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How Long Would It Take to Colonize the Universe?

How intelligent life may come to saturate, and even shape, the cosmos.

​Hollywood loves to depict future humans as intrepid spacefarers, traversing the unfathomable distances of the cosmos in stylish fighter jets with souped up faster-than-light drives. Given that we've yet to land boots on Mars, it's easy to write off such yarns as pure fantasy. But let's imagine, for a moment, that we actually desired to become a galaxy-spanning, or even universe-spanning, civilization. Could we—at least in theory—do so, without bending the fundamental laws of physics?

Physicist Jay Olson believes we can. Yes, it'll take a million generations and yes, it'll probably involve insanely advanced technology, but at the end of the day, an intergalactic diaspora may not be as crazy as it sounds. In his recent​ paper, Olson treats the grand question of whether, and how, an intelligent civilization might spread on a cosmic scale.

"In thinking about some of the ideas people have been discussing lately—the limits to technology and technological singularity, for instance—it occurred to me that it was possible to imagine life expanding on a cosmological scale," said Olson.

So, Olson set out to test the ambitious idea using a mathematical model. Not only does he show that intelligent life can theoretically come to fill the vast void of space in a fraction of the universe's lifetime, but universe spanning civilizations may influence the evolution of the cosmos itself—a profound and entirely novel suggestion.

Let's start with the assumptions here, of which there are plenty. First and foremost, Olson focuses his model on "aggressively expanding" civilizations: That is, civilizations that are spreading across space in every possible direction, to the utmost of their ability, ad infinitum.

Such a civilization may be working toward some sort of vast cosmic engineering goal. You know, like building a galaxy-spanning superbrain or whatever. Or perhaps we're talking about an artificial intelligence that, thanks to a minor programming disaster, decides to chew through energy and matter until the end of days.

"It's possible someone might create a recursively self-improving AI to accomplish a simple, open-ended task, and switch it on without sufficient safeguards," Olson said. "Very suddenly, it might come to dominate a huge region of space in its quest to fulfill simple goals."

Alien motives aside, Olson's model also makes a number of scientific assumptions. Fundamental principles of the physical universe cannot be violated, meaning—sorry Trekkies, sorry Whovians—no faster-than-light speed, no violations of basic thermodynamics, no time travel.

On the other hand, Olson assumes that aggressively expanding civilizations will have maxxed out technologically. This means that certain science fictional technologies—Dyson spheres and self-repli​cating spacecraft, for instance—are fair game.

It'll take somewhere on the order of five to ten billion years to saturate the observable universe

So basically, we're looking at super advanced civilizations seeding the universe within the boundaries of physics. Functions in the Olson's models describe how quickly a civilization's frontier expands and how long it takes for a given volume of space to become saturated with life.

"Since this stuff is brand new, and parameters are highly debatable, my main concern was coming up with a default scenario where you could kick the parameters in any direction you want with an end result that the universe is saturating with life," Olson said.

Olson's models depict life bubbling effervescently across space, expanding outward in ever-growing spheres of influence. If a civilization can travel at anywhere from 1 to 50 percent the speed of light, it'll take somewhere on the order of five to ten billion years to saturate the observable universe.

You know, no biggie.

Aggressively expanding life saturating an intergalactic slice of the universe. Credit: Jay Olson.

By tweaking parameters and competing different expansion scenarios, Olson also uncovers some interesting tradeoffs. As the velocity of a civilization's probes increases, the volume of space that species occupies grows exponentially. Yet, it's not just how fast a civilization can move that matters for cosmic domination, but how quickly it comes to use all the resources in a given swath of space—how quickly it saturates space.

"If the universe is mostly empty, you'd want to take the fastest strategy possible, but if the universe is crowded, it'd be more important to have a higher density of probes, so your species can saturate the cosmos before anyone else," Olson said.

Perhaps the most provocative finding in all this is that the physical universe itself might be affected by aggressively expanding life. As civilizations burns through matter to fuel their cosmic diasporas, they start filling the universe up with waste heat, which can lead to a small uptick in the temperature of the cosmos. What's more, the expansion of the universe itself might be slowed—just a wee bit—by this extra radiation.

See, the gravity that stitches the cosmos together comes from a few different sources: the cosmological ​constant, the energy density of stars, and pressure, resulting from the motion of particles. The waste heat produced by advanced life, Olson finds, can contribute small—but detectable—pressure to the cosmos.

"It's not completely outside the realm of possibility that you'd one day be able to look at a graph of the evolution of the universe and see a little blip that indicates life," Olson said. "To me, that's a very profound finding."

One might wonder how any of this speculation, fascinating as it is, could matter to crowded world of seven billion hungry, polluting humans. But new searches for extraterrestrial techno-signatures are popping up across the scientific community, and thought experiments like Olson's may help direct such efforts. If we were to discover intelligent life out there, the finding could reap immeasurable benefits for humanity.

"People have started searching for waste heat signatures that could indicate intelligent, energy-harnessing life forms," Olson told me. "But we need more detailed models to figure out what these signatures might actually look like, and where in the universe we should be hunting."

That is, we need to keep our imaginations—and our telescopes—pointed to the most distant horizons. Who knows, maybe we'll end up being the guys who bubble their way across the universe until the end of time.