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Tomorrow Is Yesterday

"Tomorrow Is Yesterday" is the nineteenth episode of the first season of the American science fiction television series , originally aired on on January 26, 1967. Written by and directed by Michael O'Herlihy, the episode centers on the starship USS Enterprise being hurled back in time to Earth's year 1969 due to the gravitational pull of a "black star," where it is detected as an by the U.S. , leading to the accidental beaming aboard of Air Force pilot Captain . In the story, the crew, under Captain , must navigate the complexities of to return Christopher to his jet without disrupting the , as his future actions are destined to shape significant historical events, including advancements in the space program. The episode introduces key concepts such as the maneuver around the Sun to generate temporal displacement for returning to the 23rd century, while also exploring ethical dilemmas of interference with the past. To resolve the situation, the crew erases all evidence of their presence, including Christopher's memories, ensuring history remains intact. The episode marks the first exploration of time travel in the Star Trek franchise and was developed from Fontana's original story idea—it was the first Star Trek episode written solely by a woman—making it a pivotal early entry in the series' lore. It features guest star as Christopher and highlights the series' blend of , , and , with notable scenes involving and computer interactions. Critically, "Tomorrow Is Yesterday" has been praised for its engaging premise and humor, earning an average rating of 7.9 out of 10 on from over 4,800 user votes, and it has influenced later Star Trek time travel narratives.

Background and Production

Original Broadcast

"Tomorrow Is Yesterday" originally aired on on January 26, 1967, as the nineteenth episode of the first season of : The Original Series. The episode carried production number 6149-21 and had a runtime of approximately 50 minutes. As an early first-season installment, it marked one of the series' initial explorations of themes, following the Enterprise's accidental displacement to 1969 Earth. Following its initial broadcast, the episode entered in late 1969, with reruns gaining significant popularity across independent stations in the 1970s, contributing to the show's cultural resurgence. releases began in the early 1980s, with issuing episodes on and formats, allowing fans greater access to the series outside of airings. In the digital era, "Tomorrow Is Yesterday" became available for streaming on upon the platform's launch in March 2021, alongside the remastered version of the original series.

Development

"TOMORROW IS YESTERDAY" was written by as her first solo teleplay for Star Trek: The Original Series. The script originated from an uncredited story treatment by associate producer , who conceived the core idea of the being hurled back in time. developed it into a full episode, marking the series' initial dedicated exploration of mechanics. The episode was originally planned as the second half of a two-parter following "The Naked Time," where the Enterprise's engine restart would have triggered the time displacement; however, production schedules necessitated reworking it into a standalone story. This revision decoupled it from the prior episode's events, allowing for a self-contained centered on accidental temporal . Directed by Michael O'Herlihy, the production was overseen by key staff including producer . At its conceptual core, the story introduced via proximity to a ""—an early fictional depiction of a —while the travels at speed, pulling the ship uncontrollably into Earth's past. To resolve the displacement, the script invented the maneuver, in which the ship orbits at high to generate a time and return to the present, a technique devised specifically for this episode. Script revisions emphasized setting the temporal incursion in to align with the ongoing , incorporating references to NASA's for contemporary relevance; notably, the episode accurately anticipated the day of the week for the launch, which took place on , July 16, 1969. These changes enhanced the story's ties to real-world events, underscoring themes of historical inevitability without altering broader production timelines.

Casting

The principal cast of "Tomorrow Is Yesterday" featured the core ensemble of the USS Enterprise bridge crew: as Captain , as Commander , as Dr. Leonard "Bones" McCoy, as Chief Engineer Montgomery "Scotty" Scott, as Lieutenant Nyota Uhura, and as Lieutenant Hikaru Sulu. These actors, already established in their roles by the episode's production in late 1966, provided continuity to the series' character dynamics, with the bridge crew dominating screen time during key command decisions. Guest stars included as U.S. Air Force Captain John Christopher, a pilot whose portrayal emphasized a credible military demeanor to ground the episode's time-travel premise in contemporary realism. Hal Burton appeared as Lieutenant Robert Tomlinson, an Air Force officer assisting at the Omaha Air Force Base, while played Colonel Fellini, the base's air police commander responsible for security protocols. Additional uncredited roles included the Omaha base commander and technician Webb (Richard Merrifield), who first detects the on , delivering brief but authoritative lines to initiate the plot's Earth-side tension. Casting choices prioritized actors with experience in military-themed productions to authentically depict 1960s Air Force personnel, with Perry selected for his prior television work that suited a youthful, professional pilot archetype. The episode minimized roles for non-bridge regulars like McCoy, focusing instead on the guest stars to highlight interactions between the Enterprise crew and historical figures, thereby enhancing the narrative's focus on temporal interference without overextending the supporting cast. Christopher's characterization, informed by Perry's performance, incorporated subtle familial elements tying into future space history, evoking the era's optimism about aviation and exploration.

Narrative

Plot Summary

In the teaser, the , under , encounters a "" while en route to Starbase 9 on 3113.2, causing the ship to be pulled into a time warp and hurled back to in 1969. The vessel is detected as an by a U.S. installation, prompting the launch of fighter jets to investigate. In Act One, as the attempts to evade detection, its inadvertently destroys one of the pursuing jets, forcing to order the pilot, , beamed aboard to save his life. The crew quickly realizes the implications of their displacement into the past, with Christopher now possessing knowledge of future events that could contaminate the timeline if he returns to . confines Christopher to , but the pilot attempts to , highlighting the crew's dilemma. In Act Two, First Officer researches historical records and discovers that Christopher's unborn son, Shaun Geoffrey Christopher, is destined to lead Earth's first manned mission to Saturn, a pivotal event in human . The crew debates the ethical and temporal risks of allowing Christopher to remain or return him, concluding that his presence aboard the ship has already altered potential futures, as the ship's computer predicts cascading changes to history. In Act Three, to mitigate evidence of their incursion, and helmsman beam down to the base to destroy or retrieve photographic and taped records of the , as well as debris from Christopher's jet. is captured by base security, but coordinates a rescue using Christopher's knowledge of the facility; the team successfully secures all traces of the ship's visit before beaming back. In Act Four, Chief Engineer Montgomery Scott and devise a solution using the ship's engines to perform a "" maneuver around the Sun, accelerating to generate a controlled time that propels the forward to 2267 while reversing to 1969 just prior to the initial detection. and an inadvertently beamed sergeant are returned to Earth at the exact moment before the Enterprise's appearance, with their memories of the events erased through the temporal displacement. In the resolution, the Enterprise emerges in its proper era on stardate 3114.1, with the timeline apparently restored, as Christopher's life proceeds unaltered and the crew resumes their mission without further anomalies.

Themes and Analysis

The episode "Tomorrow Is Yesterday" explores the ethics of time travel through the lens of non-interference, predating the formal establishment of the Temporal Prime Directive in later Star Trek canon but laying foundational principles for avoiding alterations to historical timelines. The crew's accidental displacement to 1960s Earth forces them to confront the potential consequences of their presence, emphasizing a moral imperative to restore the timeline without imposing future knowledge on the past. This theme underscores the episode's portrayal of time travel not as a tool for conquest but as a responsibility that demands restraint, reflecting broader ethical questions about humanity's role in shaping its own destiny. At the heart of the narrative lies a profound moral dilemma: Captain must decide whether to strand Air Force pilot Captain John Christopher on the Enterprise to safeguard the future or return him to his time, risking historical disruption. Christopher's potential influence on events, including his son's future role in space exploration, highlights the tension between individual agency and collective historical consequences, as grapples with the personal cost of non-interference. This conflict illustrates the episode's examination of personal ethics versus broader societal impacts, where 's humanistic instincts clash with the logical necessities of timeline preservation. Spock's counsel, rooted in rationality, reinforces the need for objective decision-making, deepening the portrayal of their complementary dynamic—Spock's detachment providing a counterbalance to 's . Recurring motifs evoke the optimism of the space race, juxtaposed against 20th-century military paranoia, as the is mistaken for a UFO by Cold War-era authorities. Christopher's lineage ties to future advancements in space exploration, such as his son's role in the first manned mission to Saturn, symbolizing the continuity of human progress from events like the upcoming and from military suspicion to exploratory idealism, and reinforcing the episode's commentary on in a cosmic context. Narratively, the slingshot maneuver serves as a clever to resolve the , allowing the crew to erase their incursion while foreshadowing recurring time travel tropes in the franchise, such as calculated interventions to maintain . This technique blends scientific speculation with dramatic tension, critiquing imperialistic undertones in time manipulation by affirming a "static vision" where and progress prevail without external domination.

Reception

Initial Response

"Tomorrow Is Yesterday" aired on January 26, 1967, amid the height of the and persistent suspicions of unidentified aerial phenomena, with the episode's portrayal of U.S. Air Force pilots scrambling to intercept a mysterious object mirroring public fascination and official investigations into UFOs during the era. The broadcast occurred as the series navigated mixed , with a nationwide survey of 24 television critics rating as "good" by only five, "bad" by eight, and neutral by the remaining eleven, reflecting broader skepticism toward programming. In terms of viewership, the episode achieved a Nielsen rating of 20.0, translating to about 10.98 million viewers and a 30.5 share, aligning with the first season's typical performance that averaged around 15-20% of U.S. television households. While the episode itself garnered no individual awards or nominations, it formed part of the first season's body of work that qualified for multiple nominations in the Best Dramatic Presentation category at the 1968 World .

Retrospective Reviews

In the years following its original airing, "Tomorrow Is Yesterday" has been reevaluated by critics for its blend of adventure, humor, and early exploration of ethics in the franchise. A review on Tor.com praised the as a lighthearted romp that effectively captures the fun of time travel mishaps, highlighting character-driven moments such as Kirk's witty banter during his interrogation and Spock's rare admission of error, which adds emotional depth to the crew's interactions. The A.V. Club's 2009 assessment awarded the episode a B− grade, commending its humorous elements like the military's over-the-top reactions to the as a UFO and snappy dialogue, while acknowledging the dated , particularly the awkward depiction of the ship in Earth's atmosphere. Later rankings emphasized its role in Star Trek's canon. In a 2019 list of the top 10 episodes, it placed sixth, noted for introducing ethical dilemmas around altering history, such as the crew's decision to erase Captain Christopher's memories after he witnesses future technology, foreshadowing the franchise's Temporal . BuzzFeed recommended the episode in 2018 as an ideal entry point for newcomers to the original series, arguing it showcases the show's optimistic spirit and accessible sci-fi concepts without the dated feel of the pilot, making it appealing for modern audiences dipping into classic Trek. A 2015 Reactor rewatch rated it an 8 out of 10 on the warp factor scale, appreciating the balance of tension and levity in the time displacement plot, along with strong performances that highlight Sulu's resourcefulness and the crew's camaraderie during the slingshot maneuver to return to their era. Subsequent reviews have continued to highlight its enduring appeal. A 2022 analysis described it as a "great episode" that opened possibilities for Star Trek's storytelling despite minor plot holes. In 2023, it was praised as a "worthy addition" to the season for its expansive scope and fun execution. Discussions on streaming platforms and fan sites as of 2025 have noted its self-contained story and relatable setting as an easy introduction to the crew's dynamics.

Legacy

Franchise References

The slingshot maneuver, first depicted in "Tomorrow Is Yesterday" as a method to generate a time by slinging around a star at high speeds, is directly reused in the : The Original Series episode "Assignment: Earth" (1968). In that story, the USS Enterprise crew employs the to travel back to 1968 for historical , highlighting its utility for precise temporal displacement. This same maneuver reappears in the film Star Trek IV: The Voyage Home (1986), where the crew of the Bird-of-Prey performs a solar around the Sun to journey to 1986 and retrieve humpback whales, adapting the method to reverse while underscoring its risks and imprecision. In Star Trek: Picard Season 2 (2022), the effect is explicitly referenced during discussions of temporal mechanics, with describing it as a "cruder" approach involving a star's gravitational pull at warp speed to create a temporal field, though dangerous and imprecise compared to advanced alternatives. The episode's plot to 2024 further echoes the maneuver's role in historical interventions. The temporal displacement theme in "Tomorrow Is Yesterday" finds echoes in 's "Time's Arrow" (1992), a two-part episode where the crew is pulled back to 19th-century via a mysterious rift, confronting paradoxes and historical contamination similar to the Enterprise's 1960s incursion. Callbacks to appear through his preserved lineage in , with his descendant's contributions to early affirmed as critical to historical development. The episode establishes foundational temporal protocols for avoiding historical alterations, influencing later series like , where recurring time travel arcs—such as in "Future's End" and "Relativity"—enforce strict guidelines akin to the to safeguard timelines, evolving from the ad hoc corrections seen in "Tomorrow Is Yesterday."

Cultural Significance

The episode "Tomorrow Is Yesterday" introduced the "slingshot maneuver" as a method for by orbiting a massive body like at high speeds, drawing on concepts from such as and gravitational effects. While physically inaccurate for achieving backward —requiring velocities far exceeding the in ways that violate known physics—this technique was inspired by real maneuvers used in to gain velocity. Lawrence M. Krauss, in his analysis of Star Trek's scientific plausibility, notes that the maneuver's depiction leverages the relativistic slowing of time near massive objects but overstates the feasibility for temporal displacement. The episode's "black star," described as a high-gravity object emitting no light or energy, served as an early popular media representation of what would soon be termed a ; the term itself was coined by physicist John Wheeler in late 1967, shortly after the episode's January 1967 broadcast, highlighting Star Trek's prescient engagement with emerging astrophysical ideas. Aired amid the height of the , the episode's setting in —complete with a radio broadcast referencing preparations for the moon launch—reinforced an optimistic portrayal of the U.S. space program as a beacon of technological progress and national pride. This narrative aligned with and amplified public enthusiasm for 's Apollo missions, contributing to Star Trek's broader role in shaping societal views on during a period of competition and civil rights advancements. has credited the series with inspiring generations of scientists, engineers, and astronauts by fostering a vision of inclusive, exploratory in space, with the episode's of a future-friendly intervention in Earth's history underscoring themes of responsible technological advancement. The Enterprise's detection as an by 1960s mirrored contemporary UFO sightings often linked to and space tests, subtly influencing media portrayals of encounters as potential future human achievements rather than solely alien threats. In science fiction, "Tomorrow Is Yesterday" stands as an early television example of resolving a timeline paradox, where accidental historical alterations are corrected through precise temporal restoration, predating more elaborate cinematic treatments like those in Back to the Future (1985). This approach to paradox resolution—erasing memories and repositioning individuals to preserve the original timeline—has been analyzed in histories of time travel tropes as a foundational model for ethical interventions in narratives exploring causality and free will. In the streaming era, post-2020 discussions on platforms like Paramount+ have revisited the episode for its commentary on the risks of historical meddling, drawing parallels to modern debates on AI, genetic editing, and geopolitical interventions, while space exploration histories occasionally reference it as emblematic of 1960s optimism linking fictional futures to Apollo-era realities.

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