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Physicists Gear Up To Catch a Gravitational Wave

Posted by Soulskill on from the surf's-up dept.

sciencehabit writes: A patch of woodland just north of Livingston, Louisiana, population 1893, isn't the first place you'd go looking for a breakthrough in physics. Yet it is here that physicists may fulfill perhaps the most spectacular prediction of Albert Einstein's theory of gravity, or general relativity. Structures here house the Laser Interferometer Gravitational-Wave Observatory (LIGO), an ultrasensitive instrument that may soon detect ripples in space and time set off when neutron stars or black holes merge. Einstein himself predicted the existence of such gravitational waves nearly a century ago. But only now is the quest to detect them coming to a culmination. Physicists are finishing a $205 million rebuild of the detectors, known as Advanced LIGO, which should make them 10 times more sensitive and, they say, virtually ensure a detection.

31 of 127 comments (clear)

  1. Cheaper method by ArcadeMan · · Score: 4, Funny

    Physicists are finishing a $205 million rebuild of the detectors, known as Advanced LIGO, which should make them 10 times more sensitive and, they say, virtually ensure a detection.

    A cheaper way of virtually ensuring detection is to do the experiment in a simulation.

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    1. Re:Cheaper method by MightyMartian · · Score: 4, Insightful

      Because climatologists never use field data...

      Oh wait, they do, that must me you're either a liar or a retard.

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    2. Re:Cheaper method by Dimwit · · Score: 5, Funny

      Little do they know, they ARE doing the experiment in a simulation.

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    3. Re:Cheaper method by MightyMartian · · Score: 4, Insightful

      Fortunatley, they don't, and you're still either a liar or a retard. One thing is for sure, you're beneath contempt.

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    4. Re:Cheaper method by ShanghaiBill · · Score: 5, Interesting

      That being said I fully expect gravitational waves to be discovered.

      I am not so sure. There have been other experiments that should have detected them, but didn't. If this experiment also comes up empty, then physics may be facing another Michelson–Morley moment.

    5. Re:Cheaper method by MightyMartian · · Score: 4, Insightful

      Climatologists get paid whether the world is warming or cooling, and it's not as if the politicians are doing much in regards to what the scientists are saying.

      Besides, there's a lot more profit in being a mouthpiece for the fossil fuel industry.

      But hey, maybe you can hire Ben Stein to narrate a documentary detailing how all the biolo... er climatologists are in an evil cabal to hide the truth.

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    6. Re:Cheaper method by Fire_Wraith · · Score: 3, Insightful

      If you're a climate scientist who says there's no Anthropogenic Climate Change, there are lots of Fossil Fuel groups that will shower you with money - much like Tobacco companies would to any Scientists that said Smoking doesn't cause Cancer.

      And yet, it's the ones who report the opposite that get accused of being on the take, when their findings match what everyone else in their field (except those taking money from the fossil fuel industry) almost universally report.

  2. Hmmm .... by gstoddart · · Score: 2

    So can anybody better versed in the physics fill this in a little: "an ultrasensitive instrument that may soon detect ripples in space and time set off when neutron stars or black holes merge".

    If the machine goes ping, we infer the machine is working perfectly, and somewhere a neutron star or black hole has merged? But you have no independent confirmation other than the machine going ping?

    So, set the damned thing to go ping, and claim you've found gravitational waves ... profit!!!

    Seriously, I'm confused. Surely there has to be some other way to confirm the machine works than having it tell you it worked.

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    1. Re:Hmmm .... by Anonymous Coward · · Score: 5, Informative

      There *is* a second detector (a third even!) The second main detector is in eastern Washington state. Both will have to go ping before you accept any result.

    2. Re:Hmmm .... by Dunbal · · Score: 2

      You mean like when an electric tester lets you know there's electricity by turning on a little light? Yeah it could be more simple - lick your fingers and grab this wire in that hand and this other wire in...

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    3. Re:Hmmm .... by Baloroth · · Score: 3, Insightful

      Like what? It's designed to detect gravitational waves. It's not designed to detect not-gravitational waves. Since we can't produce artificial gravitational waves (the detector would be almost pointless if we could, since it's meant to prove the existence of gravitational waves), we can't use a known test to confirm it's detecting gravitational waves and only gravitational waves, but since all our theory and all our observation says it should be detecting them and only them, it's fairly safe to assume it's actually doing so (assuming no systematic errors: a large assumption, but not an unreasonable one if everyone involved did their job). In fact, if what it detects isn't gravitational waves, it's almost more interesting, because that means it's detecting something else which isn't accounted for in our theory. If it detects nothing at all, well, that too would be interesting, since (again) our theory says it should. Either way, interesting.

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    4. Re:Hmmm .... by Anonymous Coward · · Score: 4, Informative

      I toured the LIGO in Eastern WA (which is a twin if this, but the article apparently doesn't know it exists). Basically they have two long tubes (2 miles each I think) at right angles. A laser is shined down them and bounced back and forth as much as they can to increase the effective length. Lasers are combined again and they can see by an interference pattern if one arm of the experiment gets shorter or longer than the other, which is what is theorized to happen when a gravity wave passes through.

      A couple of years ago I think they were down to 10^-25m sensitivity, which is pretty amazing to me. They could tell when a truck rolled down the highway 10 miles away, when the hydroelectric dams in the state open their spillways, and when there are big waves from a storm on the coast (200 miles away).

    5. Re:Hmmm .... by Hartree · · Score: 5, Informative

      There are two more detectors at the Hanford Washington site. A primary one like at Livingston, and a secondary one that's half the length.

      Also, there is an European experiment in Italy, called Virgo. It's currently being upgraded to similar sensitivity to the other 3.

      When they are all working, it will allow the detection to not only be verified, but the time of the events at each detector will let them triangulate the location the wave originated from.

      We're pretty darn sure of gravitational waves, as a Nobel prize was awarded in 1993 for showing that the slowing of a binary pulsar was just the right amount to account for the gravitational waves it would generate.

      These detectors will let us do gravitational wave astronomy much like we do with light and radio waves now.

      The huge news would be if they get all of them working with their maximum sensitivity and didn't detect anything. That would mean something was very wrong with their assumptions.

    6. Re:Hmmm .... by jfengel · · Score: 5, Informative

      LIGO works by measuring the distance between two tracks set at right angles. A passing gravitational wave would momentarily change the length of one leg or the other, or both, in characteristic ways.

      It measures the distance with a laser beam. It splits the beam, and sends them down the two tracks. They bounce off mirrors, and when they return, they interfere. Changes in the length will change the interference. That means that they can detect changes at distances on the order of a single wavelength of light.

      That's an interferometer, the I in LIGO. At its core, it's the same thing that Michaelson and Morley used to look for aether, and failed to find it. The trick is that this has to be even more sensitive, because the expected changes are even smaller and the contraption itself is much bigger (4 km, versus a few meters). They have to exclude all kinds of potential interference, from passing trucks to earthquakes.

      I suppose it may well go "ping" when it spots a gravitational wave, and they'll end up comparing it to other experiments. But they'll get more than a ping; they'll get a signal of the changing lengths that they can use to map the size of the wave, and even a hint of its direction.

    7. Re:Hmmm .... by MouseTheLuckyDog · · Score: 2

      I believe the OP is asking, since the deterctor only returns one bit of information, how do we know that it is a gravitational wave and not an Aras freighter passing by the solar system.

    8. Re:Hmmm .... by Wormholio · · Score: 4, Informative

      There are two more detectors at the Hanford Washington site.

      Actually, there is now only one detector at Hanford, the full length H1. The half length H2 interferometer was discontinued as part of the upgrade.

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    9. Re:Hmmm .... by Maury+Markowitz · · Score: 4, Insightful

      > These detectors will let us do gravitational wave astronomy much like we do with light and radio waves now.

      Mmmm, more like neutrino I'd say. You can't point your GWD at an object.

    10. Re:Hmmm .... by Anonymous Coward · · Score: 4, Interesting

      Yes, they are amazingly sensitive seismometers. However, I don't think they'll ever detect gravitational waves. Physcists are divided over whether the waves can be detected by the devices so far created. They rely on special and general relativity to not cancel each other out when it comes to compressing the wavelenghts of light over a long distince. The small signal strenght combined with noise combined with nearly complete cancellation probably dooms the experiment from the start.

    11. Re:Hmmm .... by Hartree · · Score: 2

      Thanks for pointing it out. My info was a bit old.

      Looks like they put components of H2 in storage and are thinking about using it for LIGO-India. I'd heard of the LIGO-India idea, but hadn't known it would use some of Hanford's equipment.

      Another detector at a long distance from the others would greatly improve the ability to localize the source. Let's hope they can get it built and not just have it remain a proposal.

    12. Re:Hmmm .... by Anonymous Coward · · Score: 2, Informative

      since the deterctor only returns one bit of information

      Except it doesn't return one bit of information. It returns a spectrum and relative phase of oscillation measurements, for each of two directions, and again for each of two directions at a different site. Not to mention all of the information associated with calibrating and configuring the device. GR makes predictions about how gravity waves would interact with the two arms and two sites. Calibration and analysis of the construction and background determine a noise floor.

    13. Re:Hmmm .... by Neil+Boekend · · Score: 2

      How often do "neutron stars or black holes merge." ?

      Once per pair, give or take.

      --
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  3. What On Earth Is Wrong With Gravity? by certsoft · · Score: 2

    They've been working on that a long time. Brian Cox visited there in a 2008 episode of BBC Horizon. I'm sure you can find a video on-line.

    http://www.bbc.co.uk/sn/tvradio/programmes/horizon/broadband/tx/gravity/

  4. Catch a Gravitational Wave by TFlan91 · · Score: 2

    Surfs up brah

  5. Where is the joke? by thebes · · Score: 2

    I was waiting for a joke containing "your momma so fat" and "gravitational waves"...I leave here disappointed

    1. Re:Where is the joke? by Anonymous Coward · · Score: 3, Funny

      Yo momma's so fat, she emits Hawking radiation.

  6. Other possibilities? by grasshoppa · · Score: 2

    Physicists are finishing a $205 million rebuild of the detectors, known as Advanced LIGO, which should make them 10 times more sensitive and, they say, virtually ensure a detection.

    That's if they even exist. Personally, I'd be more excited if they DIDN'T find any as that means there is something significantly wrong with their models, suggesting a whole new playing field yet to be discovered.

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    1. Re:Other possibilities? by Anonymous Coward · · Score: 2, Interesting

      Well, it wouldn't be the only hole in Relativity, but it would be a huge hole in Relativity. Which otherwise describes the observed Universe very, very well. It's not the best-tested theory in science; that probably goes to QED. Plus then you have to account for observations of massive stellar objects spiraling towards each other, which lose energy more-or-less as predicted by GR. See also the 1993 Nobel. New Physics is always fun, but I'm afraid that a null result would be better explained as experimental design flaws. You know, the way that every other similar experiment to date has been explained. The parallels with aether measurements are hard to avoid, but the alternative theories of gravity are, well...insufficiently predictive. Also aether was more of an assumption than a theory per se: there was never any evidence for it. Contrast with Relativity, which is undeniably a true description of reality.

      All told, while I agree with you about finding new things beyond the delineations of our theories, I don't think that a null result here would necessarily lead to much. IANAP, any corrections are appreciated.

    2. Re:Other possibilities? by blueg3 · · Score: 2

      That's why nearly ensuring detection is so attractive. If we don't detect a gravitational wave--which has been the case so far--it's a lot more meaningful with a very sensitive detector.

  7. Re:So was it by wonkey_monkey · · Score: 2

    Welp, that's another $205 million down the drain because someone forgot to ask teh internets.

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  8. I agree. by tlambert · · Score: 2, Interesting

    That being said I fully expect gravitational waves to be discovered.

    I am not so sure. There have been other experiments that should have detected them, but didn't. If this experiment also comes up empty, then physics may be facing another Michelson–Morley moment.

    I agree. Gravity waves are unlikely. In theory, we can test the idea with a direct experiment, but the cost would be in the multiple billions, and require spacecraft to loft a tetrahedral constellation of some very large masses, and then you'd have to fling another large mass at an appreciable fraction of the speed of light, probably via solar slingshot, and (effectively) have it "instantaneously appear" intersecting a non-orthogonal plane vector through the tetrahedral constellation. That'd basically give you a wave delta that you could see based on laser interferometry along the vertices of the tetrahedron.

    Assuming gravity propagates at the speed of light as a force, rather than being an artifact of space-time, which would mean you don't get any waves. Which we've so far not been able to detect, probably because they don't exist. 8-).

    1. Re:I agree. by painandgreed · · Score: 2

      Assuming gravity propagates at the speed of light as a force, rather than being an artifact of space-time, which would mean you don't get any waves. Which we've so far not been able to detect, probably because they don't exist. 8-).

      I believe I remember running across the proof for gravity waves while looking at the special relativity derivation of the Lorentz transformation. So, if gravity waves don't exist, then Special relativity is under some pressure. Of course, special relativity happens in Minkowski space which is flat and not warped due to gravity which we know is not the case anyway. Unsure about a similar proof of gravity waves using general relativity.