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In my first response to Brin at Cato Unbound (and in one followup), I agreed with him that we shouldn’t let each group decide if to yell to aliens. In my second response, I criticize Brin’s theory that the universe is silent because most alien civilizations fall into slowly-innovating “feudal” societies like those during the farmer era:
We have so far had three eras of growth: forager, farmer, and industry. … In all three eras, growth was primarily caused by innovation. …
A thousand doublings of the economy seems plenty to create a very advanced civilization. After all, that would give a factor of ten to the power of three hundred increase in economic capacity, and there are only roughly ten to the eighty atoms in the visible universe. Yes, at our current industry rates of growth, we’d produce that much growth in only fifteen thousand years, while at farmer rates of growth it would take a million years.
But a million years is still only a small blip of cosmological time. It is even plausible for a civilization to reach very advanced levels while growing at the much slower forager rate. While a civilization growing at forager rates would take a quarter billion years to grow a thousand factors of two, the universe is thirteen billion years old, and our planet is four billion. So there has been plenty of time for very slow growing aliens to become very advanced. (more)
“Slow” Growth Is Cosmo-Fast
We need to note that the ability to detect our civilization at a distance has only been possible for less than half a century and the radiated RF power is going down as communications are shifting to lower power transmitters closer to the source. A million cell phone signals starts to look a lot like natural noise at a 100 light years.
That may mean that a more advanced civilization, still limited by general relativity and thermodynamics, may evolve into not wasting any significant amount radiation at any frequencies to space and be less detectable that we are with our old TV transmissions.
Even a civilization radiated to many star systems may communicate via very narrow beams at very high frequencies where all the energy just goes from one to another planet with none wasted in open space, again being undetectable.
Other scenarios require faster than light travel, handling energy densities way beyond material limits and/or lifeforms not limited by ordinary chemistry, all of which violate our existing understanding of the laws of physics and chemistry. Life is a very low entropy state and not real compatible with high energy densities postulated by super advanced civilizations.
The St. Petersburg paradox. If there's a 50% chance of one util, 25% chance of two, 12.5% chance of four, 6.25% chance of eight, etc. the expected utility is infinite, but whatever actually happens is finite. You just aren't sure how finite.