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In Stargate (the movie) we see that, when the gate is activated, there is no wind moving from one planet to another. This suggests that air does not flow, which, in turn suggests atmospheric pressure is the same in both locations.

Is it that way? And for all planets through the series as well?

If not, why is there no wind?

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    opening the stargate is not like opening a window, remember you cant see the other side through the gate, you step into a wormhole that then moves you across space to exit out of a second gate, the wormhole surface may even be able for air to diffuse through it. otherwise to answer your main questions, no the planets are typically all in a similar range as extremes tend to be unhospitable for human life, however there are many planets that do have more extreme temperaments in the series. i believe we have seen storms on 1 of the gate, yet no water is let through the gate. – Himarm Oct 30 '14 at 15:23
  • It goes without saying that the out of universe explanation is that all planets in the series (the surfaces, anyway) are filmed on Earth, and nobody thought about different planets having different atmospheric pressures. – user11521 Oct 31 '14 at 0:59
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    Clarke's 3rd law - Any sufficiently advanced technology is indistinguishable from magic. – DoStuffZ Oct 31 '14 at 9:39
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    Um, aren't the gates one-way only for matter? – Kyle Kanos Oct 31 '14 at 13:44
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    @Dronz Pressure itself isn't really too important, we're pretty resistant to that. It's the partial pressure of certain gases (like oxygen) that's important - and presumably, that was taken care of to be at least tolerable by the terra-formers (be it the Ancients or the Goauld). Note that the Earth plants themselves would tend to balance at the same partial pressure of oxygen we like, mostly (too much gives you forest fires, too little improves oxygen production). – Luaan Oct 31 '14 at 18:32
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Matter doesn't move between planets due to pressure differential! The planets are connected by a wormhole and separated by a matter-energy-matter conversion sequence, so the rules of fluid dynamics do not have any bearing on the behaviour of either air or water in terms of how/whether they transit through the gate.

What is relevant is the threshold of pressure exerted upon the gate's event horizon before the gate decides to dematerialise that particular matter and send it through. It was explained in SG1: Watergate that standard atmosphere pressure (at least) is under this threshold, and we saw in ATL: The Shrine fear that water (with its pressure against the gate mostly coming from the sheer weight of a massive body of the stuff) is over that threshold and could flood the area around the receiving gate. This makes sense, since the pressure of an ocean is greater than the pressure of a random SG team member walking casually up to the event horizon, and obviously we know that they get through.

The other obvious counter-example is Atlantis dialling space-gates and the air not being immediately sucked out of the gate room.

That being said, the planets we've seen that actually have a breathable atmosphere appear to have one at standard Earth ground-level pressure (or, at least, roughly within Earth's usual variation) because nobody's complained about their ears popping or their eyes being pushed back into their skulls.

  • I think the Atlantis episode with keeping the shield active was just fear/safety. If the water would have flowed into the gate, it should have been hitting the shield on the receiving side and had a visible flow on the sending side. So it does match the other episodes, if the pressure basis is upon gate activation rather than all time. – Izkata Oct 30 '14 at 21:53
  • @Izkata: True; and actually that lines up with Carter's comments that the gate will "just know" that such high constant pressure is unlikely to be desirable. I still don't think we have any evidence that this has anything to do with comparative pressures, though. And, even if it does, it would have to be a logical mechanism in the gate because fluid dynamics themselves cannot be responsible here. – Lightness Races in Orbit Oct 30 '14 at 22:05
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    "sucked out?" You mean blown out. lol – fredsbend Oct 31 '14 at 8:43
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    @fredsbend: Cheers, Data! – Lightness Races in Orbit Oct 31 '14 at 10:08
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    +1, excellent point. The reason pressure differential matters in real-world physics is because the transfer of particles is always two-way. Since the Stargate only transfers matter one-way, the differential is irrelevant. – Harry Johnston Nov 1 '14 at 4:55
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The stargates have some safeties built in. One of which is handling differential pressures. In the SG-1 episode Watergate, we see a particularly egregious example. In the episode, a stargate is on Earth, another is underwater on a distant planet. When they connect the two from Earth's side, water does not start rushing into the gate on the distant planet. When they connect from the distant planet's side, the same does not happen. A sub is used to travel safely between the two planets, and the stargates enable the sub to safely cross, but there's no deluge of water.

The same thing (to a much lesser extant) happens with differing air pressures.

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    There are plenty of examples in SG:Atlantis of Star Gates being in orbit, with no sudden massive world ending decompression when they travel through one to another planet whose SG isn't in orbit :) – Moo Oct 30 '14 at 15:34
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    @Envite I haven't watched "Watergate" in a while, but I dimly remember some technobabble about how the water exerts a constant pressure on the wormhole; the gate lets the sub through because it exerts sudden pressure – Jason Baker Oct 30 '14 at 15:40
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    Advanced alien tech knows the difference. – BBlake Oct 30 '14 at 15:45
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    Also, in SG:A Inferno, a sudden increase in constant pressure might be let through. I seem to recall Sheppard radioing Atlantis to put the gate shield up when the remote gate fell in the lava. – joe Oct 30 '14 at 18:04
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    @fredsbend or, the show's science is riddled with wormholes. – Gusdor Oct 31 '14 at 11:25
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Also worth noting is the sg1 episode "a matter of time" where the gate connects to a planet near a black hole. Samantha sees smoke being sucked into the gate. The only time I've ever seen gases going through the gate. http://stargate.wikia.com/wiki/A_Matter_of_Time

In this instance think it would be better to say that proximity to black holes messes up the stargate, rather than gravity can suck gases through the gate.

  • Gravity totally "sucks gases". How do you think Earth's atmosphere stays ... y'know, on Earth? That's precisely why smoke went through the gate. – Lightness Races in Orbit Sep 25 '15 at 16:41
  • Gravity sucks thing more or less depending on their mass, so if the gravity is enough to suck a gas it should in theory suck all masive objects in the room a million times harder... But it's a classic TV tropes that physical forces apply when and where they want in TV (like a hurricane sucking a truck but not the man beside it...) – max pnj Feb 17 '16 at 14:55

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