The Theory of Everything is the eighth studio album from Ayreon, a progressive metal/rock opera project by Dutch musician Arjen Anthony Lucassen, released on 28 October 2013.

Ayreon is a musical project by Dutch songwriter, singer, musician and record producer Arjen Anthony Lucassen. Ayreon's music is described as progressive rock, progressive metal and power metal sometimes combined with genres such as folk, electronica, experimental and classical music. The majority of Ayreon's albums are dubbed "rock operas" because the albums contain complex storylines featuring a host of characters, usually with each one being represented by a unique vocalist.