Paul W.S. Anderson's initial cut of the film ran to 130 minutes and was quite graphically violent, so much so that both test audiences and the studio baulked at the finished product. Paramount ordered him to cut the film by 30 minutes and tone down some of the violence, a decision he now regrets.
The Event Horizon was named after the theoretical boundary surrounding a black hole, within which gravitational attraction is so great that nothing, not even radiation, can escape because the escape velocity is greater than the speed of light. Technically, it is where the physical universe ends and physical laws no longer apply. So the ship's name is symbolic for its journey beyond the borders of the known universe.
When Doctor Weir opens the blinds in his room during the opening sequence of the film, a whooshing sound effect can be heard. This sound effect is taken from the video game Doom, heard when the player opens a door.
Philip Eisner wrote the movie after a family tragedy. He had recently entered a multi-picture writing agreement, and in an effort to force himself to get back to work he pitched the idea of "The Shining in space" to the studio, who were very receptive. Unfortunately he had no detailed treatment yet, and the subject matter blended with his emotional state to inspire a prolonged bout of writer's block. The studio executive who had originally brought him on board, now a personal friend, helped keep Eisner on track, and the eventual first draft which was enthusiastically received.
Everyone's space suit has a flag showing future political changes on Earth. Characters portrayed by American actors wear a flag of the United States with 55 stars. Characters portrayed by British actors wear a European Union flag with 22 stars. Sam Neill's character wears an Australian flag with the Aboriginal flag in place of the Union Flag.
The model of the Event Horizon includes a complete "X-Wing" from Star Wars as part of an antenna array. The model is visible on the lower portion of the Event Horizon during the first flyby by the Lewis & Clark.
The script originally described the Gateway machine as a smooth and featureless black orb suspended in midair between large, rotating mechanical arms. It also was said to contain a stable black hole within it at all times (which the ship used as a power source), as opposed to briefly creating a temporary one. Paul Anderson decided to redesign it to involve interlocking circles as a homage to the puzzle box in Hellraiser (1987), which served as an inspiration.
Director Paul W.S. Anderson and producer Jeremy Bolt planned to put together a director's cut for some time, but most of the footage was lost or destroyed after post-production. A few of those scenes, which appear on the Special Collector's Edition DVD, survived only in videotape form, sometimes without dialog or sound effects. The DVD also includes storyboards of a space walk sequence that was abandoned for budget reasons, and the alternate ending, with commentary by Paul W.S. Anderson.
The space suits worn by the actors weighed 65 pounds (30 kilograms) each. Laurence Fishburne nicknamed his "Doris." Due to the weight, standing upright in them for longer periods could lead to back injury, but sitting down was not possible either due to the backpack. Special "hanging poles" were constructed on the set, so the actors could rest on them between takes.
Paul W.S. Anderson had originally hired British band Orbital to compose the music for the film because he had wanted to work with them since his directorial debut Mortal Kombat (1995) which had featured their music. Paramount executives balked at the idea of hiring unknowns to write music for a big budget film, Anderson then thought of Michael Kamen and the idea of "marrying" their sounds (orchestral and techno) together resulted in the film's final soundtrack.
Some of the lost footage includes a great deal more of the Bosch-influenced Hell sequences and of the orgiastic video log that was found in the Event Horizon. This was shot by both director Paul W.S. Anderson and Vadim Jean, mainly on weekends.
The Event Horizon was modeled on Notre Dame cathedral. Its long corridor resembles a church nave, and its interior is filled with cruciform shapes, columns and vaults. Also, its engines resemble rotated church towers.
The shot where Sam Neill stares out of a window which then pulls back to reveal he's on the deck of a spaceship orbiting Earth took the digital special effects house Cinesite 10 weeks to achieve. The shot lasts for 45 seconds.
According to the DVD documentary, the first cut of the film had a longer "Visions from Hell" sequence, more blood, and a different, though similar, ending. The test audience didn't like it, so it was re-cut with an alternate ending involving what director Paul W.S. Anderson called "The Burning Man Sequence." The second test audience didn't like that version, and the film was edited again. The final cut is a less-intense hybrid of both test screenings, with significantly less gore.
Andrew Kevin Walker wrote an uncredited draft of the script. Some of it ended up on screen, and one sequence was cut from the theatrical cut, where captain Miller, upon entering the Event Horizon, finds a ripped-out tooth floating around. Other scenes appear on the Special Collector's Edition, when Laurence Fishburne's crew is introduced for the first time on another rescue mission. In the DVD commentary, director Paul W.S. Anderson said he regretted deleting the scene, but it didn't help the film's pace.
Joely Richardson's character was originally written for a man. However, during auditions, director Paul W.S. Anderson had the part read by both men and women. He chose Richardson because of the 'British stage class' that she would bring to the movie, and thought it would be fun to then "douche her with gallons of blood".
Writer Philip Eisner visited the set while the space suit sequences were being filmed. The suits were so heavy that the actors risked back injuries, prompting Laurence Fishburne to stop between takes, point at Eisner, and shout mock-angrily: "You! You Eisner! You did this to me!".
The FBFX created costumes of John Mollo's original space suit designs included many practical features such as an integrated filter blower system in the bottom of the portable life support system (backpack) into the helmet to keep the visor clear and the actor cool, thousands of LEDs that pulsated rhythmically to indicate life support functionality (with a secret 'panic mode' switch to quicken the pace when the plot required it!) and industrial magnets embedded in the soles of the boots to add to the realism of scenes featuring active magnetic boots.
Paramount eschewed the overused special effects houses ILM and DreamWorks in favor of smaller studios to keep costs down. Instead they opted for Mass Illusion Cinesite (Europe) and the Computer Film Company in London.
Paramount didn't officially greenlight the film until 10 weeks before production was due to begin. This meant that the production design was unnecessarily rushed and was the reason why many leading production designers turned the film down.
The hundreds of apparent metal bolts that line the corridors of the Event Horizon are actually power transistors in a TO-3 or similar package. This can be best seen when Miller rests his head against the wall when hearing Corrick's voice.
The trivia items below may give away important plot points.
The actors were stimulated to invent a back story for their characters. Jason Isaacs based his character on his own brother, who is a doctor. In his back story, his character had underwent extensive surgery as a child, explaining the large scar over his trunk, and the visions he received from the ship were of him completely cut open. Isaacs asked if he could take home the dummy in his likeness with the chest sliced open. The special effects department was quite shocked with this request, so they told him they still needed it (even though they didn't).
For Jason Isaacs' death scene, the plan was originally for his entrails to be still attached to him as he hung over them. Isaacs was then supposed to raise his head, showing that he was still alive, prompting Laurence Fishburne's character to shoot him in the head, to put him out of his misery.
The rotating corridor (nicknamed 'meatgrinder') that separates the gravity drive from the rest of the ship, turned out to be the most problematic set piece to film. Only shots with a fixed camera could be done, since camera operators became disoriented and unable to keep the camera steady. Laurence Fishburne could not perform his run through the tunnel in one take due to the same problem; the final scene was comprised of several shorter takes. And when the fireball effect was filmed, a piece of cloth started to burn and caused a small fire.
The scene where Laurence Fishburne finds Jason Isaacs hanging in the air with his chest cut open originally ran much longer, with Isaacs' guts hanging out of him, and some of them laying on the table. Paul W.S. Anderson used a mylar mirror on an operating table to simulate the effect, with Issacs actually hanging on wires. This can be seen in the DVD's Making of Event Horizon documentary.