One morning, suddenly, all humans and any human-crafted things (roads, buildings, technologies ...) vanish, with the only exception of one single city and its inhabitants. How long can the metropolis keep functioning without the rest of human civilization?

This takes place on an Earth-like planet (but not Earth!), with our current technology level. The city is about the size of New York and is placed in a similar environment, but instead of being on the coast, it sits next to a river. The river is approximately the size of the Mississippi River.

By function I mean continues to contain at least 50 percent of it inhabitants.

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    $\begingroup$ How big is the city? Where is the city? How much of the city remains? Are there any farms nearby? If you can provide some more details you will get better answers $\endgroup$ – Chris J Aug 19 '16 at 14:17
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    $\begingroup$ Can you elaborate on what you include in "human made things"? For example, what would happen to an orchard? Would it disappear because a human planted it? Would the trees disappear because they were bred into existence from their natural wild forms? $\endgroup$ – Rob Watts Aug 19 '16 at 14:17
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    $\begingroup$ What do you mean by functioning? There will be food for a day or two, so normal function will stop almost immediately. On the other hand, it will function for a very long time as the home of small group of cannibals. $\endgroup$ – Cyrus Aug 19 '16 at 14:17
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    $\begingroup$ Similar to this question $\endgroup$ – user2448131 Aug 19 '16 at 14:31
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    $\begingroup$ also is it an metropolis with guns or without? is it a metropolis that had alot of green spaces and gardening tools? how likely is a riot? does the metropolis have a good leader that people will listen to? asking the big questions $\endgroup$ – Necessity Aug 21 '16 at 0:40

10 Answers 10


Not very long

A Metropolis consists of a lot of people in a small area. Unless we're talking about a science-fiction high-tech metropolis, they don't produce their own food, and they don't produce their own power. Otherwise, food is continually brought in from surrounding areas, and the power stations powering the city are somewhere nearby but outside of the city.

So immediately, all electricity is gone. It's unlikely that many people will have enough non-perishable food (since refrigerators aren't running anymore) for more than a week or two.

In order to survive, everyone will have to abandon the metropolis. With all roads outside of the city being gone, most vehicles will be useless and people will have to proceed on foot. Unfortunately, there's not going to be enough food for everyone in the surrounding areas unless the city was surrounded for miles and miles by orchards that did not disappear - for the amount of people that you can expect to have in a metropolis, it will be like a swarm of locusts leaving the city.

Once everyone is sufficiently spread out, both through death and people getting farther from the city, people will have a chance to survive. A lot more people will die due to accidents, disease, and being unable to figure out how to survive in a low-tech situation, but chances are good that enough people will survive for the human race to continue.

  • $\begingroup$ Though alot of people might go back for the winter. $\endgroup$ – Necessity Aug 21 '16 at 0:44
  • $\begingroup$ Also vehicles wont necessarily be useless as most vehicles can go on some slightly rough terrain and the question never said that nature grew back in the places civilization vanished, so really we would be left with some pretty good dirt trials and wide open clearings. Though the question asks how long the metropolis lasts so this doesn't matter. Very few people will stay there and its best use is a place to hole up from a harsh winter. $\endgroup$ – Necessity Aug 21 '16 at 1:01
  • $\begingroup$ @Necessity It's not only the roads, fuel will run out pretty much right away. All the industry for making, transporting and storing fuel is mostly outside of such a metropolis. $\endgroup$ – Peteris Aug 21 '16 at 8:48

Hours to Days.

T+ a few seconds; unless all the cities power requirements are met from within itself (unlikely), power dies in many if not most parts of the city. If power IS internally supplied to the city, these same things still happen, just a little slower. The internet dies horribly, as does just about everything long distance that depends on it (modern civilian telecom). Motor traffic comes to a standstill as traffic regulation devices stop working.

T+ Minutes; things will be mostly calm as your individuals stumble around and flick circuit breakers, commiserate with the neighbors about people driving their personal vehicles into telephone poles, and muse that they can’t get anything done at the office. Slowly it will start to sink in that this is not a local thing, or a quick-fix thing. Battery operated devices that connect to satellites and people with functional radios notice they can't contact anyone or anything outside the city; Ex. GPS and HAM radios. Rumors of doom, world war, alien invasion spread from within the city. (per Mindwin suggestion, thanks.)

T+1 hour and people start to die; lack of response of emergency services, hospital patients waiting on the transplant that was en-route, etc. Worse, stories about how the outside-world is just gone start to propagate inwards from the cities edges. People generally aren't panicking yet, but the undercurrent is there.

T+2-6 hours; things start going down hill; any place with food and bottled water is emptying or already empty. Individuals start to panic at this point, not able to charge their purchase to their credit cards as the processing facilities are gone as is the telecom network; theft and small scale looting starts.

T+6-12 hours; looting and riots. People are in full panic mode as stories of the outside world being gone penetrate to a majority of individuals. Food is gone from public stores. Emergency services are totally overwhelmed (being only able to deal with a 5-10% disturbance, a near total disturbance causes them to become totally ineffective.) Someone starts a fire.

T+ 12 hours; Anarchy

T+ 2 Days; people start to starve (just the start of the starvation process; people feeling true hunger for the first time in their life). A modern city only holds a few days of food within itself to support its population, and some wont have any food stores at all. Without massive and constant importing of food from outside mega-industrial-farms, there is simply not enough to sustain the majority of the population. Some individuals and groups realize this and attempt to escape the city by traveling out, looking for a better environment, Meanwhile the City steadily degenerates as people start killing and stealing from each-other more often for basic necessities.

T+ 1 Week; Large amounts of the city's population are dying. Food is gone and people are resorting to any method they can to get more. Increasing numbers are attempting to leave the city for a better place, but the resources on the way have already been consumed by preceding travelers, making it harder for the following ones. The later groups attempting to flee, weak already from starvation, are not able to travel far before they too expire.

T+ 1 Month; the city has turned largely into a ghost town and nature is starting to reclaim areas.

At almost any point you might find survivors (if there are any) from outside the city trying to make their way into or towards it, especially in the first few hours, but the numbers of individuals able to actually approach and enter the city are going to be so low as to be insignificant.

TLDR; Food and water run out quickly, It's doomed.

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    $\begingroup$ @Nex Terren, I actually think Mindwin has a point; if enough of the fringe people all start saying something often and loud enough, some of the non-fringe people are going to listen, even if not many or very seriously. People will go "yea sure, whatever..." but now the thought is in the back of their head it will only get bigger the longer nothing comes along to dis-prove it. $\endgroup$ – Marky Aug 19 '16 at 16:14
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    $\begingroup$ Okay, @Mindwin, as a tech-oriented person which one of these are more likely: A) World is going to Hell. B) Military switched GPS to military mode. C) You found a software bug! $\endgroup$ – Ranger Aug 19 '16 at 18:22
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    $\begingroup$ @NexTerren i usually carry at least my tablet and my phone, sometimes other devices too (several PkMnGO accounts). if BOTH/all devices show zero sats for both GLONASS and GPS, i'm expecting nukes, zombies, aliens or the likes very soon. Also internet, cellular signals, power and radio going dead? Sorry, end of world incoming. Also, software bugs don't happen that way. One device could be malfunction, but in the scenario painted, nope. $\endgroup$ – Mindwin Aug 19 '16 at 19:23
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    $\begingroup$ People do not starve in a matter of 2 days. I have personally fasted from all food (water only) for 39 days. Perhaps a select few with diabetes would have a reaction, but it would not be starvation. Weakness from starvation would start to occur at about 14 days, assuming water is to be found or produced. More would die from the wildfire progressing through the city (and potential panicking stampede thereby) than starvation would ever claim. $\endgroup$ – Keeta - reinstate Monica Aug 19 '16 at 20:16
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    $\begingroup$ @Keeta in my understanding people don't starve all at once, its a process that takes some time. I'm impressed that you've been able to fast for so long, I'm quite sure that I wouldn't be able to make it even close to that long. Its less about the starvation killing then the increased panic at that point; remember your talking about people that have probably never felt true hunger even once in their life. $\endgroup$ – Marky Aug 19 '16 at 21:07

A few days. Without supporting infrastructure, the city is immediately without electricity and -- more importantly -- water.

Food will last for days, maybe even weeks. Being without electricity isn't a problem for survival, but being without water is.

There aren't many sources of water in a city. Even if the city has a river, getting water to the households will be difficult. Compared to the number of inhabitants and the area a metropolis typically covers, having access to a big river does almost nothing. Having more, but smaller rivers would be more ebneficial.

The ancient Rome had the river Tiber flowing through it. In modern standards, it wasn't a metropolis. But they still needed an intricte system of aqueducts (who got the water from the "nearby" mountains), springs and public beths to get water to everyone. It is considered one of the major achievements of the time.

Modern systems all work with electricity. Without pumps running, the water pressure in the pipes will drop immediately.

People will start riots immediately. Stores will be raided for supplies. Those won't last long. After a few days, people either start dying from lack of water or leave the city. Since there isn't anything left in the wilderness, there will be plenty of sources of fresh, uncontaminated water.

So, a mass exodus paired with a lot of deaths will leave the city almost empty. There will be only a handfull of people who can gather enough water from roofs etc. left. But it will be a ghost town, nothing coming even close to 50%.

Metroplis are the most densely populated areas on the world and at the same time the most hostile in terms of survival. Lots of concrete, and not much opportunities to get fresh water or grow food, except for filtering rainfall from rooftops and using public parks.

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    $\begingroup$ But this city is situated along a major river... $\endgroup$ – user2448131 Aug 19 '16 at 15:14
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    $\begingroup$ @user2448131 How do you suspect the water is distributed from there? There will be millions of people needing water, and since there is no electricity, how will they get it? Pretty much the only way to get it is with buckets and then refill into containers. Thats not feasible for even a couple of hundred of thousands. Then there is the problem withraiders that will simply get the water from people coming back from the river. $\endgroup$ – Polygnome Aug 19 '16 at 15:28
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    $\begingroup$ Rome, Paris, Baghdad, Constantinople all had over a million inhabitants without any electricity to distribute water. If the water doesn't come to you, you go to the water. I just don't see the water being the main issue. Chaos for sure, but people can organize things as basic as collecting/diverting water. Maybe I give people too much credit. $\endgroup$ – user2448131 Aug 19 '16 at 16:36
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    $\begingroup$ @user2448131 The difference is, those cities grew slowly without electricity, and none of them has ever been as populated as New York these days. No electricity all of a sudden with all the people so very much depending on it ... I can't help myself but get on Polygnome's side. In a metropolis based on a river there are actually lots of areas the water is inaccessible and some millions flooding the accessible ones, I imagine people getting trampled to death, hundreds falling into the river and drown. People might accustome to the situation but that will take days or weeks. $\endgroup$ – Otto Abnormalverbraucher Aug 19 '16 at 16:53
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    $\begingroup$ @user2448131 have you ever been to such a city? The romans had an intricate system of aqueducts (which work by gravity) and public baths and springs to make sure water gets to everyone. It was considered one of the biggest achievements of their time, and was technology that was exported elsewhere. Such systems do exists in moden cities as well - but they depend on electricity. Water needs to be pumped nowadays. No power 0 no pumps = no pressure = no water. Furthermore, there were only a small number of multi-stoy buildings. Collect water on the roof when there are three parties above you? $\endgroup$ – Polygnome Aug 19 '16 at 17:38

I'd disagree with other answers that there would be many deaths.

A major city has a lot of resources. Most significantly, it has a mayor and top-down organisations for health, police, fire, and general civic governance. It should also have decent stocks of fuel, medicine and food to handle the transition. The first step for any sensible mayor is to declare martial law (and if anyone argues about whether that's legal, power grows from the barrel of a gun, and he's the one with the most guns). If he's smart then he'll ask for volunteers to be deputised, so that there's less us-and-them. With all the city's administration still in place, anarchy should be much reduced.

After that though, I concur with everyone else - the next step is in the direction of the exit. People need food and fuel to live, and cities can only exist if someone's bringing both in from outside.

This does depend on your definition of where the city starts and ends, of course. Detroit has a lot of bugger all in the middle, and most of its inhabitants live in surburbs 20+ miles from the actual centre of the city. Your average suburban American house might have enough land to live on, at least if your neighbours move out and you can use their backyard too (going by your 50% rule).

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    $\begingroup$ It takes about one acre to feed a single person. The average lot size (minus the house) is about 1/4 acre. So a family of four (if the two kids together eat as much as one adult) need to have 11 neighbors move away in order to have enough land to support themselves. $\endgroup$ – Rob Watts Aug 19 '16 at 17:08
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    $\begingroup$ I think you are over-estimating the ability of the government to respond; and how likely the responders are going to care in this situation to a governments call. Also; exactly how much 'land' is available. take a look at New York in google maps with satellite view... there is not a lot of ground there that is not also building. $\endgroup$ – Marky Aug 19 '16 at 17:16
  • $\begingroup$ " It should also have decent stocks of fuel, medicine and food to handle the transition". Yes, medicine is enough there for a short while. police and Fire department don#t do anythign to feed people and provide water. fuel is quickly depleted, as are water reserves, especially water reserves. Martial law is only enforceable with military power, and barracks are usually not inside any city, so they are wiped. $\endgroup$ – Polygnome Aug 19 '16 at 17:30
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    $\begingroup$ "Your average suburban American house might have enough land to live on, at least if your neighbours move out and you can use their backyard too (going by your 50% rule)." We are talking about a big metroolis. Nothing suburban there, only a lot of concrete and steel, maybe some parks. definitely not enough to feed people long-term. When talking about a mtropolis, I have ten million upwards in mind, not your run-of-the-mill small city. $\endgroup$ – Polygnome Aug 19 '16 at 17:32
  • $\begingroup$ @Polygnome NYC has only 8M inhabitants. Thus. in the US, a major metropolis has more like 4 million people. $\endgroup$ – RonJohn Dec 10 '17 at 11:52

To counter the doomsday scenarios presented, which look at cities like Detroit or New York, I honestly think if the city were similar to where I live (Redmond, WA), the end result would be different (although there would still be the panic and some riots).

The tech industry here has made Redmond a fairly well off city, and much work has been done to the parks and infrastructures, making it very friendly to bicycle and pedestrian traffic. There's a network of wildland parks running through the city. It sits between two lakes and there's a river running through it. For the most part the city is pretty edible.

Despite being a tech center (or possibly because of it), many who live here spend the majority of their free time in the surrounding national forest learning about the wildlife. Many of them would have at least a basic understanding of where to get food.

Although this sounds more like a tourism pitch, if you wanted a scenario where a metropolis survives such an event, you could have the city in question be set up similar to this so that the transition would not be as drastic.


Wartime cities under siege give us the closest glimpse to this scenario - and the human ability to survive. WWII Leningrad (St. Petersburg) was close to full cut off and suffered 900 days under siege. The city was expected to starve in a matter of weeks. The Council of Deputies of the Leningrad administration organised "First response groups" of civilians. In the next days the entire civilian population of Leningrad was informed of the danger and over a million citizens were mobilised - wikipedia In the end, there was major loss of life from starvation. A city whose goal isn't to hold back an enemy would be able to marshal those some resources towards long term survival including depopulating and spreading out.

  • $\begingroup$ en.wikipedia.org/wiki/… "Vital food supplies were thus transported to the village of Osinovets, from where they were transferred and transported over 45 km via a small suburban railway to Leningrad." When winter came, and Lake Lagoda froze, that was another transit path. $\endgroup$ – RonJohn Dec 10 '17 at 12:01


I think current studies show 1-2 months with no interaction.

The general idea in these "studies" are that without power food will spoil before it can be consumed. Canned foods and the like will last till they are consumed.

Fresh fruit, meat, dairy, and others will straight up spoil after a day or so with no intervention.

I don't agree, with these "studies". They are usually done to support a documentary or such. Yes food will spoil, but I live in FL, and when we get with a hurricane we KNOW our meat supply will last 2-4 weeks, if we take moderate care with the freezer. We can extend that to months with the use of fire to cook the meat. Cheese will last near forever if kept dry. Fruits and Milk will spoil fast. But lets pretend these "studies" are accurate.


This is a big one. A big city has a VERY limited water supply. Here in Tampa, the gravity fed water supply is around 2 hours. What's worse, as we discovered here recently is that as the pipes carrying the water dry out, they are damaged beyond repair. We had a main line break, and the city had to shut the water off for a few hours. It took months of replacing lines before the staus quo was returned. Because the city had power they could reroute the flow, but that would not be the case with out power.

In addition, all city water would become non-potable after an extremely short outage. Just moments. So you would need to boil your water. I think the idea here is that without constant pressure, back flow occurs and the water could become contaminated.

These are from personal experience, so take with a grain of salt.


When the power when out in the northeast a few years ago, everyone though NY would tear it's self apart. It didn't. Most cities are great with services and would continue to function in an "emergency" mode till a different system was put into place. Some may be overloaded. For example in the summer in FL, healthcare would certainly be swamped at first due to the heat. But cities are good at pulling this stuff together.

What happens

Nothing at first. Life goes on. An increase in heath issues is about all anyone would really be able to see. Water would become a problem fast, but it would also be solved fast. It's not hard to get water.

Cities sections would arise, neighborhoods would organis. Some of the more criminally inclined parts of town may start to have an issue, but do to the state of emergency that wouldn't last long. Some people would move away, but many would stay. Specially with the whole "if you were out side the city you vanished" thing going on. Power would be a priority, probably solar focused as there's not likely to be a huge coal deposit under the city.

In short order (hours to weeks) the long term plan for the city would be laid out, and the people would start focusing on "where did it all go"


My answer is very limited in scope and only refers to the internet, because dank memes > food.

Interestingly, if this metropolis is as big as NYC, the internet could remain somewhat functional indefinitely!

Most web services will operate a datacenter in this metropolis, and there likely will be DNS and cloudflare services too. If the city keeps its lights on (power from a local hydro dam, for example), many of these services will be accessible and functional--the internet is actually a lot more compartmentalized/local than you think! Video games that don't have master servers located in this city will have broken matchmaking, but direct ip matches should work just fine, and I'm sure someone will put out a master server patch pretty quickly for the most popular games.

Peer to peer networks should be fine too, provided they don't have a central failure point.

Fun fact: StackExchange has servers in NYC, so you'd be able to read this thread in your alternate universe!

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    $\begingroup$ Thanks for considering the non-essentials like communications infrastructure and entertainment. I really do hope Elite: Dangerous is popular enough to patch. $\endgroup$ – UIDAlexD Aug 22 '16 at 19:12
  • $\begingroup$ lol I could read my on thread while it comes true lol $\endgroup$ – Bryan McClure Aug 22 '16 at 20:44
  • $\begingroup$ According to the constraints of the Question, the hydroelectric station would have to be in the city. Otherwise, the dam and generators, plus all the transmission wires have disappeared. $\endgroup$ – RonJohn Dec 10 '17 at 12:05

I think the metropolis spreads out a bit but survives.

I was in a major flood a few years ago and our small town was cutoff for a little over 3-4 days. We lost water, gas, eletric, and phone (even the cell towers were down). A major city is very different, but I think there are enough important similarities.

For your scenario the first concern is water. You need it both for drinking and sanitation, and the rule is one gallon per person per day. In our town most people were out of water almost immediately and the river wasn't drinkable. But you've got the Mississippi, which is plenty. I don't see water distribution being the problem either, people are maybe spending a hour a day now carrying water from the river, but you have plenty of free time since jobs and schools don't mean anything any more.

Law and order. I don't buy the city-wide-rioting-until-everyone-dies scenarios. I think you're much more likely to see a police state or vigilantes if the police fail. There's a fair amount of fear and people will band together (in good and bad ways) rather than run amok.

Food. The refrigerator will stay cold enough for 48 hours. For us day 3 looked like a huge block party, since all of the meat needed to be consumed. I'd expect the same thing in the city. After the meat is gone most people have a decent amount of dry food.

Sanitation. Without running water, which requires electricity, sewage is difficult. The river could be poisoned. This is going to make things miserable, but probably not reduce the city to 50%.

In the short term (first several weeks) the city is probably fine, though it wouldn't feel like it.

In the long term, a city has enough expertise to create farms, restore electricity (perhaps hydroelectric in this case), etc.

So I think this comes down to the medium term (weeks 4-12 or so), and whether they can ramp up food production quickly enough to avoid mass starvation. I'd do the calculation this way: 3 weeks eating out of the pantry 4 weeks depleting the grocery stores 4 weeks to die of starvation

The city has about 11 weeks to produce enough food for each person. Corn, potatoes, carrots, tomatoes, etc, all take 6-10 weeks from plant to harvest. It is really close.

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    $\begingroup$ For the proposed scenario it seems that you're seriously overestimating the amount of food stored "in the system". First, people don't really have a lot food stored - especially in a metropolis where most people live in apartments without a pantry and with a general lack of storage space. If 10% of people have 10 weeks of food, 1% people have 1 weeks of food and the rest have a day or two of food, that implies just 1 week of average food stores - assuming everyone is eager to share. $\endgroup$ – Peteris Aug 21 '16 at 9:05
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    $\begingroup$ Second, the stores don't have a lot of inventory. Their inventory turnover stats e.g. csimarket.com/stocks/singleEfficiencyit.php?code=WFM imply that the food retail companies as a whole only hold ~2 weeks of their normal sales, including goods stored their wholesale distribution centers, so in stores that are actually in the metropolis there's likely less than 1 week of normal sales. And in a metropolis, a huge portion of calories eaten comes from restaurants instead of grocery stores, and those store even less supplies, needing transport bringing in food to city every single day. $\endgroup$ – Peteris Aug 21 '16 at 9:07
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    $\begingroup$ So for me it seems that it adds up to something like 2 weeks of normal food, stretchable to 4-6 weeks with strict and efficient rationing (which may not happen), and not enough to have most people be alive for harvest. - assuming that they could plant them so quickly in volume. In mostly suburban areas or less dense areas it would be easier, 50 years ago it would have been easier, in less advanced countries it would be easier (e.g less optimised inventory) but if we're really talking about the big modern metropolises e.g. NY then this is the worst possible place to be cut off from outside. $\endgroup$ – Peteris Aug 21 '16 at 9:12
  • $\begingroup$ Groceries - Kroger (which I think is probably more representative than Whole Foods) is closer to 1 month. But I think you're right about the restaurants, there is a good chance that food would have been trucked in from one of the places that is gone. $\endgroup$ – Geo4 Aug 22 '16 at 0:50
  • $\begingroup$ Pantries - I haven't lived in a city, but people have a lot more on hand than they think. Usually stuff you don't want to eat normally. Condiments, peanut butter, least favorite canned food, bag of flour, all the stuff you might throw out when you move. But yeah, it might be shorter than I'm estimating. $\endgroup$ – Geo4 Aug 22 '16 at 0:58

About one billion years


With matter-manipulating technology, which seems to be already being forged through quantum physics, such a city could last forever, or until its planet´s sun become a nova. With an advanced AI (perhaps a next-generation IBM Watson) controlling this technology and the machinery used to manipulate matter directly on subatomic levels, dwellers could live free of work or any other hindrances to simply enjoying life. Of course, after a good while those people surely would become some sort of Elois, destined to be just "happy meat".

Such a city could endure almost any kind of environment, no matter the planet or solar system, or even a charred post-apocalyptic Earth. And completely isolated from the outside, quantumly generating all its material needs.


However, human beings need more than atoms. Challenges do define a rich existence. See the most advanced welfare states on Earth. They also have the highest suicide rate. Isolation and perfect material well-being does not assure survival. One cannot assume that mind and body can be well maintained apart, for they are essentialy the same thing.

I apologise for the philosophical digression, but I just can't imagine a world without the Spirit.

Arthur C. Clarke for matter-manipulating technology and self-conserving city: The City and the Stars
H. G. Well for Elois: The Time Machine.

  • $\begingroup$ Looks good -- thanks! The English is fine. Now that you've added the explicit statements about this being feasible today or very soon, I retract my objection and will clean up the comments. $\endgroup$ – Monica Cellio Aug 22 '16 at 23:00
  • $\begingroup$ Just added a few more bits. Thanx Monica! $\endgroup$ – Divsign Aug 22 '16 at 23:16

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