Some scientific adventures are as fascinating for the casual observer as they are for an engaged specialist. One such is the Search for Extraterrestrial Intelligence (SETI), driven by the premise that if there is life on another planet (especially in the form of intelligent beings), then it could have reached a level of technological advancement equal to ours or perhaps greater. And just as we have tried to find such life out there, these alien beings may be looking for us as well.
Across the vast distances of the cosmos, electromagnetic-wave signals are our best bet to identify ourselves and others. They range from radio signals concentrated in a narrow frequency range to pulsating wideband signals.
Researchers also need to have the proper means and techniques to differentiate naturally occurring waves, like radio noise from the magnetosphere of Jupiter or the environs of stars, from those transmitted from more interesting sources. Waves from space are also distorted en route to the earth and whatever information they carry may not survive the journey intact.
Listening to neutrinos
This is why scientists have also proposed looking for neutrino signals. Neutrinos are subatomic particles. After photons, the particles of light, they are the most abundant particles in the universe. They also interact very weakly with matter, and can move relatively untouched through the same media within which electromagnetic waves would diffuse. Given these properties, it’s not far-fetched to assume that some extraterrestrial intelligence is also trying to communicate with us with neutrinos, in addition to radio waves.
There is another basis to this assumption. Scientists are still trying to understand some instances of radioactive decay that involve (i.e. are mediated by) neutrinos. Specifically, these instances of radioactive decay wouldn’t have happened unless they involved neutrinos from some source in outer space.
Mathematically, a radioactive decay obeys an exponential decay law. That is, the decay rate is proportional to the number of atoms there are. But in a 2017 experiment at Purdue University, scientists found that the decay rate of radioactive manganese declined sharply. They found that this could be explained if the rate was “responding to small changes” in the ambient flow of neutrinos.
Based on their experiment, the scientists proposed setting up such decay experiments at different sites around the world, and analyse the data collected for signs of a non-uniform neutrino flux – which could in turn be associated with events in outer space. They called their proposal NU-SETI, and wrote:
“Even though we do not yet understand theoretically why some radioactive decays are particularly sensitive to neutrino-induced perturbations, the premise of our NU-SETI proposal is that this is an experimental fact, which an advanced extraterrestrial civilisation might clearly understand and could be using to communicate with us. Given the … benefits of communication via neutrinos compared to radio waves, NU-SETI thus represents a new technology which could thus expand our reach in search of advanced extraterrestrial civilisations.”
Messaging aliens
All this said about finding alternative ways to hear from intelligent alien life in outer space, there are also schemes to message them instead. They are collectively called Messaging Extraterrestrial Intelligence (METI). While the SETI era began in early 1960, two famous examples of METI followed in the next decade.
In 1972 and 1973, NASA launched the Pioneer 10 and 11 spacecraft to study the outer Solar System. Each spacecraft carried a plaque depicting the male and the female human bodies, a property of hydrogen atoms, cosmic landmarks that could help locate the earth, and an image of the spacecraft itself.
In 1974, a group of scientists (including Frank Drake and Carl Sagan) drafted a graphical message and encoded it into radio waves that were then broadcast by the Arecibo Telescope in Puerto Rico. The waves were aimed at the M13 globular cluster, a clump of several lakh stars around 25,000 lightyears away.
METI has received a boost in the last few decades after the launch of satellites and astronomy programmes to find exoplanets orbiting other stars. Based on these efforts, scientists have been able to find worlds that could potentially host life. These worlds also become potential targets for METI efforts, rather than having to issue powerful broadcasts into a vast region of space.
The Great Silence
While it has been more than six decades since we began listening for signs of extraterrestrial intelligence, we have not been able to break what has come to be called the ‘Great Silence’ of the universe. It could mean that there is no intelligent life beyond the earth – or that we are missing what an intelligence might be broadcasting. We need to eliminate many such alternative possibilities before we can be sure that our questing efforts suffice. For example, an alien community may be too far on the other side of the Milky Way galaxy or indeed too far away for their signals to reach us in a single lifetime. Or the aliens may just be listening and not broadcasting. And so forth.
Performing SETI or METI activities is also a herculean task because we only have a few indirect methods at our disposal to traverse the long distances of space, setting aside the fact that we have no certain sense of what exactly we are looking for or what we should expect to find. Nonetheless, efforts on this front have expanded from the use of radio signals to optical telescopes to laser light to (prospectively) neutrinos.
An earthwide effort
As with the Arecibo and Pioneer plaque messages, SETI and METI practitioners also need to study different messaging options and choose based on how they are most likely to be intercepted or received in specific parts of space, or on specific worlds. They need to pay attention to the language and the content while also considering the properties of the medium of transmission.
Some METI efforts have proposed for physical structures or artefacts built by aliens. In 2015, scientists reported that light from the star KIC 8462852 (a.k.a. Tabby’s Star) – some 1,470 lightyears away – exhibited a periodic dimming pattern for which they couldn’t discern a natural explanation. One hypothesis is that some alien structure is obstructing our view of the star.
Finally, SETI and METI programmes have joined hands for a host of scientific (as well as social) initiatives designed to bring together experts from the natural sciences, the social sciences, and the humanities to conduct research and public outreach programmes. Their aim is to increase both our technical understanding and the literacy at large of human longevity and sustenance on multigenerational timescales. Of late, we have also had to countenance the interstellar aspirations of humankind, motivated as much by Elon Musk’s aspiration to ‘colonise’ Mars as by a new space race to establish bases on the moon.
All these efforts demand scholars working as a global community to understand what life is, where it can be expected to exist, what forms it can take, and how we can identify it.
Qudsia Gani is an assistant professor in the Department of Physics, Government Degree College Pattan, Baramulla.
