The painful search for gravitational waves

G-wave data

Gravitational wave detectors have a sorry history of disappointing results.

Joseph Weber at the University of Maryland first claimed to have spotted these waves in 1969. He did it by listening to the way a giant cylindrical bars vibrate, thinking that passing gravitational waves would cause them to ring like a bell. Nobody has been able to reproduce these results and they remain strongly disputed today.

Various groups still listen out for gravitational waves using Weber-like detectors. But the Ferraris in this field are a new generation of laser interferometers that are much more sensitive to the bending and squeezing of space that these waves cause as they pass by.

The trouble is that none of these detectors has ever spotted a gravitational wave either, despite the investment of hundreds of millions of dollars. One way of increasing the sensitivity is to use two or more interferometers in different parts of the world to look for wave simultaneously.

Now the results of the first  combined search using four detectors (three LIGO detectors in the US and the GEO600 in Germany) have been published and the results are again disappointing.  They took data over a period of month between 22nd February and 23rd March 2005, giving them a decent amount of data to play with. But…

“No candidate gravitational wave signals have been identified”

says the team, ominously.

That’s embarrassing because these combined searches should be sensitive enough to pick up gravitational waves from sources such as supernovae and from black holes as they collide.

So why aren’t they seeing anything? One possibility is bad luck, that there weren’t any events during the the time  the data was being taken. That seems unlikely. Another possibility is that the problem is closer to home, perhaps in the equipment, analysis or even the theory itself.

Whatever the problem, they don’t seem to be able to put their finger on it. This data is three years old which means it’s been given one almighty going over before publication.

So I wonder how these guys are feeling given that hundreds of millions of dollars and several years of work has so far produced zilch.

Ref: arxiv.org/abs/0807.2834: First Joint Search for Gravitational-Wave Bursts in LIGO and GEO600 Data

12 Responses to “The painful search for gravitational waves”

  1. Kent says:

    It is not all to waste. The technological advances that they have developed, namely the optics of detecting nanometer deviations over kilometers, is very impressive and could have great implications.

    I read somewhere, it might have been New Scientist though so take this with a grain of salt, that the actual range in space that these searches cover is tiny, somelike like 10-20 light years. I don’t recall a supernovae or blackhole collision occuring so close…

  2. rhr says:

    When LIGO was built, the expected probability of detection of a gravitational wave within 10 years of operation was estimated at 0.001-0.1 or so, IIRC. It’s not at all unexpected that they haven’t detected anything; from the outset it was known that would probably take a second-generation laser interferometer to actually detect the expected astronomical sources. But you can’t build a 2nd-gen device without building the 1st-gen first…

  3. [...] pointed out by the Physics arXiv Blog, this may just have been bad luck. Perhaps there were no black hole collisions, supernovae or [...]

  4. Zephir says:

    By AWT the gravitational waves are corresponding the longitudinal waves, which are spreading through Aether foam, i.e. across the density gradients forming our space-time, so they’re dispersed readily into CMB. They cannot be detected at large distance.

  5. wavicle says:

    Is it only me who sees parallels between attempts at finding gravity waves and the search for aether? The Michelson-Morley experiment was very innovative, but alas found nothing. There was also a lone scientist (Mach) who claimed to have detected aether, but whose results were unreproducible.

    I don’t know much about gravity waves, but at what point do you stop drawing upper limits to their intensity? How sensitive of a detector do you need to say they aren’t there at all? I definitely think they should keep looking, but if they keep finding nothing, they should maybe reconsider their approach.

  6. ZEPHIR says:

    At first, the M-M experiment cannot give a positive result, simply because it’s virtually impossible to detect every environment just by it’s waves. If some particle is serving for wave spreading, it cannot be observed just by this wave and nothing very strange is about. No object can serve as a mean of it’s own observation, as the inner and outer perspective cannot be mixed.

    By the analogous way, we cannot observe the water surface by using of water waves and nothing very strange is about. Of course, the negative result doesn’t mean, this environment doesn’t exist, after then – it just means, we’re sufficiently stupid in such extrapolations.

    In addition, the common observation of water waves by light waves cannot serve as a direct analogy of observation of light waves by using waves in vacuum, simply because in vacuum only one kind of waves can be involved in experiment. Here’s nothing strange about different results of experiments, which made in different arrangement. This doesn’t mean of course, the classical mechanics differs from reality conceptually – it just means, we aren’t using the surface wave phenomena by the same waves, like during experiments in vacuum – that’s all.

    The case of gravitational waves is analogous to the above model – it just means, we didn’t understood the underlying physical model on the principal level well. So we shouldn’t make the same mistake again: the absence of gravitational waves doesn’t mean, the relativity is wrong – it just means, we aren’t extrapolating it correctly.

  7. ZEPHIR says:

    Errata: “…this doesn’t mean of course, the classical mechanics differs from reality…” should be “…this doesn’t mean of course, the classical mechanics differs from relativity…”

  8. Jack says:

    “So I wonder how these guys are feeling given that hundreds of millions of dollars and several years of work has so far produced zilch.”

    I disagree with the sentiment here. The goal of a fundamental experiment like this is to make an accurate and unbiased measurement, not to confirm a theory.

    Unexpected null results can be as, or more, interesting than confirming results: The Michelson-Morley experiment is a classic example. If these experiments achieve a sensitivity far better than their expected sources and continue to detect nothing, then things get very interesting for the theorists!

  9. Molly says:

    Anyone noticed a paper on low cost GW detection: “Correlated Detection of sub-mHz Gravitational Waves by Two Optical-Fiber Interferometers” by Reginald T. Cahill and Finn Stokes, April, 2008. – Don’t shoot me!

  10. Jeremy says:

    Everyone seems to agree that a null result is worth the cost of scientific investigation. But the question may actually be how they felt about it, and you never feel good about it. If you can show that it just wasn’t there, yes scientific achievement. However, questions remain about the equipment and the analysis, which as I have seen were done with great skill. However, this is not necessarily a null result which can really bother you sometimes. But they will ask why, and move forward, when I have witnessed many time groups just fudging things a little bit. So as a scientific investigation, they do not have a null result, they have pushed science forward, and they have done it with a great deal of rigor and scientific integrity. They have deserved their funding.

  11. Mario says:

    Waves can be felt, observed, detected, intellectualized in so many ways, pick your wave. Oh yeah, Gravitational Waves and counterpart, Gravitational Radiation. Perhaps the speed of its waving is more of a constant occurance, slightly above what can be currently measured, as far as how we see things? I believe current theory calls for these waves to be traveling at the speed of light. If this is the case, their should be evidence everywhere, albeit smaller from the source. Detection may be a matter of matter, which eventually CERN may be able to solve; yet on the reverse side of these waves, there may be a totally different explanation, meeting at a certain crest, or otherwise.

  12. 2552 says:

    So if we haven’t detected Gravitational waves from space yet, has anyone tried to create artificial gravitational waves? Could you set up some kind of large, fast-spinning dumbbell right next to a detector?