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James King

@jamesking.io

79 followers 133 following 102 posts

Digital product designer from London. Founder at science-practice.com and co-founder at fora.health. Contributor to the Ergodicity Economics research community. jamesking.io

Posts Replies Media

James King @jamesking.io · 01/10/2026

Just made my own glanceable podcast feed using Alex’s idea. Here is a YouTube lecture on general relativity that is converted to an MP3 playing on my lockscreen (via Overcast). I can listen to the lecture and glance at the black board when needed.

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James King @jamesking.io · 03/08/2026

I am sure that @observablehq.com will add this feature soon, but until then… I made a tool that exports Observable Notebooks 2.0 documents from the new Observable site. Useful for editing locally in Observable Desktop. tools.jamesking.io/observable-n...

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James King @jamesking.io · 29/07/2026

Poundstone is really good at exposition of mathematical concepts. I really like this description of ergodicity (pic, with alt text included). The book is chock full of efficient explanations like this. Do read the book!

FORTUNE'S FORMULA

Like that other formidable E word, entropy, ergodicity is a term from thermodynamics. Nineteenth-century physicist Ludwig Boltzmann used it to describe atoms. A system is ergodic if the fate of each individual atom over time is representative of a large group of atoms.

That is best introduced with an analogy. Suppose I work in quality control at a dice company. It's my job to make sure the dice are fair. One way to test the fairness of dice is to pick a die off the production line and roll it many, many times. I can tally how often each face lands up (the tallies should be close to equal) and compute an average of the numbers rolled. It should be close to (I+2+3+4+ 5+ 6) / 6, or 3.5.

That's a lot of work for a plastic cube that's going to retail for pennies. Here's a quicker test. I scoop a big basket of dice off the production line and heave them all onto the factory floor at once.

Then I tally and average the results.
The first test involves a time average because I'm looking at an individual die's outcomes over time. The second test uses an ensemble average, for I'm using a group of dice's outcomes at a single moment in time.
Customers care about how the dice they buy will behave over time (and not so much about the other dice they didn't buy). The time average is more directly relevant. But the ensemble average is easier to use when there are truckloads of dice to inspect. It would be nice if the time average and the ensemble average were the same.
Well, there's a word for that, and it's the word you may have just learned: ergodic. Fair dice can be considered ergodic, meaning that time and ensemble averages are the same.

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James King @jamesking.io · 29/07/2026

The book tells the story of the Kelly Criterion, an application of information theory to the domains of gambling and economics. It is enormously entertaining! The contents page gives a flavour: long-running intellectual feuds interwoven with gambling schemes. It would make a great movie.

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James King @jamesking.io · 29/07/2026

Just finished reading the 20th anniversary edition of Fortune’s Formula by William Poundstone. It is such a good book. The new edition has an extra part, titled Ergodicity, which covers the work of Ole Peters and others.

The cover of William Poundstone’s book, Fortune’s Formula, 20th Anniversary edition.

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James King @jamesking.io · 30/06/2026

No, the nav is not a png. Yes, the text is selectable. Yes, including the "o"s. eiko-fried.com

A screenshot of Eiko Fried's website, cropped in close to show the navigation. Each "o" in the text of this navigation (Eik"o", Ab"o"ut, Bl"o"g etc…) has been replaced with a circular dot, representing a node in a simplified network. These are connected with other nodes outside of the text with lines that represent edges in the network.

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James King @jamesking.io · 29/06/2026

Finding the new @observablehq.com unexpectedly useful for checking my maths notation and understanding. new.observablehq.com

A screenshot of an Observablehq.com notebook with AI assistant providing feedback on mathematical notes written in Tex and Markdown.

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