Character mistake: When they first receive the alien signal, they decode it and play it as a TV signal which shows Hitler speaking at the opening of the 1936 Summer Olympics in Berlin. Kent translates what Hitler is saying as "I declare the Games in Berlin, at the celebration of the first Olympics of the New Era, as opened." Hitler actually says "the *eleventh* Olympics of the New Era." The "New Era" doesn't refer to some Nazi concept, it's used to separate the modern Olympics from the ancient ones in Greece.
Continuity mistake: There's a scene where Ellie sleeps with Palmer, then gets up quickly to go to the lab. In her haste, she departs whipping on a shirt with no bra. If she had a bra inside that tight T-shirt the contours of the cups and straps would be visible and we would see her fitting and fastening it, instead she steps outside where suddenly it appears she is now wearing a bra.
Factual error: The geography around the VLA in New Mexico is actually relatively flat - in fact one of the reasons why the array complex is there is because the land is flat. The canyon in the film was actually Canyon de Chelly, in Arizona, more than 170 miles (270 km) away. But in the film, when Ellie goes to the canyon, the radio antennas seem to be right there, insinuating that the canyon is part of the VLA's magical desert scenery.
Factual error: When Mr. Hadden reviews Ellie's life history on his airplane, he says she graduated from MIT 'magna cum laude'. This is impossible, as MIT does not award academic honors to graduates.
Factual error: A big deal is made of the fact that no camera can be installed in the pod because of the high local magnetic field. This is idiotic. It is easy to shield a video camera from an electromagnetic field. Bog standard technology.
Factual error: In the zoom-out at the very beginning, we hear broadcasts going back in time as we zoom out through the solar system. However, we hear broadcasts going back through time roughly 40 years. Shouldn't we be 40 lightyears out from Earth to hear them, rather than just in the Oort Cloud beyond Pluto? Radio waves travel at the speed of light like any electromagnetic wave. EM waves should not be confused with sound waves, which move much slower than the speed of light.
Visible crew/equipment: As Ellie runs up the stairs of the observatory after hearing the first audio transmission from space, she runs towards doors with two large glass windows in them. As she opens the doors, a crewman/cameraman is visible in the right window for a brief fraction of a second.
Factual error: At the end, after Ellie testifies before Congress, she departs the Capitol building to a waiting limo. The media is there waiting for her. Behind the reporters appears to be the Reflecting Pool, and the Washington Monument at the far end of it. However, in reality, the Reflecting Pool is actually located between the Lincoln Memorial and the Washington Monument, not the Capitol. While there are two Reflecting Pools, the columns in the movie are the columns of the Lincoln Memorial, not the Capitol. Furthermore, the steps leading to a street in front of the reflecting pool are located at the Lincoln Memorial; the Capitol has a large green lawn between it and the street.
Suggested correction: It wasn't the Lincoln Memorial, but the Treasury Building.
Continuity mistake: When the signal is first received, and they realize it is transmitting prime numbers, if you listen closely, the signal hits 11, starts over, but continues on up into the 30s, completely skipping all the prime numbers after 11.
Deliberate mistake: The slow rate of the radio telescopes at the VLA has been greatly increased for the movie. They are actually quite slow and make little to no noise.
Revealing mistake: When Ellie is traveling through space, she unbuckles herself from the chair to retrieve the compass. The chair then breaks off from the violent movements of the space pod, and slams up against the ceiling. At this moment, Ellie is in deep space in a completely weightless environment. She is floating, suspended in the pod and the chair itself floats a bit before being slammed upwards by the force of the pod movement. But, some small parts of the chair (bolts, etc.) are seen falling directly down, towards us in obvious full gravity; revealing that the scene was actually shot in normal gravity.
Continuity mistake: If the cameras inside the Sphere won't work because of the magnetic field that is being given off by the machine, then why do the cameras on the main structure work?
Plot hole: During the Congressional hearing, it is suggested that the alien signal could have been faked from a satellite - as Ellie only has her own experience to go on, it leaves her believing what happened, but still with an element of doubt. However, as a professional astronomer, Ellie would have immediately dismissed this since a simple parallax (triangulation) would have confirmed that source was at the distance of Vega - a distance far too great for any rocket to reach. (This is mentioned in the book). In fact, this is mentioned early in the film, when the employees in New Mexico calculate the source of the signal while it is transmitting prime numbers.
Continuity mistake: When the Machine is used for the second time (with Ellie in the pod) the large outer ring is set spinning. This brings the total number of spinning rings to three. However, when video of the pod falling through the machine is played back on the TV screen, the outer ring is fixed horizontally and not moving at all. Only the two inner rings are spinning.
Continuity mistake: When Ellie arrives back from her travels, the capsule lands in a net supported from four pillars, and to decellerate effectively, both the net and capsule end up in the water. However, when we view the splashdown from a CCTV camera (Cam 03) when Ellie is in quarantine, neither the net nor the pillars are to be seen. (02:01:40 - 02:03:15)
Factual error: When Foster is going to Japan, a Harrier jet transports her to a ship. The ship is underway, traveling at quite a clip according to the wake. The Harrier landed on its heliport platform, facing the stern. Harriers hover, but cannot fly backwards at more than a crawl. It would have crashed.
Suggested correction: It isn't technically a harrier just another futuristic version of a VTOL aircraft. We don't know the capabilities of a fictional aircraft.
The VTOL is military, but she steps off a small commercial plane.
Factual error: The last time Eleanor Arroway talks to S.R. Haddon, he's aboard the Russian space station Mir, and Haddon explains that he's up there because the "low oxygen" and zero gravity counteracts his cancer. In fact, there is no "low oxygen" environment aboard space stations or other spacecraft. Low oxygen content would, of course, kill any astronauts or cosmonauts in short order. The breathable air in spacecraft always has at least the same oxygen content as Earth atmosphere at sea-level. In fact, most Russian missions used excessive amounts of oxygen. S.R. Haddon's original dialogue was probably "high oxygen and low gravity," but the line was bungled and allowed to remain in the film.
Suggested correction: Also, being terminally ill, he is grasping at straws, and can't be expected to think solidly. After all, gravity wouldn't mean all that much to cancer cells in the human body, and special oxygen conditions of any kind can be generated on Earth (there is a weak possibility that low but sufficient for a human oxygen levels would slow cancer cells, which are often less efficient, more vulnerable in certain areas than healthy cells), so no need to go up, and finally, he may simply be Dennis Tito-ing and making an excuse to do so.
Continuity mistake: When Ellie is in the pod and is talking to Kent, her monitor has the word "Hadden" in the top left hand corner. In subsequent shots, there is no "Hadden" on the monitor.
Continuity mistake: When Ellie is being driven through the desert she sees The Preacher with the long hair. As it cuts between them, her seat belt goes from being folded to straight to being folded again over her right shoulder.
Continuity mistake: When Ellie drives back to the observatory after hearing the first audio transmission from space, there are several shots of her holding the steering wheel with her left hand while giving instructions to the other men. In one shot you see that the wrist-watch is turned upside down: the watch face is on the inside of the arm. In the following shot of her in the car the watch face is on the outside of the arm.
