In 2016, researchers at the Laser Interferometer Gravitational-Wave Observatory (LIGO) announced that they had made the first confirmed detection of gravitational waves. This discovery, which confirmed a prediction made by Einstein's Theory of General Relativity, opened up a new field of astrophysical research. By analyzing the waves caused by the merger of massive objects, scientists can investigate the insides of neutron stars, detect dark matter, and discover new particles around supermassive black holes.
According to a new study led by the APL-AP or the Advanced Propulsion Laboratory at Applied Physics, gravitational waves can also be used in the search for extraterrestrial intelligence. The researchers suggest that LIGO and other observatories, like Virgo and KAGRA, have the potential to look for gravitational waves created by rapidly and/or massively accelerating spacecraft. By combining the capabilities of these observatories and next-generation ones, scientists could create a RAMADAR system that could search all the stars in the Milky Way for evidence of warp-drive-like signatures.
Searching for Intelligent Life
Luke Sellers, a graduate research assistant from UCLA, led a team from the Applied Physics Lab (APL), an independent research group based in Stockholm specializing in aerospace, as well as researchers from the Technion - Israel Institute of Technology, Lund University in Sweden, and Carnegie Mellon University in Pittsburgh. The team's findings, which are the first in a series and will be published in the Monthly Notices of the Royal Astronomical Society, were the result of their work.
RAMAcraft is a term that will likely be familiar to fans of classic science fiction, specifically those who have read Arthur C. Clarke's story Rendezvous with Rama, issued in 1973. The story follows the exploration of a massive extraterrestrial spacecraft that enters the Solar System and is referred to as a "worldship," a spacecraft capable of containing a complete ecosystem and population with artificial gravity created through rotation. The concept of a worldship has become popularized through this novel.
Worldships, like megastructures, are considered potential candidates for SETI (Search for Extraterrestrial Intelligence) surveys because they would likely produce technosignatures. Following Einstein's theory of General Relativity, a massive object accelerating through space would generate waves in the fabric of spacetime. The team in this study calculated the waveforms that a linearly accelerating RAMAcraft would make based on a range of possible masses and accelerations. According to Sellers, these signals would be detectable by LIGO, Virgo, and KAGRA gravitational wave detectors, and the specific shape of the signal would allow for the detection of a RAMAcraft.
The question of whether intelligent alien life exists out there in the broader Milky Way galaxy could be answered by gravitational waves.
Gravitational Wave Signals
Sellers and his team showed that existing LIGO data could be used to search for objects within the Milky Way that are equal in mass to Jupiter (1.898x10^24 metric tons, or 2.092x10^24 US tons). They also demonstrated that SETI researchers could use LIGO data to search for objects in nearby star systems that are equal in mass to Earth's Moon (7.342x10^19 metric tons, or 8.09x10^19 US tons) based on the specific gravitational wave signals that these objects would produce. These signals could potentially be evidence of megastructures or indications of a Type II civilization on the Kardashev Scale.
In summary, the existing gravitational wave data could be used to search for a wide range of RAMAcraft, depending on the distance of the target of the survey. According to Sellers, the study showed that it is possible to detect objects as massive as Jupiter up to a distance of around 10-100 kpc (kiloparsecs), which covers the entire Milky Way galaxy, and objects as small as the Moon up to a distance of 1-10 pc (parsecs), which includes the nearest stars, such as Proxima Centauri.
To give you an idea of the types of megastructures that could be detected, researcher Anders Sandberg from the Future of Humanity Institute at Oxford estimates that a Dyson structure with a diameter of 1 AU (astronomical unit, the distance between the Earth and the Sun) would have a mass of 2.17x10^17 metric tons (2.39x10^17 US tons). Next-generation observatories such as the Laser Interferometer Space Antenna (LISA), the Deci-hertz Interferometer Gravitational-wave Observatory (DECIGO), the Big Bang Observer (BBO), and Pulsar Timing Arrays (PTAs) will be able to detect gravitational waves with much greater sensitivity at lower frequencies, potentially expanding the search volume for RAMAcraft by a million-fold.
Artist's impression of a Dyson Sphere. The construction of such a massive engineering structure would create a technosignature that could be detected by humanity.
Warp Drive Data Readings
In a previous study, researchers from the Applied Physics Lab-Aerospace presented the first general model for a physical warp drive, similar in concept to the Alcubierre Warp Drive but based on spherically symmetric warp shells and subliminal positive significance. Their research showed that any warp drive would consist of a shell of regular or exotic material moving at a certain velocity, which would produce gravitational waves.
This paper is the first in a series that investigates how gravitational waves could be used to search for techno signatures and evidence of advanced life. In future papers, Sellers and his team will examine how smaller objects closer to Earth could be detected using LIGO data. Sellers stated that they will also be conducting an actual search for these signals using past LIGO data.
The detection of gravitational waves in 2016 has revolutionized astronomy by providing scientists with a new tool to study the universe, and searching for evidence of advanced civilizations is an exciting possibility that allows scientists to test theories about the behaviors and technological capabilities of such civilizations, such as building megastructures, sending worldships through the cosmos, and developing advanced propulsion systems.
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