The Constant

"The Constant" is the fifth episode of the fourth season of the American Broadcasting Company's (ABC) serial drama television series Lost, and the 77th episode overall. It was broadcast on February 28, 2008, on ABC in the United States and on CTV in Canada. It was written by executive producer Carlton Cuse and co-creator/executive producer Damon Lindelof and directed by executive producer Jack Bender. "The Constant" was watched by 15 million American viewers and is widely regarded as Lost's best episode and one of the best episodes of television ever. It was nominated for three Primetime Emmy Awards, a Directors Guild of America Award, and a Hugo Award.

In the episode, Desmond Hume (played by Henry Ian Cusick) and Sayid Jarrah (Naveen Andrews) are being flown by Frank Lapidus (Jeff Fahey) to the freighter where Lapidus' mission is set. After going through turbulence, Desmond's consciousness unexpectedly travels through time between 1996 and 2004. The helicopter reaches the freighter and Sayid and Desmond are introduced to communications officer George Minkowski (Fisher Stevens), who is "unstuck in time" like Desmond. The writers took twice the time expected to develop the episode's script; the biggest concern was the avoidance of a temporal paradox when dealing with time travel.