There are two reasons for yet another SETI post: (1) we like the subject; and (2) it drives the creationists crazy. You know what SETI is. Those initials stand for search for extraterrestrial intelligence.
Our post’s title, as most of you recognize, starts with Enrico Fermi’s question, which is what underlies the Fermi paradox. Briefly stated, Fermi was asking this: If there are other Earth-like planets in the galaxy where life evolved, some of it intelligent, with the time to develop interstellar travel, then why haven’t they been here, and why don’t we see any sign of them?
We just found this at PhysOrg: Self-replicating alien probes could already be here. It says, with a bit of our bold font added for emphasis:
Mathematicians in Scotland calculate that “self-replicating” alien probes could already have explored our solar system and may still be here but undetectable to our current technologies.
Drs Arwen Nicholson and Duncan H. Forgan from the University of Edinburgh had previously calculated that if a Voyager-sized probe passing through the galaxy picked up speed using slingshots around stars it could travel 100 times faster than otherwise.
Rockets built with our current technology travel at only about one-tenth of 1% of the speed of light, so they’re talking about goosing that up to 10% of the speed of light. That’s a useful velocity — it would let us travel to other planets in the solar system in mere days instead of years. But the chaps from Edinburgh have loftier goals in mind. They hypothesized self-replicating probes in their computer models to calculate the timescale for such probes to disperse themselves radially across space.
Their published paper is in the International Journal of Astrobiology, but you can read it online here: Slingshot Dynamics for Self Replicating Probes and the Effect on Exploration Timescales. We’ll ignore the details of their acceleration technique (and self replication technique, and inter-probe communications) and focus on the big picture. PhysOrg continues:
In all the scenarios the scientists looked at, exploration timescales were reduced when the probes were self-replicating, and they concluded that a fleet of self-replicating probes could travel at only 10% of the speed of light and still explore the entire Galaxy in the relatively short time of 10 million years. This is a tiny fraction of the age of the Earth and the scientists say the results reinforce the idea of the “Fermi Paradox.”
We’ve seen that estimate of 10 million years before. It was probably in an old Analog article we read years ago. In our more ambitious projection, which you can see here: What Are We Learning from SETI?, we used a hypothetical speed of one-third the speed of light, and estimated that if stars with habitable worlds are plentiful and not that far from each other, then humans could populate the galaxy in only one million years. But who cares about our projections? Let’s read on about the Edinburgh work:
Dr Forgan said that the fact that we have not detected or seen any evidence of alien probes in the solar system suggests there have been no probe-building civilizations in the Milky Way in the last few million years or that the probes are so hi-tech we are unable to detect them.
Those are two possible reasons. The article ends with one more:
Another possibility is that probes could be programmed to make contact only with civilizations that pass a set measure of intelligence, which could be the ability to detect the probes.
So there you are, dear reader. Now you can let your imagination loose. Where are they?
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