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Science Technology

Gravitational Wave Detection Imminent? 326

Seumas Hyslop writes "The UK Telegraph is reporting that we may finally have equipment that are sensitive enough to measure gravitational waves, which are incredibly small and have evaded detection despite the theories that they are present as a way of explaining gravitational effects. Basically, a laser beam is split into two branches that are sent down two identical 2000 feet long tubes and back again via mirrors. Assuming the two arms remain exactly the same distance, they will cancel each other out. But the scientists think that the beams will interfere with each other owing to the effect of gravity, meaning the length of the branches is altered and a gravitational wave has been detected."
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Gravitational Wave Detection Imminent?

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  • hehe (Score:2, Informative)

    by QuantumG ( 50515 )
    The word is imminent. immanent [google.com.au] means something completely different.

    • Re:hehe (Score:3, Funny)

      by strider44 ( 650833 )
      No the headline was completely correct. The scientists are thinking that current technology can actually read gravitational waves and we're actually detecting it all the time in our minds! So not only is it immanent but it's immanently immanent!
    • What if some hungry and / or amorous rabbits are enjoying the beets near the pipes?

      Seismic activity?

      Temperature changes?

      Planes flying overhead? (sound)

      I am not sure how they can remove all this tiny tremors and vibrations and details from their detection equipment. I wish they would publish a 'how it works' that deals with stuff like that. It will be on my mind all day now.

      please type the word in this image: buffets
      random letters - if you are visually impaired, please email us at pater@slashdot.org
  • Waves? (Score:5, Funny)

    by MavEtJu ( 241979 ) <slashdot&mavetju,org> on Monday November 07, 2005 @01:31AM (#13967494) Homepage
    Bring out your gravity surfboard and roll on!
  • by Muerte23 ( 178626 ) on Monday November 07, 2005 @01:34AM (#13967503) Journal
    i won't even get into it.

    anyways, the purpose of the interferometer is to measure the differential gravitational strain between two remote masses. as a gravity wave passes (supposedly), two masses will be driven to oscillate in quadrature with one another. that means that relative to some fixed point, one mass will be drawn closer, and at a right angle another mass will be pushed further away. IIRC.

    luckily a michelson interferometer is a great way to detect these small changes, where the remote masses are mirrors. the extremely long beam paths increase the sensitity of the device. and two remote locations are needed for local error cancellation. if you have three locations (there is a LIGO opening in louisiana soon. uh, maybe) then you can actually do gravitiational wave astronomy.

    probably some LIGO person will write a better explanation, but it's late.

    m
    • by Technician ( 215283 ) on Monday November 07, 2005 @02:24AM (#13967688)
      anyways, the purpose of the interferometer is to measure the differential gravitational strain between two remote masses. as a gravity wave passes (supposedly), two masses will be driven to oscillate in quadrature with one another. that means that relative to some fixed point, one mass will be drawn closer, and at a right angle another mass will be pushed further away. IIRC.



      Now if we can only get rid of the strong local influances such as the sun and moon, then we might get some sensitivity.

      The influence of these make detecting very weak waves difficult. It is like detecting the change in sea level due to a rain storm or evaporation. Local wind caused waves and tides make detecting these minute changes difficult.
  • further reading (Score:4, Informative)

    by weighn ( 578357 ) <weighn@g m a i l . com> on Monday November 07, 2005 @01:38AM (#13967518) Homepage
    ...a karma whoring I do go...

    Gravitational Radiation [wikipedia.org] - the cosmological reference, not the meteorology ones.

    Some other gravitational wave [caltech.edu] detection projects

    Some anomalies [topology.org] in gravity theory

    and, of course, Einstein@Home [uwm.edu]

  • by Greg Hullender ( 621024 ) on Monday November 07, 2005 @01:41AM (#13967531) Homepage Journal
    I notice that GEO 600 [uni-hannover.de] actually has a US competitor called LIGO [caltech.edu] which the Telegraph [telegraph.co.uk] article seems to have missed, but according to the New Scientist [newscientist.com] apparently they're both due to go live at the same time.

    Both sites are asking for public help processing the data, via a special screensaver called Einstein@Home [uwm.edu].

    --Greg

    • by Anonymous Coward
      LIGO has been operating for years. Their first "science run"---i.e., the first stretch of time during which the main purpose was not calibration, but actual data collection---happened between 2002 and 2003, if I remember correctly. For those who are interested, GEO is just one of many similar gravitational wave detectors in the world. There is TAMA in Japan, VIRGO in Italy, LIGO (two sites in the U.S., one in Hanford, WA, and the other in Livingston, LA), and there's also one other detector somewhere in
      • LIGO is absolutely insane. A friend of mine worked on it. Around each vacuum sealed mirror at the end of the arm, there's a do-not-enter zone. I don't know for sure, but I think the instrument was sensitive enough to measure the change in the "local" gravitational field due to the human mass!
        • On TV (yes, not the most reliable source of information, I know, but after all it was one of the scientists working at GEO600 speaking) I've heard that these things pick up a lot of noise - they measure the waves on the nearby shore, cars driving on the streets nearby... From what I've heard half of the work there is actually just sifting through the data trying to filter out the noise, which is why they're now shooting up pseudo-satellites [wikipedia.org] to do the job.
  • by dnquark137 ( 717632 ) on Monday November 07, 2005 @01:49AM (#13967575)
    The interferometric GW detection systems have been under development for quite a while. These include the LIGO project in the US, the GEO in the UK/Germany, and Australia and I believe Japan and Italy have their own versions. LIGO started collecting data a couple of years ago. So now the guys in the UK turned on their instrument.

    So what's the big deal?.. Well, there isn't one. Today's instruments are pretty damn bad. I don't remember the numbers, but you'd have to run them for quite a few decades in a row for a good chance to observe one event (it would have to be something big falling into a black hole somewhere relatively close to us, or a major supernova, or something equally rare.) Essentially, you are trying to measure a ludicriously small displacement (10^-16 cm) of a macroscopic object.

    The good thing is, technology is continuing to improve, increasing the sensitivity. Furthermore, there's hope (subject to funding) of creating a space-based version of the experiment by bouncing laser beams between three satellites millions of kilometers apart. So is the GW detection imminent?.. Considering the scale and cost of the projects, it better be, but I (being a scientist and all) prefer to steer clear of that word. So provided the funding doesn't get cut, we'll very likely detect gravitational waves in a few years. But be prepared to wait.

    For more deets, check out www.ligo.caltech.edu
  • Who hired ScuttleMonkey? He's certainly no copyeditor, that's for sure. "Immanent" means "existing within". I think he meant to type "Imminent", meaning "soon to be realized".

    Between the crackpot science and the bad copyediting, I hope Taco beats him upside the head with a raw ham...
  • cloud problems.. (Score:3, Interesting)

    by Janek Kozicki ( 722688 ) on Monday November 07, 2005 @02:18AM (#13967672) Journal
    I was on a lecture about gravity waves, once. This guy showed a lot of interesting stuff, like that a best gravity wave emitter is when you place four bodies each on a node of a square, and then squash/unsquash this fictional square. Then a strong wave is emitted in perpendicular direction.

    also he said that some folks are trying to detect gravity waves by sending two laser beams through a very long tunnel, they bounce of mirrors and then interfere, so length of their way can be measured with high precision. Exactly like in the summary above.

    And guess what? They got totally different results depending if there are clouds up in the sky or not. The beams were attracted to the clouds because of cloud's mass. Of course it means that they couldn't detect any gravity waves from far away - too strong local effects.

    He also said that the only possible gravity wave detector should be placed in the space on lagrangian point.
  • Food For Thought (Score:2, Interesting)

    by mjinman ( 515540 ) *
    Ok sounds nice and all, but heres some food for thought. In order for this to work you need both 2000ft arms to be the same EXACT length. If they are not EXACT then the whole thing wont work, but in that case how will you know? Or even better when they are making it, how do they know the gravity waves arent throwing off their measurements before its even built!
    • Re:Food For Thought (Score:5, Interesting)

      by ColaMan ( 37550 ) on Monday November 07, 2005 @03:01AM (#13967791) Journal
      in order for this to work you need both 2000ft arms to be the same EXACT length.

      I presume that they have some way of adusting one path - you simply adjust it to peak brightness / least inteference. Then when something happens, it'll be a different distance either way and you'll see a null, or at least a drop.

      If you can't get a peak because the damn thing is jiggling all over the place, then it's working :-) and you'd take a long term average of the results to find a distance that has the highest peaked output and call that the centre baseline.
  • Thnak Yuo! (Score:3, Funny)

    by BigPoppaT ( 842802 ) on Monday November 07, 2005 @02:57AM (#13967785) Homepage
    Thnaks to all teh braev suols who wer willign to bern kamra to piont out teh diferense btween "immanent" and "imminent". Othrewise we all wuold haev to RFTA and haev a maeningful dicsussion. Tihs is Slasdhot, and we ca'nt haev taht heer! (Stewpid atricles!)
  • I can think of a ton of other things that would affect such a test...

    What about vibrations in the ground? 4000ft of tubing and NO vibrations? Unless the tubes were also a perfect vaccuum, the resulting pressure waves in the tubes would diffract the laser beams slightly and cause variation. (believe me, I worked for a company that makes laser imaging devices).

    Ok... now heat/cold? The length of the tubes, the positioning of the mirrors, deforming of the mirrors, etc. will be affected by this. Over 2000 f
    • by LionMan ( 18384 ) <.moc.liamg. .ta. .niets.oel.> on Monday November 07, 2005 @04:13AM (#13968012) Homepage Journal
      This is in reply to this post and a number of others on the same topic.
      Major sources of noise: seismic, acoustic, photon shot noise, thermal noise.
      1) Acoustic noise: the entire beam tube system is in vacuum, so the only mechanical vibrations can be coupled in through the mirror supports, which are suspended on thin wire. The pendulum created by the hanging mirror essentially creates a mechanical low-pass filter which reduces the effects of noise above about 10 Hz. The gravitational wave projects (on Earth, not talking about LISA here) are mostly interested in frequencies around a few hundred to a few thousand Hz.
      2) Seismic: this can cause pretty large displacement. Each of the mirrors (on its' hanging suspension) is sitting on a system of masses and springs (three levels) which creates a third order lowpass filter which further reduces noise.
      3) Photon shot noise: this rises with frequency; essentially, photons are uncorrelated random events which create a Poisson noise distribution. In a Poisson distribution, the standard deviation of count rate is equal to the square root of the count rate, so the variance is decreased by decreasing count rate at the detector. This is why the interferometric detectors operate "in null," meaning they keep the mirrors at a differential path length which is equal plus or minus integer multiples of wavelengths. This way, the output at the point where they interfere is kept dark. The idea is that it's easier to detect a difference between 0 and 1 than between 100 and 101. (There is a ton of feedback to keep the whole system in null. Read up on Pound-Drever locking to understand it.)
      4) Thermal noise: the surface of the mirror is made of atoms which jiggle in random Brownian motion. This is unavoidable unless the mirror is cooled sufficiently, which is difficult to do because of how well isolate the mirrors are. However, the Brownian motion can be averaged out over a large area by making the laser's spot size large.

      So they've thought about it a little bit. And they are also measuring other non-detector channels like seismic activity and acoustics near the detector and wind speed and ... so they can correlate with those sources.

      The NSF doesn't go around giving millions to any old project :)
  • Hundreds of scientists spend millions of dollars of money on an incredibly expensive
    method of detecting gravity waves when cheap ones somehow already exist.

    Build your own gravity wave detector:
    http://www.rexresearch.com/hodorhys/remag86/remag8 6.htm [rexresearch.com]
  • EGO - VIRGO (Score:5, Informative)

    by mennucc1 ( 568756 ) <d9slash@mennucc1.debian.net> on Monday November 07, 2005 @04:43AM (#13968108) Homepage Journal
    The european project is called EGO VIRGO [virgo.infn.it] , and it was completed some years ago. I had a chance of visiting the facility, just months before they sealed it down. The visit was a geek honeymoon with the best in contemporary advanced science. Before reading my report here, please read the summary at their website [virgo.infn.it]; you may also want to browse around this nice informational site [ego-gw.it]. Then here following are some souvenirs that are pure technical delight (please forgive any mistake, the visit was 3 years ago):
    • The vacuum tubes are 3km long, and must be perfectly linear (since a laser is traveling in them): due to earth curvature, at the middle point they are ~1meter lower w.r.t. to the ground than at the end ! (and you can see this!)
    • the laser light travels back and forth ~40 times; suppose you would use a normal mirror, reflecting 99% of the light: summing up, you would only get 60% of the light . To avoid this problem, they built a special mirror [ego-gw.it] reflecting 99.999% of the light; this mirror is made of successive layers of semiconductors, each with appropriate reflective index, each ~1 wavelenght in depth. This mirror is so advanced that they had to build a special facility in France to build it (no existing company could manufacture it!)
    • presence of the air in tubes would diffract light, so these tubes are more vacuum than the vacuum in outer space (solar system type). This is very difficult to achieve: tubes are made of stainless steel; steel usually entraps hydrogen, that then evaporates for years; to keep good vacuum, they would have needed a huge number of vacuum traps to capture these atoms of hydrogen, and that would boost the cost of the project. They instead chose to "cook the tubes" [ego-gw.it] to evaporate the hydrogen; to this end, they connected power transformators to achieve a power of ~40MW and connected it to the tubes, so that they heated up by electrical resistence (and kept cooking for some days). This was costly but it saved them a lot of money overall. If you could peek below the blue roofing, you would indeed see that the inner tube is red.
    • the VIRGO facility was a strange place: it was perfectly clean and at the same it looked dirty. I explain the oximoron: while building that project, free dust was an enemy; for this reason, there were a lot of dust traps around, that is, glueish carpets; those were of course all dirty! For the same reason, we had to wear overalls and shoe coverings, and there were a lot of air pumps that were filtrating air and keeping positive pressure in the compound.
    • that reminds me: they had to build a company to build the tube pieces, (and the compay "precooked" the pieces before shipping). They also built a robot that would solder them; this robot "chews" what it does not need, since "chewing" does not create dust.
    • if you ever fly above Pisa, look down: you can easily spot VIRGO from the airplane
  • by foreverdisillusioned ( 763799 ) on Monday November 07, 2005 @05:17AM (#13968184) Journal
    I seem to recall reading that NASA had sent up a bunch of satellites bearing very sensative equipment that were supposed to detect gravitational waves, though I don't think they were using this method of detection. Does anyone know what happened with that experiment? Do they have the results yet?

    At any rate, I think I read about it on slashdot, so I suppose I could just wait a few months for a dupe.
  • by awol ( 98751 ) on Monday November 07, 2005 @05:23AM (#13968198) Journal
    Ok, so are these gravitational "waves" real or just a construct to explain gravity?

    Essentially the trigger for this question is the whole sound/EM difference. EM is acutally the emission of "stuff" whilst sound is the propogation of energy through a medium and without the medium there is no sound just the vibration of the original source.

    It's been a long time since I read any theoretical physics and so my head hurts a little when I think about this stuff, but the "dents in space time caused by mass as balls on a rubber film" metaphor help explain the "pull" of gravity really quite nicely, if it is even remotely true. But that model suggests a "medium" through which gravity acts.
  • fantastic! (Score:2, Informative)

    by offaxis ( 573745 )
    I'm so happy for the GEO600 crew if they are in fact getting close! I've actually seen the facility - pretty amazing stuff and a very good example of how far you can push things using much brain and relatively little dollar. For example, the article didn't mention this but the arms of the interferometer do not intersect at quite 90deg due to the fact that the arms are built along the borders of farm plots.. As for filtering out noise, they filter out everything above and below particular frequencies. It's
  • by Ancient_Hacker ( 751168 ) on Monday November 07, 2005 @06:53AM (#13968459)
    Not new, there have been attempts to do this for at least 35 years. Detecting gravity waves is really hard. Gravity is close to 10^40 times weaker than electromagnetic attraction. So any detector you build has to be like REALLY stable against electromagnetic effects. Even then the predicted sensitivity to gravity is soooo loooow it requires you to hope for neutron starts hitting head on, or other such huge gravity wave generators. Even then, an ant walking by at 100 meters is likely to snafu the data.

    My hat's off to anybody in this business, they must have a lot of time and money and patience!

  • Ok, it has been decades now, and gravity waves seem to be just like dark matter - just so much phlogiston. I think or theories of gravity are way off. Nothing can move faster than light said einstein, except, says I, gravity, because gravity is actually geometry and hence everywhere instantly. No waves.
  • by Ralph Spoilsport ( 673134 ) on Monday November 07, 2005 @08:30AM (#13968823) Journal
    IANAP, but I like to read books on science, esp. physics, astronomy, cosmology, evolutionary biology, etc. Some people read cheapie novels, I'll read the latest thing from Kaku, Green, Dawkins, Darling, etc. Not that they are necessarily the best books on any given subject at any given time, but for the most part they are fairly accurate. It seems that in string theory gravity is solved in higher dimensions, but the instruments to test that are some time off from development, and so, in terms of testability, we're stuck where we've always been - somewhere between Einstein (relativity) and Bohr (quantum theory). And while everything in terms of matter seems to favour Quantum theory, Relativity is still on top of gravity, as we have yet to find a gravity wave or even a graviton. Therefore, IMHO, we have to come to ask an interesting question: What If Quantum Theory Simply Doesn't Work With Gravity? String Theory might have an explanation, but we're a long way off from being able to test String Theory's ideas about gravity, and (most importantly) a failure of Quantum Physics on Gravity is not necessarily an indication of String Theory's notions. So, if it this test fails (like all the other Gravity Wave Detectors has) when will scientists give up and figure out a new understanding of gravity? This test seems like a good one, so what will happen if it fails? And furthermore, given its expense, how can it be repeatable outside of its own instrumentation? I'm not being a troll - just asking honest questions and trying to get a better conversation in this article beyond a bunch of juvenile carping about spelling errors. RS
    • I'm not sure where you get the idea that other gravitational wave detectors have "failed". I suppose you could regard an inability to build a sufficiently sensitive detector as a "failure" of sorts, but it's not the sort of failure that would cause you to draw any conclusions about the underlying theory because nobody really expected those detectors to find anything. Those experiments have been more about techniques in constructing large interferometers than they have been about astronomy. Moreover, grav
  • by RML ( 135014 ) on Monday November 07, 2005 @09:05AM (#13969018)
    ... a gravitational wave generator patented [uspto.gov] by the NSA. I guess reverse engineering all those UFOs paid off.

    [ObDisclaimerForTheClueless: No, I don't really believe they reverse engineered UFOs. The patent's real though. Who knows, it might even work.]
  • 2000 feet long tubes

    So I guess we're not going to see a portable one any time soon. :-)
  • No need for fancy experiments. My wife detected a gravity wave using our car recently. One minute she was driving along minding her own business, next minute she was in a ditch after a rogue wave shifted the entire road out from under her.

    Anyway, that's her story and she's sticking to it.

  • by Anonymous Coward on Monday November 07, 2005 @09:38AM (#13969214)
    I see a few posts saying, "Well, we haven't seen gravitational waves yet, so maybe they don't exist." To that, I have several responses:

    1. There's no reason why we should have seen them yet; they're so weak that even LIGO I probably won't see them. (LIGO II probably will, if the equipment works as designed.)

    2. Gravitational waves have already been detected indirectly: the 1993 Nobel Prize was awarded to Taylor and Hulse for this discovery. They observed a binary star system whose orbits were inspiralling at exactly the rate that general relativity predicts for a binary system that is losing energy via gravitational waves. That rate also gives the rate at which energy is leaving the system, and allowed them to infer the speed of gravitational waves: the speed of light, to within a few percent --- also as predicted by general relativity.

    3. Even if general relativity in particular is wrong, pretty much any field theory compatible with special relativity contains wave solutions propagating at the speed of light, for demonstrable reasons of logical consistency. This holds for both classical and quantum theories (e.g. Maxwell's equations, general relativity, the Standard Model of particle physics, etc.), theories of quantum gravity like string theory, and so on. You basically have to throw out all of relativity and go back to Newtonian physics to get field theories without wave solutions.
  • Shielding Gravity? (Score:3, Insightful)

    by Free_Trial_Thinking ( 818686 ) on Monday November 07, 2005 @02:20PM (#13972061)
    This article got me thinking:

    If you can detect a gravity wave then doesn't that mean that some energy is being absorbed from it?

    If energy can be absorbed from it, then doesn't it get weaker?

    So if a gravity wave can be made weaker, then couldn't you theoretically build a gravity shield?

    And if you scaled one up, could I stand on it and float off of the earth?

    It doesn't seem right, so where am I going astray? Thanks Physicists!
  • by DynaSoar ( 714234 ) * on Monday November 07, 2005 @02:25PM (#13972104) Journal
    ...then it behooves them to offer alternative explanations for their results. "In experimental philosophy we are to look upon propositions iffered by general induction from the phenomena as accurately as or very nearly true, notwithstanding any contrary hypotheses that may be imagined, till such time as other phenomena occur, by which they may either be made more accurate or liable to exception." -- Isaac Newton, Rule IV of "Rules of Hypothesizing", in Mathematical Principles of Natural Philosophy (1687).

    The experimental design is that of the Michealson-Morley experiments. That hypothesis still stands (ie. they failed to reject the null hypothesis, a very different thing than supporting the alternative hypothesis, and the beast of proving the null hypothesis is imaginary). If they get results, it'll be on them to show the effect is due to something other than that which has so far been unable to be detected but previously theorized and hypothesized as causing the same effect they expect to find.

    Still awaiting the technology capable of testing it is the hypothesis that ether flows along the lines of a gravitational field, and so must be tested simultaneously parallel and perpendicular to gravity. Getting a vertical structure big enough but stable enough to do this is far harder than getting two perpendiculars.

    Keep in mind that in science "out of favor" and "disproven" are not the same, but in peoples minds they are taken as such. Read "The Golem" by Collins & Pinch for many entertaining examples, including the M/M experiments.

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