Really Wild Stuff

Where Are They?

The Fermi Paradox - if intelligent life is common, and star travel is possible, others should already be here.

Ward and Brownlee's Rare Earth posits that intelligent life involves many more accidents than are acknowledged by the Drake equation, including statistically unlikely "missing accidents" such as nearby supernovae. We are fortunate to be here - and it may have been billions of years since there was another planet populated with space-faring intelligence in this galaxy.

• NOTE 2019 - the solar system most likely formed in the bubble of a Wolf-Rayet star, according to the Origins project at the University of Chicago in 2017. The probability of this seeding stellar/planetary systems is significant, better than 10%

But if an intelligence is space faring, what keeps them from filling the galaxy?

First, we should understand "migration". Minds are in transition - we can't fit any more in our heads, but we can put more information and capability into our information machines, like the one in front of me. In time, most of our identity will be digital, and for aging individuals, sooner or later all of it. See DigitalImmortality. We will go to the stars as bits. Re-creating human bodies will be somewhere between inconvenient and lethally limiting, recreating the biomass to support those bodies horrendously expensive and likely impossible in the vast majority of star systems whose planetary arrangement and chemical composition does not match our own. Complex lifeforms require complex environments to survive; we find them ready-made on earth, but they will be scarce elsewhere.

So we will send out nanomachines at close to light-speed at very high expense; they will reproduce and build an environment where we can send digital copies of portions of our identities, mostly to supervise the mining of information to return home, to reimburse the expense of operating the massive systems needed to launch the replicating nanomachines in the first place. Energy is convertable to information and identity; we will not use massive amounts of energy or information to go there unless it returns more to those paying for the trip.

Space advocates like to pretend economics does not matter, that we will conquer space out of some innate desire to explore. However, exploring distant stars is an incredibly costly undertaking, and most space advocates spend more time channel surfing than creating a fortune and spending it on results they will not see in their lifetimes. Chances are, even if they tried, those who follow them will spend that fortune on yachts and sports teams instead. Economics is not about what we say we want, it is about what we do.

The cold hard fact is that a dollar spent today is worth more than a dollar spent a year from now, by an increment D, the discount rate. Typical discount rates are around 5%/year, D=0.05/year. A dollar this year is worth 1.05 compared to a dollar next year. This is different than inflation rates, economic growth rates, etc., which are often denominated in currencies that can be temporarily manipulated by governments. In the long term, individuals or nations that ignore the discount rate go bankrupt. The discount rate is ultimately set by the time horizons of individual human beings, failure, obsolescence, ignorance of future demand, and the "mischief rate" of predators (including governments).

The main thing we will extract from the universe around us is information processing, powered by star energy. But information loses value over time, a discount rate applies. Information from a computation source 10 light years away is 20 years old (round trip speed of light time), 36% of the value of locally generated information, assuming a discount rate of 5%/year. At some distance, the incremental cost of generating information remotely is more than the cost of maintaining local information generation.

Assume the value of information generation is proportional to the volume of space in light years times the distance discount, approximately e^-2Dx for small D. The volume of a spherical shell between x and x+1 light years is 4πx², so the value of expanding 1 light year is proportional to 4πx²e^-2Dx.

For D=.05, the value per light year added is:

The value near zero light years is zero - no other stars nearby, besides our own - and the value at 200 light years (a 400 year round trip) is 1 million times smaller than the value at 20 light years. At some point, the economic value of the universe beyond a small multiple of our "discount radius" is negligible.

Putting it differently, the first crop of tobacco was shipped from Virginia in 1613 (after failing to produce its first intended product, big logs for ship masts). Imagine tobacco showing up for the first time in 2013, to a version of today's world not already addicted to it, but with today's ability to test for carcinogenicity. It would never be allowed on the market, and nobody would miss it. If we set a 200ly distant colony (sight unseen) to producing /anything/ for a market 400 years from now, at our current rate of technological progress, what are the chances that the information product they would ship back 400 year later would be meaningful, not reproducable here with far less resources in far less time?

If our civilization expands to a collection of 50K Dyson shells 200 light years in diameter, it will be damned hard to distinguish from a warm infrared gas cloud. Given the time/distance discount rate, and the rarity of intelligent life, the economic value of communicating with a similar Dyson shell far across the galaxy will be negligible, not worth the effort even for a very wealthy fanatic.

Where are they? We may never care enough to make the enormous effort to find out. If we do, the likelihood of a two-way conversation is indistinguishable from zero.

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Note - there are unique environments in the galaxy that may offer value exceeding even a steep exponential effects of the discount rate; near the black hole at the center of the galaxy, advanced communities may be able to extract far more usable energy from hydrogen than fusing it to iron (0.9% of mc²), by dropping it just so into the hole. But those will be isolated communities, drowning in the noise generated by the black hole. They won't detect us and we won't detect them, unless we can observe the black hole and detect differences between a "natural" galactic black hole and a one surrounded by technology. From this distance, with a screen of stars and gas in between, unlikely.

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I am assuming a discount rate related to human lifespans. This may be invalid, the universe may be teeming with intelligence that is far slower than ours, for whom a hundred earth years is nothing, and whose discount rate is very low. Perhaps "thrifty" aliens, thinking with "Bennett-Landauer" reversable computation methods and very low energy consumption at 3 Kelvin temperatures, spread out over large regions of space, occupy much of the universe. They might harvest optical photons for chemical repair of radiation damage, but mostly subdivide them into very small bits of energy to keep the computation going, doing very slowly in parallel what we do with mere trillions of neurons much faster but with less total volume. Such beings would avoid the radiation bath and tidal stresses near stars; their communications would be impossible to hear inside the Sun's magnetopause. So they might be out there, in vast numbers, but undetectable until we build large ultra-low-frequency imagers far from the sun.

Beings like us, or our near-term digital descendants, live in a world with energetic processes and decay rates on time scales shorter than our life spans. If we are slow to exploit a resource, faster beings will snatch it first. Ultimately, it is the rate of resource conversion from harvest to operation to debris that sets the economic discount rate, and as we transition to electronic intelligences, we can expect discount rates to increase, not decrease. The economic event horizon will get closer, not more distant.