Six Degrees of Inner Turbulence is the sixth full-length studio album by progressive metal band Dream Theater. It was released as a double-disc album on January 29, 2002 by Elektra Records.
The recording is a type of concept album wherein the five songs which comprise the first disc explore different themes of lifetime struggle, such as Alcoholism, Loss of Faith and Death. The sixth song — that is, the 42-minute song occupying the second disc, separated into eight parts — explores the stories of six individuals suffering from various mental illnesses. Particularly represented are bipolar, post-traumatic stress disorder, schizophrenia, post-partum depression, autism, and dissociative personality disorder. Furthermore, the title of the album may also allude to the fact that each song on the album could be seen as a different form of inner turbulence, with the six tracks making another reference to the six degrees.
The musical styles of each section of the title track are direct reflections of the band's large variety of influences. Indeed, classical, folk and metal styles combine effortlessly within the track. Additionally, certain parts of the track are direct nods to specific songs from influential artists. The main theme, which appears in the "Overture", at the end of "Goodnight Kiss," and in the "Grand Finale," bears an unquestionable resemblance to Kansas's "The Wall" from their Leftoverture album. "Solitary Shell" is a nod to Peter Gabriel's "Solsbury Hill" both in name and in musical style. Also, parts of "Solitary Shell" bear strong resistance to Billy Joel's song "The Entertainer," mainly due to the unique synth-organ which sounds alike in both songs, played over acoustic guitar.