Remembrance of Earth's Past () is a science fiction series by Chinese writer Liu Cixin. The series is also popularly referred to as Three-Body from part of the title of its first novel, The Three-Body Problem (). The series details humanity's discovery of and preparation for an alien invasion force from the planet Trisolaris. Books Original trilogy The books in the Remembrance of Earth's Past trilogy are: The Three-Body Problem (), 2006; English translation by Ken Liu published by Tor Books on November 11, 2014. Also known in Chinese as "三体I" The Dark Forest (), 2008; English translation by Joel Martinsen published by Tor Books on August 11, 2015. Also known in Chinese as "三体II" Death's End (), November 2010; English translation by Ken Liu published by Tor Books on September 20, 2016 (September 19 in digital stores). Also known in Chinese as "三体III" Extended series The Redemption of Time (), originally posted to an internet forum as fan fiction in 2010 by Li Jun writing as Baoshu, that was later published by Chongqing Press, the original trilogy publisher, with the permission of Cixin Liu in 2011, as Three-Body X: Aeon of Contemplation (). It was translated by Ken Liu into English for Tor Books and published on July 16, 2019 as The Redemption of Time. Science fiction concepts Sophons Sophons are created from eleven-dimensional protons dimensionally unfolded down to two-dimensional protons with Trisolaran particle accelerators. While in the two-dimensional form, they are embedded in circuitry to create a supercomputer. Once online, the embedded supercomputer could control the proton's dimensional level and could fold itself back into an eleven-dimensional proton. To be seen with the naked eye, the protons could unfold themselves down to a fourth-, fifth-, or sixth-dimensional form, becoming larger with each subsequent lower dimension without changing mass. They can visually record anything and thus their secondary purpose is to act as surveillance devices, beaming the information they gather back to another sophon instantaneously via quantum entanglement. Their primary purpose for their Trisolaran manufacturers is to disrupt Earth's particle accelerators, capable of straying into the paths of fired particles and scrambling the results of experiments before re-assembling, effectively blocking advancement of the science. Since they can move through three-dimensional space at the speed of light, a single sophon is capable of disrupting all of Earth's particle accelerators. Droplets Trisolaran space probes are covered in a strong interaction force