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How Far Can Civilization Go?

Robert H. Gray, author of The Elusive Wow: Searching for Extraterrestrial Intelligence, has searched for radio signals from other worlds using the Very Large Array and other radio telescopes. You’ll find numerous links to his work in the archives here. In today’s essay, Gray takes a look at a classic benchmark for assessing the energy use of civilizations, introducing his own take on Earth’s position in the hierarchy and how these calculations affect the ongoing SETI effort. His article on the extended Kardashev scale appeared in The Astronomical Journal https://iopscience.iop.org/article/10.3847/1538-3881/ab792b. Photograph by Sharon Hoogstraten.

by Robert H. Gray

Human civilization has come an amazingly long way in a short time. Not long ago, our major source of energy was muscle power, often doing hard work, while today much more energy is available from fuels, fission, hydro, solar, and other sources without breaking a sweat. How far can civilization go?

It’s probably impossible to say how far civilizations can go in areas like art or government, because such things can’t be measured or forecast, but energy use is measurable and has trended upward for centuries.

The astrophysicist Nikolai Kardashev outlined a scheme for classifying civilizations according to the amount of energy they command, in order to assess the type of civilization needed to transmit information between stars. He defined Type I as commanding the energy available to humanity in 1964 when he was writing, Type II could harness the energy of a star like our Sun, and Type III would possess the energy of all of the stars in a galaxy like our Milky Way.

Harnessing the energy of stars might sound like science fiction, but solar panels are already turning sunlight into electricity at a modest scale, on the ground and in space. Gerald O’Neill and others have envisioned orbiting space settlements soaking up sunshine, and Freeman Dyson envisioned something like a sphere or swarm of objects capturing all or much of a star’s light.

Carl Sagan suggested using Arabic numerals instead of Kardashev’s Roman numerals, to allow decimal subdivisions, and he suggested more uniform power levels. He re-defined Type 1 as 1016 watts—very roughly the Sun’s power falling on the Earth—and he rounded off Type 2 and 3 levels to 1026 and 1036 watts respectively, so planetary, stellar, and galactic categories increase in steps of 1010 or ten billion. A simple formula converts power values into decimal Types (the common logarithm of the power in megawatts, divided by ten). In the recent year 2015, human power consumption was 1.7×1013 watts, or Type 0.72—we’re short of being a Type 1.0 planetary civilization by a factor of roughly 600. In 1800 we were Type 0.58, and in 1900 we were Type 0.61.

The 2015 total power consumption works out to an average of 2,300 watts per person, which is 23 times the 100 watts human metabolism at rest, but it’s not many times more than the 500-1,000 watts a human can produce working hard. Maybe we haven’t gone all that far, yet.

I recently extended the scale. Type 0 is 106 watts or one megawatt, which is in the realm of biology rather than astronomy—the muscle power of a few frisky blue whales or several thousand humans. That seems like a sensible zero point, because a civilization commanding so little power would not have enough to transmit signals to other stars. Type 4 is 1046 watts, roughly the power of all of the stars in the observable Universe.

One use for the scale is to help envision the future of our civilization, at least from the perspective of energy. If power consumption increases at a modest one percent annual rate, we will reach planetary Type 1 in roughly 600 years and stellar Type 2 in 3,000 years—roughly as far in the future as the Renaissance and ancient Greece are in the past. That simplistic growth rate would put us at galactic scale Type 3 in 5,000 years which is almost certainly wrong, because some parts of our galaxy are tens of thousands of light years away and we would need to travel faster than light to get there.

There are, of course, many limits to growth—population, land, food, materials, energy, and so on. But humans have a history of working around such limits, for example producing more food with mechanization of agriculture, more living space with high rise buildings, and more energy from various sources. It’s hard to know if our civilization will ever go much beyond our current scale, but finding evidence of other civilizations might give us some insight.

Another use for the scale is to help envision extraterrestrial civilizations that might be transmitting interstellar signals, or whose large-scale energy use we might detect in other ways.

If we envision ET broadcasting in all directions all of the time, they would need something like 1015 watts or 100,000 big power plants to generate a signal that our searches could detect from one thousand light years away using the 100-meter Green Bank Telescope. That means we need to assume at least a Type 0.9 nearly planetary-scale civilization—and considerably higher if they do anything more than broadcast—a civilization hundreds or thousands of times more advanced than ours. That seems awfully optimistic, although worth looking for. If we envision civilizations soaking up much of a star’s light with structures like Dyson spheres or swarms, then unintentional technosignatures like waste heat re-radiated in the infrared spectrum conceivably could be detected. Some infrared observations have been analyzed along those lines, for example by Jason Wright and associates at Penn State.

If, on the other hand, we envision ET transmitting toward one star at a time using a big antenna like the 500 meter FAST in China, then we need to assume only something like 108 watts or one-tenth of one big power plant, although the signal would be detectable only when the antenna’s needle beam is pointed at a target star. To catch intermittent signals like that, we will probably need receiver systems that monitor large areas of sky for long periods of time—ideally, all-sky and full-time—and we can’t do that yet at the microwave frequencies where many people think ET might transmit. A modest prototype microwave receiver system called Argus has been monitoring much of the sky over Ohio State University in Columbus for a decade with very low sensitivity, and an optical system called PANOSETI (Panoramic SETI) is planned by Shelly Wright of UCSD and Paul Horowitz of Harvard to potentially detect lasers illuminating us.

Detecting some signature of technology near another star would be a historic event, because it would prove that intelligence exists elsewhere. But the U.S. government has not funded any searches for signals since Sen. Richard Bryan (D-NV) killed NASA’s program in 1993, even though thousands of planets have been discovered around other stars.

Both Kardashev and Sagan thought civilizations could be characterized by the amount of information they possess, as well as by energy. An information scale much like the energy scale can be made using 106 bits or one megabit as a zero point—roughly the information content of one book. Sagan thought that 1014 or 1015 bits might characterize human civilization in 1973 when he was writing on the topic, which would be Type 0.8 or 0.9 using the power formula (he used the letters A, B, C… for 106, 107, 108… bits, but letters don’t allow decimal subdivisions). More recent estimates of humanity’s information store range from 1018 to 1025 bits or Types 1.2 to 1.5, depending on whether only text is counted, or video and computer storage are included.

Nobody knows what information interstellar signals might contain. Signals could encode entire libraries of text, images, videos, and more, with imagery bypassing some translation problems. What might motivate sending information between stars is an open question; trade is one possible answer. Each world would have its own unique history, physical environment, and biology to trade—and conceivably art and other cultural stuff as well. Kardashev thought that the information to characterize a civilization could be transmitted across the Galaxy in one day given sufficient power.

Whether any interstellar signals exist is unknown, and the question of how far civilization can go is critical in deciding what sort of signals to look for. If we think that civilizations can’t go hundreds or thousands of times further than our energy resources, then searches for broadcasts in all directions all of the time like many in progress might not succeed. But civilizations of roughly our level have plenty of power to signal by pointing a big antenna or telescope our way, although they might not revisit us very often, so we might need to find ways to listen to more of the sky more of the time.

Additional Resources

N. S. Kardashev, Transmission of Information by Extraterrestrial Civilizations, SvA 8, 217 (1964).

C. Sagan, The Cosmic Connection: An Extraterrestrial Perspective, Doubleday, New York (1973).

V. Smil, Energy Transitions: Global and National Perspectives, 2nd edition, Praeger (2017).

R. H. Gray, The Extended Kardashev Scale, AJ 159, 228-232 (2020). https://iopscience.iop.org/article/10.3847/1538-3881/ab792b

R. H. Gray, Intermittent Signals and Planetary Days in SETI, IJAsB 19, 299-307 (2020). https://doi.org/10.1017/S1473550420000038


Comments on this entry are closed.

  • Alex Tolley June 25, 2021, 20:15

    If power consumption increases at a modest one percent annual rate, we will reach planetary Type 1 in roughly 600 years and stellar Type 2 in 3,000 years—roughly as far in the future as the Renaissance and ancient Greece are in the past. That simplistic growth rate would put us at galactic scale Type 3 in 5,000 years which is almost certainly wrong, because some parts of our galaxy are tens of thousands of light years away and we would need to travel faster than light to get there.

    I (and others) have been stressing these sorts of numbers for some time. There are implications to this.

    Firstly, we could get to a K2 civ simply through growth. The problem is what comes after that. A civ that needs to keep growing, as our capitalist system requires. runs out of growth options in a cosmic eyeblink. If we want interstellar travel soon, the growth rate must be increased, but we reach our limits that much faster. All the civilization can do is increase energy efficiency for a while to delay the end, or substitute very low energy using items of value to increase GDP without much increase in energy. However, while that might work up to a point in the solar system, raw energy is needed for interstellar travel as as we know.

    Even if a civ discovers FTL, it runs up against the next limit as a K3 civ in another short time. And again to become a k4. But this creates a problem, as we assume that any other extant civilization must be long-lived to be contactable. A civilization 1 million years old is not going to be one growing at even a very slow rate. It must have either found another way to grow, or become static, or it must be in a state of sequential cultures growing and dying. (c.f. the post on A Visualization of Galactic Settlement).

    Because growth times are likely limited, it seems to me that any polity that wants to communicate has only a limited time to do so. With a 2500 year time frame to possible K2 stasis, even a single message and a reply put a limit on distance apart of any civilization, of perhaps 1250 ly. This is less than some estimates for the nearest civilization.

    One way to extend the life of a civilization within its star’s energy constraint is to abandon a physical presence and retreat into a virtual world. A computational system that uses all the energy from a star could power a virtual world[s] and allow its inhabitants to imagine any number of environments and technologies. As long as the computational effort was fixed, this civilization could “expand” in its virtual setting, allow an imaginary galactic or intergalactic civilization to unfold in this virtual environment. Expect such a computational system to be well-defended.

  • gbaikie June 26, 2021, 4:30

    “The 2015 total power consumption works out to an average of 2,300 watts per person, which is 23 times the 100 watts human metabolism at rest, but it’s not many times more than the 500-1,000 watts a human can produce working hard. Maybe we haven’t gone all that far, yet.”

    It seems if we were spacefaring we use not much more or maybe less than 2,300 watts per person.
    “Currently, the ISS has eight solar arrays generating about 160 kilowatts of power total. ” But get solar energy 60% of the time
    160 x .6 = 96 KW per hour generated. And 6 crew: 96/ 6 = 16 kw hour
    per person. Then could count transportation cost to get there. And energy used used boost station, and ect.
    But it not efficient- no one even trying to make it energy efficient. One could say everything govt ever does is not energy efficient.
    If was more cheaper to get into space- then energy efficient might be something with more interest.
    In terms energy getting to orbit is not a lot energy- not reusing the rocket, is expensive in terms of costs and all energy required to make a rocket. If payload cost is $2000 per kg- rocket fuel energy cost is about $10 per kg- granted that is still a lot energy.
    But spacefaring means one going to be using laces like the Moon and Mars which a lot cheaper in terms energy to get to the orbit.
    One could call yourself a spacefaring civilization even when electrical power cost in orbit and beyond is more expensive than Earth’s electrical power, but within few decades electrical power will cheaper in space than on the surface of Earth.
    And no, lower electrical cost in space will not mean you waste a lot electrical power. Rather, probably mean Earthlings can get cheaper electrical power and waste less energy on Earth surface. And somewhere around this point in time the energy cost instead of about $10 per kg to orbit will lower to about $1 per kg of payload to LEO, but seat price might $5 per kg- $500 to 1000 per person to orbit. Getting to earth surface from orbit as now quite cheap, and will get a lot cheaper. Shipping stuff from Space to Earth will be 1/10th of cost [and very little use of energy] than shipping stuff from Earth to orbit [and beyond].

    What is global shipping tonnage of Earth, ” In 2019, the volume of global seaborne trade was estimated to be around 11 billion tons”.
    And with spacefaring civ shipping will hundred billions tons, and cost less per 11 billion tons then the energy used to ship the 11 billion tons on Earth. But earth can only use around 11 billion ton, so space to Earth maybe 1/10th of what all is shipped within space. But from Space one might shipping different stuff than what normally shipping- one might shipping houses to Earth- or maybe baseball stadiums, though the pieces of baseball stadium are currently being shipped from somewhere on Earth- they just not delivered as one package. From space you can do this. How else are you going to get sky cities on Venus?
    The mad economic growth will involve more energy. It will like US when first building trains- and we still using that infrastructure [with cost per mile per ton- the cheapest in the world- of course US has a lot area/distance to ship stuff from place to place- or one can say, it has to be cheaper per mile per ton.]
    On Earth population density is an efficiency- but with pandemics such urban density appears having much higher cost, and there is re-thinking about it. But in space one get more density than Earth cities- there are things to work out, one has that potential. With space there is a lot possibilities, and in terms Mars- it’s possible the low gee or other factors don’t allow towns/cities on Mars. But one also could have huge natural cave structures on both Mars and Moon.
    Prediction is impossible. But you have inherent aspect of space. Electrical power can be very cheap. Nuclear energy can be very cheap. And always getting cheaper.
    And Earth is simply energy poor. And people believe their is shortage of energy on Earth- and that has been hampering economic growth, and causing us waste trillions and waste energy making stuff like solar panel and wind farms- endless other stupidity.
    I believe water in space will become cheaper than water on Earth- assuming we become spacefaring. Vacuum is cheap in space- we currently waste a lot energy making a vacuum. Lunar iron/steel will cheaper and cost less energy to make. All metals will be cheaper to mine and cheaper make into things. 3 D printing doesn’t need a spacefaring civilization, but spacefaring civilization will use and improve this technology. Only cheaper water seems like something hard to believe- but there are ocean of freshwater in space.
    I don’t think earthlings are all going to rush into space, but once it’s cheaper to live in space than on Earth, a lot people with leave Earth. But it seems in beginning most will stay within Earth’s gravity well- and lots people in LEO.
    It could take centuries before there is more people who not living on Earth surface or Earth orbits. Earth is always going to be a place to visit.
    But whenever that occurs, there should much lower energy use per person, than “2,300 watts per person”.
    But then you have people who want go to stars- This is going to take a lot energy per person. But with a lot of huge telescopes in space- they should have a much better idea of where they going to. I would guess one appeal of other stars is having more energy available than what our solar system can offer. It’s pretty good guess Sol is not ideal in this regard. And so go to other stars, in order to go to other stars- probably due to some religious belief of some kind. Something like pilgrims going somewhere. They probably, will cause all kind of trouble- and humankind will be blamed for it {obviously}.
    But it seems interstellar wars, should not cost much. It seems defensively one has an advantage, but trying to go on the offense- invading other star systems, that seems it would be expensive- unless you want to attack a non-spacefaring civilization, but of course other spacefaring civilizations could watch, and/or do more than watch {and then, it just got expensive].
    Oh, I forgot, being spacefaring civilization should stop all wars on Earth- and that will save a lot in terms of energy cost per person.
    I think mere space exploration, will do a lot to reduce wars on Earth.

    • Alex Tolley June 26, 2021, 12:27

      Comparing like with like:

      The ISS solar power arrays generate 120 KW (averaged).
      For a full complement of 6 astronauts that is 20KW per person.

      My personal electrical + gas consumption averaged over the year is 1.8 KW

      Total energy consumption per capita in the US is 9.2 KW
      Total energy consumption per capita in India is 0.8 KW

      1. Purely on power consumption to live in space, the ISS crew consumes 11x as much power as I do. (Granted that some %age of ISS power usage is for other applications than just the crew requirements).

      2. Total per capita energy consumption in the US (electricity, gas, oil, averaged over the who economy) is less than 50% of the ISS maintenance. Other western countries, such as Germany and France per capita consumption is around 50% of the US. India is around 10% of the US.

      Unless the ISS is particularly profligate, then space-faring civilization at a small scale is going to be much more energy-intensive than planet-bound ones.

      Just take your freshwater costs. Earth provides free freshwater as the sun does all the work creating it. We add energy to clean it again due to the pollutants we add in the industrial West.
      In space, all the water is only available as ice beyond the snow line. So energy is needed to retrieve it. Then the ice needs to be purified to rid it of contaminants before it becomes potable. I would suggest it is certainly no cheaper than the ISS purification of urine (distillation, or biomechanical filtration) plus the energy cost of retrieving the water.

      If you live close to Saturn’s rings, or Ceres, I grant you that water retrieval costs will be low. ;)

      • Michael June 27, 2021, 14:55

        Alex have to disagree with you on the West pollutant bit, its mainly bacterial which is everywhere and the West recycle a fair amount of water as well.

        • Alex Tolley June 27, 2021, 22:35

          Yes, bacteria are the main reason we process water. However, most rivers are now polluted with heavy metals from mining, nitrates and pesticides from ag runoff, as well as human waste. The dumping of industrial chemicals, as well as oils and other manufacturing liquid wastes, are also pollutants. You can drink directly from a spring but it is advisable to sterilize first.

      • gbaikie June 27, 2021, 19:28

        “Just take your freshwater costs.”
        Ok, US uses about 600 billion tons per year.
        My costs of freshwater is fairly low. How much would
        it cost if I were Martian? Or how much would it cost for
        1 million ton of freshwater on Mars or how much would cost to buy
        a lake of freshwater on Mars.
        Let’s say it had average depth of 20 meter and total surface area equal to 1 km diameter circle. Or it had, 785,397.5 square meters surface and 15,707,950 cubic meter or 15,707,950 tons of freshwater and surface has 1 foot frozen ice.
        How much is the lake worth?
        I would say Mars water is worth $1000 per ton. But worth it’s worth is whatever things like are selling for. So could be worth more or less than $1000 per ton [or $1 per kg of water}
        Let’s assume without knowing any better, than Mars lake water is worth $1 per kg [or if like $.1 to $10 per kg}.
        15,707,950 tons of water times $1000 per ton is 15.7 billion dollars.
        There are number of reason why it’s worth 15.7 billion dollar. One reason is current cost of energy on Mars and current costs to ship stuff from Earth.
        Let’s say I own this water on Mars and want sell it. The only way I could reasonably own the lake is if spent the money to make this lake- just finding the lake on Mars would be problematic in terms any claim of ownership. And even if I spent billion dollars making the lake- people like argue about things like who owns what. It would be better is large large of people spent the money and claim to own the lake and these people make up all kinds of rules about it.
        But as said, to make simpler say I owned or it was my job to sell.
        One way to sell it is to sell land around the lake and those land owners get rights to water in the lake.
        So the land will be a donut and the lake is donut hole, and selling pieces of the donut. So all land owners of the donut own the 15,707,950 tons of water. And each land owner has right to add or remove lake water. So lake is roughly 1 km in diameter, donut is say 1.8 km in diameter: 2,544,687.9 square meter – 785,397.5 square meter of lake = 1,759,290.4 square meter of land around the lake
        which in terms of acres is 434.73 acres.
        Per acre: 15.7 billion dollars / 434.73 = $36,114,369.85 per area
        Or about 36 million dollar for 1 acre of Mars land which includes
        15,707,950 tons of water / 434.73 = 36,132 tons of water which could be valued at $1000 per ton or $1 kg. Or if wanted buy Mars water at $1 per kg, and buy enough water, they get the Mars land for free.
        And say 10 people could buy 1 acre and paid 3.6 million for there 1/10th share and get 3600 tons of water.
        What of course is important is rights of use/access to the Lake.
        A 1 acre share gives ice area of lake in addition to the acre of land:
        lake area: 785,397.5 / 434.73 = 1,806.6 square meters of ice of lake surface or in terms of acres: 0.446 acres of lake ice.
        What lake give you other than water, is pressure. And Mars lacks pressure.
        With Earth gravity 10 meter depth of water give 1 atm of pressure.
        Mars has 0.379 of Earth gravity, 10 meter depth of water gives 0.379 atm [or 5.5713 psi]. Humans can breath without pressure suit in 2.5 psi of pressure. So a human can swim in about 5 meter depth of water on Mars without a pressure suit. Or you could swim from diving bell to diving bell in swim suit [or nude] if kept 5 meters under the surface. And for plants to grow they could grow at less than 2.5 psi of pressure. Now if water is cold, you might want to swim in a wet or dry suit.
        But other then frolicking in the “nature environment of Mars” there other advantages to having pressure on Mars. It could lower your building costs. And you in environment which has constant temperature- but if water is 5 C it could colder than the surface in the atmosphere of Mars, and even water of 15 C in wet suit, one can not stay in this cold environment for long. Without wet suit, about 30 mins. And 5 C water is quite for cold wet suit and without wet suit, one should probably limit it to few mins of this very cold water excitement.
        But going to buy real estate on Mars, you want access to cheap electrical power just you do with real estate on Earth. On Earth, you access to water lines, power lines and a sewage solution or some sort.
        And you will pay for the electrical energy and any sewage or garbage removal services, but want those kinds of services available.
        And lake is good place to put nuclear reactor. So if there is way to get electrical power cheap, that make land worth more.
        And of course the party that provided the water for the lake, probably has more water to sell- make another lake and/or add more water to lake. The Mars land beyond the donut is owned/control by the town that bought the lake and donut land around the lake. But there will costs related to land outside lake- roads and etc. But buying the 1 acre allow a ownership of other land in the future. Or if town run well, such land owners could get rich in the future. But rules governing all this not for the party selling mars water to decide.
        And if want to go to Mars, you will be buying earth water transported for your needs traveling at higher price then $1 per per kg- probably $20 per kg or more.
        Everything on Earth is lower in price- if talking about real dollar or inflation adjusted dollars. With Mars from beginning prices of everything should drop at much faster rate then we currently getting on Earth. Or Mars water will lower in price, and “worthless” land will increase in price, but paying higher price for water and the land with it, is such of like investing growth companies- most of time, you can make a lot money. And whether Martian make a lot money will largely depend on how they govern Mars. Simply things, are, if don’t punish investing, you will become rich.

        • Alex Tolley June 27, 2021, 22:31

          A nice argument, and not that different than selling lakefront properties. However, there are no surface lakes on Mars. There might be liquid water subsurface lakes, but then the you have to pump up the water supply. More likely you have to melt a glacier below the dust and regolith. That takes energy and materials to prevent the surface water boiling off. Then the water still isn’t potable, so it must be filtered before the proud lakefront-under-a-dome property owners can turn on a faucet and use the water for consumption and bathing. Wastewater – gray and black, will be precious and need recycling, initially with equipment hauled up from Earth.

          But I would agree, that ownership of such a resource would be good if you can manage to keep it. Growing potatoes like Mark Watney, but distilling them to make vodka, now that is the traditional way to make buckets of money. Open a bar and sell flavored alcohol in various concentrations.

          • gbaikie June 28, 2021, 18:07

            –Alex Tolley June 27, 2021, 22:31
            A nice argument, and not that different than selling lakefront properties. However, there are no surface lakes on Mars. —
            If there were lakes, one might have wars over them- wars are expensive. But there could be lakes- and wars might be fought over them
            “There might be liquid water subsurface lakes, but then the you have to pump up the water supply.”
            Or live underground and live near or in the lakes.
            Due Mars lower gravity the energy cost to pump up a distance is on Earth is than less 1/2 on Mars. Africans are currently pumping fossil water from under Sahara desert finding something the same or better than what have with Sahara desert is roughly what mean as Mars being viable place settlements.
            One needs a lot water, but probably not more than a typical country on Earth is currently using. But water not just domestic consumption- if Mars water cost $1 per kg, one export it to Space. And at some point in more distance future Mars could be importing cheaper water from space- plus get energy dropping that water from Mars orbital distance- or Mars gets water and hydro power. On could do same thing with Earth, but it easier with Mars [or easier than Mars is our Moon]. So I wouldn’t worry about depleting Mars or the Moon’s current water resources.
            But in of getting foothold on Mars, one only “needs” +100,000 people living on Mars and that kind level population and time, things going to a lot cheaper on Mars.
            Or the value mining lunar water or Mars water and exporting it space, is it creates Market for water in space, once done, one will be getting trillions of tons of water from Space each year. Or get more water than 600 billion tons of water used by US, or the trillion tons used by China or India per year. Like US, the main thing Mars does is grow food for the rest of the solar system- and perhaps Earth orbit. I tend think most population in space will be in Earth orbits. And next highest will be Venus orbit. But Earth currently has too low of population to cause there to be much population in space for next 500 years. And I think Mars settlements will cause Earth to develop Ocean settlements- then Earth’s existing under population will become even more apparent.
            So, important issue which I have not really thought about is where in space will most of Human population come from- Mars might not be a place to raise the kids.
            I guess probably Earth ocean settlements- where everyone gets to live on the beach.
            Nubian Sandstone Aquifer System
            “The Great Man-made River Project (GMMR) in Libya makes use of the system, extracting substantial amounts of water from this aquifer, removing an estimated 2.4 km3 of fresh water for consumption and agriculture per year. “

        • Michael T June 28, 2021, 2:15

          Looking at the resuts of a “water Market” on Earth, e.g., Australia’s Murray-Darling system, various privatised water supplies in South America and elsewhere, I’d be pessimistic about the ability to have a *civilised* system in a prospective colony (I’m not talking about some outfit’s mining outpost, so much as ongoing large societies). So I’d be a bit worried about the colony in general. There are some things that should be in the commons. Water is a basic necessity. It’s going to be difficult enough to arrange it in a colony as it is.

          • Alex Tolley June 28, 2021, 11:20

            I agree. The privatization of the UK water supply was meant to have private capital fix the estimated 30% losses in the pipes and update the systems. This did not happen. Prices were raised and water even sold to users outside of the customer service area, all the while extracting the rents charged to pay capital.

            Ian McDonald’s “Luna” novels premise a libertarian lunar society where everything, including air, must be paid for. Those unable to pay…die. Not the way I would want to live, and indeed most of the novels center around the wealthy ruling families with little shown about the lives of the poor and destitute.

            In California, we were lucky that attempts to buy and corner water rights were effectively stymied, although big ag and corporate interests still dominate the legislation on water allocation and at least one large company extracts precious water and sells it out of state.

            On the other side, treating the environment, particularly rivers as a commons, resulted in waste dumping that eventually ushered in the creation of the EPA, and still, the dumping goes on and spillages paid for by the taxpayer, not the polluter. Infrastructure from water and sewage systems are difficult and very expensive to replace, rather than just patch major breaks. Flint, Michigan residents are still having to use water deliveries as little has been done to fix the water system.

            I also recommend reading or watching the movie version of An Enemy of the People about what happens when problems upset the profits of a town. This mirrors much that we have seen during the pandemic. IMO, how to structure society so we can best manage competing goals is still a largely unsettled question.

    • Michael T June 28, 2021, 2:33

      2 things;

      1.) Developing renewable, low-carbon energy supplies is needed NOW, and we’re not likely to have practical space-based power systems for some time (much as I’d like them!). So wind and solar are not silly.

      2.) I agree/hope that space exploration may reduce tensions on Earth (much as they have done in a small way with the ISS, at least on a good day). Space exploration provides a good outlet for the adventurous that Earth is increasingly unable to provide. If people don’t have somewhere to explore/expand into/mess about in, they may seek adventure via harmful ‘games’ on Earth (yes, we could seek to behave better, anyway).

      The Apollo missions (and others) have had various motives, but in some way many people on this planet felt they’d partcipated in something great (even if not from the US) – “Hey we humans DID this!”. It is pyschologically good to some degree.

      3.) Yes, interstellar wars seem like an expensive thing. Not a good idea :-/ .

      • Patient Observer June 28, 2021, 21:48

        I am not American-centric although I am a US citizen who has been around. The Apollo program was a great engineering feat but the first satellite and the first person in space represent the true milestones in space exploration. The fact that there has been no subsequent manned lunar missions since Apollo testifies to the fact it was a one-off geopolitical endeavor but nevertheless a great engineering feat.

        Renewable energy will hardly power a Type 0.1 civilization As attractive as fusion power is from a gee-whiz example of technology, closed fuel cycle nuclear fission will be the logical choice for abundant carbon-free energy.

        Just to vent here a little, Elon Musk, Starship and the associated boondoggles will prove a huge diversion of talent and resources despite how much fun it is to imagine (the utterly ridiculous) point-to-point passenger rockets or hyper-loops or tunnel networks with high speed pods. Calling it stupid does not begin to properly describe these concepts. A sycophant media driving a click bait wave stokes the delusions of people desperate for a glossy future of ease and abundance. Yet, our standard of living continues its 40 year decline.

        Anything I say after this point is lttle more than a hunch. There are no Type 3 civilization and probably no Type 2 civilizations as well. A deeper understanding of reality (which we have yet to uncover) may channel life in a non-technical direction. It may be simply a reality that is more engulfing that anything our senses can presently create nor any technology rival.

        • Alex Tolley June 29, 2021, 14:37

          OK, so I think it is safe to say that you are not a SpaceX/Musk fanboi.

          A Starship variant was just selected by NASA as the vehicle to land on the Moon as part of the Artemis program. Are you really implying that NASA was bamboozled by SpaceX? Or are you saying it is wasteful spending despite SpaceX being by far the lowest bidder? (Wouldn’t that mean that the other contenders were the real boondoggle assuming that this program isn’t overall a boondoggle? Or is returning to the Moon a boondoggle?)

          • Patient Observer June 29, 2021, 22:55

            Yes, regarding a bamboozled NASA. Perhaps factions want to see a failed effort to return to the moon (the woke types and Green New Dealers may be just fine with an end to a manned space program).

            Or it could be a delusion. I remember the Orient Express hypersonic airliner of the 1980’s not to mention Star Wars (aka SDI). Utterly rubbish in terms of feasibility then and still not feasible 40 years later. But, as long as tax money was thrown at it by deluded politicians, NASA and aerospace contractors kept a straight face as they raked in the money.

            The “Why” is not important as the fact that a decision was made to pursue a course with a high probability of failure.

            The Falcon 9 is a pretty good piece of engineering but did not stray far from well-proven aerospace designs and materials. Still waiting for the huge cost reductions in launch costs.

            The Star Ship, a stainless steel husk fitted with under-developed engines has generated a remarkable string of failures with minor milestones such as not exploding lauded as unprecedented successes. I suggest a view of these videos addressing the Star Ship and other Musk narcissisms.


            I would appreciate comments as I wish to find something plausible about the Star Ship and Martian colonization.

            • Alex Tolley July 3, 2021, 11:02

              There are many videos of early heavier than air flight that look farcical. But we do have intercontinental passenger jets…

              For sheer chutzpah, I suppose you would include fusion? The funding for such programs has been ongoing for well over half-century, with the ITER decades away from producing net energy.

              There are many expensive engineering projects that either fail to complete, complete at multiples of the budget, prove uneconomic to run, or fail sometime after completion. I don’t think that means we should attempt them. California’s High Speed Train is definitely a boondoggle in that it was proposed partly as a vanity project and is now scaled down, hugely over budget, and hasn’t even acquired the rights of way for the track. Britain’s HST project is facing rather similar problems, but the government has secured the right of way with rather brutal use of eminent domain. In both cases, my thoughts are that just paying for more frequent trains on the existing tracks would serve the public better. In California, I suspect electric aircraft will prove economically superior to the HST and fulfill the green credentials desired.

              • Patient Observer July 3, 2021, 17:33

                From personal experience, large engineering projects are more politically and financially driven than smaller projects. Whenever money reaches a certain critical mass, the consultants, attorneys, financial advisors and the like swoop in. It seems few of them are motivated to complete a successful project Why should they? It would be the end of easy money. The California HST project is likely a good example of the foregoing.

                Having traveled on China’s HSTs I can see the attraction of the technology – fast, quiet, convenient and flexible. How flexible? A given HST train can make multiple stops lasting no more than a few minutes bringing service to smaller towns that would never be economical for air service.

                Musk fills an interesting market niche – selling hope for a glittery future amplified by a media also filling the same niche. When the societal trajectory is downward, these flimflam artists have an easy time.

                Fusion does have enough science and engineering credibility to sustain ongoing research. But, it will not provide abundant carbon-free energy for decades. Closed fuel cycle fission technology is already in large scale operation in Russia. They seem to be taking their time which is good as they have abundant natural gas and hydropower to allow an orderly transition.

                An economy that is increasingly focused on further enriching the rich does not bode well for for advancing our civilization. Another fact of money is that the financial elites want to shutdown the game while they are in control New potential members are carefully vetted before entry (thinking the new tech billionaires). Musk was a little mavericky but he just adds some spice to the game.

                Back around the tun of the century, Marshall Savage wrote a book describing a technotopia and developed a small following likely all now dispersed.

                The Millennial Project: Colonizing the Galaxy-In 8 Easy Steps

                Yup, we can be a Type 3.0 civilization at the next millennium. And the Milky Way will take on a distinct green hue from quadrillions of O’Neil cylinders (yes, that was the claim).

        • Michael T July 3, 2021, 2:02

          Certainly the first satellite and man in space were milestones, as they led to everything else.

          My point re renewables wasn’t about becoming a Type 1.0, but fixing our somewhat screwed-up Type 0.7 (with living standards problems, as you say), because that’s where we are, at the moment.

          BTW orbiting solar power arrays ARE renewables :-) .

          I didn’t mention fusion power, but it would be wonderful if it works. I could insert the 30-year joke here, but some researchers are much more optimistic. I hope they’re right. Closed-cycle fission might be an idea IF it is safe.

          Type 1, 2, 3, 4… are POSSIBILITIES, not necessarily GOALS, although I guess many would like to achieve at least some of them. There may be other pathways, and this could be why we don’t seem to see any K2’s, etc. As you imply, we might be staring right at their stuff, and not recognising it.

          As for Mr Musk, hyperloop, not-hyperloop-but-just-cars-in-tunnels, and intercontinental passenger rockets do seem to be a bit of a boondoggle at present. High-speed trains seem to be a much better, demonstrated technology in many places. But he has had success with Teslas and Space-X. As for Starship, we will see.

          • Patient Observer July 3, 2021, 17:39

            Yes, we are largely on the same page. Musk seems hellbent on being the richest man on earth and he will pump his stock bubbles as needed towards that goal.

            The engineering that positively affects the general population seems to be in China. This may be a controversial statement and I will leave it at that.

        • AlexTru July 4, 2021, 3:43

          … I am a US citizen who …

          – underestimation of “Appolo” program + overestimation of USSR space program
          – the hate to Elon Musk
          – overestimation of technology achievements in modern Russia.
          Give some signs that you probably also one of ex.USSR territory citizen…

          • Patient Observer July 4, 2021, 8:02

            That is a rather offensive response. Be assured I was born in the USA (Midwest where many of us can still think independently). Except during college and a few years after, I have always lived within a few miles from where I was born. I travel extensively as part of my job responsibilities. Last time I checked, my passport had stamps from over 60 countries. You will be pleased to know that I also have positive views of Middle East people and am comfortable in most cultures.

            My father raised me to be a skeptic of the MSM and that war is a criminal enterprise. He served in the Pacific in WW II. He was a patriotic American (as I am) but stated that Japanese soldiers were tougher and braver than Americans, We won only by massively superior resources. I suppose you would say he was unpatriotic and I would say…. The point here is that there are other views of the world beyond what is printed in the New York Times or as seen on CNN.

            I did not mention the USSR space program as you alleged. I did mention their progress in nuclear power which is easy to verify. Yes I am a big fan of nuclear power and live within a few miles of a large nuke power plant. Here is a story on the Russian efforts to close the fuel cycle:


            Don’t use the word “hate” with me. I simply call it as it see it regarding Musk as well as the present madness /desperation of our societal leaders. I apologize for the off-topic discussion but things got too personal to ignore.

          • Patient Observer July 4, 2021, 8:12

            Meant to post this link regarding fast neutron reactors and the closed fuel cycle:


            And, probably a relief to many, this will be my last comment on this topic.

  • Dimjo June 26, 2021, 8:44

    I imagine that post biological civs exist. In my naivete, I never considered energy and resource constraints as major factors in deciding to go that route.
    However, a post biological need not be constrained to virtual existence. Again, efficient energy and resource utilization suggest galaxy wide probes/drones sending back exabytes of data to the “civilization”, and not the opposite, having organic beings in tin cans flying between stars – tremendous energy wasted. Just as I may physically be in a pandemic lockdown, I turn on the news or use a VR headset to “get out”. (as an aside, maybe the Pentagon tic-tacs are drones in the zoo).
    There might be another question to consider. Which could go further, a biological civilization, or a post-biological civilization?

    • Alex Tolley June 26, 2021, 16:13

      Just as I may physically be in a pandemic lockdown, I turn on the news or use a VR headset to “get out”.

      Imagine you lived in the Centauri system. Would you turn on 4-year-old Earth news? That is the problem with galactic civilizations – lightspeed limitations prevent coordination. A 50,000 ly distance from the galactic edge to the center (at Trantor?) without FTL communication means that any “civilization” has to be very decentralized. Over the time frames involved, they would hardly remain a homogenous entity, fragmenting into myriads of different cultures. I think this would be the case even with machine civilization. Even on Earth, the insects with their preprogrammed brains and limited capabilities evolved very different lifestyles, from the solitary to the social, from the herbivorous to the predatory carnivore, to the parasitic.

    • kph June 26, 2021, 19:33

      Or something biological but at home in the void; e.g., “Tin Man”. Dangers to post-biological life might also exist, such as a loss of curiosity, motivation, or the opposite, some irresistible but resource draining problem. Assume post-biological form has echoes of its previous form in its immortal state; e.g. some emotion, awe, reward type system driving its efforts, a type of mammalian-familiar intelligence, one could argue it at a disadvantage compared to a biological life form, some hive mindset.

  • Robin Datta June 26, 2021, 9:22

    Tom Murphy is a professor of astrophysics at the University of California, San Diego. He also works for NASA monitoring the movements of the moon to centimeter precision by laser interferometry with reflectors left by the Apollo program.

    His blog is now quiescent and archived. But it has much material that is still useful, such as:
    Galactic-Scale Energy

    • Alex Tolley June 26, 2021, 16:05

      He is right and wrong. Yes, we will come up against limits once we become a K3 civilization, assuming we can even do this. He is right that any growth quickly exhausts the time limit that growth can continue – it becomes a cosmic eyeblink. But he wrong to assume that all this energy growth needs to be used on Earth. A K2 civilization would not live on Earth but in space.

      If, a big if, our [post]human future was to fill out trillions of years and beyond, dismantling stars to use their precious hydrogen in a more miserly fashion than even M-dwarfs would facilitate this. Indeed, as the universe continues to expand, the stars go cold, and the redshift makes only our sun visible, we could live in our system but burning enough hydrogen to keep our planet and any extraterrestrial colonies lit and warm.

  • Michael June 26, 2021, 12:36

    What would IC 1101 be at 5 000 000 ly’s across, a Type 3 extra large !


  • Thomas W Hair June 26, 2021, 14:26

    Not a big fan of the Kardashev Scale or the Drake Equation. KII is control of a solar system and KIII is control of a galaxy. That’s one heck of a leap, like going from a fire cracker to Castle Bravo. So, it’s not a very fluid scale because it lacks a continuous domain, thus allowing anyone to implant their bias to say K2.1 means x and K2.2 means y. It is not scientific at all. Additionally, the idea of “control” or “harnessing” of “energy” seems awfully filled with mid-twentieth century manifest destiny jet pack helicopter in the backyard stuff. I live in a 58 year old house that uses less energy than when it was built and world population is starting to level off…I suspect as we move forward those two trends will continue.

    • Alex Tolley June 26, 2021, 15:53

      Interestingly there seems some indication that the world has peaked on a per capita use of energy. Now we just need to decarbonize as well as becoming more energy-efficient within the possible limits.

      KSR’s “The Ministry of the Future” moots the rewilding of the Earth to allow 1/2 of the planet to be left in a natural state. We have a long way to go to get there, and the oceans seem particularly vulnerable right now. But it would be a worthy goal, IMO. I might even happily move if I was compensated sufficiently to allow my part of California to stop intensive farming are return to its natural state.

    • Andrei June 27, 2021, 8:14

      I fully agree, these ideas developed in one age indeed the ‘manifest destiny’ mindset was part, and certainly also the ‘more is better’ idea.
      Nowadays we see electric cars, handheld phones and other devices that would have been considered near impossible at that time.
      Especially the fact that the processor for the phone and any other device can be made extremely energy efficient. So I tend to agree with Dimjo, VR might be only just the first step on a path where we eventually might be able to upload our minds – and create one energy efficient civilization that both have the potential for very long term survival and proliferation.

      • torque_xtr June 27, 2021, 12:44

        There is probably not much room at the bottom. Our brains are very good in terms of computational efficiency; if 200 W (upper limit of brain waste heat in peak anaerobic power, typically several times lower), is divided by a classic estimate of throughput, 10^17 elementary instructions per second (36 petaflops needed for simulation, per Wiki), we get 10000 electronvolts per EI. This is just 6 orders of magnitude above Landauer limit. Not too much in terms of difference between Kardashev types. Great uploaded minds are going to be big and hot.

        • Alex Tolley June 27, 2021, 22:40

          Animal brains are proof that low energy minds are possible. I would argue that since some of the brain’s energy is used just to maintain the neurons, as well as the inefficient method to generate action potentials, that in principle we could develop computational technology that is at least as energy efficient as wetware and probably better. Have a look at the energy demand of neuromorphic chips. They are far less energy-consuming than von Neumann architectures.

  • DCM June 26, 2021, 14:52

    We won’t need sky cities on Venus. We need engineered microorganisms that will consume the components of its clouds and allow the radiation of heat. It’ll take millennia to become usable but so what?

    • Alex Tolley June 26, 2021, 15:47

      Venus with an Earth-like atmosphere will be too hot for terrestrial life. It will still need a shield to reduce the apparent luminosity of the sun. It might be easier to float those cloud cities in the HZ zone of the existing atmosphere, preferably well above the H2SO4 zone.

      But for sheer lebensraum, one really cannot beat using readily available materials to construct space cities (O’Neills and larger). KSR’s “Ultima” has a parallel earth universe dominated by advanced Aztec culture with truly vast cylindrical space habitats that dwarf anything O’Neill proposed. (Whether they are buildable without unobtanium IDK, but KSR is usually very good at staying within known physics for his hardware.)

      Unless there is some fundamental problem going this route, it still seems to me that O’neill’s logic holds, as well as Lewis’s estimates of the resources of the solar system to expand our environment, eventually making a Dyson swarm around the sun, approaching a K2 civilization.

      • DCM June 28, 2021, 11:46

        I’m all for O’Neill habitats. That’s the best way to go.
        We need to prioritize experiments with such, staring with simple biospheres with simple life forms.
        I don’t know what the temperature of Venus might be without the clouds but why shouldn’t we experiment with it? There’s no life there to destroy.
        We could manage on Mars, but building our own sites is best.

        • Alex Tolley June 28, 2021, 21:18

          A quick Google suggests Venus with an Earth-like atmosphere would have an average temperature of 70C, compared to earth at 16C. So only livable at the poles?

          • DCM June 29, 2021, 11:52

            That sounds better than floating cities in a corrosive, poisonous cloud layer.
            However, I see Venus as having other problems in view of its rotation.
            It would still be an interesting experiment in evolution of introduced life once the clouds are consumed and altered.

          • gbaikie June 29, 2021, 16:59

            Earth at Venus has problem of twice as much sunlight at surface- instead of 1120 watts per square meter of direct [1050] and indirect of 70 Watts per meter one has about twice as much sunlight. Or our sunlight can heat a dry ground surface to about 70 C and at Venus distance [if you had clear skies and dry ground and sun at zenith the ground surface could cook bacon and eggs {as compared can cook eggs on sidewalk [need sidewalk to be 70 C to cook a egg- and sometimes in right condition- it’s vaguely possible]. Humans control their environment, but trees and other life did evolve to handle such temperature. But ocean surface would not get much warmer. And Earth’s global air temperature is mostly the ocean surface. So Earth would be far more cloudy and average global temperature would be somewhere 30 to 40 C. But high humidity at more than 40 C it not comfortable and that might be cool summer day high temperature. But Things living in ocean should be ok, nature life on land would probably survive where sunlight does reach above 45 degrees above horizon – polar regions.
            But if somehow it was always cloudy then ground would not warming well above 80 C , even when sun at zenith

        • ljk June 29, 2021, 11:39

          Even Interstellar went with O’Neil space settlements in the end – after a pointless bunch of journeys into a wormhole to attempt to settle worlds in a remote galaxy with no apparent way to check on them with automated probes first or send information back!


          I still want to see them happen, especially if they become WorldShips that can roam the galaxy and thus ensure the survival of who or whatever is onboard.


          Planet-stuck humans think being stuck in even a large space vessel will be detrimental to such inhabitants, but most people right now live indoors most of the time in artificial environments.

          WorldShips will be able to visit all sorts of planets and other natural celestial bodies and if done right will probably offer more space and conveniences that what most humans experience now – and things will only get less convenient as our population numbers continue to grow.

          I have noticed a definite avoidance by the powers that be and others to discuss the real issues facing our planet, and that is human overpopulation. There are now almost five billion more humans on Earth than there were when I was born. And note that it took all of human history to reach 1 billion circa 1800. Now we are approaching 8 billion humans and the numbers will not plateau as the so-called experts once predicted.

          No I don’t think even a fleet of WorldShips will solve our population issues. Those need to be taken care of here and now, or we will think the world depicted in Soylent Green is optimistic. I see WorldShips as a way to preserve humanity and our Artilect descendants while allowing us to explore the galaxy and meet with other intelligences, hopefully on good terms.

          • Alex Tolley June 29, 2021, 17:41

            Are the O’Neill-style worldships the contemporary version of Blish’s “Cities in Flight”?

          • DCM June 30, 2021, 4:16

            Worldships aren’t intended to solve our population problem but to expand life.
            The wealthier any population gets the longer-lived individuals are and the fewer offspring they have. The alleged population problem is self-solving and doesn’t need totalitarian mass killings/sterilizations; a capitalist system that yields wealth will result in smaller populations.

  • Henry Cordova June 26, 2021, 21:48

    We talk about post-biological civilizations. Why not post-technological cultures.

    A truly advanced civilization could eventually transition to a thoroughly optimized ecosystem, stable and self-maintaining over geological and even astronomical time scales. Only energy from the host star would be required to keep the system running (although they may have to tinker with it a bit first to make it stable enough ). Or maybe they’ll just move to a world (or worlds) that can be self-sustaining or made that way. This would provide the redundancy needed to guarantee protection against catastrophe. I’m not talking about some Romantic pastoral back-to-nature movement, complete with shepherds and milkmaids, I mean a technology based on molecular machines much like the ones which naturally evolved here, but designed for our benefit–and a minimum of maintenance and a maximum of performance.

    This does not imply an abandonment of technology, but a redirecting it into what would look more like biological systems to us; rain forests, coral reefs, or other complex biological communities and ecosystems, not naturally evolved ones, but highly engineered ones self-servicing and controllable to meet any conceivable change or outside influence. “Hard tech” like fusion powered spacecraft, space lasers or radio-telescopes could be kept in reserve, just in case brute force was ever needed to deal with some future, unpredictable emergency or imbalance. Even today, in our civilization, we have hobbyists who keep up with older tech, just for fun and just in case–sailboats, celestial navigation, archery, muzzle loading firearms, horsemanship, throwing pottery, the list goes on. Once you’ve learned how to do something hard and clever, its just plain stupid to deliberately forget how to do it just because you’ve found a way that requires less skill.

    A truly advanced civilization would not just be able to dominate its environment, but would be fully capable of living in harmony with it–or modifying it so it could be lived with in harmony. If we would visit such a place we might not even realize there was a ‘civilization’ there at all. It would look like a farm, a park, or even a wilderness. But a closer look would show us even the plankton in the seas or the microbes in the soil were carefully designed and highly efficient little biological machines-artifacts.

    You see, the trouble with technology is that it needs to be managed, and that it is highly inefficient. Much of the benefit it provides has to be plowed back into the system just to keep it running–and it is always on the verge of breaking down altogether. More and more of the energy and labor we pour into it goes into just keeping the whole system running, and cleaning up after it. Without thinking, we jump into a mechanical chariot weighing a ton, powered by toxic and irreplaceable fossil fuels from deep underground, to travel across an enormous concrete infrastructure just to go buy a pack of cigarettes at the corner 7-11.

    That doesn’t sound very clever or efficient to me. We’ve constructed this Rube Goldberg monstrosity and we call it civilization.

  • AlexTru June 27, 2021, 3:39

    Detecting some signature of technology near another star would be a historic Detecting …

    This statement, is Typical SETI myth, suppose this event potentially less “historical” than Higgs boson or Gravitational Waves detection.

    • Alex Tolley June 27, 2021, 11:26

      Is it that different than ‘detecting “God”‘? I would have thought that would have profound effects on humanity, especially those majority that still follow their particular religion. Advanced ETI would be a near stand-in for a deity and therefore be an important historical event. Let’s be clear, if the myth of a son of God born to a virgin resulted in one of the largest global religions with great historical impact, why wouldn’t an actual god-like civilization that was real, not be equally as significant, inspiring new followers, organized cults and religions? I could imagine every message being scrutinized and interpreted just as QAnon messages are today, or religious leaders interpreting events to fit their religious narratives.

      Scientists will be keen to acquire as much information as they can about the ETI’s planet, biology, cultures, scientific knowledge, and technology. This would likely become a well-funded activity. Not a few political leaders will want to invoke ETI as being “on their side” in any conflicts.

      I don’t think Gray is using hyperbole at all.

      • Robin Datta June 27, 2021, 22:28

        Any “God” detected or otherwise, would belong to the time-space-causation realm, differnig from a mayfly or june bug in degree, but not in kin. : this would be clear from a little acquaintatce with the non-theistic religions (Buddhism, Jainism and two-and-a-half of the six philosophic schools of Hinduism). Such a detection would be quite unremarkable.

      • AlexTru June 28, 2021, 3:01

        … those majority that still follow their particular religion…

        If we are talking about believers…
        I am sure that potential ETI’s technological signature detection cannot change the minds of religious people, no way.
        It is idealistic illusion to suppose that scientific fact can change someone’s belief. Only some very personal experience can change it.
        As well as no detection fact cannot change minds of SETI believers :-)
        In reality potential techno signature detection can bring only one scientific fact there, somewhere is ETI, I suppose that total most of modern scientists , including pessimists believe that ETI exists somewhere in our universe, so – nothing new expected with detection.
        Accounting natural speed of light limit – no dualog with ETI is possible, no Galaxy Encyclopedia is expected, even if we can detect techno signature, we will not be able to decode any message from this signature.
        The dreams that advanced ETI will teach as “good things” are not different from any other religion on our planet.

      • Robert June 28, 2021, 13:50

        “Let’s be clear, if the myth of a son of God born to a virgin resulted in one of the largest global religions with great historical impact, why wouldn’t an actual god-like civilization that was real, not be equally as significant, inspiring new followers, organized cults and religions?”

        I take the opposite view Alex. The truth of the Gospel would protect those of us who believe from falling prey to worshipping alien beings no matter how god-like their technology or civilization seemed in comparison.

        • Alex Tolley June 28, 2021, 21:23

          As you are no doubt aware, the wealthier a country, the more secular it becomes. Arguably perhaps shifting their worship to Mammon (as Prosperity Gospel is doing to Christians in the US). Maybe aliens actually answering prayers with gifts of knowledge might just push aside existing religions? ;)

          • ljk June 29, 2021, 11:45

            You know there will be human sects that start worshipping such aliens. It is already being implied for AI…




            I think such behavior is both backwards and frankly embarrassing for a so-called civilized species, but then again we are still only half-civilized at best.

            On the other hand, Hugo de Garis sees the exact opposite of AI worship by the humans:


          • Robert June 29, 2021, 16:53

            True indeed. Christ amply warned us that wealth, comfort and security can all too easily divert one from faith to secular interests saying “How hard it is for those who are wealthy to enter the kingdom of God!” and “However, when the Son of Man comes, will He find faith on the earth?” What you said is true. Quotes are from Luke 18.

            • Alex Tolley June 30, 2021, 9:05

              I don’t want to get into a religious argument here. However, do you not understand how non-believers can see that “How hard it is for those who are wealthy to enter the kingdom of God!” is a control mechanism for elites to keep the peasants under control and accepting of their misery for a reward that only they can get after they die? Human psychology experiments show that people (actually primates) will defer gratification now in favor of a larger reward in future. What reward could be larger than eternal life in a perfect world?

              • Robert July 2, 2021, 15:03

                Not a religious argument but just a friendly exchange of views. To me it’s not “pie in the sky” designed to control the masses. It’s the real Life. Regarding this eternal life, Jesus defined eternal life simply as “to know God and the One He has sent.” Such a quality of life transcends even death and can never end.

          • gbaikie July 1, 2021, 4:54

            “As you are no doubt aware, the wealthier a country, the more secular it becomes. ”
            [[It seems to me this is the lie of the Marxist religion :) ]]

            What is meaning of secular:
            “With the Forty-second Amendment of the Constitution of India enacted in 1976, the Preamble to the Constitution asserted that India is a secular nation. … The Constitution does not recognize, it does not permit, mixing religion and State power.”

            If State has freedom of all religions and doesn’t have State religion- it can be called, secular.
            It’s difficult to determine whether US has become more secular.
            Obviously China is not secular. Nor is Russia.

            “In 1966, Time magazine famously examined whether the United States was on a path to secularization when it published its now-iconic “Is God Dead?” cover. However, the question proved premature: The U.S. remains a robustly religious country and the most devout of all the rich Western democracies.”

            -the action or process of converting something from religious to secular possession or use.
            “after the secularization of the monastery the choir stalls were sold” –
            One can say there has been many efforts of secularization but whether one considers them failures or successful these efforts even if completely successful could not make a nation more secular.
            Politicians forbidding church services, is not secular, but one call it secularization- and it’s a governmental violation religious freedom.
            But say, if Amazon prevented it’s workers from going to church, it’s also secularization.
            But Amazon pays it’s workers to go to a particular/specific church- it is, as problematic in terms of religious freedom. Either action could cause a lawsuit- in which any company could lose and have to pay damages.

            • Alex Tolley July 1, 2021, 9:52

              This chart shows the examples you gave are not the case. For example, India is in fact, a religious country. As I thought was well known, the USA is an anomaly, with relatively high religiosity despite its wealth, and Russia has a comparable religiosity to the US despite much lower wealth and once banning religion as part of Communist beliefs.
              Wealth and religion

              • gbaikie July 1, 2021, 19:02

                percentage of world population who are atheist?
                According to sociologists Ariela Keysar and Juhem Navarro-Rivera’s review of numerous global studies on atheism, there are 450 to 500 million positive atheists and agnostics worldwide (7% of the world’s population), with China having the most atheists in the world (200 million convinced atheists).”

                Ancient Rome, didn’t care what you believed, but they had laws that you had give offering to Roman Gods as it considered a civil duty [effectively a tax].
                One could call this “secular”.
                The Jewish religion considered giving offerings to other gods. as grave sin- a major violation of their covenant to their god Roman law allowed Jews not to do this civil duty, because Jewish religion was an ancient religion/custom/wisdom-or it was much much older than Rome. That would not be a secular thing to do, and Romans had problems with the believers of Christ who also considered themselves as Jew, but the Jew Christians allowed Non Jews to be believers in Christ and didn’t want to discriminate because followers of Jesus Christ didn’t want follow Jewish procedures which make them qualify as Jews.
                Or the Jews and Christian ruined the secular Roman State and led to Rome making Christianity the Roman State religion. Which is not a secular State.
                Everyone has a religion, they just might not strictly follow the rules and procedures of the various religious authorities.
                Marxist do have strict rules- and if don’t religiously follow them, then you aren’t a true Marxist. And they tend to eat their own.

    • AlexTru June 30, 2021, 3:09

      The following comments are best illustration that religious adepts and “ETI will teach us good thing” believers are not do different, both sides do not have any scientific proves of their beliefs, both are blind religions in reality.
      Let alone traditional religions, we live with religions thousands of years and will continue to live till the end of our civilization, nothing can change this Status Quo, no ETI signature detection for sure – this is not blind belief but scientific fact – homo sapiens history clearly shows it.
      In same time people mostly associated with SETI, who proclaims them self as scientists , but in same time blindly believe that “ETI (when detected) will teach us good” – in reality, good example of new religion. Yes SETI became religion, because some SETI proclamations does not have and support by scientific facts and observations.
      Opposite, if we will use Homo Sapiens history as example , we should make directly opposite conclusion.
      Agree, that single direct fact, is not correct to use, but for sure it is infinitely more correct than fantasy supported by ZERO observation (yes, 1 divided by zero – is infinity).
      I have to admit, that there is additional explanation of “ETI detection will be historic event” myth – fund rising among naive religious SETI believers.

  • torque_xtr June 27, 2021, 12:15

    Earth’s biosphere, in terms of solar energy consumption, remained almost exactly constant at K1.0 for a few hundred million years, since plants colonized land. But it is by no means stagnant. In terms of informational content of all DNA and RNA, which is roughly proportional to the living biomass, in the same period there was some growth which seems to gradually slow down. In terms of complexity, approximated by biodiversity, there is accelerating growth (but non exponential). Nature always stops exponents, just to make the way for more subtle metrics of development. I guess the ultimate one is something akin to Kolmogorov complexity…

    I cannot refrain from saying that capitalism is unnatural in this sense: it ties evolution with exponential growth. Any subexponential growth necessary has zero-annual-percentage asymptote (just by math, for any monotonically increasing subexponential function, (df/dt) / f -> 0 if t -> inf), but in it’s framework, growth approaching zero means no progress. Thus, it has to go at some point, by deepest laws of nature :-)

    • Alex Tolley June 27, 2021, 22:52

      (…) but in it’s framework, growth approaching zero means no progress.

      I wouldn’t agree with this. Firstly one can have progress even without growth of GDP/energy, simply by transitioning to intangible outputs. Informational complexity can continue to increase on a fixed energy budget. just as nature does. But I would agree if you mean capitalism as it is practiced today based on extractive industries for materials that ultimately are dumped. 100% recycling could solve that problem, in principle.

      However, if we are to expand to become a K2 civ, then there is no question that we will have to continue to extract materials to build the habitats and machines we will need to achieve this.

      But as I said before, if the energy at any stage was fixed, we could create a virtual environment and live in this, continuing to develop in that electronic world. What the total informational complexity limit in such a computer would be is an interesting question, as well as what happens when the limits are reached.

      • torque_xtr June 29, 2021, 9:44

        I’m layman in economics, just going from common saying “no growth – no development”, where 0% annual GDP increase means stagnation. But it means that it’s hard for people to imagine progress without annual growth, whatever this exactly means to them…including business owners. Of course, we should grow if we want to expand beyond Earth, and in the same time, energy/matter/space exponents absolutely cannot be forever. But this just means in the far future we will use entirely different metrics as the markers of progress. I use the biosphere analogy to illustrate that progress is possible even when energy consumption does not change for many thousands of exponential expansion timescales (time needed for plants to recolonize land after Chicxulub is some 10 kyr, if I remember this correct).

        But I propably don’t agree on unlimited virtualization possibilities. Straightforward sim capabilitity limit (without going to space) is still quite impressive. If Earth insolation is multiplied by 5% (to avoid overheating) and divided by ratio of classic-estimate computing power needed to simulate a human and Landauer limit, 1e16 W / (36 petaflops * ~ 32 elementary calculations per FLOP / 0.018 eV/calc), this gives 3e18 simulated human minds at K1.0 level. But everything works against it. Difficulty in reaching Landauer limit, likely underestimations on human brain throughput, the desire to multithread or to expand cognitive powers in virtual world (which I personally would pursue if I’ll live long enough :-) ). I guess the actual numbers are not much more than 1e13 non-augmented and non-forked humans if all quantum things are neglected. So yes, there is some room, but it’s much less than difference between information-based Kardashev classes.

        • Alex Tolley June 29, 2021, 14:24

          To make a simple example. It takes a vast amount of energy to travel physically to the stars, whether the huge laser arrays needed for Breakthrough Starship to the vast amounts of energy needed for a crewed starship. But a simulation of a starship journey uses a trivial amount of energy by comparison. A more contemporary example might be the energy differences needed to create a real building compared to a simulated building, which needn’t even obey physics. Yet the simulated minds would be able to live in such a virtual world, and even create new things, possibly even ones that would be accurate simulations of the real world.

          Of course there would be a limit, but a planet-sized computer (it may be dispersed over the solar system) using the total energy of the sun would not need to be that concerned about biosphere limits. Since simulating the real world would take more energy than the actual physical world, it might make sense to maintain a physical realm and only have the virtual realm used for some activities (a virtual “heaven” for those dying in the real world.)

          • AlexTru July 3, 2021, 3:43

            Simulation is not solution, a resources “economy” is working till you try to simulated simplified reality models, more complicated models requires more energy and material resources , so we can approach limit that requires more material resources for simulation than exists in real world.
            Other words, When we are talking about electronic simulation – we should not forget that it is provided using real (non virtual) energy and material (machinery). More complicated simulation requires more complicated machinery (energy and materials). Yes there will be technological optimization, but finally apparatus that could be built to simulate a real world will require more resources than real world, dead loop…

            • Alex Tolley July 3, 2021, 11:07

              I am not suggesting simulation allows infinite growth, but that it can maintain the growth for longer. It doesn’t have to simulate everything nor maintain the simulation for unused places, things, and people. Energy for real-world activities is almost entirely avoided by fantasy, just as they are in movies. Where simulation is expensive is maintaining the simulation of things that in the real-world no longer require energy to maintain.

              • AlexTru July 4, 2021, 3:09

                You can easily cancel “2-nd law of thermodynamic” in your simulation, but you cannot cancel it’s influence on an apparatus that will provide this simulation.
                I am afraid that simulation you mean mostly dedicated to escape reality for limited person(s) ,but no to struggle against entropy. It is drug’s like escape, it is dead, but not life.

                • Alex Tolley July 4, 2021, 10:19

                  I am afraid that simulation you mean mostly dedicated to escape reality for limited person(s) ,but no to struggle against entropy. It is drug’s like escape, it is dead, but not life.

                  Which would also be your explanation for why we cannot be living in a simulation, like the Matrix, or a simulated universe, perhaps embedded in other simulations (like turtles all the way down).

                  I don’t find that argument convincing. What if our life is but a pale shadow to “real life”?

                  • AlexTru July 6, 2021, 2:13

                    What if our life is but a pale shadow to “real life”?

                    Personally me do not believe , but I am sure none can scientifically prove that this statement is false :-)
                    I can also open my mind and suppose that we both are living in simulation, that is simulated in upper level of simulation, the is simulated in simulation etc., etc., etc – infinite (matryoshka) sublayers of simulations… I am sure that science cannot prove that this speculation is false too.
                    As well, as “negative detection” result will never be concluded by SETI… no matter how long fruitless searches will continue.

  • Ivan Vuletich June 28, 2021, 0:50

    For any advanced civilization with deep space capability, there is effectively zero relationship between energy use and interstellar communications.

    If a civilization can setup comms relays at the gravitational lenses of stars then the power levels required for error free communications drops to the 10’s of watts to tenths of a mW.



    The SETI implication of this is that any advanced civilization is going to be invisible, at least as far as long range comms is concerned. Two stars could be transmitting exabytes to each other and unless the geometry lined up exactly right a 3rd star system wouldn’t have a clue.

    • Alex Tolley June 29, 2021, 14:45

      The SETI implication of this [gravitational lens communication] is that any advanced civilization is going to be invisible, at least as far as long range comms is concerned.

      A very good point. Even leakage would be undetectable without a similarly sensitive receiver pointing in the right direction. This would require possibly millions of receivers located around the spherical surface of the gravitational focal line of our star, listening on the correct wavelengths for a particular star. An expensive project with no way to know if there is even a signal to be received. [I would like to see a SETI spokesperson advocating this to Congress. Even the DoD might balk at making such a request.]

  • ljk June 28, 2021, 11:07

    Quoting Robert H. Gray…

    “Nobody knows what information interstellar signals might contain. Signals could encode entire libraries of text, images, videos, and more, with imagery bypassing some translation problems. What might motivate sending information between stars is an open question; trade is one possible answer. Each world would have its own unique history, physical environment, and biology to trade—and conceivably art and other cultural stuff as well. Kardashev thought that the information to characterize a civilization could be transmitted across the Galaxy in one day given sufficient power.”

    My reply:

    I can believe trade of various kinds between star systems, but I have always had trouble with the idea that a civilization might send a “lesser” society their equivalent of the Encyclopaedia Galactica.

    Does a smart person give away all their knowledge and secrets to strangers? Not usually. I only see such a thing happening if we reach a certain level they approve of, or if their society is dying and they want to preserve something of themselves ala James Gunn novel The Listeners.

    Of course a tech savvy ETI could learn a lot about humanity just by listening in on our electromagnetic leakage and learning to translate it. Are other societies also so noisy and careless?

    • ljk June 29, 2021, 12:05

      I just want to add to what I wrote above that by nature I am very much for the free dissemination of knowledge to all. I do not care in principal for this idea that only a (often self) chosen few deserve to have a proper education, which they are then supposed to trickle down to the unwashed masses.

      However, as we see all too often on this planet, certain information gets misused all the time. When such knowledge isn’t being used for less than savory purposes, the means to disseminate that knowledge is more often than not left to those who would merely use it as mindless entertainment. First it was television, now it is the Internet via our access devices.

      We don’t know what is out there beyond our Sol system in terms of ETI. While I am not one of those who automatically assume there are little more than marauding aliens just waiting for pounce on us and our planet, the one thing we may have to offer another species is our unique heritage and history. I would hate to just throw it away if for no other reason than out of respect for all those who came before us to make current humanity possible.

      It may not matter in the end as any sufficiently advanced ETI could probably grab all our information with relative ease without our awareness and permission, but I think our first deliberate METI should be carefully planned, if it is not too late already. Even on the Voyager Interstellar Record, they choose not to present certain aspect of our species to avoid any potential rudeness or have them be interpreted as a lame effort to intimidate (such as showing a nuclear bomb detonation).

      Of course Trevor Paglen threw that caution to the wind to make a social point when he made The Last Pictures artifact and had it tossed into geosynchronous orbit in 2012:


    • Alex Tolley June 29, 2021, 14:28

      Why not send entertainment? (Maybe wrapped up with propaganda.) Cultural goods rarely divulge much knowledge. A sci-fi movie is not divulging any information about imaginary technology.

      • ljk June 30, 2021, 13:53

        There was a South Park episode where it was revealed that Earth was created solely to entertain higher intelligences throughout the galaxy. Our conflicts were often perpetrated by these ETI to keep them entertained (and the ratings up).


        I can see where such beings may not have created us for entertainment purposes, but derive such pleasure nevertheless. After all, we still find such comedies as The Three Stooges funny because they hit at a basic universal (literally?) level.

    • paolo June 30, 2021, 18:24

      Nah, probably 10,000 hrs of porn + virus & malwares etc…

  • wdk June 28, 2021, 11:51

    First, want to thank Robert Gray for that review of Kardeshev levels, their history and how they related to each other. And also, thanks to those who provided some interesting follow-ups with regard to terrestrial and space based power allocations. Much was derived – and it leads to more.

    Mentioning the case of the ISS, we note about 160 kw capacity and a nominal crew of six. The long time configuration of three pairs of solar arrays tracking the sun just happens to be in a state of transition. The new arrays are smaller, but with increased efficiency. This partly reflects (sic) improvements in solar cell technology. Side effects will be decreased drag ( or else more room for more arrays) and perhaps lower radiator requirements. Crew size is as much a matter of logistics from Earth as the actual support capability fo the station. Were there a dozen people on board, the system will not collapse, but the effective support capability statistics would be altered, of course.

    But it might be worth considering the efficiency of utilizing solar power in any of these civilizations. Simply to block the light from a star is not the end of the story. Whether photovoltaic or photosynthesis, some power will be surplus or even wasted. Just as with the hole or the doughnut, K-II radiators might be as important to look for as a specific characteristic.

    Per capita needs for power are based here on human units of 60 or 70 kilogram units, speaking like an industrial engineer. ET might be orders of magnitude larger or smaller – and the number in a society might not be driven by the dream of building a bigger and bigger
    megalopolis. These discussions about post biological life… such a concept just might lead to “one” – and maybe a lot of backups in the
    warehouse.- and programmed imperatives we are just too far removed from except to say, “Now if it were up to me…” And we are coming into this wondering, “What would they be like?” So it is akin to chasing our own tails as long as we have nothing on our scopes.

    Power generation to drive computational power has been one of the background arguments for the KII and KIII cases. On account of trends we see in our own energy allocations, or else the growing consumption trend in our computational requirements. Currently, we discover that some of our large tech companies support themselves with large computing clouds that have very earthbound storage compartments using up lots of energy from electrical grids. And currently (sic again) a lot of this allocation is in support of commercial transactions: catalogs, supplies, customer files, etc. In many cases this is for individuals, distinct from our personal mass ( discussed above). There are societies on Earth that vary in their emphasis on individuality vs. conformism, but I don’t think that that has reduced the information glut, at least in the short term. Perhaps it just means that for now, central authorities establish files on individuals – but that’s no guaranteen that if an authoritarian central government triumphs this data requirement will ever stop.

    A.T., above and elsewhere, has suggested that number crunching for inward facing civilizations (e.g., rational pursuit of irrational numbers?) might continue to grow so much that their power inputs could result, paradoxically, in outward expansion into the K-II realm…
    … Well, we will just have to save contemplation of that for another time, save that perhaps when some of the deep questions are resolved the computation requirements diminish and the cul de sac data sets need no longer be maintained.

  • ljk June 28, 2021, 13:30

    Did a comet affect the course of human civilization?


    • Alex Tolley June 29, 2021, 14:51

      From the article:
      “Their analysis backs up claims that an impact occurred prior to start of the Neolithic period in the so-called Fertile Crescent of southwest Asia.”

      Why didn’t the impact affect other cultures, e.g. in the Americas and Australia? If the only culture affected was one in the ME, couldn’t that just be a coincidence rather than causal?

      • ljk June 30, 2021, 15:20

        As the impact points were apparently centered around Greenland, it is possible that Australia at least could remain shielded. As for other parts of world, how much do we really know about them from prehistoric times to determine such a thing?

  • Harold Shaw June 28, 2021, 16:34

    Economists aren’t worried that we will remain stuck in the traditional symmetry between GDP and human input. They are worried about the imminent breaking of the symmetry. Biotech, nanotech, robotics and Ai are already dismantling the symmetry. The limits of collective production is meaningless to a people or persons with these mature technologies.

    You have to make a better case for why the symmetry will continue than pointing to past trends.

  • Mike Serfas June 28, 2021, 18:40

    Anthropic arguments have been said to preclude galactic colonization ( https://www.nature.com/articles/363315a0 ) with species longevity of a few million years at most.

  • Robin Datta June 29, 2021, 10:15

    Sufficiently advanced civilizaations without any botleneck in the availability of periodic table elements may be past the stage of tradng manufactured goods: transmittal of the “blueprints” or designs for components and their assembly may be all that’s needed.

    Even if the other civilization was “backward”, plans starting with lego blocks (or even sticks & stones) and proceeding therefrom may be considered. And if the manufactured goods were for one’s own civilization, von Neumann machines might be an option.

    Massive interstellar and/or intergalactic data streams may exist, and as in the case of the Internet, free for downloading by anyone with the know-how to tap into them.

  • wdk June 29, 2021, 10:53

    Got the gist of this argument between the abstract and related articles by Malcolm Gladwell which did not address galactic expansion directly.
    But key elements were the notion of the existing age of homo sapiens and the probablistic argument of where we lie on a bell curve. Not very well versed in probability myself. So to speak, prefer to study and play with calculus and d.e.’s. But I would venture to say that both Gott and Gladwell profess that we live near the crest of the bell curve with a width defined by when we were identified as a species. Hence, if homo sapiens arrived 40 or 70-k years ago, expect another 40-70k as the most likely continuation of the species. Variations due to actual events such as the bomb or miracle cures – just less likely excursions for our future – Right?

    But in addition, what is a species in this case. In the last decade we have discovered that many ancient ancestors we assumed were other branches, show up as remnant parts of our DNA. And in the past few weeks, several mideast and East Asian discoveries suggest that the
    links go back longer than we had thought, galaxy expansion in the cards or not.

    This language we call English has morphed considerably in hundreds of years, including on account of concepts alien to our ancestors. Genes mutate too, but for different reasons. Genetic and intellectual changes are likely to occur over hundreds of thousands of years, but I don’t think that they will preclude continued efforts to expand above the Earth.
    Traits prevailing earlier die out and get replaced by new ones, useful or maybe not in context, but will make homo 20,000 CE different from 2021 variety. Same with his/her language and the concepts conveyed.

    But that supposed two million year hour glass would be akin to worrying about turtle extinction due to one species disappearing a hundred million years ago. Clearly they survived past the Upper Cretaceous.

  • ljk June 30, 2021, 15:23


    [Submitted on 29 Jun 2021]

    A Dyson Sphere around a black hole

    Tiger Yu-Yang Hsiao, Tomotsugu Goto, Tetsuya Hashimoto, Daryl Joe D. Santos, Alvina Y. L. On, Ece Kilerci-Eser, Yi Hang Valerie Wong, Seong Jin Kim, Cossas K.-W. Wu, Simon C.-C. Ho, Ting-Yi Lu

    The search for extraterrestrial intelligence (SETI) has been conducted for nearly 60 years. A Dyson Sphere, a spherical structure that surrounds a star and transports its radiative energy outward as an energy source for an advanced civilisation, is one of the main targets of SETI.

    In this study, we discuss whether building a Dyson Sphere around a black hole is effective. We consider six energy sources: (i) the cosmic microwave background, (ii) the Hawking radiation, (iii) an accretion disk, (iv) Bondi accretion, (v) a corona, and (vi) relativistic jets.

    To develop future civilisations (for example, a Type II civilisation), 4×1026W(1L⊙) is expected to be needed. Among (iii) to (vi), the largest luminosity can be collected from an accretion disk, reaching 105L⊙, enough to maintain a Type II civilisation.

    Moreover, if a Dyson Sphere collects not only the electromagnetic radiation but also other types of energy (e.g., kinetic energy) from the jets, the total collected energy would be approximately 5 times larger.

    Considering the emission from a Dyson Sphere, our results show that the Dyson Sphere around a stellar-mass black hole in the Milky Way (10kpc away from us) is detectable in the ultraviolet(10−400nm), optical(400−760nm), near-infrared(760nm−5μm), and mid-infrared(5−40μm) wavelengths via the waste heat radiation using current telescopes such as Galaxy Evolution Explorer Ultraviolet Sky Surveys.

    Performing model fitting to observed spectral energy distributions and measuring the variability of radial velocity may help us to identify these possible artificial structures.

    Comments: This paper have accepted for publication in MNRAS

    Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Astrophysics of Galaxies (astro-ph.GA); Popular Physics (physics.pop-ph)

    DOI: 10.1093/mnras/stab1832

    Cite as: arXiv:2106.15181 [astro-ph.HE]
    (or arXiv:2106.15181v1 [astro-ph.HE] for this version)

    Submission history

    From: Tiger Hsiao [view email]

    [v1] Tue, 29 Jun 2021 08:57:58 UTC (843 KB)


  • Mike Serfas July 1, 2021, 8:38

    Here ya go: https://phys.org/news/2021-07-lonely-cloud-bigger-milky-galaxy.html “A scientifically mysterious, isolated cloud bigger than the Milky Way … full of hot gas with temperatures of 10,000-10,000,000 degrees Kelvin (K) and a total mass 10 billion times the mass of the sun… not associated with any galaxy and is in a ‘no-galaxy’s land'” Perhaps there is a way to read this more salaciously than the article’s authors intended?