Many popular and semi-popular books about cosmology have appeared during the last few years in which the ultimate fate of the Universe is conjectured. One such scenario stipulates that space will expand forever and will contain nothing but electrons and protons-all other "matter" having decayed-together with radiation of an immensely long (and continually increasing) wavelength. Under such conditions wouldn't the temperature of the Universe be very close to (and continually approaching) absolute zero as space expands? Now the "Third Law of Thermodynamics" states that the entropy of a thermodynamic system at absolute zero is zero. Hence it would seem that the the entropy of the Universe in this final state should be very low. But, according to the "Second Law of Thermodynamics", the entropy of the Universe in its final state should be very high. What am I missing here?
2026-03-31 19:14:20.1774984460
A question about the Laws of Thermodynamics
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The entropy per unit volume will be very low, but there will be a lot more volume.