February 27th, 2025

The three-dimensional Kakeya conjecture, after Wang and Zahl

Hong Wang and Joshua Zahl have resolved the three-dimensional Kakeya conjecture, proving that Kakeya sets have dimensions of three, while introducing new strategies and insights, though the maximal function version remains unresolved.

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The three-dimensional Kakeya conjecture, after Wang and Zahl

Recent advancements in geometric measure theory have been made by Hong Wang and Joshua Zahl, who have resolved the three-dimensional Kakeya conjecture. This conjecture posits that a Kakeya set, which contains a unit line segment in every direction, must have both Minkowski and Hausdorff dimensions equal to three. Their preprint outlines a proof that establishes a lower bound on the volume of unions of tubes in various configurations, significantly advancing previous results that focused on lower bounds for intermediate dimensions. The proof, spanning 127 pages, employs a sophisticated strategy involving induction on scales and a detailed analysis of both sticky and non-sticky cases of the conjecture. The authors build on earlier work, including the "Wolff hairbrush argument," and introduce new ideas to tackle the complexities of the proof. They also explore the organization of Kakeya-type sets into larger structures, which aids in establishing the necessary volume bounds. While the maximal function version of the conjecture remains unresolved, the methods presented provide substantial insights and bounds that contribute to the ongoing discourse in the field.

- Wang and Zahl have resolved the three-dimensional Kakeya conjecture.

- The conjecture states that Kakeya sets must have dimensions of three.

- Their proof involves complex strategies, including induction on scales.

- The work builds on previous results and introduces new concepts for tackling the conjecture.

- The maximal function version of the conjecture is still open for exploration.

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By @Y_Y - about 2 months
The original Kakeya problem is a really nice one for students, in that it's easy to understand and visualise, but has an unintuitive answer.

In this sense it's like Borel-Kolmogorov and imho much better than Banach-Tarski which is trotted out frequently, but actually very difficult to understand (both relatively and absolutely).

https://en.wikipedia.org/wiki/Kakeya_set#Kakeya_conjecture

https://en.wikipedia.org/wiki/Borel%E2%80%93Kolmogorov_parad...