Well, yeah, that's what this whole thread is about.Starglider wrote:Actually energy is the main limiting factor.
Something, again, easier said than done. All food today is from industrialised agriculture like that of the American midwest. To convert to even a significant fraction of this model would require significant investments in time and energy, assuming it is even viable for the ever growing populace. A lot of waste exists in the system today that could be rooted out for starters and cheaper.
Given indefinite energy supplies (for chemical processing, construction and lighting) and unrestricted genetic engineering, vast amounts of food can be grown in a relatively limited amount of space (with hydroponics and quorn-type food reprocessed from fungi, bacteria and algae).
Yes, but even with the massive benefits of such plants in Australia which they're having to look at now, there is always the problem of getting the water to places nowhere near the coast (the coastal regions having the majority of the wealth and also being the most vulnerable to global warming).
Large scale desalination becomes practical with abundant (i.e. lots of solar or fusion) energy.
No doubt about that. It's a wait-and-see thing now since industry and gov'ts don't seem to really be dedicated to CO2 or other GHG cutting measures (50% by 2020? Pathetic).
This will be a short term issue as long as their are fossil fuels left. Once they're (essentially) all gone, either we pumped out enough CO2 to make the earth intolerably hot or we didn't - there probably won't be much we can do to make a difference (late stage carbon capture and reforestation will help, but not much). Assuming CO2 levels eventually return to normal without cooking the earth, waste heat is eventually an issue. By the time we get to that point macroengineering solutions such as sticking lots of IR-absorbing plates at the Earth-Sun L1 point will probably be practical.
Which doesn't change the fact that reserves does not equal production capacity. We have enough uranium now to last us hundreds of years at present rates, but when populations are growing along with their energy use per capita, this forms a bottleneck. All of the above assumes infinite energy, which is the issue we're looking at now that may make or break the species as a whole (not looking at the human factor and only looking at whether it's technically feasible is like programming software without taking into account the user). There will always be an upper limit to our population in a closed system like Earth (matter-wise, obviously the sun inputs a great deal of energy every second). There is also only so much land for people to live, cultivate and manufacture on. So saying we can recycle, use renewable energy and so on is missing the point. It is all finite and growth of the economy makes the absurd assumption of infinite resources, and so humans will have to, whether they like it or not, stop growing somewhere down the line. It happens with every species, and technology is not going to alter that. Colonising other planets and using resources outside our planet is the only alternative, but after you've eaten your way through all of Sol, you face the same situation again, and so expansion goes on and on. It would be interesting if in the centuries to millennia this takes place, evidence of another species doing the same will be found. Perhaps the Fermi Paradox will require we never reach that far to ever find out from whatever unknown factor may or may not be inhibiting such ventures.Commodities shortages are not equivalent to energy shortages because they are not actually used up. When we dig up ore, refine it and build it into something we are turning a diffuse hard to get at source into a highly concentrated easy to get at source. It's not as if we're firing all this copper and iron and tungsten off into space - it's sitting around in highly refined form just waiting to be collected up and melted down. When the cost gets high enough to justify this, it will be. Whoever said early that the Greeks had it easier than post-apocalyptic humans would (finding fairly pure lumps of metal on the surface) was a moron - post apocalyptic humans rebuilding civilisation would find a vast amount of easily worked metal (and nice concentrated metal oxide sources) all over the planet. Shortages of things like fertiliser are a little trickier, because we spread those elements out a lot more, but it's nothing that abundant energy, chemical engineering and genetic engineering can't overcome.
Shortages of usable energy are the only carrying capacity type problem that rate as a major risk. If we get over that, things like biological warfare (or just superplagues), global nuclear war, militarised nanotechnology, self-enhancing AI and even asteroid impacts are a more serious threat to human civilisation.
Of course, human affairs and natural disasters will always be there to prune us off even before we get anywhere near the next major Liebig law incorporating factor.
. Firstly, we don't know how to make room temperature supercondutors yet (even in theory) and chilling a cable of that length down to LN2 temperatures is going to require a lot of extra energy and mass. Secondly there's the problem that superconductors have relatively low current density thresholds before they stop superconducting (often violently, if there's a lot of power going through the system), compared to the thermally limited current densities achievable on conventional copper cables, which is going to drive up the elevator mass even further. Your best bet is probably some sort of 'hyperconductor' - materials that transmit electrons near-ballistically at room temperature, for a very low but nonzero resistance. There has been a flurry of research recently on ballistic electron transmission in carbon nanotubes, so you may get lucky and be able to reuse your elevator structural elements as power cables.
