A few points. First, why are they looking for extra-terrestrial intelligence without any evidence that such life exists? Second, why do they think it's possible to distinguish evidence of extra-terrestrial intelligence from natural signals? Third, would finding such a signal really prove the existence of extra-terrestrial intelligence? Fourth, why do they choose to look for certain specific types of evidence for extra-terrestrial life?
The first answer is that they look at the vast complexity of the universe and find it improbable, given their assessment of the odds, that human beings are alone as the only intelligent life in the universe. This is very similar to ID proponents looking at life and finding it improbable that evolution alone can explain everything that we see. In both cases, it's an opinion based on a probability assessment rather than any evidence at all. For the record, I look at the odds, even assumming that the universe works via entirely natural processes and think it's entirely possible that we are the only intelligent life in the universe. At the very least, I take a look at the Fermi Paradox and apply Occam's Razor. Perhaps that's the perspective that allows me to see just how much SETI is based on faith and belief rather than evidence and why I see so much similarity between the two.
The second answer is that they believe that purposefully created things exhibit characteristics different enough from randomly generated natural effects that the artificial or created can be sorted from the natural. This is the same assumption made by ID advocates -- that biological features purposefully created can be distinguished from those biological features created as a part of a natural process. At it's core, it's an assumption that the natural can be distinguished from the artificial or created because the purpose and intelligence behind it's creation distinguish it from natural phenomena.
The third answer is that it wouldn't "prove" anything to scientific skeptic. Any signal of the sort being mentioned here could always be the product of some unexplained natural process. Just as the evolutionist can dismiss any example of irreducable complexity by saying that we just haven't figured out how it evolved yet, the ET skeptic could claim that any simple ET signal is the product of some natural process that we haven't discovered yet. So in both cases, even if you find the evidence, it doesn't prove the case. It simply increases or decreases the odds.
The fourth answer is that the ET signals they are looking for are based on their own human assumptions about what they'd do if they were designing such a signal and, more importantly, based on what they know natural signals look like. They are looking for signals that look "not nautral". The ID advocates are looking for biological features that are "not natural". The SETI entusiast can't tell you for certain what an ET signal would look like just as the ID advocate can't tell you for certain what a created biological feature would look like. It's the same idea. We know what natural looks like and know what some artifical or created things look like so let's find things that look "not natural" or like other things that we know are created.
Feel free to correct me if any of the above answers are straw men in your opinion.
If I want to put a real skeptic's hat on, I'd say that both are matters of faith. And by the standards of many ID critics here, SETI certainly doesn't look any more like science. So why does SETI get considered science and ID doesn't? Because while SETI involves faith and/or wishful thinking, it doesn't involve God.
ID points to complexity alone as evidence for a claim of an "artifical" source of design plan. It ignores the evidence of chemical and physical laws producing a multitude of complex systems.
That's like saying that SETI points to the vastness of the universe, alone, for a claim that extra-terrestrial intelligence exists. In many ways, they are playing the exact same odds game from the other side. The ID advocates look at the complexity of life and get a gut feeling that natural processes, alone, can't explain it. As a result of their odds assessment that errs on the side of improbability, they also have no trouble believing that ET intelligence doesn't exist and SETI is silly. Evolutionists, on the other hand, look at the complexity of life and get a gut feeling that natural processes, alone, can explain it. As a result of their odds assessment that errs on the side of possibility, they also have no trouble believing that the same thing has happened all over the universe and that ET intelligence just must exist.
Both are positions of faith. Neither position is based on any hard evidence that what's being believed in actually exists. Both sides are playing the odds as they see them.
ID simply says it is complex thus it is artifical. Why? It's artificial because it is complex. That's not science - that's fallacious logic.
What I think that really is is a straw man. What ID claims is that there are types of complexity that can't be explained naturally. They cite not simply complexity but irreducable complexity, and that's important. Evolution suggests a process by which we get from there to here via evolutionary steps. The reason why ID looks for evidence in complexity is that a complex process that cannot be explained as resulting from evolutionary steps would be evidence for intelligent design. It's the flip side of what SETI people are doing. They see the random complexity of signals as being natural and thus see a pure and simple signal as signs of artificial intelligence. But in both cases, skeptics can site a natural process we just haven't discovered yet and, in both cases, it's fundamentally a matter of looking for something that wouldn't be explained by existing natural theories. Whether it's a search for simplicity or complexity is irrelevant and a red herring.
Reduced to the same sort of straw man, I could claim, "SETI simply says it is simple thus it is artificial. Why? It's artificial because it's simple. That's not science - that's fallacious logic." Would that be a fair assessment of SETI in your opinion?
The difference is that SETI has a hypothesis, a set of assumptions about possible intelligent beings. It makes testable predictions.
ID has no such hypothesis and makes no predictions.
Hypothesis - life exists on one planet thus it may exist on another.
Support - An advanced technological life form exists on Earth, preliminary data requiring more research indicates the possibility that life has or does exist on other planets (Mars, Jupiter and Saturn moons - Titan, Io, Europa, certain meteorites) Study aims - if life exists on another planet and has advanced to a broadcasting technology, it may broadcast signals in a type similar to Earth - powerful, narrow band transmissions that DO NOT exist in nature. Therefore, scanning frequencies may produce a record of such signals.
Second, why do they think it's possible to distinguish evidence of extra-terrestrial intelligence from natural signals?
As stated in the article and explicitly at the SETI site, the requirements for artificial signals are specific to narrow band, high energy signals that do not occur in nature.
Third, would finding such a signal really prove the existence of extra-terrestrial intelligence?
It would give evidence to an artificial signal source. That would support the hypothesis.
Fourth, why do they choose to look for certain specific types of evidence for extra-terrestrial life?
It's called science - you make a specific prediction and a use very specific conditions for experimentation and data. Otherwise, it becomes unsubstantiated anything goes wishful thinking - like ID.
This is very similar to ID proponents looking at life and finding it improbable that evolution alone can explain everything that we see.
Wrong - as another poster stated, it's like painting a bullseye and firing a bullet at it (scientific research) and firing a bullet and then painting a bullseye around it.
The third answer is that it wouldn't "prove" anything to scientific skeptic. Any signal of the sort being mentioned here could always be the product of some unexplained natural process
It could, which is why there are other projects that take possible artificial signals and do further study. That;s another major difference between science and ID - critical study.
The ID advocates are looking for biological features that are "not natural".
Absolutely wrong - ID assumes that naturally occurring structures are too complex to be natural simply because they are complex. SETI at least compares known artificial signals to natural ones and makes distinction on verifiable and repeatable studies - ID can not claim that. If supporters do - they lie.
So why does SETI get considered science and ID doesn't? Because while SETI involves faith and/or wishful thinking, it doesn't involve God.
No, because SETI uses scientific method. ID does not.
What ID claims is that there are types of complexity that can't be explained naturally.
Every claim by ID can and has been explained by natural causes.ID supporters refuse to acknowledge the mountains of evidence provided by molecular biology, organic chemistry, and physics. Nature continually produces complex forms through the interaction of many natural laws.
Whether it's a search for simplicity or complexity is irrelevant and a red herring.
Not if the "search for simplicity" has explicit requirements formulated before the experiment and before any conclusions are made. ID fails utterly in that the conclusion is made first and the search is non-specific and changing - completely failing any objectivity or reproducibility.
Would that be a fair assessment of SETI in your opinion?
Absolutely not - as stated in many posts and articles, SETI uses the scientific method. ID does not - it has nothing of science to it. It paints a bullseye around it's conclusion. It uses a fallacious method and a fallacious non-conclusion.