The exhaustion of resources appears to play a large role in reducing the number of alien civilizations which might be touring the galaxy at any one time, and so thinking through how bad it has to be would be useful in gaining a better appreciation of the impact. A recent post discussed construction of the large arcologies needed for very high levels of recycling. But simply living in an arcology of that size implies there would need to be transportation of some kind. Would that be the worst sector for recycling losses? Assuming there is more than one arcology on the alien planet, would transportation between cities be a worse loss that transportation within the city?
An earlier post, dedicated to obtaining reasonable limits on population for an alien civilization living on one planet, with all of them at a high standard of living, as measured in energy consumption, came up with a population limit of 10 billion, divided into a thousand cities of 10 million citizens each. The cities were, for the purpose of getting some idea of the scale, 10 km by 10 km in footprint, and were 100 stories high. Travelling 10 km by walking, or whatever aliens use as a substitute for walking, seems like a time-consuming thing, if done frequently, so some method of speeding up transportation would be needed for this. Vertical elevators seem to be a reasonable choice, but if there were ramps, small vehicles could be used. Horizontally small vehicles would work, or some sort of tram system would as well. Ten kilometers is not long enough to require high-speed transportation, so anything imaginable would work, and not much volume inside the arcology would be necessary for it. Furthermore, short distances like that would allow even batteries from our era to be used, to say nothing of what might be developed after a thousand more years of science. So, electricity can be used, which sets a bound on how much recycling losses might be caused. If something is more efficient, relative to recycling, that would lower the bound even more.
So aliens could putter around the city in small electric vehicles, small enough to fit inside an elevator, and get from one corner of their city to another in some minutes. An arcology is necessarily designed to minimize transportation, so the average trip would be much less that this, and likely most trips would be short walking distance ones.
Other transportation within the city might involve heavy loads being moved from one part of the city to another. There would be large load corridors, and the same argument about the maximum distance being short enough for electric power, and the usual distance being short as well, indicate that there is no need to consider than transportation within the arcology would be a large sink for recycling. Vehicles and elevators and trams all wear out, leaving some residue in the environment, which would be the largest recycling burden. Just to get some ballpark estimates, consider a typical vehicle which is in constant use for its lifetime, running at 10 km/hr 12 hours a day, meaning 120 km per day or 40 thousand km/ year. If there were tires on it, and they wore out at these low speeds after 160 thousand km, tire wear might be 10% of the weight of the tire, meaning tread loss, over four years or 2.5% over one year. This compares with 0.1% as a target. If this is the most significant loss that the vehicle suffers, and tires are 3% of the total weight, the vehicle is suffering a 0.08% total annual weight loss.
It is, of course, not the same thing to lose tread as to lose metal parts of the vehicle, and lumping them all together may be an illegitimate way of figuring out overall recycling capability. One cannot make new tires from old metal parts of the vehicle. Can future technology make tire tread that lasts ten times as long as we do? Can tires be dispensed with and some levitation be used instead which has very low recycling losses? Can tires be made of other materials which share the composition with body parts? Compare these engineering challenges with the effort needed to solve them. An advanced civilization mastering all technology that is physically possible and which recognizes that high recycling rates are necessary for its survival would likely figure out how to beat this loss. The fact that we might find a 2.5% loss when a 0.1% is desired seems a solvable problem, given the long time and large effort available to solve it.
This leaves intercity transportation as a possible recycling sink. The previous post indicated a thousand cities might be a reasonable estimate, and if the planet has a good fraction of its surface as area where cities can be built, they could be separated by up to half the circumference of the planet. Maybe 20 thousand km is a reasonable number for coarse estimating of the maximum travel distance.
If there were a large amount of travel on the planet, then it would be useful to see if the level of recycling losses on this longer distance transportation would necessarily much higher than some target figure like 0.1%. If there were very few trips, the losses would not significantly degrade the overall recycling rate of the alien civilization. So the first question is, in such an advanced civilization, what is the demand for long-distance travel.
There is no business travel, as there is no business, as everything is automated and done just the same this year as for the last hundred years. There is personal travel, but without migration, such things as face-to-face renewal of acquaintances would not necessarily occur between cities, but only within cities. Why would there be migration? There is no job-seeking which draws people from one city to another. Work is voluntary and occasional. Educational training would be transmissible from one city to another, with no need to go from one to another to be trained; and training in all cities would be optimized back in the days of the grand transitions. No city would have a monopoly on one type or even any better training or education than any other. There seems to be virtually no need for intercity travel for personal reasons.
This leaves tourist travel. The cities are all the same, but unless the planet has been engineered to be uniform, there would still be interesting places to go, where natural sights were the best. This could involve a large amount of travel, especially considering that there is no employment obstructing the use of time. The other side of this coin is that professional media experts could go to all of these, and record the absolutely best views at the best time of the day or year, and make them available to everyone. Going to a nature site would result in a poorer view of whatever is there, and not in all seasons, and not when the fauna is present, and so on.
What about relaxation? Perhaps the alien citizens like beaches, or mountaintops, or rivers or something else to simply go and relax there. Or perhaps relaxation is totally understood since the neurological grand transition, and relaxing is best done in a chamber best suited for it, with the environment chosen, the scenery chosen, special foods or drinks chosen, breezes chosen, motion chosen, and whatever else that could aid in relaxation already there.
What about competitive travel? Wouldn’t one city’s best athletes, debaters, poets, musicians, artists, and all the other things they might compete at which we don’t have a clue about, all want to go to the intercity competitions? The numbers are what make the difference here. A single person or team from each city doesn’t add up to much travel.
So far, travel numbers are low, and that means that even if recycling losses are worse in intercity transportation than elsewhere, the total isn’t going to be affected much. If that were all the possible losses, recycling would not be significantly degraded by transportation.
That isn’t all the possible losses, however. Generating new resources involves transportation of significant materials around the planet. Mining sources are not uniformly spread around the crust. And as far as mining goes, transportation is only one source of recycling losses connected with it. It deserves a separate post.
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