If a civilization wants to maximize computation it appears rational to aestivate until the far future in order to exploit the low temperature en- vironment: 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 analyzes the assumptions going into the hypothesis and how physical law and observational evidence constrain the motivations of aliens compatible with the hypothesis. [...]
As the universe cools down, one Joule of energy is worth proportionally more. This can be a substantial (1030) gain. Hence a civilization desiring to maximize the amount of computation will want to use its energy endowment as late as possible: using it now means far less total computation can be done. Hence an early civilization, after expanding to gain access to enough raw materials, will settle down and wait until it becomes rational to use the resources. We are not observing any aliens since the initial expansion phase is brief and intermittent and the aestivating civilization and its infrastructure is also largely passive and compact. [...]
As noted by Gershenfeld, optimal computation needs to make sure all internal states are close to the most probable state of the system, since otherwise there will be extra dissipation. Hence there is a good reason to perform operations slowly. Fortunately, time is an abundant resource in the far future. In addition, a civilization whose subjective time is proportional to the computation rate will not internally experience the slowdown.
That is not dead which can eternal lie: