Hacker News Reader

Comment by jchanimal | Hacker News Reader

I can't help but think of https://en.wikipedia.org/wiki/Seveneves about the aftermath of the splitting of the moon.

Worth pointing out square/cube factors here. You can't have an ant the size of an elephant because while an animals strength goes up as its length squared its weight goes up with its length cubed. And a piece of rock the size of the moon doesn't shatter into seven pieces the way a piece of rock a meter across would. It splashes.

Yeah, planets are puddles.

It's also easy to forget the brown-dwarf-hot body inside the Moon (and the star-hot one beneath our feet). Thanks to the rock insulators between us and them, and our universal heat sink. A disassembled Moon exposing mantle material... even with T^4 blackbody energy scaling, a bolide rain a year later very won't be a problem for humans. Comparing lunar mantle with Sun, say 6x cooler, 390x closer, and say <10x angular smaller - 390^2 beats 6^4, leaving what, a new 100x "Sun"?

I liked your comment but then I "fact-checked" it. OT but curious how wrong this is: https://chat.openai.com/share/638e5461-7a4d-4c12-9103-da1b81...

Oops, estimation fail, thanks! Attempt to double spend "closer" - on both "smaller" and "cooler". A sun-hot Moon gets you only a second Sun. A lunar-mantle-hot Moon gets you merely an extra dim red dwarf "sun". The "100x" brighter was wrong. More like 1000x dimmer?

The ChatGPT looks surprisingly ok. It struggled where textbooks and such are less than wonderful. So it raises the irrelevant Sun's core, and says "The Sun's energy output is vastly greater due to nuclear fusion reactions, emitting a massive amount of radiation across the electromagnetic spectrum. The Moon, lacking such reactions, emits no comparable energy.", perhaps reflecting the textbook "Sun shines because fusion" vs "Sun glows because hot, and hot things glow (with color and intensity proportional to temperature^4), and fusion is why it's still hot billions of years after forming". Though in a way it's true - "The Moon lacking such reactions, and being small, has cooled off and greatly dimmed since its last big formation impact". :)

The "Brown dwarfs typically range between about 1,000 and 2,500 degrees Celsius at their surface, far hotter than the Moon's mantle." seems inconsistent with [1].

Thanks for the check!

[1] graph: https://media.springernature.com/lw685/springer-static/image... source: Fig 2 on page 9 of https://hal.science/hal-02863845/document [PDF]

Although curiously, most processes theoretically capable of exposing large amounts of lunar mantle would likely generate a decent fraction of that heat just on their own merit.

My god, I saw this comment and thought it'd be fun to pick up something by Neal Stephenson. After all, I loved Cryptonomicon back in college. But it's 880 pages! As a slow reader, this is sadly not something I'll ever get to.

You've been misled by the publisher. Seveneves has about 600 pages. After that, the pages are filled with some kind of fan fiction sort-a related, but pretty dumb, novella (confusingly named "Part Three").

Now, seriously. While the first two parts are great, the third is awful. You can actually skip the part 3, it is completely superfluous (and again, dumb), the story works without it better.

The last part was a nice change of pace after the super depressing middle section. It was a relief to see how the humanity was able to survive and adapt.

> super depressing middle section

That's IMHO Stephenson at his best.

> It was a relief to see how the humanity was able to survive and adapt.

Could be, but the execution of that was very lacking. The story arc, characters just don't cut it. Additionally, I was particularly disappointed at the genetic determinism, which Stephenson surely knows is extremely dubious. I suspect that the only reason he wrote / included this part into the book is the allegory of the seven Eves.

I found the same thing with "Fall, or Dodge in Hell" - the first part was great, the second awful. I'm wondering if Stephenson just can't handle multi-act stories.

I agree and even though I usually have a lot of complaints about Stephenson's later books, I just keep reading them for some reason. There are real high and low points. He's the only author who I've read completely and I love to complain about him.

Stephenson is just very inconsistent. Some of his work is real treasure, some just meh. He's famous for building fascinating worlds, getting some action going, but then not being able to deliver a satisfying ending (e.g. Snow Crash, Diamond Age).

Anathem is for me his only well-rounded book where he delivers on all fronts.

I disagree with The_Colonel. Part 3 has a different setting from the rest of the book, but is still part of the overall story. It is a logical extrapolation of the first two parts, and specifically follows up on a plot twist that appears at the end of part 2.

Listen to the audio book. I did, and it's very good.

I wouldn't call myself a slow reader, but I just don't have the time to sit and read paper books very often. Instead I listen to audio books while driving, doing chores, etc.

I have a family member who is a slow reader, but thanks to audiobooks, finishes over a hundred books a year.

FWIW, I read it in just a few days because I became so engrossed by the story.

Or Life As We Knew It for a good YA novel, post-apocalyptic survival after a huge asteroid nudges the moon to a different orbit and destroys the climate on earth.

Reply on news.ycombinator.com