The researchers, from Oxford’s Future of Humanity Institute, ask if advanced civilisations – who would likely be burning through power sources due to vast increases in computational ability – might make the decision to go into a hibernation of sorts (“aestivation“) in order to take advantage of more energy-friendly conditions in the deep future:
[E]arly civilizations have a far greater chance to colonize and pre-empt later civilizations if they wish to do so. If these early civilizations are around, why are they not visible? The aestivation hypothesis states that they are aestivating until a later cosmological era.
The argument is that the thermodynamics of computation make the cost of a certain amount of computation proportional to the temperature. Our astrophysical and cosmological knowledge indicates that the universe is cooling down with cosmic time. As the universe cools down, one Joule of energy is worth proportionally more.
…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.
In short, the paper says, very big civilisations might have a small footprint because they have “relocated most of their activity to the future”. Advanced civilizations might have “seen it all”, the researchers say, and so “do not gain much more information utility from hanging around in the early era”.
To ‘relocate their activity to the future’, the researchers say, advanced aliens could have figured out a way to either just ‘hibernate’, or otherwise perhaps even regulated their “mental speed” to change their subjective experience of time to enable them to ‘traverse’ large periods of time with minimum impact.
The paper is obviously all very speculative, even if they do offer real science (much of it too complex for me) to try and back up their hypothesis (they also note that the paper didn’t originally aim to solve the Fermi Paradox, but rather was a consideration of how advanced civilizations might manage their resources).
But if you’re going to have some fun speculating about hibernating ancient aliens, why not go hog wild and throw in some Lovecraft to paint a picture? That’s exactly what the authors do to illustrate their scenario of ‘sleeping Old Ones’, inserting the two following quotes into their paper:
That is not dead which can eternal lie.
And with strange aeons even death may die.
The Old Ones were, the Old Ones are, and the Old Ones shall be.
Not in the spaces we know, but between them. They walk serene
and primal, undimensioned and to us unseen.
H.P. Lovecraft, The Dunwich Horror and Others
Maybe they should have put ‘eldritch’ in front of every second noun just to really set a Lovecraftian tone…