In 1950, Enrico Fermi raised an innocuous but deeply unsettling question: in a galaxy filled with planets and star systems, why don’t we see any other signs of life? The question—now known as Fermi’s Paradox—has engaged astronomers, philosophers, and everyone in between for the intervening decades. Now, a team of researchers suggests a new reason we may not have seen intelligent life in our universe.
Their solution, published in The Astrophysical Journal, is straightforward: Extraterrestrial life may not need to be doing all that. The researchers explored whether a next-generation space telescope could spot solar panels on a nearby exoplanet. The team concluded that, should such intelligent life exist and get its power through solar energy, it probably doesn’t require the amount of energy necessary for us to spot it.
“The implication is that civilizations may not feel compelled to expand all over the galaxy because they may achieve sustainable population and energy-usage levels even if they choose a very high standard of living,” said Ravi Kopparapu, a researcher at NASA’s Goddard Space Flight Center and the paper’s lead author, in a Goddard release. “They may expand within their own stellar system, or even within nearby star systems, but galaxy-spanning civilizations may not exist.”
In the paper, the researchers explore whether silicon-based solar panels could be detected on an Earth-like exoplanet. They chose silicon-based panels because the element is more abundant than other elements used for solar energy, and (at least on Earth) is relatively cheap to mine and use in manufacturing.
The team imagined they were observing the Milky Way’s exoplanets with the Habitable Worlds Observatory, the marquee project of NASA’s Great Observatories program. The first phase of development on the next-generation exoplanet-focused telescope is slated for 2029.
The team modeled an Earth-like planet with different levels of silicon solar panel coverage and tested whether the Habitable Worlds Observatory could detect those signs of technology from a distance of 30 light-years. The team found it would take at least several hundred hours to detect the technosignatures, if 23% of that exoplanet’s land were covered in solar panels.
The team notes that only 9% of land coverage on Earth would be necessary to sustain 30 billion humans at a high standard of living. Nearly a quarter a planet’s land being covered in solar panels is, perhaps obviously, an extreme scenario and would be superfluous to energy requirements on Earth.
“Large-scale stellar-energy harvesting structures may especially be obsolete when considering technological advances,” said study co-author Vincent Kofman, a researcher at NASA Goddard and American University, in the same release. “Surely a society that can place enormous structures in space would be able to access nuclear fusion or other space-efficient methods of generating power.”
The study assumes an extraterrestrial civilization would make use of solar energy from its host star; of course, aliens might use any number of power sources, including those beyond the limits of our imagination.
But, specific power source aside, we may not see signs of intelligent life in the universe because space is big, and we’ve only had the tools to look—really look—for a few decades, or a century at a push. Our galaxy has been around for billions of years, and our universe for billions more. As pointed out by the SETI Institute, “the Fermi Paradox is a very large extrapolation from a very local observation. You might just as well look out your window and conclude that bears, as a species, couldn’t possibly exist because you don’t see any.”
The recent study makes a lot of assumptions about alien technology and its visibility, but modeling these scenarios is important; once the Habitable Worlds Observatory and other next-generation telescopes are in operation, the projects will have several premises with which to start their search.
