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Space NASA Science

Biggest Detector To Look For Gravitational Waves 109

Posted by kdawson
from the mission-of-gravity dept.
Hugh Pickens sends in coverage in the Telegraph of a joint NASA-ESA experimental mission, to launch around 2020. It involves three spacecraft orbiting the Sun, separated by 3 million miles, each with a payload of two lasers and a 4.6-cm cube of gold-platinum alloy. The point of it all is to look for gravitational waves. The mission is called LISA, a reasonably non-strained acronym for Laser Interferometer Space Antenna. The Telegraph makes a point of LISA being the largest experiment ever constructed (in terms of its dimensions). Neither that newspaper nor the project page at NASA mentions how much the experiment will cost, but it's almost certainly an order of magnitude or more above the $66 million estimated for a gravitational wave detector the size of the galaxy, which we discussed last fall.
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Biggest Detector To Look For Gravitational Waves

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  • by SimonInOz (579741) on Monday May 10, 2010 @07:16PM (#32163436)

    I read that as a 4.6m cube of gold/platinum alloy and was thinking that was just the sort of thing Lex Luthor would want to steal.

    Now come on, it'd make a great show ...

    • I don't think so.

      Lex looks more like the kind of guy that would take forty cakes. He would take 40 cakes. That would be as many as four tens. And that would be terrible.

    • Sure ... except it's a 4.6 centimeter cube, not a 4.6 meter cube. Not worth stealing if you're Lex Luthor

  • by BitHive (578094) on Monday May 10, 2010 @07:17PM (#32163454) Homepage

    Shooting all our remaining gold into space so they can shine lasers at it. Typical.

    • Cash4Gold is going to make a killing!

      I knew those wise investors had it right all along...

    • by BraksDad (963908)
      This would ensure we could all see our gold glittering across the night sky. Puts a new meaning to stars wearing jewelry.
    • by Garridan (597129)

      Don't worry, our currency isn't based on our gold stores anymore. Didn't Ron Paul teach you people anything?

      OTOH, 2 kg of gold is worth about $77k. Price of a similar amount of lead? Less than $5. Oh... you don't want it to react to the atmosphere (um... in space)? Plate it in gold, or better yet, cover it in enamel for $5 more. Makes you wonder how they spend the rest of the billions of dollars, doesn't it? I whole-heartedly support our space program, but this just pisses me off.

      • Re:Lousy Democrats (Score:5, Interesting)

        by jandoedel (1149947) on Tuesday May 11, 2010 @03:45AM (#32166484)
        it's only the thin coating surrounding the mass that is made of a gold/platinum alloy, not the entire cube. So it is NOT 2kg of gold...
        actually gold coatings are used quite a lot for these things.

        They have a mass floating freely in space, and surrounding it is this gold/platinum coat, that never touches it, it just flies around it and has microthrusters to keep it away from the central mass. This gold/platinum coat is shielding the mass from some external influences, like the solar magnetic field, so that the central mass only feels the influence of the gravitational waves.
  • by TwineLogic (1679802) on Monday May 10, 2010 @07:21PM (#32163498)

    This detector would be 3,000,000 miles across when measured from one man-made component to another. The article linked to as a 'galaxy sized detector' is actually about a proposal to observe pulsars looking for the effect of gravitational waves.

    When observing pulsars, I assume it is not possible to be 100% of what one is seeing, considering that pulsar observations continue to accumulate and scientists have not had the chance to see a pulsar close-up.

    In comparison, using man-made scientific instruments, which are much more under the control of the investigating scientists, to perform the measurement is more trustworthy than observing pulsars. In this regard, the huge scale of the equipment (3 Million Miles) is very significant -- the instruments will be able to make a fine measurement across this distance -- and comparing it with the size of the galaxy is not really a valid comparison.

    On the other hand, the snark-value of the comparison was high, and providing the link without these details only raised the snark-tasticness.

    • Re: (Score:3, Informative)

      by Anonymous Coward

      ...the huge scale of the equipment (3 Million Miles) is very significant -- the instruments will be able to make a fine measurement across this distance -- and comparing it with the size of the galaxy is not really a valid comparison.

      It's a valid comparison because, when you're using pulsars to detect gravitational waves, the effective size of your detector is the distance from one pulsar to another, which is (some large fraction of) the size of the galaxy. Okay, pulsars aren't man-made - but if we deliberately set out to make the transmitter component of a galaxy-sized gravitational-wave detector, we wouldn't be able to produce anything nearly as suited for the task as they are. They keep time as well as our best clocks, and are tri

      • by JakartaDean (834076) on Monday May 10, 2010 @10:58PM (#32165066) Journal

        It's a valid comparison because, when you're using pulsars to detect gravitational waves, the effective size of your detector is the distance from one pulsar to another, which is (some large fraction of) the size of the galaxy. Okay, pulsars aren't man-made - but if we deliberately set out to make the transmitter component of a galaxy-sized gravitational-wave detector, we wouldn't be able to produce anything nearly as suited for the task as they are. They keep time as well as our best clocks, and are trillions of times as powerful as any radio transmitter we could build (and they need to be, if we want to see them at these distances).

        The snarkiness is entirely justified, I think, as a response to the Telegraph's claim that LISA is the largest gravitational wave detector, when it's not. This doesn't mean that it isn't useful, though. LISA and pulsar observations are sensitive to gravitational waves of different frequencies - about 10^-1 and 10^-9 Hz respectively - so they're complementary techniques in the same way that (say) optical and radio astronomy are.

        Wikipedia http://en.wikipedia.org/wiki/Gravitational_wave [wikipedia.org] does a pretty good job of describing these things, with the bonus that it doesn't say anything about "proving" Einstein's theory of general relativity. The take-home point is how tiny these waves are. The predicted energy is enough to distort space by 10 ^-20. From the stupid wording in the Telegraph article, the satellites will be 5 million kilometres apart, and will be able to detect displacements of "40 millionths of a millionth of a metre." So, they can detect displacement of 40*10^-12 / 5*10^9 which I get as 8*10^-22, so good enough I guess. The scales are unimaginable to me, at both ends.

        • by wall0159 (881759)

          "The scales are unimaginable to me, at both ends."

          Yup -- doesn't maths rock? It allows our stupid ape-brains to grok deep truths! :-)

        • by L4t3r4lu5 (1216702) on Tuesday May 11, 2010 @06:34AM (#32167108)
          Well, 5000000km is just under 4 x the diameter of the sun (1.4m km), and "40 millionths of a millionth of a metre" is as close to matter 1/333 the average thickness of a cell membrane (3nm).

          Hope this clears things up for you :)
    • 3,000,000 miles across when measured from one man-made component to another.

      The article linked to as a 'galaxy sized detector'

      comparing it with the size of the galaxy is not really a valid comparison.

      There has to be at least one good, snarky, yo' mama joke in there.

  • Costing (Score:5, Insightful)

    by kakapo (88299) on Monday May 10, 2010 @07:25PM (#32163522)

    From memory, LISA is usually listed as being in the $1.5- $2 billion dollar range, which puts in the same category as Hubble or the forthcoming James Webb telescope.

    Worth every penny, too, in my opinion.

    • Re: (Score:2, Informative)

      by ganv (881057)
      Definitely worth every penny. Gravitation wave detection will bring a completely new window on the universe. Even the first radio telescopes or the first infrared telescopes only opened up a new part of the electromagnetic spectrum, and the space observatories have simply allowed higher resolution. Gravitational observatories will be the first to see an entirely new type of radiated energy. The sensitivity of LISA and the frequency band they can study allows them to detect common gravity wave sources...
  • So I didn't RTFA (Score:3, Interesting)

    by jasno (124830) on Monday May 10, 2010 @07:26PM (#32163538) Journal

    What happens if they don't find anything?

    Do gravitational waves radiate energy? Have we seen instances, such as during a supernova, where there was missing energy which could be explained by them?

    • Re:So I didn't RTFA (Score:5, Informative)

      by jasno (124830) on Monday May 10, 2010 @07:28PM (#32163566) Journal

      I guess they do carry energy, and we think we've seen proof of it: http://en.wikipedia.org/wiki/Hulse-Taylor_binary [wikipedia.org].

    • by Xaedalus (1192463)
      Along these lines, how would we know if we've discovered a wave? And what would distinguish a graviton wave from a ripple in space-time?
      • Re: (Score:3, Informative)

        by John Hasler (414242)

        A gravitational wave is a "ripple in space-time".

        • A gravitational wave is a "ripple in space-time".

          ...according to general relativity, which has not been reconciled with quantum mechanics yet.

          • by Lotana (842533)

            What does gravity has to do with quantum mechanics? I was under the impression that such ripples would be larger than the size required for quantum effects to occur.

            • Re: (Score:3, Informative)

              by MrZilla (682337)

              What does gravity has to do with quantum mechanics?

              Oh nothing at all. It's just one of the biggest unsolved problems in physics at the moment.

              • Ok, they aren't conciliated. But quantum mechanics (QM) says nothing about gravity (that is the problem), while general relativity (GR) is nearly all about gravity. So, in a gravity experiment, people will expect the universe to behave the way GR says it will, not QM.

                Now, ok, maybe the universe won't behave like GR says it will. I guess after detecting a wave, people will try to look for its causes. If there are lots of waves without a cause that fits it under GR (unlikely), I guess people will start to con

                • Anyway, QM has nothing to do witht he [sic] experiment.

                  What if GR is wrong and some currently unknown theory of quantum gravity is right?

    • If they're not able to obtain meaningful results (for example if something goes wrong, or the signal/noise ratio somehow gets botched so that results aren't trustworthy), it'll just improve the state of the art of the engineering involved (=not worth it).

      If OTOH obtained measurements are solid, then any result is useful, even if 'the meter reads zero'. Remember this experiment would serve to support or dis-prove a theory, so either result would advance the science fields involved.

    • What happens if they don't find anything?

      Then it re-enforces the notion that we're living in universe that cheats. Like a simulation would.

      We already have data that fits the theory [blogspot.com] so perhaps this space probe could show that it was wrong, somehow. It seems better to spend money chasing promising results, though.

      • What happens if they don't find anything?

        Then it re-enforces the notion that we're living in universe that cheats. Like a simulation would.

        We already have data that fits the theory [blogspot.com] so perhaps this space probe could show that it was wrong, somehow. It seems better to spend money chasing promising results, though.

        Noting for reference that said link has nothing to do with simulated reality [wikipedia.org] (e.g. The Matrix).

  • not funded yet (Score:5, Informative)

    by bcrowell (177657) on Monday May 10, 2010 @07:26PM (#32163542) Homepage

    I believe the slashdot summary and TFA are misleading, because they make it sound like LISA will definitely be built. According to the WP article [wikipedia.org], LISA is competing against two other space-based science projects for funding, and the decision won't be made until 2013.

    Personally, I would love to see LISA fly. Gravitational waves were first predicted in about 1914. Most aspects of general relativity have been tested pretty thoroughly at this point, but almost a century later we still have no direct confirmation that gravitational waves exist (although there is very strong indirect evidence). And if they can be detected, then it opens up an entirely new way of doing astronomy: not with electromagnetic waves, but with gravitational ones.

    • Re:not funded yet (Score:5, Informative)

      by Chris Burke (6130) on Monday May 10, 2010 @07:49PM (#32163736) Homepage

      The NASA and JPL mission pages don't make it clear that this is unfunded as of yet either, which is annoying since I've been reading up on this experiment for some time and am pretty excited about it!

      I, too, would love to see LISA fly. We really do need robust tests of gravity waves, and a whole new world of observations will open up to us if it pans out.

      One of the coolest things about the mission itself that I read about is the 'drag free' aspect. To ensure that the test masses are in free-fall around the sun without interference by things like the pesky solar wind, they're housed free-floating in a chamber inside the LISA spacecrafts themselves. The spacecraft absorbs the solar wind or other outside forces while measuring any change in relative position to the test mass and using micro-thrusters to keep itself centered on the mass and thus in the same free-fall drag-less orbit. Effin cool imo, even if I don't think it's first time it's been done. :)

      • The spacecraft absorbs the solar wind or other outside forces while measuring any change in relative position to the test mass and using micro-thrusters to keep itself centered on the mass and thus in the same free-fall drag-less orbit. Effin cool imo

        If I understand you correctly, you're saying that to keep the mass in the proper orbit and, I have to assume, from banging against the walls of its containment chamber, the spacecraft adjusts its position in relation to the mass, right? Effin' A, that's effin' cool.

        • by Chris Burke (6130)

          That's my understanding as well, yep. It's a brilliant way to compensate for drag without having to measure the drag, just the resulting deviation from freefall.

          • Brilliant indeed. It makes me very happy that in a world that often seems so full of stupidity, there are people who are smart enough to figure that sort of thing out.

        • by Trecares (416205)

          But wouldn't that mean the cube's trajectory lead into the sun? The cubes would be drawn to the sun, and since the cube moves, the satellite has to move inwards, falling into the sun? Kind of reminds me of that Stargate episode where they had to tinker with the space mine heh.

      • by Cyberax (705495)

        Yes, it's not the first time.

        Gravity Probe B did the same with _rotating_ _gyroscopes_. In hard vacuum. Cooled to liquid helium temperature.

        Now that is cool!

      • > The spacecraft absorbs the solar wind or other outside forces while
        > measuring any change in relative position to the test mass and using micro-
        > thrusters to keep itself centered on the mass and thus in the same
        > free-fall drag-less orbit.

        That method could be used to test the Pioneer Effect. You would, of course, need to keep the center of mass of the spacecraft near the center of mass of the test mass, not merely keep the test mass from touching the walls of the chamber.

        • > The spacecraft absorbs the solar wind or other outside forces while
          > measuring any change in relative position to the test mass and using micro-
          > thrusters to keep itself centered on the mass and thus in the same
          > free-fall drag-less orbit.

          That method could be used to test the Pioneer Effect. You would, of course, need to keep the center of mass of the spacecraft near the center of mass of the test mass, not merely keep the test mass from touching the walls of the chamber.

          The system I read about used microwaves to measure the position of the test mass inside the chamber, which obviously impart momentum to the mass, so I imagine you would need to keep the test mass centered as much as possible to have any kind of precision.

          • measure it from the 6 (or three if sphere) points that are equidistant from the test mass, thus while the measurement imparts some force, you are applying that force on all 6 sides of the cube.

            • Microwave intensity follows the inverse square law so as the ball drifts from centre it experiences asymmetric force. Its picky but thats the name of the game in this experiment.

              Also what about photons which naturally come off the inside of the cavity?

              • someone smarter than me obviously (or not so smarter given the imperial - metric all time best screw up) is figuring that part out. :-)

  • Damn, I thought one could just write papers to prove something. Now we have to spend millions.
    • Damn, I thought one could just write papers to prove something. Now we have to spend millions.

      In science, the only things you can prove by writing papers is that you are able to write, or that you understand math (since ultimately, math is a matter of definition - by humans).

      Proving anything else requires field-testing one way or another. Where 'field-testing' may be done in your kitchen sink, if possible.

      • since ultimately, math is a matter of definition

        ... Or the definition of matter is math.
      • > Where 'field-testing' may be done in your kitchen sink, if possible.

        Or, if you are a theoretical physicist, by somebody else.

      • by lxs (131946)

        You've obviously never met a theoretical physicist. Many are of a deep seated belief that reality is but a mere shadow of their maths. Luckily the good ones keep a sense of humor about it and give a nod in the direction of reality now and then.

        • > You've obviously never met a theoretical physicist. Many are of a deep
          > seated belief that reality is but a mere shadow of their maths.

          They are right.

  • As I recall, the last LISA was [also] a grossly overpriced failure.

  • by future assassin (639396) on Monday May 10, 2010 @07:59PM (#32163830) Homepage
    Won't the Ferengi attack the satellites to steal the gold-pressed latinum?
  • by stewardwildcat (1009811) on Monday May 10, 2010 @09:22PM (#32164434)
    Just to let you all know, LISA and the Pulsar observations are not observing the same things. Sure they are fighting to detect the first gravitational waves but they are looking at different regimes. Its like comparing the GBT radio telescope to Hubble, they are fundamentally different even if they are looking for the same type of objects. http://www.physik.hu-berlin.de/qom/research/freqref/lisa [hu-berlin.de] explains what frequencies LISA will be sensitive to. The Pulsar array is most sensitive to 10^-4 where as LISA is higher frequencies. LIGO is even higher in frequency. You learn about different objects and new phenomena by studying ALL frequencies available to you. Many astronomy projects are expensive as hell but they develop new technologies that benefit our daily lives. Who knows what laser interferometry in space will generate for the public funding the project.
  • Wouldn't a lump of lead work as well and be cheaper?
    • Re: (Score:3, Insightful)

      by SteveFoerster (136027)

      Given how much it will cost to get these things into orbit around the sun, I'm guessing the cost of the actual materials is comparatively trivial.

      • You are probably right, but it still does not answer the question. The lump of lead is still much cheaper, so there has to be a good justification for using funds on the gold and platinum, instead of more or better instrumentation, more propellant, or other such costs of the project.

        (There is also a PR angle: the use of such classic luxury materials sounds extravagant to taxpayers...)

    • by Lord Crc (151920)

      Wild guess, perhaps it has something to do with reflective and thermal properties of the material?

      They're using the mass as a reference for the satellite position, so I assume they measure the distance to the mass using lasers, hence the need for the mass to be reflective.

      Also to increase accuracy I'm guessing that they'd want to minimize the change in physical size of the mass due to thermal fluctuations.

      Or I could be completely wrong and they do it just cause it sounds cool :D

      • It's unlikely to be due to the reflectivity, if it was the case, a coated cube would be enough. Gold and platinun are known for their stability, so I guess they were choosed because the vacuum inside the ships isn't expected to be perfect (as a second tought, duh, it's inside a ship, so it can't be) and they don't want the cubes to absorb the gases around them.
        • > It's unlikely to be due to the reflectivity, if it was the case, a coated
          > cube would be enough.

          It is coated with gold, probably primarily for reflectivity.

          > I guess they were choosed because the vacuum inside the ships isn't
          > expected to be perfect (as a second tought, duh, it's inside a ship, so it
          > can't be)...

          It is inside a special chamber inside a spacecraft. It will have the best vacuum possible.

          > ...and they don't want the cubes to absorb the gases around them.

          There won't be any.

          • It's inside a spacecraft, that has walls, that will exalate gas at low pressures. But, ok, if it is coated, that is probably for surface effects (probably reflection).

            I (miss)understood from the text that it was made of gold and platinum.

    • > Wouldn't a lump of lead work as well...

      No. Platinum is much denser and also much harder. The cube is plated with gold because it is highly reflective and inert.

  • Years ago I rented a tiny travel trailer that was quite old. The rent deal was fabulous and the guy that owned the park was a good fellow. At any rate I seem to have created my own gravity wave. I bedded a young woman and in the act of passion all four legs of the bed shot right through the floor. I never missed a stroke.
    The fellow that owned the park came to make the repair the next day while the girl was still there. After he put in a

  • ... each with a payload of two lasers and a 4.6-cm cube of gold-platinum alloy ...

    ... which they intend to use as a duodynetic field core. 5 or 6 pounds should be sufficient.

  • by smooth wombat (796938) on Tuesday May 11, 2010 @08:23AM (#32167680) Homepage Journal

    We know the Holy Grail is to have a Grand Unified Theory of the four forces. To date, three have been combined with gravity being the lone holdout.

    Is there a reason why gravity can't be a force unto itself but rather, the result of the other three forces? By that I mean, since the Strong and Weak forces hold things together, is there some reason they can't be creating gravity with their forces weakening the further out you go, similar to how radio waves get weaker as they propagate outwards.

    Even though this experiment is an attempt to detect gravitational waves, since we haven't found any to date, could the above be a different explanation for why we haven't found any (yet)?

    • by hansraj (458504)

      Is there a reason why gravity can't be a force unto itself but rather, the result of the other three forces? By that I mean, since the Strong and Weak forces hold things together, is there some reason they can't be creating gravity

      I am having comprehension problem with what you wrote (Not a native English speaker..). Do you mean to ask:

      A) Why gravity couldn't be independent of the other three forces?, or
      B) Why couldn't gravity be a manifestation of the other forces over a distance?

      I might be wrong (IANAP) but the Standard Model already unifies the three other forces except Gravity. That means that if you can show that gravitational interaction arises from strong and weak interactions then essentially you have shown that the Standard

      • B. I know I wasn't quite as elegant in my language as I should have been, but it's one of those questions I've had rattling around my skull for some time and would pop out if I met Hawking, Kaku, etc.

        The question has always been, why is gravity the weakest of the three even though it's the one we're most familiar with? My solution (yeah right) would be because the other three forces are so much stronger that like radio waves, their strength decreases the further out you go.

        Again, since we haven't detected

        • > Again, since we haven't detected any gravitational waves, using either
          > Occam's Razor or Sherlock Holmes' comment about eliminating the impossible
          > and whatever is left, no matter how improbable, must be the truth...

          One of the things that is left is that our detectors are not yet sensitive enough.

    • by Chris Burke (6130)

      We know the Holy Grail is to have a Grand Unified Theory of the four forces. To date, three have been combined with gravity being the lone holdout.

      Actually, the three forces we've unified are electricity, magnetism (as electromagnetism) and then the weak force into the "electroweak". The Strong force has yet to be unified.

      Since GR came along to describe gravity not as force but as geometry, the desire to unify it has been lessened. Not that that people don't want to. But surely unifying the electroweak

    • There has been some attempts in the past to marry electromagnetism and gravity. This was because some of the equations look very similar, one of the most famous attempts is the "Kaluza Klein theory" [wikipedia.org]. This extends general relativity to 5 dimensions from there Einstein's and Mazwell's equations "pop" out. However it never got further than that as there are problems with the theory. But as I am not a physicist I have no idea on the merits or drawbacks of this approach.

      A more recent hypothesis to explain grav

  • Will we ever find out if 64 really is the answer? Is our universe base 8?

Parkinson's Law: Work expands to fill the time alloted it.

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