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Jan 5, 2022
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If you want a recent movie that doesn’t focus on *America’s* response, I can’t recommend highly enough you check out the Chinese big-budget sci-fi blockbuster _The Wandering Earth_. I found it refreshing to see a movie in which humanity confronts a global crisis via engineering, politics and various human-interest subplots in which - for no particular reason - everyone important to the story happens to be Chinese.

https://youtu.be/vzoGinOmHDA

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There is a thirty-second aside where someone mentions that a joint China/Russia/India (or something like that) coalition also tried a comet deflection mission but it failed. They were clearly trying to nod to this possibility while also wanting to keep the focus on the US.

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I was surprised there was no speculation that the US sabotaged it to ensure they could still get all the valuable stuff in the comet.

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Jan 4, 2022
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"Who doesn't believe in the existence of COVID-19?"

https://www.bbc.co.uk/news/world-us-canada-53892856

This is a fairly extreme weakman, but it's certainly not a strawman.

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Jan 4, 2022
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He was very far from the only commentator who said that. (But I share your bafflement that anyone's having that take.)

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I too find it very hard to see Meryl Streep playing the President of the US without thinking of Hillary Clinton. Aside from that, there wasn't much Clintonian in Orlean's character (except where Clinton and Trump correspond), though the part about polling driving her smoking might be something.

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I also thought the President was supposed to be a Hillary standin until she opened her mouth.

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President Streep had a line where she said she wanted to check Sexy Science Man's astronomy with people from a real university, Harvard. Or something along those lines.

I figured fawning at the Ivy Leagues was a dig at democrats.

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Movie reviewer Tim Brayton interpreted President Orlean as being a conflation of Trump and Clinton:

> A character who can be best described as "what if Donald Trump was also Hilary Clinton?". So on the one hand, blind incuriosity; on the other, smug Ivy League credentialism. On the one hand, oafish provincialism; on the other, sneering technocratic condescension. On the one hand, making America great again; on the other, yass kweening. She even wears both red and blue pantsuits at different points in the film.

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Also, why is nobody pointing out that Streep played Susan Orlean in Adaptation and in this film plays President Orlean? Is Don't Look Up a sequel to Adaptation? "Orlean" isn't exactly a common last name, this can't be a coincidence.

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They're both named after Joan of Arc, the Maid of Orleans.

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I kept thinking of Adaptation every time I heard the name of the character in this movie. I totally forgot that she was also played by Meryl Streep!

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Jan 4, 2022
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You definitely did not watch the movie.

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He didn't even read the article.

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Yeah sure, it's full of soviet movies where the average new soviet man is a complete moron, the secretary of the communist party is an idiot dooming everybody for short term thinking, and a guy in charge of a huge part of the economy too greedy to do even his own self interest.

(Before you engage in some sophistry on how the Ivy league and Hollywood are the real government... I have already read all moldbug. Did not make sense, does not make sense now)

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Moldbug is straightforward: distilling away the many walls of texts and mad-at-literally-everyone-and-everything rants, his one and only message is "The world is fallen because I am not the king of America*"

*(or "Columbia")

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Jan 4, 2022Edited
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To be honest, from all I've read I wasn't aware it had jokes. Either the reviews are unfair or the jokes were not worth mentioning, and since the reviewers have included people who stated they wanted to like the film, I doubt it's the former possibility.

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I didn't see this movie because I was in the mood for a laugh; I wasn't expecting one, didn't get one, and it seemed entirely beside the point in any case. I care about it as an illustration of a really important and underappreciated problem.

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Jan 4, 2022
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This was one of many respects in which I didn't expect to like it and in fact didn't. Still seems important.

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I honestly don't even remember the jokes except the really dry ones, like normies shitting on Big Ten schools.

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Jan 4, 2022
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I'm glad someone mentioned this! That was, more-or-less, the only part of the movie which actually got me to laugh.

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I didn't expect it to be funny, although Adam McKay *can* be very funny, e.g., Eastbound and Down.

I watched it as mere Hollywood spectacle and found it enjoyable and unintentionally apolitical. Its lack of coherent messaging is a virtue. It isn't funny, but it is entertaining. The acting and visuals are good.

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Jan 4, 2022
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This was my interpretation, too. It's a movie about the challenges of consensus building, even in the face of an existential problem. The scientists found the comet, but they didn't have all the answers and frequently undermined themselves.

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I think it's true that that's what the movie is about, but that there are also key disagreements between Adam McKay and most of the commenters here about how this dynamic comes into being.

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Well, everyone is entitled to an opinion. The movie was so full of tropes it is hard to take any message seriously. Start with the notion that the initial effort to blow up or move the "comet" ... That is stupid beyond description, certainly in the current day. And, by the way, comets are mainly frozen ice. They don't have all the chemicals the so-called corporate CEO lusts for. Just a really stupid move that will, nevertheless, capture the imaginations of the smart set. You know, like Scott.

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The tropes are the point.

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Wait, why is it stupid to try to move the comet? I think astronomers and others take comet deflection pretty seriously - see https://en.wikipedia.org/wiki/Asteroid_impact_avoidance#Comet_deflection_possibility .

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Also, will probably ban this commenter for a month for a combination of being nasty and wrong, but I'll wait to see if they have some response to this first.

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Are you genuinely sure the commenter was wrong or did you skip the process of finding out so that you can be smug about it?

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I don’t think Scot was smug. I think he was stung by being labeled as a member of the “smart set”, and over reacted a wee tad.

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Yep. I asked the question because it seemed relevant to the discussion, not rhetorically. I do not know the answer to my question, though I suspect you are right.

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I think if somebody comes to a home on invitation to hang out and chat about movies, and call the host an idiot, and the host shows the offender the door and asks not to come back for a while - there's not much basis to complain. Maybe on objective scale it's a bit of overreaction, but playing stupid games wins stupid prizes...

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You were invited? I had to pay to get in here!

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"Home" is an awful and totally misleading metaphor for any form of social media.

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If you read the entirety of the single sentence comment you replied to it sure seems like he's still waiting for a final decision on whether the guy is wrong.

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He provided a link demonstrating that the commenter is wrong, and has given the commenter a chance to explain why he isn't wrong. I don't see any process skipping or smugness from Scott here. Maybe from you though.

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Fair enough. I was just trying to point out that it's hard to draw a hard line between what's wrong and what's not. I think it was in keeping with the spirit of Scott's post. If I'm wrong, then hey, I'm wrong!

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Are you really sure you're making a good point, or did you skip the process of thinking it through to act smug about it?

Does the fact that I'm directing this phrase at *your* post, to which it seemingly doesn't really apply, in order to point out that your post is itself directing the phrase at a comment to which it seemingly doesn't really apply, actually show that your point — that it is hard to know when this phrase can fairly be applied — is valid after all and *not*, in fact, a smug misapplication?

Or does it show that a thinker of my calibre (heavy, obviously) can quickly and reliably tell when it is, indeed, fair to apply this criticism, and when it is not? Or does it instead show that unwarranted confidence in the level of one's own understanding is, truly, endemic, and the post was making a good point after a—

[transmission ends in burst of smug meta-reasoning]

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The latter, obviously.

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I'm pretty confident that from an engineering and orbital mechanics perspective, a comet massive enough to wipe out all life on earth could probably not be deflected given 6-months-to-impact notice, with our current state of preparation. I think we're much closer to being able to do so than we were 20 years ago, given the success of spacex, but the limiting factors are pretty extreme.

edit: obviously, this depends on a variety of factors including its trajectory (a slow-approaching comet would be easier to deflect than one shooting in at a fraction of C)

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To be fair, a more accurate analog to either COVID or climate change would be a comet large enough to, say, wipe out a large city when it impacts or maybe create tidal waves that deluge coastal cities- total casualties of, say, 10-20 million people. Worth paying attention to, but also not world-ending.

I'm *guessing* a comet that small could conceivably be deflected with today's technology if you detonated a couple thousand nukes on one side, assuming you got enough manpower and resources behind the project. But... on the other hand, most people on earth could just ignore the problem and it wouldn't make any serious difference to their lives, and a strategic evacuation of affected areas might make more economic sense.

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delivering "a couple thousand nukes" to a point in deep space in a couple months (remember, every day closer increases the delta-V needed to deflect) sounds basically impossible.

edit: additionally, you'd likely need some kind of timing trick to get that to work? because nukes aren't like TNT, if a nuke goes off next to another nuke, it generally doesn't "trigger a chain reaction", the other nuke usually just is blown apart without a nuclear detonation.

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Yes it was a silly approach shown, in a comedic film meant to parody reality...I think that was the point and it was an intentional joke for the audience. Where even the most intelligent people doing their best to get the truth out don't seem to know a lot about comets vs asteroids or about realistic methods to deflect dangerous objects in space.

It was a wink at the audience that none of the characters were working with fully correct information.

Like in the parody movie Airplane! where it is a jet plane and you can hear the propellers in the background the entire film. In this case it was everyone talking about a comet when an asteroid would have made more sense.

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I'd say it would be highly technically and logistically challenging to deliver a thousand nukes into deep space and wire them all to detonate simultaneously, but bear in mind that nuclear warheads themselves are not that large (it's the delivery system that's bulky.)

https://www.quora.com/How-large-is-an-ICBM-warhead?share=1

I'm not sure how many of those you could squeeze into a Dragon capsule, but if you could deliver 25 per trip and do a launch every 3 days, then in 120 days (4 months) you'd have 1000 warheads in space.

I have no idea what the specific mass/energy of a city-destroying comet would be, and whether that many warheads would suffice, but someone here can probably do the math. Again, the question is whether it would be cheaper and easier to just evacuate at-risk areas and rebuild afterward.

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ICBMs already carry multiple warheads, look up MIRVs

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Delivering the nukes in a constant stream would probably be better logistically and a less fragile approach in general than setting off a single big bang.

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I did the calculations for deflection with only one month notice in https://astralcodexten.substack.com/p/movie-review-dont-look-up/comment/4300386, and for many comets you would need only a tiny fraction of one nuke, not thousands of nukes. Suppose such a comet (3e9 kg) were in a solar orbit at nearly escape velocity from the sun (42 km/s) and then fell to earth, which would give it 11 km/s of velocity from rest. It would impact at about 43 km/s if the Earth were at rest relative to the sun:

You have: (42**2 + 11**2)**(1/2)

You want:

Definition: 43.416587

But Earth's orbital velocity is another 29.8 km/s, so depending on the relative angle of the Earth's orbit and the comet's orbit at the intersection point, the impact speed could be anywhere between 13.6 km/s and 73.2 km/s. Barring a gravitational assist from another planet during the same comet pass, it can't be higher than that because a comet moving faster than that wouldn't be in orbit around the Sun at all; it would be an interstellar intruder like ʻOumuamua.

13.6 km/s would give it 300 PJ of impact energy, 60 megatonnes of TNT, about an eighth of Tsar Bomba [correction: slightly larger than Tsar Bomba], which as far as we know didn't injure anybody. But if it had hit a city, it would have largely destroyed the city:

You have: half 3e9 kg (13.6 km/s)**2

You want: PJ

* 277.44

/ 0.0036043829

You have: half 3e9 kg (13.6 km/s)**2

You want: megatonnes tnt

* 60.155195

/ 0.016623668

At the other extreme, 73.2 km/s would be 8 exajoules, 1.7 gigatonnes TNT:

You have: half 3e9 kg (73.2 km/s)**2

You want: EJ

* 8.03736

/ 0.12441896

You have: half 3e9 kg (73.2 km/s)**2

You want: megatonnes tnt

* 1742.6793

/ 0.00057382903

That's three or four times the size of Tsar Bomba [no, 350 times] and eight times the size of the Krakatoa eruption, which produced a two-year-long volcanic winter.

In conclusion, the impact of such a comet would probably be city-destroying rather than planet-destroying, but it would not be technologically challenging to prevent it, just as with keeping covid under control.

But there are other comets out there that are three or four orders of magnitude larger. Fortunately, there aren't nearly as many of them, and we know where most of them are.

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You should only need 1 nuke. If it is still a long ways away from earth you would only need to deflect its path slightly and a nuke has lots of energy. A nuke does however have very little mass. You would likely need to drill into the comet and use the nuke to split it so that the two pieces (likely one large one small) would split apart with the large part adequately deflected.

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Interestingly, nuclear-scale impactors hit earth every couple of years! A 170 kt tnt-equivalent asteroid blew up over the Bering sea in 2019. They generally miss populated areas (or, more rarely, air-burst high enough up to avoid mass casualties, as in the case of the Chelyabinsk Oblast bolide, which was about a half megaton and injures a bunch of people).

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But we are just sort of blithely rolling the dice every few years that one of these things isn't going to hit manhattan and kill three or four million people in five seconds.

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I've seen documentaries making a reasonable case for the math of asteroid insurance, though I'd agree that having a more reliable warning + deflector system would be preferable. Probably have to wait until we get that space bridge installed in 2087.

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An interesting assertion. We can take as a minimum the impactor thought to be responsible for Meteor Crater (about 50m across) and as a maximum the Chicxulub impactor (10-75 km). The former has a kinetic energy of ~120 MT while the latter about 10^9 MT. So that's about how much energy you need to supply to deflect it if you discover it too late for anything other than a wide angle deflection to work. (The world's supply of thermonuclear weapons probably totals about 1400-3000 MT.) If you catch it far enough away that a small angle will work, multiply approximately by the sine of the angle required.

I would say in terms of the sheer energy to be supplied, it is perhaps barely possible. But when you add in the logistics -- transporting thousands of tons of devices and heavy machinery, and either the exquisitely complex and sophisticated robots or the large well-trained human crew necessary to use the force precisely, to interplanetary distances, in an era when the biggest rockets we have are barely able to throw a metric ton or two to Mars -- I would say it moves into the realm of implausible even for quite small impactors.

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But we would certainly try! lol

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I did the calculations for one month notice in https://astralcodexten.substack.com/p/movie-review-dont-look-up/comment/4300386, and it looks like it would be pretty straightforward from an engineering perspective, just because the amount of energy required is so small. (Getting bureaucratic approval for a launch within a week or two, with nukes on it, is the harder aspect of the problem.) Agreed that relativistic projectiles would not be so easy.

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SpaceX (or so) could probably just launch without bureaucratic approval? They can deal with the legal fallout later?

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I don't think they can in fact launch rockets without approval from the US government (I think there are controls in place to prevent this) and they are internally a bureaucracy as well. But the potentially larger problem is getting the warheads.

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SpaceX could probably launch *once* without bureaucratic approval, if they were willing to deal with "legal fallout" that would make all their future launches much more difficult. But this is a problem that will take much more than a single launch to solve.

Legally, SpaceX needs FAA approval to launch anything, even from an offshore or foreign site, and the bureaucrats in question can call on uniformed men with guns to enforce the rules. We can hope that whoever is running the executive branch of the government would make sure that's not a problem in this scenario, but if POTUS is being an ass (or an incompetent buffoon), then SpaceX can't fix the problem alone/

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FWIW, the science consultant on the movie, Amy Mainzer, agrees with you:

"McKay and Mainzer first connected two years ago, when McKay was writing the screenplay. One issue was Comet Dibiasky’s size, which McKay had imagined at thirty-two kilometres in diameter. “I said, ‘No, no—if it’s too big, people just throw up their hands,’ ” Mainzer recalled. They settled on nine kilometres: big enough to wipe out humanity, but small enough that there was a chance of stopping it. Mainzer had pushed for a longer interval between discovery and impact, since you’d want four or five years to build a comet-busting spacecraft, but, for dramaturgical reasons, McKay stuck with six months. “It would be like doing ‘Jaws’ where the shark attacks take place over a fourteen-year period,” he said."

Source: https://www.newyorker.com/magazine/2021/12/27/how-to-design-a-world-killing-comet

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I haven’t seen the actual movie, but surely whether or not deflecting an interstellar body within 6 months is ‘possible’ depends hugely on the mechanics of exactly where it’s predicted to hit, and which way we’re moving at the time.

For instance, if it’s predicted to hit perpendicular to the Earth’s direction of motion, and ‘hit’ means ‘graze the trailing edge’ then a 1-second delay in impact time converts that to missing the Earth’s atmosphere completely (we move about 30km/s Google tells me). I haven’t sat down and done the maths, but that seems pretty doable. Certainly a very different scenario from ‘it’s hitting dead centre at the precise point in our orbit when we’re also heading straight for it’

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For almost any impact, nudging the impactor off course by a couple of Earth diameters (sideways) would be sufficient to prevent it. Time before impact and size/composition of the object are the main factors in the difficulty of deflection. Difficulty of reaching it far in advance is also a factor, and that can depend on which way the Earth is heading at the time as well as the impactor's trajectory. But the angle of impact is not so important.

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In the part 4 of Axis of Madness, Species War, the hive mind is faced with a similar situation. A 60 mile in diameter asteroid is headed towards earth, and it has very little time to decide what to do. The description of the colision is earth shattering. And the description of degeneracy leading to the formation of the hive is even more explicit.

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Agreed, although I think it's more accurate to say that our ability to do so has waxed and waned in direct proportion to the heavy-lift vehicles humanity has at its disposal. We probably had a better shot in the 70s than we did in the 90s.

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I could hear John Schilling screaming at the screen from where I was.

At *best*, the original attack would deflect the comet, not destroy it, and only *barely* deflect it.[1]

But if you live in a world where the Deflect Mission can happen, then the proper response is to just let Deflect Mission happen, and then attempt to do Capture Mission on the now barely-deflected comet.

[1] We can't even deflect it.

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Very good point. All the sensible options leave the comet largely intact and on almost the same trajectory. Still, if the writers want to turn "Deflect Mission" into "Blow Comet to Smithereens Mission" for dramatic purposes, that would be one of the lesser sins of this screenplay.

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Ignoring orbital mechanics, to deflect a 9km diamter comet made of ice by 1 earth diameter over six months, would take 30 kT of energy. Seems small.

https://www.wolframalpha.com/input/?i=1%2F2+*+%284%2F3+*+pi+*+%284.5km%29+%5E3+*+density+of+water+%29+*+%28earth+diameter+%2F+six+months%29%5E2

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yes, but you're ignoring travel time and lead time; let's say it takes 2 months to decide and build our response. I think that would be shockingly quick, but regardless.

You might be thinking "so what, 4 months is only 50% more energy needed!", but we still need to factor in how long it takes us to make the intercept. let's say our comet is moving at roughly 30 km/s relative to the earth; this is fast, but this is also the orbital velocity _of the earth_, so most asteroids and all comets will be moving faster (relative to the sun) than that.

reaching low earth orbit from the ground takes roughly 10 km/s of delta-v. a Falcon 9 rocket can deliver 22.8 tons to low earth orbit. a laden Falcon 9 rocket weighs 550 tons. let's be crazy and just pretend we can ship a falcon 9 up, piece by piece, on falcon 9s (or, more realistically, put one in orbit and then shuttle fuel to it) in one month. this gives us, in orbit, a rocket that can impart 10 km/s of delta-v on a 22.8t payload, sitting in space. That's pretty good, we've never been anywhere near that amount of power in space before. with 3 months left, if we assume our comet is closing at 15 km/s and our rocket is closing on it at 10 km/s, we should meet it with roughly 36 days left. a nuke could probably still do that? it's "only" about 6 times your estimate, so 180 kT of kinetic energy? that's a lot, but relatively little compared to nukes. but remember that nukes do not impart 100% of their energy on a comet/asteroid; at the limit, one would expect them to impart 50% of their energy (imagine exploding against a flat wall), but I think much less of it would actually go to kinetic energy.

The nuke-to-kinetic energy calculation is beyond my paygrade. I also think the "launching an entire, fueled falcon 9 to LEO" scenario is ludicrously optimistic, and while you could do your launch piecemeal (i.e. send things straight at the comet rather than waiting to assemble in LEO) and that's probably better, I think it's still pretty far from clear-cut.

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Yes, certainly am ignoring all that - was just talking about the physics of it which is what I thought the claim was. You're right that even if we have something ready to go, the intercept time is unavoidable. Sending a falcon 9 up piecemeal obviously isn't something we can do right now, but orbit-refuellable starships might fit the bill, Musk says a fully-fuelled one with 100 tons of cargo would have 7km/s of delta v, which is getting close to the Falcon 9's 10km/s. If some of the 100T was itself a vehicle with its own propulsion, you could get even more delta v.

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That's also assuming 100% conversion of nuclear explosion energy to asteroid kinetic energy, which isn't plausible. Even 1% isn't plausible. For scenarios that don't involve Bruce Willis drilling a hole into the asteroid, the coupling is closer to 0.01%.

The scenarios that involve launching Bruce Willis out to the comet with a bunch of nuclear warheads, involve him watching the comet whiz past at better than fifty kilometers a second, lamenting the fact that we don't have engines capable of matching that sort of velocity.

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Disclaimer: I'm an idiot. This thought that occurred to me is likely idiotic. So go easy on me.

But, rather than blowing it out of it's orbit why not instead land thrusters on the comet and change its trajectory that way. I have no idea about the numbers, it's probably as unlikely as trying to nudge it out of orbit with nuclear bombs, but it's still a possible scenario if you're looking at all scenarios, right?

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That's been discussed for asteroids that we can track and predict twenty years into the future, and that have lower relative velocities than comets. In that context, it's reasonable.

Comets come out of the deep dark of trans-Neptunian space on very short notice(*), and at speeds great enough that flying out to meet them in a timely manner and then reversing course to rendezvous with and land on them while carrying any significant payload is impractical with current or near-future technology.

* Except for the periodic comets that we already know about, and none of those are impact threats.

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You have to admit that it's a good jab - you've unfortunately (perhaps unintentionally) become one of the leading lights of a group of people who can generally be described as "extremely smart, but also extremely dumb". I should know - I've followed you for years and I'm very much that.

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what do you mean by this and who is it addressed to?

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It's a late response to a comment waaaay upthread, with the result that it seems to have been buried down here. No matter - the issue was resolved amicably it seems.

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Yes. There are certainly a lot of scientific inaccuracies in the movie, but that's not too bad imo given the genre we're in here.

The basic idea of deflecting a comet with nukes is serious, even if basically all details in the movie pertaining to implementation are not. (Also, the detection scene is fairly silly. But then again, not a big deal really)

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From the Wikipedia article Scott posted:

> With one year of notice, and at an interception location no closer than Jupiter, it could also deal with the even rarer short period comets

From the _Don't Look Up_ Wikipedia article:

> [Female scientist] discovers a previously unknown comet just inside of Jupiter's orbit at 4.6 au from the Sun. Her professor [] calculates that it will impact Earth in about six months

Read together, it seems like the deflection depicted in the movie is significantly more challenging than the one described in the Wikipedia article (which itself relies on rockets more powerful than any currently in service)

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It's an open question, although in all likelihood we would be completely powerless to deflect a mass-extinction class comet/asteroid with current level technology. The delta v change required simply requires a tremendous amount of energy, given the kinetic energy of the astronomical body itself. Maaaaybe if you catch it really far away? People are trying to investigate it though. Stay tuned for the results of the DART mission. :-) For context, the impacted object in this mission will be a minor-planet moon 170 meters across...

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I'm not sure it's that unrealistic. If you catch it 1 month out, you need enough delta v to move it by the radius of the Earth or so over the course of a month. That's like 2.5 m/s. If you assume this thing is a sphere of diameter 170 meters with the density of water, that's something like 1.5*10^10 J, which is a lot, but not on the scale of nuclear weapons.

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How would earth's gravity play into that? If you changed the comets's path, but not enough, would gravity pull it back towards the earth?

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It should affect things a bit. Gravity will increase the scattering cross-section some. I haven't done the calculation, but I would imagine that the effect will be small because the comet will be traveling by the Earth fairly quickly (and thus there will be fairly little time for gravity to have an impact).

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The comment would probably be on a hyperbolic orbit relative to Earth (meaning if it doesn’t hit it will just blow right by, not be captured into an Earth orbit) and presumably Earth’s gravity would already be taken into account when you worked out that it was on a collision trajectory. Probably doesn’t change the calculation terribly much.

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Mostly confirmed, but you overestimated the mass by an order of magnitude [correction: the energy, by a factor of 2], and also 1.5e10 J is only 4200 kWh, so we're talking about only a few thousand watts of rocket power. Calculations provided with GNU units 2.19 for reproducibility:

$ units

Currency exchange rates from FloatRates (USD base) on 2019-05-31

3460 units, 109 prefixes, 109 nonlinear units

You have: earthradius/month

You want: m/s

* 2.4226732

/ 0.41276718

You have: spherevol(half 170 m) water / gravity

You want:

Definition: 2.5724408e+09 kg

You have: half spherevol(half 170 m) water (2.42 m/s)**2 / gravity

You want: J

* 7.5326211e+09

/ 1.3275591e-10

You have: half spherevol(half 170 m) water (2.42 m/s)**2 / gravity

You want: kilotonnes tnt

* 0.0016332407

/ 612.27964

You have: half spherevol(half 170 m) water (2.42 m/s)**2 / gravity

You want: kWh

* 2092.3948

/ 0.00047792129

You have: 1.5e10 J

You want: kWh

* 4166.6667

/ 0.00024

You have: half spherevol(half 170 m) water (2.42 m/s)**2 / gravity month

You want: W

* 2864.3935

/ 0.00034911405

https://en.wikipedia.org/wiki/Comet mentions several comets in that size range, but also says Halley's Comet and a few others are three or four orders of magnitude larger than that, 1e13 to 3e14 kg. Such a comet would require three or four orders of magnitude more energy to deflect given only a month's warning, 1-10 kilotonnes TNT instead of a few megawatt-hours. Probably that could be delivered with current human capabilities as a small nuke but not as, for example, ion engines. Starship will change that if it works.

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I think I just missed the factor of 2 in E = 1/2 m v^2. (7.5e9 is half of 1.5e10).

But yeah, this is probably in the range where you could use rockets rather than than nukes. Though both cases run into the issue of trying to turn energy into momentum losing you a lot unless you have reaction mass to spare.

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Oh yeah, sorry.

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I appreciate the tip from the other comment, but I'm not sure what these numbers are referring to? Could you walk me through it a bit more explicitly?

Would a comet only 170m^3 really pose an existential threat to life on earth or even be visible from the ground for long, though? In the other thread I was positing a comet large enough to wipe out millions (but not the planet)- can you estimate what size that would be and the effort needed to deflect it, given 6 months' warning?

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Sorry, I can't find the specs for the comet in the other thread.

Looking at this one though... googling "comet impact velocity" says that we should expect something like 50km/s. Using this exactly, we compute the impact energy on Earth as...1.3e19 J.

That's... probably not wiping out all life on Earth. It's like 100x the energy of the biggest nukes, but something like 100,000x short of the impact that killed the dinosaurs.

If we scale the mass up by five orders of magnitude though, that is probably enough to kill most people and still means that a nuke will deliver enough energy (if delivered properly) to divert it.

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170 cubic meters would not be big enough to matter. Objects that size hit Earth every year or so without anybody noticing. The Chelyabinsk meteor was about 4000 cubic meters and would have done major damage if it had hit a city instead of exploding in the upper atmosphere, injuring a thousand people and giving instant sunburns to some of them.

170 meters in diameter is 2.6 million cubic meters:

You have: spherevol(half 170 m)

You want:

Definition: 2572440.8 m^3

That's big enough to wipe out millions, but not the planet. If you had 6 months instead of 1 month to deflect it, you'd need to change the comet's velocity by only one sixth as much, about 400 millimeters per second:

You have: earthradius/6 months

You want: mm/s

* 403.77887

/ 0.0024766031

This would require about 3% as much energy, about 200-300 MJ for the 170-m-diameter size we were talking about:

You have: half 3e9 kg (earthradius/6 months)**2

You want: MJ

* 244.55607

/ 0.0040890419

Or about 70 kilowatt hours, or 50 kg TNT:

You have: half 3e9 kg (earthradius/6 months)**2

You want: kWh

* 67.932241

/ 0.014720551

You have: half 3e9 kg (earthradius/6 months)**2

You want: kg tnt

* 53.025223

/ 0.01885895

This could be a rocket of under 100 watts, a few hundred newtons of thrust, depending on how long it had to operate (there's a tradeoff where you can use lower power over a longer period of time, but requiring more total energy).

You have: 3e9 kg 400mm/s/2months

You want: N

* 228.15911

/ 0.0043829064

As for walking you through it a bit more explicitly, can you be more specific about which parts are unclear? Is it the GNU Units syntax, the Newtonian physics, or something else? Maybe you understood all of that and I just made a dumb calculation error?

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Extinction-level comets/asteroids, such as the one in the movie/the one that wiped the dinosaurs, are more on the 5/10km diameter range. Assuming the same density, here alone we're talking about a 3640-fold increase in mass (assuming 170 vs. 10000 meter diameter bodies). You're also being optimistic on the average density, but I doubt you'd be off by more than a factor of 1-2x, hence all things considered a rather small deviation when compared to the former.

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Yeah, I think we came to this conclusion elsewhere. A 7000-fold increase still leaves nukes with easily enough *energy* output to deflect it, though there is still an issue with how effectively you can turn that energy into momentum.

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I used the wrong formula (area of circle instead of volume of sphere). The energy is actually ~200k times higher. Please see my other comment. Also, agree with the problem of effective use of a bomb to impart momentum on a celestial body.

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Extinction-level impactors are more on the 5-10km diameter range. Considering the same density and velocity relative to Earth, mass sphere r=5000/mass sphere r=85 =~ 203541 times more kinetic energy than Didymoon. Also quite unsure how effective a nuke or any other kind of high-yield explosive device would be an efficient way to impact momentum on a celestial body, given that most energy would not be directed at the body (assuming a spherical blast, which seems reasonable).

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So, the good news mechanically is that the earth is really small by cosmic standards. Hitting a target like the earth from months or years away requires extreme precision. Even a small change in velocity is generally enough to turn a hit into a miss, and the power of that disruption increases the further out from impact it is. I know in some cases, simply painting the object white to increase the pressure exerted by the sun's light would be sufficient, if you had enough lead time. A sufficiently large nuclear weapon could also potentially nudge it enough. There's more we could (and should!) do to prepare, but we aren't entirely helpless, especially if Starship works out (which would enable us to put a high-delta-v high-payload mission together in a hurry).

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To be clear, I don't mean to imply you're completely wrong. There's lots of scenarios where we'd be pretty much screwed, especially if we detected it really shortly before impact. But doing something about it with ~current technology isn't physically ridiculous, and there is a subset of scenarios where we have more warning where you could put a meaningful mission together. I also think the near-future outlook may improve a great deal.

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Someone should make a series of questions on metaculus to determine what's the largest impactor that humans could deflect given 0.5/1/2/10/100 years advance notice.

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I'm wondering what the resolution mechanism will be.

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I'm 75% confident that the internet would still exist in some form the next day after a chixculub-equivalent impact, and 98% confident humans would still exist ten years later.

* Animals were immediately buried under 10cm of debris 1600 miles from the impact, but lots of humans will survive that by being farther away or inside buildings

* magnitude 9 earthquake on average across the entire globe, which would be very bad, but won't kill everyone.

* Datacenters are connected to each other by underground cables that likely survive, and many of them have dedicated primary and backup generators nearby.

* Most of the starlink satellites would not be destroyed by ejecta.

* Cooling and partial dimming of sunlight will reduce global agricultural productivity by a lot for many years (wild guess: 40-80%, Help me on this if you have more specific data). We can supplement it with LED grow lights. A human consumes 100 watts of food, and crops are ~0.4% efficient in sunlight, but much more efficient when illuminated by LEDs that only produce the appropriate frequencies. LEDs themselves are 85% efficient. So I guess it's going to take 3000-10000 watts of electricity to grow enough food for one person. Total global electrical capacity of ~10^13 watts could support 1-3 billion people on grow lights. So it seems very plausible that less than half of the humans will starve.

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My thinking is this: A comet is an ice ball, at worst a dirty one. Not sure they can be “diverted”. Heck it responds to solar “wind” by elongating, not moving. Maybe shattered into smaller ice balls. But moved? I have my doubts. A meteor? Better chance but it’s mass relative to a comet? Hmmm.

My objection was to what I saw as a simplistic “believe the scientists, not the greedy capitalist” theme. A commenter here noted that tropes were the point. But that really is my point. It was not believable but the movie seeks to shape a false science - in my view - to push a narrative that is just not supported. The narrative of Trump/capitalism versus “truth”. It’s a bit much, particularly in our current milieu of “believe the science” where the science is sometimes suspect and doesn’t consider alternatives. And is often political - on both sides.

Scott, my comment was snarky and smart-assed for sure. But “nasty” I am not so sure. But it’s your blog, your site, and clearly you can ban me if you choose. I can live with that. Heck, I think that was my first comment here. Maybe I just don’t really get the posting etiquette.

Thanks for the reply.

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All right, fine, you clearly care enough to defend yourself pretty well, so I'll hold off on banning for now.

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OK, Scott, but I still take issue with the disproportionate size of the ban you considered imposing on someone who was briefly snide about you -- as compared to what you're willing to mete out to someone who goes after somebody else. I'm moving up to here a comment about this matter that was originally lower in the thread, but seems more appropriately placed here:

Jeez Scott, as low-quality comments go this one seems relatively low in toxicity and discourtesy. Until the last sentence it's just rambly personal reactions to the movie, plus some info about comets which yeah, we know. Then at the end he says something snide about you. And you're proposing to ban the person for a *month*?! It's not the length of the sentence I object to, it's the inequity. A couple threads ago I posted a complaint, civil in tone, about someone on Substack whom I thought was publishing misinformation about covid vaccination, and got showered with half a dozen *ridiculously* rude, mocking and insulting comments by one individual, comments with no argumentive substance to them at all, and you only banned that person for a week. The term "incivility" really doesn't cover the level of nastiness and savagery this person was dealing out. Privately I thought, Wow, what does this guy have to do to get banned for longer than a week -- threaten murder?

And now you want to ban someone for a *month* for a post that has one little sarcastic sneer at the end about your membership in the smart set?

And by the way, the same poster who savaged my posts then liberally sprinkled the whole rest of the thread with multiple responses to other people's posts. Most were content-free, just pure stoopit sneer. Want some examples?

-"You people crack me up."

-"Friendly reminder: You don´t get it."

-"Yes, great handwaving pains with no actual basis in the data."

I'm not crazy about how much your standards vary depending on whether the person getting shit on is Self or Other. Others are selves too.

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"I know people are rude to you, but what about ME!"

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Well, not exactly. My point isn't that rudeness to me is more important than rudeness to others, it is that a recent episode of rudeness to me was vastly greater in both degree of rudeness and in number of rude comments. And the rest of my point was that it was not a great look for Scott to propose a month-long ban for the lower-scale rudeness, to him, and a much shorter ban for a way bigger load of rudeness to another member of the forum — whether the other member of the forum was me or, for instance, you, Adam.

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People being rude to Scott can discourage Scott from writing more great articles. That is much worse than e.g. people being rude to me.

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Once a person becomes an internet janitor they very rarely make good decisions about how to use their mop and bucket. Scott is no exception.

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I feel like I have a pretty consistent policy of banning people who are rude to others more than to me - this is part of why MarxBro rarely gets banned. The main thing that annoyed me about this post was him calling people who believe you can deflect comets "stupid beyond description, certainly in the current day" - you can read the comment policy here, it's very clear that the combination of insulting and wrong gets you banned. But I was also annoyed about the "this movie is bad so it appeals to the smart set" stuff - I realize I'm at risk of compulsive anti-elitism and cultivating a comment section that does that too, and so I try to be harsh on people who are snide, extremely anti-elite, have few actual things to say, and wrong about the facts all at once.

I haven't yet read this poster's other bad comments. I am not able to read every comment on this blog. The main reason I read this comment and not others is that this was the first comment on this post. I'm working on getting a "report comment" function available, but it's not ready yet.

Also consider the possibility that the reason bad posters don't get banned as often as they should is that whenever I even moot the possibility of a banning, people write long comments like this one about how biased and mean and selfish I am, and so I dread having to even consider it.

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"I feel like I have a pretty consistent policy of banning people who are rude to others more than to me - this is part of why MarxBro rarely gets banned."

I'm not rude at all. The only time I got banned was when I pointed out one of your blogger acquaintances was manipulating quotes in a misleading way.

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OK, Scott, having thought all this over I’ve realized what my real complaint is, and also what it isn’t.

What my complaint isn’t:

I don’t really mind your not displaying the wisdom of Solomon in your response to a piece of snark. Threatening to ban the poster still seems like an overreaction to me, but maybe I’m wrong, and anyhow you don’t have to be perfect to stay in my good graces. In hosting this forum you are giving a lot of people something quite special and good, and I feel grateful and not inclined to make a fuss about little things.

What my real complaint is:

There is *too much incivility* on this forum, and I’m pretty sure the amount is increasing. It’s cutting into the pleasure of being here — at least it’s cutting into *my* pleasure. I really don’t know what to do about the increase in low-grade incivility —things like silly gotchas, unkindness, irritable bickering etc. Moderating aimed at low-level incivility may be destructive of the ecosystem, and anyhow it’s too time-consuming to be practical. But I’ll settle for a reduction in the highest level of incivility, verbal abuse, of which I have seen a fair amount in recent threads. I’ll post some thoughts about incivility and how to handle it on the next open thread.

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You can definitely divert it with a big enough nuke - not through the shock wave (vacuum), but through the asymmetric outgassing caused by the *massive* radiation flux, which produces thrust. This works for asteroids as well as comets

Moving the closest approach of some comet a certain amount then becomes a question of bomb yield and intercept time (earlier intercepts need smaller dV for obvious reasons)

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