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>He contends that there likely isn't a sentient civilization within about a billion light years of us because the signature of Dyson spheres would be unmistabka

>He contends that there likely isn't a sentient civilization within about a billion light years of us because the signature of Dyson spheres would be unmistabkable and unmissable. How do we know an advanced technology would absolutely use Dyson spheres? I'm not asking to challenge but in serious inquiry. Off the top of my head it just seems a highly advanced civilization might be able to come up with something completely different to meet their energy needs.

ben_w 8y ago
It would have to violate the laws of thermodynamics to not be visible. I’m not saying “no” (my brother has wondered if dark energy could be waste output of such civilisations, for example), but we have zero reason to treat the idea as anything more than the softest of science fiction.
- lainga 8y ago
  The GP didn't ask how you would make a Dyson sphere that was invisible, but why it was certain the Dyson sphere would be built at all.
  - ben_w 8y ago
    Ok, but the effect of the energy output of any civilisation is basically the same, and for the same reasons. It doesn’t matter if it’s a star or TARDIS whose inside is eternally expanding and you’re grabbing energy from its internal dark energy field, if you use that energy, you get hot, and that heat is visible. Unless you can violate the laws of thermodynamics.
    - bane 8y ago
      Maybe collect the heat and release it as a laser towards very sparsely populated parts of the sky? Perhaps that helps stabilize the sphere in the orbit of its star?
      - db48x 8y ago
        A Dyson Sphere is not a solid object. Instead, it's many small objects each of which is in a stable orbit. https://www.youtube.com/watch?v=pP44EPBMb8A&t=331s https://www.youtube.com/watch?v=pP44EPBMb8A&t=331s Also, a huge laser can certainly direct energy in a direction that nobody will notice. Unfortunately, creating the laser beam also creates waste heat, and that waste heat can be seen. Even collecting waste heat generates waste heat that you cannot collect. On the other hand, if you want a huge laser for some other purpose (such as vaporizing distant planets), then a Dyson Sphere is the ideal way to create one. https://groups.google.com/forum/#!msg/sci.space.tech/uh5iB9XntHU/FAXMCwCOr34J https://groups.google.com/forum/#!msg/sci.space.tech/uh5iB9X...
        bane 8y ago
        > A Dyson Sphere is not a solid object. Instead, it's many small objects each of which is in a stable orbit. Actually, we've never seen one so we have no idea how one might be engineered! It could for example be a "fog" of worlds that extends out past several local AU and to us would look nothing more like a dust cloud obscuring their local star. There wouldn't be a telltale signal of a Dyson Sphere, just another star with a big dust cloud. Imagine a civilization like this, those closer to the star get more power literally, and those on the outskirts and in the shadows of the other worlds become dependent on the more inner worlds to re-radiate their absorbed energy, or to condense and lase the energy outwards to the shadow worlds...at some cost that limitless free energy can't pay for. Beyond some distance the worlds become so cold that the inhabitants freeze to death and exile of your entire world at the whims of the inners becomes a real punishment. Dead worlds are recycled for mass for the growing population of the inners, or repurposed for other things. There are billions of such worlds. Perhaps they are customarily shaped as small ringworlds and rotate in a complex manner to produce gravity and a daynight cycle. Dead or frozen worlds may have a reflective sail hoisted along the inner opening and expeditionary generation ships are sent out to nearby stars powered by lasers collected from hundreds of inner worlds. Successful colonies may start to immediate transform the mass of nearby planetary systems into new "dust" clouds rather than settle on the planetary surfaces. Many adjacent Dyson spheres may look to us like just interstellar gases between several stars containing an unusual amount of organic molecules but could be the exchange of trillions of generation ships moving mass and energy back and forth between stars. Such a civilization could eventually become nomadic in a way, moving from star to star as they burn out, leaving behind frozen husks of trillions of dead ringworlds.
    - tzs 8y ago
      I wonder if advanced civilizations would use a lot of energy? We always imagine they have very advanced physics and engineering, to do things like take apart planets to build mega-structures and things like that, but usually don't think about their other sciences. My guess is that by the time they have gotten that far in physics, they have also gotten way ahead of us in biology. They'll have wiped out disease and illness, stopped aging, and only die by choice or accident. They'll have figured out geology and ecology and climatology and psychology. I suspect that the final steady state for most civilizations that don't end up wiping themselves out by doing something stupid is a relatively small (by our standards) population of essentially immortal beings, living on a world they have restored to a largely pre-civilization state, using less energy by far that we are using but using it way more efficiently.
- Pharmakon 8y ago
  Of course if we’re talking about an FTL-capable civilization then our understanding of physics is out of the window to begin with. I don’t think it’s reasonable to expect a civilization with FTL to make Dyson spheres or swarms, and it may be thst even if FTL is impossible it could be I desirable to build them. If the need to hide distinct technosignatures for some reason (Dark Forest perhaps) then any civilization would avoid Dyson structures.
  - ben_w 8y ago
    FTL makes it worse. The only tech we need for us to Dyson up (95%?) of our entire visible light cone is self-replicating factories that work in a vacuum on (for example) Mercury: http://ukspace2015.co.uk/presentations/36 http://ukspace2015.co.uk/presentations/36 FTL makes that 100%, from beyond out cosmic horizons, even if it turns out that FTL isn’t automatically also a time machine like we currently think it is. Pocket universes might help? I don’t know though, I’m saying that only because I’ve not seen them ruled out.
cletus 8y ago
> How do we know an advanced technology would absolutely use Dyson spheres? This depends on what question you're trying to answer. The Fermi Paradox is a good one because you don't need to ask "would a civilization always use Dyson spheres?" It takes just one to use them within a billion years to be a sufficient counterexample. Would they be universally used? Who knows? Dyson spheres are such an attractive idea because there's no new physics required here (like negative mass for wormholes and warp drives). It's largely just an engineering problem. Now it does require a fairly economical method of getting off-world but all of this seems relatively likely within the next 100-200 years. So it's (relatively) low tech and attractive in terms of providing living area for unit mass (many, many orders of magnitudes better than living on planets). It's worth noting that you don't even need nuclear fusion to make this all work (although that makes it much easier) and it's not a given that we'll have practical nuclear fusion. If you don't have nuclear fusion, what is your energy source? The alternatives other than harnessing solar output are much, much higher technologies like using black holes (which is also theorized about as a starship drive).
- jessaustin 8y ago
  ...no new physics required... Is this true? The mass required would generate forces that would rip apart any materials we've encountered. A Dyson belt could just be in some unstable sort of orbit, but a Dyson sphere has to be strong enough to hold itself in shape.
  - cletus 8y ago
    "Dyson sphere" is a misnomer in that at some point this was conflated to mean a shell than physically encompasses a star. That was never the original meaning or intent, which is why some people (including Isaac Arthur) prefer the term "Dyson swarm" as being true to the original idea and clear in intent. A Dyson sphere/swarm is simple a sufficient cloud of habitats orbiting the star as to essentially block out the vast majority of its light, kind of like how droplets of water block light in a fog.
    - semi-extrinsic 8y ago
p1mrx 8y ago
If a civilization has portable nuclear fusion (plug your spaceship into a suitcase for power), then there's no reason to hang out near a star. People living inland never think about how to obtain salt anymore.
- saagarjha 8y ago
  They’d have to collect fuel from somewhere…
  - 0-_-0 8y ago
    From space for example: https://en.wikipedia.org/wiki/Bussard_ramjet https://en.wikipedia.org/wiki/Bussard_ramjet
- dwaltrip 8y ago
  If you want to use vastly more energy than a portable fusion reactor can provide, the nearest star is probably the best place to get it.
- Cthulhu_ 8y ago
  Nuclear fusion is not magic infinite energy; the amount produced is limited by the amount of fuel being used. I mean how much power is generated from fusion anyway? Especially at the scale (suitcase) you mentioned? I dunno where your remark about salt comes from either; a lot of salt intended for consumption is dug up from the ground (salt mines).
i_feel_great 8y ago
There is Larry Niven's Ringworld [0], which proposes a ring instead of a sphere. 0.https://en.wikipedia.org/wiki/Ringworld https://en.wikipedia.org/wiki/Ringworld
amelius 8y ago
It also sounds logical: why would you waste energy by radiating it if you can retain it?
- krapp 8y ago
  It's also a waste of energy to work to capture energy you don't intend to use. Using less energy more efficiently is also logical.
  - amelius 8y ago
    More energy is more computation.
    - krapp 8y ago
      That doesn't mean an advanced civilization would need to harness the output of an entire star for computational power. Unless maybe it's storing everything on blockchain.

ben_w 8y ago

It would have to violate the laws of thermodynamics to not be visible. I’m not saying “no” (my brother has wondered if dark energy could be waste output of such civilisations, for example), but we have zero reason to treat the idea as anything more than the softest of science fiction.

lainga 8y ago
The GP didn't ask how you would make a Dyson sphere that was invisible, but why it was certain the Dyson sphere would be built at all.
- ben_w 8y ago
  Ok, but the effect of the energy output of any civilisation is basically the same, and for the same reasons. It doesn’t matter if it’s a star or TARDIS whose inside is eternally expanding and you’re grabbing energy from its internal dark energy field, if you use that energy, you get hot, and that heat is visible. Unless you can violate the laws of thermodynamics.
  - bane 8y ago
    Maybe collect the heat and release it as a laser towards very sparsely populated parts of the sky? Perhaps that helps stabilize the sphere in the orbit of its star?
    - db48x 8y ago
      A Dyson Sphere is not a solid object. Instead, it's many small objects each of which is in a stable orbit. https://www.youtube.com/watch?v=pP44EPBMb8A&t=331s https://www.youtube.com/watch?v=pP44EPBMb8A&t=331s Also, a huge laser can certainly direct energy in a direction that nobody will notice. Unfortunately, creating the laser beam also creates waste heat, and that waste heat can be seen. Even collecting waste heat generates waste heat that you cannot collect. On the other hand, if you want a huge laser for some other purpose (such as vaporizing distant planets), then a Dyson Sphere is the ideal way to create one. https://groups.google.com/forum/#!msg/sci.space.tech/uh5iB9XntHU/FAXMCwCOr34J https://groups.google.com/forum/#!msg/sci.space.tech/uh5iB9X...
      - bane 8y ago
        > A Dyson Sphere is not a solid object. Instead, it's many small objects each of which is in a stable orbit. Actually, we've never seen one so we have no idea how one might be engineered! It could for example be a "fog" of worlds that extends out past several local AU and to us would look nothing more like a dust cloud obscuring their local star. There wouldn't be a telltale signal of a Dyson Sphere, just another star with a big dust cloud. Imagine a civilization like this, those closer to the star get more power literally, and those on the outskirts and in the shadows of the other worlds become dependent on the more inner worlds to re-radiate their absorbed energy, or to condense and lase the energy outwards to the shadow worlds...at some cost that limitless free energy can't pay for. Beyond some distance the worlds become so cold that the inhabitants freeze to death and exile of your entire world at the whims of the inners becomes a real punishment. Dead worlds are recycled for mass for the growing population of the inners, or repurposed for other things. There are billions of such worlds. Perhaps they are customarily shaped as small ringworlds and rotate in a complex manner to produce gravity and a daynight cycle. Dead or frozen worlds may have a reflective sail hoisted along the inner opening and expeditionary generation ships are sent out to nearby stars powered by lasers collected from hundreds of inner worlds. Successful colonies may start to immediate transform the mass of nearby planetary systems into new "dust" clouds rather than settle on the planetary surfaces. Many adjacent Dyson spheres may look to us like just interstellar gases between several stars containing an unusual amount of organic molecules but could be the exchange of trillions of generation ships moving mass and energy back and forth between stars. Such a civilization could eventually become nomadic in a way, moving from star to star as they burn out, leaving behind frozen husks of trillions of dead ringworlds.
  - tzs 8y ago
    I wonder if advanced civilizations would use a lot of energy? We always imagine they have very advanced physics and engineering, to do things like take apart planets to build mega-structures and things like that, but usually don't think about their other sciences. My guess is that by the time they have gotten that far in physics, they have also gotten way ahead of us in biology. They'll have wiped out disease and illness, stopped aging, and only die by choice or accident. They'll have figured out geology and ecology and climatology and psychology. I suspect that the final steady state for most civilizations that don't end up wiping themselves out by doing something stupid is a relatively small (by our standards) population of essentially immortal beings, living on a world they have restored to a largely pre-civilization state, using less energy by far that we are using but using it way more efficiently.
Pharmakon 8y ago
Of course if we’re talking about an FTL-capable civilization then our understanding of physics is out of the window to begin with. I don’t think it’s reasonable to expect a civilization with FTL to make Dyson spheres or swarms, and it may be thst even if FTL is impossible it could be I desirable to build them. If the need to hide distinct technosignatures for some reason (Dark Forest perhaps) then any civilization would avoid Dyson structures.
- ben_w 8y ago
  FTL makes it worse. The only tech we need for us to Dyson up (95%?) of our entire visible light cone is self-replicating factories that work in a vacuum on (for example) Mercury: http://ukspace2015.co.uk/presentations/36 http://ukspace2015.co.uk/presentations/36 FTL makes that 100%, from beyond out cosmic horizons, even if it turns out that FTL isn’t automatically also a time machine like we currently think it is. Pocket universes might help? I don’t know though, I’m saying that only because I’ve not seen them ruled out.

cletus 8y ago

> How do we know an advanced technology would absolutely use Dyson spheres? This depends on what question you're trying to answer. The Fermi Paradox is a good one because you don't need to ask "would a civilization always use Dyson spheres?" It takes just one to use them within a billion years to be a sufficient counterexample. Would they be universally used? Who knows? Dyson spheres are such an attractive idea because there's no new physics required here (like negative mass for wormholes and warp drives). It's largely just an engineering problem. Now it does require a fairly economical method of getting off-world but all of this seems relatively likely within the next 100-200 years. So it's (relatively) low tech and attractive in terms of providing living area for unit mass (many, many orders of magnitudes better than living on planets). It's worth noting that you don't even need nuclear fusion to make this all work (although that makes it much easier) and it's not a given that we'll have practical nuclear fusion. If you don't have nuclear fusion, what is your energy source? The alternatives other than harnessing solar output are much, much higher technologies like using black holes (which is also theorized about as a starship drive).

jessaustin 8y ago
...no new physics required... Is this true? The mass required would generate forces that would rip apart any materials we've encountered. A Dyson belt could just be in some unstable sort of orbit, but a Dyson sphere has to be strong enough to hold itself in shape.
- cletus 8y ago
  "Dyson sphere" is a misnomer in that at some point this was conflated to mean a shell than physically encompasses a star. That was never the original meaning or intent, which is why some people (including Isaac Arthur) prefer the term "Dyson swarm" as being true to the original idea and clear in intent. A Dyson sphere/swarm is simple a sufficient cloud of habitats orbiting the star as to essentially block out the vast majority of its light, kind of like how droplets of water block light in a fog.
  - semi-extrinsic 8y ago

p1mrx 8y ago

If a civilization has portable nuclear fusion (plug your spaceship into a suitcase for power), then there's no reason to hang out near a star. People living inland never think about how to obtain salt anymore.

saagarjha 8y ago
They’d have to collect fuel from somewhere…
- 0-_-0 8y ago
  From space for example: https://en.wikipedia.org/wiki/Bussard_ramjet https://en.wikipedia.org/wiki/Bussard_ramjet
dwaltrip 8y ago
If you want to use vastly more energy than a portable fusion reactor can provide, the nearest star is probably the best place to get it.
Cthulhu_ 8y ago
Nuclear fusion is not magic infinite energy; the amount produced is limited by the amount of fuel being used. I mean how much power is generated from fusion anyway? Especially at the scale (suitcase) you mentioned? I dunno where your remark about salt comes from either; a lot of salt intended for consumption is dug up from the ground (salt mines).

i_feel_great 8y ago

There is Larry Niven's Ringworld [0], which proposes a ring instead of a sphere. 0.https://en.wikipedia.org/wiki/Ringworld https://en.wikipedia.org/wiki/Ringworld

amelius 8y ago

It also sounds logical: why would you waste energy by radiating it if you can retain it?

krapp 8y ago
It's also a waste of energy to work to capture energy you don't intend to use. Using less energy more efficiently is also logical.
- amelius 8y ago
  More energy is more computation.
  - krapp 8y ago
    That doesn't mean an advanced civilization would need to harness the output of an entire star for computational power. Unless maybe it's storing everything on blockchain.