I still don't understand why you need to build a Dyson sphere and then transport the energy to where it's needed when you can build decentralized fusion reactors. What am I missing?
The scale.
The reason to build a Dyson Sphere (or Swarm) is that you want all (or at least a large fraction) of the energy output of a star. To "build decentralized fusion reactors" that can provide the same scale of energy is even less practical than building a shell around a star and would require far more materials! Also, fusion is really simple when the ignition energy is provided for free by the gravitational compression of something the size of a star, and not so simple when you're trying to get it started on a small scale using any other form of energy for ignition. The bottom line is we don't really know if small-scale, controlled, net-energy-positive fusion is possible at all, but if it is it has a lot of overhead costs... you then have to deal with ignition energy, containment, etc. You're trying to make a mini-star and keep it tame. The physics are not favorable to this, they are favorable to star-sized stars, where gravity and fusion energy pressure can balance each other for millions of years.
Feed most of the energy of star to lasers and end up with weapon that will melt planets across the galaxy.
Honestly, don't need to expand across the galaxy if have Dyson Sphere, which could be explanation of Fermi Paradox.
To minimize theta, we need to either increase D or decrease lamda.
Lets assume we would be able to make far infrared high power lasers, at say 10,000 nm = 1e-5 m wavelength.
Lets assume we would be able to make D, the diameter of our laser beam, similar to the diameter of a typical planet, for Earth it is ~13,000 km = 13e6 m.
Theta = 1e-5 / 3.14 / 13e6 ~= 1e-13 radians.
Sun is ~ 25,000 light years from the center of our galaxy, ~= 25e3 y 3e8 m/s 31.5e6 s/year ~= 1e20 m.
Laser beam diameter, there far away, would be: 1e-13 *1e20 = 1e7 m, similar to the diameter of Earth, not much further diverged, focused and delivering the wast amount of energy all over the planet thereby evaporating it to a gas.
Indeed, what you say about the melting far away planets is possible, in theory.
We are not capturing 10-15% of the sun's total power output.
My guess is that if you can build Dyson spheres you can build fusion reactors.
> This far the most efficient fusion reactor humanity has available to it exists approximately 1 AU away
Efficient in terms of what? With what are you comparing it to?
If you have the time and raw resources, it was possible with 1960s technology.
[1] https://en.wikipedia.org/wiki/List_of_artificial_objects_in_... .
Unless we have some magical solution which can convert waste heat into electricity and thus making such satellite working with 100% effectivity, then such satellite needs to transmit energy with very limited power otherwise it will fry itself up.
Additionally high power laser has currently something around 80% of efficiency. So if you have 10kW of input from solar array on one side, then you are transmitting 8kW via laser and 2kW into satellite itself as a heat. And again, we are in vacuum of space, so good luck with radiating 2kW of power into vacuum.
The fact, that you can't get rid of waste heat would need whole satellite to work close to 100% effectivity, which we don't have technology today
Would millions or billions of them be better? Yes.
Your description of it as a megastructure might explain some of the confusion: it wouldn't be a structure, but rather a formation of satellites not physically connected to each other.
How do you build a swarm of satellites? Well, first you make 1 satellite, then you make another... :)
My description is Freeman Dyson's description. Naturally you are allowed to come up with ImPostingOnHN's Swarm, which includes a case of zero satellites and no effect on the star emission whatsoever.
> How do you build a swarm of satellites? Well, first you make 1 satellite, then you make another... :)
Sure and the end state of completing Dyson Swarm in Solar system is not achievable with the technology we have. Now let's move on to discuss if one man with a rifle but no vehicle constitutes a Motor Rifles brigade.
Sure, for one possible end state.
The point is that we have the technology to start, because we've already started. Thus, it is achievable given enough time and effort with our current level of technological advancement.
The part we don't know how to do yet is getting the material. Building structures that large in space, the resources for it have to come from space, we cannot lift it off Earth. So we need to figure out how to mine asteroids, and maybe also how to mine Mercury. Either one would be sufficient at the start. Neither of those are a well-understood problem, let alone solved, so that's where you should invest resources if you're a billionaire looking to start a Dyson sphere and think SpaceX is on track for launch cost reduction.
I think in terms of science and engineering difficulty, it's a pretty even race as to which is more difficult between making fusion actually produce net useful energy and being able to mine & refine materials from an asteroid + build a sustainable life support system.
The reason fusion "seems easier" is because it is economically far more achievable, and there's a lot more political will behind it so it feels more possible.
Dont know what cheap means for them, but it will never be for free because abundance happens when the supply exceeds demand and I dont see the scenario where the demand for energy is declining in a long run.
It's the railgun problem: railguns let you trade complicated, unstable ammunition for cheap, stable slugs of metal. But the railgun imposes so much wear on its barrel, and the barrel itself is so much more expensive than in a traditional gun, that you've obliterated your cost savings.
Likewise, it's irrelevant if fusion reactors can provide infinite energy from a single gram of hydrogen, because the reactor housing itself will be an impossibly complex machine with an extremely low lifespan from dealing with the energies involved.
Is fusion possible? Probably. Will it ever be more economical than solar panels? Nope.
https://www.reddit.com/r/askscience/comments/14dtio/contactl...
https://www.reddit.com/r/AskScienceDiscussion/comments/18i71...
https://en.m.wikipedia.org/wiki/Coilgun
It would seem that even without contact there's wear issues with both force exerted on the rails or coils from the magnetic forces and also with creating plasma as the projectile exits?
The small mindness.
It's like an 1800s dude thinking aliens would do interstellar travel by having very huge horses, oh no wait...a billion of them (but still somewhat big)
"This is what an advanced race would do...with our current understanding" is an oxymoron
This metaphor doesn’t make sense to me.
I'm guessing it's more like making a living space in the sphere itself or somewhere nearby and using the energy there (maybe exporting some percentage to Earth).
Because if we're able to build the sphere itself, we probably would already know some way to cool it down in space so it doesn't burn itself, wasting all the money that went to its construction.
No, if we have a dyson sphere, we are everywhere playa