
“The moon blew up without warning and for no apparent reason” - mhb
https://jasmcole.com/2017/09/20/the-moon-blew-up-without-warning-and-for-no-apparent-reason/
======
jasmcole
Hey, author here. As several of you have noted, there are a lot of tweaks to
speed this simulation up - making it 2D increases (unphysically) the collision
rate, the particles have overly large collision radii, and the fragmentation
threshold is quite soft initially but then quite high for small masses.

Regardless, I hope the video is fun - the sudden burst of fragmentation makes
for quite the sight.

~~~
skizm
Thought you meant you were Neal Stephenson for a second!

Quick question: If I haven't read the book, but want to, are there any
spoilers in the article?

~~~
madaxe_again
You should definitely read the book, however. Hell, his entire corpus is one
“whoa” after another.

Still, Seveneves < Anathem, in my jumped up not so humble opinion!

~~~
wrinkl3
Anathem is probably Stephenson's best novel, and I say that as a huge fan of
Cryptonomicon and Snow Crash. I've actually found his last few novels lacking,
still struggling to finish The Rise and Fall of D.O.D.O. and REAMDE. I do wish
he'd stop trying to reverse-engineer RPG settings and got back to his post-
cyberpunk roots.

~~~
Florin_Andrei
REAMDE - don't take it seriously. The author basically just took a vacation
and wrote a mindlessly fun action book. If you read it as such, it's pretty
good. It's definitely written from a Western perspective, but it does have
some pretty astute insights about East European mentalities and culture (I say
this as someone straddling the fence between West and East culturally).

DODO is not pure Stephenson. The personality of the other writer (Nicole
Galland) quite clearly changes the atmosphere. It's the first NS book where
characters' emotions are actually given some attention, and the first where
female characters are described from a first-person perspective (in a way
that's convincing).

~~~
2sk21
REAMDE was surprisingly good and I learned a lot about gold farming in the
process.

------
Symmetry
Very nifty, but the fragmentation of bodies wouldn't look anything like in
Seveneves or this sim in real life.

[http://hopefullyintersting.blogspot.com/2015/06/seveneves-
an...](http://hopefullyintersting.blogspot.com/2015/06/seveneves-and-roche-
limit.html)

~~~
mnw21cam
Agreed. In all likelihood, the seven parts would collide a bit, heat up a lot,
and generally lump back together into a new moon. On that scale, the moon is
_really_ soft. So much so that each of the seven individual lumps would
probably flow into a roughly spherical shape before colliding with anything.

~~~
Florin_Andrei
Right. What most people don't realize is that at planetary scale (or even at
Moon scale) things are fluid. There are no solids at that scale. Gravity
dominates all other interactions except gas pressure - and that only for
things made mostly of gas.

That being said, I would love to see an accurate, 3D, high resolution
simulation of the scenario described in Seveneves.

~~~
Symmetry
It's not exactly what you wanted but this is pretty close. If I'd run into it
earlier I'd have put it in the blog post.

[https://www.youtube.com/watch?v=0XDZR_gENo8](https://www.youtube.com/watch?v=0XDZR_gENo8)

------
ajr0
This book [0] was quite enjoyable to read.

I realize the article is about far beyond the book, but in case anyone has not
read it yet, I highly recommend it as some good grade Sci-Fi.

[0] [https://www.amazon.com/Seveneves-Neal-
Stephenson/dp/00623345...](https://www.amazon.com/Seveneves-Neal-
Stephenson/dp/0062334514/ref=sr_1_1?ie=UTF8&qid=1506006374&sr=8-1&keywords=seveneves+Neal+Stephenson)

~~~
felipesabino
Oh, Seveneves! I once listed it as the book that disappointed me the most [1]
and seeing cool stuff like this simulation reminded me why again.

I think my explanation still reflects my opinions on the book and might be
relevant here:

> I didn't know it before I started reading it, but the book plot is divided
> in 2 (very different) acts.

> The first one just captivates you in a way that makes it very hard to stop
> reading or even thinking about it when you are reading.

> Little did I know when the second act started and oh man, it was a complete
> struggle. It seems that the pace changes completely to an almost stall and
> the book just became complete unreadable for me.

> While the first act took me days, the second took me weeks and weeks to go
> further in the book and even with my kindle saying I still had 15% to
> finish, I got so frustrated that I just quit and never even had the
> curiosity to know how it ends.

[1]
[https://www.reddit.com/r/books/comments/65z04t/what_book_dis...](https://www.reddit.com/r/books/comments/65z04t/what_book_disappointed_you_the_most/dgg7nts/?utm_content=permalink&utm_medium=user&utm_source=reddit&utm_name=frontpage)

~~~
magic_beans
What was so different between the two acts?

~~~
eric_h
The first act is about how the present day human race survives the moon being
destroyed. The second takes place 5000 years in the future and is essentially
about the return to earth.

I don’t share GP’s opinion, I quite enjoyed both acts. I do agree that the
pace of the two is quite different - the first being a bit more sci-fi
thriller pace and the second is a bit more contemplative.

~~~
Jemaclus
There's actually three acts: Earth, Space, Moon. It's really a trilogy smushed
up into one book.

I agree, though. The first two acts were great, and the third fell flatter
than the earlier two. But I enjoyed it nonetheless. It's nice to imagine what
would happen, and it's pretty hard scifi throughout, albeit greatly
accelerated.

~~~
rtkwe
Yeah, though I tend to like breaking it into 'the end of Earth and our efforts
to survive that end' and 'what happens to a society that's been through that
trauma and their return home' split. The time jump really makes the jump feel
more solid between book/acts 2 and 3 to me.

------
gus_massa
Nice simulation.

But I think that the assumption that all the collisions are elastic is too
unrealistic. I expect that adding the inelastic collisions, where two
fragments can merge in a bigger fragment, would produce a very different
result, where a big chunk (50%?) of the moon is reconstructed and get to a
stable almost circular orbit.

For comparison: "What Made the Moon? New Ideas Try to Rescue a Troubled
Theory" [https://www.quantamagazine.org/what-made-the-moon-new-
ideas-...](https://www.quantamagazine.org/what-made-the-moon-new-ideas-try-to-
rescue-a-troubled-theory-20170802/) HN discussion:
[https://news.ycombinator.com/item?id=15094302](https://news.ycombinator.com/item?id=15094302)
(59 points, 27 days ago, 18 comments)

~~~
CWuestefeld
This was my first beef with the book. It seems to me that

1) the forces involved in smashing the big chunks into smaller pieces make the
inelastic-ness of this significant, and because of this

2) there would not be the accelerating self-destruction that eventually turns
into the white rain.

Physics aside, the idea that multiple non-communicating groups, separated for
5000 years, would be able to communicate, is unrealistic. Two friends who are
linguistic professors tell me that the idea is preposterous.

------
tehsauce
For anyone interesting in toying with a Barnes-Hut gravity simulator that can
handle lots of particles and produce pretty pictures, here's one I made last
year for fun. [https://github.com/PWhiddy/Nbody-
Gravity](https://github.com/PWhiddy/Nbody-Gravity) Takes about a minute to set
up and start generating images and video (mac/linux only, sorry)

~~~
inetsee
"(mac/linux only, sorry)"

Don't be sorry. There's lots of software out there that I am interested in
from a quick read of its description, but I have to pass on it because it's
either Mac-only, or Windows-only.

(And, yes, I am aware of Wine and the existence of some emulators for older
versions of the Mac OS.)

~~~
oh_sigh
Also, the AWS free tier lets you get a windows VM for 750 hrs/month for
absolutely $0.

~~~
tehsauce
I have actually tested this nbody sim on the aws linux free tier :)

------
CodeCube
I love this post so much ... as a fan of Kerbal Space Program, the sentence,
"as long as you can deal with hundreds of pages of orbital mechanics" is super
interesting :P

~~~
jasmcole
I'm not even exaggerating. If you're into KSP, I think you'll like the book!

------
Negative1
As a huge fan of Neal Stephenson I found Seveneves to be one of his worst
books. Cryptonomicon, Diamond Age, Snow Crash; some of my favorite books so
the length of the book has nothing to do with it. The characters were flat,
unbelievable and unlikable. The dialogue was weak and awkward. The scenario
felt contrived and uninspired (the moon blew up, earth had to evacuate; yep,
Cowboy Bebop already set a high bar for this story).

I listened to this one in the car (10+ hours for books a week thanks to my
drive). Maybe it was a rough week but I had to stop halfway through because it
completely lost me. Maybe it gets better but having read the spoilers I really
can't imagine how.

But hey, your mileage may vary.

~~~
jsolson
With you on this one -- I've got all of his major works in first editions --
Seveneves is the only one I actively disliked. It's probably the only one I'll
never read again. Beyond being intensely depressing (near future enough that
everyone you know and love dies on the page... horribly), the plot felt about
as strongly held together as an average episode of network television, and the
characters managed to be both boring and unlikable.

------
rightisleft
If you liked this, you should read the Broken Earth series:

[https://www.goodreads.com/series/112296-the-broken-
earth](https://www.goodreads.com/series/112296-the-broken-earth)

~~~
loeg
They're pretty different. By the way, the connection to Seveneves is kind of a
spoiler for the first two books of Broken Earth.

~~~
frinxor
Your post was more of a spoiler !

------
logreybaby
Has anyone considered that the witches from "The Rise and Fall of D.O.D.O."
are responsible for the moon's destruction?

~~~
Florin_Andrei
That's a hell of an ODEC.

~~~
aeorgnoieang
> ODEC

?

~~~
Florin_Andrei
A fictional device in the DODO book. Describing it would be a spoiler.

~~~
aeorgnoieang
Thanks

------
leni536
I wonder how it would go in 3D. In 3D the relatively tiny Moon pieces have
much smaller rate of hitting each other and fragment into smaller pieces.

~~~
yoodenvranx
Isn't the whole process pseudo-2D even in a 3D simulation? The moon initially
moves on a plane around the and I guess most of it's broken pieces would stay
in that plane?

~~~
stefs
this might be true, but i don't see why it should be. if two pieces collide at
a high speed and shatter explosively, why would they stay confined to a single
plane?

~~~
mikeash
I think the plane change would be small, since the velocity change experienced
by the fragments would be small compared to the orbital speed. For empirical
support of this idea, consider Saturn.

~~~
Retric
Ring formation has an intermediate dust phase.
[http://curious.astro.cornell.edu/about-us/66-our-solar-
syste...](http://curious.astro.cornell.edu/about-us/66-our-solar-
system/planets-and-dwarf-planets/saturn/276-why-are-saturn-s-rings-flat-
intermediate)

Another consideration the moon does not orbit the earths equator but Uranus,
Saturn, and Jupiter's rings do. This suggest tidal forces play a major role
and you would not end up with a ring in the same inclination as the Moon's
orbit.

------
gasbag
This is tangential to the article, but one of the more interesting and less-
discussed aspects of Seveneves is the ubiquitous surveillance that everyone is
living under. Most characters hardly give it a thought most of the time. The
way that this later becomes essentially an epic myth composed of original
footage, and how it has tangible effects on subsequent cultures, is kind of
fascinating.

------
ytjohn
On barely related note, I immediately thought about Three Moons Over Milford,
in which the moon breaks into three chunks and rains meteorites down on the
surface. As it turns out the tile comes from Seveneves, which has a similar
concept. The TV show focuses on the life of the townspeople, while Seveneves
focuses on the science and drama of the exploded moon. Stephenson started
working on his book in 2004, completing it in 2013. TMOM came out in 2006.

Again, these are two completely different stories with only a common catalyst,
but I wonder if the idea for TMOM may have come from someone that knows
Stephenson (ie, he mentioned the idea in 2004/5 to someone that ran with it),
or if the creators are even aware of the other.

[https://en.wikipedia.org/wiki/Three_Moons_Over_Milford](https://en.wikipedia.org/wiki/Three_Moons_Over_Milford)

[https://www.nealstephenson.com/seveneves.html](https://www.nealstephenson.com/seveneves.html)

------
unwaryquerier
Check out
[https://en.wikipedia.org/wiki/Kessler_syndrome](https://en.wikipedia.org/wiki/Kessler_syndrome)

Similar but with low earth orbit

------
ryan606
Last I read, Ron Howard was involved in producing the movie adaptation. Anyone
seen any update on this project recently?

~~~
gasbag
I haven't heard anything since the announcement. IMDB's last update was in
January. It's not just Ron Howard though--it's also a bunch of the people who
worked on the Apollo 13 film, which seems like a very good fit.

Unlike a lot of folks, I liked the second part of Seveneves, but I won't miss
it if they cut it from the film. I don't even know how they'll fit the whole
first part in without a 3.5 hour running time.

------
tw1010
I absolutely loved this blog post. This, incidentally, is the perfect thing to
blog about if you're looking for ideas. Just read books and things outside
what is normally part of the engineering culture, in the meanwhile keeping all
the things you're good at (e.g. mathematical modelling) or interested in in
the back of your mind. When you stumble upon the intersection of things you're
technically good at and things you read about, do some cool research or write
some code and then post it on HN and there you go.

~~~
pault
I agree, but I don't think Neal Stephenson is outside of engineering culture.
:)

~~~
SOLAR_FIELDS
I was frankly surprised seeing this thread just how popular Stephenson is
here. It makes sense though.

------
ergothus
First, spoilers for the first few chapters below, if you care about such
things.

This (neat!) article and the comments here (so far) miss/skip a few details
(or my mind is making fake memories again).

1\. Regarding the destruction of Earth - IIRC, while the pounding (and
subsequent geological and atmospheric responses) the Earth was to receive was
an ELE, the real kick in the teeth was the cumulative heat generated as much
of a moon's worth of mass burned up in the atmosphere.

2\. Regarding whether the moon would just sit there fragmented or mirror the
descriptions of the book - IIRC, the moon didn't just break, it was _broken_
(by what is never known). So whatever thing wielding a massive physics bat did
that, it can also impart all sorts of momentum. Pretty easy to say that if you
can get the end result from SOME starting conditions, that those starting
conditions could have been created by the Deus Ex Machina.

I know no orbital physics, but isn't the solar system is a great example of
showing how big rocks in orbit become fewer, smaller rocks given enough
iterations? So far as I know, asteroids occasionally manage to strike one
another (defying the vastness of space by their numbers and persistence) and
asteroids can capture smaller bits, but on the whole asteroids are getting
smaller, not larger (albeit at a cosmically slow pace).

'Course, I could be wrong. Had an hour long argument with a friend who said
that there was no angle that would allow one mass to capture another
approaching mass approaching into orbit, while I was relying on my experience
of reading of various suspected "captures". After much googling, we decided he
was right from a two-body position, but that the Sun ( or other mass) can
provide the necessary nudge to turn a swingby into a lasting orbit, so I could
be right too.

------
Florin_Andrei
> _I thoroughly recommend it, as long as you can deal with hundreds of pages
> of orbital mechanics._

You say that as if it's a bad thing.

~~~
cjsuk
This is the warning I got when I borrowed someone’s three volumes of Feynman’s
lectures in physics except with pages of calculus. It was a wise warning.

------
robterrell
Wow, this is perfectly timed for me. I just read Seveneves last week.
Interesting that this simulation results in a "white sky" event half a year
after the moon explodes -- in the book this takes a few years.

~~~
delecti
The article mentions that he chose to use a larger than accurate size for the
simulated earth to speed up the simulation. That suggests that "in real life"
it would in fact take longer.

------
seansoutpost
You should have used Parambulator to create a more precise model :) Awesome
job.

------
SunTzu9087
So... one big thing I recall from the book is the collective collisions turn
the world into an enormous ball of fire for decades. If (according to the
simulation) the number of collisions tapers off after a couple years, does
that mean the world would be habitable again in short order? I understand
that, for the purposes of the book's arc, the planet needed to be rendered a
literal hell for as long a time as possible... but perpetual burning seemed a
bit far-fetched.

------
mmaunder
Aw! I thought Seveneves was amazing and the orbital mechs made it even better.
(Author sounded like it was tedious in the opener)

I absolutely LOVE it when a scifi author gets that stuff right and it's great
working it through in your head as you absorb the story they're weaving.
Really added something to the book. Very much like Arthur C. Clarke's work -
stuff that would work that way in real life.

------
robotcookies
Does this account for the size of the pieces? Every time they fragment, the
pieces would get smaller making it less likely to hit another.

------
m1el
While the simulation is really cool, I doubt it represents the reality
(assuming the Moon blew up).

Why I think so: the planets have formed out of space debris, they didn't all
fall into the star.

> Pairwise collisions between bodies – most of the collisions are approximated
> as elastic.

Yeah, that's one reason why.

> A static mass at the origin of a 2D co-ordinate system – this is Earth

Why not simulate the Earth too?

~~~
marcosdumay
> Why I think so: the planets have formed out of space debris, they didn't all
> fall into the star.

Nearly all of them did, there is way more mass on the Sun than orbiting it.

~~~
mikeash
Just to put a number on "way more": the Sun contains 99.86% of all known mass
in the solar system.

Of the 0.14% of the solar system that isn't the Sun, Jupiter accounts for
roughly two thirds of it.

------
Adamantcheese
Neat! But wouldn't Earth's gravity be affected by all the additional mass from
moon-meteorites hitting it? It probably wouldn't be by much, but possibly
enough to have an effect on how long it would take before the number of
collisions leveled off.

------
User23
More support for the exploding planets hypothesis!
[https://www.bibliotecapleyades.net/sumer_anunnaki/esp_sumer_...](https://www.bibliotecapleyades.net/sumer_anunnaki/esp_sumer_annunaki23.htm)

------
lloeki
Is the second paragraph of TFA spoiling the whole book, or is that just part
of the premise that is set up during the first chapter or so? Because it just
sounds like a _massive_ spoiler.

~~~
unoti
The moon breaks up in the opening sentences of the book. But the realization
that it'll destroy the planet doesn't come for some time later. That part is a
bit of a spoiler. But the moon blowing up just can't be good for the planet
long term, so maybe it's not too big of a spoiler.

Earth is the Ned Stark of Seveneves.

~~~
mikeash
I checked it out on Amazon, and the threat to the Earth is out in the open by
the 27th page of the story in the hardcover edition. It's also literally the
first sentence in the blurb on the back cover.

------
scosman
Bill Gates loves this book:
[https://www.gatesnotes.com/Books/Seveneves](https://www.gatesnotes.com/Books/Seveneves)

------
odammit
If you don’t get the reference and you like scifi Seveneves is awesome. It’s
not hard scifi.

I managed to finish it in two days. Super entertaining.

Anywho, this visualization is cool to see after reading the book.

~~~
aeorgnoieang
> It’s not hard scifi.

I'd say it's pretty hard sci-fi. What's harder?

~~~
odammit
There are _fish_ people. So...?

~~~
aeorgnoieang
There are currently mammals living in the water, some people already have
webbed feet, the "fish people" had evolved over 5,000 years, and their
ancestors may have had access to advanced genetic tech. The book also
references epigenetics pretty heavily in that part of the book; presumably
that's involved in the evolution of all of the different surviving human
groups.

It certainly wasn't the _hardest_ science element of the book, but it seems
pretty well supported for scifi.

That was also one pretty minor element of the book as a whole.

I still can't think of another book that's 'harder' scifi (and not also like
really-close-near-future).

------
bawana
so how much does this contribute to global warming? no, seriously, how much
does temp actually rise and can an equilibrium temp be predicted? Roughly how
much of the energy can be accommodated by phase change of the oceans into gas?
Once the increased vapor content in the air is calculated, then a predicted
greenhouse event can be calculated.

------
VectorLock
I'd love to see the source code for this.

------
blocked_again
Am I the only one who gave up reading Seveneves because of pages and pages of
complicated orbital mechanics?

~~~
vkou
No, I know of other people who did. I was personally bored by those sections,
since I already have a good understanding of them - so I skimmed through
parts.

------
jjallen
This article should come with more of a SPOILER ALERT for a book I would like
to read at some point.

~~~
ghaff
It's not a spoiler by any meaningful definition of the word.

~~~
jjallen
Isn't just the title of this Hacker News entry and the connection with the
book a massive spoiler? Could argue it got me intrigued, but wondering what
Stephenson intended. (I always wonder about not putting spoilers in movie
trailers for instance)

~~~
sorenjan
The title of this post, "The moon blew up without warning and for no apparent
reason", is the very first sentence in the book [0]. It's not a spoiler for
any meaningful definition of the word, the word spoiler should be reserved for
things that spoil the enjoyment of a work, like a surprise ending.

[0] [http://www.nealstephenson.com/news/2015/04/13/seveneves-
exce...](http://www.nealstephenson.com/news/2015/04/13/seveneves-excerpt/)

~~~
lukejduncan
For what it's worth, when Stephenson does readings he always reads passages of
the book that won't give spoilers. He made a statement when reading seven eves
"let me tell you now. The moon blows up. That's not a spoiler, it's the first
sentence. And no, I won't tell you why. It blows it in the first sentences so
I don't have to come up with a reason." (My paraphrasing)

------
hodder
Pretty cool work. Thanks for sharing. Articles like this are what makes HN
great.

------
Anatidae
Well, shucks. There goes my idea for blowing up the moon next 4th of July.

Now, how am I going to out-do the neighbor now?

------
SubiculumCode
That was pretty damn cool

------
cschmidt
The first 11 words are cool. But my favorite was the chapter heading that said
"Five Thousand Years Later".

~~~
no_protocol
I think that is a spoiler, can you remove it?

~~~
zbentley
It might be a spoiler, but it's also a fascinating thing about this book. If
it were broken in half, into two books, at the point GP refers to, they would
barely even be in the same Dewey Decimal section. The two parts of this novel
are incredibly different--moreso than almost any other fiction books I've
read. A lot of people are unhappy about that; they get into the
ambience/groove of one part and have to deal with a massive
stylistic/thematic/character shift. Personally, I love it.

~~~
treerock
I'd recommend Cloud Atlas. It's like 6 very different books in one.

[https://en.wikipedia.org/wiki/Cloud_Atlas_(novel)](https://en.wikipedia.org/wiki/Cloud_Atlas_\(novel\))

~~~
delecti
It's also a rare example of a book whose movie adaptation is really worth
watching. I watched the movie first, and I think both the book and movie are
better thanks to the other. The book makes it clear how each story exists in
the next, and the movie gives a better sense of how the themes of the books
tie together, despite their differences.

To anyone who reads Cloud Atlas, I strongly recommend you also watch the
movie, and vice versa.

