So, what are the chances that we’re going to come into contact with intelligent life that didn’t originate on Earth? Well, if you take the vastness of the universe as a guide, it seems pretty unlikely that Earth is the only place to house intelligent life, as recently stated by NASA head Bill Nelson [3]. The more pertinent questions are: where are they, what level of development are they at, and, given the time taken to send and receive signals across a vast galaxy, are they still around?

Communicating Extra-Terrestrial Intelligent (CETI) civilizations have been studied for a while now. Among others, the Search for Extra-Terrestrial Intelligence (SETI) institute [4] has been scanning the stars for alien life for decades without clear success, although they provide a great deal of data and training for exoplanet researchers.

Yuri Milner’s Breakthrough Listen Project [5], supported by the late, great, Prof. Stephen Hawking, now uses various telescopes and the SETI institute to search for CETIs. Its scientists are currently interpreting received radio signals, and grappling with issues in dealing with distant signals and radio interference [6].

By watching the light from a star dim as a planet passes in front of it, researchers are able to learn about that planet [7]. A lot of searching for life on faraway planets involves taking a close look at their atmospheres, and looking for chemicals like chlorofluorocarbons (CFCs) [8], such as those historically found in hairspray, which could indicate environmental damage caused by a technologically capable civilization. The interesting point about CFCs is that they would likely be present in an exoplanet atmosphere up to 100,000 years after use, much longer than short-term biomarkers like oxygen, making them a useful tool for detecting long-extinct civilizations, where oxygen is no longer present in the atmosphere.

Ever-larger and more powerful telescopes have increasingly allowed scientists to search our corner of the galaxy for Earth-like planets, [9]  but are aliens already watching us? Well, it appears that life on Earth could have been viewed from 1715 star systems within 100 parsecs of the Sun since the dawn of early human civilization. That means that CETIs could view our development, as several of these systems host known exoplanets.

Radio-waves from Earth have already passed through 75 of our nearest star systems. This means that the inhabitants of nearby exoplanets with a similar technological capability to us could potentially be able to see and study Earth in a limited way as we pass across the Sun, even tracking post-industrial revolution changes in our atmosphere’s CO2 levels.

NASA recently proposed a new framework for communicating with scientists and the public about the search for new lifeforms [10]. This is particularly important in the wake of social media, when practically any discovery can be bent and twisted out of all sense to produce sensational news articles. The suggested protocols would help scientists show their findings to an understandably intrigued public, while retaining the sense and integrity of the information they’re sharing. Crucial, in an age in which first contact with other civilizations could potentially occur, and be the source of wide-spread panic [11].

But where are all the aliens, now? Taking life on Earth as a guide, scientists estimate there could currently be anywhere from tens to hundreds (depending on the model used) of CETIs in our galaxy [12]. If these were spread uniformly across the galaxy, although there’s no particular reason why they would be, this would mean that the nearest CETI would be thousands to tens of thousands of light years away, rendering communication anywhere between tricky to practically impossible at our current level of technological development.

Could there be aliens already here? Ok, we’re delving a little more into the realm of not-entirely-baseless sci-fi, here. The term unidentified flying object (UFO) was coined by the US military in the 1950’s to describe unexplained (at least to the general populace and those without sufficient security clearance) moving objects in the sky.

US Congress recently commissioned an unclassified report on UFOs, which was released in mid-2021 amid a flurry of expectation and disappointment [13], as the preliminary report reads like a nine-page shrug of the shoulders [14]. To paraphrase the text: hundreds of pilots and ground spectators have seen things in the sky that move weirdly and maybe shouldn’t be up there, but mostly eye-witness reports aren’t a lot to go on. Two US Navy pilots recently went on record describing a white object in the sky that mirrored their movements while flying, but recordings of such events are scarce [15].

In 2020, a 3-m tall monolith was discovered in the desert of Utah, only to be removed a few days later. Talk of space travellers resurfaced, as similar structures were also erected in California and Romania [16], although these appear to be art installations rather than extra-terrestrial structures. If nothing else, this shows that if aliens do decide to visit, they should arrive in giant monoliths, as this is clearly an image of alien tech that we’re very comfortable with. Kubrick would have loved it.