedia.org/wiki/No-hair_theorem">no-hair conjecture</a>. </p>
<p>Gravitational waves provide an extremely robust way of testing the “hairiness” of a black hole. Just like hitting the surface of a drum, a black hole will ring with characteristic oscillations. Each frequency of oscillation, and also the rate at which that oscillation is damped, depends only on the mass and rotation rate of the black hole.</p>
<p>So when you measure a single frequency and its damping time you determine everything about the black hole. Measure a second frequency from the same black hole and – if general relativity is right – you will learn exactly the same thing as with your first measurement. If these two measurements are inconsistent with one another, general relativity is wrong!</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/11128/original/3qydtmtd-1338247046.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/11128/original/3qydtmtd-1338247046.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=576&fit=crop&dpr=1 600w, https://images.theconversation.com/files/11128/original/3qydtmtd-1338247046.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=576&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/11128/original/3qydtmtd-1338247046.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=576&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/11128/original/3qydtmtd-1338247046.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=723&fit=crop&dpr=1 754w, https://images.theconversation.com/files/11128/original/3qydtmtd-1338247046.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=723&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/11128/original/3qydtmtd-1338247046.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=723&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Neutron stars harbour the densest matter and the strongest gravitational fields in the universe.</span>
<span class="attribution"><span class="source">Wikimedia Commons</span></span>
</figcaption>
</figure>
<h2>Nuclear physics</h2>
<p>Gravitational waves will do much more than just test Einstein’s theory of gravity. They will also allow us to understand matter in conditions inaccessible on Earth.</p>
<p>When we observe <a href="http://imagine.gsfc.nasa.gov/docs/science/know_l1/pulsars.html">neutron stars</a> today we are doing so using electromagnetic radiation – light, radio waves, X-rays, etc. Each of these types of waves are emitted from different heights above the surface of the neutron star: some from very close to the surface of the star and some from much further out in the atmosphere. </p>
<p>But the really interesting physics is in their centre. Here, the densities are more than 100,000,000,000,000 times that of water! Magnetic fields inside neutron stars are up to 100,000,000,000 larger than the strongest fields ever produced on Earth. </p>
<p>Gravitational waves are neither scattered nor absorbed. A gravitational wave therefore offers a view into the heart of a neutron star, a region forever hidden to us by conventional means. Probing the interior of neutron stars will give us new insight into the way matter behaves in some of the most extreme environments found in the universe.</p>
<h2>The universe as a whole</h2>
<p>The gravitational wave detection effort is, first and foremost, experimental physics. But the second stage of gravitational wave science will introduce the new field of <a href="http://www.einstein-online.info/elementary/gravWav/gw_astronomy">gravitational wave astronomy</a>.</p>
<p>All sources of gravitational waves that we hope to observe will come from the cosmos. </p>
<p>One of the exciting burst sources for the LIGO collaboration are from <a href="http://en.wikipedia.org/wiki/Core-collapse_supernova">core-collapse supernovae</a> – those spectacular explosions that occur at the end of a star’s life. </p>
<p>As with observations of neutron stars, core-collapse supernovae are <a href="http://www.encyclopedia.com/doc/1O80-opticaldepth.html">optically thick</a>, implying light observed does not come from anywhere near the core of the explosion. Gravitational waves will directly probe the core of these collapsing objects.</p>
<p>A truly exciting prospect is that of <a href="http://arxiv.org/abs/1105.5843">multi-messenger astronomy</a> – the simultaneous observation of a light signal and gravitational wave from the same event. There are <a href="http://www.anu.edu.au/physics/cgp/Research/loocup.html">existing programs</a> within the LIGO collaboration that will analyse gravitational wave burst signals in real-time and trigger optical telescopes to look at the corresponding patch of sky. </p>
<p>Projects such as these will enable us to catch supernovae and <a href="https://theconversation.com/flash-aah-aah-could-a-gamma-ray-burst-eradicate-all-life-on-earth-5291">gamma-ray bursts</a> in the act, not only providing stringent confirmation of the gravitational wave signal, but also allowing us to study such events in all their gory detail.</p>
<p>Coalescing compact objects such as black holes, neutron stars and white dwarfs are excellent sources of gravitational waves.</p>
<figure>
<iframe src="https://player.vimeo.com/video/28966581" width="500" height="281" frameborder="0" webkitallowfullscreen="" mozallowfullscreen="" allowfullscreen=""></iframe>
</figure>
<h2>Observing black holes</h2>
<p>It has already been mentioned that observations of black holes will allow us to rigorously test Einstein’s gravity, but they will be able to do so much more. </p>
<p>One of the most promising sources for LIGO are coalescing black holes. </p>
<p>Imagine two black holes in mutual orbit. As they emit gravitational waves, the system loses energy and the orbit becomes tighter. This process continues until the black holes eventually merge. An entire waveform, as predicted from computer simulations, is shown below.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/11129/original/38t9t8n2-1338248887.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/11129/original/38t9t8n2-1338248887.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=144&fit=crop&dpr=1 600w, https://images.theconversation.com/files/11129/original/38t9t8n2-1338248887.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=144&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/11129/original/38t9t8n2-1338248887.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=144&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/11129/original/38t9t8n2-1338248887.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=181&fit=crop&dpr=1 754w, https://images.theconversation.com/files/11129/original/38t9t8n2-1338248887.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=181&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/11129/original/38t9t8n2-1338248887.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=181&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Artists rendering of a coalescing binary system during the inspiral, merger and ringdown phases.</span>
<span class="attribution"><span class="source">Wikimedia Commons</span></span>
</figcaption>
</figure>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/11130/original/52gmjgh9-1338248958.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/11130/original/52gmjgh9-1338248958.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=247&fit=crop&dpr=1 600w, https://images.theconversation.com/files/11130/original/52gmjgh9-1338248958.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=247&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/11130/original/52gmjgh9-1338248958.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=247&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/11130/original/52gmjgh9-1338248958.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=310&fit=crop&dpr=1 754w, https://images.theconversation.com/files/11130/original/52gmjgh9-1338248958.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=310&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/11130/original/52gmjgh9-1338248958.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=310&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Gravitational wave signal during the inspiral and merger phase as calculated using modern computer simulations.</span>
<span class="attribution"><span class="source">LIGO</span></span>
</figcaption>
</figure>
<p>It turns out that specific properties of these waveforms encode information about the two black holes, and also information about their distance. </p>
<p>Nobel Laureate <a href="https://theconversation.com/profiles/brian-schmidt-4963">Brian Schmidt</a> and his team used observations of supernovae as <a href="https://theconversation.com/how-far-away-is-everybody-climbing-the-cosmic-distance-ladder-3548">standard candles</a> to probe the expansion of the universe, work which led to them winning the 2011 <a href="http://www.nobelprize.org/nobel_prizes/physics/laureates/2011/schmidt.html">Nobel Prize</a>. Similarly, binary black hole coalescences are known as gravitational wave standard sirens (distinct from the <a href="http://studentorgs.gwu.edu/sirens/">all-female cappella group</a>).</p>
<p>These standard sirens provide an extremely important <em>independent</em> measure of the expansion of the universe. Unlike the standard candles, it turns out that the sirens are completely independent of the <a href="https://theconversation.com/how-far-away-is-everybody-climbing-the-cosmic-distance-ladder-3548">cosmic distance ladder</a> and can therefore be used to test its robustness.</p>
<h2>The more exotic</h2>
<p>In my failed attempt at brevity I have skipped many aspects in which gravitational wave science will further our understanding of the universe. </p>
<p>For example, consistent observations of black holes and neutron stars will aid our understanding of their distribution throughout the galaxy and the local universe. In turn, this will develop our knowledge of the way these objects, as well as galaxies and clusters form and evolve. </p>
<p>And then there’s the more exotic – such as attempts to directly probe the vibrations of <a href="http://www.space.com/3334-cosmic-superstrings-sing-gravity-waves.html">cosmic strings</a>, <a href="http://www.gravityresearchfoundation.org/pdf/awarded/2005/Clarkson_Maartens_FOURTH_2005.pdf">the number of dimensions of the universe</a>, or <a href="http://www.scientificamerican.com/article.cfm?id=gravity-waves-inflation">the imprints left from cosmic inflation</a>. </p>
<p>But perhaps the most exciting prospect of all is that we will discover aspects of the universe that no-one had anticipated. </p>
<p>The focus on gravitational wave science is extremely broad. When gravitational waves are successfully detected in the coming years, it’s fair to say that the fun will only just be beginning.</p>
<p><strong>This is the second of two articles on gravitational waves by Paul Lasky. It follows on from <a href="https://theconversation.com/rippling-space-time-how-to-catch-einsteins-gravitational-waves-7058">Rippling space-time: how to catch Einstein’s gravitational waves</a>.</strong></p>
<p><strong>You can help the search to understand the universe by donating valuable computer time to the <a href="http://www.einsteinathome.org/">Einstein@Home</a> project.</strong></p><img src="https://counter.theconversation.com/content/7314/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Paul Lasky receives funding from the Australian Research Council. He is affiliated with the LIGO Scientific Collaboration.</span></em></p>
In my previous article we discussed the “who, what, when, where and how” of the worldwide gravitational wave detection effort. The observant observer will have noticed we’re still missing the “why”. Why…
Paul Lasky, Postdoctoral Fellow in Gravitational Wave Astrophysics, The University of Melbourne
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/7058
2012-05-21T04:47:58Z
2012-05-21T04:47:58Z
Rippling space-time: how to catch Einstein’s gravitational waves
<figure><img src="https://images.theconversation.com/files/10847/original/prpy74pp-1337562803.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The global push to detect gravitational waves could provide an enormous return for science.</span> <span class="attribution"><span class="source">Wikimedia Commons</span></span></figcaption></figure><p>Albert Einstein made an executive decision to revolutionise our understanding of gravity in <a href="http://onlinelibrary.wiley.com/doi/10.1002/andp.19163540702/abstract">a paper published in 1916</a>. Nearly 100 years on, a key prediction of Einstein’s theory has eluded direct detection. A global effort to detect gravitational waves may nostalgically do so on the 100-year anniversary.</p>
<p>Gravitational wave physics holds the key to understanding multiple facets of our universe. Among many other things, gravitational wave experiments have the potential to:</p>
<ul>
<li><p>understand the correctness of Einstein’s theory in regions of the universe unable to be observed by other methods</p></li>
<li><p>directly probe the physics of exotic objects such as <a href="https://theconversation.com/scary-monsters-and-supermassive-black-holes-4661">black holes</a>, <a href="http://imagine.gsfc.nasa.gov/docs/science/know_l1/pulsars.html">neutron stars</a>, <a href="http://imagine.gsfc.nasa.gov/docs/science/know_l2/dwarfs.html">white dwarfs</a>, supernovae, <a href="https://theconversation.com/flash-aah-aah-could-a-gamma-ray-burst-eradicate-all-life-on-earth-5291">gamma-ray bursts</a>, <a href="http://io9.com/5661564/cosmic-strings-are-super+massive-ultra+thin-cracks-in-the-universe">cosmic strings</a> and so on</p></li>
<li><p>provide new and independent tests of cosmology including the rate of <a href="https://theconversation.com/measuring-an-accelerating-universe-brian-schmidts-nobel-lecture-4734">expansion</a> of the universe.</p></li>
</ul>
<p>The scientific return of gravitational wave science is undeniably massive (although it should be mentioned that the required investment is also high, with individual experiments costing hundreds of millions of dollars). </p>
<p>To understand this scientific potential, we must first understand how gravitational waves are created and detected. For this, we require an understanding of Einstein’s theory of gravity – <a href="https://theconversation.com/explainer-einsteins-theory-of-general-relativity-3481">general relativity</a>.</p>
<h2>Einstein’s Relativity</h2>
<p>Somewhat counter-intuitively, general relativity asserts that gravity is <em>not</em> a force. Instead, it is the result of objects travelling the <a href="https://theconversation.com/explainer-gravity-5256">shortest possible distance</a> between any two points in a curved geometry. This is not the three-dimensional geometry of space, but that of four-dimensional space-time (i.e. one time plus three space dimensions). </p>
<p>There is a beautiful analogy involving a bowling ball and a marble on a trampoline. Imagine placing the bowling ball on the surface of the trampoline. This acts to curve the trampoline in a region around the ball, analogous to the curvature of space-time around a massive object such as the sun.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/10823/original/n8yptygz-1337325701.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/10823/original/n8yptygz-1337325701.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=275&fit=crop&dpr=1 600w, https://images.theconversation.com/files/10823/original/n8yptygz-1337325701.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=275&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/10823/original/n8yptygz-1337325701.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=275&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/10823/original/n8yptygz-1337325701.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=345&fit=crop&dpr=1 754w, https://images.theconversation.com/files/10823/original/n8yptygz-1337325701.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=345&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/10823/original/n8yptygz-1337325701.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=345&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Large objects act to curve their surrounding space-time.</span>
<span class="attribution"><span class="source">http://www.zamandayolculuk.com/cetinbal/htmldosya1/RelativityFile.htm</span></span>
</figcaption>
</figure>
<p>If we ignore friction, we can imagine rolling a marble on the surface of the trampoline such that it orbits the bowling ball. There are no forces acting between the two balls – the bowling ball curves the surface of the trampoline, and the marble simply rolls along <a href="http://www.thefreedictionary.com/geodesic">geodesics</a> of this curved surface. </p>
<p>Analogously, there are no “forces” acting between the sun and Earth – the sun curves space-time, and Earth travels along a geodesic of this curved space-time.</p>
<h2>But what are gravitational waves?</h2>
<p>As our small marble rolls over the surface of the trampoline, like ducks swimming through water, very small ripples in the fabric of the trampoline are generated and move away from the marble. </p>
<p>Analogously, when any mass moves through space, ripples are generated in the fabric of space-time that travel away from the moving object at the <a href="http://www.speed-light.info/">speed of light</a>. These ripples are gravitational waves. </p>
<p>These waves carry energy from the system, and this fact was used in 1974 to <a href="http://www.nobelprize.org/nobel_prizes/physics/laureates/1993/"><em>indirectly</em> infer their existence</a>. <a href="http://www.nobelprize.org/nobel_prizes/physics/laureates/1993/hulse-autobio.html#">Russell Hulse</a> and <a href="http://www.nobelprize.org/nobel_prizes/physics/laureates/1993/taylor.html">Joseph Taylor</a> measured the orbit of a binary neutron star system with great accuracy, finding that the orbit shrunk by 3mm every eight hours. </p>
<p>This observation matched the predicted energy loss due to gravitational waves with such accuracy that, in 1993, Hulse and Taylor were awarded the Nobel Prize in physics.</p>
<h2>How do we directly detect these waves?</h2>
<p>Hulse and Taylor’s detection of gravitational waves was indirect, in the sense that they only inferred their existence by ruling out other options. Since the 1960s, physicists have attempted to build gravitational wave detectors that will <em>directly</em> detect their presence. </p>
<p>To understand methods for direct detection, we must first understand the effect a gravitational wave has on particles as it passes. </p>
<p>Consider a ring of particles placed in a perfect circle. A gravitational wave passing will make these particles deform into an ellipse, oscillate back into a circle and then into another ellipse perpendicular to the first. This pattern will continue as the gravitational wave passes through our ring of test particles.</p>
<figure><a href="http://upload.wikimedia.org/wikipedia/commons/5/5c/Gravwav.gif"><img width="440" alt="Ring of test particles influenced by gravitational wave." src="http://upload.wikimedia.org/wikipedia/commons/5/5c/Gravwav.gif"></a><figcaption>A ring of test particles influenced by a gravitational wave.</figcaption></figure>
<p>This motion of test masses suggests an obvious method for detection – <a href="http://en.wikipedia.org/wiki/Michelson_interferometer">Michelson interferometry</a>. The nuts and bolts of interferometry involve splitting a single laser beam in two, each travelling at right angles to the other. Each beam travels a certain distance, hits a mirror and returns to the original point at which they split, recombining to form a single beam once more.</p>
<p>If no gravitational wave is present, each beam will travel the same distance, and the combined beam will have a certain <a href="http://en.wikipedia.org/wiki/Interference_(wave_propagation)">interference pattern</a> caused by the recombination of the light. But when a gravitational wave passes through the system, the relative length of each arm will oscillate back and forth, and the resultant interference pattern will display this motion. Sounds easy …</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/10850/original/8cv6m5q6-1337571584.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/10850/original/8cv6m5q6-1337571584.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/10850/original/8cv6m5q6-1337571584.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=561&fit=crop&dpr=1 600w, https://images.theconversation.com/files/10850/original/8cv6m5q6-1337571584.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=561&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/10850/original/8cv6m5q6-1337571584.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=561&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/10850/original/8cv6m5q6-1337571584.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=705&fit=crop&dpr=1 754w, https://images.theconversation.com/files/10850/original/8cv6m5q6-1337571584.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=705&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/10850/original/8cv6m5q6-1337571584.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=705&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A Michelson interferometer is used to detect gravitational waves. As a wave passes, each of the arms of the interferometer changes length by different amounts.</span>
<span class="attribution"><span class="source">Wikimedia Commons</span></span>
</figcaption>
</figure>
<p>The entire difficulty in detecting gravitational waves is their size. </p>
<p>Our trampoline analogy is again useful. A large bowling ball rolling along the surface of the trampoline will give off significantly larger ripples than our original marble. Likewise, the motion of Earth through space gives off relatively small ripples compared to that of a <a href="http://astronomy.swin.edu.au/cosmos/S/Supermassive+Black+Hole">supermassive black hole</a>.</p>
<p>Exotic events such as <a href="http://imagine.gsfc.nasa.gov/docs/science/know_l2/supernovae.html">supernovae</a> or the merging of two <a href="http://imagine.gsfc.nasa.gov/docs/science/know_l2/black_holes.html">black holes</a> therefore provide the best candidates for the emission of large gravitational waves. And by a “large” gravitational wave, I mean small! The strongest waves change the position of particles by no more than one part in 1,000,000,000,000,000,000,000. </p>
<p>And this is exactly the difficulty in measuring these waves. To successfully detect some of the largest gravitational waves in the universe, we need to measure a change in distance on the order of one part in 1,000,000,000,000,000,000,000. This number explains why it has taken almost 100 years to detect gravitational waves!</p>
<h2>A worldwide detection effort</h2>
<p>A worldwide network of Michelson interferometers has been built to directly detect these tiny gravitational waves. There is the <a href="http://www.ligo.caltech.edu/">Laser Interferometer Gravitational-wave Observatory (LIGO)</a>, which is a network of three detectors located in the US. There is the <a href="https://wwwcascina.virgo.infn.it/">Virgo detector</a> located near Pisa, Italy and there is the <a href="http://www.geo600.org/">GEO600</a> detector near Hannover, Germany.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/10827/original/6qm5jsyh-1337327011.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/10827/original/6qm5jsyh-1337327011.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/10827/original/6qm5jsyh-1337327011.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/10827/original/6qm5jsyh-1337327011.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/10827/original/6qm5jsyh-1337327011.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/10827/original/6qm5jsyh-1337327011.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/10827/original/6qm5jsyh-1337327011.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">LIGO gravitational wave detector in Hanford, USA.</span>
<span class="attribution"><span class="source">LIGO</span></span>
</figcaption>
</figure>
<p>There are further plans to build gravitational wave detectors in <a href="http://gwcenter.icrr.u-tokyo.ac.jp/en/">Japan</a>, <a href="https://dcc.ligo.org/public/0075/M1100296/002/LIGO-India_lw-v2.pdf">India</a> and even in <a href="http://elisa-ngo.org/">space</a>, although these latest plans have been temporarily shelved.</p>
<p>We even have a mini-gravitational wave detector in our own backyard, with active plans to expand to a full-size version in the medium term. The <a href="http://www.gravity.uwa.edu.au/">Australian International Gravitational Observatory (AIGO)</a> is a facility for the development of gravitational wave technology located in Gingin, outside Perth. </p>
<p>More than 60 scientists across Australia are active members of the LIGO Scientific Collaboration (a collaboration now totalling more than 800 people) working on topics ranging from laser and mirror technologies to source modelling and data analysis. </p>
<p>(It should also be mentioned that Michelson interferometers are not the only way to directly detect gravitational waves. One of the other most promising methods is through <a href="http://en.wikipedia.org/wiki/Pulsar_timing_array">pulsar timing arrays</a>, where the neutron stars are now part of the detector not the source. Australian astrophysicists are leading the world in this field through the <a href="http://www.atnf.csiro.au/research/pulsar/ppta/">Parkes Pulsar Timing Array project</a>.)</p>
<p>Of all the interferometric detectors it is the LIGO/Virgo collaboration that is expected to see first light. These detectors have recently shut down to upgrade to their “advanced” phase, which will give another factor of ten in sensitivity. </p>
<p>The advanced detectors will come online sometime in 2015, giving the very real possibility that gravitational waves will first be directly observed in general relativity’s centenary year.
<br>
<em>This is the first of two articles on gravitational waves by Paul Lasky. The second will provide details of the exciting physics, astronomy and cosmology we can learn once gravitational waves have been successfully detected.</em></p><img src="https://counter.theconversation.com/content/7058/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Paul Lasky receives funding from the Australian Research Council. He is affiliated with the LIGO Scientific Collaboration.</span></em></p>
Albert Einstein made an executive decision to revolutionise our understanding of gravity in a paper published in 1916. Nearly 100 years on, a key prediction of Einstein’s theory has eluded direct detection…
Paul Lasky, Postdoctoral Fellow in Gravitational Wave Astrophysics, The University of Melbourne
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/5256
2012-03-01T03:16:06Z
2012-03-01T03:16:06Z
Explainer: gravity
<figure><img src="https://images.theconversation.com/files/7936/original/gc2wqd29-1329871724.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">There's more to gravity than apples falling from trees.</span> <span class="attribution"><span class="source">Cea</span></span></figcaption></figure><p>I have spent almost 40 years trying to detect gravity waves.</p>
<p>When I started there were just a few of us working away in university labs. Today 1,000 physicists working with billion-dollar observatories are quietly confident <a href="https://theconversation.com/gravity-waves-scientists-wave-back-squeezing-light-beyond-quantum-limit-3342">the waves</a> are within our grasp.</p>
<p>If we are right, the gravity wave search will have taken 100 years from the date of Einstein’s prediction.</p>
<p>In 100 years’ time the discovery of Einstein’s gravity waves will be one of the landmarks in the history of science. It will stand out like the discovery of <a href="http://www-spof.gsfc.nasa.gov/Education/wemwaves.html">electromagnetic waves</a> in 1886, a quarter of a century after these waves were predicted by physicist <a href="http://www.sparkmuseum.com/BOOK_MAXWELL.HTM">James Clerk Maxwell</a>.</p>
<p>The problem of talking about gravity waves is that you can’t explain them without explaining Einstein’s idea of gravity. Recently I began to ask why it is so difficult to explain gravity, why the concept is met with glazed eyes and baffled looks. Eventually I came up with a theory I call the Tragedy of the Euclidean Time Warp. </p>
<h2>Discarding Euclidean ideas</h2>
<p>My theory starts 2,300 years ago with the Greek mathematician <a href="http://www.notablebiographies.com/Du-Fi/Euclid.html#b">Euclid</a>’s book of geometry called <a href="http://aleph0.clarku.edu/%7Edjoyce/java/elements/elements.html">Elements</a> – the most influential book in the history of science. </p>
<p>Elements has been in print for more than 2,000 years and published in more than 1,000 editions. It was a basic school text for <a href="http://www-history.mcs.st-and.ac.uk/Biographies/Galileo.html">Galileo</a>, <a href="http://Galileo.phys.Virginia.EDU/classes/109N/lectures/newton.html">Isaac Newton</a>, <a href="https://theconversation.com/explainer-einsteins-theory-of-general-relativity-348">Einstein</a> and every educated person up to the baby-boomer generation. I still have the plain, slim edition that I used when I was in year eight. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/7921/original/5qvbj3hp-1329867426.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/7921/original/5qvbj3hp-1329867426.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=371&fit=crop&dpr=1 600w, https://images.theconversation.com/files/7921/original/5qvbj3hp-1329867426.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=371&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/7921/original/5qvbj3hp-1329867426.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=371&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/7921/original/5qvbj3hp-1329867426.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=466&fit=crop&dpr=1 754w, https://images.theconversation.com/files/7921/original/5qvbj3hp-1329867426.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=466&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/7921/original/5qvbj3hp-1329867426.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=466&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Euclid’s Elements in Latin, venice 1482.</span>
<span class="attribution"><span class="source">Joe King</span></span>
</figcaption>
</figure>
<p>The basic concepts from Elements are still taught in all primary schools and high schools throughout the world every day. We all know those concepts – parallel lines never meet, the sum of the angles of a triangle is 180º, the <a href="http://jwilson.coe.uga.edu/emt669/student.folders/morris.stephanie/emt.669/essay.1/pythagorean.html">Theorem of Pythagoras</a> and the perimeter formula for a circle (P = 2πr).</p>
<p>For centuries Euclidean geometry has moulded the way we think and today we all have an intuitive conception of space that is defined by Euclidean geometry.</p>
<p>The problem with Euclid’s book is that it cements a false idea about space. It is a shock to think that it is wrong but even so, gravity cannot be explained without discarding Euclidean geometry. </p>
<h2>The link to General Relativity</h2>
<p>The possibility of a flaw in Euclid’s book was first raised by the mathematician <a href="http://www-history.mcs.st-and.ac.uk/Biographies/Gauss.html">Carl Gauss</a> in the 1820s. He published a <a href="http://scienceworld.wolfram.com/biography/Gauss.html">theorem</a> that said you could measure the shape of space by measuring angles and distances. He even tried to measure the shape of space on Earth by measuring the sum of the angles of a triangle between three mountain tops. </p>
<p>Some 90 years later, Einstein published his beautiful <a href="https://theconversation.com/explainer-einsteins-theory-of-general-relativity-3481">Theory of General Relativity</a>, which gave us our current explanation for gravity. His theory is conceptually simple, but mathematically complex. Matter curves space and time, and gravity arises because of the way matter floats in this deformed space.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/7924/original/wrsgtdqq-1329869078.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/7924/original/wrsgtdqq-1329869078.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=265&fit=crop&dpr=1 600w, https://images.theconversation.com/files/7924/original/wrsgtdqq-1329869078.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=265&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/7924/original/wrsgtdqq-1329869078.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=265&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/7924/original/wrsgtdqq-1329869078.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=332&fit=crop&dpr=1 754w, https://images.theconversation.com/files/7924/original/wrsgtdqq-1329869078.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=332&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/7924/original/wrsgtdqq-1329869078.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=332&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Spacetime curvature near Earth.</span>
<span class="attribution"><span class="source">Johnstone</span></span>
</figcaption>
</figure>
<p>One of the key observations that confirmed the theory of curved space was made in Australia in 1922. The <a href="http://www.physics.uwa.edu.au/__data/assets/pdf_file/0014/621122/PhysHist9.pdf">Wallal expedition</a> obtained photos during a solar eclipse, from which the bending of the light as it passed by the sun were measured.</p>
<p>I think is rather shocking that today, 90 years later, we still teach geometry as if space were flat.</p>
<p>The reason our culture has not assimilated curved space is that we were all indoctrinated with Euclidean geometry during childhood. By the time we are adults it takes a painful re-think to adapt to a new way of thinking.</p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/7935/original/56fnxnsw-1329871448.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/7935/original/56fnxnsw-1329871448.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=951&fit=crop&dpr=1 600w, https://images.theconversation.com/files/7935/original/56fnxnsw-1329871448.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=951&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/7935/original/56fnxnsw-1329871448.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=951&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/7935/original/56fnxnsw-1329871448.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1195&fit=crop&dpr=1 754w, https://images.theconversation.com/files/7935/original/56fnxnsw-1329871448.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1195&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/7935/original/56fnxnsw-1329871448.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1195&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Euclid, Oxford University Museum of Natural History.</span>
<span class="attribution"><span class="source">Mark A Wilson</span></span>
</figcaption>
</figure>
<p>Trainee school teachers are rarely exposed to general relativity, so the teaching profession remains entirely free from Einstein’s beautiful theory. Generation after generation, this cycle continues. We are trapped in this Euclidean time warp. This is a tragedy not only because truth is important, but because students are disengaged by the stale teaching of obsolete 19th century physics.</p>
<h2>A primary school experiment</h2>
<p>Last year I tried to catch 11-year-olds before they were indoctrinated. <a href="http://rosalie.wa.edu.au/">Rosalie Primary School</a>, in suburban Perth, agreed to host me, and I began six, weekly sessions with 30 primary school kids. Here is how we learnt that the force we call gravity arises because time is warped by matter.</p>
<p>First we talked about straight lines. How do we tell if lines are straight? Can you draw straight lines on balloons or the surface of the earth? What do surveyors do when they are building a straight fence? They always use sight lines, and when it comes down to it, straightness is always measured with light.</p>
<p>Then we considered drawing triangles on the earth. Suppose you start at the North Pole, travel south to the equator, turn left and travel 90º of <a href="http://www-istp.gsfc.nasa.gov/stargaze/Slatlong.htm">longitude</a> eastwards before taking another right turn to head back to the pole. We could all see that this triangle would have 90º + 90º + 90º – a total of 270º and definitely not what Euclid said.</p>
<p>Einstein said we should think about space and time together – what we call <a href="http://www.abc.net.au/science/articles/2001/10/29/275021.htm">spacetime</a>. But spacetime has four dimensions and we all agreed that our brains just don’t work properly for four dimensions.</p>
<p>So instead we agreed we could use just distance and time to keep it simple. We could then draw the spacetime diagram for the journey to school or for a water balloon falling from the <a href="http://www.gravitycentre.com.au/leaning-tower-of-gingin/">Leaning Tower of Gingin</a>, a full size steel replica of the Leaning Tower of Pisa, at an upcoming excursion.</p>
<p>Everyone could draw a spacetime diagram for their journey to school and point to the places where distance was not increasing but time was passing – waiting at the lights – and the steep bits when they were speeding down the freeway.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/8174/original/f65hxd62-1330467106.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/8174/original/f65hxd62-1330467106.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=849&fit=crop&dpr=1 600w, https://images.theconversation.com/files/8174/original/f65hxd62-1330467106.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=849&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/8174/original/f65hxd62-1330467106.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=849&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/8174/original/f65hxd62-1330467106.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1067&fit=crop&dpr=1 754w, https://images.theconversation.com/files/8174/original/f65hxd62-1330467106.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1067&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/8174/original/f65hxd62-1330467106.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1067&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p>The next step in explaining Einstein’s theory of gravity is to think about the length of a trajectory in spacetime. Einstein said things in free-fall always have the shortest trajectory in spacetime. At first sight this is a weird idea. How can you measure a trajectory when one axis is distance and the other axis is time?</p>
<p>The journey-to-school diagram looks completely different if you change your units from seconds to minutes or meters to miles and the idea of the length of trajectory is pretty meaningless when both axes have different units.</p>
<p>The only sensible way to measure spacetime is to use a speed to enable us to measure time in space units. Using <a href="http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/measure_c.html">lightspeed</a> as the conversion factor we can convert any time to the number of meters travelled by light in <a href="http://Galileo.phys.Virginia.EDU/classes/109N/lectures/spedlite.html">that time</a>.</p>
<p>If you drop a water balloon from the Gingin Tower it takes almost three seconds to hit the ground. A spacetime diagram of its trajectory is a <a href="http://demonstrations.wolfram.com/VelocityOfAFallingObject/">parabola</a> that starts 45 meters above the ground, and hits the x-axis (time axis) three seconds later. But three seconds in time is 3 x 300,000km, or nine million meters.</p>
<p>The balloon travelled 900m meters in time. To full-scale the graph would stretch twice as far as the moon. The spacetime diagram is extremely elongated! </p>
<p>So now we can plot spacetime trajectories using meters for both distance and time, and I can now imagine using a tape measure to measure the length of any trajectory in meters.</p>
<h2>Floating and falling in space</h2>
<p>Now we come back to Einstein’s theory. It says that if you allow something to float freely in space, or fall from a tower, its trajectory in spacetime will always be the shortest.</p>
<p>Since a shortest line normally means a “straight line” Einstein is saying that free-floating trajectories are “straight lines” in spacetime (technically they are called <a href="http://www.black-holes.org/relativity5.html">geodesics</a>). </p>
<p>Anything you do to prevent free-floating (like holding on to the water balloon on top of the tower rather than releasing it) will make the trajectory longer.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/7930/original/96n85fkj-1329869187.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/7930/original/96n85fkj-1329869187.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/7930/original/96n85fkj-1329869187.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/7930/original/96n85fkj-1329869187.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/7930/original/96n85fkj-1329869187.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/7930/original/96n85fkj-1329869187.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/7930/original/96n85fkj-1329869187.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Gingin Tower, Western Australia.</span>
<span class="attribution"><span class="source">Author</span></span>
</figcaption>
</figure>
<p>Now comes the Eureka moment. For the water balloon on the tower I want you to retort indignantly: “This is nonsense. It is obvious that the not-falling spacetime trajectory is always shorter than the falling trajectory!”</p>
<p>In one case the balloon fell down 45 meters, while in the other it did not even move in space, although it kept on going in time just as before. One trajectory was roughly diagonal on the spacetime graph but the other just moved parallel to the x-axis. This is like saying the hypotenuse of a right-angled triangle is shorter than its sides.</p>
<p>I reply: it is not nonsense! Einstein is correct because time depends on height above the earth. Time is warped. Time on the top of the tower is running 4 parts in one million billion times faster than it is on the ground. </p>
<p>Another way of saying this is that a clock on the top of the tower runs faster by four <a href="http://whatis.techtarget.com/definition/0,,sid9_gci212105,00.html">femtoseconds</a> for every second. This is enough to stretch the time axis by just enough that not falling is actually longer than falling.</p>
<p>And there is yet another way of saying this. Gravity is the force you have to apply to objects to prevent them from freely floating in space. You do not feel gravity while you are falling because there is no force. You are just following the shortest path in spacetime.</p>
<p>What we call gravity is the result of the warping of time by the mass of the earth. Gravity is a force exerted by the earth to stop you from falling.</p>
<p>We all have a destination in spacetime that is called old age. Nature tries to make things get to this destination quickest.</p>
<p>An astronaut becomes an old astronaut quickest if he is floating around in the space station. The astronaut is higher above the surface of the earth than the top of the Gingin Tower. Time on the space station runs even faster than on top of the tower. Therefore the astronaut ages quicker there than on the earth’s surface or at the top of the tower. It takes forces to delay the progress of time.</p>
<p>We have a good planet that reliably provides continuous forces to us to prevent us free floating (i.e. falling) to the centre of the earth. So our planet is a time machine that delays our ageing (but just by a millisecond in a lifetime!).</p>
<p>The most astonishing thing about my program with Rosalie Primary School was that the kids were not astonished. My colleagues Grady Venville and Marina Pitts and I measured their learning and asked them if they thought they were too young to learn this stuff. By a large majority they thought they were not too young and they thought it was really interesting.</p>
<p>Physicists and astronomers deal with curved space every day, and even our GPS navigators have to correct for the warped spacetime around the earth. In May 2011, NASA’s <a href="http://www.nasa.gov/mission_pages/gpb/">Gravity Probe B spacecraft</a> found that the perimeter of an orbit around the Earth <a href="http://einstein.stanford.edu/highlights/status1.html">failed</a> to match its Euclidean value by 28 millimeters – not a large discrepancy but just the value predicted by Einstein.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/7925/original/4dkc446j-1329869082.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/7925/original/4dkc446j-1329869082.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/7925/original/4dkc446j-1329869082.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/7925/original/4dkc446j-1329869082.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/7925/original/4dkc446j-1329869082.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/7925/original/4dkc446j-1329869082.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/7925/original/4dkc446j-1329869082.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Gravity probe B.</span>
<span class="attribution"><span class="source">NASA/MSFC</span></span>
</figcaption>
</figure>
<h2>Not too difficult to teach</h2>
<p>In spite of modern science, the general belief among educators is that Einstein’s physics is too difficult to teach in school. As a result, science students enter university indoctrinated with 2,300-year-old Euclidean geometry and 300-year-old Newtonian physics. </p>
<p>Very few go on to discover the Einsteinian reality of curved space and warped time. The lucky few who get to study Einsteinian physics have difficulties because the fundamental concepts contradict all their past learning.</p>
<p>Most students who go on to become school teachers maintain the Newtonian mindset and so education remains in a Euclidean timewarp! The drastic decline in science at school and university could in part be due to our failure to challenge young people with modern ideas such as these.</p>
<p>If we start young enough, everyone can easily learn that the world is non-Euclidean, and then appreciate that the geometrical formulae we learn at school, such as Newton’s Law of Gravitation, are convenient approximations for everyday life.
<br>
<em>See more <a href="https://theconversation.com/topics/explainer">Explainer articles</a> on The Conversation.</em></p><img src="https://counter.theconversation.com/content/5256/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Blair receives funding from the Australian Research Council</span></em></p>
I have spent almost 40 years trying to detect gravity waves. When I started there were just a few of us working away in university labs. Today 1,000 physicists working with billion-dollar observatories…
David Blair, Director, Australian International Gravitational Research Centre, The University of Western Australia
Licensed as Creative Commons – attribution, no derivatives.
tag:theconversation.com,2011:article/3342
2011-09-13T04:06:47Z
2011-09-13T04:06:47Z
Gravity waves, scientists wave back: squeezing light beyond quantum limit
<figure><img src="https://images.theconversation.com/files/3536/original/r825559_7533813.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C836%2C536&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">We know they're out there, and now we're closer than ever to finding gravity waves.</span> <span class="attribution"><span class="source">NASA</span></span></figcaption></figure><p>Detecting gravity waves is a major goal for astrophysicists.</p>
<p>We know they should be there, but we haven’t found them yet. But today we are one step closer.</p>
<p>By literally squeezing light on a quantum level, we are refining our detection instruments to an extent never seen before.</p>
<p>I am part of <a href="http://www.ligo.org/about.php">the LIGO Scientific Collaboration</a> that has performed the first large scale demonstration of an exquisitely elegant new measurement technique. The <a href="http://www.nature.com/nphys/journal/vaop/ncurrent/full/nphys2083.html">results are published in Nature Physics</a> this week.</p>
<p>Remarkably, we have broken through the quantum measurement barrier that up to now set a limit to the sensitivity of our detectors. </p>
<p>This barrier is related to the famous <a href="http://plato.stanford.edu/entries/qt-uncertainty/">Heisenberg uncertainty principle</a> but in gravitational wave detectors is more easily understood as being due to the particle-like nature of <a href="http://www.wisegeek.com/what-is-a-photon.htm">photons</a>.</p>
<p>Our demonstration proves that real gravity detectors can surpass this barrier, revealing new horizons for <a href="http://imagine.gsfc.nasa.gov/docs/features/topics/gwaves/gwaves.html">gravitational wave astronomy</a>. </p>
<h2>What came before</h2>
<p>The search for the <a href="http://science.hq.nasa.gov/kids/imagers/ems/waves3.html">electromagnetic waves</a> predicted by <a href="http://www.gap-system.org/%7Ehistory/Biographies/Maxwell.html">James Clerk Maxwell</a> reached a climax when <a href="http://www.sparkmuseum.com/BOOK_HERTZ.HTM">Heinrich Hertz</a> succeeded in detecting waves transmitted across a table in 1886. </p>
<p>Hertz saw no benefits from his experiments, saying, “I am just trying to prove that Maestro Maxwell was correct.” Others quickly saw the possibilities and it was not long before we had the radio.</p>
<p>Today, thousands of physicists across the planet are trying to prove another maestro, Albert Einstein, was correct by building what you could think of as gravity radios. </p>
<p>These devices, officially known as <a href="http://www.gravity.uwa.edu.au">gravitational wave detectors</a>, are designed to allow us to tune into the gravity waves <a href="http://www.allaboutscience.org/theory-of-relativity.htm">predicted by Einstein in 1916</a> as part of his theory of general relativity. </p>
<p>Vast amounts of gravitational wave energy is <a href="http://theconversation.com/an-eye-to-the-future-of-astronomy-a-cosmic-pick-n-mix-985#waves">believed to be continually passing through the earth</a>, and yet it remains undetected so far.</p>
<p>Our gravity receivers are based on laser technology. Gravitational waves are a bit like sounds that travel through empty space at the speed of light. </p>
<p>As with sounds, they make things vibrate, but they couple to matter so weakly that only the most exquisitely sensitive instruments can detect them. </p>
<figure>
<iframe src="https://player.vimeo.com/video/28966581" width="500" height="281" frameborder="0" webkitallowfullscreen="" mozallowfullscreen="" allowfullscreen=""></iframe>
</figure>
<p></p><figcaption>A neutron star merger and the gravity waves it produces. <span>NASA/Goddard Space Flight Center</span></figcaption><p></p>
<h2>Black holes and sensitivity</h2>
<p>The <a href="http://www.nasa.gov/audience/forstudents/k-4/stories/what-is-a-black-hole-k4.html">birth of a black hole</a> creates a tsunami of rippling space. More energy is given out than the sun emits in a billion years. </p>
<p>When two black holes coalesce, the burst of energy that travels out at the speed of light carries a power equal to that of more than a hundred-billion-trillion suns. </p>
<p>But so far we cannot detect even these enormous bursts because our sensitivity to the vibrations of the 40 kilogram mirrors of our detectors is still not high enough.</p>
<p>This weeks announcement heralds a breakthrough in our ability to measure the tiny vibrations of the detector’s mirrors.</p>
<p>Over the past two decades, gravitational wave detectors have been improved a million-fold, but they have always come up against the quantum measurement barrier. </p>
<p>Up to now the only way of reducing the uncertainty of our measurements has been to increase the number of photons by using enormously powerful laser light. </p>
<p>Great effort has gone into developing high-power laser detectors, and a new generation of these detectors is now under construction. </p>
<p>They are almost certain to detect gravity waves through the use of hundreds of watts of laser light, built up by resonance to almost a million watts inside the detector – we build up light in the detectors the same way you can build up a child’s swing with lots of small pushes.</p>
<p>But this is a brute force approach.</p>
<p>Our report shows that by squeezing light, we can get around the sensitivity problem in a much more elegant way.</p>
<h2>The big squeeze</h2>
<p>The quantum barrier arises because the invisible quantum fluctuations that appear to fill every point of empty space leak into the detectors at the point of measurement. </p>
<p>These fluctuations are invisible, but we realised they could be “squeezed”. </p>
<p>Squeezing is a method of changing the randomness of light, and is based on the weird phenomenon called <a href="http://www.abc.net.au/science/articles/2004/11/18/2839606.htm">quantum entanglement</a> that Einstein dismissed as “spooky action at a distance”. </p>
<p>The technology used in this case was pioneered by the <a href="http://cgp.anu.edu.au/">Centre for Gravitational Physics</a> at ANU, refined by scientists at the <a href="http://www.aei.mpg.de/english/contemporaryIssues/home/index.php">Albert Einstein Institute in Germany</a>, and tested on a detector called <a href="http://www.geo600.org/">GEO600 in Hanover</a>. </p>
<p>A device called a light squeezer that uses <a href="http://thefutureofthings.com/news/7195/detecting-photon-entanglement.html">entangled photons</a> is used to squeeze the ghostly quantum fluctuations where they enter the detector. </p>
<p>The method is the first demonstration of quantum entanglement being used to improve sensitive instruments. </p>
<p>Using squeezing, the team was able to measure vibrations 100,000 times smaller than the nucleus of a typical atom.</p>
<h2>How ripples become waves</h2>
<p>This result is just the start. </p>
<p>Gravity research is riding a wave of innovation. At our Gingin <a href="http://www.gravity.uwa.edu.au/">Gravity Centre</a> we are researching other methods of creating quantum entanglement, as well as creating springs and rods made from pure light that enable gravitational wave detectors to extract more energy from passing waves.</p>
<p>The US, UK and Germany have offered Australia a $140 million detector called <a href="http://www.aigo.org.au/">LIGO-Australia</a>, proposed to be installed at the Gingin centre. </p>
<p>It’s designed to fill the need for a southern hemisphere detector that will allow much better triangulation of incoming waves, helping to turn all the detectors in the world into a single omnidirectional telescope able to monitor and pinpoint every black hole birth in the universe.</p>
<p>Not only will such findings make waves – they will also, with any luck, help scientists to discover some.</p><img src="https://counter.theconversation.com/content/3342/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Blair receives funding from the Australian Research Council. He is affiliated with the Australian Consortium for Gravitational Astronomy and the LIGO Scientific Collaboration</span></em></p>
Detecting gravity waves is a major goal for astrophysicists. We know they should be there, but we haven’t found them yet. But today we are one step closer. By literally squeezing light on a quantum level…
David Blair, Director, Australian International Gravitational Research Centre, The University of Western Australia
Licensed as Creative Commons – attribution, no derivatives.