There is an initial question to ask related to the possibility of SETI finding alien life that is not asked - how many alien beings have technology we cannot detect because its superior or inferior to ours.
It seems likely that life developed at different times
It seems likely our technology would be primative to any space travelling beings.
Next their may be aliens who are our peers in many ways -
ie not space travellers - but have developed technologies we cannot detect that do a similar job to our radio waves etc
This would seem to rule out a big chunk of possible SETI contacts as being either too advanced to find or too primative or not on our wave lengths and so being undetectable.
I guess the other underlying question is who are you looking for and why ?
Also do aliens already know we are here and are they hiding from us ?
The article is interesting it starts
"The Universe seems like a lonely place.
We know - we're proof of it - that intelligent civilizations (yes, civilizations) are possible. Finding signs of other civilizations in the Milky Way galaxy is not such a simple matter, but we do have tools at our disposal. Based on our own technological capabilities, we can extrapolate what signals alien technology might emit, and search for those.
These signs are called technosignatures, and our efforts in the search for extraterrestrial intelligence (SETI) revolve around them, particularly in radio wavelengths."
However there may be other ways of living and being outside our current society and understanding
We consider ourselves advanced but we could be very primative.
Each human age or epoch has somewhat considered itself to know all
We leave some "primative" humans on earth issolated on their islands or in the jungle because of the damage we could do and have done to others from our contact and consider ourselves advanced for doing so.
Could other beings be doing the same to us ?
Many of us are unwilling to talk to other humans we consider strange.
Alternatively our governments could be hiding their existing knowledge of alien life and technology from us, and SETI could just be a smoke screen to "show" nothing has been found
Such a strategy would be no great surprise if it were true. Governments hide much lesser secrets and continue to do so.
So what evidence exists to say aliens are more advanced and are hiding from us making SETIs role questionable?
The universe is about14 billion years old.
Some advanced life probaly exists that may be a billion years old.
Imagine what knowldge could have been gained over say just 1 billion years of existence -
meaning that such Beings could be able to travel and communicate at speeds or ways we can only vaguely if at all comprehend.
Perhaps they could split their consciousness in some way so as to watch their own arrival at a destination and so deliberately avoid contacting us.
In any event why would someone who could fold time and space to arrive instantly, or travel at warp speed, talk to most or any of us? We would be like children or less than children
Quantum entanglement highlights how space and time may make no difference to communication and may even indicate the possibility of foreknowledge of an event.
Quantum entanglement shows it is possible that information can travel faster than the speed of light. However we are not yet clever enough to work out how to get there and use it
It's a pipe dream that violates the laws of physics, and not even quantum mechanics can give us a way out.
www.forbes.com
There is also some evidence of a higher consciousness - for example random number generators can be used to indentify and predict that an unknown major event is about to happen. This indicates something is either malfuntioning in multiple unconnected locations or some foreknowledge exists.
It has also been shown that after a major event has happened, the event continues to effect the random number generator and it continues for an extended time to "malfunction"
Ideas and Insight From National Geographic
blog.nationalgeographic.org
So SETI may be looking for a needle in a field of haystacks that have needles it cannot see.
There could be other dimensions of existence that we cannot yet see or meaningfully detect let alone communicate with or understand
Travel and communication could be instant for some life forms and time and space as we understand it may not exist. So distance may be meaningless for such beings making SETI research very limited to only our alien peers who have developed similar technologies
Just because we dont understand or cannot comprehend does not mean its not possible
200 years ago people did not dream of jet travel, nuclear power or that exploring space was possible, let alone being able to communicate instantly over 1000s of miles or doing so meaningfully with other life forms here on earth.
We still cannot talk to the animals, whales birds or plants on earth so why would advanced life that can reach earth in a few days, months or years or even instantly talk to us or reply to SETI signals ?
See the article below
I wrote an essay several years ago titled “SETI’s Mission Impossible.” I argue that the complexity of any extraterrestrial life form that could evolve to the point that it could produce radio signals which could be detected by radio telescopes on Earth is virtually impossible. Using human beings as a proxy, I challenged the famous Drake Equation used to estimate the likelihood of civilizations on other planets with capabilities similar to ours – that is to the point where they could send out radio waves. As opposed to the Drake Equation’s seven variables, I identified 57, but used only 40, which are assumed to be sequential and thereby calculated as a factorial. The end result for succession of 40 conditions in order for life like ours to exist on another planet would be 40!, which is 8.16^47. That is to say, the chances of another alien civilization like ours is a little under one in 8.16 trillion, trillion, trillion, trillion. So, clearly, the Search for Extraterrestrial Intelligence is all but impossible.
For those who might be interested in this essay, see
https://www.academia.edu/32892272/SETI_S_Mission_Impossible_05-07-2017.pdf