Sorry, SETI, ET not phoning
Yesterday I attended Seth Shostak's standard talk about the work at the SETI institute. I know others from the institute such as Frank Drake and Jill Tarter who inspired the Jodi Foster character in the movie Contact. I wanted to see what was new. (Once, by the way, I went on an eclipse cruise where Drake and Tarter were passengers. On a dive boat, somebody talked about the movie Contact, so I told them that Tarter was on the ship, and she had inspired the character. The woman was amazed and asked, "You mean she met an extraterrestrial?")
I have a lot of sympathy for this cause, for the search is important and the payoff extremely so. But I must report a serious lack of optimism. Read on to find out why...
There are two ways you might detect remote intelligence. You could detect their deliberate, "Here we are, Hello there!" signals or you might detect their general communications or activities not intended as a deliberate signal.
Problem is, it's hard to imagine that an advanced civilization, trying deliberately to signal us, would be incapable of making a signal that would have been seen by our first cursory look. Even with our meagre technology, we can build a laser, for example, that would pulse brighter than the sun (for a nanosecond) if aimed at a star. Space is vast, but the number of stars within a few hundred light years is small, and a "Here we are" project would not broadcast an omnidirectional signal. Instead, it would send powerful signals aimed right at all suitable stars. What we are capable of doing (the nanosecond pulses) could be detected by people looking with telescopes -- and the SETI teams are doing just that, so far with no success. But you don't have to imagine a little more technology or a little more will creating a much more visible signal. Indeed, it's not too far beyond our abilities to have fired off a nuclear powered space probe that could get far enough away from our star to be easy to resolve as it blinks.
Indeed, in the "Cow Seti" proposal, a scheme was devised that should be visible to the naked eye, if sent by aliens who wanted to be seen by the naked eye.
Now we don't know the capaibilities of an advanced alien race. But it sure seems likely that if they wanted to make sure we could see them, we would see them. Or hear their deliberate radio. Unlike we, who know little of what abilities they might have, they know all about the likely abilities of a lower-tech society. It's possible they are not interested in meeting creatures at our level, and are blasting something very visible to some future technology. In which case, hunting deep with our current technology is a waste. To give credit, the search for these signals is not complete.
So if they aren't sending a deliberate hello we can see, we can still hope for their accidental signals. Problem is that while universal claims about other beings are unwise at best, one universal claim that makes sense is a desire for efficiency. Humans, with just a century of radio under our belt, are quickly moving towards becoming radio invisible. We've learned that small, low powered transmitters, spaced close together are far better than big, high power omnidirectional ones. Where we must go long distance, directional signals are the obvious win. Not only do general broadcasts waste power, they interfere with other broadcasts over a wide area for no reason. (There is one exception in radar, but radar is very low information.)
Worse, our most modern radios, such as ultrawideband and CDMA, would have seemed like noise to the radio engineers of 50 years ago, if they could have picked them up at all. If we couldn't detect even our own radios after a few decades, it's a tough slog to detect the radios of beings we presume have a great deal more technological ability than we do.
Eric Drexler and others proposed that while we might not see their signals, we might see their works. A powerful civilization needs energy, and would eventually start using up all the energy of their stars, building what's known as a Dyson sphere (proposed by Freeman Dyson) around it. If this were happening, stars would be going dim to our telescopes, and more to the point, they would be going dim in growing, roughly spherical patches in galaxies around the universe. But Drexler looked, and could not find evidence of that.
I applaud new ways of looking for evidence, such as Drexler's search, or the scans for photon pulses. But I fear an approach should either generate immediate success (because they are trying to be found, and will be good at it) or be dropped after the first pass. The sort of long, painstaking search invovled in UCB's Seti-at-home screen saver project, while cool, effectively presumes that ET is trying to signal us, but is not very good at it and they can't make a signal which is obvious to our technology.
If there is an ET trying to signal us, I suspect it will be blindingly obvious once we reach whatever level of technology is needed to see their signals at all.
Of course, my judgement of the most workable answer to Fermi's Paradox is that we're quarantined by aliens with a Prime Directive not to interfere. The SETI crews will never buy into that one, becuase it makes their plight particularly sad. They would be looking for signals from ETs that are deliberately hiding them from us, a game the SETI teams would be unlikely to win. The reason the Prime Directive is a palatable answer to Fermi is that it doesn't require that some problem in getting a signal to us occur for every possible alien race in the history of the universe. All it requires is that the particular race that's close to us follows this rule, and hides the others from us.