14 KiB
[BST][MK][HSF] How much can be done with carbon?
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Author: u/DataPacRat Amateur Immortalist*
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URL: https://www.reddit.com/r/rational/comments/3i6ncx/bstmkhsf_how_much_can_be_done_with_carbon/
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Score: 6
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Created: 2015-08-24T09:55:34
Post:
I'm drafting up some eusocial posthumans - Borg without the hivemind and with a wider array of body plans - and even more important than knowing what they can do is figuring out what they can't do. What are the limits of physical structures that can be built using relatively abundant bio-available atoms, such as carbon?
How efficient can organic photovoltaics be made, if one isn't limited to what can be evolved from existing chlorophyll-based organisms? How densely can energy be stored? How strong can support members, exoskeletal armour plates, or skin be made to be? How much processing power per unit of weight/volume/power? Is superconductivity feasible? Which rarer elements would be worth going out and about to hunt down?
How toxic would the chemicals involved be? What necessary secondary systems would be required to connect them to something resembling a human's biochemistry? What further complications and limitations might be involved that I don't know enough to ask about?
(And while I'm asking about such things - I'm planning on using bioluminescence instead of pheromones. Is the yellow-green of fireflies' luciferin the colour that can be generated most efficiently? If some other form of light generation is used, is there any other colour that is a natural fit with nanotube-and-graphene surfaces? (My imagination wants me to write about black surfaces with areas of cyan glow, but I honestly don't know if it's feasible for organically-produced light to have a wavelength as short as 500 nm.))
Comments:
u/Nepene [+9] (5 hours later)
Organic photovoltaics aren't going to work well without transition metal ions. Most biology uses transition metal ions to handle all the fiddly ionization stuff. They're order of magnitudes better at that sort of stuff than carbon.
They'd probably use organic cells, doped wit a small amount of transition metal ions. The best of them have shown around 10% efficiency.
https://en.wikipedia.org/wiki/Photosynthetic_efficiency
Which matches stuff here.
https://en.wikipedia.org/wiki/Energy_density
Fat is already pretty close to the physical limits of storage efficiency, which is just alkane chains stacked together in long lines. If you want better you need to go nuclear, so need more than carbon.
http://news.discovery.com/tech/print-body-armor.htm
You can have some pretty tough armor, tougher than steel.
You can probably have circuits as good or slightly better than ours with carbon nanotubes, with advanced enough technology, or diamond.
https://en.wikipedia.org/wiki/Organic_superconductor
Organic superconductors aren't as good as ones you can get with more exotic mixes.
On elements you need.
https://en.wikipedia.org/wiki/Carbon_nanotubes_in_photovoltaics
Indium is a big one, it's excellent for making transparant conductive layers. It's not usually used in biology.
On health risks, carbon nanotubes are seriously toxic, like asbestos. Little knives of carbon that can tear apart lungs. You'll need a better repair system for the lungs and skin. Calorie requirements will likely be notably increased. If they're injured they'll be a serious health hazard for those around.
http://www.chm.bris.ac.uk/motm/GFP/GFPh.htm
They can make many glow in the dark chemicals, which they did by taking a fluorescent protein and mutation it. These could be used to alter bioluminescent lights.
u/DataPacRat [+2] Amateur Immortalist (11 hours later)
They'd probably use organic cells, doped wit a small amount of transition metal ions. The best of them have shown around 10% efficiency.
I hadn't realized that sugarcane could reach such a high efficiency compared to other crop plants. I may use a version of its biochemistry as the standard energy-gathering method, with organic photovoltaics as an option when transition elements can be acquired in enough quantity.
https://en.wikipedia.org/wiki/Energy_density
Fat is already pretty close to the physical limits of storage efficiency
Close, but a few tables in that article suggest some possibilities with slightly higher densities - diesel and gasoline, or some of the poly-whatsit plastics. Due to some of the obvious complications, if I do use them they may have to be segregated into external organisms/devices, or at least specialized body cavities, which may provide some useful additional colour for the hive.
I had to dig up a different article to get the actual name of the transparent spheres (N-tert-butoxycarbonyl (Boc)-protected diphenylalanine), but I'm willing to adopt the substance wholesale.
Organic superconductors aren't as good as ones you can get with more exotic mixes.
True; I think I'm going to drop the idea, and stick with room-temperature computing.
On health risks, carbon nanotubes are seriously toxic, like asbestos. Little knives of carbon that can tear apart lungs. You'll need a better repair system for the lungs and skin.
That ties in quite well with my existing plans for the colony to be an ideal environment for its members, but requiring protective gear for outsiders to come visit. (My initial plan was simply for jumpsuits which flashed at the right wavelengths and in the right patterns to avoid triggering instinctive defensive behaviours.)
http://www.chm.bris.ac.uk/motm/GFP/GFPh.htm
They can make many glow in the dark chemicals, which they did by taking a fluorescent protein and mutation it. These could be used to alter bioluminescent lights.
As the saying goes, "Excellent". I now get to do a bit more digging on ECFP.
u/ArgentStonecutter [+3] Emergency Mustelid Hologram (an hour later)
Blue turns out to be a really difficult pigment to make. Most animal species that have blue coloration do it via refraction effects.
u/DataPacRat [+1] Amateur Immortalist (11 hours later)
https://www.google.ca/search?q=ecfp+fluorescent+protein&tbm=isch :)
u/ArgentStonecutter [+1] Emergency Mustelid Hologram (13 hours later)
Is this something that's efficient enough to be used for external signalling like the common green/yellow luciferins?
u/DataPacRat [+1] Amateur Immortalist (16 hours later)
If not, it appears to be an easy protein to tweak and improve: http://www.nature.com/nbt/journal/v22/n4/full/nbt945.html , http://www.allelebiotech.com/mTFP1 .
u/SvalbardCaretaker [+3] Mouse Army (3 hours later)
Solar energy: https://en.wikipedia.org/wiki/Shockley–Queisser_limit
Max strenght of C materials would probably diamond. https://en.wikipedia.org/wiki/Young's_modulus
For nanotechnical energy storage limits, Neal stevenson in "diamand age" uses "one nanotech hand granade has more energy than a consumer gas tank" - dont know how hard that one is.
As for light production, you can of course have basically any frequency in the available visible spectrum, without stepping on anyones toes.
Superconductors, science is not yet done and records get broken every year. Progress is still slow, my bet is on there being room-temperature supraconductors.
https://en.wikipedia.org/wiki/Limits_to_computation
Rare elements, you have again pretty much full freedom. Uranium/thorium etc are interesting for easy energy density, but if you have nanotech/superconductors you would use fusion most of the time.
u/Transfuturist [+1] Carthago delenda est. (4 hours later)
For energy storage, nanotech represents the possibility of stable ultracapacitors, as capacitance depends on the surface area between the two, er, layers. IANAEE. This also means that they could be made to degrade catastrophically, with ahem energetic results, but I'm not sure what that would look like.
u/Farmerbob1 [+2] Level 1 author (19 hours later)
Well, I've played around with some carbon in one of my original fiction works. This stuff was seriously considered, but I certainly wouldn't say it's all rational.
If I'm remembering my math right, carbon nanotube twisted fibers can create muscles that are 200 times stronger than human muscle in cross section.
The character that I created was human, with an AI presence within his body that basically forced him into trans-humanism, not entirely against his will, but not without a lot of irritation and misgivings over time.
Before he started being able to reprogram matter using Handwavium, The AI had replaced his bones with layers of graphene bound together with carbon nanotubes. Artificial spider silk was used to create subdermal armor. His muscles were threaded with twisted carbon nanotubes. The armor he wore was layers of graphene, bound together with carbon nanotubes, and padded between graphene layers with silk.
His body generates a hyper oxygenated chemical which is roughly as energetic as jet fuel. This is what the AI in him uses for energy to power the nanites which are basically replacing most of the mitochondrial functions. It generates a LOT of heat when he goes beyond human normal exertion levels.
To deal with the heat of extreme exertion, the armor is covered with a matting of nanofiber hairs designed to create an absurd amount of surface area to wick heat. The armor is not worn like normal armor. There are carbon fiber straps that are drawn through the skin and attached to the bones and the armor by the AI, creating a nearly unbreakable connection to his skeleton, and a supplemental path for heat to leave the body. He has a blood cooler which is supplemental to the armor which ties into the major blood vessels of the chest. The higher his blood pressure gets, the more expanded the blood cooler gets, unrolling down his back like a cartoon red carpet, exposing more and more supplemental cooling surface area.
Needless to say, he has a pretty severe weakness to heat. The same armor that keeps him from cooking himself can kill him quickly if he's set on fire and can't very quickly deal with the fire.
If you want to use a bit of that, fine. I'm sure that at least parts of it won't be rationally justifiable, but I suspect that some parts of it might be useful.
u/DataPacRat [+3] Amateur Immortalist (a day later)
It generates a LOT of heat when he goes beyond human normal exertion levels.
some parts of it might be useful.
Reminding me that exerting superhuman strength is likely to generate superhuman levels of heat, which would need to be handled to prevent the brain from frying, is almost certainly going to be useful. :)
u/Farmerbob1 [+2] Level 1 author (a day later)
One of my other characters in the series had a massive body at one point, and generated isopropyl alcohol as an alternative to water-based sweat. Again, dangerous around heat.
u/DataPacRat [+2] Amateur Immortalist (20 hours later)
Could someone check my math?
Cleveland gets just over 2200 hours of sunlight per year. Sunlight contains around 1300 watts per square meter. If we're using sugarcane metabolism with 10% efficiency, then multiplying that out seems to suggest that a square meter of collecting surface provides a squinch over 1 gigajoule per year.
A baseline human metabolism needs about 2000 kilocalories per day, which multiplies out to about 3.06 gigajoules per year.
I'm at least 10% confident that I've made a mistake there - that even with genetically tweaked sugarcane biochemistry, you'd need a lot more than 3 square meters to provide the energy needs of a baseline human's metabolism. (And that isn't even getting into enhanced metabolisms, yet.) Am I missing a few layers of inefficiencies, did I mix up which version of calories to use, or blunder in some other way?
u/Farmerbob1 [+2] Level 1 author (a day later)
Hrm. Cleveland gets about 4.07 kWh/m2 per day
A kWh = 3,600,000 Joules
a Joule = 0.000239005736 kilocalories
A kWh = 860.4206496 kilocalories
A human needs 2000 kilocalories per day
A human needs 2.324 kWh per day
Assume 10% efficiency
A human then needs 23.24 kWh per day
A human needs 5.71 m^2 of Cleveland average annual solar energy at 10% efficiency to meet caloric needs.
5.71m^2 is a lot more than 3m^2, but probably still a lot less than you were expecting.
It can be difficult to really grasp the concept, but most animals are quite efficient if they aren't exerting themselves heavily and are in good condition. Michael Phelps at his peak ate 12,000+ calories a day to allow him to train.
We rarely need to accommodate temperature differentials in excess of a few degrees from our core body temperature. We have no processes in the body that I am aware of which require phase changes in any matter. Hundreds of millions of years of evolution have made our cellular processes quite efficient, even if we as a species have only been around for a pittance of that time.
u/DataPacRat [+2] Amateur Immortalist (a day later)
5.71m2 is a lot more than 3m2, but probably still a lot less than you were expecting.
Earlier today, my guess at my potential mistake was that the '2200 hours of sunlight per year' figure I used didn't take into account inefficiencies from the angle the sun was shining at, and I Fermi-estimated that that roughly doubled the surface area needed. 6 m^2 per human seems to be close enough to the ballpark of 5.71 that I think we're on the right track, and I can start scaling up the figures to deal with cyber-driders, soldier castes, and other such anatomies.