Definition:Hilbert 23/18b

Hilbert $23$: Problem $18$b

The Densest Sphere Packing

The densest packing of identical spheres in space obtains a density of $\dfrac \pi {3 \sqrt 2} = \dfrac \pi {\sqrt {18} }$:

$\dfrac \pi {\sqrt {18} } = 0 \cdotp 74048 \ldots$

Historical Note

The Hilbert 23 were delivered by David Hilbert in a famous address at Paris in $1900$.

He considered them to be the oustanding challenges to mathematicians in the future.

There was originally going to be a $24$th problem, on a criterion for simplicity and general methods in proof theory, but Hilbert decided not to include it, as it was (like numbers $4$, $6$, $16$ and $23$) too vague to ever be described as "solved".