Gravitational waves are the echoes of massive cosmic disturbances that travel across space and time, and two research teams are on the cusp of proving their existence.
Nearly a century after Einstein’s theory of relativity predicted the existence of gravitational waves, we may finally have the technology to detect these mysterious cosmic phenomena. Gravitational waves don’t get nearly as much public fascination as other predictions of general relativity, like black holes and time travel, but studying them will similarly revolutionize our understanding of astrophysics.
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Gravitational waves finally received some time in the science-fiction spotlight in the 2014 film Interstellar, where they provided data that saved humanity from famine. But contrary to the film’s depiction, they do not result from Matthew McConaughey’s tinkerings with dust and threads woven into the fabric of the universe. In reality, these ripples in space-time originate from terrifically violent cosmic events that send relativistic vibrations throughout space.
The waves generated by this pair of orbiting black holes would challenge even the most seasoned of surfers.
Only major events like emerging black holes and exploding supernovas can accelerate enough mass to generate gravitational waves. When two supermassive black holes merge, they release more energy as gravitational waves than the combined electromagnetic radiation (light energy) from all the stars and galaxies across the universe. Up until now, we have been limited to observing these astronomic objects based on their electromagnetic emissions. While this has led to massive leaps in our understanding of the universe, the detection of gravitational waves will be like turning on the volume for a previously silent film.
Essentially, these waves propagate the relativistic warping that happens at the event horizon of a black hole. But despite the gargantuan amounts of energy involved, gravitational waves only create quantum-sized disturbances in space-time that require highly sensitive technology to detect.
There are a few ground-based projects in development that aim to capture the effects of gravitational waves on laser beams, using “interferometry.” This technology works by splitting a laser beam down two vacuum tunnels with mirrors at each end. The beams are then reflected back to their starting point, where a detector can pick up any changes in frequency caused by the action of gravity as the light particles traveled. But since gravitational waves work on such a small scale, they require colossal detectors. The Laser-Interferometer Gravitational-wave Observatory, for example, uses 4-km-long tunnels so that the laser beams travel far enough for gravity to have a measurable effect.
The LISA Pathfinder mission, on the other hand, intends to set up a physics lab in space that can observe gravitational waves without interference from Earthly commotions. The detector will suspend two masses of gold-platinum alloy in the freefall of space, protected from solar radiation by a carefully constructed spacecraft free of magnetic materials. The two masses will hang millions of kilometers apart, but the detector’s laser interferometer will be able to pick up a change in distance of even the tiniest fraction of a meter.
For now, the LISA Pathfinder mission is testing its technologies in preparation for a formal launch within the next two decades. With this project as well as other missions in the works, it looks like our century-long hunt for these elusive signals may soon come to fruition. It’ll probably be a while before we figure out how to harness gravitational waves to send messages across space and time like Matthew McConaughey’s character, but we are surely on the cusp of an astrophysical breakthrough.