The time machine was going to be a fridge
In early drafts of Back to the Future, the time machine was a refrigerator, taken to a nuclear test site. The film-makers worried children might climb into old fridges and get trapped, and they changed it to a car. They chose the DeLorean because its stainless-steel body and gull-wing doors made it look like a spaceship, which suits a scene where a farming family in 1955 mistakes it for an alien craft.
To travel, the car has to reach 88 miles per hour, and the FLUX CAPACITOR needs 1.21 GIGAWATTS of power — a huge amount, roughly the output of a large power station. DOC BROWN first gets it from PLUTONIUM.
Marty was played by someone else for six weeks
The director, Robert Zemeckis, wanted Michael J. Fox to play MARTY McFLY, but Fox was busy with a television series. Eric Stoltz was cast instead and filmed for about six weeks before the director decided it was not working. Fox was then allowed to do both jobs: he filmed the television series by day and the film at night, sleeping only a few hours.
None of Stoltz's scenes made it into the final film, and Fox's quick comic timing is often credited as a big reason the film works.
Lightning at the clock tower
The key to getting Marty home is knowing exactly when LIGHTNING will strike the CLOCKTOWER of HILL VALLEY: 10.04 in the evening on a Saturday in November 1955. Doc rigs a wire from the tower to the street so the car will catch the bolt at 88 miles an hour. Real lightning carries a vast amount of electricity for a tiny fraction of a second, which is the idea behind the plan. Our weather page covers how lightning forms. Hill Valley's town square with its clock tower is a set at Universal Studios in California, and it has appeared in dozens of other films and television shows.
EINSTEIN, Doc's dog, becomes the first time traveller when he is sent a minute into the future in the car's first test.
Children believed hoverboards were real
In Back to the Future Part II, Marty rides a HOVERBOARD in the year 2015. Robert Zemeckis joked in an interview that hoverboards were real and that parents groups had stopped toy companies selling them. Many children believed him, and toy shops were asked for them for years.
The film's vision of 2015 got some things right, including video calls and flat screens on the wall, and some things wrong, including flying cars. In the film a sports ALMANAC lets BIFF TANNEN win fortunes by betting on results he already knows.
Marty's SKATEBOARD, his girlfriend JENNIFER, and the parents he has to bring together all play their part. The last line of the first film, as Doc takes off into the FUTURE, is that where they are going, they do not need ROADS.
The story of travelling back in TIME to meet your own parents as teenagers became one of the best-loved in cinema.