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Our Next Billion Years

Humanity only just arrived on Earth. But its future is in the cosmos.

By Max Tegmark
Oct 6, 2017 5:00 AMApr 20, 2020 2:55 AM
Future Space Cosmos Tech Art - Charles Glaubitz
(Credit: Charles Glaubitz)


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Thirteen point eight billion years after its birth, our universe has awoken and become aware of itself.

From a small blue planet, tiny conscious parts of our universe have begun gazing out into the cosmos with telescopes, repeatedly discovering that everything they thought existed is merely a small part of something grander: a solar system, a galaxy and a universe with over a hundred billion other galaxies arranged into an elaborate pattern of groups, clusters and superclusters. Although these self-aware stargazers disagree on many things, they tend to agree that these galaxies are beautiful and awe-inspiring.

But beauty is in the eye of the beholder, not in the laws of physics. So before our universe awoke, there was no beauty. This makes our cosmic awakening all the more wonderful and worthy of celebrating: It transformed our universe from a mindless zombie with no self-awareness into a living ecosystem harboring self-reflection, beauty and hope — and the pursuit of goals, meaning and purpose. Had our universe never awoken, then it would have been completely pointless — merely a gigantic waste of space. Should our universe permanently go back to sleep due to some cosmic calamity or self-inflicted mishap, it will become meaningless.

On the other hand, things could get even better. We don’t yet know whether we are the only stargazers in our cosmos, or even the first. But we’ve already learned enough about our universe to know that it has the potential to wake up much more fully than it has thus far. Perhaps life will spread throughout our cosmos and flourish for billions or trillions of years. And perhaps this will be because of decisions we make here on our little planet during our lifetime.

To me, the most inspiring scientific discovery ever is that we’ve dramatically underestimated life’s future potential. Our dreams and aspirations need not be limited to centurylong life spans marred by disease, poverty and confusion. Rather, aided by technology, life has the potential to flourish throughout a cosmos far more grand and inspiring than our ancestors imagined.

So if technology can shatter our old perceived limits of life, what are the ultimate limits? How much of our cosmos can come alive? How much energy, information and computation can it extract? These ultimate limits are set not by our understanding, but by the laws of physics. This, ironically, makes it easier in some ways to analyze the long-term future of life than the short-term future.

Whereas today’s supermarkets and commodity exchanges sell tens of thousands of items we might call “resources,” future life that’s reached the technological cap needs mainly one fundamental resource: so-called “baryonic matter,” meaning anything made up of atoms or their constituents (quarks and electrons). From a physics perspective, everything that future life may want to create — from habitats and machines to new life-forms — is simply elementary particles arranged in some particular way. Once future life has bumped up against the physical boundaries of what it can do with its matter, there is only one way for it to do more: get more matter. And the only way it can do this is by expanding into our universe. Spaceward ho!

Surround the Sun

When it comes to the future of life, one of the most hopeful visionaries is Freeman Dyson. He scoffed at how unambitious we humans were, pointing out that we could meet all our current global energy needs by harvesting the sunlight striking an area smaller than 0.5 percent of the Sahara desert. But why stop there? Why not simply put all the sun’s energy output to use?

Inspired by Olaf Stapledon’s 1937 sci-fi classic novel Star Maker, where rings of artificial worlds orbit their parent star, Dyson published a description in 1960 of what became known as a Dyson sphere. His idea was to rearrange Jupiter into a biosphere in the form of a spherical shell surrounding the sun, where our descendants could flourish, enjoying 100 billion times more biomass and a trillion times more energy than humanity uses today. He argued that this was the natural next step: “One should expect that, within a few thousand years of its entering the stage of industrial development, any intelligent species should be found occupying an artificial biosphere which completely surrounds its parent star.”

If you lived inside a Dyson sphere, there would be no nights: You’d always see the sun straight overhead, and all across the sky, you’d see sunlight reflecting off the rest of the biosphere, just as you can nowadays see sunlight reflecting off the moon during the day. If you wanted to see stars, you’d simply go “upstairs” and peer out at the cosmos from the outside of the Dyson sphere.

A low-tech way to build a partial Dyson sphere is to place a ring of habitats in circular orbit around the sun. To completely surround the sun, you could add rings orbiting it around different axes at slightly different distances, to avoid collisions.

To be long-lived, a Dyson sphere would need to be dynamic and intelligent, constantly fine-tuning its position and shape in response to disturbances and occasionally opening up large holes to let annoying asteroids and comets pass through without incident. Alternatively, a detect-and-deflect system could be used to handle such system intruders, optionally disassembling them and putting their matter to better use.

For today’s humans, life in a Dyson sphere would be disorienting at best and impossible at worst. But that need not stop future biological or non-biological life-forms from thriving there. Certain variants would offer essentially no gravity at all, and on others you could walk only on the outside (facing away from the sun) without falling off, with gravity about 10,000 times weaker than you’re used to. You’d have no magnetic field (unless you built one) shielding you from dangerous particles from the sun. The silver lining is that a Dyson sphere the size of Earth’s current orbit would give us about 500 million times more surface area to live on.

Harness Dead Stars

Although Dyson spheres are energy efficient by today’s engineering standards, they come nowhere near pushing the limits set by the laws of physics. Einstein taught us that if we could convert mass to energy with 100 percent efficiency, E = mc2 — an amount of mass m would give us an amount of energy E, where c is the speed of light. Since c is huge, this means a small amount of mass can produce a humongous amount of energy. If we had an abundant supply of antimatter (which we don’t), then a 100 percent efficient power plant would be easy to make. Simply pouring a teaspoonful of anti-water into regular water would unleash the energy equivalent to 200,000 tons of TNT, the yield of a typical hydrogen bomb — enough to power the world’s entire energy needs for about seven minutes.

In contrast, our most common ways of generating energy today are woefully inefficient. Digesting a candy bar is merely 0.00000001 percent efficient, in the sense that it releases a mere ten-trillionth of the energy that it contains. If your stomach were even 0.001 percent efficient, then you’d only need to eat a single meal for the rest of your life. Today’s nuclear reactors do dramatically better by splitting uranium atoms through fission, but they still fail to extract more than 0.08 percent of their energy. Fusion is more efficient than fission, but even if we enclose the sun in a perfect Dyson sphere, we’ll still never convert more than about 0.08 percent of the sun’s mass to energy we can use, because once the sun has consumed about a tenth of its hydrogen fuel, it will end its lifetime as a normal star, expand into a red giant, and begin to die. How can we do better?

Black Hole Power Plants

In his book A Brief History of Time, Stephen Hawking proposed a black hole power generator, where black holes swallow matter and then convert matter into radiation by evaporating, but there are major challenges with making this process fast enough to be useful. Another interesting strategy is to extract energy not from the black hole itself, but from matter falling into it. Nature has already found a way of doing this all on its own: the quasar. As gas swirls even closer to a black hole, forming a pizza-shaped disk whose innermost parts gradually get gobbled up, it gets extremely hot and gives off copious amounts of radiation. As gas falls downward toward the hole, it speeds up, converting its gravitational potential energy into motion energy, just as a skydiver does. The motion gets progressively messier as complicated turbulence converts the coordinated motion of the gas blob into random motion on ever-smaller scales. Eventually, individual atoms begin colliding with each other at high speeds — having such random motion is precisely what it means to be hot, and these violent collisions convert motion energy into radiation.

By building a Dyson sphere around the entire black hole, at a safe distance, this radiation energy can be captured and put to use. The faster the black hole spins, the more efficient this process gets, with a maximally spinning black hole delivering energy at a whopping 42 percent efficiency.

(Credit: Charles Glaubitz)


Future intelligent life might be able to build what I call a “sphaelerizer:” an energy generator acting like a diesel engine on steroids. A traditional diesel engine compresses a mixture of air and diesel oil until the temperature gets high enough for it to spontaneously ignite and burn. After that, the hot mixture re-expands and does useful work in the process, say pushing a piston. The carbon dioxide and other combustion gases weigh about 0.00000005 percent less than what was in the piston initially, and this mass difference turns into the heat energy driving the engine.

A sphaelerizer would compress ordinary matter to a couple of quadrillion degrees, and then let it re-expand and cool once entities known as sphaelerons had converted most quarks into electrons and related particles. We already know the result of this experiment, because our early universe performed it for us about 13.8 billion years ago when it was that hot: Almost 100 percent of the matter got converted into energy, with less than one billionth remaining in the form of quarks and electrons, which make up all the matter we observe in our universe today. So it’s like a diesel engine, except a billion times more efficient!


If eating dinner is 10 billion times worse than the physical limit on energy efficiency, then how efficient are today’s computers? Even worse than that dinner, as we’ll now see.

Seth Lloyd, an MIT quantum computer pioneer, showed that computing speed is limited by energy. This means that a 1-kilogram computer, equivalent to a small laptop, can perform at most 5*1050 operations per second — that’s a whopping 36 orders of magnitude more than the computer on which I’m typing these words. We’ll get there in a couple of centuries if computational power keeps doubling every couple of years. He also showed that a 1 kg computer can store up to 1031 bits, which is about one billion billion times better than my laptop.

Actually attaining these limits may be challenging, even for superintelligent life. However, Lloyd is optimistic that the practical limits aren’t that far from the ultimate ones. Indeed, existing quantum computer prototypes have already miniaturized their memory by storing 1 bit per atom. Scaling that up would allow storing about 1025 bits per kilogram — a trillion times better than my laptop. Moreover, using electromagnetic radiation to communicate between these atoms would permit about 5*1040 operations per second — 31 orders of magnitude better than my CPU.

The potential for future life to compute and figure things out is truly mind-boggling: In terms of orders of magnitude, today’s best supercomputers are much further from the ultimate 1 kg computer than they are from the blinking turn signal on a car, a device that stores merely 1 bit of information, flipping it between on and off about once per second.

Star-farers of Catan

General relativity says it’s impossible to send rockets through space at the speed of light, because this would require infinite energy. So, in practice, how fast can rockets go?

In 1984, physicist Robert Forward pioneered a clever laser-sail rocket design. Just as air molecules bouncing off a sailboat sail will push it forward, light particles (photons) bouncing off a mirror will push it forward. By beaming a huge solar-powered laser at a vast ultralight sail attached to a spacecraft, we can use the energy of our own sun to accelerate the rocket to great speeds. Forward calculated that this could let humans make the 4-light-year journey to the Alpha Centauri solar system in merely 40 years. Once there, you could imagine building a new giant laser system and continuing to star-hop throughout the Milky Way Galaxy. But why stop there? Since Forward’s design, there’s been dramatic progress in artificial intelligence.

The possibility of computer superintelligence makes the future look much more promising for those with intergalactic wanderlust. If you remove the need to transport bulky human life-support systems and add AI-invented technology, intergalactic settlement suddenly appears rather simple. Forward’s laser sailing becomes much cheaper when the spacecraft merely need to be large enough to contain a “seed probe,” a robot capable of landing on an asteroid or planet in the target solar system and building up a new civilization from scratch. It doesn’t even have to carry the instructions with it. All it has to do is build a receiving antenna large enough to pick up more detailed blueprints and instructions transmitted from its mother civilization at the speed of light. Then, it uses its newly constructed lasers to send out new seed probes to continue settling the galaxy one solar system at a time.

Once superintelligent AI has settled another solar system or galaxy, bringing humans there is easy — if humans have succeeded in programming the AI with this goal. All the necessary information about humans can be transmitted at the speed of light, after which the AI can assemble quarks and electrons into the desired humans. This could be done either in a low-tech way by simply transmitting the 2 gigabytes of information needed to specify a person’s DNA and then incubating a baby to be raised by the AI, or the AI could assemble quarks and electrons into full-grown people who would have all the memories scanned from their originals back on Earth.

This means that if there’s an intelligence explosion, the key question isn’t if intergalactic settlement is possible, but simply how fast it can proceed. For example, if it takes 20 years to travel 10 light-years to the next star system with a laser-sail system, and then another 10 years to settle it and build new lasers and seed probes there, the settled region will be a sphere growing in all directions at a third of the speed of light on average.

Cosmic Spam

Last but not least, there’s the sneaky Hail Mary approach to expanding even faster than any of the above methods will permit: using Hans Moravec’s “cosmic spam” scam. By broadcasting a message that tricks naive freshly evolved civilizations into building a superintelligent machine that hijacks them, a civilization can expand essentially at the speed at which their seductive siren song spreads through the cosmos.

Since this may be the only way for advanced civilizations to reach most of the galaxies within their future light cone and they have little incentive not to try it, we should be highly suspicious of any transmissions from extraterrestrials! In Carl Sagan’s book Contact, we earthlings used blueprints from aliens to build a machine we didn’t understand — I don’t recommend doing this ...

We Come in Peace

So far, we’ve only discussed scenarios where life expands into our cosmos from a single intelligence explosion. But what happens if two expanding civilizations meet?

Europeans were able to conquer Africa and the Americas because they had superior technology. In contrast, it’s plausible that long before two superintelligent civilizations encounter one another, their technologies will plateau at the same level, limited merely by the laws of physics. This makes it seem unlikely that one superintelligence could easily conquer the other even if it wanted to. Moreover, if their goals have evolved to be relatively aligned, then they may have little reason to desire conquest or war. For example, if they’re both trying to prove as many beautiful theorems as possible and invent as many clever algorithms as possible, they can simply share their findings and both be better off. After all, information is very different from the resources that humans usually fight over, in that you can simultaneously give it away and keep it.

Some expanding civilizations might have goals that are essentially immutable, such as those of a fundamentalist cult or a spreading virus. However, it’s also plausible that some advanced civilizations are more like open-minded humans — willing to adjust their goals when presented with sufficiently compelling arguments. If two of them meet, there will be a clash not of weapons but of ideas, where the most persuasive one prevails and has its goals spread at the speed of light through the region controlled by the other civilization. Assimilating your neighbors is a faster expansion strategy than physical settlement, which inevitably progresses slower than the speed of light. This assimilation will not be forced, such as that infamously employed by the Borg in Star Trek: It will be voluntary, based on the persuasive superiority of ideas, leaving the assimilated better off.

Embracing Technology

Because sci-fi authors are often dismissed as unrealistic romantic dreamers, I find it ironic that most sci-fi and scientific writing about space settlement now appears too pessimistic in the light of AI. For example, we saw how intergalactic travel becomes much easier once people and other intelligent entities can be transmitted in digital form, potentially making us masters of our own destiny not only in our solar system or Milky Way Galaxy, but also in the cosmos.

If we don’t keep improving our technology, the question isn’t whether humanity will go extinct, but how? What will get us first — an asteroid, a supervolcano, the burning heat of the aging sun or some other calamity? If instead of eschewing technology, we embrace it, then we up the ante: We gain the potential both for life to survive and flourish and for life to go extinct even sooner, self-destructing due to poor planning. My vote is for embracing technology, but proceeding not with blind faith in what we build, but with caution, foresight and careful planning. Life’s future potential in our universe is grander than the wildest dreams of our ancestors, so let’s make the most of it!

From the Book: LIFE 3.0: BEING HUMAN IN THE AGE OF ARTIFICIAL INTELLIGENCE by Max Tegmark. Copyright © 2017 by Max Tegmark. Published by Alfred A. Knopf, an imprint of The Knopf Doubleday Publishing Group, a division of Penguin Random House LLC.

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