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Cloud-chamber clouds

Naturevolume 417page808 (2002) | Download Citation


In the old 'Star Wars' Project, one scheme was to launch particle beams from Earth at the orbiting weaponry in space. The snag, of course, is that such beams are easily absorbed by the atmosphere, especially by clouds. The answer was to launch the beam as a series of pulses. The first beam would travel a certain distance before being absorbed and scattered; the next would ride in the expanded and clarified tunnel driven by the first, and would go further; ultimately the last pulse would break through into clear aerospace and would deliver its deadly energy to the space-borne threat. The whole process would take much less than a second.

Daedalus now connects this idea with the sad fact, bemoaned by every farmer, that endless clouds scud merrily over his fields but deposit no rain on his parched land. Many attempts have been made to make such annoying clouds rain, by seeding them from aircraft or even by firing cannon at them from the ground. Daedalus's scheme recalls the latter. He plans to fire a carbon dioxide laser at the clouds, followed by an electron beam or one of alpha particles. Unlike the Star Wars scheme, these co-linear beams will not reach space. They are intended to be broken up in the clouds, ideally near the tops of the most promising ones.

Wilson's cloud chamber is the crucial experiment here. In this device, the tiny racing fundamental particles precipitate enormously larger droplets along their track, revealing the particles to watchers or cameras. Daedalus reckons that the disruption of a cloud top by his beam system should release enormous numbers of wilsonian droplets, which will fall slowly through the cloud. As in ordinary rainfall, they will be further amplified by collision. Each droplet will collide with those beneath. It will grow in the process, fall faster, and collide more frequently with more cloud droplets. Ultimately, full-sized raindrops will fall out of the base of the cloud.

The beam gadget, though smaller and cheaper than the Star Wars device, will still be costly. Farmers will probably hire it by the day, and use it to wet all their land for that day. But it should then transform farming. It should make it a far more predictable business, less dependent on chance water. A cloud is just a mass of small water droplets: it ought to rain, and any device that encourages this process is going with the grain of atmospheric physics.


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