SETI stands for the Seek for Extra-Terrestrial Intelligence. Kindly note that the word 'radio' appears nowhere in that phrase, yet searching for synthetic radio transmissions from extraterrestrial civilizations seems to be near synonymous with SETI, http://carlkruse.org/2018/05/28/memorial-day-reflections/
as bolstered by way of the popular film "Contact" (based mostly on Carl Sagan's novel). Now there is nothing mistaken with radio SETI. The seek for radio waves has been well thought out and would seem to supply up the utmost chance for success. But, there are more ways to skin the SETI cat (because it have been), and after 49 years of searching primarily through radio, I suggest that some more methods be adopted and explored. Any a part of the electromagnetic (EM) spectrum is suitable and up for investigation, equivalent to optical SETI (looking for laser beams) or infrared SETI (searching for Dyson Spheres) or just in search of alien artifacts (as in the novel/film "2001: A Area Odyssey"). From that, we note that one can approach the study of UFOs and/or ancient astronauts as representing a form of SETI. Whatever investigation tells you that extraterrestrial intelligence (ETI) exists, or once existed, or doesn't exist at all (and a negative result is as important as a positive one) is SETI.
Why do SETI at all? That's an obvious first question. Thankfully, there are lots of good answers to that question. There's pure scientific curiosity for starters - exploring just for the sake of exploring. Then there's the more philosophical approach in that SETI helps to better determine our place within the cosmos. A negative answer is just as essential as a constructive reply in determining whether or not humanity is unique, prime of the heap, one of the great unwashed cosmic crowd, or the new boy on the block. SETI has a sensible side too in determining the existence of potential neighbors which may very well be sources of profit and/or threats to us. Clearly, a select few scientists, SETI fans, have long felt that SETI was, and is, price doing. Radio SETI is (as of this writing), a fairly mature science now forty nine years old.
Now if seven is a lucky number, then seven occasions seven must be even luckier, yet, some 49 years after the first radio SETI experiment (Project Ozma) was performed by Dr. Frank D. Drake, there's be no luck in detecting any sign of any other technological extraterrestrial civilization (forty nine years as I write this - it is even longer now). What does this suggest to us as a life form with an evolved technological civilization? The place are our 'kin' on the market among the many stars?
Firstly, it suggests that radio SETI isn't going to be quite as easy as first envisioned. The number-crunching back in these early days instructed that ETI with a suitable detectable technology (radio emissions or relatively transmissions) can be fairly common. Though solely a relative few of those haystack stalks have been sifted for that needle, it's changing into clearer that type of SETI is not going to be simple; N (the number of technologically radio communicating ETI within the cosmos) isn't going to be an especially large number. So, some constraints on the SETI idea and logic have come house to roost.
By way of the search to this point, it's clear (to me anyway) that there are not any Type III civilizations (able to harness the energy output of an entire galaxy) in any galaxy even remotely 'close' (in cosmic phrases) to us. If there were any Type 2 civilizations (ability to command the energy output of an entire star) nearly in our own galaxy it ought to have proved pretty apparent by now. There have been after all many false alarms, but additionally a number of cases that appeared like a positive signal was received. Alas, all have been one-offs and have never been picked up again. Without verification, those 'wow' signals remain enigmas, but not proof positive of extraterrestrial intelligence (ETI).