I most definitely did not just watch Avengers: Age of Ultron. But because it happens to be relevant, and not inspiration for this post (oh, no, it's just a coincidence), I'll provide some backstory. Heavy spoilers if you haven't seen the movie, and not just in the spoiler block below. (The very question I want to ask implies some plot details.)

Near the end of the movie, Ultron engineers a device that levitates a city, planning to raise it to a very high altitude and drop it, with the impact killing off the human race. The only way the Avengers can stop it is to destroy the city mid-flight, but that would kill everyone on it. So they have to get everyone in the city to safety in a very short time.

I'm not concerned about how one actually pops a city out of the ground, or about how one will destroy it before it hits again. I'm just thinking about the evacuation process. So let's assume the following:

  • Nobody in the Marvel Universe need actually exist.
  • Superheroes, fancy science, or other things that we don't currently have a hold of can exist, though.
  • The time period is present day.
  • The city's population is about half a million people. In fact, let's say it's Staten Island.
  • The landmass's exact size isn't relevant, but it is large enough to tear a big-ass hole in the Earth upon impact.
  • From liftoff to impact is about an hour.
  • You can have any rescue technology you want as long as it's not more advanced than the thing that brought the city aloft in the first place.
  • No one knew in advance that this would happen.
  • The goal is to save every single person. Every. Period.
  • We can worry about where to put everybody later, just get them off of this airborne deathtrap!

Given all of this, how would I save half a million people from a floating city in an hour?

  • 4
    $\begingroup$ "You can have any rescue technology you want as long as it's not more advanced than the thing that brought the city aloft in the first place." Well wtf is the thing that brought the city aloft int he first place? $\endgroup$
    – Aify
    Commented Jul 12, 2016 at 3:51
  • $\begingroup$ Agree with Aify, about what is that for a magic technology. But I'm 100% sure that my tool from this answer (search for: Note about Venus scrap, snake elephant) is capable to save: every single person. Every. Period. This tool is less advanced technology then gravity manipulation tools, almost our today level. You might to encapsulate any human, search for each, support their live if needed - and transport in any place where you need that. 15m to react, 15m to rollout, 15m evacuation, and 15 minutes break for lunch. $\endgroup$
    – MolbOrg
    Commented Jul 12, 2016 at 5:24
  • $\begingroup$ I think people (except for @MolbOrg, who should totally write a proper answer that I'd love to read) is focusing too much in how the city flies and not enough on the really interesting point: The goal is to save every single person. Every. Period. That's the difficult thing. The interesting problem. The rest is logistics, a side note, a paragraph, tops. $\endgroup$
    – xDaizu
    Commented Jul 12, 2016 at 15:19
  • $\begingroup$ @xDaizu idk, answered, feel free to ask if something not clear $\endgroup$
    – MolbOrg
    Commented Jul 12, 2016 at 21:13
  • $\begingroup$ Parachutes come to mind..... $\endgroup$
    – Thucydides
    Commented Jul 12, 2016 at 21:19

5 Answers 5


Without magic or insane future technology, it can't be done. It's hard enough getting a small group of people to do anything, much less 500,000 in the midst of a disaster.

People will panic, and areas of high densities of people, people will get trampled to death. Think WalMart on Black Friday.

Even if you were to attempt to rescue people, how would communicate with all 500,000 people? Not everyone will be watching TV, using a phone, listening to the radio, etc. Then there will be the people who won't believe there is a disaster happening.

Even if you could keep people calm and organized, the ability to move 500,000 people in an hour is impossible. There would be traffic jams, long lines, confusions etc. And that is just talking about the people who can move. There are people in hospitals, jails, and other places where they have no ability to be moved. You can't just hit pause on people in surgery.

Depending on the evacuation point or points, many people will not even have the ability to make it to the evacuation point in an hour. People will be stuck in elevators, trapped in buildings, unwilling to move etc. etc.

Speaking from personal experience, I was in a car, 15 minutes from home when a freak snowstorm hit. It took 5 hours from that point to get home. I also lived in the DC area during 9/11, it showed the ability for people to move in a sudden disaster was not possible. Everything was shutdown, people were literally walking out of the city as there was no way to get out.

Mass transit will not work either, electricity, communication, traffic lights, trains etc. will all be disabled.

In the end, without magic or super-advanced teleportation, it cannot be done.

  • 1
    $\begingroup$ I totally agree with you, even without the floating city part (that would disable electricity, phones, destroy most buildings, therefore blocking roads), it is not doable. $\endgroup$
    – PatJ
    Commented Jul 12, 2016 at 4:12
  • 1
    $\begingroup$ This is not a fun or interesting answer. Also, the reasons for why it can't be done are shallow at best. $\endgroup$
    – xDaizu
    Commented Jul 12, 2016 at 7:47
  • 3
    $\begingroup$ @xDaizu its not supposed to be fun or interesting. the OP asked for a reality check, and this is the reality. $\endgroup$
    – Keltari
    Commented Jul 12, 2016 at 14:57
  • $\begingroup$ @Keltari I'd argue that this site is about fun and/or interesting stuff. We are building worlds! And yes, sometimes a reality check may seem like it throws your ideas to the ground, and yet, it can be done in an interesting way. You can say "that can't be done" and give a detailed explanation. Or say "no, BUT..." and give a counter-proposition. That's the kind of "no" answer that make StackExchange great. Yours just seem... lackluster. But that's just my opinion. One opinion, one vote. A downvote. But hey, you still have more ups than downs so I might be in the wrong here! ^^ $\endgroup$
    – xDaizu
    Commented Jul 12, 2016 at 15:06
  • $\begingroup$ @xDaizu and i would argue you are wrong as he asked for a reality check. $\endgroup$
    – Keltari
    Commented Jul 12, 2016 at 15:07

"And today we proudly announce the grand opening of the world's largest parachute manufacturing and assembly plant! Here we have over HALF A MILLION parachutes ready to go at a moments notice! Hey, what is that shaking? Why are we lifting into the sky?"

  • $\begingroup$ This would be fine if you could plan, fund, build, inspect, and stock it within an hour. $\endgroup$
    – JesseTG
    Commented Jul 12, 2016 at 16:57
  • $\begingroup$ The parachutes are ALREADY there, ready to ship out, on the grand opening. They were riding a huge surge in the popularity of skydiving. They had a REALLY successful kickstarter campaign :) $\endgroup$
    – Jason K
    Commented Jul 13, 2016 at 13:25

The only thing that seems capable of lifting a landmass the size of Staten island airborne or floating for around an hour before falling to earth again could be a form of antigravity. Having established the existence of antigravity, then that can be used to rescue people from the airborne deathtrap because it's no more advanced that the technology that got it airborne in the first place. So there!

Since we now have antigravity, send in squads of police, armed force, ambulance corps, fire fighters and emergency services volunteers who will fly in courtesy of the standard antigravity flight-suits that would be standard equipment for rescue and emergency personnel.

While they can fly individuals from the floating landmass to the ground, but this will take too long. Hundreds of floating antigravity loudspeakers are sent over the landmass and its 500,000 people. Order them to run to the edges of the floating landmass and jump off. A large-scale antigravity field will allow all the falling people to waft gently to the ground (but most definitely not in the impact area). Persons with a fear of heights and who will be unable to jump off any floating landmass, will be transported to the ground by the personnel with antigravity backpacks and/or flight-suits.

The people who jump will enjoy the wonderful experience safely to the ground. Those who are transported to the ground by individual fliers will do so with with eyes firmly shut. Some of whom may simply to have kept their eyes closed as the fliers might simply transport from them deep inland of Staten island, carry them to the edge where the Staten Islanders can be dropped into the gentle arms (metaphorically speaking) of the large-scale antigravity (AG) field.

Because a large-scale AG field is operating below Staten Island this will in all likelihood extend the time Staten island is a floating landmass. But it also allows the setting up of an even larger scale AG field to keep Staten island airborne for as long as it takes to evacuate everybody.

There remains the minor problem of what to do with the floating landmass that Staten island has become, but this WB SE question isn't about that, so I will leave that as an exercise for the reader.

Personally, and this is just me, I'd waft the runaway Staten Island to where it originally came from and allow to gently settle back down to terra firma and it can resume being the Island New Yorkers love and cherish. YMMV.

I am sure people will be aware this requires a lot of social organisation to enable squads of trained personnel equipped with antigravity to rush to rescue of people trapped on floating landmass. Also the ability to deploy antigravity field generators capable capturing falling people and lower them gently to the ground. Good points! However, once antigravity is available then will be always the chance that some megalomaniac will fling landmasses the size of Staten Island in the direction of Up and suitable countermeasures will be put in place, in advance, to take care of emergencies like this.

if you want to protest -- But antigravity isn't part of today's tech kit. Yes how true. But if we didn't have antigravity, then there's no way Staten island would be sailing through the air for an hour before crashing. No need to rescue anybody. Basically you can't have one without the other. You know it makes sense.

  • $\begingroup$ You absolutly nail the point You can have any rescue technology you want as long as it's not more advanced than the thing that brought the city aloft in the first place., maybe even a bit overdone (xD) but I think you don't go in enough detail about the REALLY interesting point: The goal is to save every single person. Every. Period.. I would like an edit going in more detail about how to achieve that. :) $\endgroup$
    – xDaizu
    Commented Jul 12, 2016 at 15:17
  • $\begingroup$ Forgot the last zero on 500,00(0) mate $\endgroup$
    – Dent7777
    Commented Jul 12, 2016 at 20:42
  • $\begingroup$ Depending on how large the antigravity zone is, people could just step off the edge and float away. $\endgroup$
    – Thucydides
    Commented Jul 12, 2016 at 21:21
  • $\begingroup$ @xDaizu As requested the edit has been done. I have invented nothing more than was assumed to be part of the technology in the OP's question. $\endgroup$
    – a4android
    Commented Jul 13, 2016 at 6:35
  • 1
    $\begingroup$ @Dent777 Well spotted, matey. The extra nothing has been added to the answer. $\endgroup$
    – a4android
    Commented Jul 13, 2016 at 6:36

Hack and repurpose the device lifting the city.

If it has the power to lift the city, it has the power to bring it down safely in its original place. Or just keep floating it, if people like the idea of a flying city. Or if their previous neighbours prefer their new lake to having the city next door.

The technology of the device would probably be more valuable than the city with its inhabitants anyway. Not that anyone would say that out where media might hear it. So capturing the device and gaining control of it should be top priority in any case.

You might need to supply extra energy in form of generators.

  • $\begingroup$ I'm not sure if these assumptions are correct; a NASA space shuttle rocket can bring the shuttle up, but is unable to safely return it or keep it floating, stable. Still, an interesting approach if the technology does allow. $\endgroup$
    – Ranger
    Commented Jul 12, 2016 at 13:39
  • $\begingroup$ No, because the city has to be destroyed at the end of the hour; either upon impact or to prevent impact. $\endgroup$
    – JesseTG
    Commented Jul 12, 2016 at 16:32
  • $\begingroup$ @NexTerren The space shuttle rocket has easily enough power to bring the space shuttle rocket down. It just doesn't have the propellant or the programming. (Or even control systems.) Let us just say there is a reason I used word "power" in the answer and not terms like ability or capability... But yes, you are of course correct that you cannot generally assume that a device can do a safe landing just because it can do a lift off. But in this specific scenario the possible issues are more manageable so it should be true. $\endgroup$ Commented Jul 13, 2016 at 20:09
  • $\begingroup$ @JesseTG Even if preventing the destruction is easier than evacuation? You probably want to be more realistic than Hollywood movies? $\endgroup$ Commented Jul 13, 2016 at 20:10

Saving humans is honorable task and not so often is asked here at WB, so it's worth to think about.

Keltari provided pretty solid answer why not, in current state of everything.

Although our current state of everything is far from perfect, and beyond our current demands. Besides floating islands happens cataclysms, affecting even more peoples. Tsunami Mortality Estimates and Vulnerability Mapping in Aceh, Indonesia

Approximately 1 year after the tsunami, Indonesian government estimates totaled 129775 deaths, 38786 missing, and 504518 tsunami-displaced persons in Aceh Province.

Some countries have special forces to act in such situations. So it's safe to assume to have such force on Earth level, as UN squad with top notch technologies, which actions might be justified world wide, after actions have took place.

For such limited time, ability to make fast decisions is crucial.

What we are talking about, island

Google maps, Staten Island

  • land area 151 $\small km^2$
  • population 470000

Besides the fact our current big(more then 10k peoples) cities are not suited for rapid evacuation, this place is even worse, only 4 bridges connects it to mainland. Without panicking, with strict order 4 peoples per car, 6m per car (bumper bumper traffic) with average speed 40 km/h, 4 directions - evacuation capabilities are 30 peoples/sec, 4.5 hours evacuation time - not bad actually, and this is with one line traffic, and we have at least 2, and Verrazano-Narrow Bridge have at leas 6 lanes as I may see.

Way much better then I initially have assumed.

So 70000 tesla autopilot-ed cars may evacuate 470k peoples in 40 minutes - 20 min in, 20 min out, at 120km/h speed, 7 peoples per car. At this scenario peoples themselfs, their will to cooperate will be a problem, immobile peoples problem also not solved, bridges have to be intact, but for 99% existing technologies isn't so bad. Tesla have to think about emergency evacuation plan firmware for their cars.


Situation is same as for slime, peoples are point of interests, who have to be transported in minimum time and effort to save location.


As human behavior is main problem in evacuation we have to force them for proper one, but to keep hassle at minimum in after evacuation time we will evacuate houses, trees, grass, pets, rats, worms, everything.

Let say 10m deep layer of that island. Ok it can be done with tool. But let focus on only human evacuation, it's more interesting.


Let assume UN emergency base are 5000km or less away from location, this is approximately 10 bases per Earth, or less in case continents only. To implement our plan We have to drop, let say per each square km, 2000t (2m tick layer which may cover that square km) of our technological slime, or 300k tonnes of it per island, it's like a big tanker of slime.

4 bases may take actions, to launch something like 100k tonnes per each base - launching is done Launch loop style. (not literary by Launch loop, just principle)
This is kinda tricky part, because we have to deploy tool to place in less then 10 minutes, but having tool and not having plan about rapid deploy makes no sense, but it can be done, just 30M speed. Also not having energy for that situation also makes no sense, it have to be stored long before actions, in form of kinetic energy or something else.

Altitude of transporting is something like 20-30km - to be able to use atmosphere to prevent tool to orbit or earth escape - and have control about that part of problem.

After arrival on place part have to be released at altitudes 20-30 km over the place. They may form flying mat - and descent an needed speed profile and cover entry island. Searching each hole for human presence and puppies. and cats. and any living creature from carbon and water food included. Detection of such stuff can be done automatically, without human interactions, it's kinda how geologist's searching for valuable materials with help of neutron sources, with MRI

Each base have to have personnel which have to be involved in to actions, and take special attentions to places like hospitals, data centers, library's, research facilities, nuclear reactors, chemical facilities, flying jets, airplanes, helicopters.

It's enough to assign 1 from personnel per 10-20 evacuees, 50-100 from personnel per each place that demands higher attention.

Each found carbon-water based object - have to be encapsulated in shell, supplied with oxygen removed CO2 if it produces it.

Each object with mass above 2kg have to receive message about reasons and short explanation why evacuation is happening, with promise to explain future information later in near future.

All objects mass 0.5 kg who produces CO2 and higher have to be checked possibly being humans. (actually it's not hard task to distinguish human body from all others objects)

Humans object have to be assigned priority over all other objects and acceleration limit to 1-2g, special orientation in space, live support (like space suit), monitoring of vital function, engaging combatant live support algorithms in case of demand(artificial air breading, heart stimulation, blood cleaning, etc all kinda paramedic stuff which I'm not familiar with but they keep lives with very limited resources - tool can do better, way much better).

So real tricky part will be something like ongoing delicate operations, on brains and such, one of possible solutions evacuate building - replace fundamental with tool, make connections electricity etc, or evacuate this room, may be more tricky. But evacuating entry medical facility makes sense. It have to build tool way in first place, but tool non distribution treaty and that political nonsense u know.

10 bases with 5000 personnel each can totally take control over situation and pay pretty close enough attention for each human found.

Tool can form VR goggles, transfer data and electricity, air water - so informing and controlling humans will be possible task. Also it will help to prevent some claustrophobic effects, injuries connected with panic reaction.
That also allows to make avatars for bases personnel, so they may act usual human way in situation where standard algorithms not working (there are also another advantages in that - algorithms can be fast programmed by human actions, like to days CGI effects but better and not about CGI effects.)

After collecting - tool, technological slime spit out capsules with evacuees and capsules fly to UN base in Sahara desert, probably at ballistic missile speeds, or aircraft style - depends on what is better in that situation. Or form sort of floating mat like ants do, with train lines with how much lanes we need.

ask in comments if something not clear, do not know what to add more, big task and there are lots of details, but general picture have to be more or less clear. I have notice it's not grey goo it's less advanced technology, but many stuff gree goo may do, tool may do also - almost everything at 0.1mkM scale with some limitations, but at least in this case abilities have some similarities.


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