The Russo Brothers said Back to the Future is one of their favorite films, and we know it exists in the Marvel Cinematic Universe since it even got referenced in Avengers: Endgame. I'm talking directly, as in lines like Scott Lang's "So you’re saying Back to the Future is bullshit?" (Never!) However, eagle-eyed Endgame fans also noticed a more subtle tribute to the Back to the Future franchise, which also shares a similar time travel plot (and music by Alan Silvestri).
Here's a screenshot of the original Reddit post:
That shows the full view, but here's a clip of the actual movement showing the visual similarities:
That definitely seems like it was an intentional reference, especially since Back to the Future was already such an unexpectedly big part of Avengers: Endgame.
Back to the Future co-writer/producer Bob Gale talked to The Hollywood Reporter about the references to his films in Endgame:
I was delighted to learn from Endgame that all of the Marvel superheroes are fans of Back to the Future. I knew our movie had been seen in almost every part of our world, but I had no idea we’d been playing in other parts of the multi-verse too. Now I need to find out if we’re owed some money from those multi-verse theatrical runs, and if not, why my contract didn’t cover those territories!
Back to the Future is one of our favorite films, and the rules of that movie are ubiquitous; they have informed pop culture for 40 years. And we wanted to do something different. We didn’t realize how complicated it would be to create new rules and have people go with us, but we learned very early on in the test screenings that people are really committed to those Back to the Future rules — if you shoot yourself, you should die. We spoke with a few physicists, and there’s a lot of theories about how time travel could work. We chose the multiverse theory.
There are still some lingering time travel questions about Avengers: Endgame, but there's no doubt the filmmakers were heavily influenced by Back to the Future -- and the shark that still looks fake. Endgame fans can check out every inch of the movie in its current home release, or watch it this Tuesday when Disney+ finally shows up.