Six years and nearly 400 million dollars later, the Laser Interferometer Gravitational-Wave Observatory (LIGO) still hasn’t turned up the evidence for gravitational waves. Gravitational waves are predicted by fundamental Einstein general relativity theories, but we haven’t been able to detect them. Is it because the first generation laser interferometers are not sensitive enough? Is it because LIGO needs more time to see through the cosmic noise to root out the gravitational wave signature? This is a deeply worrying non-development for physicists as a null result means that something isn’t quite right. We are certain (in theory) that these waves should be rippling through space-time (after all, massive objects are colliding and exploding all the time throughout the Universe), but if we can’t detect the things in our own cosmic back yard, something must be awry. In a recent publication, LIGO scientists have discussed the lack of evidence for gravitational waves, but remain upbeat that they can still be found…



I find myself getting a little uncomfortable when discussing laser interferometers in the search for gravitational waves. On the one hand, the physicists involved are doing some cutting-edge science to search for one of the most observationally difficult things to find; and if they do find a gravitational wave signature it will provide the direct evidence for one of Einstein’s critical general relativity predictions. On the other hand, a huge amount of money has been ploughed into the LIGO project, and despite all the optimistic predictions, it has still generated few results. Unfortunately, the latter is persisting in a new publication from the LIGO scientists.

Using data from three years ago, observational results were combined from the US LIGO detectors and the German GEO600. Looking at a month-period from February to March 2005, the analysis is not good news; no gravitational waves were found during this international effort (combining the US and German detectors would have seriously increased the sensitivity of the results, so this is very bad). The team even go as far to say “No candidate gravitational wave signals have been identified.” Oh dear.

As pointed out by the Physics arXiv Blog, this may just have been bad luck. Perhaps there were no black hole collisions, supernovae or spinning lumpy neutron stars that month? Possibly. It seems more likely that the instrumentation isn’t sensitive enough or something isn’t quite right with the theory. These two options would be terrible news for the LIGO team and other laser interferometer groups around the world.

However, many would argue that this is only the first-generation of laser interferometers and that we are learning so much simply by using an developing the technology. Unfortunately, science funding doesn’t work like that. Try asking for the next half-billion dollars from the NSF when the first $400 million experiment didn’t produce results. I can guarantee there will be little enthusiasm for a gen-2 LIGO proposal…

Still, we have to remain optimistic, after all, six years isn’t very long. The longer LIGO takes data, the better refined the results become. Perhaps LIGO scientists need to think outside the box on this one… why do I get the feeling that the results from LIGO are not as benign as we think, there could be another effect that gravitational waves have on the local Universe we haven’t taken into account. Oddly, this reminds me of a quote in one of my favourite films, Indiana Jones: Raiders of the Lost Ark:

Indiana: Balloq’s medallion only had writing on one side? You sure about that?

Sallah: Positive!

Indiana: Balloq’s staff is too long.

Indiana, Sallah: They’re digging in the wrong place!

Perhaps the LIGO physicists are also digging in the wrong place…

Source: Physics arXiv Blog