After decades of planning, construction has finally begun on the Square Kilometer Array (SKA), which will be the world’s largest radio astronomy observatory when it is completed in 2028. The final version of the SKA will use thousands of dishes and up to one million low-frequency antennas located in South Africa and Australia to study the sky at radio wavelengths. It also will be a valuable new tool for SETI, because it will have enough sensitivity to intercept potential alien transmissions at large distances. Its search space will include many exoplanetary systems, some of which will be habitable. A subset of those may contain life, possibly even intelligent life.
The Fermi Paradox: Where is everybody?
For that reason, the SKA raises our hopes of finding an explanation for what’s often called the Great Silence. Also known as the Fermi Paradox, this refers to the puzzling observation that we have as yet seen no clear evidence for the existence of extraterrestrial intelligent life, despite the vast number of stars out there and the expectation that most of them have planets and moons. (And no, even though the number of UAP sightings has increased, the U.S. government still hasn’t found proof for alien spacecraft on Earth.)
A recent survey by Geoffrey Marcy and Nathaniel Tellis adds to the long list of non-detections over the past 60 years or so. The researchers went looking for transient light pulses at optical and near-infrared wavelengths in the Galactic Plane, which might have been evidence of extraterrestrial beacons. They found none.
Solutions to the Fermi Paradox
It could well be, of course, that we’re simply not using the right technology to detect extraterrestrials. I raised this possibility once at a SETI meeting hosted at Arizona State University. Imagine using a walkie-talkie in modern New York, then wondering why no one responds. The reason is simple: The conversation has moved to Facebook and TikTok. Extraterrestrials might be out there chatting away, but using a technology we haven’t even conceived of.
This is just one possibility. So many explanations for the Fermi Paradox have been advanced that whole books have been written on the subject. Among the most recent ideas is one proposed by Amri Wandel from the Hebrew University of Jerusalem in Israel, who suggests that planets hosting biology are relatively common, while those that host advanced technological life are rare. If so, it would be unlikely that technologically advanced civilizations would be close enough to each other to strike up a conversation. And there may be little motivation for extraterrestrial civilizations to explore all the habitable worlds out there if the odds of finding someone intelligent to talk to are low.
In that scenario, nobody would bother to explore exoplanets unless they detect a technosignature from another nearby world. Radio signals have been escaping Earth for only a century or so, and therefore have reached no farther out than 100 light-years. We shouldn’t expect a response from anyone farther than 50 light-years away, given the round-trip signal time. Finding an extraterrestrial intelligence (ETI) that close to us requires that such civilizations be very abundant.
Wandel’s assumption that biology is common on other planets, but ETI is not, is consistent with both the Rare Earth hypothesis and the Cosmic Zoo hypothesis. It is also what we would expect from the evolution of life on our own planet. We’ve only been able to build telescopes for a few hundred of the four billion years that life has existed on Earth. What are the chances that some nearby civilization is at exactly our stage of technological development? Pretty low, probably.
Further exacerbating the problem is the notion of a so-called Great Filter: If advanced civilizations do arise, they might not last for very long. There have been many intelligent life forms on our planet (for example, dolphins, apes, crows, elephants, and octopuses, to just name a few) for millions of years, yet only humans have graduated to the point where we can build space probes — and that only very recently. Unfortunately, some of the technologies associated with space travel can also be used for self-destruction.
Another possibility is that ETI civilizations are plentiful, but just don’t want to be detected. Perhaps they adhere to some kind of “Prime Directive” like in Star Trek, bound not to intervene in the evolution of young civilizations. Carl Sagan pointed out that if an ETI civilization is way ahead of us in technology, their actions would appear to us like magic. Just imagine a spy drone flying over a camp of Neanderthals. Aliens may consider Earth as some kind of nature preserve or zoo, which they observe from time to time without being observed themselves.
Still, accidents may happen, and they could inadvertently show themselves. Could that be an explanation for some of the UAP sightings now being investigated by NASA? New technologies may help us figure out what’s behind some of these mysterious events, but it’s an incredibly challenging problem, and no quick answers are likely.
Aliens may not act like humans
One thing we must be careful about is not to assume aliens will behave exactly like we do. In older SETI literature, especially that having to do with robotic interstellar Von Neumann probes, it was assumed that ETI would explore and colonize the galaxy — just as historical civilizations have done on Earth. Wandel assumes the opposite: ETI won’t be interested in colonization but only will expend its limited resources on interstellar exploration if a technosignature is detected. It’s difficult to say what humans will do if we become that technologically advanced. Perhaps it’s because I’m an astrobiologist, but I would want to explore all possibly inhabited worlds, technosignatures or not.
Once the Square Kilometer Array is online, we may get closer to a resolution of the Fermi Paradox.