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The study was limited to looking for inefficient Dyson spheres that leaked a lot of energy in the infrared. Efficient Dyson spheres would be emitting at just ab

The study was limited to looking for inefficient Dyson spheres that leaked a lot of energy in the infrared. Efficient Dyson spheres would be emitting at just above the cosmic microwave background level and would thus be undetectable.

dredmorbius 10y ago
Evidence of absence is awfully hard to come by. Significant evidence of insufficiently advanced Dyson Spheres seems somewhat compelling. What's the internal temperature of an efficient Dyson sphere? Or conversely, what's the minimum size of such a sphere around various star classes to maintain a goldilocks-zone internal temperature? What are the mass requirements of such a sphere? How do the nonrotating elements of that maintain themselves against stellar gravity? At some point in the thermal life of the sphere, it's got to maintain a steady-state flux of energy out to energy in. At a galactic scale, that's probably going to be detectable. It's also quite possible that there are astral objects around which one would prefer not to build Dyson spheres. Black holes, say, or neutron stars, or binary or multiple star systems (a sphere around a single star is likely complex enough). Etc. I've never found the Dyson sphere concept particularly compelling myself. Interesting concept, but challenging to pull off. But then, what do I know, best I can claim is to have blown up a single planet. And that was with the assistance of alien technology.
- danieltillett 10y ago
  >What's the internal temperature of an efficient Dyson sphere? Or conversely, what's the minimum size of such a sphere around various star classes to maintain a goldilocks-zone internal temperature? What are the mass requirements of such a sphere? How do the nonrotating elements of that maintain themselves against stellar gravity? I think the confusion might be you are thinking about a classical Dyson sphere and not what would be built by a civilisation trying to most efficiently use the resources available. An efficient system would be composed of a set of independent (but co-ordinated) energy collectors arranged in a series of shells (for lack of a better name lets call this structure a Tillett Onion). The inner shells will be quite hot, but the outer shells will be very cold. The emission spectra of the Onion will be determined by the outermost layer, which if it is out near the orbit of Pluto, will be close to the background temperature of interstellar space. If these collectors are coordinated they can use some of the energy they capture to maintain their orbit. These energy collectors don’t need to use much matter (they can be one atom layer thick) since all they are doing is capturing the energy released by the inner shells. This really needs a more detailed write up than a post buried on HN :)
  - dredmorbius 10y ago
    So, using some values off the Web, notably 0.0077g/m^2 for the weight of graphene, and computing the mass of a spherical shell at Pluto's radius, roughly -- 40 AU from a central star, I get (using GNU Units): You have: 4 * pi * 40au^2 * 0.0077g/m^2 You want: million gigatonne * 86.618649 / 0.011544858 How's that compare to the mass of one typical rocky planet? You have: earthmass / 86.6 million gigatonne You want: Definition: 68986.619 So, 1/70,000th an Earth Mass. Turns out that there's not all that much carbon on Earth -- it's 730 ppm, but that's still a total abundance of about 50x what would be needed for our Pluto-diameter shell. On the other hand, that means that at best, using an entire Earth's worth of carbon, you could create a Pluto-orbital-radius graphene Dyson sphere 50 atoms thick. But Pluto's kinda way out there. What if we make the sphere the size of Earth's orbit instead. Surely that's going to save us a few orders of magnitude of matter, right? Not quite. About 1.5 OOM. We go from ~90 million gigatonne to 2 million gigatonne. The difference between squares and cubes matters. So, on the positive side, you get about 2,000 layers of graphene, but you're still using up all of Earth's available carbon to do that. There are more abundant minerals -- silicon or magnesium or iron, for example. But you'd still be using planetary-mass quantities for any substantial structure (or multiples of structures orbiting independently and forming a sphere). Which is what Dyson's also proposed. And my thought is that a Dyson "sphere" comprised of, say, multiple flat sheets of stuff orbiting a star, would tend to have a few issues, such as solar wind, and occasional emissions from incomplete closure. You've also got the question of how you're going to move all that captured energy from where it's been captured to where you plan to use it. And you still need a cold end to your hot end. https://en.m.wikipedia.org/wiki/Abundance_of_the_chemical_elements https://en.m.wikipedia.org/wiki/Abundance_of_the_chemical_el... http://www.geek.com/science/geek-answers-what-is-graphene-1575393/ http://www.geek.com/science/geek-answers-what-is-graphene-15... http://www.mathopenref.com/spherearea.html http://www.mathopenref.com/spherearea.html http://hyperphysics.phy-astr.gsu.edu/hbase/solar/soldata3.html http://hyperphysics.phy-astr.gsu.edu/hbase/solar/soldata3.ht...
    - danieltillett 10y ago
      > And you still need a cold end to your hot end. That is interstellar space @ 2.7K :) I actually just went through the calculations on my blog and to achieve a 99% Carnot efficient Dyson sphere (emitting at 58K) it would need to have a radius of ~7 AU - somewhere between Jupiter and Saturn [1]. There is plenty of mass to achieve that in the solar system and it would be also be undetectable in the infrared. 1. https://www.tillett.info/2016/08/03/carnot-efficient-dyson-spheres-are-undetectable-by-infrared-surveys/ https://www.tillett.info/2016/08/03/carnot-efficient-dyson-s...

dredmorbius 10y ago

Evidence of absence is awfully hard to come by. Significant evidence of insufficiently advanced Dyson Spheres seems somewhat compelling. What's the internal temperature of an efficient Dyson sphere? Or conversely, what's the minimum size of such a sphere around various star classes to maintain a goldilocks-zone internal temperature? What are the mass requirements of such a sphere? How do the nonrotating elements of that maintain themselves against stellar gravity? At some point in the thermal life of the sphere, it's got to maintain a steady-state flux of energy out to energy in. At a galactic scale, that's probably going to be detectable. It's also quite possible that there are astral objects around which one would prefer not to build Dyson spheres. Black holes, say, or neutron stars, or binary or multiple star systems (a sphere around a single star is likely complex enough). Etc. I've never found the Dyson sphere concept particularly compelling myself. Interesting concept, but challenging to pull off. But then, what do I know, best I can claim is to have blown up a single planet. And that was with the assistance of alien technology.

danieltillett 10y ago
>What's the internal temperature of an efficient Dyson sphere? Or conversely, what's the minimum size of such a sphere around various star classes to maintain a goldilocks-zone internal temperature? What are the mass requirements of such a sphere? How do the nonrotating elements of that maintain themselves against stellar gravity? I think the confusion might be you are thinking about a classical Dyson sphere and not what would be built by a civilisation trying to most efficiently use the resources available. An efficient system would be composed of a set of independent (but co-ordinated) energy collectors arranged in a series of shells (for lack of a better name lets call this structure a Tillett Onion). The inner shells will be quite hot, but the outer shells will be very cold. The emission spectra of the Onion will be determined by the outermost layer, which if it is out near the orbit of Pluto, will be close to the background temperature of interstellar space. If these collectors are coordinated they can use some of the energy they capture to maintain their orbit. These energy collectors don’t need to use much matter (they can be one atom layer thick) since all they are doing is capturing the energy released by the inner shells. This really needs a more detailed write up than a post buried on HN :)
- dredmorbius 10y ago
  So, using some values off the Web, notably 0.0077g/m^2 for the weight of graphene, and computing the mass of a spherical shell at Pluto's radius, roughly -- 40 AU from a central star, I get (using GNU Units): You have: 4 * pi * 40au^2 * 0.0077g/m^2 You want: million gigatonne * 86.618649 / 0.011544858 How's that compare to the mass of one typical rocky planet? You have: earthmass / 86.6 million gigatonne You want: Definition: 68986.619 So, 1/70,000th an Earth Mass. Turns out that there's not all that much carbon on Earth -- it's 730 ppm, but that's still a total abundance of about 50x what would be needed for our Pluto-diameter shell. On the other hand, that means that at best, using an entire Earth's worth of carbon, you could create a Pluto-orbital-radius graphene Dyson sphere 50 atoms thick. But Pluto's kinda way out there. What if we make the sphere the size of Earth's orbit instead. Surely that's going to save us a few orders of magnitude of matter, right? Not quite. About 1.5 OOM. We go from ~90 million gigatonne to 2 million gigatonne. The difference between squares and cubes matters. So, on the positive side, you get about 2,000 layers of graphene, but you're still using up all of Earth's available carbon to do that. There are more abundant minerals -- silicon or magnesium or iron, for example. But you'd still be using planetary-mass quantities for any substantial structure (or multiples of structures orbiting independently and forming a sphere). Which is what Dyson's also proposed. And my thought is that a Dyson "sphere" comprised of, say, multiple flat sheets of stuff orbiting a star, would tend to have a few issues, such as solar wind, and occasional emissions from incomplete closure. You've also got the question of how you're going to move all that captured energy from where it's been captured to where you plan to use it. And you still need a cold end to your hot end. https://en.m.wikipedia.org/wiki/Abundance_of_the_chemical_elements https://en.m.wikipedia.org/wiki/Abundance_of_the_chemical_el... http://www.geek.com/science/geek-answers-what-is-graphene-1575393/ http://www.geek.com/science/geek-answers-what-is-graphene-15... http://www.mathopenref.com/spherearea.html http://www.mathopenref.com/spherearea.html http://hyperphysics.phy-astr.gsu.edu/hbase/solar/soldata3.html http://hyperphysics.phy-astr.gsu.edu/hbase/solar/soldata3.ht...
  - danieltillett 10y ago
    > And you still need a cold end to your hot end. That is interstellar space @ 2.7K :) I actually just went through the calculations on my blog and to achieve a 99% Carnot efficient Dyson sphere (emitting at 58K) it would need to have a radius of ~7 AU - somewhere between Jupiter and Saturn [1]. There is plenty of mass to achieve that in the solar system and it would be also be undetectable in the infrared. 1. https://www.tillett.info/2016/08/03/carnot-efficient-dyson-spheres-are-undetectable-by-infrared-surveys/ https://www.tillett.info/2016/08/03/carnot-efficient-dyson-s...