Entropy of the microwave background radiation in the observable universe

  title={Entropy of the microwave background radiation in the observable universe},
  author={Yun-song Piao},
  journal={Physical Review D},
We show that the cosmological constant at late-time places a bound on the entropy of microwave background radiation deposited in the future event horizon of a given observer, $S\ensuremath{\le}{S}_{{\ensuremath{\Lambda}}_{0}}^{3/4}$. This bound is independent of the energy scale of reheating and the FRW evolution after reheating. We also discuss why the entropy of microwave background in our observable universe has its present value. 
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