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I don't know Stargate: SG-1 well enough to find episode titles, so I hope people will bear with me (or one who is wiser might edit this and add them).

In a number of situations in the show, we see the wormhole open and most of the team goes through, but one person may remain for a moment to say a farewell or something, then go through the gate and the gate closes immediately after they step in it. In others, we see, from the SGC side, several team members come through the wormhole, then a pause, then the remaining member come through and the gate closes.

But there are also times when the team all walks through close to each other and the gate closes immediately after they all go through.

At the end of "Shades of Grey" (S03E18), the episode where Jack O'Neill goes undercover to find the humans stealing alien technology, he opens the gate, steps through, and keeps his hand in the gate to keep it open so others cannot close the gate and dial elsewhere.

Is there a set of rules for when the gate can close? Do they somehow signal the gate that there are a set number of people going through? Does SGC keep the gate open with a radio signal until the last team member is through?

This is one of the few times I'd accept that it's a writing issue and they do what's needed for the situation, but I'm wondering: is there an in-universe explanation for why the wormhole waits for another person, then closes, and other times it does not?


Added as an afterthought: there are also cases where they send a UAV or other probe through a gate and keep it open so they can receive telemetry. I would assume they are either using the SGC computer to keep the gate open, or that the radio signal is enough to keep it open, but that's another situation to consider, too.

  • I vaguely remember a theory that, since it can prevent atmosphere from going through the gate, the Stargate can also detect changes in air pressure and shutdown when no one is moving towards it anymore... – Izkata Jan 7 '12 at 0:13
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    This is addressed in one of the episode commentaries. The wormhole looks at the show-script and if it says "[wormhole closes]", then the wormhole closes. – Valorum Nov 11 '18 at 18:26
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The Stargate wiki lists a collection of known 'rules' about wormhole physics - no mention of the 'holding open'.

But, generally, the 'rules' are driven by plot - for example, they are able to close the gate in the second episode The Enemy Within while someone's head was partly inside the event horizon. This, of course, had fatal consequences.

In other episodes, like the one you mention (the season 2 episode Touchstone) and several others, the wormhole is 'held open' by someone putting their hand in or the muzzle of their rifle (either at the origin or destination end of the wormhole).

We don't really see any specific control over the wormholes closing in a lot episodes - but thanks to the few instances we do see (like The Enemy Within) we can assume that there is more going on behind the scenes. We don't generally see this, because it's probably treated as an 'everyday' device (like we generally don't see characters go to the toilet on TV).

  • Holding the gate open is part of the Stargate, not part of wormhole physics. The Stargate will not shutdown or transmit an object unless it has detected the entire object has passed the event horizon, or the 38 minutes run out. – Izkata Jan 7 '12 at 0:00
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    Actually, when things are going smoothly, they seem to have a lot of control. O'Neal orders them to "shut er down" on several occasions. – Ashterothi Jan 7 '12 at 0:13
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    The Earth gate was jury rigged, so it stands to reason that you could manually bypass a number of safeties, namely the one that prevented the disengagement of a wormhole while something was within the event horizon. – Chad Levy Jan 7 '12 at 6:22
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    @Bobby: Radiation can go through in both directions but matter can only go one way. (It's never really explained why.) – user1030 Jan 7 '12 at 15:15
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    @JoeWreschnig It's a safety feature of the Stargates, not a feature of wormhole physics - see stargate.wikia.com/wiki/Stargate for more information. (Wormholes support travel in both directions by both matter and energy, but the event horizon would destroy matter either way. The Stargates convert matter into energy to allow it to survive the process, but only allow travel in one direction) – Izkata Jan 7 '12 at 17:20
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From my understanding a big part of how long the gate stays open is based on power consumption. Shut off the power, shut off the Stargate. This is reinforced by discussions about how different technologies (DHD vs SGC powergrid) can hold open a gate, and discussing the maximum time that people can hold it open (Anubis held it for about 30 min IIRC). Also in some cases the Wormhole gets external power, which messes with their ability to shut it off, such as in A Matter Of Time (S02E15).

Basically the Stargate requires massive amounts of power to remain stable, this power is generally provided by the dialing gate, but has been also gained as feedback from the end point. The further the Stargate is reaching, the more power is required.

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There are a few rules, but in fairness they are rather inconsistent in several regards. That being said it has been stated that radio signals can hold the gate open as can partially dematerialised objects.

Power requirements aren't an issue, power is only required to cause the wormhole to open, at which point the power is generated by the gate itself, normally this limited the operation time to a maximum of 38 minutes, though this can be extended by a large external power source (such as a black hole).

Stargate command does have the ability to disconnect an outgoing wormhole, (demonstrated in s01e03 "The enemy within"). We can assume that if you are in control of an outgoing wormhole (via dialling computer or DHD) you can actively control when it opens and closes. However you have no control of the incoming wormhole, beyond being able to stop it forming in the first place.

How does the outgoing stargate/DHD know to stay open or close without manual operation? There doesn't seem to be any clear specifications beyond "the gate will stay open if something holds it open" (a radio signal will do) or "there is an object in transit". The 'opening side' can control when the wormhole opens and closes. We would assume that some system allows the gate to disconnect after a set period of time with nothing travelling down it (this is really inconsistent in the show, and never explained, sometimes it's less than a second, sometimes it's minutes).

Though perhaps this can be manipulated from the incoming side via use of radio waves of other form of radiation, as these can travel in both directions, though this at best would only keep the gate open (and not close it) and we would assume this can be overridden at the 'outgoing' side.

  • There are no instances of "rejecting" an incoming wormhole that I've ever seen. The only thing they could do was close the iris. This doesn't reject an incoming wormhole. I like the rest of your answer so I'm not giving a down vote. – Jim2B Mar 23 '15 at 14:29
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We know that they have transmitters carried on them, though we do rarely see them. So maybe they turn them on so they can send a weak radio signal. This would be not enough to be detected long range, but enough to keep the gate open at close range.

  • radio signals don't go directly through the stargate, they go in all directions and so some of them go through. I can accept that when they come back from a planet with no technology, there is no radio waves that can keep the door open as soon as the last one pass the stargate But when they leave earth... the base should be full of radio signals (from the talkies for exemple) and so the door should never close until the 38min limit – max pnj Feb 18 '16 at 13:38

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