The search for extraterrestrial intelligent life
However, radio telescopes were able to detect signals within the electromagnetic spectrum that originated from beyond the solar system. In 1959, physicists Giuseppe Cocconi and Philip Morrison suggested advanced civilizations might exist and that it might be possible to communicate with them. Specifically, the first paragraph of their article in the journal Nature stated:
After discussing which frequencies might be the most useful, they concluded:No theories yet exist which enable a reliable estimate of the probabilities of (1) planet formation; (2) origin of life; (3) evolution of societies possessing advanced scientific capabilities. In the absence of such theories, our environment suggests that stars of the main sequence with a lifetime of many billions of years can possess planets, that of a small set of such planets two (Earth and very probably Mars) support life, that life on one such planet includes a society recently capable of considerable scientific investigation. The lifetime of such societies is not knows; but it seems unwarranted to deny that among such societies some might maintain themselves for times very long compared to the time of human history, perhaps for times comparable with geological time. It follows, then, that near some star rather like the Sun there are civilizations with scientific interests and with technical possibilities much greater than those now available to us.
To the beings of such a society, our Sun must appear as a likely site for the evolution of a new society. It is highly probably that for a long time they will have been expecting the development of science near the Sun. We shall assume that long ago they established a channel of communication that would one day become known to us, and that they look forward patiently to the answering signals from the Sun which would make known to them that a new society has entered the community of intelligence. What sort of a channel would it be?
The reader may seek to consign those speculations wholly to the domain of science-fiction. We submit, rather, that the foregoing line of argument demonstrates that the presence of interstellar signals is entirely consistent with all we now know, and that if signals are present the means of detecting them is now at hand. Few will deny the profound importance, practical and philosophical, which the detection of interstellar communications would have. We therefore feel that a discriminating search for signals deserves a considerable effort. The probability of success is difficult to estimate; but if we never search, the chance of success is zero.
Hence the search began. Amongst the early searchers was Frank Drake, who eventually postulated an argument that attempts to identify the number of intelligent civilizations in the Milky Way based on probabilities. This became known as the Drake equation (note: click on image to expand it):
As you can see, the Drake equation has a lot of variables, and it is beyond the scope of our course to discuss them in detail. But if you are intrigued and are willing to invest ~7min, we recommend you watch this excellent Ted Talk. In the assignment for this module you will be asked to do some sample calculations yourself.
The main point here is that unfortunately the Drake equation does not have an agreed upon answer because uncertainty within the variables allows for a wide range of conclusions. Nevertheless, radio astronomers keep searching. The most prominent organization conducting the search is SETI (Search for Extraterrestrial Intelligence). The most prominent result of that search to date has arguably been the WOW! Signal, detected in 1977.
This video has a nice detailed explanation of it. Unfortunately, not only has the WOW! Signal not been a link to extraterrestrial intelligence, in 2016 is was proposed that the signal originated from inside the solar system from the hydrogen cloud surrounding two comets that had not been detected during the time of the signal.
So, in short, we have not detected an unequivocal signal from an advanced civilization. This lack of positive results, otherwise known as the question “Where is everybody?”, is generally referred to as the Fermi-paradox, after the physicist Enrico Fermi. It should be noted that he was not the first to ask this and that he asked this question in 1950, several years before the searching began in earnest. Nevertheless, he is generally credited with it.
And there is no agreed upon answer to the Fermi Paradox. A large number of answers have been proposed. Alien civilizations may simply not exist. It has been proposed that alien civilizations are quite rare, that they tend not to spread throughout the galaxy, that they only broadcast signals for a short time or use frequencies we don’t. A number of explanations suggest a series of unhappy endings for those civilizations, ranging from natural catastrophes to some form of self-destruction. In fact, the latest proposal suggests that life on alien worlds is extinguished quickly due to runaway heating or cooling on their fledgling planets.
And of course it has been suggested that they are simply ignoring us, or that they are here, but that they are not acknowledged. That last explanation is generally in the realm of UFO conspiracy, which tends to rely on a large number of people being in the know. Sadly, if the truth is out there, we, the authors, are not part of the privileged who know.
So we will stick to the widely accepted answer that there is no evidence of extraterrestrial intelligence and look at the question “What are the required ingredients and conditions for life?” next.
