Aliens have recently been in the spotlight, thanks to congressional hearings on Unidentified Anomalous Phenomena (UAPs), sometimes known as UFOs. While the prospect of aliens visiting Earth is intriguing, the most likely scenario is that aliens live on faraway worlds. We already know that potentially habitable planets exist and that intelligent life has evolved on at least one of them, so why not many more? However, after 60 years of looking for evidence of extraterrestrials “out there,” we have found nothing. So, what does this mean?
Although it may appear strange at first, an absence of evidence might provide information about the cosmos. We cannot simply conclude that alien civilizations do not exist because we have found no definitive technological radio signals from them. A lengthy silence after decades of research, on the other hand, tells us something about the possibility of aliens, or at least our odds of discovering them. That is the focus of a new study published in the journal Acta Astronautica, which examines the statistics of the search for alien civilizations thus far.
The study employs Bayesian statistics to assess the likelihood of discovering an extraterrestrial technosignal. One of the most important elements of Bayesian statistics is that it focuses on the likelihood of an outcome rather than the certainty of an event. It is the betting person’s interpretation of the universe. There are two major assumptions in this scenario. The first is that we know intelligent life can arise in the cosmos (at least if humans are intelligent), and the second is that we haven’t discovered any signals in 60 years.
The author adds a couple extra assumptions to this. The first is that sentient civilizations appear at random times and places. In other words, Earth has no special location in the universe and is just as likely as anywhere else to encounter aliens. The second is that if an alien society transmits signals into space, they are either directed in all directions, as human radio transmissions are, or are randomly directed. If, for example, most civilizations directed their transmissions toward the galactic center, we would be unlikely to detect them being 30,000 light-years away.
Given what we know, these assumptions seem acceptable. Or, at the very least, they are not as absurd as other assumptions. Given all of this, the author determined an upper limit for alien technosignatures. There is a 95% chance that no more than five galaxy-wide alien signals will be emitted per century. This indicates that Earth has a 50/50 chance of receiving a signal in the next 1,800 years. So, unless an alien culture deliberately directs a signal our way, our chances of detecting something anytime soon are slim.
That doesn’t imply we shouldn’t look any farther. However, if you need evidence for aliens in the near future, it may be worthwhile to watch the congressional hearings on UAPs after all.
Source : Grimaldi, Claudio. “Upper bounds on technoemission rates from 60 years of “silence”.” Acta Astronautica (2023).
