Sir Walter Raleigh is perhaps best known for laying down his cloak in the mud for Queen Elizabeth I (though sadly this act of chivalry is probably a myth!) However, he also started a mathematical quest which to this day remains unsolved.
Sir Walter posed a simple question to his mathematical assistant, Thomas Harriot. How can I calculate the number of cannon balls in a stack? Harriot solved this problem without difficulty but started to wonder about a more general problem. What arrangement of the balls takes up the least space?
Harriot wrote about the problem to his colleague Johannes Kepler, best known for his work on planetary orbits. Kepler experimented with the problem and concluded that an arrangement known as the face centred cubicpacking, a pattern favoured by fruit sellers, could not be bettered. This statement has become known as "Kepler's conjecture" or simply the sphere packing problem.