We have yet to find any traces of extraterrestrial intelligence, a vexing problem known as the Fermi Paradox. A new solution to the “where are all the aliens?” conundrum suggests that advanced aliens do exist—but they’re in a self-imposed state of hibernation, waiting for a future era of the cosmos in which they can flourish to the greatest extent possible. How very convenient.

The Universe as we observe it today is not as it was billions of years ago, nor does it appear as it will billions of years from now. New research accepted for publication in the Journal of the British Interplanetary Society suggests that conditions in our current Universe are far too warm for a digital, computer-based civilization, and that it makes sense for such beings to enter into a state of aestivation—hibernation, but in response to excess heat—until the cosmos is much colder in the far, far future. At that stage, with stellar objects dispersed across an enlarged Universe, information processing can occur with far greater speed and efficiency, enabling an advanced civilization to achieve more than what’s possible under current cosmological conditions.

But back up a sec: digital aliens? Indeed, an increasing number of futurists, astrobiologists, and SETI experts are starting to think that advanced intelligence eventually transitions into a digital mode of existence. Living as digital beings within powerful supercomputers, post-biological aliens (or future posthumans) will demand unhindered access to powerful and efficient means of information processing—a hypothetical mode of existence known as “dataism.”

But as Anders Sandberg, Stuart Armstrong, and Milan Ćirković argue in their new JBIS paper, there’s a cost to information processing, particularly when the computer performing those calculations is temperature dependent. As computer scientists and information physicists know, the potential for information processing increases as temperature decreases (energy is required to cool a blazingly fast computer, after all). So rather than squander energy and resources in the current era, Sandberg and company believe it makes more sense for an advanced, computer-based civilization to aestivate and wait until the Universe is much colder than it is today.

The current background radiation of the Universe is roughly three degrees Kelvin above absolute zero. That may seem like a trivial amount of “warmth” to you and me, but to a computer-based civilization, it could represent an intolerable amount of heat. Trillions of years from now, when the background radiation will be reduced to practically nothing, thanks to the expansion of the universe and extinguishment of most stars, information processing will be able to proceed at a rate 1030 greater than what’s achievable today, the researchers calculate.

“An advanced civilization may have explored a big chunk of the universe, done what is doable with existing nature, and now mostly have internal ‘cultural’ things to do,” explains Sandberg at his blog. “These things can be regarded as information processing. If they want to maximize processing they should not do it today but wait until the cold future when they will get tremendously more done. They should hence aestivate.”

If this hypothesis is true, ancient extraterrestrial civilizations exist, they’ve already explored much of the galaxy, and they’re now difficult to observe. We may even be living in a region of space that’s considered the “property” of one of these civilizations. Importantly, Sandberg says we should be able to see signs of an aestivating civilization, even though they’re dormant.

“The thing to look for is a suspicious absence of processes that would waste resources useful for the aestivators,” Sandberg told Gizmodo. Specifically, he says we should be on the lookout for process that prevent a variety of astrophysical phenomena: stars from converting mass into energy, stars imploding into black holes, galactic winds losing gas into intergalactic space, galaxy collisions, and galaxy clusters getting separated by the expansion of the universe. We don’t see anything preventing these processes from occurring at the moment (a strike against this hypothesis), but Sandberg says scientists should be on the lookout for unusual zones in which these natural cosmological process have been dramatically diminished.

Another way to potentially detect these sleeping civilizations would be to mess with their stuff, but that could be very dangerous. “[We could] try to set off some process that really would upset the aestivators—like launching a lot of self-replicating probes to pave the reachable universe with our infrastructure,” said Sandberg. “If the aestivators are halfway competent their robot guardians will show up to stop that. Which might make this a very risky way of testing the hypothesis.”

A hypothetical megastructure constructed by an advanced alien civilization. Image: Shkadov Thruster L. Blaszkiewicz/CC

The aestivation hypothesis offers a tidy explanation to the Fermi Paradox—the surprising observation that we’ve never seen signs of aliens—but it’s not without problems. David Brin, an astrophysicist, SETI expert, and science fiction author, says the new paper is clever, but the concept has several flaws.

“If you are getting better at launching ever faster ships, that can out-race last year’s models, when does it make sense to actually launch one?,” he told Gizmodo. “Likewise, while you may get better at computation in a colder universe, you are foregoing all the computation that you might accomplish, if you just kept cranking away during the warmer times.”

Sandberg argues this isn’t the case, and that advanced aliens can’t have their cake and eat it, too.

“Imagine having a wallet with a limited number of dollar bills (energy) and buying cakes after Christmas that are getting cheaper over time (eventually leveling out at some low price),” he told Gizmodo. “If you want to get as much cake as possible, you should save your bills until the cakes reach their minimum price. Anything else will get you less cake.”

He says an alien civilization can certainly strive to improve its computational efficiency in the current cosmological era, but while this might be what computation-maximizing civilizations do in the present, using up any resources now will mean far, far fewer resources in the distant future.

Brin also believes that aestivation is an exceptionally dangerous strategy.

“If you ignore the physical world in favor of dataism, you may be surprised by something that erupts in objective reality and bites you, while you slept in search of better (computational) times,” he said. Brin thinks opportunistic, non-dataist aliens may find a way to breach the defenses of the aestivators and wreak havoc.

Interestingly, Sandberg himself doesn’t believe in the aestivation hypothesis, but he says it’s important to investigate the possibility. “If you don’t check your less favored hypotheses you are not doing science,” he said. At the same time, the aestivation strategy is still something we may want to consider for ourselves in a few billion years, he added.

“The cool part is that it actually does suggest a fair bit of new things to look for—galaxies with a suspicious absence of heavy stars or gas loss, galaxies being moved, that sort of thing,” he told Gizmodo. “I think that whatever the answer to the Fermi paradox is—we are alone and responsible for the future of the universe, intelligent life is always doomed, there is some rather low ceiling on technology, the aliens are here in some form, or we are fundamentally wrong about something essential—is going to be mindblowing. But it might take a long, long time to get that answer.”

[Journal of the British Interplanetary Society (pre-print available here)]