Robert Owen, <firstname.lastname@example.org>, forwards a proposal from Allen
Tough for SETI:
> Any extraterrestrial intelligence that we detect is likely to be far ahead
> of us in knowledge and technology, perhaps 100,000 years or more.
Probably much more, when you consider that life on earth began over 3 billion years ago. If it takes about 3 billion years to go from the start of life to a civilization like ours, then an alien culture "only" 100,000 years in advance of ours is actually the same age to within 0.003%. This would be an incredible coincidence. It is far more likely that any advanced alien civilization is tens or hundreds of millions of years more mature than our own.
> This means that we should vigorously pursue and support these three
> promising strategies for detecting near-Earth ETI:
> (1) implement several of the eight ways of searching for
> physical evidence of an alien object in the solar system
> or even on our planet;
> (2) invite contact through invitations on the World Wide Web;
> (3) Become sufficiently prepared for contact, thus encouraging
> ETI to respond.
> We should also pursue the most promising strategies for detecting evi-
> dence from many light-years away:
> (4) Try to detect astroengineering projects, high energy use,
> byproducts, or other distant evidence of a technological
> (5) radio and optical searches.
The problem with number 1 is that there are plenty of people who will claim that such evidence already exists, in the form of UFO reports, alien abductions, mysterious artifacts, construction of the pyramids, etc. All the vast literature of pseudoscience will be brought into the fray. Enthusiasts of all stripes will all come out of the woodwork, and the noise will overwhelm any signal that might be there. Maybe some fraction of UFO reports really are aliens; maybe some ancient artificats were built with their help. But I don't think our investigative methodologies are up to the task of producing a satisfactory or convincing affirmative answer from the kind of data that is available.
Numbers 2 and 3 also seem questionable. They presuppose that aliens are waiting for certain events before they contact us. Even if this is so, there is no evidence whatsoever that taking the recommended steps will make contact more likely. In fact, if we assume that the lack of alien contact indicates a desire to avoid altering our culture, then attempts to seek them out might make them even less likely to cooperate, since any communications in that context would have greater impact.
Number 4 is perhaps reasonable, but it still seems to assume a certain inconsistency on the part of the aliens. They are not the stay-at-homes of classical SETI, content to send out radio signals and passively observe the universe. They are out there, actively interacting with and manipulating the resources that are available, certainly a more likely pattern given the nature of life and evolution.
But for number 4 to make sense we have to assume that the aliens' engineering activities are avoiding earth and the solar system. Otherwise we would probably see the evidence with our current technologies. So we have this inconsistency that aliens are engaging in (hypothetically) observable astro-engineering activities on a large scale, but they are avoiding earth's vicinity despite the fact that there seem to be ample useful resources locally.
Of course it is not impossible that such a discrepancy may exist, and we are all familiar with the many hypotheses which have been created to explain this apparent difference in behavior. But it is still not what one might have predicted a priori. It has to be considered to cast doubt on the likely success of approach number 4.
This leads to number 5, the classical approach of looking for beamed or leaked signals. This really only makes sense if there are obstacles which make interstellar travel infeasible. We can't rule this out, but from what we understand it should be possible to travel to the stars, although it may not be easy.
Ultimately, it seems that there are three possibilities. Either there are no (advanced) aliens, in which case SETI is not going to work. Or there are aliens and they are trying to talk to us, in which case we have to wonder why SETI hasn't worked yet. Or, third, there are aliens and they are avoiding talking to us, in which case SETI is likely not to work until they want to talk. All in all it doesn't look like a very good bet at this point.