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Earthdate 2003-11-02

Big Trees

A year ago Impearls published visionary physicist Freeman Dyson's remarkable essay “The World, The Flesh, and The Devil,” an exploration of the future of mankind and technology in the light of physicist J. D. Bernal's similar-titled book from way back in 1929.  In honor of the occasion I'd like to discuss chapter IV of Dyson's essay entitled “Big Trees.”  Here Dyson presents several ideas which are arresting from the point of view of those interested in the future of humanity in space.

1.  The tiny worlds between the stars — the comets, or “reefs of space” — are numbered in the billions just in the vicinity of our own Sun, and thus very likely outnumber planetary systems and their planets across the galaxy by a similar astronomical factor.  (There may also be many more-normal-sized “rogue planets” — as science-fiction author Poul Anderson termed them — between the stars.)  These small cometary worlds are composed of the substances of life (water, carbon, nitrogen), and given their numbers, the total surface area exceeds that of the terrestrial planets by a factor of thousands.  Think of that: thousands of times more surface area to live on than planets provide.

Moreover, since these worldlets are small, commonly perhaps 10 miles (16 km) in diameter, occupying the entire three-dimentional volume of such a world ought not to be impractical as well, further increasing the habitable space.  I might note that a single 16-km diameter spherical comet has a surface area of 800 square km — about the size of New York City (remember James Blish's Cities in Flight series?) — and a volume of 2,100 cubic km.

2.  Dyson proposes that we colonize and grow trees on comets.  Read the chapter for how he suggests modifying trees to enable them to thrive in such an environment.  Once accomplished, as he points out, on any cometary body 10 miles or so in size the force of gravity is so slight that wood is capable of supporting its own weight to an arbitrary height.  Thus, as Dyson says, “from a comet of ten-mile diameter, trees can grow out for hundreds of miles, collecting the energy of sunlight from an area thousands of times as large as the area of the comet itself.  Seen from far away, the comet will look like a small potato sprouting an immense growth of stems and foliage.  When man comes to live on the comets, he will find himself returning to the arboreal existence of his ancestors.”

Considering a 10-mile comet with foliage growing out for 200 miles in all directions, say, or some 640 km in diameter, the “surface” area of such a treed worldlet (the area absorbing stellar light for purposes of photosynthesis) would be 1,300,000 square km (about the size of the Volga or Missouri River drainage basins on Earth), and including within an inhabitable, arboreal space of 140,000,000 cubic km — about half the volume of the Atlantic or Indian Oceans.  That's just for one such “tiny” world!  (Larry Niven's Integral Trees might provide some slight introduction to that sort of environment.)

3.  As Dyson points out, the distances between such cometary worlds are far smaller than we've come to expect in considering the “voids” between stars.  Rather than light years, the distances would often be light days or less.  Thus, colonization beyond the Solar System will very likely progress differently from the usual expectation in science fiction of some grand expedition between the stars.  Rather, probably, the comets will be colonized layer by layer out from the Sun, and by the time the nearest stars are approached, the relatively small planetary domains within will seem wholly irrelevant, except for research.

I'll close with Dyson's own:  “We shall bring to the comets not only trees but a great variety of other flora and fauna to create for ourselves an environment as beautiful as ever existed on Earth.  Perhaps we shall teach our plants to make seeds which will sail out across the ocean of space to propagate life upon comets still unvisited by man.  Perhaps we shall start a wave of life which will spread from comet to comet without end until we have achieved the greening of the Galaxy.  That may be an end or a beginning, as Bernal said, but from here it is out of sight.”



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