European Space Mission Could Solve 100-Year-Old Gravitational Wave Mystery

LISA Pathfinder
The LISA Pathfinder at IABG's space test center in Ottobrunn, near Munich, Germany, on August 31. It will soon move to its launch site in French Guiana. ESA/P. Siberot

Since Albert Einstein predicted the existence of gravitational waves with his theory of general relativity in 1915, physicists have been on the hunt to confirm their existence. These waves are ripples in the spacetime continuum which, if discovered, could allow us to look back to the origins of the universe. Now, a forthcoming $478.6 million European Space Agency (ESA) mission could be about to take a step towards finding them.

Last week, the ESA's LISA Pathfinder probe was removed from display at the IABG space center near Munich, Germany, and packaged up to go to its launch site in French Guiana. In November, it will be blasted nearly one million miles into space, and its team hopes it will provide a proof-of-concept that gravitational waves exist, and that they can be detected.

Scientists believe that gravitational waves are caused by cataclysmic events, such as the merging of supermassive black holes or collisions between separate galaxies. However, despite the massive energy needed to produce the waves, they are very faint and difficult to detect. A ground observatory stands little chance of detecting them as something as simple as a passing train could interfere with the detectors, Gizmodo reports.

This is where the Pathfinder comes in. Its purpose is to test, in space, the technologies required for detecting gravitational waves. If the Pathfinder can prove the technology works, the ESA will be able to confidently scale up the project. Pathfinder is a precursor to a full-scale mission by the ESA, called L3, which has a tentative launch date of 2034, and will reportedly cost more than $1.3 billion.

Paul McNamara, project scientist at LISA Pathfinder, has high hopes for the mission. So far, astronomers and physicists have investigated the universe using electromagnetic radiation, such as infrared, X-rays and gamma rays. If gravitational waves could be detected, a whole new realm of discoveries may await.

"We're adding a completely new dimension, something that's not electromagnetic. We can see the universe as it is today, [but] with gravitational waves we can actually hear the universe. It's like a sound, a vibration of spacetime," says McNamara.

Unlike electromagnetic radiation, which is scattered as it passes through the matter in the universe, gravitational waves can penetrate through matter and be used by scientists to look much further back into the history of the universe.

As objects move further away from Earth, the light emitted by them becomes shifted towards the red end of the light spectrum. The degree of this shifting is referred to as redshift, and a higher redshift value means light is coming from a more distant galaxy. Currently, the furthest galaxy ever discovered, EGS8p7, has a redshift value of 8.68. McNamara estimates that, if gravitational waves were detected, they would allow us to see parts of the universe with a redshift value of 30. In other words, more than three times as old as what we currently see. "We can see things [with gravitational waves] which you just can't see with electromagnetic light. So basically, we open up this whole new way of observing the universe," he says.

Matt Whyndham, a lecturer in the Department of Space & Climate Physics at University College London, says the detection of gravitational waves would allow "a new form of astronomy" to develop. He uses the analogy of an earthquake to show how the waves would allow us to discover things not visible with light in the electromagnetic spectrum.

"If you're looking at an island that has an earthquake on it, you can look at it through a telescope and see it through light," says Whyndham. "If you've got an earthquake detector, you can feel it in the ground. So the gravitational wave is like an earthquake detector, but of the galaxy or the universe."

He emphasizes that if the mission could throw some light on the mystery of gravitational waves, it would constitute a massive advance. "They've been on the blackboard for getting on 100 years, and this would be the first time that we would have been able to detect them with a machine," he says.