August 15, 1993

Article at Toronto Star

High hopes global net will capture gravity waves

Professor David Blair of the University of Western Australia


SYDNEY - Gravity waves have been called the drums of heaven and the last window into the universe. The tiny ripples in the fabric of space shimmer through the Earth every now and then, yet are undetectable. But this may soon change.

Astrophysicists are planning a global network of observatories using new ideas and technologies to catch the elusive waves and begin answering some of the basic questions of the universe. 

“We expect enormous amounts of energy to be flowing about in the universe,” says Professor David Blair of the University of Western Australia. He heads a project to build a $41 million gravity wave observatory near Perth. It is one of three planned by 1999 - a second is being built in California and a French-Italian project is slated for Pisa, Italy.

“Space is the stiffest stuff in the universe. It is a billion billion billion times stiffer than diamond, the hardest material we know,” says Blair. “Today we know how to listen to it too, because like a drum or a metal gong, it can vibrate.”

All stellar bodies like the sun are heavy enough to slightly distort the structure of space. Normally, the three-dimensional structure of space is stiff enough to resist serious disturbances.

But when massive stellar objects accelerate, as when a star explodes into a supernova or two huge stars collide, they send ripples through the three dimensions of space as a stone sends ripples through a pond.

The whole of space, like a huge tanker at sea, is jostled slightly by such a passing wave. But the ripples are tiny, just a billionth the size of an atom - a level of accuracy only now becoming technically possible to measure.

The Australian observatory, being built with help from India and Argentina, is a so-called laser interferometer consisting of two vacuum tubes, each 3 kilometres long and intersecting in an L-shape.

A powerful laser zaps a mirror at the centre of the L, splitting it into 30 beams that criss-cross along the tunnels. The lasers must be more powerful, efficient and stable than any yet built, and the mirrors 1,000 times better.

When a gravity wave passes through the Earth it will set off a tiny fluctuation in lasers, detected in the mirrors, as every atom on Earth resonates slightly.

“The technology is difficult but the physics in it is a very simple idea,” says UWA physicist Peter Turner. “The beauty of the idea is that you can look further away and further back in time. Unlike light, gravity waves are not blocked out by intervening galaxies or interstellar dust.”

Gravity waves travel at the speed of light, some 300,000 kilometres per second. Light from the very beginning of the universe reaches us, but it is too dim after travelling so far. Gravity waves should overcome this.

Gravity is the last window of the energy spectrum still untapped by scientists, who have probed everything from ultraviolet light to radio waves. Around the world they are working to image gravity but have yet to succeed.

Blair, an astrophysicist, is considered a world authority on the nascent science. At UWA his team has built a smaller-scale observing device called a resonant bar detector. The 1.6-tonne bar of niobium is a rare superconducting metal. Kept in a vacuum and chilled to minus 269 degrees Celsius, it has such high acoustic properties that if struck it would ring for weeks.

It is one of seven such detectors around the world, but is the only one using niobium, a metal so rare the 3-meter bar represents 3 per cent of the world’s refined supply. The others use aluminum but at present are only sensitive enough to spot a supernova explosion within 50 light years.

Although a gravity wave has never been seen, physicists are confident they exist. Circumstantial evidence has been found in collapsed stars. “If we don’t find them, or they’re much weaker or much stronger than we expect, then our views of cosmology will have to be drastically revised,” Turner says.

Scientists say seeing gravity waves will allow them to test some basic theories of the universe, from its rate of expansion to how galaxies form. It may even give scientists a glimpse into something once thought impossible to see - the hellish “event horizon” of a black hole.

This is the edge of the black hole, or massive collapsed star so heavy it creates a deep well in the structure of space, where matter is sucked in and crushed. Nothing can escape its gravitational pull, not even light beams.