Foundations of Physics

, Volume 49, Issue 8, pp 820–829 | Cite as

Comment on ‘The Aestivation Hypothesis for Resolving Fermi’s Paradox’

  • Charles H. Bennett
  • Robin Hanson
  • C. Jess RiedelEmail author


In their article, ‘That is not dead which can eternal lie: the aestivation hypothesis for resolving Fermi’s paradox’, Sandberg et al. try to explain the Fermi paradox (we see no aliens) by claiming that Landauer’s principle implies that a civilization can in principle perform far more (\({\sim } 10^{30}\) times more) irreversible logical operations (e.g., error-correcting bit erasures) if it conserves its resources until the distant future when the cosmic background temperature is very low. So perhaps aliens are out there, but quietly waiting. Sandberg et al. implicitly assume, however, that computer-generated entropy can only be disposed of by transferring it to the cosmological background. In fact, while this assumption may apply in the distant future, our universe today contains vast reservoirs and other physical systems in non-maximal entropy states, and computer-generated entropy can be transferred to them at the adiabatic conversion rate of one bit of negentropy to erase one bit of error. This can be done at any time, and is not improved by waiting for a low cosmic background temperature. Thus aliens need not wait to be active. As Sandberg et al. do not provide a concrete model of the effect they assert, we construct one and show where their informal argument goes wrong.


Foundations of computation Aestivation Thermodynamics of computation Landauer’s principle Fermi’s paradox Adiabatic computing Classical information theory 



Research at Perimeter Institute is supported by the Government of Canada through the Department of Innovation, Science and Economic Development Canada and by the Province of Ontario through the Ministry of Research, Innovation and Science.


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© Springer Science+Business Media, LLC, part of Springer Nature 2019

Authors and Affiliations

  1. 1.IBM Watson Research CenterYorktown HeightsUSA
  2. 2.Department of EconomicsGeorge Mason UniversityFairfaxUSA
  3. 3.Perimeter Institute for Theoretical PhysicsWaterlooCanada

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