Saturday, March 09, 2013

A Dyson hemisphere

kw: book reviews, science fiction, space fiction, space aliens, space travel

In their first collaboration, Larry Niven and Gregory Benford have come to lead that subgenre of Science Fiction that combines hard science, some blue-sky projections thereof, and believable sociology of both human and alien societies. In the case of Bowl of Heaven, the hard science keeps all speeds below that of light and accepts certain other known limitations of physics, the projections (or speculations) push engineering to the scale of a solar system and also posit a ramscoop that uses superconducting magnetic fields a few thousand times greater than any so far known, and the sociology involves a dozen or so humans confronted by not just one or a few quite alien species, but a profusion of them, in a colossal engineered ecosystem.

Most SciFi aficionados know the concept of a Dyson Sphere, the product of a society that captures all the radiation of a star as its energy source. Though Dyson first conceived of a hollow sphere, the concept was soon modified to encompass myriads of large, stellar-light-capturing orbital habitats in a thick shell about the star, sufficient to block all or nearly all of its light, and emitting waste heat primarily at wavelengths between 8 and 20µ (the human body's thermal radiation, at 310K, peaks at 10µ). So far, no deep-infrared stars suggestive of such structures have been observed. The orbital mechanics of such a system are formidable, and collisions might be so frequent as to make the scheme impracticable.

Niven's best-known foray into the partial Dyson Sphere arena has been the famous Ringworld series. Now we have an even more ambitious engineering project: Build a hemisphere centered on a flare star (a late K or early M star that tends to have a strong stellar wind), that supports many (quadrillions, I suppose) steerable mirror segments. Its radius is roughly an AU (150 million km). A wide ring at the equator supports a habitat with the area of many trillions of km², and the structure rotates to produce centrifugal "gravity" in the habitable ring. There is a hole at the center (the rotational axis of the hemisphere) with a special function. The mirrors reflect the star's light to focus on an area at the "rear" of the star (we can presume its axis of rotation), heating it and focusing its stellar wind into a jet that passes through the hole in the hemisphere. This begins to drive the star. Some sort of engines in the hemisphere counteract its orbital instability until the star begins to accelerate sufficiently to closely balance the tendency of the hemisphere to fall inwards. Then the job of the engines is quite a bit easier, or at least less energetic. Now you have a "ship" that is similar in size to the orbit of Earth or perhaps Mars, that can cross interstellar space over a span of millions of years.

This idea by itself could be fodder for a simple high-concept novel. For Niven and Benford it is mainly backdrop. Put it out there, make it a few tens of millions of years old, populate it with a cadre of large, birdlike alien species and an uncountable number of "adopted" alien species whose members they have plucked from star systems as they swung by in ages past. Then add US.

A ramscoop from Earth, bearing colonists heading for a star they've named Glory, catches up with this star-centered Bowl. Now, we all know that paying a visit to aliens who can engineer on such a scale is quite foolhardy. But it happens that the colonists, most of whom are in frozen sleep, have a problem. The small "awake" crew has discovered that the ship's top speed is a few percent low. Low enough that they can't keep a crew awake and alive long enough to get to Glory. They figure the Bowl might be able to supply them with materials they can use to replenish their stores, so they do pay the ill-advised visit, and of course the landing crew is partly taken captive and partly escapes to re-learn their Boy Scout skills as they flee hither and yon, evading capture while they learn what they can about the Bowl and the habitat.

I have wondered in the past just how big a spinning structure could be, to produce about 1g of apparent gravity. It turns out that the stress intensity for 1g of centripetal acceleration increases linearly with radius, such that the strongest known steel could not produce 1g when the radius is greater than a few hundred meters. Perhaps some kind of carbon nanotube assembly could hold together a structure of a km or so diameter. Both Ringworld and the Bowl would require materials with a tensile strength a few million times greater than any known. However, I was able to keep such considerations from marring my enjoyment of the book and its concepts, and I trust so can most SciFi readers.

A great deal goes on in this 400-page book, as we glean insights into the various cooperating "big bird" denizens and some of the Adopted species, and as one human group begins to learn to communicate with their "hosts" while the other searches for understanding and some kind of bargaining leverage. Here, the volume ends. I suppose a trilogy is planned (though the authors promise but one sequel, Shipstar).

The possibilities of quite distinct psychologies that the authors explore in the big birds are fascinating. Is our human Bicameral Mind going to be a handicap or a detriment, compared to their more unified psychology? It makes me wonder if the future volume(s) will explore the possibility that human psychology could become more unified, making our "unconscious" more consciously accessible.

There is a character, Fred, that I found myself identifying with. He is socially awkward but totally at ease with machines and computer code. In a conversation he describes his problem-solving technique, which takes advantage of sleep, and I was saying, "Yes! That's just what kept my programming career going for 4 decades!". I figure that either Niven or Benford must do this, or they know quite well someone who does and has described it. It is comparatively rare as an explicit technique, though many people have experienced waking up with a worrying problem solved.

Now I have my marching orders, to track the progress of the next volume, Shipstar, and any possible successor volumes. I can hardly wait.

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