Einstein’s theory of general relativity is one of the greatest discoveries ever made, and so far its validity has been confirmed by every test scientists have thrown at it. However, one hypothesis stands in its way: gravitational waves were predicted by Einstein over 100 years ago but have so far eluded detection.
The fact that gravitational waves have not yet been found does not necessarily mean that the search is futile. Einstein predicted that gravitational waves in the fabric of space-time would be produced by changes in its curvature in the vicinity of large masses, but unfortunately space-time does not take kindly to bending.
Detecting these changes in curvature requires an incredible level of precision – even the collision of two neutron stars, some of the most massive objects in the universe, would only cause a change in the space-time near Earth by about a millionth of the diameter of an atom.
The LISA Pathfinder, launched on December 2nd this year, will test the technology behind the 3 million kilometre-long detectors that will form the basis of the 2034 eLISA mission. To test the stability of these detectors, LISA will shield two gold-platinum cubes in free-fall from disturbances due to sunlight, magnetic fields and high-energy particles and track any deviation from their expected path with lasers.
A detector of this size will pick up a much wider range of sources and frequencies than a ground-based detector and, it is hoped, will be able to make the first direct observations of gravitational waves.
These spacecraft may confirm or deny the existence of gravitational waves; they may even provide evidence for brand new theories. Whatever happens, making these precise measurements will not be easy. As Andreas Freise, a collaborator from the University of Birmingham, puts it: “In space, you cannot go back and adjust things. They have to work the first time.”