October 21 is "Back to the Future Day." It was first celebrated 2 years ago because in "Back to the Future Part II," Marty McFly travels to October 21, 2015. Here are 3 time traveling fast facts:

1. Michael J. Fox Was, Then Wasn't... Then Was Marty McFly

Director Robert Zemeckis originally wanted Michael J. Fox for the lead role of Marty McFly, but the young actor declined because he was too busy playing Alex Keaton on Family Ties. After Johnny Depp, John Cusack, and Ralph Macchio tried out for the part, Eric Stoltz was cast.

But after more than 5 weeks of shooting the film, Zemeckis and co-writer Bob Gale admitted that Stoltz’s style of comedy just wasn’t working for the script. More of a method and cerebral actor, Stoltz just couldn’t do physical comedy they were looking for to match the tone of their script.

Stoltz was paid off to exit the film, and after negotiations with the producers of Family Ties, including a work schedule from hell, Fox signed on and reshot Stoltz’s scenes. It was later discovered that actor Christopher Lloyd, who played Doc Brown, had never learned Eric’s real name. He had always referred to him as “Marty” on set.

But Stoltz’s McFly lives on in an alternative universe, as imagined by the science fiction series Fringe.

2. Doc Brown’s Time Machine Was a Refrigerator

In previous drafts of the script, the mad scientist’s time machine was originally a “time chamber” made from a refrigerator, which at one point in the script was meant to protect McFly from a nuclear blast. Fortunately, that idea was nixed. Unfortunately, it was later used by Steven Spielberg in the fourth Indiana Jones film.

Zemeckis and Gale eventually decided on the DeLorean car because of its strange, futuristic look. Only 9000 cars were ever manufactured before production ended in 1982.

And if you know the film by heart, you remember that the car needed to accelerate to 88 miles per hour in order for the time-flux capacitor to achieve time travel capability. The reason behind that specific number had nothing to do with math or science, and everything to do with the production designers thinking “88” looked cool on the digital speedometer.

3. The Film Was Almost “Spaceman from Pluto”

Universal Studios executive Sid Sheinberg was not a man of risks, and was concerned by the poor box-office performances of time travel movies Time Bandits, Somewhere in Time, and The Final Countdown. He suggested the alternative title “Spaceman from Pluto,” based on a payoff punchline in the film.

Fortunately, executive producer Spielberg killed that idea, according to Empire. Sheinberg did manage to make one significant change: switching Doc Brown’s animal companion, Einstein, from a chimpanzee to a sheepdog. He believed no movie with a monkey had ever been financially successful.

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