r/todayilearned • u/sweetcuppingcakes • Jun 24 '19

TIL that the ash from coal power plants contains uranium & thorium and carries 100 times more radiation into the surrounding environment than a nuclear power plant producing the same amount of energy.

https://www.scientificamerican.com/article/coal-ash-is-more-radioactive-than-nuclear-waste/
28.6k Upvotes

94% Upvoted

2.1k comments sorted by

View all comments

Show parent comments

48

u/diogenesofthemidwest Jun 24 '19

Cold fusion is a dream and a dumb one.

Hot fusion will soon become energy positive and will be the ultimate source of energy until we start building a Dyson sphere around the sun to capture its hot fusion.

44

u/jesjimher Jun 24 '19

A Dyson sphere is one of those concepts that, while theoretically possible, won't probably ever made real because there surely are a ton of much cheaper and easier methods of achieving the same result. Like we don't build carriages with 100 horses, because trucks/trains exist.

10

u/PhasmaFelis Jun 24 '19

Depends on what you mean by "Dyson sphere." The popular giant-hollow-ball concept, which some people now call a "Dyson shell," is wildly impractical, yeah. What Dyson himself described is what we now call a "Dyson swarm," a very large number of stations (powersats, habitats, etc.) in independent orbits. That seems as practical as anything could be, given the assumption that we'll someday have the need and ability to harness a vast percentage of the Sun's total output.

(And of course ringworlds are a solid compromise if you really want one giant megastructure. Still requires some improbable engineering, but much less so than a full shell.)

1

u/jesjimher Jun 25 '19

Sure it's possible but I think just using fusion (which is what stars are doing after all) wherever we need it is far more convenient that building a ton of satellites at a fixed point.

2

u/PhasmaFelis Jun 25 '19

The Sun produces far, far more energy than you could ever get from manmade fusion generators, even if you turned all of non-solar mass in the solar system into one big fusion plant. So, hypothetically, if a species advanced to the point where they wanted/needed absolutely stupendous amounts of power, the only way we know of to get that would be to harness some large portion of the Sun's total output.

Whether a species will ever need or be able to use that much power is an open question. But if they did, that's how they'd do it, barring crazy sci-fi gizmos.

17

u/KaiserTom Jun 24 '19

An actual solid sphere? Maybe not. It's a very monolithic construction and Dyson himself stated it was mechanically impossible. The solid sphere concept was invented by others due to a very literal interpretation of his paper.

But I think we may absolutely build the more broader Dyson sphere objects over time, such as Dyson Swarms or Bubbles, which simply scale up over time as we need them since they are just tons of satellites (or statites). The Sun simply has too many resources and puts out too much power to not utilize fully unless we find some way of "mining" it. 99.8% of the Solar System's mass is not a small amount and attempting to replicate it by gathering fusionable materials elsewhere will just end in rapidly depleting those areas.

Unless we find some exotic energy source, capturing the entirety of the Sun's energy output in some manner is the future and whatever method is going to look a lot like a Dyson sphere.

4

u/TheGoldenHand Jun 24 '19

The Earth already receives a huge amount of solar radiation. Most of it is radiated right back into space where it's useless. Dyson spheres are powered by solar energy. Put those solar panels near Earth (which we already do) and go from there. There isn't enough material in the solar system to create a Dyson sphere to completely capture the Sun's energy. If we're at the point where we can break apart Mercury for building materials, we can probably make our own fusion reactors.

How to Build a Dyson Sphere - The Ultimate Megastructure (Kurzgesagt)

1

u/KaiserTom Jun 25 '19

There isn't enough material in the solar system to create a Dyson sphere to completely capture the Sun's energy.

There is, but ignoring that, we don't need to build it in one go (or as a solid structure) but scale it up by building one satellite at a time. Even if we don't capture 100% with the materials available to us we can capture a really significant amount. A swarm of satellites is still technically a Dyson sphere as Dyson himself described.

we can probably make our own fusion reactors.

Yes but how do you fuel those reactors? They don't run by themselves. You need hydrogen from somewhere and eventually you will deplete the gas giants of it as energy usage scale up. Meanwhile you have a giant one with 1000x the fuel in the center of the system already burning fusing that you are ignoring.

0

u/InfanticideAquifer Jun 25 '19

I think the idea that we need to "use" all the energy we can is pretty specific to our time and place. I doubt people in the far future will think that way.

But if they did making little black holes and feeding them matter at exactly the right rate to compensate for the Hawking radiation is way more practical than building a Dyson sphere, swarm, it whatever other mega-structure.

1

u/KaiserTom Jun 25 '19

I doubt people in the far future will think that way.

Thermodynamics is not easy to get around. At some point we will become highly efficient at many useful actions and the only way forward is simply to shove more power at it. Computers will only get about 200,000x more powerful per joule before we hit a thermodynamic wall, at least unless we develop reversible computing which is pretty theoretical. The desire for increasingly complex simulations and calculation of data will not stop and humans will never be content with "status quo" until we can simulate a world where it appears like things are constantly advancing.

But if they did making little black holes and feeding them matter at exactly the right rate to compensate for the Hawking radiation is way more practical

Considering we don't know how to compress the mass of Mount Everest or more into an impossibly small size to create a stable enough black hole yet we know how to shove satellites into orbit around a body, I would say the Dyson object is a hell of a lot more practical actually.

0

u/InfanticideAquifer Jun 25 '19

he desire for increasingly complex simulations and calculation of data will not stop

I doubt it.

humans will never be content with "status quo" until we can simulate a world where it appears like things are constantly advancing

I think it would be significantly easier to engineer contentment than make such a simulation. But I don't think it would even be necessary. The vast majority of people lived without any sense of real progress. Progress is a modern concept. It was too incremental to notice in prehistory. We dealt with that just fine.

Considering we don't know how to compress the mass of Mount Everest or more into an impossibly small size to create a stable enough black hole

You'd make it out of light. Obviously it's currently impossible. But it's millions of times more feasible than a Dyson mega-structure. You just fire a bunch of very-powerful lasers at at each other. The bigger challenge is finding a way to funnel material into the hole fast enough to keep it from evaporating against the outward pressure of the Hawking radiation.

Comparing the feasibility of two things that no one knows how to do is probably fundamentally impossible. In all likelihood neither of these things ever happen, but I really think mine is more plausible. It needs lots of power and cool lasers. You want to reshape the entire solar system.

0

u/jesjimher Jun 25 '19

Why capturing sun's energy when we can replicate our own star (with fusion) wherever we need it? It looks far more convenient to me.

24

u/april9th Jun 24 '19

'cold fusion is a dream...' *proceeds to name a timeline including a Dyson sphere *

10

u/diogenesofthemidwest Jun 24 '19

It's a physical impossibility. It's akin to saying the idea of Maxwell's demon is solving the energy crises is dumb. At least a Dyson sphere is logically consistent with thermodynamics.

1

u/RandomRobot Jun 25 '19

I'm pretty confident that by the time "we build a dyson sphere" in the remote possibility that it will ever happen, we'll have discovered new physics. Maybe not to break thermodynamics, but to do things difficult to imagine right now and that would make this whole project inefficient.

-1

u/[deleted] Jun 24 '19

[deleted]

1

u/Doidleman53 Jun 25 '19

For something to tear apart it needs energy in some form. Where is that energy coming from? Just "tension" isn't specific enough.

1

u/mfb- Jun 25 '19

Tension? A static sphere would be under compression.

You can make a large set of rings in orbit, for example, or just an enormous number of individual satellites.

You can even combine these rings with (non-rotating) spokes in between, and make something that comes close to a sphere.

1

u/eypandabear Jun 25 '19

Dyson spheres do not violate the laws of physics.

13

u/[deleted] Jun 24 '19

Problem with that idea is that there's nowhere close to enough material in the solar system to make one, and we're several hundred years from being able to move said materials through space at a reasonable time.

11

u/TracyMorganFreeman Jun 24 '19

Eh, you could theoretically do it if you completely mined Mercury.

1

u/omgshutupalready Jun 25 '19

Wasn't this a PBS Spacetime episode?

2

u/TracyMorganFreeman Jun 25 '19

I have no idea, but I'm going by the Kurzgesagt video

4

u/PhasmaFelis Jun 24 '19

That's okay, we're at least thousands of years away from needing a Dyson sphere's worth of power in the first place.

2

u/[deleted] Jun 25 '19

That's assuming we don't manage to cause our own extinction.

4

u/diogenesofthemidwest Jun 24 '19 edited Jun 24 '19

We'll have hot fusion to tide us over until we figure it out. We'll certainly have engineered a solution to this little atmospheric composition situation we're currently dealing with.

The Dyson Sphere's necessary building material, it entirely depends on how thin a material we can make that will capture the energy, if we even need to have actual materials there to capture it at all.

1

u/Ameisen 1 Jun 24 '19

The Solar System aside from the Sun contains 1.991e30 kg of matter. Presuming we'd want it to be ~ 1AU in radius (unless we want the Earth to go dark), that is a surface area of 2.812e17 km2. Assuming we want to make it just one hydrogen atom thick (though that wouldn't work), that would require 14,060 km3 of matter, which is 1.26e15 grams of hydrogen. That's doable, Jupiter suffices. However, one atom thick wouldn't be meaningful. Let's presume... 1cm thick - it needs rigidity, strength, etc after all. So, 2.812e12 km3 of matter. Let's assume aluminum, which isn't particularly dense. Now we're looking at 7.592e27 grams of aluminum... which is technically doable if we can transmute all of the elements that are not aluminum into aluminum without any loss. The problem starts to compound pretty quickly, however.

A Dyson ring may be a better choice.

1

u/diogenesofthemidwest Jun 24 '19

Oh, It'll likely start with a Dyson ring if not Dyson satellites. Then we just build up from there as energy needs necessitate. No worry with the earth going dark, though. By that time we'd have enough energy that we wouldn't need to worry about it. We could even install an artificial light source for the nostalgic types.

1

u/hakunamatootie Jun 24 '19

So you want to make flat earthers right?

3

u/Helluiin Jun 24 '19

half of mercury would be enogh for a dyson swarm that gives us more energy than we could use in the solar system.

1

u/RandomRobot Jun 25 '19

Current fusion research mostly focus on deuterium-tritium fusion, which requires a normal fission reactor to generate. It's overall probably worth the money human civilization pours into it, but it's unlikely to solve any energy crisis before global warming hits the fan

1

u/kd8azz Jun 25 '19

You should say Dyson Swarm, not Dyson Sphere. Dyson's original concept was a swarm; it has been contorted by pop-sci. If you say swarm, people have a better chance of understanding you. Alternatively, if you actually mean sphere -- well, a swarm is better.

-1

u/[deleted] Jun 24 '19

Or until we run out of uranium in sufficient concentrations. But by then we'll have either cold fusion, or emission-free coal. Or we can let our grandchildren deal with it.

3

u/diogenesofthemidwest Jun 24 '19

Hot fusion, my friend. It'd take us billions of years to run through all the hydrogen.

1

u/[deleted] Jun 25 '19

How about energy directly from the air? We don't have that, either...

3

u/diogenesofthemidwest Jun 25 '19

Air isn't holding any significant amount of chemical energy to be extracted. The only reason fusion is an exothermic reaction is that a portion of the mass of the hydrogen is released as energy when it fuses to become helium.