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I don't get this argument. Let's just posit that every single advanced civilization ends up building lots and lots of Dyson spheres (which I'm totally unconvin

I don't get this argument. Let's just posit that every single advanced civilization ends up building lots and lots of Dyson spheres (which I'm totally unconvinced of). Now, can you prove that there are no such spheres out there? No, you can't. You can only prove that a whole lot of stars have no sphere, but maybe we suck at detecting them and there's one right next to us. The only conclusion the argument draws if that advanced aliens are not yet nearly finished enclosing all the stars in spheres, and you might try to determine an upper limit to the rate of stars with Dyson spheres without us noticing.

danieltillett 10y ago
The argument is once you have one civilisation that can create von Neumann probes [1] then that civilisation will spread through the universe wrapping each star in a Dyson sphere [2] that will capture all the light. It only takes one civilisation in the universe to do this and all stars will cease to shine. The fact that we can see stars in the night sky means that they don’t have Dyson spheres around them hence there are not civilisations ahead of us - at least within the visible universe. 1. https://en.wikipedia.org/wiki/Self-replicating_spacecraft https://en.wikipedia.org/wiki/Self-replicating_spacecraft 2. https://en.wikipedia.org/wiki/Dyson_sphere https://en.wikipedia.org/wiki/Dyson_sphere
- corecoder 10y ago
  Sure, but are we sure these probes are instantaneous? What if it takes more than zero time to build a Dyson sphere? As I said earlier, you're only proving that they have been building spheres for less time than it takes to finish up the whole universe, which they say is big.
  - danieltillett 10y ago
    The probe’s spread and and dyson sphere building does not need to be instantaneous, just that it had to have happened in the past. For example, if we were to create von Neumann probes and have them spread across the galaxy, it would take less than 100,000 years for the probes to reach every star. When you compare this to how long it took for our civilisation to evolve on Earth it is a blink of an eye. An interesting thought is if a new von Neumann spewing civilisation arose in the galaxy we would not have much warning before it reached us. The probes would be travelling just behind the light front and so would reach us only a little before the information that the stars between the probes origin and us went out. About the only way you could detect such an event is to look at very distant galaxies for examples that had spherical chunk taken out of them. I should get around to writing this all up in a blog post because it is such an interesting topic :)
    - robbiep 10y ago
      There was a quote yesterday in HN (either here or through wiki) saying it would take 500,000 years for von Neumann probes to spread throughout the Galaxy. Not meaningfully different on cosmic timescales, but still. Also, your thought on the probes travelling behind the light front implies that they are going to be travelling at relativistic speeds. Is that realistic?
      - danieltillett 10y ago
        Yes they could be travelling just under the speed of light if the probes are very small and they are being accelerated by an energy source (say laser) at the origin.
        robbiep 10y ago
        But then it needs to break away (and actually brake) at the next system, replicate at outrageous speeds, and fire a bunch more at a heap more stars
        danieltillett 10y ago
        If they are sent as a swarm you could bounce the laser off one to slow a second. This way you would not need to transport fuel. Also since you are aiming at stars you could use a hub and spoke model which would speed up the takeover process since you could bypass the build stage for most stars.
        robbiep 10y ago
        Cool. Interesting. Thanks for your thoughts
    - cgriswald 10y ago
      > About the only way you could detect such an event is to look at very distant galaxies for examples that had spherical chunk taken out of them. There have been actual studies searching for the waste heat of Dyson spheres[0]. You basically image an "empty" part of the sky in the visual spectrums and look for infrared waste. (The studies turned up nothing but were also limited in scope.) [0] - http://arxiv.org/abs/1408.1134 http://arxiv.org/abs/1408.1134
- Tloewald 10y ago
  This is a completely speculative argument. It's like arguing about building a computer that can simulate reality. It just keeps getting bigger and more complicated and consuming more power and running slower as you learn about the new things it has to do, and soon the "possible in theory" becomes larger than the observable universe.
widerporst 10y ago
I agree with you and I also don't think that existence of intelligent life will necessarily lead to all stars being surrounded by Dyson spheres. Maybe there are other sources of energy that are easier to harvest for an advanced civilization. However, in case there actually is a Dyson sphere around a star, it will probably emit energy in the form of infrared radiation and we should be able to detect it. Especially if there are billions of stars like that.
- danieltillett 10y ago
  You can only detect a Dyson sphere in the infrared if the Dyson sphere is relative close into the star. If the outer sphere is at the orbit of Pluto then the emission would be close to the cosmic microwave background [1]. 1. https://en.wikipedia.org/wiki/Cosmic_microwave_background https://en.wikipedia.org/wiki/Cosmic_microwave_background
  - Phlarp 10y ago
    Where are you going to find the material to build a sphere around a star the size of Pluto's orbit? How are you going to arrange this material into energy harvesting equipment in a way that results in a net positive energy outcome?
    - danieltillett 10y ago
      The energy collector sphere only needs to be one atom thick and spaced just below the wavelength you want to capture. There is more than enough matter in our solar system to do this at the orbit of Pluto if you use a series of shells.
      - Tloewald 10y ago
        And you do this why? You're making the assumption that capturing all of a star's energy is somehow a good thing. Something worth devoting goodness knows what effort to. And whoops another comet destroyed a ludicrously big section of it.
dredmorbius 10y ago
Dyson spheres would have a distinctive IR signature, which hasn't been observed. Particularly not at galactic scales. Recent news on this via studies.
- danieltillett 10y ago
  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 :)

danieltillett 10y ago

The argument is once you have one civilisation that can create von Neumann probes [1] then that civilisation will spread through the universe wrapping each star in a Dyson sphere [2] that will capture all the light. It only takes one civilisation in the universe to do this and all stars will cease to shine. The fact that we can see stars in the night sky means that they don’t have Dyson spheres around them hence there are not civilisations ahead of us - at least within the visible universe. 1. https://en.wikipedia.org/wiki/Self-replicating_spacecraft https://en.wikipedia.org/wiki/Self-replicating_spacecraft 2. https://en.wikipedia.org/wiki/Dyson_sphere https://en.wikipedia.org/wiki/Dyson_sphere

corecoder 10y ago
Sure, but are we sure these probes are instantaneous? What if it takes more than zero time to build a Dyson sphere? As I said earlier, you're only proving that they have been building spheres for less time than it takes to finish up the whole universe, which they say is big.
- danieltillett 10y ago
  The probe’s spread and and dyson sphere building does not need to be instantaneous, just that it had to have happened in the past. For example, if we were to create von Neumann probes and have them spread across the galaxy, it would take less than 100,000 years for the probes to reach every star. When you compare this to how long it took for our civilisation to evolve on Earth it is a blink of an eye. An interesting thought is if a new von Neumann spewing civilisation arose in the galaxy we would not have much warning before it reached us. The probes would be travelling just behind the light front and so would reach us only a little before the information that the stars between the probes origin and us went out. About the only way you could detect such an event is to look at very distant galaxies for examples that had spherical chunk taken out of them. I should get around to writing this all up in a blog post because it is such an interesting topic :)
  - robbiep 10y ago
    There was a quote yesterday in HN (either here or through wiki) saying it would take 500,000 years for von Neumann probes to spread throughout the Galaxy. Not meaningfully different on cosmic timescales, but still. Also, your thought on the probes travelling behind the light front implies that they are going to be travelling at relativistic speeds. Is that realistic?
    - danieltillett 10y ago
      Yes they could be travelling just under the speed of light if the probes are very small and they are being accelerated by an energy source (say laser) at the origin.
      - robbiep 10y ago
        But then it needs to break away (and actually brake) at the next system, replicate at outrageous speeds, and fire a bunch more at a heap more stars
        danieltillett 10y ago
        If they are sent as a swarm you could bounce the laser off one to slow a second. This way you would not need to transport fuel. Also since you are aiming at stars you could use a hub and spoke model which would speed up the takeover process since you could bypass the build stage for most stars.
        robbiep 10y ago
        Cool. Interesting. Thanks for your thoughts
  - cgriswald 10y ago
    > About the only way you could detect such an event is to look at very distant galaxies for examples that had spherical chunk taken out of them. There have been actual studies searching for the waste heat of Dyson spheres[0]. You basically image an "empty" part of the sky in the visual spectrums and look for infrared waste. (The studies turned up nothing but were also limited in scope.) [0] - http://arxiv.org/abs/1408.1134 http://arxiv.org/abs/1408.1134
Tloewald 10y ago
This is a completely speculative argument. It's like arguing about building a computer that can simulate reality. It just keeps getting bigger and more complicated and consuming more power and running slower as you learn about the new things it has to do, and soon the "possible in theory" becomes larger than the observable universe.

widerporst 10y ago

I agree with you and I also don't think that existence of intelligent life will necessarily lead to all stars being surrounded by Dyson spheres. Maybe there are other sources of energy that are easier to harvest for an advanced civilization. However, in case there actually is a Dyson sphere around a star, it will probably emit energy in the form of infrared radiation and we should be able to detect it. Especially if there are billions of stars like that.

danieltillett 10y ago
You can only detect a Dyson sphere in the infrared if the Dyson sphere is relative close into the star. If the outer sphere is at the orbit of Pluto then the emission would be close to the cosmic microwave background [1]. 1. https://en.wikipedia.org/wiki/Cosmic_microwave_background https://en.wikipedia.org/wiki/Cosmic_microwave_background
- Phlarp 10y ago
  Where are you going to find the material to build a sphere around a star the size of Pluto's orbit? How are you going to arrange this material into energy harvesting equipment in a way that results in a net positive energy outcome?
  - danieltillett 10y ago
    The energy collector sphere only needs to be one atom thick and spaced just below the wavelength you want to capture. There is more than enough matter in our solar system to do this at the orbit of Pluto if you use a series of shells.
    - Tloewald 10y ago
      And you do this why? You're making the assumption that capturing all of a star's energy is somehow a good thing. Something worth devoting goodness knows what effort to. And whoops another comet destroyed a ludicrously big section of it.

dredmorbius 10y ago

Dyson spheres would have a distinctive IR signature, which hasn't been observed. Particularly not at galactic scales. Recent news on this via studies.

danieltillett 10y ago
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 :)