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Solving Fermi's Paradox

One of the besetting sins of today's intellectual climate is the habit of overspecialization. Too often, people involved in one field get wrapped up in that field's debates and miss the fact that the universe is not neatly divided into watertight compartments. With this excuse, if any is needed, I want to shift the ground of The Archdruid Report's discussion a bit and talk about Fermi's paradox.

First proposed by nuclear physicist Enrico Fermi in 1950, this points out that there's a serious mismatch between our faith in technological progress and the universe our telescopes and satellites reveal to us. Our galaxy is around 13 billion years old, and contains something close to 400 billion stars. There's a lot of debate around how many of those stars have planets, how many of those planets are capable of supporting life, and what might or might not trigger the evolutionary process that leads to intelligent, tool-using life forms, but most estimates grant that there are probably thousands or millions of inhabited planets out there.

Fermi pointed out that an intelligent species that developed the sort of technology we have today, and kept on progressing, could be expected eventually to work out a way to travel from one star system to another; they would also leave traces that would be detectable from earth. Even if interstellar travel proved to be slow and difficult, a species that developed starflight technology could colonize the entire galaxy in a few tens of millions of years - in other words, in a tiny fraction of the time the galaxy has been around. Given 400 billion chances to evolve a species capable of inventing interstellar travel, and 13 billion years to roll the dice, the chances are dizzyingly high that if it's possible at all, at least one species would have managed the trick long before we came around, and it's not much less probable that dozens or hundreds of species could have done it. If that's the case, Fermi pointed out, where are they? And why haven't we seen the least trace of their presence anywhere in the night sky?

Fermi's paradox has been the subject of lively debate for something like half a century now, and most books on the possibility of extraterrestrial life discuss it. There are at least two reasons for that interest. On the one hand, of course, the possibility that we might someday encounter intelligent beings from another world has been a perennial fascination since the beginning of the industrial age - a fascination that has done much to drive the emergence of the folk theologies masquerading as science in today's UFO movement.

On another level, though, Fermi's Paradox can be restated in another and far more threatening way. The logic of the paradox depends on the assumption that unlimited technological progress is possible, and it can be turned without too much difficulty into a logical refutation of the assumption. If unlimited technological progress is possible, then there should be clear evidence of technologically advanced species in the cosmos; there is no such evidence; therefore unlimited technological progress is impossible. Crashingly unpopular though this latter idea may be, I suggest that it is correct - and a close examination of the issues involved casts a useful light on the present crisis of industrial civilization.

Let's start with the obvious. Interstellar flight involves distances on a scale the human mind has never evolved the capacity to grasp. If the earth were the size of the letter "o" on this screen, for example, the moon would be a little over an inch and three quarters away from it, the sun about 60 feet away, and Neptune, the outermost planet of our solar system now that Pluto has been officially demoted to "dwarf planet" status, a bit more than a third of a mile off. On the same scale, though, Proxima Centauri - the closest star to our solar system - would be more than 3,000 miles away, roughly the distance from southern Florida to the Alaska panhandle. Epsilon Eridani, thought by many astronomers to be the closest star enough like our sun to have a good chance of inhabitable planets, would be more than 7,500 miles away, roughly the distance across the Pacific Ocean from the west coast of North America to the east coast of China.

The difference between going to the moon and going to the stars, in other words, isn't simply a difference in scale. It's a difference in kind. It takes literally unimaginable amounts of energy either to accelerate a spacecraft to the relativistic speeds needed to make an interstellar trip in less than a geological time scale, or to keep a manned (or alienned) spacecraft viable for the long trip through deep space. The Saturn V rocket that put Apollo 11 on the moon, the most powerful spacecraft to date, doesn't even begin to approach the first baby steps toward interstellar travel. This deserves attention, because the most powerful and technologically advanced nation on Earth, riding the crest of one of the greatest economic booms in history and fueling that boom by burning through a half billion years' worth of fossil fuels at an absurdly extravagant pace, had to divert a noticeable fraction of its total resources to the task of getting a handful of spacecraft across what, in galactic terms, is a whisker-thin gap between neighboring worlds.

It's been an article of faith for years now, and not just among science fiction fans, that progress will take care of the difference. Progress, however, isn't simply a matter of ingenuity or science. It depends on energy sources, and that meant biomass, wind, water and muscle until technical breakthroughs opened the treasure chest of the Earth's carbon reserves in the 18th century. If the biosphere had found some less flammable way than coal to stash carbon in the late Paleozoic, the industrial revolution of the 18th and 19th century wouldn't have happened; if nature had turned the sea life of the Mesozoic into some inert compound rather than petroleum, the transportation revolution of the 20th century would never have gotten off the ground. Throughout the history of our species, in fact, each technological revolution has depended on accessing a more concentrated form of energy than the ones previously available.

The modern faith in progress assumes that this process can continue indefinitely. Such an assertion, however, flies in the face of thermodynamic reality. A brief summary of that reality may not be out of place here. Energy can neither be created nor destroyed, and left to itself, it always flows from higher concentrations to lower; this latter rule is what's called entropy. A system that has energy flowing through it - physicists call this a dissipative system - can develop eddies in the flow that concentrate energy in various ways. Thermodynamically, living things are entropy eddies; we take energy from the flow of sunlight through the dissipative system of the earth in various ways, and use it to maintain concentrations of energy above ambient levels. The larger and more intensive the concentration of energy, on average, the less common it is - this is why mammals are less common than insects, and insects less common than bacteria.

It's also why big deposits of oil and coal are much less common than small ones, and why oil and coal are much less common than inert substances in earth's crust. Fossil fuels don't just happen at random; they exist in the earth because biological processes put them there. Petroleum is the most concentrated of the fossil fuels, and the biggest crude oil deposits - Ghawar in Saudi Arabia, Cantarell in Mexico, the West Texas fields, a handful of others - represented the largest concentrations of free energy on earth at the dawn of the industrial age. They are mostly gone now, along with a great many smaller concentrations, and decades of increasingly frantic searching has failed to turn up anything on the same scale. Nor is there another, even more concentrated energy resource waiting in the wings.

If progress depends on getting access to ever more concentrated energy resources, in other words, we have reached the end of our rope. The resources now being proposed as ways to power industrial civilization are all much more diffuse than fossil fuels. (Nuclear power advocates need to remember that uranium-235, which has a great deal of energy when refined and purified, exists in very low concentrations in nature and requires a hugely expensive infrastructure to turn it into usable energy, so the whole system yields very little more energy than goes into it; fusion, if it even proves workable at all, will require an infrastructure a couple of orders of magnitude more expensive than fission, and the same is true of breeder reactors.) More generally, it takes energy to concentrate energy. Once we no longer have the nearly free energy of fossil fuels concentrated for us by half a billion years of geology, concentrating energy beyond a certain fairly modest point will rapidly become a losing game in thermodynamic terms. At that point, insofar as progress is measured by the kind of technology that can cross deep space, progress will be over.

We can apply this same logic to Fermi's paradox and reach a conclusion that makes sense of the data. Since life creates localized concentrations of energy, each planet inhabited by life forms will develop concentrated energy resources. It's reasonable to assume that our planet is somewhere close to the average, so we can postulate that some worlds will have more stored energy than ours, and some will have less. A certain fraction of planets will evolve intelligent, tool-using species that figure out how to use their planet's energy reserves. Some will have more and some less, some will use their reserves quickly and some slowly, but all will reach the point we are at today - the point at which it becomes painfully clear that the biosphere of a planet can only store up a finite amount of concentrated energy, and when it's gone, it's gone.

Chances are that a certain number of the intelligent species in our galaxy have used these stored energy reserves to attempt short-distance spaceflight, as we have done. Some with a great deal of energy resources may be able to establish colonies on other worlds in their own systems, at least for a time. The difference between the tabletop and football-field distances needed to travel within a solar system, and the continental distances needed to cross from star to star, though, can't be ignored. Given the fantastic energies required, the chance that any intelligent species will have access to enough highly concentrated energy resources to keep an industrial society progressing long enough to evolve starflight technology, and then actually accomplish the feat, is so close to zero that the silence of the heavens makes perfect sense.

These considerations suggest that White's law, a widely accepted principle in human ecology, can be expanded in a useful way. White's law holds that the level of economic development in a society is measured by the energy per capita it produces and uses. Since the energy per capita of any society is determined by its access to concentrated energy resources - and this holds true whether we are talking about wild foods, agricultural products, fossil fuels, or anything else - it's worth postulating that the maximum level of economic development possible for a society is measured by the abundance and concentration of energy resources to which it has access.

It's also worth postulating, along the lines suggested by Richard Duncan's Olduvai theory, that a society's maximum level of economic development will be reached, on average, at the peak of a bell-shaped curve with a height determined by the relative renewability of the society's energy resources. A society wholly dependent on resources that renew themselves over the short term may trace a "bell-shaped curve" in which the difference between peak and trough is so small it approximates a straight line; a society dependent on resources renewable over a longer timescale may cycle up and down as its resource base depletes and recovers; a society dependent on nonrenewable resources can be expected to trace a ballistic curve in which the height of ascent is matched, or more than matched, by the depth of the following decline.

Finally, the suggestions made here raise the possibility that for more than a century and a half now, our own civilization has been pursuing a misguided image of what an advanced technology looks like. Since the late 19th century, when early science fiction writers such as Jules Verne began to popularize the concept, "advanced technology" and "extravagant use of energy" have been for all practical purposes synonyms, and today Star Trek fantasies tend to dominate any discussion of what a mature technological society might resemble. If access to concentrated energy sources inevitably peaks and declines in the course of a technological society's history, though, a truly mature technology may turn out to be something very different from our current expectations. We'll explore this further in next week's post.

What do you think? Leave a comment below.

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