How much extra energy external energy is required to get an energy flux on Mercury of a billion times that leaving the sun? I have an idea, but my statmech is rusty. (the fourth root of a billion?)
And do we have to receive the energy and convert it to useful work with 99.999999999% efficiency to avoid melting the apparatus on Mercury?
I have no idea, I never took the relevant physics classes.
For concreteness, suppose we do something like this: We have lots of solar panels orbiting the sun. They collect electricity (producing plenty of waste heat etc. in the process, they aren’t 100% efficient) and then send it to lasers, which beam it at Mercury (producing plenty more waste heat etc. in the process, they aren’t 100% efficient either). Let’s suppose the efficiency is 10% in each case, for a total efficiency of 1%. So that means that if you completely surrounded the sun with a swarm of these things, you could get approximately 1% of the total power output of the sun concentrated down on Mercury in particular, in the form of laser beams.
What’s wrong with this plan? As far as I can tell it couldn’t be used to make infinite power, because of the aforementioned efficiency losses.
To answer your second question: Also an interesting objection! I agree melting the machinery is a problem & the authors should take that into account. I wonder what they’d say about it & hope they respond.
Yeah, though not for the reason you originally said.
I think I’d like to see someone make a revised proposal that addresses the thermal management problem, which does indeed seem to be a tricky though perhaps not insoluble problem.
Ok, I could be that someone. here goes. You and the paper author suggest a heat engine. That needs a cold side and a hot side. We build a heat engine where the hot side is kept hot by the incoming energy as described in this paper. The cold side is a surface we have in radiative communication with the 3 degrees Kelvin temperature of deep space. In order to keep the cold side from melting, we need to keep it below a few thousand degrees, so we have to make it really large so that it can still radiate the energy.
From here, we can use Stefan–Boltzmann law, to show that we need to build a radiator much bigger than a billion times the surface area of Mercury. It goes as the fourth power of the ratio of temperatures in our heat engine.
The paper’s contribution is the suggestion of a self replicating factory with exponential growth. That is cool. But the problem with all exponentials is that, in real life, they fail to grow indefinitely. Extrapolating an exponential a dozen orders of magnitude, without entertaining such limits, is just silly.
I’m still interested in this question. I don’t think you really did what I asked—it seems like you were thinking ‘how can I convince him that this is impossible’ not ‘how can I find a way to build a dyson swarm.’ I’m interested in both but was hoping to have someone with more engineering and physics background than me take a stab at the latter.
My current understanding of the situation is: There’s no reason why we can’t concentrate enough energy on the surface of Mercury, given enough orbiting solar panels and lasers; the problem instead seems to be that we need to avoid melting all the equipment on the surface. Or, in other words, the maximum amount of material we can launch off Mercury per second is limited by the maximum amount of heat that can be radiated outwards from Mercury (for a given operating temperature of the local equipment?) And you are claiming that this amount of heat radiation ability, for radiators only the size of Mercury’s surface, is OOMs too small to enable dyson swarm construction. Is this right?
How much extra energy external energy is required to get an energy flux on Mercury of a billion times that leaving the sun? I have an idea, but my statmech is rusty. (the fourth root of a billion?)
And do we have to receive the energy and convert it to useful work with 99.999999999% efficiency to avoid melting the apparatus on Mercury?
I have no idea, I never took the relevant physics classes.
For concreteness, suppose we do something like this: We have lots of solar panels orbiting the sun. They collect electricity (producing plenty of waste heat etc. in the process, they aren’t 100% efficient) and then send it to lasers, which beam it at Mercury (producing plenty more waste heat etc. in the process, they aren’t 100% efficient either). Let’s suppose the efficiency is 10% in each case, for a total efficiency of 1%. So that means that if you completely surrounded the sun with a swarm of these things, you could get approximately 1% of the total power output of the sun concentrated down on Mercury in particular, in the form of laser beams.
What’s wrong with this plan? As far as I can tell it couldn’t be used to make infinite power, because of the aforementioned efficiency losses.
To answer your second question: Also an interesting objection! I agree melting the machinery is a problem & the authors should take that into account. I wonder what they’d say about it & hope they respond.
A billion times the energy flux from the surface of the sun, over any extended area is a lot to deal with. It is hard to take this proposal seriously.
Yeah, though not for the reason you originally said.
I think I’d like to see someone make a revised proposal that addresses the thermal management problem, which does indeed seem to be a tricky though perhaps not insoluble problem.
Ok, I could be that someone. here goes. You and the paper author suggest a heat engine. That needs a cold side and a hot side. We build a heat engine where the hot side is kept hot by the incoming energy as described in this paper. The cold side is a surface we have in radiative communication with the 3 degrees Kelvin temperature of deep space. In order to keep the cold side from melting, we need to keep it below a few thousand degrees, so we have to make it really large so that it can still radiate the energy.
From here, we can use Stefan–Boltzmann law, to show that we need to build a radiator much bigger than a billion times the surface area of Mercury. It goes as the fourth power of the ratio of temperatures in our heat engine.
The paper’s contribution is the suggestion of a self replicating factory with exponential growth. That is cool. But the problem with all exponentials is that, in real life, they fail to grow indefinitely. Extrapolating an exponential a dozen orders of magnitude, without entertaining such limits, is just silly.
I’m still interested in this question. I don’t think you really did what I asked—it seems like you were thinking ‘how can I convince him that this is impossible’ not ‘how can I find a way to build a dyson swarm.’ I’m interested in both but was hoping to have someone with more engineering and physics background than me take a stab at the latter.
My current understanding of the situation is: There’s no reason why we can’t concentrate enough energy on the surface of Mercury, given enough orbiting solar panels and lasers; the problem instead seems to be that we need to avoid melting all the equipment on the surface. Or, in other words, the maximum amount of material we can launch off Mercury per second is limited by the maximum amount of heat that can be radiated outwards from Mercury (for a given operating temperature of the local equipment?) And you are claiming that this amount of heat radiation ability, for radiators only the size of Mercury’s surface, is OOMs too small to enable dyson swarm construction. Is this right?