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Posts by Jordan Ellenberg

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Minor Epiphany Concerning the World Columbian Exposition of 1894 and John Hughes It was felt that the 1894 exposition in Chicago needed a big iron monument to rival the Eiffel Tower, and a man named George Washington Gale Ferris had the decisive insight that what the occasion d…

quomodocumque.wordpress.com/2026/04/08/m...

1 week ago 3 0 1 0
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Brewers 8, Red Sox 6 I was in Boston for Pesach and stuck around an extra day because some more Wisconsinites, the mighty Milwaukee Brewers, were also coming into town to play the Boston nine. CJ and I took in the game…

quomodocumque.wordpress.com/2026/04/07/b...

1 week ago 4 1 0 0
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Armiversary Twenty years ago this week (I thought it was twenty years ago today, but I just went back and checked and it was April 3, 2006) I fell down a flight of stairs at MSRI and broke the absolute fuck ou…

quomodocumque.wordpress.com/2026/04/06/a...

1 week ago 3 0 0 0
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The College Boy and His Problems “The High School Boy and His Problems” (pdf at link) is a 1921 book by Thomas Arkle Clark, Dean of Men at the University of Illinois. I think “The High School Boy and His Problems…

quomodocumque.wordpress.com/2026/04/05/t...

2 weeks ago 2 0 0 0
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In which my daughter invents science While we ate our pizza I was talking with AB about differential equations, which they’re about to start doing in calculus. We talked about y’=y. “This is why populations grow expo…

quomodocumque.wordpress.com/2026/03/10/i...

1 month ago 5 1 1 0
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The Irrational Decision Ben Recht’s book The Irrational Decision: How We Gave Computers the Power to Choose for Us comes out tomorrow! I was privileged to get my copy early. And if you want an opinionated, informed,…

quomodocumque.wordpress.com/2026/03/09/t...

1 month ago 17 4 0 0
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Networking and granfallooning It has come to my attention that students at prestigious universities are referring to the practice of cold-emailing alums of their school and asking for Zoom calls to discuss possible summer inter…

quomodocumque.wordpress.com/2026/02/27/n...

1 month ago 4 0 0 0
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In which I rescue Harvard’s grading system The Harvard faculty is proposing to hard-cap A’s at 20% per course, leading to an undergraduate crashout the good old Yard has not seen the likes of since,the dining hall discontinued the Chi…

quomodocumque.wordpress.com/2026/02/25/m...

1 month ago 7 2 0 0
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Waiting for Godot (Gen-X rewrite) Here’s a good use case for LLMs — they are quite good at recovering the text from files you saved on a Macintosh word processor in the early 90s and have been transporting from computer…

quomodocumque.wordpress.com/2026/02/18/w...

2 months ago 2 1 1 0
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Now pitching, Cadeler Wellvich Barring any last-minute moves, and despite being linked to just about every big-name pitcher on the free-agent market, the Orioles will go into 2026 as they left 2025, without a clear #1 starter. D…

quomodocumque.wordpress.com/2026/02/06/n...

2 months ago 1 0 0 0
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What’s the entropy of a random integer? Surely people have thought about this but I couldn’t find anything on a short search. The question: let n be a random integer, say in [N,2N]. It factors as the product of p_i^a_i. So you can …

quomodocumque.wordpress.com/2026/02/03/w...

2 months ago 3 0 1 0
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Dick Gross Dick Gross died last month. Much has already been written, and during his lifetime too, about his immense contributions to modern number theory. So I won’t try to cover that here — don&…

quomodocumque.wordpress.com/2026/01/18/d...

3 months ago 8 1 0 0
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It’s a good old-fashioned Wisconsin booger-freezer out there! One of my favorite weather sayings. And I ran into a neighbor on my way home from the errand I was running so I got to say it in person, always a treat. 3 degrees Fahrenheit, sunny and windy in Mad…

quomodocumque.wordpress.com/2026/01/19/i...

3 months ago 2 0 0 0
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If one is not to make a mess of life “One must be fond of people and trust them if one is not to make a mess of life, and it is therefore essential that they should not let one down.” From E.M. Forster, “What I Belie…

quomodocumque.wordpress.com/2026/01/17/i...

3 months ago 2 0 0 1
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Bruhat intervals that are large hypercubes New paper up on the arXiv! With Nicolas Libedinsky, David Plaza, José Simental, Geordie Williamson, and (unofficially) Adam Zsolt Wagner. A bunch of algebraic combinatorists! And this is a combinat…

quomodocumque.wordpress.com/2026/01/12/b...

3 months ago 4 2 0 0
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Dyadiku I made a game. It’s like Sudoku but dyadic. It’s called Dyadiku. Try it! I’m very interested to see whether people find it playable and fun — in particular, does it admit a …

quomodocumque.wordpress.com/2026/01/05/d...

3 months ago 4 0 0 0
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Reaching the masses (not a Marxist post) Six popular math authors, including me, did a round-table interview for the Notices of the American Mathematical Society about talking about math to the non-academic public, or, as the Notices call…

quomodocumque.wordpress.com/2026/01/05/r...

3 months ago 3 0 0 1
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Self-portrait with about one quarter of Richard Serra’s sculpture Equal Visit the post for more.

quomodocumque.wordpress.com/2025/12/23/s...

3 months ago 6 0 0 0
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The American people have just one fixed idea “The American people have just one fixed idea and, since that dominant thought is money, it follows that their spirit has a certain uniform and unpleasant dryness… prodigality is an unf…

quomodocumque.wordpress.com/2025/12/19/t...

4 months ago 5 2 0 0
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How I know zombies aren’t real This piece of marketing doggerel from McDonald’s, concerning their Xmas-special Grinch meal, is the most foully defiling attempt to imitate Dr. Seuss’s verse I’ve ever encountered…

quomodocumque.wordpress.com/2025/12/12/h...

4 months ago 3 0 0 0
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Another example: sets of arcs and loops with bounded intersection Yet another example of the kind of problem that falls under the sphere packing / cap set / Turan umbrella I blogged about last week. Let G be SL_2(Z) and H be upper triangular matrices. Then G/H is…

quomodocumque.wordpress.com/2025/12/03/a...

4 months ago 2 0 0 0
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Random Americans, ethnic stereotypes, and large language models I have been reading about the tendency of poll respondents to overestimate the size of small population subgroups (e.g. if you ask Americans what proportion of Americans are Jews, they’ll say…

quomodocumque.wordpress.com/2025/11/30/r...

4 months ago 4 1 1 0
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“Not Vegan” I saw a guy today wearing a hoodie that said “Not Vegan.” I’m not vegan either, not even close, but come on. This is like wearing a “Yankees Suck” shirt. I hate the Ya…

quomodocumque.wordpress.com/2025/11/27/n...

4 months ago 5 0 2 0
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Mathgiving Happy Thanksgiving to all my American readers, and hey, everyone else too — gratitude is global. In the US, this is the start of the season where people customarily think about their charitab…

quomodocumque.wordpress.com/2025/11/27/m...

4 months ago 6 1 0 0
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Sphere packing, cap set, and the Turán problem are all the same thing OK, they are not really the same thing. But I got you reading, right? Here’s the sense in which they’re all the same thing. Let G be a group and H < G a subgroup. Let m > 1 be an …

quomodocumque.wordpress.com/2025/11/24/s...

4 months ago 6 0 0 0
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Let us now praise United Airlines I did manage to get home last night from Providence, despite widespread cancellations and delays caused by the government shutdown de-staffing air traffic control. United was speedy, flexible, and …

quomodocumque.wordpress.com/2025/11/08/l...

5 months ago 3 0 0 0
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I reviewed a book about the math foundations crisis for the New York Times I thought the book had some interesting virtues but was also quite badly overwritten, and very confusing in its treatment of the mathematics. Here’s my review. For length reasons I wasn’…

quomodocumque.wordpress.com/2025/11/07/i...

5 months ago 6 0 1 0
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Risk Modeling and Management for Natural Disasters Innovation by the Numbers | National Academies Learn more from the National Academies of Sciences, Engineering, and Medicine

I'm moderating an online discussion for the National Academies today, 3pm eastern, on math, risk management, and natural disasters!

www.nationalacademies.org/event/45862_...

6 months ago 7 0 0 0
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MacArthur Fellows: Wisconsin and Williams The 2025 MacArthur Fellows have been announced, and I’m very pleased that two of the 22 awardees are my UW-Madision colleagues: congratulations to Ángel F. Adames Corraliza from atmospheric a…

quomodocumque.wordpress.com/2025/10/08/m...

6 months ago 5 0 0 0
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Claudia Prieto, “Tus Ojos” Claudia Prieto is a Venezuelan singer-songwriter about whom I know next to nothing except that she recorded this gorgeous song, “Tus Ojos,” in 2018. By the way, I found out about this s…

quomodocumque.wordpress.com/2025/09/30/c...

6 months ago 3 1 0 0