Stories
Slash Boxes
Comments
Search

News for nerds, stuff that matters

Slashdot Log In

Log In

Create Account  |  Retrieve Password

LIGO Fails To Detect Gravity Waves

Posted by kdawson on Wed Jan 23, 2008 05:09 AM
from the listen-harder dept.
Space Science
planckscale writes "Last weekend, LIGO (the Laser Interferometer Gravitational-Wave Observatory) did not detect gravitational radiation in association with a gamma ray burst (GRB). The non-detection was actually a valuable contribution, as it helped to distinguish between competing models for what powers GRBs. The detector is due to be upgraded this year for even more accurate measurements. The interferometer is constructed in such a way that it can detect a change in the lengths of the two arms relative to each other of less than a thousandth the diameter of an atomic nucleus."
+ -
story

Related Stories

Submission: LIGO fails to detect gravity waves by planckscale (579258)
This discussion has been archived. No new comments can be posted.
The Fine Print: The following comments are owned by whoever posted them. We are not responsible for them in any way.

LIGO Fails To Detect Gravity Waves 50 Comments More /

 Full
 Abbreviated
 Hidden
More
Loading... please wait.

  • As a matter of interest... (Score:4, Interesting)

    by gnalre (323830) on Wednesday January 23 2008, @05:19AM (#22151038)
    This is another failiure in the long history of trying to detect gravity waves.

    As a matter of interest what would be the consequences to modern physics if Gravity waves do not exist?

    • Re:As a matter of interest... (Score:5, Funny)

      by rucs_hack (784150) on Wednesday January 23 2008, @05:53AM (#22151202)
      As a matter of interest what would be the consequences to modern physics if Gravity waves do not exist?

      There will be less for spectators to do when gravity scores?

    • Re:As a matter of interest... (Score:5, Funny)

      by Anonymous Coward on Wednesday January 23 2008, @06:05AM (#22151258)
      Of course it doesn't exists, there is only Intelligent Falling.

        • Re:As a matter of interest... (Score:5, Interesting)

          by VernonNemitz (581327) on Wednesday January 23 2008, @09:07AM (#22152516) Journal
          Actually, ONE possible problem with the experiment has nothing to do with the sensitivity of the detector. See, there is a fundamental and unproved ASSUMPTION in Physics that gravity waves must travel at the speed of light, and therefore when a gamma-ray burst happens, we expect any gravity waves from the event to arrive at the same time as the gamma-ray photons. But if they don't have to travel at light-speed, then they can exist and be detectable, just not at the same time as the gamma rays.

          • Re: (Score:3, Interesting)

            by Chris Burke (6130)
            See, there is a fundamental and unproved ASSUMPTION in Physics that gravity waves must travel at the speed of light

            Well, if you're referring to gravity waves being limited to at most c, then that's a pretty safe assumption. It basically means you're assuming that causality exists (i.e. effects occur after causes). It would be an extremely bizarre universe if that were not true.

            Though I suppose Newton considered it a pretty safe assumption that time was constant for all frames of reference. Must have seem

            • I've always been confused about why 'c' and 'causality' are considered one in the same.

              Lets say you create a gravity generator. You put it 1 light year away from a gravity receiver. You also put a big honkin' flashlight on that gravity generator.

              Now, lets say that gravity is instant. You turn on the gravity generator and the big honkin' flashlight. The receiver instantly notes the increase in gravity, and one year later sees the flashlight. How is causality violated? The receiver did not see the e

              • Re:As a matter of interest... (Score:4, Informative)

                by Jamu (852752) on Wednesday January 23 2008, @02:42PM (#22157238)
                Those two gravity events are outside the light cone [wikipedia.org]. Other observers can see those events differently [wikipedia.org]. For example, another observer can see that the gravity increased at the "receiver" before it was "generated". If you can send information that way, then someone else can send information backwards [wikipedia.org] in time.

                • A big IF (Score:3, Informative)

                  by mangu (126918)

                  If you can send information that way, then someone else can send information backwards in time.

                  Unfortunately, too many physicists aren't very familiar with the theory of information. [wikipedia.org]

                  If one can state the one basic principle in that theory it is that to send or store information you have to spend energy, increasing the entropy in the universe. However, thermodynamics is a macroscopic phenomenon, at quantum dimensions all phenomena are reversible. In quantum dimensions one could say that time is bidirectional

                    • This is at somewhat of a tangent to the discussion, but I've always thought of the speed of light as representing something fundamental that clearly cannot be exceeded, as follows:

                      I took my last university physics course in 1991 and my memory of the details is very, very fuzzy. But I do remember a specific conclusion that I came to based on what I was learning, and I have retained that conclusion along with a vague idea of what led me to it, which was:

                      Light is electromagnetic radiation. Breaking this term

    • Bummer (Score:5, Informative)

      by tqft (619476) <ianburrows_au@yah[ ]com ['oo.' in gap]> on Wednesday January 23 2008, @06:11AM (#22151288) Homepage Journal
      1) General Relativity as formulated by Einstein (and a lot of other similar derivates - are there many?) would be in serious doubt. An exam question I had was take GR and show gravity waves exist - you basically show how the wave equation falls out of the formulas and these things carry momentum out of a system.

      2) You then need to explain stuff such as Mercury's orbit precession and observed effects of double Neutron stars slowing down - the FSM stirring his planetary meatball lunch slower?

        • Re:Bummer (Score:5, Interesting)

          by JohnFluxx (413620) on Wednesday January 23 2008, @07:08AM (#22151540)
          He's talking about, for example, where we have observed two neutron stars are orbiting each other, and their orbiting speed is slowing down. If you say that it's because they are giving off 'gravity waves' and thus losing energy in that way, then the theory exactly matches the results.

          Personally I'd side with LIGO being wrong or not sensitive enough or something. At least until there's a bit more evidence.

    • Re:As a matter of interest... (Score:5, Informative)

      by BlackGriffen (521856) on Wednesday January 23 2008, @06:16AM (#22151304)
      It would be a serious blow to the picture in General Relativity of gravity warping space-time itself if we go for too long without detecting gravitational waves using length measurements as an interferometer does. This is especially true if we ever improve the accuracy of our measurements to the point where we can predict that we should observe gravitational waves but don't.

      What we would replace it with that could explain all of the observations that GR predicts I don't personally know, but it's a good day in physics when a theory is proved wrong because it means that we've done our job.

    • Re:As a matter of interest... (Score:4, Insightful)

      by master_p (608214) on Wednesday January 23 2008, @06:30AM (#22151358)
      Other types of waves (e.g. sound waves, energy waves etc) are composed of particles. What is a gravitational wave composed of? of gravitons? gravitons are not proven to exist. If a gravitational wave has energy (as well as momentum and angular momentum) then what kind of energy is contained in the wave? where does this energy come from?

      • Re:As a matter of interest... (Score:5, Informative)

        by dlevitan (132062) on Wednesday January 23 2008, @06:42AM (#22151420)

        Other types of waves (e.g. sound waves, energy waves etc) are composed of particles. What is a gravitational wave composed of? of gravitons? gravitons are not proven to exist. If a gravitational wave has energy (as well as momentum and angular momentum) then what kind of energy is contained in the wave? where does this energy come from?
        Theoretically, gravitational waves are gravitons, just as light/EM waves are photons. Gravitons have not been detected and there is no solid theory for them, but to be consisted with the rest of particle physics, they need to exist. One of the ways GWs are generated are by inspiraling binary neutron stars or black holes. As they circle each other, GWs are produced and the rotational energy of the binary is sent out in the GWs. This is not a significant effect until in the vest last stages of a merger, at which point it will cause the system to lose enough energy for the two objects to collide.

        We have seen binaries losing energy in a manner consisted with GW predictions, so there is a good chance the theory of GWs is correct.

        • Re: (Score:3, Interesting)

          by Chemicalscum (525689)

          Gravitons have not been detected and there is no solid theory for them, but to be consisted with the rest of particle physics, they need to exist.

          One of the results of string theory, that the proponents of string theory point out as one of its greatest successes, is the prediction of the existence of the graviton. They were not trying to derive the graviton from the theory, they found that the theory predicted an unexpected particle. When they looked at it closer they then realized that it had the expe

      • > What is a gravitational wave composed of? of gravitons?

        General relativity predicts that gravity waves exist. Quantum mechanics predicts that all energetic wavelike phenomena can be thought of as made up of particles. So putting the two together suggests that gravity waves can be thought of as being made up of particles, and a good name for these particles is 'graviton'. But there are big problems with combining general relativity and quantum mechanics and there isn't a very good theory of gravitons.

    • Re: (Score:3, Interesting)

      by IWannaBeAnAC (653701)

      As a matter of interest what would be the consequences to modern physics if Gravity waves do not exist?

      They do exist. There have been measurements done of the slowing down of a rotating binary pulsar, which is a prediction of Einstein's theory of General Relativity, where the system will emit gravitational radiation and slowly lose energy. This was the subject of the 1993 Nobel prize in Physics [nobelprize.org].

  • diameter? (Score:3, Insightful)

    by bwd234 (806660) on Wednesday January 23 2008, @05:25AM (#22151062)
    "...of less than a thousandth the diameter of an atomic nucleus."

    Would that be a hydrogen nucleus... a uranium nucleus? Please be more specific.

  • ...she could hang glide on a Dorito! (Score:5, Funny)

    by MobileTatsu-NJG (946591) on Wednesday January 23 2008, @05:26AM (#22151066)

    LIGO Fails To Detect Gravity Waves
    Well that's one Yo Mama joke used against me that can finally be laid to rest.

  • Well of course they can't! (Score:4, Funny)

    by Rik Sweeney (471717) on Wednesday January 23 2008, @06:04AM (#22151252) Homepage
    They're little plastic blocks that kids build things with. Granted, you can make things like the Millenium Falcon with them but it can't actually fly.

    Oh wait, you said LIGO, nevermind.

  • There is no gravity (Score:4, Funny)

    by heikkile (111814) on Wednesday January 23 2008, @06:06AM (#22151262) Homepage
    There is no gravity - Earth sucks!

  • This is not significant (Score:5, Informative)

    by dlevitan (132062) on Wednesday January 23 2008, @06:36AM (#22151382)
    For all the people arguing over whether or not this is a failure of LIGO or not...it doesn't really say much at all. Initial LIGO (which is currently running) is more of a proof of concept sold as a viable project. But if you look at the expected rates of detection, the absolute high end for all binary sources is less than one event/year. The low end is between 4 events every 10000 years and 4 events every 100 years. The other source types are not any better.

    This article basically says that because LIGO is known to not be sensitive enough to measure past a certain distance from Earth (which encompasses the Andromeda galaxy, in whose direction this burst occurred) and because no detection was seen, the burst was not caused from a source in the Andromeda Galaxy.

    I suppose that after spending all this money its not a bad thing that LIGO can actually produce some useful results (though I doubt they were amazingly useful). Advanced LIGO should be able to do the job - but not for another 5-6 years. At that point, the minimum event rate is supposed to be around 1/year and we should finally get some sort of positive detection.

    Personally I'm hoping Advanced LIGO does work, because otherwise all this money will have gone to waste and the field of gravitational wave astronomy will be even more damaged than it already is. The thing is, many people in astronomy who are not affiliated with LIGO are not excited by it. Maybe that interest will be rekindled when Adv LIGO actually works, since right now its more of an engineering problem than an astronomy or physics problem. More people are interested in LISA which (if it ever launches) should have many more interesting sources. Its amusing seeing LIGO people try to point out the flaws of LISA while trying to explain why LIGO doesn't work, but then maybe I'm biased since I am working on LISA (though I have worked on LIGO in the past).

  • Go LISA (Score:3, Informative)

    by Zoxed (676559) on Wednesday January 23 2008, @06:40AM (#22151412) Homepage
    Perhaps the LISA [wikipedia.org] (NASA/ESA) project will have more luck (2015+).

  • An interesting question... (Score:4, Interesting)

    by sapphire wyvern (1153271) on Wednesday January 23 2008, @06:57AM (#22151480)

    I looked at the Wikipedia article about LIGO and noticed this interesting question in the discussion. No one has answered it there. Apparently it's from some forum somewhere. Maybe someone here can explain the solution to this "conundrum" for me?

    Just getting back to LIGO for a while (sorry if this isn't strictly on topic), I understand that two long laser beams, at 90 degrees to each other, split from one laser source originally by a semi-silvered mirror, are re-combined at a sensitive detector to see whether their wave forms are cancelling or reinforcing. A passing gravity wave will sequentially lengthen and shorten the wavelength of only one of these light beams because the space-time continuum is distorted in only the direction of travel of the gravity wave. This, it is assumed, will cause the interference of the two laser beams to vary also - causing a variation in the light level measured at the detector. I still don't see why LIGO will work because a gravity wave is indiscriminate in the way it distorts things.

    Everything is embedded in our 4-space, including the laser light waves lying along the direction taken by the gravity wave. As the gravity wave compresses and then dilates space-time, the LIGO tube and the laser beam within it will compress and dilate in perfect synchrony. Even the human observers' heads will compress and dilate as the gravity wave passes! The number of light waves per unit length of the LIGO tube (the laser wavelength) will appear unchanged because the actual physical length of the tube will shorten and lengthen as the light waves do, and as the eyeballs of the experimenters do too. If the waves of the re-united beams were re-inforcing peak-to-peak before the gravity wave arrived, they will remain peak-to-peak as the gravity wave passes through also. This alteration in the length of the tube, or arm, of the LIGO experiment, together with the variation in the wavelength of the laser beam, will be completely undetectable for that reason.

    It's not a case of the gravity waves being too weak to detect, their influence is universal within our frame of reference and therefore cannot be directly detected .. by definition! The above is the way I see the situation. But dozens of scientists have spent billions of dollars designing LIGO, so I have to conclude I'm completely incorrect in my reasoning. Can anyone tell me how you can measure a distortion of space-time (4-space) if you, and every tool you use to measure the distortion, including light, are part of the same space-time being distorted?

    I'd be fascinated to see what's wrong with the reasoning here!

    • Re:An interesting question... (Score:5, Informative)

      by JohnFluxx (413620) on Wednesday January 23 2008, @07:18AM (#22151596)
      > As the gravity wave compresses and then dilates space-time, the LIGO tube and the laser beam within it will compress and dilate in perfect synchrony.

      This part isn't correct. The laser beam will be redshifted and change its wavelength, however it will still travel at the speed of light, c. Since the distance between the two ends is less, it will travel that distance in a shorter time.

    • Re: (Score:3, Informative)

      by dlevitan (132062)

      Everything is embedded in our 4-space, including the laser light waves lying along the direction taken by the gravity wave. As the gravity wave compresses and then dilates space-time, the LIGO tube and the laser beam within it will compress and dilate in perfect synchrony. Even the human observers' heads will compress and dilate as the gravity wave passes! The number of light waves per unit length of the LIGO tube (the laser wavelength) will appear unchanged because the actual physical length of the tube will shorten and lengthen as the light waves do, and as the eyeballs of the experimenters do too. If the waves of the re-united beams were re-inforcing peak-to-peak before the gravity wave arrived, they will remain peak-to-peak as the gravity wave passes through also. This alteration in the length of the tube, or arm, of the LIGO experiment, together with the variation in the wavelength of the laser beam, will be completely undetectable for that reason.

      Basically, as a gravitational wave passes through a section of space time, that section will dilate and contract. To the light between the mirrors (which is not affected because light always travels at the same speed in a vacuum) there is now an additional distance to go. It may make more sense to imagine the light as a stream of photons that have zero volume and thus can't be stretched. When it hits the mirror, it will now be out of phase with the Fabry-Perot cavity and will exit, thus generating a signal

      • Re:An interesting question... (Score:5, Informative)

        by bodan (619290) <bogdanb@gmail.com> on Wednesday January 23 2008, @11:14AM (#22154156)
        In fact the length of the space between the mirrors (and any length whatsoever) is _defined_ as the time light spends traveling between the two. This is the definition of distance in GR. It works because the speed of light is constant for everyone everywhere (in GR); the same thing causes all the other funny effects of relativity, for instance the same object having different lengths for different observers.

        So, by the same definition, a piece of space is lengthened or shortened _iff_ light spends a longer or shorter time traveling it. The speed of light never changes, but due to conservation laws its _frequency_ changes.

        Very approximately, imagine the pulse of light starting at the far mirror. The EM wave makes (say) 100 oscillations in 100 seconds (totally out of scale with the real experiment, but that's not important). If the length between the mirrors is constant, the 100 wave peaks will hit the close mirror in 100 seconds. But if the distance between mirrors changes (eg, due to a gravity wave compressing space) _during_ the 100-pulse emission, the last peaks will have less space to travel than the first peaks. This means that the close mirror will be hit by 100 peaks in, say, 90 seconds. So the frequency of the wave went from 1 Hz to 10/9=1.1Hz. The waveform was deformed (compressed), but its speed was constant. (Note that the effect happens _only_ if the space changes shape _during_ the pulse. If it changes, say, between two 100-oscillation pulses spaced apart, you'll still get the travel time difference, but not the frequency shift. LIGO uses continuous lasers, though.)

        The LIGO can't actually measure the change because it's much smaller than in this example. So it sends the lasers in perpendicular directions, and reflects them back. Because gravity waves stretch space differently in each direction (except if their direction happens to exactly bisect the angle between the arms), a passing gravity wave will force the two beams to go slightly out of phase. The difference between the two beams is (barely) detectable for big waves.

  • No one has detected gravitational waves... Yet (Score:5, Insightful)

    by mbone (558574) on Wednesday January 23 2008, @09:17AM (#22152620)
    There have been no direct detections of gravitational waves so far. There have been indirect detections (most robustly with the various binary millisecond pulsars, whose orbits slowly decay due to their radiating energy away in gravitational waves), but no direct detections. However, this was not really seen as an issue, as gravitational wave searches before LIGO suffered from the problem that there were no known sources strong enough for them to detect with good probability. You have to start somewhere, and there is always the chance of either good luck, say a close supernova, or some unknown source that is stronger than expected, but I believe that this is the first actual event whose gravitational waves, by a reasonable model, had a chance of being detected with existing equipment. One such non-detection means nothing - maybe the Gamma Ray Burst occurred way behind the Andromeda Galaxy, for example. If this is consistently repeated, we will eventually conclude that there is something wrong with our physics or our astrophysics, but it is much too soon for that.

  • Graviatational radiation (Score:3, Insightful)

    by rotenberry (3487) on Wednesday January 23 2008, @09:45AM (#22153022)
    Many persons have implied that not detecting gravitational radiation will somehow invalidate General Relativity. Unless I am mistaken, every theory of gravitation that requires that

    1. Forces due to massive bodies (gravity) to propagate at the speed of light, and
    2. Energy to be conserved

    must also have gravitational radiation. Information propagates at infinite speed in Newton's theory of gravity, so there is no gravitational radiation.

    • Re:Fails? (Score:5, Informative)

      by LaskoVortex (1153471) on Wednesday January 23 2008, @05:49AM (#22151176)

      I'll spell it out for you. This is not a failure of gravitational wave detection technology.

      What you apparently do not understand is that this device can detect gravitational waves. However, it did not detect gravitational waves that correlated with a gamma wave burst originating in Andromeda. Normally such bursts arise from well known phenomena, such as a collision of black holes. But in this case, the collision could not have been from one of these well known phenomena.

      What the article suffers from is bad writing. It should have been put in the positive--something like "the gamma-ray burst originated from a novel mechanism". Now, because astrophysicists can not account for the burst, they must go back and (1) study other similar phenomena and/or (2) revise astrophysical theory to explain the heretofore inexplicable gamma ray burst. Why is this burst inexplicable at this point? Because they did not detect gravitational waves that correlated with the burst.

      • Actually, I don't think the article is saying that any rethinking of GRBs needs to be done here. The non-detection just proves the burst was from a lot farther than the Andromeda galaxy. That's a good thing, and in-line with some theories if I'm not mistaken. Last I'd read, these bursts can be so violent that they might kill all life forms in the galaxy where they occur. We really don't want them to be common enough to ever happen in our neck of the woods.

      • Re:Fails? (Score:5, Informative)

        by Rudisaurus (675580) on Wednesday January 23 2008, @06:25AM (#22151338)

        I'll spell it out for you. This is not a failure of gravitational wave detection technology.

        What you apparently do not understand is that this device can detect gravitational waves.
        How do you know it can? A gravitational wave has never been directly observed.

      • Re:Fails? (Score:4, Insightful)

        by bluFox (612877) on Wednesday January 23 2008, @06:27AM (#22151344) Homepage Journal
        Any instrument needs to be calibrated before it can be used for detection. Which means that it has to detect gravitational waves *directly* on some event that is known to produce gravity waves. Apparently LIGO [wikipedia.org] has not been able to detect *any* waves directly until now. Until it does that I think the grandparents question (If the gravity waves exist at all) holds good. Since LIGO has not been able to detect any waves, I do not understand how they can claim tha non-detection is a major event.

      • can it? (Score:3, Insightful)

        by nguy (1207026)
        What you apparently do not understand is that this device can detect gravitational waves.

        That has never been demonstrated. For all we know, gravitational waves may simply not exist.

      • Re:Fails? (Score:5, Informative)

        by agranero (1225404) on Wednesday January 23 2008, @07:33AM (#22151662)
        Yes. This is no failure in the dectection technology. People at LIGO have estimated what they can detect and what they cannot. This puts an upper bound in the energy of the gravitational waves that were emitted by the GRB source. If it emitted more they would have detected them. This shows GRBs theories have a long way to go. We dont even know the total intrinsic amount of energy of a GRB source. If the source radiates in a polar pattern (like a lighthouse) we only see a small fraction of the GRB sources that exists (when the beam is directed toward the earth), in this case the intrinsic amount of energy is much smaller. If the GRB radiates like a star in all directions the intrinsic amount of energy is MUCH bigger. We can estimate the maximum size of the source bases in the timing of the event (if it has very fast variations it must be smaller because the information to coordinate this variation cannot propagate faster than light). But we dont know much more. This "failed" experiment is as important fot GRBs theory as the "failed" experiment in detecting the aether wind by Michelson and Morley was for the birth of Relativity. It shows we must review our theories. Airton da Fonseca Granero

          • Re: (Score:3, Interesting)

            by bluFox (612877)
            From the wiki GW [wikipedia.org] and here [wikipedia.org] : The gravitational wave has been indirectly shown to exist by showing that the evolution of orbit of the binary system is in precise agreement with the loss of energy predicted by gravitational waves. Note that this was not done by LIGO. It was observed using convensional Radio telescopes. More over the LIGO [wikipedia.org] is a *direct* detector of Gravitational waves. So I would like to know if LIGO has ever detected gravitational waves. If not the claim is questionable.

            • Re: (Score:3, Informative)

              by arminw (717974)
              ....The General Theory of Relativity says they should move at the speed of light......

              If gravity is confined to the speed of light, the Sun should have lost its planets long ago. For example, simple Newtonian math tells us that the Sun and Jupiter "KNOW" about each other right NOW or in a very short amount amount of time, not 43 minutes later. the Earth and the Sun "feel" each other's gravity instantaneously, not with an eight minute delay. The sun and the center of our galaxy communicate by gravity without

                • Re: (Score:3, Informative)

                  by arminw (717974)
                  ....But reality is Non-Newtonian.....

                  For the electromagnetic interaction, relativity has been experimentally shown, but gravity is still pretty much a mystery. We know that matter somehow gives rise to an acceleration we call gravity. There is no way to tell the difference between this acceleration due to gravity and the acceleration of matter by some means. There is no experiment you could do inside, if you were sealed into a closed rocket, to tell whether your cabin was being accelerated through space at
    • Yes Neo, there is no gravity.

        • Re: (Score:3, Funny)

          by mi (197448)

          Your analogy falls apart before it even gets out of the gate.

          As predicted, the bites are already being ripped out of my flesh...

          • Although I have to agree the analogy was terrible.
            You are certainly right, it was truly horrible! I wonder where he got this idea that he could post an analogy without cars on Slashdot. He must be new here.

    • Re:Of couse, they could *both* have it wrong... (Score:5, Interesting)

      by boot_img (610085) on Wednesday January 23 2008, @06:38AM (#22151402)

      ... but I would call this simply "bad" science - You can't use one poorly-understood phenomenon to explore another.
      You are incorrect. Gravitational waves (the phenomenon) are a very clear and very well understood prediction of the theory of General Relativity. So I would say that this is as far from "bad" science as you can get. If, ultimately, gravitational waves are not detected by LIGO and its successors that would prove GR was incorrect. And that would be a huge scientific advance.

        • Re:Of couse, they could *both* have it wrong... (Score:5, Insightful)

          by dlevitan (132062) on Wednesday January 23 2008, @07:21AM (#22151614)

          Maybe it's just the skeptic in me, but did you just claim that it's a very clear and well understood prediction? Doesn't that imply hypothesis phase? Isn't LIGO part of the observation phase? I have a hard time swallowing the idea that it's a solid theory when we haven't even been able to create any reliable, reproducible scientific observations.
          There are "clear and well understood" theories and there are not clear and poorly understood theories. GR has made several correct predictions that have been tested. The same theory has also predicted gravitational waves of which there is indirect observation (merging binaries). We haven't made any direct observations but that's only a matter of time and money.

          Looking at not clear and poorly understood theories, there is string theory, which has changed so many times that its not even close to the original anymore. The latest on string theory is that certain parts of it mimic what we know already, but exactly how it operates no one has any idea of. Another example is quantum gravity. Again, we have a general idea, but nothing concrete. However, just because we don't know the more correct theory doesn't mean we can't use the initial theory. Newtonian mechanics did not become wrong after QM and GR. Its just not as accurate.

                • Re: (Score:3, Informative)

                  by dlevitan (132062)
                  Well, light is sort of separated. You won't feel the gravitational wave passing through you because the effect is so small and everything will be stretched along with you. However, light has no width and so when the distance between the mirrors increases, it goes out of phase with the cavity and turns up as a signal. Remember that light always travels at the same speed in vacuum, which is why this works.

    • Re: (Score:3, Insightful)

      by rasputin465 (1032646)
      but I can recall someone arguing that gravity has the estrange property of been instantaneous.

      Actually, it's the opposite. Prior to GR, Newton's theory of gravitation predicted that gravitational effects travel instantaneously. After Einstein developed the theory of Special Relativity which, among other things, forbids energy/information from traveling faster than the speed of light, he spent the next ~10 years developing a theory of gravity which was consistent with this (in physics-speak, we say that

All trademarks and copyrights on this page are owned by their respective owners. Comments are owned by the Poster. The Rest © 1997-2009 Geeknet, Inc.