Here's the Drake Equation:
The term under question is the "f-sub-l" or "f(l)" term - the term describing the number of terran planets that engender "life."
I don't really care what sorts of values you want to apply to the f(i) and f(c) terms. Make 'em 100% if you like! And make L equal to 10 billion years if you like! Even add a "G" term at the beginning of the equation if you like, to reflect the number of galaxies in the universe. "Reasonable" values for R, f(p) and n(e) we can estimate from our observations of near-space.
But try as you like, you cannot escape the fact that f(l) is near zero!
And here's why...
Information Theory tells us that meaningful codes or programmes do not arise by chance. They need programmers, or designers! If true, then the DNA code and programme could not have arisen by chance. It needed a programmer or designer! Now it is just possible that this designer constructed more than one such design in our Cosmos, but I doubt it. Where's the evidence? I mean REAL evidence - not shadowy conspiratorial paranoic suspicions or Sci-fi flights of fancy. Real Evidence. It doesn't exist!
But even on a more basic level, begin with the following "a priori" principles:
Try starting a thought process beginning with these and resolve to not entertain contradictions in any of your logical thinking. Then see where it takes you. Spend a fair bit of time at it. At least several months. You might be surprised where you end up. (I'll entertain in several months - after we've survived the Y2K Armageddon - any responses which are the result of this mental process, and which come out to a conclusion contrary to the one expressed herein.)
We puny humans can already produce an interstellar signal which is easily identifiable as NOT random background radiation, and which is of greater energy density over a narrow beam and bandwidth than anything else in the universe. So we already shine out into the Universe (albeit only a few dozen light-years thereinto) like a bright beacon! Surely any civilization more advanced than us (and "reasonably," according to the thinking of those who believe in the possibility, there should be civilizations several billions of years advanced over us who a long time ago would have entered the "radio/SETI" phase we're now going through) has already been doing this for up to billions of years. The radio universe should be spangled with such signals almost anywhere we look, IF ANYONE ELSE IS OUT THERE! But it isn't. There's NOTHING! Nada. Rien. Nichts. Butkus.
Face it, folks. WE'RE IT!
The meaning of life, the universe and everything may be 42, but N <= 1!
So why would goofs like us participate in something like SETI@Home? It's because we KNOW SETI will have a null result, and we want to get the analysis over with quickly, so people can recognize this fact soon and to begin to think about WHY there was a null result. In other words, to come to their senses and finally abandon any thoughts of finding LGM out there, and get down to considering the REAL issues posed by the Cosmos! Like, why does the Cosmos exist with just us in it, who are able to ask questions about whether there's life elsewhere, only to find that the answer is NO?
We humans placed information on the Voyager craft announcing to the Universe who we are, what we are and where we are. So who will find this information? The likeliest candidate would be an earthling, who encounters the derelict spacecraft somewhere in interstellar space after (if ever) humans develop WARP drive for their spaceships. They'll most likely be retrieved back to Earth, and end up in some future avatar of the Smithsonian. They WILL NOT be found by LGM, Klingons, Vulcans, Romulans, Cardassians, Q entities, Vorlons, Minbari, Borg, Drazi, Centauri, Z'hadumians or anything else!
Sci-Fi is fun, but it's just that - FI!
Now, there is one unfortunate weakness in my strategy. That is, that a null result from SETI will likely be taken as meaning "ET is out there. We just haven't found him yet." And then this sort of costly research will continue ad infinitum.
This is the logical flaw of "Appeal to the Future." I.e. an idea is "obviously" correct, and some future discovery will prove it so! This validates the idea forever! But unfortunately, this IS a logical error, since it can be used to validate almost any outrageous idea.
Better to rely on strict, rigorous logic which is based on reasonable a priori assumptions like those indicated above (rather than interminable experiment in search of some mythical "holy grail" like ET), which PROVES beyond a shadow of a doubt that ET isn't out there!