A pair of cast listings for Avengers: Endgame is fueling rumors of time travel in the film. Specific plot details have been scant for MCU's upcoming film, with Marvel Studios staying tight-lipped about what to expect. This has spawned countless fan theories about what might go down, and the concept of time travel continues to be one of the most popular elements factoring into almost every single theory regarding the Phase 3 capper.
The fact that the time travel theory in Avengers: Endgame is backed up by numerous set photos and interviews from people involved in the film, it's nearly conclusive that the film will see the Avengers revisiting several monumental moments in the MCU that have a direct relation to the Infinity Stones, like The Avengers' Battle of New York. The latest information on the film, however, hints at Avengers: Endgame traevling back to the 1970s.
Avengers: Endgame's cast listing on IMDb (via: CBR) implies that the film will feature scenes set in the '70s with Monica Mathis playing "70s Car Girl #1" and Miles Webb as "70's Scientist/Lab Worker." Considering that rumors of time travel factoring in the film have been swirling around since Avengers: Infinity War's release, this pair of casting might see the Avengers revisit the '70s as part of their efforts to find a way to defeat Thanos (Josh Brolin). Otherwise, this can also be a flashback sequence made possible by Tony Stark's (Robert Downey Jr.) Binarily Augmented Retro-Framing (B.A.R.F.) device, which will be utilized in the flick.
The '70s is a relatively uneventful decade on the bigger scheme of things in the MCU, but several milestones happen during this time for the Stark family. Tony was born at the beginning of the decade, while his father Howard Stark continued tinkering on the arc reactor technology in the following years. It was also in 1974 where the final Stark Expo took place before it was revived under Tony's supervision in 2010. Given these details, as well as rumors of Howard appearing in Avengers: Endgame after actor John Slattery was spotted on the set of the film last September, there's a good chance that whatever goes down in the '70s-set scene will have something to do with the Starks. The '70s Scientist/Lab Worker role also backs this up considering Stark Industries' focus on science and technology.
Assuming the sequence will focus on the Starks, it's curious to know how Howard factors into Avengers: Endgame given that he's been dead for a couple of decades. He did have connections to the Infinity Stones, having found the Tesseract/Space Stone in the Arctic waters while looking for a lost Captain America (Chris Evans) and studying it before handing it over to S.H.I.E.L.D., so it's possible that he discovered something about the specific elemental crystal that could be a game-changer in terms of how the Avengers might defeat Thanos. Another possibility is an unexplored piece of technology that could help Tony with his suit or any kind of paraphernalia that would allow them to fully time travel - perhaps something that would allow for the Quantum Realm to be fully explored and utilized (like the hand device the heroes were seen wearing in set photos). Otherwise, it could just be Tony stumbling on another video of his father from the '70s, like what happened in Iron Man 2.