The Search for Extraterrestrial Intelligence, SETI, is a science program that has been ongoing for just over half a century and it has as its basic purpose the investigation of our galaxy and the wider universe in an effort to determine whether or not there exist communicating intelligence other than ourselves in other parts of the universe. So far, no evidence of the existence of any such intelligence has been found but the effort has not been on for that long and investigations continue. However, if it were announced tomorrow that investigators had definitely discovered the existence of intelligent life elsewhere in the cosmos, what would be the possible effect on earth society?
I suspect that the news that the search had achieved success would elicit different responses from different sets of people. Certainly, amongst those who had dedicated their lives to the search and the millions who had supported their effort, there would be a feeling akin to jubilation, only more so. We are not alone; life, and intelligent life at that, is a dynamic that replicates itself throughout the universe.
On the other hand, there would be those who would be terribly upset at such a success.
Religious bigots, who believe that Homo sapiens are a unique phenomenon, would be most upset. Having reduced God to Homo sapiens writ large, it would be very difficult for them to come to terms with the idea that perhaps we are not the only children of God; that God has diverse children scattered all around the entire universe.
But rejection would also come from other bigots, not necessarily religious ones.
Racists, for instance, who can barely tolerate the existence of humans slightly different from themselves, are not likely to receive the news with joyous hearts. All manner of denunciations would pour out. The whole thing is nothing but a hoax, designed by government, scientists, Christian fundamentalists, Islamic fundamentalist, take your choice, to undermine the essential basis of society as they conceive it. Even if they accept the validity of the contact, then perhaps the extraterrestrial folk are demons and we had all better prepare for Armageddon, or whatever it is that anyone's particular belief structure describes the final battle by.
Another group who are likely to be less than pleased by the news of success would likely be the movers and shakers of current terrestrial society: politicians, business leaders, religious leaders (who often do not believe in the stuff they preach that creates bigots, fundamentalists, etc. out of other folk), and the like. The question must arise in their minds: What does this do to my source of power?
But, between those who would rejoice at the news and those who would lament, would be the vast majority of humanity, who, if they took any notice, would probably go "great", or some other such comment, and proceed with their lives. Indeed, it is probable that half or more of the population would be totally unmoved: when one lives on a dollar or less a day, the fact that some other folk live a couple or more trillion miles away is unlikely to constitute a matter of great importance.
As to the practical effects on human society, as opposed to the reactions of the inhabitants of earth, the answer must be that it is unlikely to be very great.
The distances between the stars preclude any likelihood of substantial impact on the doings and goings on of human society. Consider, even if the extraterrestrials were our next door neighbours, so to speak, from Alpha Centauri, a conversation at light speed would take more than eight years to go round; if they came from even just farther off, Tau Ceti, say, it would take some 20 or more years. And, the farther out from us the putative communicators are, the longer it takes in order to carry on a meaningful conversation.
But, perhaps they would come over and take over the earth, or wipe us out, or something, now that they know we are here. Well, current science tells us that the speed of light is an insuperable barrier. If current science is right, then we have ample time to prepare before they ever get here. If current science is wrong, and science has been known to be wrong from time to time, and the extraterrestrials have discovered how to circumvent the speed of light, well...........
In truth, it seems more than likely that a SETI success would be no more than a seven day wonder for the vast majority of earth folk. It would be of more interest to the scientists who would, hopefully, get more grants to further the search.