A paper http://arxiv.org/abs/0901.3863 about minimum civilization density etc...Drake equation revisited

An interesting but flawed analysis.

The entire basis of the article is phony: a misunderstanding of the premise of SETI. The article is based on the assumption that the signal SETI is looking for is being broadcast blindly in all directions; this is not what SETI is looking for. SETI scientists know that such a signal would be essentially impossible to find since an omnidirectional signal broadcast blindly would either a) be too weak for our technology to detect and/or b) require an implausible amount of power to have any chance of being successfully detected by any other civilization at all.

SETI is not based on the assumption that ET will broadcast a signal in all directions blindly and that our radio telescopes will eventually stumble onto such a signal.

SETI is essentially based on the assumption that ET will be broadcasting a signal to US.

For SETI to have any fundamental chance at success, ET must be broadcasting a targeted signal specifically to the Earth, and it must be doing so over a very long period of time (possibly millions of years+).

There are many good reasons to believe that such a scenario is plausible. Even our own nascent astronomical technology is currently capable of detecting biosignatures in the atmospheres of planets orbiting other stars, for example. It's not difficult to imagine that an older civilization with more advanced technology would not only be aware of the existence of Earth, but also that it harbors life.

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"...probably more likely, is Lc < D where the maximum distance
of the signal is reached sometime after the CC has already become extinct
and ceased actively broadcasting."
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Under what plausible scenarios could a civilization long-lived enough to have broadcast from one end of the galaxy to another become extinct?

What conceivable "likely" events act to limit the lifetime of such a civilization?

In fact, I challenge anyone here to name a "likely" scenario in which a civilization actively broadcasting into interstellar space over a period of thousands of years would go extinct.


The point is essentially moot since the author never considers the very likely scenario in which the broadcaster is not the civilization itself but a probe or automaton essentially capable of indefinite self-sustained operation.

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"It is also assumed that no other factors such as colonization or interstellar travel are present."
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Given the timescales being considered (100,000 years+ for an electromagnetic signal to travel from one end of the galaxy to the next), it strikes me as rather phony to discount colonization or interstellar travel.

Human colonization of the solar system has arguably been underway since the first moon landings. Our unmanned probes sit on Venus, Mars, and as far as Titan. Bear in mind that this early colonization of our solar system began roughly half a century after the invention of the first radio transmitter.

In other words, colonization of space began roughly 50 years after mankind first harnessed radio waves!

In another 100 or 200 years does it not seem likely that a permanent human presence will have been established outside of Earth?

"For example, even assuming the average CC has a lifetime of 1,000 years,
ten times longer than Earth has been broadcasting, and has a signal horizon
of 1,000 light-years, you need a minimum of over 300 CCs in the galactic
neighborhood to reach a minimum density. For example, if there were only
200 CCs in our galactic neighborhood roughly meeting these parameters,
probabilistically they will never be aware of each other."

If the average CC has a lifetime of 1,000 years, assuming that conditions for star systems with enough metalicity to harbor Earth-like terrestrial worlds have existed for roughly 8 billion years, probabilistically no two CCs will ever overlap in time within the same galaxy in the first place, rendering the entire issue completely moot.

It strikes me as incredibly unlikely that the human species will exist for no more than another 1,000 years.





.....and besides, wouldn't an older civilization, anywhere from hundreds of thousands to millions of years older than our own, be aware of the potential density of communicating civilizations and the probability of contact?

IF successful communication is their goal, wouldn't it be prudent to assume that they would be completely aware of the problems, even moreso than ourselves, and that they would have devised reasonable methods of overcoming or at least dealing with these problems?

A self-sustaining autonomous probe capable of transmitting a signal for millions, possibly billions of years would make the issue of civilization density largely irrelevant.