The plot does not revolve around the sun dying in the normal sense: this is not due for around five billion years based on our understanding of nuclear fusion. It has instead been "infected" with a "Q-ball" - a supersymmetric nucleus, left over from the big bang - that is disrupting the normal matter. This is a theoretical particle that scientists at CERN are currently trying to confirm, and was one of the many contributions of the science advisor. The film's bomb is meant to blast the Q-ball to its constituent parts which will then naturally decay, allowing the sun to return to normal.
In the original screenplay, the Icarus payload was the same size, but was made of highly compressed dark matter (there is no mention of needing fissile material) and had the same mass as the moon, so it had its own gravity (one-sixth the Earth's normal). The science advisor pointed out problems with using a bomb that massive, so it was reduced to the mass of Manhattan. A take with the original line can be seen on the DVD, in a deleted scene.
Alex Garland wrote the film as a "love letter" to psychologically-minded science-fiction, and also a film about atheism and "meeting God". He and director Danny Boyle differed in their interpretation of this aspect of this film, but found this did not affect the content of the movie. Garland remarks that they had reached "the same two interpretations that could be made from the world around us".
The distinctive golden color of the space suits was intended to make them memorable to sci-fi fans. The character "Kenny" from South Park was used as a design reference for the funnel-shaped helmet. A small number of suits and helmets were built as wearable costumes, so the actors could experience the claustrophobia and react appropriately.
The name of the spaceships - Icarus - is symbolic. Icarus is a character in Greek Mythology. His father, Daedalus, made a pair of wings for himself and his son so that they could escape from a prison. He made them from feathers and wax. Before they took off, Daedalus warned his son not to fly too close to the sun, as the wax will melt, nor too close to the sea, as the feathers will dampen. But overcome by the feeling that flying gave him, Icarus soared through the sky, too close to the sun. His wings melted and Icarus fell into the sea.
Director Michael Winterbottom had originally hoped to use the film's sets on the production's off days to shoot his own science fiction comedy. Permission was never worked out and Winterbottom's film was canceled.
Cliff Curtis had to leave filming early for personal reasons, so several shots of him (such as entering the bomb compartment) had to be provided by a double wearing dark glasses and a baseball cap. These were deleted when that part of the "test-firing" scene was given to Rose Byrne's character. You can view his double's work on the deleted scenes included on the DVD.
The name of physicist Robert Capa has been taken from photographer Robert Capa, made famous because of his legendary "Falling Soldier" photo, that depicted a falling soldier in the very moment of being killed by a bullet.
On the DVD commentary, the Science Adviser Brian Cox bets the viewer £10 that they (CERN) will not discover the Q-ball particle that disables the Sun in this film's plot. He invites an email to claim the bet. That claim is due in 2017. (In the same commentary, Dr Cox also says that scientists do not gamble!)
In the last few scenes of the film (at around 1h 30 mins) just as the sun shield floats away, you can see an image gleaming in design of the shield. The image is in fact Icarus, the boy from Greek mythology who flew too close to the sun.
Cillian Murphy worked with leading physicist Brian Cox to learn all about advanced physics. This included touring the CERN facility in Switzerland and learned to copy physicists' mannerisms. Murphy ended up copying some of Cox's personal idiosyncrasies, such as his frequent hand movements. The actor also studied Henri-Georges Clouzot's classic The Wages of Fear to have an understanding of the type of suspense that Danny Boyle was attempting to create. Murphy has claimed that his involvement in Sunshine converted him from agnosticism to atheism.
The role of Searle was originally written as a slightly stuffy British character. Cliff Curtis was really interested in playing the character and was given an audition on the strength of his performances in Training Day and Whale Rider.
Kaneda, the captain, was originally written as an American, but scientist and space experts persuaded Danny Boyle to change the nationality, to make it more in keeping with the international nature of space missions. Hiroyuki Sanada was recommended to Boyle by Kar Wai Wong.
When producer Andrew Macdonald first pitched the script to 20th Century Fox, they were reluctant to go near a sci-fi script after the commercial tanking of Solaris. The project ended up at Fox's specialized arm, Searchlight.
Danny Boyle and Alex Garland worked on the script for over a year. They then spent a second year in pre-production, filmed for three months and then spent another year editing and working on the visual effects.
The cast members all underwent space training and learned how to scuba dive. Among the films that Danny Boyle insisted they all watch were The Right Stuff and For All Mankind. Boyle also took his cast on a tour of a nuclear submarine to help them better understand cramped living conditions. He also had them experience weightlessness in the zero G environment of an acrobatic plane.
Filming took place in the 3 Mills Studios in East London. The film employed 8 stages, 17 sets and numerous detailed models. Three film units worked on the film at any one time over the course of the 15 week filming schedule.
The film is comprised of 750 visual effects. Normally, effects are farmed out to several different effects houses. However, Danny Boyle chose just the one to make it easier to keep an eye on progress. This explains why the film was in post-production for a year.
One of the biggest challenges facing the visual effects team was to create the sun itself. This was done with CGI and turned out to be the longest CGI sequencing ever done by a London production house.
The interior of the ship was built entirely on London sound stages. Production designer Mark Tildesley deliberately chose to make the ship messy with lots of exposed wiring to resemble the exposed nerves of the crew.
Even though it appears that the characters Capa and Cassie have more of a relationship in the film, the character biographies given to the actors prior to filming stated that Chris Evans' character, Mace dreams of Cassie (played by Rose Byrne ) every night.
Danny Boyle was so impressed with Michelle Yeoh's audition, that he told her that she could choose any part in the script and he would give it to her - he was even prepared to change the gender if she had chosen a male character. She ultimately decided on Corazon, the biologist.
Danny Boyle originally planned for there to be a sex scene between Capa (Cillian Murphy) and Cassie (Rose Byrne) in the ship's oxygen garden. He eventually scrapped it because he felt that the idea of sex and romance in space would be too ridiculous.
The trivia items below may give away important plot points.
In some earlier versions of the screenplay, the Icarus ships used rotating sections to provide artificial gravity. This is not used in the finished movie, so people experience normal Earth gravity everywhere while aboard the ships (apart from a short moment in the Icarus II airlock before it is re-compressed). An early storyboard shows the crew boarding the stricken Icarus I and finding that the only gravity is "sideways", towards the bomb.
Many of the computer graphic effects were built around an on-set, physical effect, so that the actors had something to respond to. Many of the actors took on these scenes themselves. Cliff Curtis deserves a special mention, as he blocked his nostrils and ears with cotton wool so he could be blasted from all directions with dust.
When the crew enters Icarus 1, flash frames appear on screen when the flashlights point into the camera. These frames are pictures of the crew of Icarus 1 taken from the group photo seen later. Another few flash frames are seen later when Capa learns that there is a 5th crew member on board.
The final scene is filmed on Gärdet, Stockholm, Sweden. The Sydney Opera House has been added to give the impression that it had snowed in Sydney, where such weather is very rare. Right across the street from the monoliths lies the Swedish Film Institute and the film-school Dramatiska Institutet.
For the scene in which Chris Evans's character Mace is fixing the Icarus 2 in the coolant, to make his breath appear that it was cold, Evans was actually entering extremely cold water with each take. His teeth chattering is a real reaction.
In the original script Mace would have slowly frozen to death, having become too weak to pull himself out of the coolant tank. Danny Boyle was impressed by the character and didn't think that alone could stop him, so the trapped leg was devised to seal his fate.
The DVD commentaries from director Danny Boyle and consultant Brian Cox conflict on whether Trey actually committed suicide, as first appears, or whether Pinbacker killed Trey and made it look like a suicide, which is what happened according to Boyle. Cox states that Benedict Wong felt his character had in fact committed suicide. When Mace opens the drawer there are two scalpels missing, which could support either scenario. However, it seems very unlikely that the insane Pinbacker would have sufficient motive or patience to fake Trey's suicide, especially when he later is seen trying to murder the rest of the crew as fast as he can.