The battle for the greatest sci-fi episode in TV history is a tough one. Among the top ranks are episodes from heavy hitters like Star Trek, Doctor Who, Battlestar Galactica, and The Twilight Zone. Yet, while those franchises might top “best sci-fi series” competitions, the game changes when considering best episodes. A great hour of TV is one that stands both alone and as part of a whole, with writing, acting, direction, and all elements of production coming together to create something unforgettable.
ABC’s Lost may have lost fans in its later years, but at its peak, its hours were revered for being both serialized and self-contained. 18 years ago, Season 4’s “The Constant” pulled off one of the greatest and most emotional time-travel stories in sci-fi television. According to IMDb reviews, it remains among the highest-rated television episodes of all time, with a near-perfect score and thousands of 10/10 reviews, some still trickling in nearly two decades later.
Lost’s Time Travel Masterpiece “The Constant”
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“The Constant” aired on February 28, 2008, when Lost was already considered the most popular and influential show on network television. Created by J. J. Abrams, Damon Lindelof, and Jeffrey Lieber, it begins as a survival drama about the passengers of Oceanic Flight 815 stranded on a mysterious island, but over time, the science fiction skew became more apparent, introducing things like an electromagnetic anomaly and a scientific research organization called the Dharma Initiative. In Season 2, the series introduced a new character, Desmond Hume, played by Henry Ian Cusick. By Season 3, Desmond was experiencing flashes of the future.
Season 4’s “The Constant,” written by Lindelof and Carlton Cuse, begins with Desmond traveling by helicopter from the freighter to the Island, where he starts uncontrollably shifting between 2004 and 1996. While flashbacks are a regular Lost staple, what Desmond experiences is different because his consciousness actually inhabits his past self. The episode establishes that exposure to the Island’s electromagnetic energy is what made Desmond vulnerable to this phenomenon.
Physicist Daniel Faraday, played by Jeremy Davies, then explains that Desmond’s mind is rejecting the displacement (like to how other test subjects in his experiments suffered fatal neurological damage). To survive, Desmond must establish a “constant,” or someone emotionally significant who exists in both time periods and can anchor his consciousness. Desmond identifies his constant as his lover Penny Widmore, played by Sonya Walger. In 1996, Desmond convinces Penny to answer her phone on Christmas Eve, 2004. In the present timeline, his consciousness deteriorates until he successfully reaches her. The call stabilizes his mind and resolves the displacement.
Why “The Constant” Is Still Considered One of the Greatest Sci-Fi Episodes Ever Made
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Often time travel, especially when written into a television episode, falls into one of three camps: a slew of corny, predictable tropes, thin time-travel logic that fails to check out under scrutiny, or so complex it’s hard to hang on. “The Constant” manages to avoid all of these common pitfalls. Its mechanism is clear yet surprising, sticking to its own rules while remaining relatively simple, and anchoring itself within Desmond’s tragic love story. The phone call between Desmond and Penny is the standout scene, delivering an incredible emotional payoff to what had been building for nearly two seasons.
The episode almost feels like a mini-movie, where character comes together with a classic sci-fi subgenre to create something greater than the sum of its parts. At the same time, it manages to move the needle of Lost’s central mystery forward, even just a little. Cusick’s portrayal of Desmond received overwhelming acclaim, with many calling it one of the strongest performances of the series. Of all Lost’s self-contained character dramas, this is easily one of the most affecting. While the series as a whole remains controversial and is often left out of sci-fi conversations in favor of more obvious choices, it undoubtedly earned its just deserts for making a modern sci-fi masterpiece with “The Constant.”
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