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The whole concept of a Dyson sphere is kinda idiotic. Any civilization that is capable to build one, it is probably able to work out fusion energy very efficie

The whole concept of a Dyson sphere is kinda idiotic. Any civilization that is capable to build one, it is probably able to work out fusion energy very efficiently. There is no point to go and harness energy around a star or a black hole, when you can just produce it locally with a lot less resources/waste and materials. The sun itself is actually very inefficient in producing energy. There is no need to harness the sun million of km away, when you can recreate it in your home planet. The only way to produce a dyson like of sphere, is to tame an over-heated sun, and reflect away un-needed energy. But there is no point to build one to just harness it. It makes great sci-fi stories, but that's about it. Scientifically, it just doesn't make sense.

hutzlibu 5y ago
It depends on the amount of energy the civilisation needs. Lets say, you want to manufacture new planets/planetary sized spaceships. You would need very big fusion reactors and you probably want to save the special fusion fuel for those, when they are on their voyage to other worlds. Because then they need fusion. But why build a fusion reactor, when you already have a big one avaiable?
- mclightning 5y ago
  Because you can build a more efficient one? You could make it portable, controlled, modular etc etc
  - hutzlibu 5y ago
    Yeah. All needed for interstellar travel for example. But for manufacturing planets?
    - mclightning 5y ago
      Why would you want to manufacture a gravity well? There are plenty of them
      - hutzlibu 5y ago
        How many earth sized planets do we have in our solar system?
        mclightning 5y ago
        If you're limited by the compounds available within the solar system, you should forget about building a dyson sphere for other reasons, or building a planet, or any kind of activity that will disturb the orbits of planets. Few planets are similarly sized as Earth already btw, although with varying densities.
        hutzlibu 5y ago
        Ok, earth sized is mainly about 1 g. So yes, also with earths density to be precice. That leaves only venus as a existing alternative. And I just assume that a civilisation advanced enough to build a dyson sphere, can handle the non trivial orbital mechanics, too. But maybe still cannot travel FTL. So indeed rather choose to build planets, or planet sized space stations. That would require lots of energy and maybe the need to harvest the sun directly and control the light going out towards the planets.
  - deleted 5y ago
    [deleted]
zaarn 5y ago
There is a point still, because a star is massively more efficient at fusion by way of "production at scale" effects. The additional benefit is the amount of power. With the power of a star at your disposal, beaming your energy using lasers and microwaves, even if only 1% efficient, would instantly solve the energy needs of any planet in a solar system. If we did it, we could instantly colonize all planets in our solar system because things like "running an AC on Mercury" or "Hovercraft in Jupiter Atmosphere" becomes trivial when you have limitless power. Heck, you could start projects like moving planets in orbits or collecting astroids to built a planet if you wanted. Black holes are the stage after that since you can use a spinning black hole to convert a given mass into energy at >10% efficiency (given E=MC^2). That would allow a civilization to power multiple solar systems at the cost of a few planets per year. Granted, the sphere is difficult to build, but that is what you have dyson swarms for.
- TheOtherHobbes 5y ago
  The sphere isn't difficult to build. It's impossible to build. It's unstable without active stabilisation. The stabilisation has to be perfect because otherwise you get massive distorting spherequakes propagating through it, which will make it a very uncomfortable ride for a short time and will soon tear it apart. A perfect spherical stabilising solution with components and sensors that are light minutes - or possibly light hours - from each other is impossible because of the signalling delays. Ringworlds have the same problem. Even if the ring is made of infinitely strong unobtanium, it won't stay in a useful orbit for long enough to be built, never mind inhabited. Swarms have more potential, because you can build them with sparse shells and move things around to handle instabilities. But you still need massive computational effort to keep swarm units from colliding with each other, possibly at very high speed. None of this matters, because the limiting factor for civs is collective intelligence, not energy. We already have access to far more energy than we could possibly use on earth for any technology that's actually buildable. But we're not using it because we don't have the species IQ to make the right choices.
  - wruza 5y ago
    collective intelligence, not energy This. The entire “moving planets” and “powering asteroids” theme is just a projection of our historical aggressive reproduction, which is not even a requirement for an advanced civilization. Earth alone could serve us a few billions of happy years, if we didn’t have the happy urge to multiply until critical shortage. That’s far from intelligent, imo.
guerrilla 5y ago
> a lot less resources/waste and materials. The sun itself is actually very inefficient in producing energy. Umm... The sun is about 2×10^30 kilograms. The rest of the solar system is about 3×10^27 kilograms and we kind of need it to live on and make things with. Put in other words, the entire solar system including the Sun is 1.0014 Solar masses. Why not go with the process we have rather than fusing everything we have to do the same thing? If you're saying that we don't need that much energy then I think that's pretty meaningless since we have no idea what we could get up to or need in the far future.
mytailorisrich 5y ago
I don't think that how efficient the production is really matters because stars do produce that energy anyway and for free as far as we are concerned. The question is one of efficiency and cost of collecting it.
- arrow7000 5y ago
  I'm surprised not more replies say this. So what if it's inefficient? It's happening anyway and it's not like you can siphon the hydrogen off and do anything else with it. What kind of purism is it to not tap the largest energy sources in existence because you bristle at their inefficiency.
  - jjk166 5y ago
    > It's happening anyway and it's not like you can siphon the hydrogen off and do anything else with it. Actually this is another megastructure process known as Star Lifting. And it's not just hydrogen you can siphon off - the sun, by virtue of its immense size, contains the overwhelming majority of every element in the solar system. Unfortunately because they burn up so quickly, the hydrogen isotopes we would use in fusion reactors are actually incredibly rare in the sun. The sun is estimated to have about the same amount of deuterium as Earth's oceans. On the other hand, Helium-3, another potential fusion fuel, is very abundant - about 10-20 Earth Masses are present. Still though, burning all this helium 3 at the same energy production rate of the Sun would only last us 870,000 years - a drop in the bucket compared to the lifetime of the sun.
DocTomoe 5y ago
Why does man use hydro-power even though it is a rather silly idea if he has the technological prowess to generate a lot more power basically at will, basically anywhere, with a lot less resources destroyed, thanks to nuclear energy? Well, hydro energy is just there, requires comparatively little ongoing maintenance, and has less catastrophic failure modes. I think the same caveats work for Dyson spheres.
- stephanheijl 5y ago
  > has less catastrophic failure modes Given incidence of dam bursts like the 1975 Banqiao dam failure[1], with an estimate death toll of 26,000 to 240,000 people and flooding of over 12,000 square kilometers, I'm inclined to disagree with this assessment. [1]https://en.wikipedia.org/wiki/1975_Banqiao_Dam_failure https://en.wikipedia.org/wiki/1975_Banqiao_Dam_failure
  - goohle 5y ago
    Can you compare number of deaths because of dam failure with number of deaths because of flood and no dam to protect from flood? I.e. should we stop to build dams for flood protection because of telegraph failure at Banqiao dam?
    - heavenlyblue 5y ago
      "We should not do tooth fillings because tooth fillings fail and then you're in pain"
    - stephanheijl 5y ago
      I am not claiming we should not have dams, or refrain from using dams to provide hydroelectricity. My point of contention is the assertion that hydro energy has less catastrophic failure modes than nuclear (presumably fission). Clearly the failure modes for hydro dams are at least on par with those of nuclear installations, given that we have historic evidence that they can inflict tens of thousands of casualties. Hypothetical scenarios can be constructed for both methods of power generation (What if Braidwood plant melts down, somehow killing the 5 million people living within a 50 mile radius? What if the Three Gorges Dam busts, inundating an area inhabited by 600 million people?[1]) Either way, it is far from obvious to me that hydro has the superior safety profile, especially when their fatality rates are on the same order of magnitude even when the Banqiao incident is removed[2]*. [1] https://web.archive.org/web/20210620174812/https://www.japantimes.co.j https://web.archive.org/web/20210620174812/https://www.japan... p/opinion/2020/09/01/commentary/world-commentary/big-china-disaster/ [2] https://ourworldindata.org/safest-sources-of-energy https://ourworldindata.org/safest-sources-of-energy * Sovacool et al. (2016), the source of the data in [2] includes a hydro fatality rate per tWh 2.4x larger than nuclear when Banqiao is included.
healsjnr1 5y ago
But what are you fusing? If you want efficiency I guess you'll be using deuterium etc, of which we only have so much. After that your efficiency declines until... Well you end up with fusion reactors that look like the sun. You also end up fusing all the mass that we need to live our lives on and make stuff out of. If you don't think a civilisation could ever need the amount of energy that a Dyson sphere could provide, that's fine, we don't need one. But if you imagine a civilisation that does need the energy a Dyson sphere can provide, then they make a lot of sense.
- DonHopkins 5y ago
  >But if you imagine a civilisation that does need the energy a Dyson sphere can provide, then they make a lot of sense. It's the inevitable end-result of Bitcoin.
ithinkso 5y ago
As others pointed out, it depends on your energy needs. You need matter for fusion and almost all of the matter of the solar system is in the sun so you can either extract mass from the sun and do the fusion yourself or... let the sun do the fusion, as it already does, and just harness that
- Symmetry 5y ago
  Extracting mass from a star is a lot easier than trying to build a Dyson sphere around it. https://en.wikipedia.org/wiki/Star_lifting https://en.wikipedia.org/wiki/Star_lifting Even without considering what to do with the resultant mass star lifting is just good stellar husbandry for a civilization looking to last.
  - raattgift 5y ago
    That solar corona really hates your molecular bonds passionately. It's not too keen on metal crystals either. It's hard to see how to ignore that level of hatred as one approaches the photosphere en route to scooping out stuff below that, especially if it flares or reconnects through you and your gear "in close orbit around the star's equator". Your gear and repair & installation techs are much safer a couple gigametres away. If you really want to extract mass from a star, just wait long enough, or find one ready to release a suitable amount. There are plenty of options from CMAs to flares to UV Ceti style flare stars, to deflagrating white dwarfs, novas, and supernovas. Let the star's nuclear energy do the "heavy lifting", eliminating all the problems catalogued before the "... plasma jets hundreds or thousands of astronomical units long ... [t]he details of extracting useful materials from [that has] not been extensively explored". (The linked article at the top discusses relativistic jets driven by million-solar-mass and larger black holes. The jets are likely to be more constant and/or more predictable than natural mass outflows from stars, but extracting and storing energy from that is even less "extensively explored". An option in between is to use the natural mass flow from a companion star onto a compact star (white dwarf, neutron star, black hole) by sticking the moral equivalent of a water wheel into the stream. It's just a (compared to water hot & sparse) fluid flowing downhill, and there are plenty of examples in our galaxy.)
Sebb767 5y ago
If you scale up your local reactor enough, you basically end up with something resembling a Dyson sphere.
marcyb5st 5y ago
Because to power a type 2 civilization you need around 4 * 10^26W (as the paper states). Over a year that is around 10^31 kWh worth of energy. Assuming fusion can transform 1% of the input mass in energy you need ~ 1.4 * 10^19 kg per year. To put that number into perspective mount Everest weights 2.7×10^14 kg [1] so thousands Everests worth of mass. That is a lot of mass to extract and transport to the power stations (accelerate, decelerate). So it just makes sense to only needing to build the facilities to collect the power from existing sources (stars, black holes) without the logistics of transporting the fuel. Moreover, the space around a star or black hole is real estate that would go unused otherwise, while asteroids, moons, ... are more likely usable by such an advanced civilization. [1] https://www.quora.com/What-would-the-estimated-weight-of-Mount-Everest-be https://www.quora.com/What-would-the-estimated-weight-of-Mou... (I took the highest estimate in the first answer)
- snek_case 5y ago
  You also have to realize that the Kardashev scale [0] is something invented by someone in 1964. It's more a science fiction idea than some law of nature. We can't take for granted that this is some natural progression for every technological civilization. > it just makes sense to only needing to build the facilities to collect the power from existing sources (stars, black holes) without the logistics of transporting the fuel. Yeah OK, but then you have to transport your entire reactor to the fuel. For that matter, you also have to transport the energy where it's needed once you've harnessed it. [0] https://en.wikipedia.org/wiki/Kardashev_scale https://en.wikipedia.org/wiki/Kardashev_scale
- PaulHoule 5y ago
  The counter is that most of the usable mass in the universe is in interstellar objects such as comets and free planets which are 50% water ice or so, rich in organic materials and can be consumed completely to build habitats. With D + D fusion (easy to believe compared to CNO) an interstellar civilization could be essentially independent of stars. I'm sure part of the resolution of the Fermi paradox is that dry inside-the-frost-line planets like Mercury, Venus, Earth and Mars are not the generic places you find life. If things were a bit different I could see a would-be Galileo on an less cooked version of Io or a more cooked version of Europa who looks at the Earth with a spectroscope and sees oxygen and has a huge amount of trouble with his local "church" that thinks it is impossible to have life on a planet with less tidal activity, less radiation, inside-the-frost-line dryness, etc. Even if creatures like us became interstellar we might have millions of kilometers of condominiums and shopping malls in the oort cloud and could care less about inner solar system planets.
misja111 5y ago
I agree but I would say that any advanced enough civilisation will even be able to eliminate the need to grow their population and energy requirements. I don't see any requirement why an intelligent civilisation would need to grow its population forever. It seems far more intelligent to attack the cause of the energy need instead of building crazy structures like Dyson spheres around black holes.
vimacs2 5y ago
This comment demonstrates both confusion of the Dyson sphere concept with it's sci-fi bastardisation as well as a lack of understanding of scale, and especially of the mechanics of black hole power production. Dyson spheres (or Dyson swarms as they are often called to prevent such confusion) were never originally envisioned as a single impossibly large rigid sphere encompassing a star. They are rather a massive collection of structures that are able to utilize all the energy output of a star. This means that you could start construction on one today in an iterative fashion and immediately benefit from it. The technology required to build a tier 1 swarm is not advanced. All you need is the ability to build a thin reflector (aluminium foil would work) with radio and a basic onboard computer. You do not even need onboard propellant because a reflector can generate the required thrust for minor corrections with solar pressure alone. These reflectors can then concentrate that light from close in to the star out to collectors further out in the system. This essentially makes your habitable zone as large as you want since you can also light entire planets this way and only utilize less than a percent of a percent of your total energy budget. The real challenge is having good enough automation to construct and send these stations out without requiring too much oversight, and getting good enough at construction off earth (since you really don't want to deal with that gravity well). We're definitely close to having the required automation technology and we should be performing the first manufacturing off earth before the end of the next decade. Artificial fusion can be made far more efficient than the fusion in the core of our sun, yes. However, the sun outputs enough energy to light 2 billion earths worth of surface. Moreover, it essentially contains all of both the hydrogen and rocky material in the solar system with the other bodies being essentially a rounding error in comparison, so even in a controlled fusion based economy, you would still create a Dyson sphere like construct since you would be using that star as your main fuel and mass source. Black holes though? They make even aneutronic fusion look like a fire cracker in comparison. You're getting less than a percent mass energy conversion with even the best theoretical fusion models there are, whereas with black holes, you can get anywhere from 16% to 40% depending on the technique and mass range of the black hole. Stellar black holes have so much energy inside that they would dwarf even our star (consider that their progenitors were stars with far more mass than our own and with an even bigger disparity in power output). They also last for periods of time that make even red dwarfs look like still births. If you could make artificial ones in the gigaton and megaton ranges, then they can also make for amazing batteries. In this case, you are able to tap the hawking radiation emitted for power and this promises potentially even greater efficiencies than the stellar mass ones (albeit, you would not be gaining a net power gain here, this is strictly for power storage and potentially gravity generation purposes).
deleted 5y ago
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vardump 5y ago
With a black hole, you can generate energy out of any mass, including iron (Fe) and lead (Pb). Something no (fusion) reactor will ever be able to do.
JohnJamesRambo 5y ago
How do people expect to- A.) Keep it in place and not hit the star/black hole. B.) Avoid it being demolished by intercepting every piece of space trash, comet, asteroid in a solar system?
- jjk166 5y ago
  A realistic dyson sphere is not a single structure held up by mechanical forces. Instead it's an incredibly large number of independent, sail-like panels where the radiative pressure pushing the panel away from the star is equal to the gravitaional pull towards the star, allowing the panel to sustainably "hover." Panels would need some method of active positioning for initial alignment and dealing with variations in radiative pressure, so they can potentially move out of the way of debris. Alternatively, since you have the infrastructure in place for making truly mind boggling numbers of these, you just let them get destroyed and replace them.
- mekoka 5y ago
  Your questions have no readily available answers. Don't be suckered in by the occasional HN fever, which in this instance may manifest itself in asserting knowledge about type-II level technological challenges, from our pre-type-I mechanical pedestal.
cryptonector 5y ago
The whole concept of a Dyson sphere is kinda idiotic. Any species that has Malthusians will never get to where it needs a Dyson sphere because their Malthusians lack vision and make up for that in hate. It's a safe bet that any species with IQ less than about 130 on a human scale will have a surfeit of Malthusians. Looking around HN, we have lots of Malthusians in our species. EDIT: Inb4 the downvotes.
Cyberthal 5y ago
There is no kinda idiotic. There is a somewhat stupid. A Dyson sphere is foolish because one can simply build a small local fusion reactor instead of using the giant free one nearby? Imagine a sphere of reflective particles around a star. Planets within would never experience nightfall. Free energy would be everywhere. Sounds useful. Moreover, such a solar system would be difficult to detect. If it is mobile, and uses a low-signature form of propulsion such as UFOs exhibit, then it would be extremely elusive. This solves the problem of someone launching stealth asteroids at one's base at relativistic speeds. Moving a solar system presumably requires tremendous power. Using a star as the fusion reactor presumably helps.

hutzlibu 5y ago

It depends on the amount of energy the civilisation needs. Lets say, you want to manufacture new planets/planetary sized spaceships. You would need very big fusion reactors and you probably want to save the special fusion fuel for those, when they are on their voyage to other worlds. Because then they need fusion. But why build a fusion reactor, when you already have a big one avaiable?

mclightning 5y ago
Because you can build a more efficient one? You could make it portable, controlled, modular etc etc
- hutzlibu 5y ago
  Yeah. All needed for interstellar travel for example. But for manufacturing planets?
  - mclightning 5y ago
    Why would you want to manufacture a gravity well? There are plenty of them
    - hutzlibu 5y ago
      How many earth sized planets do we have in our solar system?
      - mclightning 5y ago
        If you're limited by the compounds available within the solar system, you should forget about building a dyson sphere for other reasons, or building a planet, or any kind of activity that will disturb the orbits of planets. Few planets are similarly sized as Earth already btw, although with varying densities.
        hutzlibu 5y ago
        Ok, earth sized is mainly about 1 g. So yes, also with earths density to be precice. That leaves only venus as a existing alternative. And I just assume that a civilisation advanced enough to build a dyson sphere, can handle the non trivial orbital mechanics, too. But maybe still cannot travel FTL. So indeed rather choose to build planets, or planet sized space stations. That would require lots of energy and maybe the need to harvest the sun directly and control the light going out towards the planets.
- deleted 5y ago
  [deleted]

zaarn 5y ago

There is a point still, because a star is massively more efficient at fusion by way of "production at scale" effects. The additional benefit is the amount of power. With the power of a star at your disposal, beaming your energy using lasers and microwaves, even if only 1% efficient, would instantly solve the energy needs of any planet in a solar system. If we did it, we could instantly colonize all planets in our solar system because things like "running an AC on Mercury" or "Hovercraft in Jupiter Atmosphere" becomes trivial when you have limitless power. Heck, you could start projects like moving planets in orbits or collecting astroids to built a planet if you wanted. Black holes are the stage after that since you can use a spinning black hole to convert a given mass into energy at >10% efficiency (given E=MC^2). That would allow a civilization to power multiple solar systems at the cost of a few planets per year. Granted, the sphere is difficult to build, but that is what you have dyson swarms for.

TheOtherHobbes 5y ago
The sphere isn't difficult to build. It's impossible to build. It's unstable without active stabilisation. The stabilisation has to be perfect because otherwise you get massive distorting spherequakes propagating through it, which will make it a very uncomfortable ride for a short time and will soon tear it apart. A perfect spherical stabilising solution with components and sensors that are light minutes - or possibly light hours - from each other is impossible because of the signalling delays. Ringworlds have the same problem. Even if the ring is made of infinitely strong unobtanium, it won't stay in a useful orbit for long enough to be built, never mind inhabited. Swarms have more potential, because you can build them with sparse shells and move things around to handle instabilities. But you still need massive computational effort to keep swarm units from colliding with each other, possibly at very high speed. None of this matters, because the limiting factor for civs is collective intelligence, not energy. We already have access to far more energy than we could possibly use on earth for any technology that's actually buildable. But we're not using it because we don't have the species IQ to make the right choices.
- wruza 5y ago
  collective intelligence, not energy This. The entire “moving planets” and “powering asteroids” theme is just a projection of our historical aggressive reproduction, which is not even a requirement for an advanced civilization. Earth alone could serve us a few billions of happy years, if we didn’t have the happy urge to multiply until critical shortage. That’s far from intelligent, imo.

guerrilla 5y ago

> a lot less resources/waste and materials. The sun itself is actually very inefficient in producing energy. Umm... The sun is about 2×10^30 kilograms. The rest of the solar system is about 3×10^27 kilograms and we kind of need it to live on and make things with. Put in other words, the entire solar system including the Sun is 1.0014 Solar masses. Why not go with the process we have rather than fusing everything we have to do the same thing? If you're saying that we don't need that much energy then I think that's pretty meaningless since we have no idea what we could get up to or need in the far future.

mytailorisrich 5y ago

I don't think that how efficient the production is really matters because stars do produce that energy anyway and for free as far as we are concerned. The question is one of efficiency and cost of collecting it.

arrow7000 5y ago
I'm surprised not more replies say this. So what if it's inefficient? It's happening anyway and it's not like you can siphon the hydrogen off and do anything else with it. What kind of purism is it to not tap the largest energy sources in existence because you bristle at their inefficiency.
- jjk166 5y ago
  > It's happening anyway and it's not like you can siphon the hydrogen off and do anything else with it. Actually this is another megastructure process known as Star Lifting. And it's not just hydrogen you can siphon off - the sun, by virtue of its immense size, contains the overwhelming majority of every element in the solar system. Unfortunately because they burn up so quickly, the hydrogen isotopes we would use in fusion reactors are actually incredibly rare in the sun. The sun is estimated to have about the same amount of deuterium as Earth's oceans. On the other hand, Helium-3, another potential fusion fuel, is very abundant - about 10-20 Earth Masses are present. Still though, burning all this helium 3 at the same energy production rate of the Sun would only last us 870,000 years - a drop in the bucket compared to the lifetime of the sun.

DocTomoe 5y ago

Why does man use hydro-power even though it is a rather silly idea if he has the technological prowess to generate a lot more power basically at will, basically anywhere, with a lot less resources destroyed, thanks to nuclear energy? Well, hydro energy is just there, requires comparatively little ongoing maintenance, and has less catastrophic failure modes. I think the same caveats work for Dyson spheres.

stephanheijl 5y ago
> has less catastrophic failure modes Given incidence of dam bursts like the 1975 Banqiao dam failure[1], with an estimate death toll of 26,000 to 240,000 people and flooding of over 12,000 square kilometers, I'm inclined to disagree with this assessment. [1]https://en.wikipedia.org/wiki/1975_Banqiao_Dam_failure https://en.wikipedia.org/wiki/1975_Banqiao_Dam_failure
- goohle 5y ago
  Can you compare number of deaths because of dam failure with number of deaths because of flood and no dam to protect from flood? I.e. should we stop to build dams for flood protection because of telegraph failure at Banqiao dam?
  - heavenlyblue 5y ago
    "We should not do tooth fillings because tooth fillings fail and then you're in pain"
  - stephanheijl 5y ago
    I am not claiming we should not have dams, or refrain from using dams to provide hydroelectricity. My point of contention is the assertion that hydro energy has less catastrophic failure modes than nuclear (presumably fission). Clearly the failure modes for hydro dams are at least on par with those of nuclear installations, given that we have historic evidence that they can inflict tens of thousands of casualties. Hypothetical scenarios can be constructed for both methods of power generation (What if Braidwood plant melts down, somehow killing the 5 million people living within a 50 mile radius? What if the Three Gorges Dam busts, inundating an area inhabited by 600 million people?[1]) Either way, it is far from obvious to me that hydro has the superior safety profile, especially when their fatality rates are on the same order of magnitude even when the Banqiao incident is removed[2]*. [1] https://web.archive.org/web/20210620174812/https://www.japantimes.co.j https://web.archive.org/web/20210620174812/https://www.japan... p/opinion/2020/09/01/commentary/world-commentary/big-china-disaster/ [2] https://ourworldindata.org/safest-sources-of-energy https://ourworldindata.org/safest-sources-of-energy * Sovacool et al. (2016), the source of the data in [2] includes a hydro fatality rate per tWh 2.4x larger than nuclear when Banqiao is included.

healsjnr1 5y ago

But what are you fusing? If you want efficiency I guess you'll be using deuterium etc, of which we only have so much. After that your efficiency declines until... Well you end up with fusion reactors that look like the sun. You also end up fusing all the mass that we need to live our lives on and make stuff out of. If you don't think a civilisation could ever need the amount of energy that a Dyson sphere could provide, that's fine, we don't need one. But if you imagine a civilisation that does need the energy a Dyson sphere can provide, then they make a lot of sense.

DonHopkins 5y ago
>But if you imagine a civilisation that does need the energy a Dyson sphere can provide, then they make a lot of sense. It's the inevitable end-result of Bitcoin.

ithinkso 5y ago

As others pointed out, it depends on your energy needs. You need matter for fusion and almost all of the matter of the solar system is in the sun so you can either extract mass from the sun and do the fusion yourself or... let the sun do the fusion, as it already does, and just harness that

Symmetry 5y ago
Extracting mass from a star is a lot easier than trying to build a Dyson sphere around it. https://en.wikipedia.org/wiki/Star_lifting https://en.wikipedia.org/wiki/Star_lifting Even without considering what to do with the resultant mass star lifting is just good stellar husbandry for a civilization looking to last.
- raattgift 5y ago
  That solar corona really hates your molecular bonds passionately. It's not too keen on metal crystals either. It's hard to see how to ignore that level of hatred as one approaches the photosphere en route to scooping out stuff below that, especially if it flares or reconnects through you and your gear "in close orbit around the star's equator". Your gear and repair & installation techs are much safer a couple gigametres away. If you really want to extract mass from a star, just wait long enough, or find one ready to release a suitable amount. There are plenty of options from CMAs to flares to UV Ceti style flare stars, to deflagrating white dwarfs, novas, and supernovas. Let the star's nuclear energy do the "heavy lifting", eliminating all the problems catalogued before the "... plasma jets hundreds or thousands of astronomical units long ... [t]he details of extracting useful materials from [that has] not been extensively explored". (The linked article at the top discusses relativistic jets driven by million-solar-mass and larger black holes. The jets are likely to be more constant and/or more predictable than natural mass outflows from stars, but extracting and storing energy from that is even less "extensively explored". An option in between is to use the natural mass flow from a companion star onto a compact star (white dwarf, neutron star, black hole) by sticking the moral equivalent of a water wheel into the stream. It's just a (compared to water hot & sparse) fluid flowing downhill, and there are plenty of examples in our galaxy.)

Sebb767 5y ago

If you scale up your local reactor enough, you basically end up with something resembling a Dyson sphere.

marcyb5st 5y ago

Because to power a type 2 civilization you need around 4 * 10^26W (as the paper states). Over a year that is around 10^31 kWh worth of energy. Assuming fusion can transform 1% of the input mass in energy you need ~ 1.4 * 10^19 kg per year. To put that number into perspective mount Everest weights 2.7×10^14 kg [1] so thousands Everests worth of mass. That is a lot of mass to extract and transport to the power stations (accelerate, decelerate). So it just makes sense to only needing to build the facilities to collect the power from existing sources (stars, black holes) without the logistics of transporting the fuel. Moreover, the space around a star or black hole is real estate that would go unused otherwise, while asteroids, moons, ... are more likely usable by such an advanced civilization. [1] https://www.quora.com/What-would-the-estimated-weight-of-Mount-Everest-be https://www.quora.com/What-would-the-estimated-weight-of-Mou... (I took the highest estimate in the first answer)

snek_case 5y ago
You also have to realize that the Kardashev scale [0] is something invented by someone in 1964. It's more a science fiction idea than some law of nature. We can't take for granted that this is some natural progression for every technological civilization. > it just makes sense to only needing to build the facilities to collect the power from existing sources (stars, black holes) without the logistics of transporting the fuel. Yeah OK, but then you have to transport your entire reactor to the fuel. For that matter, you also have to transport the energy where it's needed once you've harnessed it. [0] https://en.wikipedia.org/wiki/Kardashev_scale https://en.wikipedia.org/wiki/Kardashev_scale
PaulHoule 5y ago
The counter is that most of the usable mass in the universe is in interstellar objects such as comets and free planets which are 50% water ice or so, rich in organic materials and can be consumed completely to build habitats. With D + D fusion (easy to believe compared to CNO) an interstellar civilization could be essentially independent of stars. I'm sure part of the resolution of the Fermi paradox is that dry inside-the-frost-line planets like Mercury, Venus, Earth and Mars are not the generic places you find life. If things were a bit different I could see a would-be Galileo on an less cooked version of Io or a more cooked version of Europa who looks at the Earth with a spectroscope and sees oxygen and has a huge amount of trouble with his local "church" that thinks it is impossible to have life on a planet with less tidal activity, less radiation, inside-the-frost-line dryness, etc. Even if creatures like us became interstellar we might have millions of kilometers of condominiums and shopping malls in the oort cloud and could care less about inner solar system planets.

misja111 5y ago

I agree but I would say that any advanced enough civilisation will even be able to eliminate the need to grow their population and energy requirements. I don't see any requirement why an intelligent civilisation would need to grow its population forever. It seems far more intelligent to attack the cause of the energy need instead of building crazy structures like Dyson spheres around black holes.

vimacs2 5y ago

This comment demonstrates both confusion of the Dyson sphere concept with it's sci-fi bastardisation as well as a lack of understanding of scale, and especially of the mechanics of black hole power production. Dyson spheres (or Dyson swarms as they are often called to prevent such confusion) were never originally envisioned as a single impossibly large rigid sphere encompassing a star. They are rather a massive collection of structures that are able to utilize all the energy output of a star. This means that you could start construction on one today in an iterative fashion and immediately benefit from it. The technology required to build a tier 1 swarm is not advanced. All you need is the ability to build a thin reflector (aluminium foil would work) with radio and a basic onboard computer. You do not even need onboard propellant because a reflector can generate the required thrust for minor corrections with solar pressure alone. These reflectors can then concentrate that light from close in to the star out to collectors further out in the system. This essentially makes your habitable zone as large as you want since you can also light entire planets this way and only utilize less than a percent of a percent of your total energy budget. The real challenge is having good enough automation to construct and send these stations out without requiring too much oversight, and getting good enough at construction off earth (since you really don't want to deal with that gravity well). We're definitely close to having the required automation technology and we should be performing the first manufacturing off earth before the end of the next decade. Artificial fusion can be made far more efficient than the fusion in the core of our sun, yes. However, the sun outputs enough energy to light 2 billion earths worth of surface. Moreover, it essentially contains all of both the hydrogen and rocky material in the solar system with the other bodies being essentially a rounding error in comparison, so even in a controlled fusion based economy, you would still create a Dyson sphere like construct since you would be using that star as your main fuel and mass source. Black holes though? They make even aneutronic fusion look like a fire cracker in comparison. You're getting less than a percent mass energy conversion with even the best theoretical fusion models there are, whereas with black holes, you can get anywhere from 16% to 40% depending on the technique and mass range of the black hole. Stellar black holes have so much energy inside that they would dwarf even our star (consider that their progenitors were stars with far more mass than our own and with an even bigger disparity in power output). They also last for periods of time that make even red dwarfs look like still births. If you could make artificial ones in the gigaton and megaton ranges, then they can also make for amazing batteries. In this case, you are able to tap the hawking radiation emitted for power and this promises potentially even greater efficiencies than the stellar mass ones (albeit, you would not be gaining a net power gain here, this is strictly for power storage and potentially gravity generation purposes).

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vardump 5y ago

With a black hole, you can generate energy out of any mass, including iron (Fe) and lead (Pb). Something no (fusion) reactor will ever be able to do.

JohnJamesRambo 5y ago

How do people expect to- A.) Keep it in place and not hit the star/black hole. B.) Avoid it being demolished by intercepting every piece of space trash, comet, asteroid in a solar system?

jjk166 5y ago
A realistic dyson sphere is not a single structure held up by mechanical forces. Instead it's an incredibly large number of independent, sail-like panels where the radiative pressure pushing the panel away from the star is equal to the gravitaional pull towards the star, allowing the panel to sustainably "hover." Panels would need some method of active positioning for initial alignment and dealing with variations in radiative pressure, so they can potentially move out of the way of debris. Alternatively, since you have the infrastructure in place for making truly mind boggling numbers of these, you just let them get destroyed and replace them.
mekoka 5y ago
Your questions have no readily available answers. Don't be suckered in by the occasional HN fever, which in this instance may manifest itself in asserting knowledge about type-II level technological challenges, from our pre-type-I mechanical pedestal.

cryptonector 5y ago

The whole concept of a Dyson sphere is kinda idiotic. Any species that has Malthusians will never get to where it needs a Dyson sphere because their Malthusians lack vision and make up for that in hate. It's a safe bet that any species with IQ less than about 130 on a human scale will have a surfeit of Malthusians. Looking around HN, we have lots of Malthusians in our species. EDIT: Inb4 the downvotes.

Cyberthal 5y ago

There is no kinda idiotic. There is a somewhat stupid. A Dyson sphere is foolish because one can simply build a small local fusion reactor instead of using the giant free one nearby? Imagine a sphere of reflective particles around a star. Planets within would never experience nightfall. Free energy would be everywhere. Sounds useful. Moreover, such a solar system would be difficult to detect. If it is mobile, and uses a low-signature form of propulsion such as UFOs exhibit, then it would be extremely elusive. This solves the problem of someone launching stealth asteroids at one's base at relativistic speeds. Moving a solar system presumably requires tremendous power. Using a star as the fusion reactor presumably helps.