If you envision science-fictiony science projects as children that come in generations, then the generation that gave birth to SETI is a pretty impressive generation indeed. The minds behind it are contemporary with (and sometimes, identical to) the minds that came up with ways to find black holes, with nanotechnology, with asteroid mining, with AI, with digital communications, and with dozens of other technologies we live with every day.
As aspiration, SETI is wondrous. I love it. Can't get enough of it, in fact. And you can't find a better spokesman for a fringey-science area than Seth Shostack, who is a seriously grounded guy and a major mensch (and a pleasure to listen to). And it's predicated on things like The Drake Equation, and on the grandest notion in all of science (and science fiction): That the universe might just be teeming with intelligent life, and no matter how far we grow, an infinite horizon will still lie before us.
But as science? It's kind of like that kid in your first grade class who looked promising, was ultra-cute and really smart, and then wound up sort of lazing through life living in his parent's garage and working on his guitar licks hoping he'll be the next Slash. SETI hasn't accomplished much. A few promising (and unreplicated) data points aside, they haven't found anything yet.
The interesting question for me is: Why? Or, as Enrico Fermi put it, the most important question we must face is: "Where is everybody?"
Fermi is one of a whole host of SETI critics that have groused about the project over the years (many of the critics are also supporters), and they bring up a lot of good points about problems with the project. There's one angle, though,that I've not heard attacked (the fact that I haven't heard it does not mean that it hasn't been done, only that if it has I'm ignorant on the matter). My objection to SETI (a project which I love), is this:
If intelligence is out there, and communicating with radio, and at the right distance for us to have picked up its signals in the last few decades, it is overwhelmingly probable that we would fail to recognize it as anything but noise.
It's not something you might expect most people to have known at the start of SETI (since it started back in analog days), but imagine, if you will, how Earth's history would look if you were an alien conducting his own SETI program.
First, you start hearing scratchy jazz and classical music records. Then, you begin picking up TV broadcasts. A decade later, those broadcasts begin featuring footage of nuclear war. Then, another sixty years on, the signals start to fade. There's less going on. Then, eventually, nothing. To your ears, it would sound as if we all died. But life on Earth is doing very well, better than ever, with amazing amounts of space activity, technological innovation, and more communications every day than you could digest in a thousand years...
...but almost none of it is going on in the analog radio space. We've gone digital. Digital signals have to be decoded. They're all just ones and zeros--signal/no signal. We've gone digital because digital signals are higher fidelity under most circumstances. We've gone digital because digital can transmit ANY kind of data, not just voice and video. We've gone digital because you can compress digital signals for faster transfer speeds. And we've gone digital because encrypting our communications makes them harder to tap.
Analog to digital. Digital to multiplexed. Multiplexed to compressed. Compressed to encrypted. Encrypted to quantum-encrypted. Bits to Qbits. And, to the listener who doesn't know the technology, every step sounds more and more random. At some point, even mathematical regression won't be able to disentangle the encoded signals from background noise without knowing the encoding scheme beforehand (right now we can detect that there are patterns in the signals we generate--this won't always be possible). In other words...
Any sufficiently advanced transmission is indistinguishable from noise.
I wonder if that principle right there isn't the real solution to the Fermi Paradox. It may just be possible that the universe IS teeming with intelligent, technological life, and we can't hear them...
...because we don't know the right computer language.