A century after Albert Einstein published his theory of general relativity, researchers have finally hunted down direct evidence for its last prediction - gravitational waves.
These waves are distortions in the very fabric of the universe, produced by cataclysmic events when incredibly massive objects collide, releasing massive bursts of energy. Examples of such events are mergers of spiralling neutron stars or black holes.
Today a large international team at LIGO (Advanced Laser Interferometer Gravitational-Wave Observatory) announced they have detected an unambiguous signal of gravitational waves for the first time.
The waves detected were produced by the merging of two massive black holes 1.3 billion years ago, when here on Earth all we had were primitive multicellular life forms.
The two black holes are estimated to have been about 29 and 36 times the mass of our Sun - as they spiralled and crashed into each other, about three times the mass of the Sun was converted into gravitational waves in a mere fraction of a second.
The signal detected from this monumental event was detected on 14 September last year, and the information about it was carried within these gravitational waves. This type of direct knowledge about black holes is unprecedented in physics.
“It's a new sense we can use to explore the universe around us,” says astronomer Dr Alan Duffy from Swinbourne University in Melbourne. “It’s a capacity humanity now has for the first time in our history.”
“It would have been wonderful to watch Einstein’s face had we been able to tell him,” says Rainer Weiss, emeritus professor of physics at MIT.
A feat of engineering
Physicists have been searching for direct evidence of gravitational waves for several decades. When Einstein himself realised his theory predicted these waves, he thought they would be too weak to detect.
In 1974 scientists did find indirect evidence of gravitational waves, provided by a pulsar which was losing energy at the exact rate predicted by general relativity - in 1993 this discovery earned a Nobel Prize in Physics.
The search for direct gravitational wave signals or 'chirps' has since been spearheaded by the ambitious LIGO project built specificially for this purpose. It is a pair of two detectors located in Livingston, Louisiana, and Hanford, Washington, in the United States. A real triumph of scientific engineering, these instruments are calibrated to detect space-time perturbations significantly smaller than the width of an atom.
LIGO research is carried out by more than 1000 scientists from the United States and 14 other countries, including a strong contribution from Australian researchers.
Launching a new field of astronomy
The success of the LIGO experiment will have serious implications in the field of astrophysics, and scientists are elated to have opened a “new window” on the universe. This historical achievement is the start of a new branch of astronomy.
“With this discovery, we humans are embarking on a marvelous new quest: the quest to explore the warped side of the universe - objects and phenomena that are made from warped spacetime," says physicist Kip Thorne, one of the original proponents of LIGO. "Colliding black holes and gravitational waves are our first beautiful examples.”
“What is groundbreaking and almost impossible to imagine in one decade can rapidly become routine by the next, and that's just the natural progress in science,” says Alan Duffy.
Gravitational wave astronomy will let us look further back in time, and gain information about inconceivably distant objects that we couldn’t obtain by the current means we have for observing the night sky and beyond.
"There are undoubtedly going to be exciting things that we learn about black holes, ultimately trying to conceive what happens at the very limit of our understanding - but the true ramifications will take decades, just like all other Einstein's predictions," says Duffy.
The first of the papers describing these results was published today in Physical Review Letters.