FAQs about the Stargate franchise, mostly about the Stargate device operation, with answers compiled from the Stargate Wiki, Stargate Subreddit, and GateWorld. Spoilers abound, obviously.
The iris is positioned three micrometers from the event horizon of the gate. This is close enough to prevent matter from remolecularizing [SG1: “Children of the Gods”]. The unstable vortex of the kawoosh is itself matter, so instead of being projected outward, the energy and base particles that would create the kawoosh hit the iris before forming the vortex, causing it to heat up instead of be destroyed. Sokar used this to his advantage, attacking the iris with a particle accelerator [SG1: “Serpent’s Song”].
The kawoosh starts smaller than the diameter of the gate and balloons outward, so the ramps and platforms supporting the gates are out of its path. This is apparent when observing the phenomenon from the side.
The iris control system responds to GDO requests with a “come on through” signal as the iris is being opened, or a “do not proceed” signal otherwise. GDO users enter their code, check the response, then decide to continue through the gate or not.
This process is never shown on camera, however Colonel Ben Pierce mentions the “do not proceed” response at one point, so it can be assumed there is a corresponding “come on through” signal [SG1: “Endgame”].
The event horizon demolecularizes matter that enters it for transmission through the worm hole. Since matter travel is one-way, any object that enters the destination gate is simply destroyed after the gate shuts down. This happened when a MALP fell back into a horizontal gate [SG1: “A Hundred Days”]. Anything partially inserted can still be removed [SG1: “New Ground”].
Since objects retain their velocity and direction, it would be impossible to retrieve an object that entered a destination gate from the buffer, as its last motion was into the event horizon.
Traveling through the back of a gate is never addressed, but presumably it has the same demolecularization effect without travel. [One of the Stargate novels has Teal’c mentioning it is an unpleasant death.]
There is an apparent directionality to wormholes that means matter can only be transmitted in one direction. Major Samantha Carter suggests this when questioning an Air Force cadet’s assumptions about wormholes [SG1: “Prodigy”]. Also, after connecting to a gate directly in line with a star (and bypassing safety protocols to do so), the wormhole created by the SG-1 team picked up a heavy element and deposited it in the star [SG1: “Red Sky”]. Electromagnestism, gravity, and other massless phenomenon can be transmitted either direction.
This is never addressed. The simplest explanation is that the event horizon overpowers or otherwise interferes with visible light passing through. Possibly, for safety reasons, the gates filter EM radiation outside of a specific frequency range to prevent highly energetic rays from being transmitted.
Real-world: not having to portray another environment through the portal every time is much simpler from an effects standpoint. It also creates a sense of mystery and wonder that facilitates the plot.
Having been demolecularized, it is destroyed. Normally, gates have safety protocols that prevent the wormhole from being disengaged while something is partially inserted into the event horizon of either gate. This is used by Jack O’Neill to “keep the door open” [SG1: “Shades of Grey”], and by Eli to prevent Destiny from entering FTL [SGU: “Air, Part 3”]. However, there are circumstances where the wormhole may disengage while and object is still partially inserted. The 38 minute limit has been shown to cause a disconnect despite activity in the wormhole [SG1: “Serpent’s Song”]. Presumably the safety protocols cannot prevent this from happening despite something being inserted into either gate [SGA: “38 Minutes”]. When Kawalsky was killed using the SGC gate [SG1: “The Enemy Within”], this was due to the lack of a DHD; they were able to simply cut the power to the gate, and their dialing computer was not capable of handing off power supply duty to the destination gate.
Possibly because it would interfere with object detection, the Puddle Jumpers have warnings against using their cloak while going through a gate [SGA: “The Shrine”].
Stargates seem to have a sophisticated ability to simulate anything that has been partially inserted. For example, when an arm is inserted then removed, there are no apparent ill effects. This means blood cells that had passed the event horizon were allowed to come back through the veins of the arm. The gate must be capable of identifying and remolecularizing the cells that should be traveling back into the partially inserted limb. Likewise, the MALP would get stuck as soon as parts crossed the event horizon if the gate didn’t simulate already inserted components.
This simulation capability must also include mimicking the support a partially inserted limb would provide, so that travelers can simply step through. Also, when Teal’c deposits the corpse of Apophis into the gate, the body is supported by the event horizon even after being inserted [SG1: “Serpent’s Song”].
Real-world: it’s far simpler to have people step through the event horizon instead of need to jump or manuever in some other way. This also explains why the show moved away from the rough ride that initial gate travel had, with an explanation about stellar drift alignment. It’s dangerous and complicated to need to do a stunt every time someone steps through.
There are some instances where this doesn’t seem to be the case, and objects partially inserted are transmitted through:
In 1945, Ernest Littlefield traveled through the Earth stargate trailing an airhose behind him. After stepping through, the wormhole disengaged, severing the hose. However, Littlefield and his suit made it through to P3X-972/Heliopolis. [SG1: “The Torment of Tantalus”]
In 2000, Colonel Jack O’Neill was trapped on P5C-768/Edora for several months after Edora‘s stargate was knocked over and buried by a meteorite. As part of the rescue plan, Teal’c fired a harpoon and rope so he could go through without falling back into the event horizon. [SG1: “A Hundred Days”]
In both of these instances, the partially inserted object was line of some sort. In the case of Teal’c the assumption can be that the harpoon was not actually transmitted until he stepped through with the reel and the rest of the line. The simulation capability that must exist allowed the line to stay in position until Teal’c stepped through and began pulling himself up.
In the case of Littlefield, it’s probable that the power was interrupted to the gate, given the technology being used to control it at the time. The gate has sophisticated object detection, and a built-in safety protocol may have detected unreliable power supply and decided the air hose, which was effectively attached to the environment, was not part of the object, transmitting Littlefield and his suit before power was lost.
Real-world: these two circumstances are more likely goofs created for dramatic effect or ease of storytelling. Also, the complete object transmission rule wasn’t explicitly stated until much later in the series, when plot necessitated it.
The FN P90 fires more powerful rounds than the MP5 used early on in the Stargate program. It also has a higher magazine capacity and rate of fire. Combined with armor piercing rounds, it is an extremely effective weapon against armored Jaffa. The SG teams do not use appropriated Goua’uld staff weapons because those are less effective when combined with Tau’ri training and tactics. O’Neill, with the help of Carter and Rak’nor, provides a demonstration of how a staff weapon is a “weapon of fear” while the P90 is a “weapon of war” [SG1: “The Warrior”]. SGC personell do use Zats more frequently later on, presumably as more of the weapons can be procured through seizure or other means.
It is important to note that most of the SG teams are exploration-oriented. Heavier weaponry would be a hindrance in many cases, either as a literal weight slowing them down, or by intimidating locals they are seeking to form relationships with. Sometimes, the teams enter with only sidearms after making contact via the MALP [SG1: “Icon”]. The P90 is powerful, yet low profile, making it suitable for the situations the teams typically encountered. For missions where combat was anticipated, heavier weaponry can be seen. When facing the replicators, SG-1 armed themselves with SPAS-12 shotguns. There is likely also an element of personal preference when choosing loadout [SG1: “Heroes”].
Real-world: the P90 ejects shell casings downward instead of to the side the way the MP5 and other weapons do. This makes it more favorable for filming; the actors do not have to be positioned so that the ejected shells miss other actors, crew, or equipment. Its unusual design also looks more futuristic, and the weapon has since become an icon of the franchise.
During Stargate SG-1, season 7, Major Carter uses a gun that is a hybrid of various other weapons (“Carter Special”). According to the DVD commentary, this is because blanks for the P90 were in short supply due to the Iraq War.