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Comment by gewa | Hacker News Reader

How is this not violating the second law of thermodynamics ? It seems like the entropy as a whole is getting lower.

Did you read the article?

    The new film works by a process called radiative cooling. This takes
    advantage of that fact that Earth’s atmosphere allows certain wavelengths
    of heat-carrying infrared radiation to escape into space unimpeded. Convert
    unwanted heat into infrared of the correct wavelength, then, and you can
    dump it into the cosmos with no come back.

    the work is done by the huge temperature difference, about 290°C, between
    the surface of the Earth and that of outer space.

Could we cover large portions of the Earth with this material and reverse global warming?

Probably wouldn't be cost-effective, but it'd work in principle.

If you floated thousands of square miles of it on the surface of the oceans, yes. But that first assumes a reasonable time payback of the CO2 burden of manufacturing the stuff in the first place, which is not a given. It's obviously not practical for oceans, but it might protect ice caps and glaciers.

Because it's radiating the heat out into space, you need to consider the entropy of the complete Earth-Space system, which is actually increasing.

Entropy is decreasing locally, sure, but the Earth is not an isolated system, so it's not violating the second law.

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