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hugh comments on Superstimuli, setpoints, and obesity - Less Wrong
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I'm not sure what this has to do with the thread, although it is interesting. Can you back up your conclusions with some data? Assuming sucrose is metabolized in the Kegg pathway, the energy generated is easily calculable. I haven't found good numbers on combustion engine efficiency for running on sucrose (how does one design such an engine?); my understanding was that even petrol engines have very low efficiencies, but I could be wrong about that.
You are partially correct: I have erred in deeming the thermal efficiency of typical high-T-gradient heat engines greater than that of humans (whose organs exploit more modes of energy conversion than those in a heat engine).
However, the conclusion is robust when comparing from the appropriate baselines. To find the total energy-to-mechanical-energy conversion efficiency, you have to factor in the energy losses in generating the sugar to begin with. This gives sugar cane as having the highest photosynthetic efficiency of 8% (light energy to sugar chemical energy).
That must be applied against the 28% thermal efficiency (sugar energy to mechancial energy) I calculate for humans [1], leaving 2.2% net light-to-mechanical efficiency (neglecting distribution energy costs for the sugar).
This is still inefficient compared to other means of using the same sunlight. Taking a characteristic solar cell efficiency on the low end of 6% (light to electricity), with a characteristic efficiency of 90% (electricity to mechanical) gives a 5.4% net light-to-mechanical efficiency -- still significantly higher than that of growing sugar and feeding it to humans!
[1] Human efficiency estimated from the following assumptions: 816 Cal/hr burned by a 200 lb individual climbing stairs at 0.30 m/s; this gives an energy consumption rate of 952 W and mechanical output of 267 W, or 28% efficiency, though again this is only sugar-to-mechanical efficiency.
I claim, that given sugar, using it for human consumption is one of the least wasteful things to do with it.
In the future, if there is an option between powering organic people with sugarcane-produced sugar and powering cybernetic people with solar cells, and we can choose to be either organic or cybernetic, then your argument will be valid—assuming there are no other options, which is silly. For right now, people need food. Converting sunlight into other forms of energy in other ways is fine and good, but personally, I would also like to keep growing food for me and my brethren.
This is a big caveat. A typical person burns much more energy maintaining homeostasis than they do in moving. Following that, brain activity is the second-largest energy sink. While athletes can quadruple their caloric requirements (indicating that mechanical energy can become the largest drain on energy), I think calculating energy conversion with your example is suspect.
Okay, now I think I see the source of our miscommunication: you're assuming humans have an important use in addition to manufacturing products, while I wasn't.
Is your composure of these comments an example of a human manufacturing products?
I still think using sunlight through an organic / metabolic pathway is more efficient form of manufacturing rational discourse than using solar cells and electricity. Unless, of course, you are not human, which might explain your apparent disregard for human utility, but introduces the question of why you are bothering to converse with one.
You might give him information about how to better make paperclips, or he might persuade you to help him.
Alternatively, he's engaging in a very protracted joke.