During the 1930s, astronomers came to realize that the Universe is in a state of expansion. By the 1990s, they realized that the rate at which it is expansion is accelerating, giving rise to the theory of “Dark Energy”. Because of this, it is estimated that in the next 100 billion years, all stars within the Local Group – the part of the Universe that includes a total of 54 galaxies, including the Milky Way – will expand beyond the cosmic horizon.
At this point, these stars will no longer be observable, but inaccessible – meaning that no advanced civilization will be able to harness their energy. Addressing this, Dr. Dan Hooper – an astrophysicist from the Fermi National Accelerator Laboratory (FNAL) and the University of Chicago – recently conducted a study that indicated how a sufficiently advanced civilization might be able to harvest these stars and prevent them from expanding outward.
To put it simply, the theory of Dark Energy is that space is filled with a mysterious invisible force that counteracts gravity and causes the Universe to expand at an accelerating rate. The theory originated with Einstein’s Cosmological Constant, a term he added to his theory of General Relativity to explain how the Universe could remain static, rather than be in a state of expansion or contraction.
While Einstein was proven wrong, thanks to observations that showed that the Universe was expanding, scientists revisited the concept in order to explain how cosmic expansion has sped up in the past few billion years. The only problem with this theory, according to Dr. Hooper’s study, is that the dark energy will eventually become dominant, and the rate of cosmic expansion Universe will increase exponentially.
As a result, the Universe will expand to the point where all stars are so far apart that intelligent species won’t even be able to see them, let alone explore them or harness their energy. As Dr. Hooper told Universe Today via email:
“Cosmologists have learned over the last 20 years that our universe is expanding at an accelerating rate. This means that over the next 100 billion years or so, most of the stars and galaxies that we can now see in the sky will disappear forever, falling beyond any regions of space that we could reach, even in principle. This will limit the ability of a far-future advanced civilization to collect energy, and thus limit any number of things they might want to accomplish.”
In addition to being the Head of the Theoretical Astrophysics Group at the FNAL, Dr. Hooper is also an Associate Professor in the Department of Astronomy and Astrophysics at the University of Chicago. As such, he is well versed when it comes to the big questions of extra-terrestrial intelligence (ETI) and how cosmic evolution will affect intelligent species.
To tackle how advanced civilizations would go about living in such a Universe, Dr. Hooper begins by assuming that the civilizations in question would be a Type III on the Kardashev scale. Named in honor of Russian astrophysicist Nikolai Kardashev, a Type III civilization would have reached galactic proportions and could control energy on a galactic scale. As Hooper indicated:
“In my paper, I suggest that the rational reaction to this problem would be for the civilization to expand outward rapidly, capturing stars and transporting them to the central civilization, where they could be put to use. These stars could be transported using the energy they produce themselves.”
As Dr. Hooper admits, this conclusion relies on two assumptions – first, that a highly advanced civilization will attempt to maximize its access to usable energy; and second, that our current understanding of dark energy and the future expansion of our Universe is approximately correct. With this in mind, Dr. Hooper attempted to calculate which stars could be harvested using Dyson Spheres and other megastructures.
This harvesting, according to Dr. Hooper, would consist of building unconventional Dyson Spheres that would use the energy they collected from stars to propel them towards the center of the species’ civilization. High-mass stars are likely to evolve beyond the main sequence before reaching the destination of the central civilization and low-mass stars would not generate enough energy (and therefore acceleration) to avoid falling beyond the horizon.
For these reasons, Dr. Hooper concludes that stars with masses of between 0.2 and 1 Solar Masses will be the most attractive targets for harvesting. In other words, stars that are like our Sun (G-type, or yellow dwarf), orange dwarfs (K-type), and some M-type (red dwarf) stars would all be suitable for a Type III civilization’s purposes. As Dr. Hooper indicates, there would be limiting factors that have to be considered:
“Very small stars often do not produce enough energy to get them back to the central civilization. On the other hand, very large stars are short lived and will run out of nuclear fuel before they reach their destination. Thus the best targets of this kind of program would be stars similar in size (or a little smaller) than the Sun.”
Based on the assumption that such a civilization could travel at 1 – 10% the speed of light, Dr. Hooper estimates that they would be able to harvest stars out to a co-moving radius of approximately 20 to 50 Megaparsecs (about 65.2 million to 163 million light-years). Depending on their age, 1 to 5 billion years, they would be able to harvest stars within a range of 1 to 4 Megaparsecs (3,260 to 13,046 light-years) or up to several tens of Megaparsecs.
In addition to providing a framework for how a sufficiently-advanced civilization could survive cosmic acceleration, Dr. Hooper’s paper also provides new possibilities in the search for extra-terrestrial intelligence (SETI). While his study primarily addresses the possibility that such a mega-civilization will emerge in the future (perhaps it will even be our own), he also acknowledges the possibility that one could already exist.
In the past, scientists have suggested looking for Dyson Spheres and other megastructures in the Universe by looking for signatures in the infrared or sub-millimeter bands. However, megastructures that have been built to completely harvest the energy of a star, and use it to transport them across space at relativistic speeds, would emit entirely different signatures.
In addition, the presence of such a mega-civilization could be discerned by looking at other galaxies and regions of space to see if a harvesting and transport process has already begun (or is in an advanced stage). Whereas past searchers for Dyson Spheres have focused on detecting the presence of structures around individual stars within the Milky Way, this kind of search would focus on galaxies or groups of galaxies in which most of the stars would be surrounded by Dyson Spheres and removed.
“This provides us with a very different signal to look for,” said Dr. Hooper. “An advanced civilization that is in the process of this program would alter the distribution of stars over regions of space tens of millions of light years in extent, and would likely produce other signals as a result of stellar propulsion.”
In the end, this theory not only provides a possible solution for how advanced species might survive cosmic expansion, it also offers new possibilities in the hunt for extra-terrestrial intelligence. With next-generation instruments looking farther into the Universe and with greater resolution, perhaps we should be on the lookout for hypervelocity stars that are all being transported to the same region of space.
Could be a Type III civilization preparing for the day when dark energy takes over!
By popular request, Isaac Arthur and I have teamed up again to bring you a vision of the future of human space exploration. This time, we bring you practical construction tips from a pair of Type 2 Civilization engineers.
To make this collaboration even better, we’ve teamed up with two artists, Kevin Gill and Sergio Botero. They’re going to help create some special art, just for this episode, to help show what some of these megaprojects might look like.
I’d also like to congratulate Gannon Huiting for suggesting the topic for this collaboration. We both asked our Patreon communities to brainstorm ideas, and his core idea sparked the idea for the episode. You get one of my precious metal meteorites, which I guarantee will give you a mostly worthless superpower.
We’ll tell you the story of what it took to go from our first tentative steps into space to the vast Solar System spanning civilization we have today. How did we extract energy and resources from the Moon, planets and even gas giants of the Solar System? How did we shift around and dismantle the worlds to provide the raw resources of our civilization?
Humanity’s ability to colonize the Solar System was unleashed when we harvested deposits of helium 3 from the Moon. This isotope of helium is rare on Earth, but the constant solar wind from the Sun has deposited a layer across the Moon, though its regolith.
Helium 3 was the best, first energy source we got our hands on, and it changed everything. Although other kinds of fusion reactors can produce more energy with more efficiency, the advantage of helium 3 is that the fusion reaction releases no neutrons. This means you can have a fusion reactor on your starship or on your base with much less shielding.
We still use helium-3 reactors when living creatures need to be close the reactor, or the ship can’t afford to carry around heavy shielding.
The Helium 3 is found within the first 100 cm of the lunar regolith. Harvesting it started slowly, but in time, our mining machines grew larger, and we stripped this layer completely off the Moon. There are other repositories across the Solar System, in the regolith of Mercury, other moons and asteroids across the Solar System, and in the atmospheres of the giant planets. We later switched to getting our Helium 3 from Uranus and Neptune, but the Moon got everything started.
One of our big problems with building in space was getting raw materials. Just about every place that has the supplies we needed was at the bottom very deep gravity wells which made accessing those materials a lot harder. Asteroid and moons offered us a large supply of material that was not locked inside such deep gravity wells.
These asteroids also gave us a big initial head start on developing space-based infrastructure as they contained a great deal of precious metals that we could bring home to help fund our endeavors.
For all that, the entire Asteroid Belt contains much less material than Earth’s own Moon. The ease of mining and transport on these bodies made them a critical source of raw materials for building up the early Solar Infrastructure and many of them became homes to rotating habitats buried deep inside the asteroid, where millions of people live comfortably shielded from the hazards of space and support themselves mining the asteroid around them.
These asteroids and moons often contained water in the form of ice, which is vital to creating life-bearing habitats in space, as well as fuel and propellant for many early-era spaceships.
However, even if the entire Asteroid Belt was ice, instead of it being a fairly smaller percent of the mass, that would still only be the approximate mass of Earth’s Oceans. There was a plentiful supply for early efforts but not enough for major terraforming efforts on places like Mars or creating many artificial habitats.
Water is incredibly scarce in the inner Solar System, but becomes more plentiful as we make our way further out, past the Solar System’s Frost Line. Deeper out past the planets we find enough water to make whole planets out of, as hydrogen and oxygen are the first and third most abundant elements in the Universe. Also, for the most part these come in convenient iceberg-sized packages, low enough in mass to have a small gravity well and to be movable.
Mastering the Solar System required moving very large objects in space. For the less massive objects, we could put a big thruster on it, but for the largest projects, such as moving planets with atmospheres (which we’ll get to later in this article), another technique was required.
To move large objects around, without touching them, you need a Gravity Tractor.
Want to move an asteroid? Use the gravity of a less massive object, like a spaceship. Hold the spaceship close to the asteroid, and their gravity will put them together. Fire your rocket’s thrusters to keep the distance, and you slowly pull the asteroid in any direction you like. It takes a long time, and does require fuel, but you can use this technique to move anything anywhere in the Solar System.
Put a massive satellite into orbit around an asteroid. When the satellite is on one side of the asteroid it fires its thrusters towards the satellite. And then on the other side of its orbit, it fires its thrusters away from the satellite. The satellite will have been pushed twice in the same direction. To an outside observer that satellite has moved, though on the asteroid it will seem to have been nudged closer than put back.
Don’t forget that the satellite pulls on the asteroid with just as much force as the asteroid exerts on the satellite. Earth pulls on the Sun just as hard as it pulls on us, but it’s more massive so it doesn’t move as much. But it does move, and so by pushing on the satellite towards the primary then pushing away on the opposite side, we move the primary body.
We can also take advantage of momentum transfers from gravity to alter the course of an object by making a close flyby. You can use this gravitational slingshot to use the gravity of a planet to change the move large objects into a new trajectory.
Over time, we put gravitational tugs into orbit around every chunk of rock and ice that we wanted to move, shifting their locations to the best places in the Solar System.
Some places gave us raw materials. Other places would serve as our homes.
Earth is the third closest planet to the Sun and it will always be the environment we’re trying to replicate. Earth is, well, it was… home.
For all the millions of other worlds across the Solar System, we made them capable of hosting life with a little work. Often we could make them habitable just by increasing the amount of energy they received from the Sun.
Creating artificial gravity by spinning a habitat or breathable air by doming it over did us no good if there wasn’t enough light to melt ice into water or let plants grow.
The farther you get from the Sun, the less light you get, but we bounce light that would have been lost, concentrating it to let life flourish. The Sun gives off over a billion times the light that actually reaches Earth, so there’s no shortage in quantity, just concentration.
To double the light reaching a planet like Mars, you would need a mirror surface area of twice the size of Mars. But not twice the mass of Mars. For every square meter of land on Earth, there’s about 10 billion kilograms of mass under our feet. A mirror on Earth wouldn’t weigh much more than a kilogram a square meter, but in space we can go far thinner. Any one of millions of small asteroids in the solar system contains enough material to make a planetary surface’s worth of mirrors.
Lenses or parabolic reflectors let us move light in from far more densely concentrated locations closer to the Sun. Reflecting light also allows us to remove harmful or less useful invisible wavelengths like ultraviolet or x-rays.
This allowed us to make almost any place warm and bright enough. We took distant moons and asteroids far from the Sun, and gave them a collar of thin mirrors bouncing light into a parabolic dish. By bouncing this light into rotating habitats safely buried inside the asteroid, we created warm, lush garden worlds in environments so cold that air itself would condense into a liquid.
For most of the Solar System we wanted to warm planets up. But for Venus and Mercury, we needed to cool them down. We did this by placing shades between them and the Sun to reflect away some of the light hitting them.
The easiest way to do this was to position an opaque material between the planet and the Sun, at the L1 Lagrange point. At this point the gravitational pull of the planet counteracts the pull of the Sun allowing a large thin solar shade to remain in position with minimal energy. This way the planet is cooled.
But we did better than merely cool, we shaped the light to our needs. With a collection of many small shades, we avoided putting a visible dark spot on the Sun. Sunlight comes in many frequencies, from radio to x-rays; some were more valuable to us than others. Plants mostly use red and blue light, while green light doesn’t help with photosynthesis. So blocked a decent amount of green light, some blue, and no red, and cooled the planet without harming plant life and without really altering how the light looked to our eyes.
We engineered the perfect material for our shades which was mostly transparent to the wavelengths of light we wanted and mostly reflective or absorptive to the ones we didn’t.
Ultraviolet is a good example. We wanted some to get to our planet, as it does help as a sterilizing agent to biological processes and it helps make ozone, but we wanted to cut most of that out. Even better, about half of the light coming from the Sun is in infrared, which we can’t see and which plants don’t use.
We blocked most of that and seriously lowered temperatures on Venus and Mercury.
We set up shades to block the light from reaching our planets. And we did the same with dangerous radiation streaming from the Sun. We set up a concentrated magnetic shield at the Mars-Sun L1 Lagrange point, which catches and redirects high energy particles. This protects a world from the Sun, but it doesn’t prevent harmful cosmic rays, which can come from any part of the sky.
Our own planet Earth has a robust magnetosphere, and it’s the main reason we have air to breath and don’t absorb dangerous radiation from the Sun and space.
Places like Mars don’t. For this purpose, we created artificial magnetospheres. We considered trying to get Mars’ core spinning fast and hot so that rapid spinning molten ferromagnetic materials would generate a protective magnetosphere.
But that was too much effort. We didn’t actually care what generated the magnetic field, we just wanted the magnetic field. In the end we deployed a constellation of electromagnetic satellites around every world exposed to space. These satellites could do double duty, harvesting solar radiation and generating an artificial magnetosphere.
Cosmic rays and radioactive particles from the Sun were captured and redirected safely away from the world, allowing us to roam freely on the surface.
Once we had made acquired the resources of every world in the Solar System, we began our next great engineering effort. To move and dismantle the worlds themselves. To create the optimal configuration that gave us the most living space and the most usable energy. We began the construction of our Dyson swarm.
Moving planets is almost impossible. But not completely impossible. How do you get all that energy to move a world without melting it? The orbital energy of Earth around the Sun is approximately 30 million, trillion, trillion joules. That’s equal to all the energy the Sun puts out over a few months.
Of course, the Sun is slowly warming up, and while estimates vary, it’s generally accepted that in about a billion years it will have warmed up enough that Earth would be uninhabitable. Moving the Earth was inevitable.
To move the Earth outward to counteract the increased solar luminosity, we needed to add orbital energy. A lot of energy.
Earlier, we discussed using gravity tractors and gravitational slingshots to slowly and steadily move objects around the Solar System. This technique works at the largest scales too.
A gravity tractor could slowly and steadily move an entire planet if you had enough time and fuel. Because we already had mastery of all the asteroids in the Solar System, we put them into orbits that swept past worlds.
Each gravitational slingshot gave or stole orbital momentum from the world, pushing it closer or farther from the Sun.
We also used orbital mirrors to bounce sunlight from the Sun. With enough of them, deflecting their light in the same general directional while maintaining an orbit around the planet, we could move worlds without touching them or heating them up from the light beams.
With enough satellites to keep the net gravitational force on the planet homogenous, we didn’t have to worry about tidal heating, allowing us to move a planet far faster.
In the future, we’ll use a king-size version of this to move the entire Solar System, using the star as the power source, called a Shkadov Thruster. We will push the Sun and every star we control into a constellation that matches our needs. But that’s a problem our Type III civilization engineers will have to worry about.
We always needed ice. For water, for fuel and for air. And the outer Solar System had all the ice we could ever need. We brought comets and other icy bodies in from the outer Solar System to bring water to the planets we’re terraforming – Mars, Venus, and the large moons of the Solar System.
Pushing ice is a tricky process, but the comet itself is the source of fuel, either liquid hydrogen and oxygen as the propellants or using the hydrogen for a fusion torch drive. However we have an alternative trick we can use.
We just talked about using energy beams, focused sunlight, lasers, or microwave beams to push objects outward from the sun. You can also move inward by reflecting the beam off at an angle, removing orbital momentum. This lowers their orbit into the Solar System.
By setting up energy collectors on comets, we could beam power out them, and use that energy to melt atoms into gas and accelerate them away with a magnetic field, just like an ion drive. This let us take high-strength lasers and microwave beams powered from the inner Solar System and use it to tractor comets inward. The propellant melted off the comets could carry away far more momentum than the energy beam added, though at the cost of losing some of your mass in the process.
One by one we identified the icy bodies in the Kuiper Belt and Oort Cloud, installed an ice engine, and pulled them inward, to the places we needed that water the most.
The day to day energy for our civilization comes from the Sun. Solar collectors power the machines, computers and systems that make day-to-day life spanning the Solar System possible.
Just as the ancient Earth civilizations used hydrocarbons as a store of fuel, we depend on hydrogen. We use it for our rocket fuel, to manufacture drinking water, and most importantly, for our fusion reactors. We always need more hydrogen.
Fortunately, the Solar System has provided us with vast repositories of hydrogen: the giant planets, Jupiter, Saturn, Uranus and Neptune all made up of at least 80% hydrogen. But harvesting the planets for their hydrogen isn’t without its challenges.
For starters, the gravity on the surface of Jupiter is nearly 25 m/s2, which is nearly three times the surface gravity of Earth. On top of that, Jupiter’s magnetosphere produces intense radiation fields through its entire system. You can’t spend much time near Jupiter without receiving a lethal radiation dose.
We deploy huge robotic scoopers to swoop down into Jupiter’s gravity well, skim across the upper cloud tops, funneling in as much hydrogen as they can. On board compressors liquefy the hydrogen, or refine it into the more energy dense metallic hydrogen. The fuel is then distributed across the Solar System through the interplanetary transport network.
For Uranus and Neptune, where the gravity well is less extreme, we have permanent mining stations which float in the cloud tops, harvesting raw materials for return back to space. These factories are a huge improvement over the more expensive scoop ships. Smaller cargo ships ferry the deuterium, helium-3 and hydrogen up to orbit, for an energy hungry Solar System.
In order to construct our Dyson Swarm, we will eventually need to dismantle almost all the planets and moons in the Solar System to provide the raw materials to house countless people.
This process has begun, and we we have a number of options. For some worlds, we plan to just keep mining and refining them with robotic factories until they are gone, but this can be quite time consuming and often we would rather do our refining and manufacturing elsewhere.
Instead, we have set up very large mass drivers running around the object to launch material directly towards its desired destination. To avoid building up angular momentum inside the shrinking mass of the planetoid, we run these giant cannons in both directions. This prevents it spinning so fast that it tears itself apart. There’s very little gravity holding these objects together after all.
For the smaller objects that’s actually just fine. When we want to disassemble a smaller asteroid or moon into rock and dirt for the inside of a cylinder habitat, we construct a cylindrical shell around the asteroid, and spray material from the asteroid onto the cylinder, giving it some spin and artificial gravity to hold the material up, or rather down to its surface. We spin the asteroid faster and faster until it flies apart, transferring its material and its angular momentum to the cylinder.
With larger asteroids we send a series of cylinders past them in a chain, painting their interiors with the material we will turn into dirt later on, until we run out of asteroid.
For full blown minor planets and moons, which are much more massive but still fairly low in gravity and lacking an atmosphere, we pump matter up tubes to high above the planetoid to fill freighters, get compacted into cannon balls to be launched elsewhere, or simply pumped into rotating habitats being built nearby.
Mercury is already half consumed. In a few more generations, it will be a distant memory.
Perhaps our greatest accomplishment is the work underway at Jupiter and Saturn. We are now in the process of dismantling these worlds to harvest their resources.
The largest machines humanity has ever built, fusion candles, have been deployed into the atmospheres of Jupiter and Saturn. These enormous machines scoop up raw hydrogen from Jupiter to run their fusion reactors. One side of the fusion candle fires downward, keeping the machine aloft. The other end blasts out into space, spewing material that can be harvested from orbit.
Not only that, but these candles provide thrust, pushing Jupiter and Saturn slowly but steadily into safer, more useful orbits for our civilization. As we use up the hydrogen, their mass will decrease. Uranus and Neptune will follow slowly, from farther out in the Solar System.
Eventually, eons into the future, we will have dismantled them down to their cores. There is more than a dozen times the mass of the Earth in rock and metal down at the core of Jupiter. More raw materials than any other place in the Solar System.
The long awaited construction of our fully operational Dyson swarm will finally begin. We’ll miss the presence of Jupiter and Saturn in the Solar System, and remember them fondly, but humanity needs room to stretch its legs.
Of course, as huge as the gas giants are compared to Earth, the Sun is far bigger, and contains not just hydrogen and helium but thousands of planets worth of heavier elements, which are spread around the sun, not just concentrated deep down.
Trying to scoop matter off a star is much harder than out of gas giant, though conveniently, we can take advantage of all that energy the Sun is giving off to power our extraction.
The material on the Sun is also ionized, so it reacts strongly to magnetic forces, and the Sun generates a massively powerful magnetic field too. In fact, our Sun ejects about a billion kilograms of matter a second as solar wind. We have a few ways to increase this flow and harvest it.
The first is called Thermal Driven Outflow. We hover mirrors over the surface, reflecting and concentrating light down on spots on the Sun’s surface to heat it up and increase the mass being ejected. This kicks up an eruption much like a solar flare, feeding more solar wind.
We then place a large ring of satellites around the Sun’s equator, connected to each other by a stream of ionized particles generating a huge current, themselves running that stream off solar power. This ring creates a powerful magnetic field pushing outward toward the Sun’s poles, and sending the super-heated matter in that direction.
Hovering over the poles further out, we have a giant ring sucking up sunlight and generating a huge toroidal magnetic field. All the matter we stir up on the sun and off the poles is sucked through that and slowed down for collection. It’s a lot like the VASIMR Drive, using a magnetic nozzle, so that nothing has to touch the ultra hot plasma. Giant Plasma Thrusters essentially acting as the pump to gather the matter, it stays in place using the momentum it’s stealing from the particles it is slowing down, again it’s a giant plasma thruster.
We will eventually build far more of these rings around the Sun, spaced up and down from the equator, and intermittently shut off the power beam holding them aloft. As all the satellites in that ring drop, building up speed, we switch the power for the beam back on and their plummet stops and they push back up to their original position. We do this with all the rings, in sequence, pushing much larger waves of matter toward the poles than the Thermal Driven Outflow method provides, and we call this option the Huff-n-Puff Method.
And there you have it, our tips and techniques to harvest all the resources from the Solar System. To push and pull worlds, to heat them up, cool them down and use their raw materials to house humanity’s growing, ever expanding population.
As we nearly achieve our Type II civilization status, and control all the energy from our Sun and all the resources of the Solar System, we set our sights on a new goal: doing the same thing for the entire Milky Way Galaxy.
Perhaps in a few million years, we’ll create another guide for you, to help you make this transition as efficiently as possible.
When you consider that age of the Universe – 13.8 billion years by our most recent counts – and that which is “observable” to us measures about 93 billion light years in diameter, you begin to wonder why we haven’t found signs of extra-terrestrial intelligence (ETI) beyond our Solar System. To paraphrase Enrico Fermi, the 20th century physicists who advanced the famous Fermi Paradox – “where the heck are all the aliens?”
Essentially, aestivation is a prolonged state of torpor that organisms enter into during a particularly hot or dry period. Similar to what hibernating animals do during the winter, this state is designed to keep creatures alive until more favorable conditions emerge. And when applied to the cosmos, this concept could explain why one of the key things astronomers have been looking for – i.e. activity – has been lacking.
This is not the first time Sandberg has addressed questions arising out of the Fermi Paradox. In a previous study, he and Stuart Armstrong (also a research associate with the FHI and one of the co-authors on this study) extended the Fermi Paradox to look beyond our own galaxy, addressing how more advanced civilizations would feasibly be able to launch colonization projects with relative ease (and even travel between galaxies without difficulty).
In the end, they concluded that civilizations from millions of galaxies should have been able to reach us by now, which only serves to bring the Fermi Paradox into greater focus. If these early civilizations are around, why are they not visible to us? The reason for this, they claim in this new study, has to do with the thermodynamics of computation.
According to this basic rule, the cost of a certain amount of computation is proportional to the temperature it generates. For some time, astronomers and cosmologists have been aware that the Universe is steadily cooling down over the time. Not only is star formation in galaxies slowly dying out over the course of billions of years, but even the cosmic background radiation is becoming colder.
As such, it makes sense that ancient and advanced civilizations would want to wait for cooler conditions to prevail. Sandberg explained to Universe Today via email:
“The core idea is that if advanced civilizations mainly or solely care about computation, then it is rational for them to wait until the Universe is much older than now. The reason is that the energy cost (which will eventually limit how much computation you can do) is proportional to temperature, and this means that the far future is vastly more hospitable than the hot present. If this were true, we have a nice explanation for the apparent absence of big old civilizations. It would also lead to observable consequences: a reduction in processes that waste resources they would want in the late eras.”
Timing is a key feature to this hypothesis. Much like the theory that humanity may have arrived early to the Universe, this theory states that the lack of detection has to do with species being in different places in their biological/technological evolution. In this case, the aestivation period of early civilizations has coincided with the subsequent rise of humanity as an space-faring and technologically-adept species.
Herein lies another reason why ancient civilizations might want to take a cosmic nap. Given how long life needs in order to emerge – humanity took roughly 4.5 billion years to get to where it is today – then it stands to reason that ancient civilizations might want to skip ahead a few eons in order to let new races emerge.
“There is an entropy cost to irreversible logical operations, including error correction,” said Sanders. “So unless there is some magical energy source or entropy sink, if you want to do as much computation as possible you should wait until the cosmic background radiation levels off. In addition, civilizations may want to go to the future if they want to meet other, independently evolved civilizations. If intelligence is rare in time and space but aestivates to the far future, then it will meet there.”
Of course, the aestiation hypothesis (much like the Drake Equation and the Fermi Paradox) is based on a few assumptions about what ETI would be capable of. These include:
There are civilizations that mature much earlier than humanity.
These civilizations can expand over sizeable volumes, gaining power over their contents.
These civilizations have solved their coordination problems.
A civilization can retain control over its volume against other civilizations.
The fraction of mature civilizations that aestivate is non-zero
Aestivation is largely invisible.
In other words, the hypothesis assumes the existence of civilizations that are more advanced than humanity which is based on the notion that they have had billions of years to develop elsewhere in the Universe. These civilizations would be higher on the Kardashev Scale (between Level II and III) by now, meaning that they had evolved to the point where they could harness the energy of entire star systems and perhaps even galaxies.
Also, it assumes that these civilizations would have become space-faring races that had expanded to occupy parts of the cosmos that lie well beyond their own star systems. Ultimately, those civilizations that have chosen to become dormant would therefore be invisible to us since they are not currently traveling between stars and galaxies, smashing up planets to create megastructures, or consuming entire stars for fuel.
You know, the kind of stuff we think mega-civilizations would do. Which naturally raises the question, how might we be able to detect such civilizations at rest? To this, Sandberg has a few possible suggestions, ones which ETI-hunters may want to heed:
“Look for galaxies that either move out of the way of galaxy collisions or towards big clusters by ejecting mass or energy in one direction, or have an unusually low number of heavy blue-white stars, or otherwise avoid losing gas to interstellar space. Or, try launching a self-replicating space probe to pave the universe and see if somebody stops you.”
As with all things having to do with aliens and ETI, a measure of guess-work is required here. And some would naturally argue that it is also possible that advanced civilizations are not subject to the same limitations we humans are, which would limit our ability to speculate here. In the end, we humans are required to theorize about what we don’t know based on what we do – aka. the “low-hanging fruit” approach.
The findings reported in the study were also the subject of a talk that took place at the second annual meeting of the UK SETI Research Network (UKSRN), which took place on September 11th and 12th, 2014, at Birkbeck College in London.
During the 1960s, Freeman Dyson and Nikolai Kardashev captured the imaginations of people everywhere by making some radical proposals. Whereas Dyson proposed that intelligent species could eventually create megastructures to harness the energy of their stars, Kardashev offered a three-tiered classification system for intelligent species based on their ability to harness the energy of their planet, solar system and galaxy, respectively.
With missions that are now capable of locating extra-solar planets (i.e. the Kepler Space Observatory) scientists have been on the lookout for signs of possible alien megastructures. Unfortunately, aside from some very arguable results, no concrete evidence has yet come to light. Lucky for us, in a study from the Free University of Tbilisi, Professor Zaza Osmanov offers some new insight on why megastructures may have eluded us so far.
While fascinating, the idea of alien megastructures invariably suffers from the same problem as all other attempts to find signs of intelligent life in our Universe. Basically, if intelligent life exists, why have we consistently failed to find any evidence of it? This conundrum, which was summed up by Enrico Fermi in the 1950s (thereafter known as the Fermi Paradox), has hung like a shadow over all our efforts.
For example, in the summer of 2015, a team of astronomers announced that they found what might be an indication of an alien megastructure around Tabby’s Star (KIC 8462852). However, they were quick to point out that any number of possibilities could explain the strange dimming pattern coming from the star, and subsequent studies offered even more plausible explanations – such as the star having consumed a planet at some point in its past.
To this, Osmanov has argued that the problem is that we are looking in the wrong places. Last year, he wrote a research paper in which he ventured that an alien super civilization – i.e. one that was consistent with a Level II Kardashev civilization – would likely use ring-like megastructures to harness the power of their stars. This is in contrast to the traditional concept of a “Dyson’s Sphere”, which would consist of a spherical shell.
Furthermore, he argued that these Dyson Rings would likely be built around pulsars rather than stars, and offered estimates on their dimensions which were dependent on the rotational speed of the pulsar. According to Osmanov’s latest study, titled “Are the Dyson rings around pulsars detectable?“, Osmanov extends the problem of spotting alien megastructures to the observational realm.
Specifically, he addressed how alien megastructures could be spotted by identifying their infrared energy signatures, and at what kinds of distances. By examining how such structures would vary in terms of the amount of IR radiation they would emit, he believes that they could be spotted within our local Universe using existing instruments.
Once again, it comes down to the diameter of the structures, which would in turn depend on the type of pulsar they orbit. As he states in the paper:
“A couple of years earlier before publishing the paper of Kardashev, the prominent physicist Freeman Dyson has suggested that if such superadvanced (in the terminology of Kardashev, Level-II) extraterrestrials exist, for increasing efficiency of energy consumption they can construct a thin spherical shell with radius ?1AU surrounding a host star (Dyson 1960).It has been argued that for such distances the sphere will be in the so-called habitable zone (HZ) and therefore the sphere will have the temperature of the order of (200 – 300 K), making this object visible in the infrared spectrum.”
Extending this to pulsars, Osmanov estimates that the habitable zone around a relatively slowly-rotating pulsar (with a period of about half a second) would be on the order of 0.1 AU. According to his calculations, a ring-like megastructure that orbited a pulsar at this distance would emit temperatures on the order of 390 K (116.85 °C; 242.33 °F), which means that the megastructure would be visible in the IR band.
From this, Osmanov concludes that modern IR telescopes – such as the Very Large Telescope Interferometer (VLTI) and the Wide-field Infrared Survey Explorer (WISE) – would have the necessary capacity to monitor nearby pulsars for signs of alien megastructures. He further concludes that for this purpose, these telescopes would have an effective range of up to 200 parsecs (~652 light years).
In addition, he goes on to state that within this volume of space, multiple candidates could be found and examined using these same existing instruments:
“We have considered the sensitivity of VLTI and by taking into account its higher possible angular resolution, 0.001 mas, it has been shown that the maximum distance ~0.2 kpc leads to the IR spectral density of the order of 7.4 mJy, which in turn, can be detected by the VLTI. We have argued that by monitoring the nearby zone of the Solar System approximately 64 pulsars are expected to be located inside it.”
Beyond these distances, up to the kiloparsec range (about 3260 light years), the angular resolution of these telescopes would not be enough to detect the structure of any rings. As such, finding megastructures at this distance would require telescopes that can conduct surveys in the UV band – which corresponds to the surface temperatures of neutron stars (7000 K). However, this would have to wait upon the development of more sensitive instruments.
“As we see, the search of infrared rings is quite promising for distances up to -0.2 kpc, where one will be able to monitor potentially 64 ± 21 pulsars by using the IR instruments,” he concluded. “Observation of distant pulsars (up to -1kpc), although will significantly increase the total number of potential objects – to 1600 ± 530, but at this moment the UV instruments cannot provide such a level of sensitivity.”
So while the range would be limited, the opportunities for testing this hypothesis would not. All told, between 43 and 85 candidates exist within the observable volume of space, according to Osmanov’s estimates. And with existing IR telescopes – and next-generation telescopes like the James Webb Space Telescopes – up to the task, some surveys could be conducted that would yield valuable information either way.
The concept of alien megastructures remains a controversial one, and for good reason. For one, the potential evidence for such structures – i.e. the periodic dimming of a star – can easily be explained by other means. Second, there is an undeniable degree of wishful thinking when it comes to the search for extra-terrestrial intelligence, which means that any findings could be subject to bias.
Nevertheless, the search for intelligent life remains a very fascinating field of study, and a necessary one at that. Not only would finding other examples of life in our Universe put to rest one of the most burning existential questions of all time – are we alone? – it would also allow us to learn a great deal about what other forms life could take. Is all life carbon based, are there other possibilities, etc? We would like to know!
In the end, the Fermi Paradox will only be resolved when we find definitive evidence that there is intelligent life out there other than our own. In the meantime, we can expect that we will keep searching until we find something. And anything that make this easier by telling us where we should (and what specifically to look for) is sure to help.
The night sky, is the night sky, is the night sky. The constellations you learned as a child are the same constellations that you see today. Ancient people recognized these same constellations. Oh sure, they might not have had the same name for it, but essentially, we see what they saw.
But when you see animations of galaxies, especially as they come together and collide, you see the stars buzzing around like angry bees. We know that the stars can have motions, and yet, we don’t see them moving?
How fast are they moving, and will we ever be able to tell?
Stars, of course, do move. It’s just that the distances are so great that it’s very difficult to tell. But astronomers have been studying their position for thousands of years. Tracking the position and movements of the stars is known as astrometry.
We trace the history of astrometry back to 190 BC, when the ancient Greek astronomer Hipparchus first created a catalog of the 850 brightest stars in the sky and their position. His student Ptolemy followed up with his own observations of the night sky, creating his important document: the Almagest.
In the Almagest, Ptolemy laid out his theory for an Earth-centric Universe, with the Moon, Sun, planets and stars in concentric crystal spheres that rotated around the planet. He was wrong about the Universe, of course, but his charts and tables were incredibly accurate, measuring the brightness and location of more than 1,000 stars.
A thousand years later, the Arabic astronomer Abd al-Rahman al-Sufi completed an even more detailed measurement of the sky using an astrolabe.
One of the most famous astronomers in history was the Danish Tycho Brahe. He was renowned for his ability to measure the position of stars, and built incredibly precise instruments for the time to do the job. He measured the positions of stars to within 15 to 35 arcseconds of accuracy. Just for comparison, a human hair, held 10 meters away is an arcsecond wide.
Also, I’m required to inform you that Brahe had a fake nose. He lost his in a duel, but had a brass replacement made.
In 1807, Friedrich Bessel was the first astronomer to measure the distance to a nearby star 61 Cygni. He used the technique of parallax, by measuring the angle to the star when the Earth was on one side of the Sun, and then measuring it again 6 months later when the Earth was on the other side.
Over the course of this period, this relatively closer star moves slightly back and forth against the more distant background of the galaxy.
And over the next two centuries, other astronomers further refined this technique, getting better and better at figuring out the distance and motions of stars.
But to really track the positions and motions of stars, we needed to go to space. In 1989, the European Space Agency launched their Hipparcos mission, named after the Greek astronomer we talked about earlier. Its job was to measure the position and motion of the nearby stars in the Milky Way. Over the course of its mission, Hipparcos accurately measured 118,000 stars, and provided rough calculations for another 2 million stars.
That was useful, and astronomers have relied on it ever since, but something better has arrived, and its name is Gaia.
Launched in December 2013, the European Space Agency’s Gaia in is in the process of mapping out a billion stars in the Milky Way. That’s billion, with a B, and accounts for about 1% of the stars in the galaxy. The spacecraft will track the motion of 150 million stars, telling us where everything is going over time. It will be a mind bending accomplishment. Hipparchus would be proud.
With the most precise measurements, taken year after year, the motions of the stars can indeed be calculated. Although they’re not enough to see with the unaided eye, over thousands and tens of thousands of years, the positions of the stars change dramatically in the sky.
The familiar stars in the Big Dipper, for example, look how they do today. But if you go forward or backward in time, the positions of the stars look very different, and eventually completely unrecognizable.
When a star is moving sideways across the sky, astronomers call this “proper motion”. The speed a star moves is typically about 0.1 arc second per year. This is almost imperceptible, but over the course of 2000 years, for example, a typical star would have moved across the sky by about half a degree, or the width of the Moon in the sky.
The star with the fastest proper motion that we know of is Barnard’s star, zipping through the sky at 10.25 arcseconds a year. In that same 2000 year period, it would have moved 5.5 degrees, or about 11 times the width of your hand. Very fast.
When a star is moving toward or away from us, astronomers call that radial velocity. They measure this by calculating the doppler shift. The light from stars moving towards us is shifted towards the blue side of the spectrum, while stars moving away from us are red-shifted.
Between the proper motion and redshift, you can get a precise calculation for the exact path a star is moving in the sky.
We know, for example, that the dwarf star Hipparcos 85605 is moving rapidly towards us. It’s 16 light-years away right now, but in the next few hundred thousand years, it’s going to get as close as .13 light-years away, or about 8,200 times the distance from the Earth to the Sun. This won’t cause us any direct effect, but the gravitational interaction from the star could kick a bunch of comets out of the Oort cloud and send them down towards the inner Solar System.
The motions of the stars is fairly gentle, jostling through gravitational interactions as they orbit around the center of the Milky Way. But there are other, more catastrophic events that can make stars move much more quickly through space.
When a binary pair of stars gets too close to the supermassive black hole at the center of the Milky Way, one can be consumed by the black hole. The other now has the velocity, without the added mass of its companion. This gives it a high-velocity kick. About once every 100,000 years, a star is kicked right out of the Milky Way from the galactic center.
Another situation can happen where a smaller star is orbiting around a supermassive companion. Over time, the massive star bloats up as supergiant and then detonates as a supernova. Like a stone released from a sling, the smaller star is no longer held in place by gravity, and it hurtles out into space at incredible speeds.
Astronomers have detected these hypervelocity stars moving at 1.1 million kilometers per hour relative to the center of the Milky Way.
All of the methods of stellar motion that I talked about so far are natural. But can you imagine a future civilization that becomes so powerful it could move the stars themselves?
In 1987, the Russian astrophysicist Leonid Shkadov presented a technique that could move a star over vast lengths of time. By building a huge mirror and positioning it on one side of a star, the star itself could act like a thruster.
Photons from the star would reflect off the mirror, imparting momentum like a solar sail. The mirror itself would be massive enough that its gravity would attract the star, but the light pressure from the star would keep it from falling in. This would create a slow but steady pressure on the other side of the star, accelerating it in whatever direction the civilization wanted.
Over the course of a few billion years, a star could be relocated pretty much anywhere a civilization wanted within its host galaxy.
This would be a true Type III Civilization. A vast empire with such power and capability that they can rearrange the stars in their entire galaxy into a configuration that they find more useful. Maybe they arrange all the stars into a vast sphere, or some kind of geometric object, to minimize transit and communication times. Or maybe it makes more sense to push them all into a clean flat disk.
Amazingly, astronomers have actually gone looking for galaxies like this. In theory, a galaxy under control by a Type III Civilization should be obvious by the wavelength of light they give off. But so far, none have turned up. It’s all normal, natural galaxies as far as we can see in all directions.
For our short lifetimes, it appears as if the sky is frozen. The stars remain in their exact positions forever, but if you could speed up time, you’d see that everything is in motion, all the time, with stars moving back and forth, like airplanes across the sky. You just need to be patient to see it.
Now, I’m no futurist, but I think I can predict one thing. Humans love to use energy, and in the future, we’re going to use even more of the stuff.
Let’s hope it’s clean energy, like that handy source of photons in the sky: the Sun. Not dirty forms of energy, like screams, unobtainium, liquid Shwartz, or using humans as batteries.
Once we really get our hands on a clean, unlimited source of energy, you can expect our usage to grow and grow until every human on Earth is using as much energy as a small country.
We will climb our way up through the Kardashev scale of energy usage, from Type 1, to Type II to Type III. Type III! Can you even imagine what would happen at that point?
Oh, you have no idea what I’m talking about? No problem.
The Kardashev Scale was originally developed by the Soviet astronomer Nikolai Kardashev in 1964. He looked at the advancement of humanity’s need for energy, and then just extrapolated when what our future energy demands would look like – and how they’d be supplied.
He broke them into three types. A Type I civilization would have complete and total mastery over all the energy of its planet. A Type II civilization would be masters of all the energy produced by their home star, and a Type III civilization would own all the energy in their home galaxy.
It was a pretty clever way to categorize the mighty capabilities of future civilizations, and it’s fueled the imagination of many sci-fi writers.
Where are we now along the Kardashev Scale? How long will it take for us to unlock each civilization level? Assuming we survive, of course.
Kardashev estimated that the total energy usage of a Type I civilization based on the amount of sunlight that falls on Earth. Our planet receives about 2 x 10^17 watts of power from the Sun.
Is that a lot? Is sure sounds like a lot. In 2013, the total human power consumption was 12.3 terawatts. So, doing a little math, we get about 1/14,000th the total potential power output that falls on the Earth.
It sounds like we’ve got a long way to making up that difference. But wait a second, we’re in the realm of exponential growth now, which has a surprising way of sneaking up on you.
Freeman Dyson, the famous physicist, estimated that it’ll only take about 200 years to fully utilize the energy falling on the Earth. That seems amazing, but when you consider that Germany was able to pump out 25 gigawatts of power in April, 2015, it doesn’t stretch your imagination too far.
Where do we go from there?
Kardashev estimated a compounding energy usage of 1% per year. And so, if you extrapolate forward from our current energy usage, he figured it would take about 3,200 more years to reach Type II status, where we’re extracting 100% of the energy pouring out of the Sun – all 4 x 10^26 watts.
Probably by using Dyson sphere, cloud or other Dyson-related polygon. We might have to dismantle all the planets to do it, but that’s just what we’ll do to keep up with our ravenous energy needs.
I know you look around your house, see your various appliances, and you’re unable to imagine how you could use that much power. But trust me, you will. You might have nanofactories, spinning out furniture made of pure diamond. Or a massive, planet-sized computer calculating the answer to life the universe and everything. Or a console that’ll let you play Witcher 3 without dropping frames. When energy is cheap and clean, all kinds of impossible ideas become reasonable.
Continuing this 1% compounding energy usage, Kardashev figured we’d be using up all the energy of our host galaxy within a few hundred thousand years – 10^37 watts -, but that’s mostly because of the time it takes to travel to from star to star. The Milky Way measures 120,000 light-years across, so even colonizing the entire galaxy couldn’t happen faster than that.
Imagine an entire galaxy, with every solar system completely dismantled and every star enclosed in a Dyson cloud of energy extracting solar cells. And yet, constant growth inevitably predicts it.
Is that it? Is that as much as a future civilization could colonize? Hardly, they would really just be getting started. A future civilization with that much energy at their disposal would be able to expand outward at just shy of the speed of light, eventually colonizing everything that the laws of physics would enable them to get to.
Eventually the expansion of the Universe, accelerated by dark energy would bring their colonization to a stop. Galaxies would drop over the cosmic horizon, forever out of reach. Vast cosmic power with no where else to go.
Thanks to Kardashev, we’ve got a great way of considering our place in the Universe. Assuming we don’t wipe ourselves out, we’ve got a bright future ahead.
Beam us up, Scotty. There’s no signs of intelligent life out there. At least, no obvious signs, according to a recent survey performed by researchers at Penn State University. After reviewing data taken by the NASA Wide-field Infrared Survey Explorer (WISE) space telescope of over 100,000 galaxies, there appears to be little evidence that advanced, spacefaring civilizations exist in any of them.
First deployed in 2009, the WISE mission has been able to identify thousands of asteroids in our solar system and previously undiscovered star clusters in our galaxy. However, Jason T. Wright, an assistant professor of astronomy and astrophysics at the Center for Exoplanets and Habitable Worlds at Penn State University, conceived of and initiated a new field of research – using the infrared data to assist in the search for signs of extra-terrestrial civilizations.
And while their first look did not yield much in the way of results, it is an exciting new area of research and provides some very useful information on one of the greatest questions ever asked: are we alone in the universe?
“The idea behind our research is that, if an entire galaxy had been colonized by an advanced spacefaring civilization, the energy produced by that civilization’s technologies would be detectable in mid-infrared wavelengths,” said Wright, “exactly the radiation that the WISE satellite was designed to detect for other astronomical purposes.”
This logic is in keeping with the theories of Russian astronomer Nikolai Kardashev and theoretical physicist Freeman Dyson. In 1964, Kardashev proposed that a civilization’s level of technological advancement could be measured based on the amount of energy that civilization is able to utilize.
To characterize the level of extra-terrestrial development, Kardashev developed a three category system – Type I, II, and III civilizations – known as the “Kardashev Scale”. A Type I civilization uses all available resources on its home planet, while a Type II is able to harness all the energy of its star. Type III civilizations are those that are advanced enough to harness the energy of their entire galaxy.
Similarly, Dyson proposed in 1960 that advanced alien civilizations beyond Earth could be detected by the telltale evidence of their mid-infrared emissions. Believing that a sufficiently advanced civilization would be able to enclose their parent star, he believed it would be possible to search for extraterrestrials by looking for large objects radiating in the infrared range of the electromagnetic spectrum.
These thoughts were expressed in a short paper submitted to the journal Science, entitled “Search for Artificial Stellar Sources of Infrared Radiation“. In it, Dyson proposed that an advanced species would use artificial structures – now referred to as “Dyson Spheres” (though he used the term “shell” in his paper) – to intercept electromagnetic radiation with wavelengths from visible light downwards and radiating waste heat outwards as infrared radiation.
“Whether an advanced spacefaring civilization uses the large amounts of energy from its galaxy’s stars to power computers, space flight, communication, or something we can’t yet imagine, fundamental thermodynamics tells us that this energy must be radiated away as heat in the mid-infrared wavelengths,” said Wright. “This same basic physics causes your computer to radiate heat while it is turned on.”
However, it was not until space-based telescopes like WISE were deployed that it became possible to make sensitive measurements of this radiation. WISE is one of three infrared missions currently in space, the other two being NASA’s Spitzer Space Telescope and the Herschel Space Observatory – a European Space Agency mission with important NASA participation.
WISE is different from these missions in that it surveys the entire sky and is designed to cast a net wide enough to catch all sorts of previously unseen cosmic interests. And there are few things more interesting than the prospect of advanced alien civilizations!
To search for them, Roger Griffith – a postbaccalaureate researcher at Penn State and the lead author of the paper – and colleagues scoured the entries in the WISE satellites database looking for evidence of a galaxy that was emitting too much mid-infrared radiation. He and his team then individually examined and categorized 100,000 of the most promising galaxy images.
And while they didn’t find any obvious signs of a Type II civilization or Dyson Spheres in any of them, they did find around 50 candidates that showed unusually high levels of mid-infrared radiation. The next step will be to confirm whether or not these signs are due to natural astronomical processes, or could be an indication of a highly advanced civilization tapping their parent star for energy.
In any case, the team’s findings were quite interesting and broke new ground in what is sure to be an ongoing area of research. The only previous study, according to the G-HAT team, surveyed only about 100 galaxies, and was unable to examine them in the infrared to see how much heat they emitted. What’s more, the research may help shed some light on the burning questions about the very existence of intelligent, extra-terrestrial life in our universe.
“Our results mean that, out of the 100,000 galaxies that WISE could see in sufficient detail, none of them is widely populated by an alien civilization using most of the starlight in its galaxy for its own purposes,” said Wright. “That’s interesting because these galaxies are billions of years old, which should have been plenty of time for them to have been filled with alien civilizations, if they exist. Either they don’t exist, or they don’t yet use enough energy for us to recognize them.”
Alas, it seems we are no closer to resolving the Fermi Paradox. But for the first time, it seems that investigations into the matter are moving beyond theoretical arguments. And given time, and further refinements in our detection methods, who knows what we might find lurking out there? The universe is very, very big place, after all.
The research team’s first research paper about their Glimpsing Heat from Alien Technologies Survey (G-HAT) survey appeared in the Astrophysical Journal Supplement Series on April 15, 2015.