Aliens Need Not Wait To Be Active

In April 2017, Anders Sandberg, Stuart Armstrong, and Milan Cirkovic released this paper:

If a civilization wants to maximize computation it appears rational to aestivate until the far future in order to exploit the low temperature environment: This can produce a 1030 multiplier of achievable computation. We hence suggest the “aestivation hypothesis”: The reason we are not observing manifestations of alien civilizations is that they are currently (mostly) inactive, patiently waiting for future cosmic eras. This paper analyses the assumptions going into the hypothesis and how physical law and observational evidence constrain the motivations of aliens compatible with the hypothesis. (more)

That is, they say that if you have a resource (like a raised weight, charged battery, or tank of gas), you can get at lot (~1030 times!) more computing steps out of that if you don’t use it  today, but instead wait until the cosmological background temperature is very low. So, they say, there may be lots of aliens out there, all quiet and waiting to be active later.

Their paper was published in JBIS in a few months later, their theory now has its own wikipedia page, and they have attracted at least 15 news articles (1 2 3 4 5 6 7 8 9 10 11 12 13 14 15). Problem is, they get the physics of computation wrong. Or so says physics-of-computation pioneer Charles Bennett, quantum-info physicist Jess Riedel, and myself, in our new paper:

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 (∼1030 times more) irreversible logical operations (e.g., error-correcting bit erasures) if it conserves its resources until the distant future when the cos- mic 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. (more)

That is, the key resource is negentropy, and if you have some of that you can use it at anytime to correct computing-generated bit errors at the constant ideal rate of one bit of negentropy per one bit of error corrected. There is no advantage in waiting until the distant future to do this.

Now you might try to collect negentropy by running an engine on the temperature difference between some local physical system that you control and the distant cosmological background. And yes, that process may go better if you wait until the background gets colder. (And that process can be very slow.) But the negentropy that you already have around you now, you can use that at anytime without any penalty for early withdrawal.

There’s also (as I discuss in Age of Em) an advantage in running your computers more slowly; the negentropy cost per gate operation is roughly inverse to the time you allow for that operation. So aliens might want to run slow. But even for this purpose they should want to start that activity as soon as possible. Defensive consideration also suggest that they’d need to maintain substantial activity to watch for and be ready to respond to attacks.