Mirror, mirror upon the wall, which is the oldest universe of all?

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In Brazil, they say the hart has no wrinkles. But human faces do, and this is a simple way of telling the age of a person. It's a bit like counting the rings in the trunk of a tree. Now it seems that the Universe might be able to do something similar. We only need to hold the mirror (actually, mirrors, see below) in front of it and let (laser) light shine on its wrinkles. It's called laser interferometry, and the wrinkles are gravitational waves.

The Theory of General Relativity predicts (and requires) the existence of gravitational waves. These are the effect of distortions in gravity force made by matter in the fabric of space-time (see here for a dynamic presentation). Imagine a sufficiently heavy ball laying on a flexible net, roll the ball and the net would curve differently and accordingly. Likewise, any moving mass in space-time will produce gravitational waves. The modification in the net/space-time is almost instantaneous, which means that gravitational waves propagate at the speed of light (for an introduction see here).

Several projects are currently addressing the observation of gravitational waves:
- the US project Ligo (Laser Interferometer Gravitational Wave Observatory) and LISA
- the French/Italian project VIRGO
- the Japanese project TAMA300
- the British/German project GEO 600, which has been recently activated.

The task of GEO 600 is to (try to) detect such ripples created in the fabric of space-time by merging black holes, exploding stars and neutron stars, in other words anything so massively dramatic to leave some trace in space-time.

GEO 600 fires a laser into L-shaped tunnels. If there is a gravitational wave passing through the Earth, this will disturb the laser, since it will have the effect of slightly squeezing and squashing our planet. How slightly? Very, very slightly: fractions of the diameter of a proton (one of the particles constituting the nucleus of an atom). This is why building a gravitational wave catcher is an extraordinary challenge. The level of sensitivity must be orders of magnitutes smaller than the thinner hair.

Any successful detection would corroborate Einstein's theory, and would enable scientists to look into the earliest moments of life of the Universe, by observing the remnant gravitational waves from the Big Bang.

Here is how GEO 600 might detect gravitational waves (from BBC Science).

"Two coalescing black holes circling each other [1] are expected to emit gravitational waves that move out at the speed of light.
At GEO 600, a high-powered laser [2] is fired at a 'beam splitter' - a semi-transparent mirror - which divides the beam down two vacuumed tunnels.
Mirrors [a+b] at the far ends bounce the light back; more mirrors [c+d] extend the measuring distance, and yet more [e+f] are used to recycle the power and enhance the signal.
The light paths from the separate arms are recombined and sent to a photodetector.
If a gravitational wave has passed through the observatory, it will have changed the length of the arms and the signal should be evident when analysed by computer".

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