The LISA Pathfinder experiment has resulted in a near-perfect freefall of masses in space. This investigation could advance physicist's search for gravitational waves, the confirmation of which could radically alter knowledge of the nature of the universe.
Gravitational waves were first predicted by famed physicist Albert Einstein in his general theory of relativity. They are waves in the fabric of space-time, caused when massive objects move through space. Black holes merging together are capable of producing the phenomenon, as are rotating pairs of neutron stars or the explosion of supernova. Despite the massive energies produced in these events, gravitational waves are feeble by the time they traverse the tremendous distance to Earth. Because of this, these waves were only detected for the first time in September 2015.
LISA Pathfinder, managed by the European Space Agency (ESA), launched into space in December 2015. The spacecraft was designed to release a pair of masses into freefall and precisely measure their movements in an effort to detect evidence of gravitational waves. After two months, the masses were measured to be moving under the influence of gravity alone without outside interference.
"A crucial aspect is placing two test masses in freefall, monitoring their relative positions as they move under the effect of gravity alone. Even in space this is very difficult, as several forces, including the solar wind and pressure from sunlight, continually disturb the cubes and the spacecraft," mission engineers at ESA report.
The positive results from this latest experiment confirms a larger gravitational wave experiment could be successfully carried out in space.
Each of the cubes in the experiment, manufactured from gold-platinum, would weigh nearly 4.5 pounds here on Earth and measure almost an inch along each edge. The pair were sent into freefall just slightly over 15 inches apart from each other. An external shield, separate from the cubes, falls in sync with the pair, protecting the experiment from the outside pressures, which could disrupt measurements.
Effects as slight as electrical charges delivered by cosmic rays could alter the experiment. To counter this effect, the shield strikes the cubes with ultraviolet light, removing the charges.
Analysis of the LISA Pathfinder experiment was detailed in the journal Physical Review Letters.