In a book so stuffed with insights and quirky oddments that it belongs on the shelf of anyone interested in interstellar flight, Carl Sagan and I.S. Shklovskii once made a stunning calculation. Their 1966 volume Intelligent Life in the Universe (San Francisco: Holden-Day) presents the argument that with an average annual growth rate of just 1/3 of one percent, energy demand will outstrip the total solar radiation falling on the Earth by a factor of 100,000 within 2500 years. The re-building of the Solar System into something like a Dyson sphere may be inevitable.

But isn’t it a pipe dream to assume that growth will continue at even these modest levels? That was certainly my initial response, for so many things can throw a spanner into a civilization’s works. But Andrew Kennedy (The Chronolith Project, Seville Spain) takes a hard look at growth issues in a recent paper with interesting results. Kennedy believes that growth is far more tenacious than generally accepted. Economic collapse? Ponder that the average recession time in past centuries was between 8-10 years, whereas all our recessions since the Great Depression are better measured in months rather than years.

Disease? Even the Black Death in Europe exerted only a temporary brake on growth. Figuring a death rate of perhaps one-third of the population (the figure varies widely depending on the source), the population did not rise to pre-1349 levels until 1600. Both warfare and trade were severely reduced. But note what happened next:

…150 years or so afterwards, America had been discovered, improved ship-building and navigation (using the recent Western version of the compass) made journeys to the Far East commonplace, ships had sailed around the world (in AD 1521), and Europe was trading with China and India. The spread of credit-based banking and the invention of double entry bookkeeping had brought investment funds into play, and warfare had picked up again.

Kennedy’s examples from both Europe and the Americas are too numerous to list, but I found his thoughts on climate change interesting. The ‘Little ice Age’ that began at the start of the 14th century produced widespread famine and economic contraction, raising the price of English wheat to six times the norm amidst squalor and desolation. But by 1330, Edward III was turning castles from military installations into palaces even as war continued on the Continent. Wealth was being accumulated, great cathedrals built and the shipping industry revitalized in a trade renaissance fueled by spices, silks, wines and furs. The Bay of Biscay became known as the ‘sea of the English.’

Can the momentum continue? As a medievalist by training, I find Kennedy’s optimism about growth hard to swallow, but then my worldview was shaped by the notion of fortune’s wheel continually turning, as medieval a conceit as is imaginable (though passed along from Rome via Boethius). Nonetheless, the growth argument has a place in interstellar discussions, and Kennedy’s purpose is to apply it to the broader issue of how long an interstellar voyage should be delayed given the expectation that further growth will produce faster spacecraft that will catch the original one.

We’ll look at how Kennedy handles this again shortly, and I also want to bring in the thoughts of Marc Millis, who addressed these issues at the latest New Trends in Astrodynamics conference in Princeton. I have that presentation here and want to get into the meat of an argument that was so neatly captured by A.E. van Vogt in his story “Far Centaurus,” in which interstellar travelers finally reach the Centauri stars only to find that Earthmen with faster ships have landed long before them. Millis calls this issue ‘Zeno’s paradox in reverse.’ More about Zeno, paradoxes and Centauri missions as we move past the Thanksgiving holiday here in the States.

The paper is Kennedy, “Interstellar Travel: The Wait Calculation and the Incentive Trap of Progress,” Journal of the British Interplanetary Society Vol. 59, No. 7 (July, 2006), pp. 239-247.