Summer of Math Exposition

Presented by 3Blue1Brown 3blue1brown

Why Are There 180 Proofs for Euclid's Theorem?

Audience:

Tags: number-theoryproofs

Often the most famous theorems have hundreds of different proofs. But why do so many mathematicians “waste” their time reproving the same theorem over and over again? To answer this question, we look into three different proofs of Euclid’s Theorem (i.e. there are infinitely many primes) to see that each proof provides us with new insights and is therefore not just a repetition. If you only have time to watch around 10 minutes of the video then I recommend 00:00 - 05:45; 14:37 - 17:03; 24:08 - 26:10


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6.7 Overall score*
40 Rank
20 Votes
12 Comments

Comments

8

This was a very well-made explainer, and I enjoyed it overall! I think the connection to topology might be a a little oversold, since the topology is just packaging a number-theoretic proof (not using any serious results from topology). Great job overall!

7

The three proofs chosen are very beautiful, and the exposition is quite good. I have the following comments:

  1. The first few seconds of the video, where you “state” the same theorem in “different” ways, are quite confusing. You might lose some of the audience here. The statements do not seem to make sense, and you make a poor first impression.

  2. The sound quality is not great. This can be partially solved by using subtitles, but you need to leave space for them at the bottom of the screen so they don’t cover your text.

  3. I think that the relevant audiences for the different proofs are quite different. Anyone who can understand the last two is probably already familiar with the first one.

  4. In the first proof, the splitting into two cases feels artificial.

  5. As far as I know, the divergence of the sum of reciprocals of the primes is due to Euler. His proof was different, and it is perfectly fine to skip it and go straight to Erdős’s proof, but it is misleading not to mention Euler.

  6. In the second proof you “used” the uniqueness of factorization into primes. This is a non-trivial fact (actually more complicated than the theorem itself), so you need to mention it if you rely on it. However, you do not actually need to use it at all, since if it were false it would only be “in your favor.”

  7. The internet is not a good place for sarcasm (see Poe’s law -https://en.wikipedia.org/wiki/Poe%27s_law). So the sentence “for mathematicians a donut is the same as a cup,” in the context you gave, could be misleading instead of funny.

  8. You could have mentioned that the last proof, when compiled, actually becomes the first one.

  9. It is a bit misleading to present Furstenberg’s proof alongside other major results as “bridges” between areas. Furstenberg’s proof is really just a curious, fun example, unlike the other substantial results. To be fair, you did include the name of Furstenberg (and not just his proof) as the title of the bridge. Furstenberg indeed built important bridges between these topics, which fit well in the diagram. Moreover, one could argue that those substantial bridges drew some of their inspiration from Furstenberg’s presented proof. But you did not mention any of this…

Good luck

6.5

Talking about there being variety of proofs is definitely intriguing and the selection of these 3 proofs perfectly fits the premise. I like the attention to detail and the diagrams. The quotes help add a layer of narrative. However, in a lot of the frames there is simply too much text present in the visuals which begs the question whether I’d be better off just reading the proof in a written medium instead of watching the text animate on a video.

8.9

Each of the major proofs have been expressed in detail and with the right pacing. Recommend for all math enthusiasts.

8

Great video with a simple motivation that allows us to explore quite deep mathematics, surprisingly related to the topic. The only thing I need to pick on is the visual style. While it looks good and is very clean, for me it’s just a bit boring. I think I’m just tired of Manim animations and would appreciate a bit more original approach perhaps? Nonetheless great efforts. Good job!

6.3

This video is put together well, but not particularly ambitious. I believe that you motivate looking into the different proofs well and that the examples you chose fit together in a nice, coherent story. The way you go through the proofs comes off as rather dry — that is probably due to the topic of number theory, but especially in the third proof I think there would have been great potential to link your set of linear functions and their topology in a rewarding, visual way. As it were, I didn’t see the links there beyond the formulae, and this kind of topology really needs better explainers on the web. Visually, the video is close to an animated slideset and thus doesn’t fully leverage the medium, though this is tricky with your topic. All in all, I’d say this is a useful explainer that could have gone further beyond established formats.

6

This was a pretty good exploration of a few proofs. Maybe you could have elaborated on the connection to Legendre’s conjecture to show in more detail how this “deeper insight” comes about. It was hard to follow the big picture of Erdős’s proof, so some more outlining or commentary to tell that story would have been nice. I liked the quotes you selected.

6.7

Nice set of proofs, and the technical details were a lot easier to follow from the way the equations were shown

original proof - I liked how we avoided needing modular arithmetic ideas by just dividing over the reals and considering fractional part Erdos proof - helpful visualizations that made something purely algebraic Topology example - connecting this abstract open set def of a topology to the more geometric coffee cup example seemed like a stretch

7

I enjoyed the three proofs and I think it’s important to show multiple proofs of the same fact. Well done on the video.

9

Some parts in the latter two proofs may be difficult for beginners to follow as they do not explain some foundational facts, such as all integers having a unique prime factor decomposition, or why in Furstenberg’s proof the intersections must be infinite sets. However, the logic is tight and well-explained and Euclid’s proof is very easy to follow, and the whole video sets up the conclusion with a great message.

5

The notion, the premise of the video, is the most engaging.

3

This video seems to be lacking an audience: although the motivation suggests that we are trying to reach people outside of the sphere of research mathematicians, most of the runtime is composed of technical arguments that will be hard for them to follow.

Personally, I found the “3b1b-style” animations in the algebra to be more distracting than helpful— it felt like I was losing information that I needed to keep the logical flow in my head.

The timestamps that you suggested, focusing on the (beauty) sections, is a good abbreviation of the video. These were both important to supporting the thesis and were just fun to listen to. I see the dilemma you’re working with here (we don’t want to omit/cheapen the proofs, even though they take a while to explain) and I don’t really see what to do beyond making it an appendix XD

PS: I love the blitza as a contradiction symbol :3