The Eternal Flame is a hard science-fiction novel by Australian author Greg Egan and the second part of the Orthogonal trilogy. The novel was published by Night Shade Books on 26 August 2012 with a cover art by Cody Tilson and by Gollancz on 8 August 2013 with a cover art by Greg Egan.[1][2][3] The novel describes the journey of the generation ship Peerless, which has departed in The Clockwork Rocket,[4][5][6] and the development of new technology as well as changes of the society on board. An essential task is the construction of an engine not needing any fuel to generate thrust, but instead perfectly balancing out the radiation it emits with the energy this generates. To make such a process work, the universe of the novel is based on a Riemannian instead of a Lorentzian manifold (which describes our own universe, where emitting radiation instead consumes energy), changing the rules of physics. The details are described by Greg Egan on his website.[7] The story is continued in The Arrows of Time.[8][9][10]