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OK, let's talk about energy generation for a minute. If we assume there exists some completely new physics, then... that could be anything. Advanced civilizatio

OK, let's talk about energy generation for a minute. If we assume there exists some completely new physics, then... that could be anything. Advanced civilizations could take on any form. We can speculate all day about magic and elves too. If we don't assume any new physics and / or thermodynamics, then that constrains the discussion a lot. We have two basic ways of generating a lot of power, fission and fusion. Fission uses fissile materials, which are relatively rare, not just on Earth, but in the Universe at large. There's plenty enough for us at our current energy generation needs, but not nearly enough for a galaxy spanning civilization. That leaves us with fusion. Fusion reactors, as currently conceived use Helium-3 or something like that. There's enough of that around the solar system to power a civilization for a long time, even though the mass of oddball elements like Helium-3 make up a very tiny fraction of the total mass of the solar system (which is mostly the Sun with a smidgen of Jupiter). Most of the solar system's mass is plain hydrogen: one proton and one electron. Is it possible to fuse most / all of this mass in the solar system? Yes. We won't go into the details, but trying to fuse regular hydrogen (regular protons) together is highly impractical outside of the core of a star. Preferably a red dwarf type star which can more completely burn its fuel than our own Sun will, and live a lot longer to boot (a trillion years vs. ~10 billion for the Sun). So now we're talking about some kind of solar collectors, and if you want to collect _all_ the energy from a star, you want a sphere of some sort. Or a swarm of objects in orbit achieving the same effect. Hence Dyson sphere / swarm.

raverbashing 5y ago
> and if you want to collect _all_ the energy from a star, For what? What are you doing with it? Not to forget the fact that all energy used eventually turns into heat. All of it (with the exception of electrochemical transformations). You're bringing all of that into Earth you're cooking everybody alive. How are you bringing that energy from the sphere to (wherever place)? Putting solar panels on Earth itself works much better. Heck, make a Dyson sphere on Earth (facing outside), that makes more sense.
- ansible 5y ago
  It is typically assumed that by the time you are making a Dyson swarm, that most life exists digitally. And spread out through the solar system. So in the best case scenario, you are powering computronium, upon which trillions of sophonts live out their digital lives. Hopefully doing some science, or at least playing some interesting games. A vast distributed network. In the worst case scenario, Blockchain and spam emails. Either way, people will put that energy to use. With a Dyson swarm, energy is received on the inside, towards the star, and heat is radiated outward. Lower power systems can run off the heat radiation of the inner swarm similarly. It is all eventually released as very low level heat, but diffused across the entire outer surface of the swarm. No hotspots... because someone would come along and use it. The Earth would also likely be deconstructed by this time, so don't worry about the biosphere, there won't be any.
- naasking 5y ago
  > For what? What are you doing with it? One example: powering lasers for light sail ships to colonize other star systems.
  - raverbashing 5y ago
    You are not pushing a light sail ship to another star system, sorry. Light sails are "theoretically" possible but you don't need that much energy to push something that's feasible to push. Or better, there's a better source of light radiation: the sun itself. No need for a laser, just use a focusing mirror and you can have 100x more pressure than just from the sun itself.
    - ansible 5y ago
      Light sails are practical, and have already been tested in orbit. https://www.planetary.org/articles/lightsail-2-successful-flight-by-light https://www.planetary.org/articles/lightsail-2-successful-fl... Light from the Sun isn't coherent, and you can't focus it with mirrors very far away. Lasers have many orders of magnitude less divergence when talking about distances measured in light-years.
eloff 5y ago
It's premature to say what's practical with fusion and what isn't. It's entirely possible that we find a way to build an efficient hydrogen fusion reactor. In which case it might not make sense to travel so far away from our planet just to collect energy from photons when that costs more than just doing the fusion ourselves. Remember it's actually more expensive to travel towards the sun than away from it (because you have to shed velocity relative to the starting velocity on Earth.) It's too arrogant to think we know the answer to that now.
- ansible 5y ago
  > It's premature to say what's practical with fusion and what isn't. It's entirely possible that we find a way to build an efficient hydrogen fusion reactor. Would it not surprise you that fusion in general has been studied extensively by physicists for nearly a century? It takes very high temperatures, pressures and quantum tunneling to get two protons to fuse. Here's some reading to get you started: https://courses.lumenlearning.com/physics/chapter/32-5-fusion/ https://courses.lumenlearning.com/physics/chapter/32-5-fusio... Or read about how the Large Hadron Collider works.
  - eloff 5y ago
    It doesn't surprise me. Your arrogance does though, I didn't expect you to double down on an unreasonable position. How can we possibly know what we don't know yet. Not about how fusion works in theory, but about the limits of the economics of fusion reactors at any point in the future. What I'm saying is it's too soon to say what's possible with fusion and what isn't. We don't even have a break even reactor yet. We can even say for certain that we ever will.
    - ansible 5y ago
      > It doesn't surprise me. Your arrogance does though, I didn't expect you to double down on an unreasonable position. I'd give your criticism some consideration if I thought you had even the slightest knowledge of what we're talking about. Let's talk about the core of the Sun, where p-p fusion takes place. Remember, I said at the top: no new physics. The core of the Sun is hot, like really, really hot. How hot? 15 million Kelvin. So no solid material ... made of atoms ... can be anywhere close by because it would vaporize. You can talk about active cooling or whatever, and that's not going to help. But let's assume we have some magical material that can deal with that temperature, and keep going. We're going to skip the pressure that really hot plasma is under, and assume we have terrifically awesome magnetic confinement that can handle that. We don't actually, but let's move on. The other problem with 15 million K is that all that energy wants to radiate away. Yes, you want to absorb some of that radiation (hard gamma, by the way, very nasty) as part of the energy generation process, but if you let the plasma cool off, the reaction rate drops. "Cool" in this context is relative, at 7 million K, the reaction rate is very close to zero. The last problem we will talk about today is volume. The above conditions get us a fusion power density of... 276 watts / cubic meter. To have a fusion plant that generates 1GW of power, we'd need to contain a cube 153 meters on a side of 15 million Kelvin plasma. Oh, wait, that assumes the magnetic containment and everything else requires zero power to run. So we'll have to go bigger, much bigger. Are you starting to understand the scale of the problem... trying to design a proton - proton fusion reactor? I am not the arrogant one, I'm just listening to the fusion scientists who have been studying how all this works. > We don't even have a break even reactor yet. We can even say for certain that we ever will. And here you are expressing doubt that we'll achieve even the easiest kind of fusion reactor. We have achieved fusion, just to be clear. We can reach the temperatures and pressures to see some reactions. Assuming civilization does not collapse (climate change, war, etc) we will be able to engineer a fusion reactor that is some kind of practical. But it won't be proton-proton.
naasking 5y ago
> We have two basic ways of generating a lot of power, fission and fusion I think there are more. Like radiation from evaporating black holes.
- ansible 5y ago
  > I think there are more. Like radiation from evaporating black holes. Evaporating black holes? Yes, if you are willing to wait a very, very long time, and have collectors over a large area. However, if you want to get stuff done before your protons evaporate, you could instead throw matter into a black hole, thus increasing its mass. The radiation given off by the accretion disc is substantial, and can be collected... over a large area. IIRC, the mass-to-energy efficiency is something like 40%, which is really good. They are a little difficult to set up however...
  - naasking 5y ago
    I mean, we're talking about timescales and construction projects like Dyson spheres. It's entirely feasible that people with such technology could create microscopic black holes that evaporate quickly for these purposes. Hawking radiation at this scale is substantial.
    - ansible 5y ago
      Ah, yes, I do recall reading about that somewhere. That is an interesting prospect, with a very high mass-to-energy efficiency. Of course it requires careful management of inflowing matter. And you can shut if down if needed by stopping the inflow, assuming you have enough stored energy to recreate the micro black hole sometime later.
      - naasking 5y ago
        You'll probably enjoy this video: https://youtu.be/EzZGPCyrpSU https://youtu.be/EzZGPCyrpSU Good channel too.
    - kragen 5y ago

raverbashing 5y ago

> and if you want to collect _all_ the energy from a star, For what? What are you doing with it? Not to forget the fact that all energy used eventually turns into heat. All of it (with the exception of electrochemical transformations). You're bringing all of that into Earth you're cooking everybody alive. How are you bringing that energy from the sphere to (wherever place)? Putting solar panels on Earth itself works much better. Heck, make a Dyson sphere on Earth (facing outside), that makes more sense.

ansible 5y ago
It is typically assumed that by the time you are making a Dyson swarm, that most life exists digitally. And spread out through the solar system. So in the best case scenario, you are powering computronium, upon which trillions of sophonts live out their digital lives. Hopefully doing some science, or at least playing some interesting games. A vast distributed network. In the worst case scenario, Blockchain and spam emails. Either way, people will put that energy to use. With a Dyson swarm, energy is received on the inside, towards the star, and heat is radiated outward. Lower power systems can run off the heat radiation of the inner swarm similarly. It is all eventually released as very low level heat, but diffused across the entire outer surface of the swarm. No hotspots... because someone would come along and use it. The Earth would also likely be deconstructed by this time, so don't worry about the biosphere, there won't be any.
naasking 5y ago
> For what? What are you doing with it? One example: powering lasers for light sail ships to colonize other star systems.
- raverbashing 5y ago
  You are not pushing a light sail ship to another star system, sorry. Light sails are "theoretically" possible but you don't need that much energy to push something that's feasible to push. Or better, there's a better source of light radiation: the sun itself. No need for a laser, just use a focusing mirror and you can have 100x more pressure than just from the sun itself.
  - ansible 5y ago
    Light sails are practical, and have already been tested in orbit. https://www.planetary.org/articles/lightsail-2-successful-flight-by-light https://www.planetary.org/articles/lightsail-2-successful-fl... Light from the Sun isn't coherent, and you can't focus it with mirrors very far away. Lasers have many orders of magnitude less divergence when talking about distances measured in light-years.

eloff 5y ago

It's premature to say what's practical with fusion and what isn't. It's entirely possible that we find a way to build an efficient hydrogen fusion reactor. In which case it might not make sense to travel so far away from our planet just to collect energy from photons when that costs more than just doing the fusion ourselves. Remember it's actually more expensive to travel towards the sun than away from it (because you have to shed velocity relative to the starting velocity on Earth.) It's too arrogant to think we know the answer to that now.

ansible 5y ago
> It's premature to say what's practical with fusion and what isn't. It's entirely possible that we find a way to build an efficient hydrogen fusion reactor. Would it not surprise you that fusion in general has been studied extensively by physicists for nearly a century? It takes very high temperatures, pressures and quantum tunneling to get two protons to fuse. Here's some reading to get you started: https://courses.lumenlearning.com/physics/chapter/32-5-fusion/ https://courses.lumenlearning.com/physics/chapter/32-5-fusio... Or read about how the Large Hadron Collider works.
- eloff 5y ago
  It doesn't surprise me. Your arrogance does though, I didn't expect you to double down on an unreasonable position. How can we possibly know what we don't know yet. Not about how fusion works in theory, but about the limits of the economics of fusion reactors at any point in the future. What I'm saying is it's too soon to say what's possible with fusion and what isn't. We don't even have a break even reactor yet. We can even say for certain that we ever will.
  - ansible 5y ago
    > It doesn't surprise me. Your arrogance does though, I didn't expect you to double down on an unreasonable position. I'd give your criticism some consideration if I thought you had even the slightest knowledge of what we're talking about. Let's talk about the core of the Sun, where p-p fusion takes place. Remember, I said at the top: no new physics. The core of the Sun is hot, like really, really hot. How hot? 15 million Kelvin. So no solid material ... made of atoms ... can be anywhere close by because it would vaporize. You can talk about active cooling or whatever, and that's not going to help. But let's assume we have some magical material that can deal with that temperature, and keep going. We're going to skip the pressure that really hot plasma is under, and assume we have terrifically awesome magnetic confinement that can handle that. We don't actually, but let's move on. The other problem with 15 million K is that all that energy wants to radiate away. Yes, you want to absorb some of that radiation (hard gamma, by the way, very nasty) as part of the energy generation process, but if you let the plasma cool off, the reaction rate drops. "Cool" in this context is relative, at 7 million K, the reaction rate is very close to zero. The last problem we will talk about today is volume. The above conditions get us a fusion power density of... 276 watts / cubic meter. To have a fusion plant that generates 1GW of power, we'd need to contain a cube 153 meters on a side of 15 million Kelvin plasma. Oh, wait, that assumes the magnetic containment and everything else requires zero power to run. So we'll have to go bigger, much bigger. Are you starting to understand the scale of the problem... trying to design a proton - proton fusion reactor? I am not the arrogant one, I'm just listening to the fusion scientists who have been studying how all this works. > We don't even have a break even reactor yet. We can even say for certain that we ever will. And here you are expressing doubt that we'll achieve even the easiest kind of fusion reactor. We have achieved fusion, just to be clear. We can reach the temperatures and pressures to see some reactions. Assuming civilization does not collapse (climate change, war, etc) we will be able to engineer a fusion reactor that is some kind of practical. But it won't be proton-proton.

naasking 5y ago

> We have two basic ways of generating a lot of power, fission and fusion I think there are more. Like radiation from evaporating black holes.

ansible 5y ago
> I think there are more. Like radiation from evaporating black holes. Evaporating black holes? Yes, if you are willing to wait a very, very long time, and have collectors over a large area. However, if you want to get stuff done before your protons evaporate, you could instead throw matter into a black hole, thus increasing its mass. The radiation given off by the accretion disc is substantial, and can be collected... over a large area. IIRC, the mass-to-energy efficiency is something like 40%, which is really good. They are a little difficult to set up however...
- naasking 5y ago
  I mean, we're talking about timescales and construction projects like Dyson spheres. It's entirely feasible that people with such technology could create microscopic black holes that evaporate quickly for these purposes. Hawking radiation at this scale is substantial.
  - ansible 5y ago
    Ah, yes, I do recall reading about that somewhere. That is an interesting prospect, with a very high mass-to-energy efficiency. Of course it requires careful management of inflowing matter. And you can shut if down if needed by stopping the inflow, assuming you have enough stored energy to recreate the micro black hole sometime later.
    - naasking 5y ago
      You'll probably enjoy this video: https://youtu.be/EzZGPCyrpSU https://youtu.be/EzZGPCyrpSU Good channel too.
  - kragen 5y ago