"Where is everybody?" the Italian physicist Enrico Fermi once asked, when faced with the apparent contradiction between the high probability for the existence of alien life and the lack of any conclusive evidence for the existence of extraterrestrials.
Over the years, several solutions to the "Fermi's paradox" have been put forward, including one that points out that the universe is staggeringly huge and that Earth and its denizens are mere specks of dust floating in one of its billions of galaxies. For the pessimists, though, the lack of any clear extraterrestrial signals is evidence that we might just be alone in the vast and cold void of the universe.
Two new studies, based on observations conducted by two separate teams, seem to bolster the pessimists’ case. The observations, made using the Keck 10-meter telescope in Hawaii and the Green Bank observatory in West Virginia, found no evidence that aliens exist — or if they do, that they are trying to communicate with anyone.
The first study details observations of 692 stars (belonging to all spectral types) made by the Stephen Hawking-backed $100 million Breakthrough Listen project during the first year of its operation. The project, which used the Green Bank telescope to scan these stars in the 1.1 gigahertz to 1.9 gigahertz frequency — believed to be the most promising bandwidth in the hunt for ET — did find 11 promising signals, but detailed analysis indicated that it is unlikely that any of these signals originated from artificial extraterrestrial sources.
“The basics of searching for signatures of extraterrestrial technology are quite simple. Artificial signals can be distinguished from natural processes through features like narrow bandwidth; irregular spectral behavior, pulsing, or modulation patterns; as well as broad-band signals with unusual characteristics. However, human technology emits signals (known as radio frequency interference) similar to the ones being searched for. This means that algorithms must be designed to ensure that signals are coming from a fixed point relative to the stars or other targets being observed, and not from local interferers (including Earth-orbiting satellites),” Breakthrough Listen explained in the study. “From these results we can infer that fewer than ∼ 1 percent of stars within 50 pc possess transmitters emitting narrow-band radio signals between 1-2 GHz a t a level equal to Earth’s brightest transmitters in the same band.”
The other study, accepted for publication in the Astronomical Journal, took a different approach. It sifted through high-resolution spectra of 5,600 nearby stars — at least 2,000 of which are warm, Earth-like planets — to look for laser emissions in the 3 kilowatt to 13 megawatt range.
Scientists have previously hypothesized that technologically advanced aliens could be using some kind of “directed energy” systems (read lasers) to either broadcast their presence or to propel their spacecraft. If so, Earthbound scientists should be able to detect these signals.
However, analysis of data collected by the Keck Telescope’s high-resolution spectrometer over the past decade failed to reveal any unusual laser bursts.
“Of course, one might wonder if an advanced civilization could fool us by purposely beaming laser emission lines having wavelengths consistent with those that arise naturally in chromospheres of stars,” the researchers wrote in the study. “It would be difficult for us to distinguish such purposeful, nefarious camouflage from naturally occurring chromospheric lines. Indeed, all stars exhibiting emission lines in their spectra could be interpreted as laser emission from shy civilizations attempting to hide among the chromospheric weed.”
So, to get back to the initial question — where is everybody? Even if we presuppose that there are several intelligent alien civilizations capable of beaming out signals to the universe, and even if these signals are continuously washing over us, it is possible that we might still lack the technology to detect them.
The other possibility, of course, is that intelligent civilizations are either extremely rare in the universe or extremely short-lived.
Either that, or they don't exist.
“A common suggestion is that advanced civilizations would be thousands or millions of years more advanced than humans. If so, they would likely know of our existence and our technological capabilities (and limitations),” the authors of the study wrote. “We rule out models of the Milky Way in which over 0.1% of warm, Earth-size planets harbor technologies that, intentionally or not, are beaming optical lasers toward us. We may begin to wonder if arguments along the lines of the so-called Fermi paradox have some merit.”