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Long ago, in lands that were always warm, people got ice from the heavens.
At sunset, they poured water into shallow earthen pits or ceramic trays insulated with reeds. All through the night, the water would radiate its heat into the chilly void of space. By morning, it turned to ice — even though the air temperature never dropped below freezing.
This wasn’t magic; it was science.
For centuries, desert dwellers in North Africa, India, and Iran tapped into the law of physics called radiative cooling. All objects — people, plants, buildings, planets — give off heat in waves of invisible light. On a clear, starry night, that radiation can rise through the atmosphere until it escapes Earth entirely. Coldness, which is really the absence of heat, is created through this invisible connection to the cosmos.
The world now cools off with the help of more than 3.5 billion refrigerators and air conditioners, a number that is quickly growing. But those appliances are also a major source of greenhouse gas emissions. In seeking relief from the heat, humans are making the globe even hotter, compounding the demand for cooling.
To break that cycle, University of California at Los Angeles materials scientist Aaswath Raman wants to turn ancient technology into a 21st-century tool.
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By Sarah Kaplan
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James' World 2 
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