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Comment by geocrasher | Hacker News Reader

This is very interesting and I appreciate the author's take on his own work: That it's not, by a long shot, the whole solution. It's great that he modeled the physics and all, and he acknowledges that the amount of work to turn that simulation into a landed rocket is just staggering.

The scale of the complexity comes seems analogous to the complexity of starting with nothing- no raw materials- and building something complex like an internal combustion engine.

Step 1: Find iron ore. Wait, what?

Step .5 answer "What is iron?"

Step .4 "What is ore?".

Step .3 "shoveling is hard."

Step .2 Banging rocks together.

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This sort of thing always runs into 'need the tool to make the tool' loops, where you end up substituting an inferior version long enough to get you to the next level.

Bootstrapping a working metal workshop from first principles would require you to re-run a substantial part of history including the re-invention of lost processes. You'll also likely get killed because quite a few of those processes are anything but safe. Our modern days materials science is very hard-won knowledge, and there aren't a whole lot of shortcuts on that route even if you have the knowledge itself.

Indeed! After I posted I remembered the book "How to Invent Everything" which takes the case of a time traveler stuck in the past with a guide to invent civilization from scratch. It's a cool read:

https://www.howtoinventeverything.com/

Looks interesting, thanks for the recommendation. Another one is "The Toaster Project", about how a guy made (well, sort of) a toaster from scratch:

http://www.thomasthwaites.com/the-toaster-project/

Bootstrapping civilization is a bit of a sub-thread in the three Zones Of Thought books by Vernor Vinge. Definitely my favourite SciFi books

I got bored in the second one when I realized there wasn't going to be any space travel, but otherwise I agree.

Assuming you mean Children Of The Sky (second as in sequel to the first one published), that one actually deals with this topic (bootstrapping technological advancement) maybe more than the other two.

I assume you didn't mean A Deepness In The Sky (second published, but almost stand-alone, super interesting dealing with practicalities of interstellar civilization in a universe with real speed limits) or A Fire Upon The Deep (second in-universe timeline)

I can't keep the titles straight, but yeah, I think it was Children Of The Sky. I just remember the story wandered away from scifi into political intrigue and didn't really move on from that.

There was also a lot of discussion about bootstrapping technological advancement in the first book published, which was interesting.

Clickspring more or less did this with his antikythera mechanism build

Thank you, I'll have to check that out.

> Step .2 Banging rocks together.

a cpu is just a rock that we tricked into thinking. but not to make it seem overly simplified, first you have to flatten the rock and put lightning inside it.

You're missing quotation marks around that quote.

:%s/thinking/computing/g

“If you wish to make an apple pie from scratch, you must first invent the universe.”

    ― Carl Sagan

The YouTube show How to Make Everything. Did this. They started the tech tree from the very beginning by making simple hand stone tools and then building up tool by tool to more sophisticated technologies.

If all you have is a hand. Even getting the wood to make a handle for your axe is hard.

https://youtube.com/playlist?list=PLLXfVEsLI-qRC_MAQZcVxpjtF...

Seems to me like a lot of the difficulty would be that the natural resources you need, in the absence of civilization, are scattered all over the planet, let alone deep underground.

I vaguely remember reading something about how even in the earliest days of making flint arrowheads, there were massive centralized mines that archaeologists have found. It wasn't like just because you were in the stone age chipping rocks, every location was equally accessible to the resources you needed. Similar to now, where you need a particular type of sand for concrete, or for fracking, or...

Interestingly there's technologies we might not be able to replicate if needed, as we've mined out the purest resources that we know of.

Particularly nuclear technology, since so much early experimentation was dependent on ores like from the Shinkolobwe mine in Congo with 65% uranium. These days finding ore with 1% uranium is considered a good find.

https://en.wikipedia.org/wiki/Shinkolobwe

Maybe our nuclear waste will fill the same niche in a post apocalyptic reconstruction of society?

The author says exactly that at the end of the article:

Its tempting to go “woah I just figured out how SpaceX lands their rockets!!”, but sadly, that’s not really true.

Once you have generated a physically possible trajectory that gets you where you want to go, there’s a whole host of things that you need to do to actually go follow that trajectory: state estimation, closed loop feedback control, dynamically updating that trajectory based on real time conditions… and many more that someone who is an actual aerospace engineer (which I am not) would know. Beyond that, these solvers take a long time to run, and online (real time) optimization is incredibly hard to pull off correctly and safely: one wrong input and your solver could just spit back “fail”, causing the thing to fall out of the sky.

Indeed I was trying to allude to his own take on it, that it's just a fraction of what's needed. I reworded it clearer. :)

yeah, just not in the title. He's in fact way off.

For one thing, it seems like the change in fuel mass, and its centroid relative to the body center of pressure, would be kind of important. But this was super- interesting as is. I’m glad it was posted here.

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