The document discusses the mechanism of aggregation of amyloid beta monomers to form amyloid fibrils. It states that monomers first aggregate to form a high-energy nucleus of a few chains, represented by a hexagonal arrangement. Once this nucleus is formed, aggregation proceeds energetically downhill to create the amyloid fibril. However, the structure of the nucleus and the steps between unstructured monomers and amyloid form are still unknown.