When atomic nuclei fuse—as in the sun, where hydrogen nuclei fuse into helium billions and billions of times each second—the result is a more complex, more intricately organized, lower-entropy atomic cluster. In the process, some of the mass of the original nuclei is converted into energy (as prescribed by E = mc2), mostly in the form of a burst of photons that heats the star’s interior and powers the release of light from the star’s surface. And it is through such fiery starlight, which is itself a torrent of outward streaming photons, that the star transfers copious quantities of entropy to
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