5 ms·

"when the sun in fact does proton/proton, proton/deuterium, and helium 3/helium 3 fusion at a relatively slow rate under extremely high pressure." We actually

"when the sun in fact does proton/proton, proton/deuterium, and helium 3/helium 3 fusion at a relatively slow rate under extremely high pressure." We actually don't know how the Sun does fusion. If we did, we'd have created it here on Earth already.

ryanpandya 3y ago
I thought we're pretty clear that it's thanks to absolutely colossal mass, which... Can't really happen on earth since it requires the mass of a huge number of earths.
- wheelerof4te 3y ago
  Then we need to find another way to generate fusion power, or admit that it's impossible to do on this planet. Throwing lumps of cash at fusion power venture capital feels almost like a money-laundering fraud.
  - varjag 3y ago
    The whole fusion energy effort since 1950s is about finding another way.
  - Maken 3y ago
    At least it's not crypto and it's not actively hurting anyone.
    - RC_ITR 3y ago
      Until the tritium leaks...
  - ben_w 3y ago
    > Then we need to find another way to generate fusion power, or admit that it's impossible to do on this planet. Yes. Here are the currently known alternatives off the top of my head: * Fusion bomb * Inertial electrostatic confinement (14 year olds have done this for highschool science fair projects) * Virtual cathodes (Polywell, technically also an IEC variant) * Magnetic confinement (Tokamaks: the big expensive doughnuts) * Field-reversed configuration (technically also magnetic, but these are magnetic "smoke rings", Helion Energy does this) * Z-pinch (again magnetic, but different) * Laser confinement (NIF) * Muon-catalyzed fusion (no chance of this becoming mainstream unless we can convince muons to stop decaying) IIRC all of these have demonstrated that it's physically possible; some even show promise. (I've been wanting to write a plasma physics simulation to see if I can improve on the Fusor design since I was at university; now chatGPT writes acceptable code, I keep asking myself why I've not yet made this happen…)
andruby 3y ago
There’s a difference between knowing the physical and chemical reactions and being able to reproduce it. We have reproduced it, but not yet sustainably and in an economically profitable way. We can’t reproduce exactly what the sun is doing, because we don’t want the whole planet to run fusion. One of the large problems to solve, as I understand it, is containment. No need for containment on the sun.
- simiones 3y ago
  > One of the large problems to solve, as I understand it, is containment. No need for containment on the sun. Containment, in the context of fusion, doesn't refer to preventing the reaction from running rampant. It refers to keeping the reactants in a small confined space so the reaction can continue at all. The sun achieves this containment through the least efficient means: it's gigantic mass means that the reactants are forced together by the force of gravity. Plus, the shear quantity of superhot plasma helps ensure that energetic particles have an excellent chance to hit another core, keeping the reaction going. Note that the solar core, where the vast majority of solar fusion happens, is ~0.25 of the sun's radius, so ~25 Earth radii. Quite hard to get the amount of plasma on Earth. The entirety of the Earth doesn't have even a fraction of the Sun's mass, so that is impossible to reproduce. So we need to rely on much more violent forces to achieve a similar level of containment as the Sun.
ben_w 3y ago
> We actually don't know how the Sun does fusion. If we did, we'd have created it here on Earth already. We know we can't do what the sun does here on Earth, and we also know that we don't want to what the sun does. We can't, because the cube-square law means the sun stays hot enough for long enough for this to happen even though a reactor on the ground would cool down almost immediately. We don't want to, because the reaction happens over the course of billions of years giving the sun a specific power output similar to rotting cabbages.

ryanpandya 3y ago

I thought we're pretty clear that it's thanks to absolutely colossal mass, which... Can't really happen on earth since it requires the mass of a huge number of earths.

wheelerof4te 3y ago
Then we need to find another way to generate fusion power, or admit that it's impossible to do on this planet. Throwing lumps of cash at fusion power venture capital feels almost like a money-laundering fraud.
- varjag 3y ago
  The whole fusion energy effort since 1950s is about finding another way.
- Maken 3y ago
  At least it's not crypto and it's not actively hurting anyone.
  - RC_ITR 3y ago
    Until the tritium leaks...
- ben_w 3y ago
  > Then we need to find another way to generate fusion power, or admit that it's impossible to do on this planet. Yes. Here are the currently known alternatives off the top of my head: * Fusion bomb * Inertial electrostatic confinement (14 year olds have done this for highschool science fair projects) * Virtual cathodes (Polywell, technically also an IEC variant) * Magnetic confinement (Tokamaks: the big expensive doughnuts) * Field-reversed configuration (technically also magnetic, but these are magnetic "smoke rings", Helion Energy does this) * Z-pinch (again magnetic, but different) * Laser confinement (NIF) * Muon-catalyzed fusion (no chance of this becoming mainstream unless we can convince muons to stop decaying) IIRC all of these have demonstrated that it's physically possible; some even show promise. (I've been wanting to write a plasma physics simulation to see if I can improve on the Fusor design since I was at university; now chatGPT writes acceptable code, I keep asking myself why I've not yet made this happen…)

andruby 3y ago

There’s a difference between knowing the physical and chemical reactions and being able to reproduce it. We have reproduced it, but not yet sustainably and in an economically profitable way. We can’t reproduce exactly what the sun is doing, because we don’t want the whole planet to run fusion. One of the large problems to solve, as I understand it, is containment. No need for containment on the sun.

simiones 3y ago
> One of the large problems to solve, as I understand it, is containment. No need for containment on the sun. Containment, in the context of fusion, doesn't refer to preventing the reaction from running rampant. It refers to keeping the reactants in a small confined space so the reaction can continue at all. The sun achieves this containment through the least efficient means: it's gigantic mass means that the reactants are forced together by the force of gravity. Plus, the shear quantity of superhot plasma helps ensure that energetic particles have an excellent chance to hit another core, keeping the reaction going. Note that the solar core, where the vast majority of solar fusion happens, is ~0.25 of the sun's radius, so ~25 Earth radii. Quite hard to get the amount of plasma on Earth. The entirety of the Earth doesn't have even a fraction of the Sun's mass, so that is impossible to reproduce. So we need to rely on much more violent forces to achieve a similar level of containment as the Sun.

ben_w 3y ago

> We actually don't know how the Sun does fusion. If we did, we'd have created it here on Earth already. We know we can't do what the sun does here on Earth, and we also know that we don't want to what the sun does. We can't, because the cube-square law means the sun stays hot enough for long enough for this to happen even though a reactor on the ground would cool down almost immediately. We don't want to, because the reaction happens over the course of billions of years giving the sun a specific power output similar to rotting cabbages.