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The most unexpected answer to a counting puzzle

3Blue1Brown · Youtube · 202 HN points · 5 HN comments
HN Theater has aggregated all Hacker News stories and comments that mention 3Blue1Brown's video "The most unexpected answer to a counting puzzle".
Youtube Summary
If this doesn't blow your mind, I don't know what will.
Part 2: https://youtu.be/jsYwFizhncE
Part 3: https://youtu.be/brU5yLm9DZM
Brought to you by you: http://3b1b.co/clacks-thanks

New to this channel? It's all about teaching math visually. Take a look and see if there's anything you'd like to learn.

NY Times blog post about this problem:
https://wordplay.blogs.nytimes.com/2014/03/10/pi/

The original paper by Gregory Galperin:
https://www.maths.tcd.ie/~lebed/Galperin.%20Playing%20pool%20with%20pi.pdf

Evidently, Numberphile also described this problem (I had not known):
https://youtu.be/abv4Fz7oNr0
You'll notice that video has an added factor of 16 throughout, which is not here. That's because they're only counting the collisions between blocks (well, balls in their case), and they're only counting to the point where the big block starts moving the other way.

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These animations are largely made using manim, a scrappy open source python library: https://github.com/3b1b/manim

If you want to check it out, I feel compelled to warn you that it's not the most well-documented tool, and it has many other quirks you might expect in a library someone wrote with only their own use in mind.

Music by Vincent Rubinetti.
Download the music on Bandcamp:
https://vincerubinetti.bandcamp.com/album/the-music-of-3blue1brown

Stream the music on Spotify:
https://open.spotify.com/album/1dVyjwS8FBqXhRunaG5W5u

If you want to contribute translated subtitles or to help review those that have already been made by others and need approval, you can click the gear icon in the video and go to subtitles/cc, then "add subtitles/cc". I really appreciate those who do this, as it helps make the lessons accessible to more people.

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3blue1brown is a channel about animating math, in all senses of the word animate. And you know the drill with YouTube, if you want to stay posted on new videos, subscribe: http://3b1b.co/subscribe

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All the comments and stories posted to Hacker News that reference this video.
I also love the idea that computation (ie rule/recipe-following) is fundamental to nature/reality, but I don't think it's pure-maths that is the bedrock.

Pure maths (as a tendency, not strictly) focuses on formal systems that are on the consistent end of the spectrum (as those are the ones that can be used to build more maths on top of). Nature probably doesn't (or needn't) have this restriction/tendency! Formally consistent might be higher performing in many cases (more stable over long time-spans, like dna), but it is not the end of the story as to what is ultimately possible in rule-following systems! Any sense of determinism demands this, even if the system makes its own rules as the universe/reality - the ultimate all, with nothing outside of it - must. Whether this fully gives way to a properly random (like an oracle of rand) system at the quantum level is still an open question.

It is possible to expand ones view of nature/ultimate-reality to include other rule-systems (such as including inconsistent or entirely 'complete' systems.) This can have more coverage (completeness) of any particular model, or even be totally incomplete and inconsistent! These 'degenerate' (according to maths) formal systems might sometimes be the ones that happen to work in nature/reality. Once you do this extension, now you're talking about computation, admitting a broader class of rule-following than pure maths. You can argue that the two are equivalent because sure, anything can be translated between them - i'm more talking about tendencies here. The computational universe includes lots of formal systems that are abhorrent or impractical to mathematical understanding, so mathematicians avoid them, but nonetheless they are still rule-following! Nature/evolution probably uses/finds those rules where they are the best performing solution (through its exploration of possibilities).

As to 'optimal end-states', I'm afraid you've lost me there. I gave up teleology (the idea that the universe or nature or evolution have any obvious goals) a long time ago, how could anything like that (high level) feed-in to reality? There is no hint of this in all of science. What self-organises and self-replicates is what persists. This self-support might even reach down into physics!

To me, religion is nearly the opposite to all of this: An explanatory system that says explanation-of-reality='fixed string' with no update method available. Very incomplete (unless ridiculously long, which current examples of religion are not) and inconsistent: The fixed string might assign True and False at once, or neither - to new knowledge that falls outside the original scope of its meaning.

So no, I don't think that this pi-result suggests that religion and science have a commonality here. Pi is awesome (even though very constructible) and we should probably expect to find it [0], especially in places like this (pure QM) that involve geometry.

[0] https://youtu.be/HEfHFsfGXjs

Oct 03, 2019 · s_gourichon on Spaghetti Sort (2018)
Reminds me how you can compute pi in a hilariously inefficient yet very interesting way with a physics engine by counting collision of 3 blocks bouncing with one another: https://youtu.be/HEfHFsfGXjs
This is a time someone must cite 3Blue1Brown: [(183) The most unexpected answer to a counting puzzle - YouTube](https://www.youtube.com/watch?v=HEfHFsfGXjs)
This is the second video in a series, first video: https://www.youtube.com/watch?v=HEfHFsfGXjs
Jan 20, 2019 · 155 points, 25 comments · submitted by espeed
edh649
The explanation video: https://www.youtube.com/watch?v=jsYwFizhncE
earthicus
An interesting response to the explanation video from u/functor7 on reddit:

https://www.reddit.com/r/math/comments/ahz8k3/so_why_do_coll...

PuffinBlue
This is kind of a plea for help - how can I learn maths 'via' geometry?

I just can't get my head around 'numbers'. I can't seem to really visualise them or understand what they are. I know this sounds weird. With language or abstract things like 'problems' I can almost see them in my head. I can analyse a problem and all it's flows of cause and effect in a visual way. That's literally what happens in my head.

But with numbers I can't understand them at a basic level. Like - what are they? How do I visualise them?

When it comes to geometry it's almost like it's the 'language' of my brain, how I think, in terms of shape and form and translation and dimension.

I'll give you an example. I learnt Pythagoras theorem aged about 13 or something. But didn't truly understand it until I was about 20 something when I saw a diagram showing graphically the squares of the sides like this[0].

I really need to start at the absolute beginning, like build of a whole foundation of what maths is based on geometry. Does that even exist?

This might not be possible, but if I can even get started it would be great.

[0] https://mysteriesexplored.files.wordpress.com/2011/08/pythag...

PinkMilkshake
I think I know what you are getting at. You may have something like dyscalculia[1], but I'm not a doctor.

There are several mental models used for picturing numbers. I think the most popular is the number line [2]. Common Core uses this in a clever way. I've never found it useful personally.

I suspect some people might see numbers as purely symbolic and perform purely symbolic operations. When the symbol 2 and the symbol 3 have the operation 'add' applied, it yields the symbol 5. Or something.

I think I mostly visualize the numbers as a quantity of solid objects. So I think of 3 as 3 things. This has limitations. I can break objects apart but how do you visualize 3.767? So some of it is intuitive.

There is evidence that the human mind can only encode exact quantities up to four [3], after that they use an estimate. [4] So maybe your situation is the norm. What I mean is, sometimes it can feel like everyone else has 'got it' and you're the one lacking, when in reality everyone is just as bad.

[1] https://en.wikipedia.org/wiki/Dyscalculia [2] https://en.wikipedia.org/wiki/Number_line [3] https://en.wikipedia.org/wiki/Parallel_individuation_system [4] https://en.wikipedia.org/wiki/Approximate_number_system

abecedarius
Just one suggestion, but https://www.euclidea.xyz/ is a great place to start. Visual Group Theory sounds appropriate too: https://www.amazon.com/Visual-Group-Theory-Problem-Book/dp/0...
brianpgordon
I think this is a better image for the Pythagorean theorem:

https://i.imgur.com/UxZ3fQR.png

empath75
Have you watched the khan academy videos? He leans on geometry and visual intuition quite a lot.
earthicus
If you managed to survive high school algebra, you might be able to 'redo' your basic math education with a geometric bent from Stillwell's book 'Numbers and Geometry', which teaches the classical link between the two subjects that has been eliminated from elementary education to some extent. However, the kind of intuition he presents is still semi-abstract - it's not a super duper picture heavy book - but I think it's about as close to what you're asking for as you are likely to find.

https://www.amazon.com/Numbers-Geometry-Undergraduate-Texts-...

jhrmnn
Geometric proofs of problems that do not seem to be geometric are the most satisfying in my experience.
ColinWright
I wrote about this nearly four years ago:

https://aperiodical.com/2015/03/%cf%80-phase-space-and-bounc...

It doesn't have nifty visualisations, but the (mythical) interested reader might find this a useful complement to the video and explanation provided there.

Edit: Thought so - I did submit my write-up at the time:

https://news.ycombinator.com/item?id=9202913

jsweojtj
Your links to the original paper are broken in that writeup.
ColinWright
Bother.

Thanks for the catch, I'll get onto the hosts and get them to fix them.

Cheers.

ColinWright
And for completeness - now fixed. Thanks again.
qualsiasi
I wrote a small Java program to verify the collision count, just because I was bored and laying on the sofa:

> https://github.com/Qualsiasi85/collision-pi

warning: code is a mess - and may have all sorts of nasty bugs, but after all this has been done for fun and doesn't need to be "enterprisey" :)

I do like this kind of videos, they tickle my fantasy and keep alive my passion in programming (that is slowly dying because of work! :) )

Outermeasure_A
There was an ACM problem a few years ago where it was asked to count the collisions. We implemented the simulation and noticed the digits of PI but we didn't actually proven the fact. Got AC.
Aardwolf
Nice, but I miss the more fundamental series of 3Blue1Brown like "the essence of linear algebra" series, the "essence of calculus" series, and the unfinished "deep learning" series from more than a year ago

Shame that this awesome visualization method he uses isn't used more for more fundamental concepts to learn from the ground up rather than specific puzzles like lately, I learned a lot from the "essence" series!

empath75
The solution he posted is about using phase spaces, not really about this problem in particular.
ragebol
> Shame that this awesome visualization method he uses isn't used more ...

The animation engine is on GitHub so you can make your own: https://github.com/3b1b/manim

kowdermeister
I think the are in the works, but it's just a guess. There's a subreddit for fans, you might post your wish list :)

https://www.reddit.com/r/3Blue1Brown/

Aardwolf
By the way, I don't want to sound unhappy about the videos, the answer for sure is interesting indeed, I totally don't want to say it's bad content at all, it's awesome in every way, graphics, audio, explanation, ... :D
thanatropism
The essence of linear algebra is vector spaces and linear transformations. It's not entirely impossible (although probably way more difficult) to learn it without reference to Euclidean spaces and geometric reasoning.

Should be called "The intuition for linear algebra". But heck, the whole reason we have and teach the mathematical method is that intuition either breaks down in interesting cases (e.g. stochastic integrais versus "an area under a curve" integrals) or limits you (linear algebra in function spaces, etc).

It's a nitpick. I love 3b1b.

cordonbleu
we should probably make an attempt to distance the term gravity from our model of the universe. when a mass is in motion an inertial wave is created, this is an inertial reference frame, the frame dragging that occurs is a set of harmonics, that are nodes in the hyperbolic field structure of spacetime. these nodes correspond to dividends of Pi, thus any inertial phenomenon "spirals down hyperbolicly" into subspace to become heat [quantum field pertuberance]
3blues1brown
3blue1brown’s voice is like nails on a chalkboard. Hearing it for more than half a minute is tedious, hearing it more than once is regrettable.
kylnew
I understand maybe 30% of 3blue1brown’s videos, mostly due to his excellent visualizations, but he really gets me excited for math in a way I’ve not experienced before. How does he make such awesome visualizations? Does anyone know what tools are being used?
danra
A few tools, detailed in his FAQ page. https://www.3blue1brown.com/faq/
nradk
He has written a python library called "manim" for his visualizations https://github.com/3b1b/manim
chrisdsaldivar
He built a python library for his visualizations called manim available on his github [1].

[1] https://github.com/3b1b/manim

Jan 15, 2019 · 2 points, 0 comments · submitted by xorfish
Jan 14, 2019 · 3 points, 0 comments · submitted by mykowebhn
Jan 13, 2019 · 40 points, 0 comments · submitted by jgamman
Jan 13, 2019 · 2 points, 0 comments · submitted by xucheng
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