100% of the energy from the sun is reflected back into space, it's just shifted from a low-entropy state to a high-entropy state, and from a high frequency (ultraviolet) to a low frequency (infrared). But does the total number of photons change as a result? Are there more low frequency photons, then, in order to make the same amount of energy?


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Reflection, by definition, sends the same photons back. So it can't change the frequency of the photons or their number or the entropy (at least locally, it can't).

What you probably want to talk about is complete absorption and black-body re-radiation of the energy. That's something else than reflection.

Yes, if the planet is in balance, then, of course, it has to emit a higher number of photons that have a lower energy and lower frequency each because the energy of a single photon is related by $E=hf$ to the frequency. The entropy is essentially proportional to the number of photons, so it emits more entropy than it absorbs, and the entropy is increasing.

  • $\begingroup$ The frequency of a true reflection is altered by the doppler effect. Of course we can have a temporal energy imbalance as the planet may be heating up/cooling down on average at any given moment. Wheras with reflection (ignoring photon time of flight issues), we won't get a temporal imbalance of energy. $\endgroup$ Jun 6, 2011 at 16:50

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