Following a €3-million design study funded by the European Union, physicists today unveiled their plans for a gravitational wave telescope designed to open a new window on the universe. Researchers hope that the €1-billion Einstein Telescope (ET) will not only be able to detect the minute ripples in space-time that detectors hope to spot this decade, but to make detailed observations of the cosmic catastrophes—including merging black holes or neutron stars and collapsing supernovae—that create them. "It will provide a complementary picture of the universe, related to mass," says Michele Punturo of Italy's National Institute of Nuclear Physics in Perugia, ET's scientific coordinator.
Predicted by Einstein's theory of general relativity, gravitational waves are notoriously difficult to detect. The current generation of detectors, including the twin LIGO instruments in the United States, Virgo and GEO600 in Europe, and TAMA in Japan, have so far drawn a blank, although they have put limits on gravitational emissions from various potential sources. They work by bouncing laser beams back and forth along two orthogonal arms kilometers in length. As a gravitational wave passes it will compress one arm and stretch the other while an interferometer where they meet attempts to measure the minute length difference—less than the width of an atomic nucleus. LIGO and Virgo are currently being upgraded to advanced versions which will have at least 10 times their original sensitivity. Researchers expect that this second generation will detect tens of sources per year after they come online around 2015. "If a source is not detected after 1 year there is something really wrong with the theory or the detector," Punturo says.
ET represents the first of a third generation of detectors and aims to achieve another 10-fold improvement. Its arms will be 10 kilometers long and will be built in tunnels more than 100 meters underground. The tunnels will actually contain two detectors operating at different frequencies which together will cover all frequencies detectable on Earth: 1 hertz to 10 kilohertz. Researchers hope the ET will go much further than simple detection of sources and discern some of their properties. With luck it will be able to look far back into the history the universe beyond the formation of the cosmic microwave background radiation, when the universe was opaque to electromagnetic rays.
The 3-year ET design study involved more than 200 scientists. The researchers' aim now is to keep their team together and begin developing the laser, optical, and mechanical technologies necessary to build the ET. "We need to transform this collection of ideas into a real device," Punturo says. For that they will need more funding and they will also have to begin the delicate process of building a collaboration of national funding bodies to finance its construction.