Unfortunately, they are dealing with low probabilities. First I will address the possibility of our presence being detected. The probability that any civilization has detected our presence is very small. We have been emitting electromagnetic energy for about 100 years so the sphere of detection is 200 light-years in diameter. This is a very small part of our galaxy. The Milky Way Galaxy is 100,000 light-years across. Some studies have looked at the number of star systems within that 200 light-year sphere that are capable of having viable exoplanets and the number is small. Also, since signal strength drops off as the square of the distance, detection of any of our emissions becomes more difficult the further away an extraterrestrial civilization is. The best chances of detecting that we exist is via the transit method assuming that any civilizations capable of looking are in our orbital plane. Regarding our detection of emissions from other civilizations (what SETI is looking for), the problem of signal strength dropping off as the square of the distance will be a problem. The distances across our own galaxy, let alone the observable universe, are vast. From a signal to noise perspective, it isn't clear to me that SETI efforts are on a firm technical footing. However, I was part of SETI@home for a number of years. It was an interesting distributed computing effort.

"Absence of proof is not proof of absence. It's a big universe out there; it is very likely that we haven't looked in the right direction at the right time and in the right way to notice that we are not alone."

SETI is basically looking for life "as we know it". Beings with basically the senses and approximate level of intelligence (or higher) than we have. That makes sense. We don't have the capabilities to look elsewhere, yet.

But I've often wondered: what about "life as we DON'T know it"? We live on an insignificant rock in a narrow temperature range that averages about 15 degrees above zero Celsius, or about -283 degrees C. over absolute zero, zipping around an insignificant star in an obscure corner of a pretty mundane galaxy. Almost all of the real estate in that galaxy as far as we know is a lot hotter, colder and/or gassier than in the narrow envelope where we live. Taking that into consideration, it is pure hubris to think that humanity, or even carbon-based life as we know it on Earth, is the only game in town. We don't have the capability--yet--to ascertain if life exists on those other environments. We may possibly never know. But it is only our self-centered conceit to think, based on that, that it doesn't exist.

"Absence of proof is not proof of absence." I like that.

Of course not. The fake "scientific" theory known as Marxism did that. But it's a perfect example of a pretty theory of "how things oughta be", that was a proven failure, even 60 years ago when my high school civics teacher made us study "Das Kapital", and Star Trek was on the air, showing us an example of happy shiny space men living in a future cashless paradise, conquering the universe at "warp 9" (which, even at 9x the speed of light, would still be a five month voyage to make it to the nearest star).

While I am a life-long sci-fi fan, I much prefer to solve real-world problems with real science, rather than fantasies.

No. Warp is actually a cubed function. Warp 9 is 729x the speed of light. I can't believe I actually know this.

Excellent point! That's the beauty (and disaster) of fake "science". The moment someone pokes a hole in it, you can just say "well, what I meant to say was... (Climate Change!)"

Warp 9 was 9 times the speed of light when Kirk was battling Tribbles. I seem to recall, it was even mentioned in the first series. Then somebody who stayed awake in 3rd grade did the math, and suddenly somebody with an 8th grade grasp of math declared it a cube function. Theory saved!

Of course that's just my theory, but I will stick to it long after I am proven wrong, because that's what we "scientific" types always do!