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I recently watched the Avengers: Age of Ultron. As far as I understand, Ultron had set up a trap which would have caused the extinction of human life (and of a lot of other life, and possibly of robotic life...). That is, he was going to play it like the dinosaurs and drop a huge meteorite, then sit back and watch what happens. The meteorite was the unhappy city of Sokovia.

Since the city at the end is destroyed and falls in debris, the potential energy is released all the same in the atmosphere. I mean: it is not actually needed that the city drops "in a piece".

This means that ... Ultron won, surely?

  • From what I remember, the city didn't get to the height he wanted, so it didn't drop as hard as he wanted. – DCShannon Mar 10 '16 at 18:34
  • But whatever energy was accumulated (a HUGE amount) was released nonetheless. It doesn't work like a threshold: nothing below and extinction above. It works like a continuum: you release more and more megaton the higher you reach. – Francesco Mar 10 '16 at 18:36
  • It does work like a threshold. Increasing damage up to the point where there's an extinction. There was a lot of damage, but no extinction. – DCShannon Mar 10 '16 at 18:37
  • There are two separate questions here. Choose one./ – Valorum Mar 10 '16 at 18:37
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    Given that the world seemed pretty not destroyed in Ant-Man, I think we can say Ultron failed. – Rogue Jedi Mar 10 '16 at 21:14
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The only reason Ultron's plan would have worked in the first place was that the impact would have triggered the exotic metals located under the city. The "asteroid impact" aspect, taken by itself, just wouldn't do the job done.

Supposing the city to be approximately 2km in diameter (thanks Richard!) and given that the rock lifted appeared to be conical with a roughly 30 degree angle, that's about 10 million cubic meters, equivalent to a spherical mass approximately 1250m in diameter.

If we lift that mass to somewhere between geosynchronous orbit and the Moon's orbit (it doesn't make all that much difference exactly where in this range) and then drop it, it will hit atmosphere at about 8km/s.

The Earth Impact Effects Program can be used to estimate the outcome.

At 200km from the point of impact, the earthquake would cause "slight to moderate" damage to well-built ordinary structures. The air blast would shatter glass windows, and there might be "occasional larger fragments" of ejecta.

If you are only 100km away the outlook is more dire: the air blast would cause some types of buildings to collapse.

At 10km from the point of impact you're in for a really bad day. :-)

It isn't too unrealistic to suppose that there might be one or more large cities within 200km of the impact point, so there might be several million people in danger. But we're not talking about an extinction level event.

Taking this into consideration, I think it safe to say that dropping the city while still in the atmosphere, particularly if you blow it up first, would not be particularly dangerous to anyone who wasn't too close.

  • @Richard: (1) it seemed ... inappropriate ... to take your answer to my question and turn it into an answer that could be considered to be competing with your answer here. Making it community wiki was my way of compromising on that. (2) I totally didn't know that; either I missed it when watching or have since forgotten it. Isn't that an answer in its own right? Blowing up the city prevented the exotic metals from being triggered by the impact, hence no ELE. – Harry Johnston Mar 14 '16 at 2:26
  • @Richard, I've rewritten the first paragraph accordingly. – Harry Johnston Mar 14 '16 at 2:29
  • This is the back of the envelope estimate that I hoped for. Thanks for taking the time to do it! – Francesco Mar 14 '16 at 7:03
  • If I remember correctly weren't the thrusters pushing the city up designed to reverse and accelerate it down on decent making it go faster than that 8km/s? Either way I doubt it would make much difference. – DasBeasto Mar 17 '16 at 12:21
  • @DasBeasto: assuming the thrusters weren't somehow more powerful on the downward run, and noting that the city had been rising for quite a few minutes when the Avengers destroyed it and still wasn't above the cloud layer, I don't think that could much more than double the energy of impact. That would push out the radius of destruction, of course, but still not a threat to mankind as a whole. (That's based on an estimate in my head, mind you, I may have misremembered the math.) – Harry Johnston Mar 17 '16 at 19:39
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Stark's solution resulted in a large part of the city being vapourised. That means that even though some of the city did impact the Earth (based on the images below, possibly as little as 1-2% of the original mass), it lacked sufficient heft to create the ELE that Ultron was aiming for.

Tony Stark: Maybe if we cap the other end, keep the atomic action doubling back.

FRIDAY: That could vaporize the city, and everyone on it.

Steve Rogers: The next wave's gonna hit any minute. What have you got, Stark?

Tony Stark: Well, nothing great. Maybe a way to blow up the city. That'll keep it from impacting the surface if you guys can get clear.

Steve Rogers: I asked for a solution, not an escape plan.

Tony Stark: Impact radius is getting bigger every second. We're going to have to make a choice.

Natasha Romanoff: Cap, these people are going nowhere. If Stark finds a way to blow this rock...

Steve Rogers: Not 'til everyone's safe.

enter image description here

Since the city itself was evacuated, most of the Avengers escaped unharmed and given that the impact was insufficient to cause much damage beyond the immediate vicinity of the city and its valley, it's hard not to view Ultron's plan as an unqualified failure on pretty much every count.

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    If we accept the phsyics presented in the movie, this is 100% correct. +1 If we don't accept the physics in the movies, then there are a lot of other things to complain about. – DCShannon Mar 10 '16 at 18:52
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    @DCShannon - Pfft. Physics schmysics. – Valorum Mar 10 '16 at 19:03
  • @Richard I admit that I wasn't sure to have followed well the dialogue. The script you quote confirms my understanding: blowing up the city to keep it from impacting the surface is (unfortunately) inconsistent with the same threat that the movie has set up. The "vaporization" has to go somewhere... – Francesco Mar 10 '16 at 19:06
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    @Francesco - Well, at least a reasonable proportion seems to have turned into light and noise as well as mysterious blue energy that was dissipated into the general environment. – Valorum Mar 10 '16 at 19:23
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    The total energy released isn't the only variable. It's also a question of where that energy goes. A million small impacts don't throw as much dust into the high atmosphere as one huge impact does. No dust in the upper atmosphere, no nuclear winter, no ELE. – Stephen Collings Mar 10 '16 at 19:33

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