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

Here’s a neat idea for a concert that’s going to blow a few minds if it ever takes to the stage.

A combination of three or more notes played together is called a chord. We know that certain musical chords sound happy while others sound sad (although nobody knows why). The mood of a piece of music then depends on the combination of chords being played. More than a few weighty tomes have been written about the way one chord can be transformed into another and the effect this has on the mood of the music.

But Kaca Bradonjic, a physicist at Boston University, says that musicians appear to have ignored one of the fundamental ways of changing the pitch of a note: the Doppler shift. He points out that it ought to be possible for an observer moving at a specific velocity to hear a sad sounding note as a happy one and vice versa.

Which means that the mood of a piece of music depends on the relative  velocities of the audience and performers.

He calculates for example that to hear a C major chord as a C minor, the listener would need to be travelling at about 43 miles per hour, directly away from the source. That’s a fair speed. And the accelerations necessary to vary this effect from one note to another during a concert would make this one helluva roller coaster ride.

Talking of which, a (very quiet) roller coaster might be the perfect venue for  the first concert of this type.

Ref: arxiv.org/abs/0807.2493: Relativity of musical mood