In Stargate SG-1 S02E16, The Fifth Race, SG-1 (Captain Carter, Teal'c and two other members, who replaced Colonel O'Neill and Dr Jackson) is "trapped" on planet in binary system, where second star has risen and is slowly raising temperature - Samantha Carter says, in one moment, that it's going to reach 200°F soon - and dialing device is locked mid-dial. Yet, SGC manages to dial the planet and send them instructions how to repair the device and off-world team makes it back.

Why didn't they come back when Earth first dialed P9Q-281 to contact SG-1? I mean, from my understanding, stargate wormhole is two-directional, meaning it doesn't matter which end it was activated from, yet it seems like it is one-directional from the events of this episode...

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    "it seems like it is one-directional from the events of this episode" Yeah and pretty much every other episode. Where did you get this idea from? Aug 25, 2014 at 11:37

4 Answers 4


One of the fundamentals of SG-1's fictional wormhole physics is that wormholes are bi-directional, but the stargates can only send matter one direction. There are a handful of exceptions to this rule, most notably for radio signals that allow for two-way communication, but matter can only be transported from the origin to the destination.


No, the wormholes are one-way. Matter can only pass through from the dialling end, although radio waves can go back the other way. See the detailed Wikipedia article.

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    Radio waves, gravity, subatomic particles, and other plot-bits can travel both ways.
    – Jeff
    Jul 5, 2012 at 18:23
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    @Jeff Simplistically/in general, energy can pass both ways. Matter can only pass one way because the Stargate itself has to convert it into energy before transmission and after receiving. I'm not actually sure where subatomic particles land on "is it matter or energy?" within the Stargate universe.
    – Izkata
    Jul 5, 2012 at 18:37
  • +1 I also wonder why light never traveled both ways.... but hey i guess that wouldn't be a mysterious if it did. Jul 6, 2012 at 6:07

I tend to imagine it in one of 2 ways:

1) It being somewhat like a one-way street. You enter the outgoing gate, and exit the destination gate. However, there is nothing to stop you from entering the destination gate and arriving at the outgoing gate...except the cars (energy in the case of the stargate). There is nothing stopping you from riding your bike against traffic on a one-way street, though you're not going to arrive, considering how you'll get smashed up by cars and such. Timing doesn't enter into it either, as you're traveling many lightyears through the stargates.

2) (this answer is much more 'canon' in that it uses pre-established facts about the gates). Stargates encode matter that passes through them, stores it in a buffer, and then forwards the resulting data to the destination gate, which then rematerializes the information contained within the buffer. So, in this sense, they're like letters. You take your thoughts and write them down (encode matter), put them in an envelope (store in buffer), it's picked up by postman (sent to destination), placed in mailbox (stored in dest. buffer), and finally opened by recipient (rematerialized). Now, try sending a reply in the same envelope, carried by the same postman who stops and picks up letters from the outgoing gate. he won't be picking it up at the destination, and the meta data on the envelope won't be correct.

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    I think you've stretched the analogy a bit far. Stargates are not postmen. Aug 25, 2014 at 11:38
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    That's what metaphors and analogies do. No, stargates are absolutely not mailmen. Butt i'm not claiming they are.
    – acolyte
    Aug 25, 2014 at 19:06
  • No, but you can't just randomly pick a thing and invent comparisons to form an analogy then use that analogy to prove a point about the original thing. Aug 25, 2014 at 20:49

SG canon very clearly establishes that although communication through the stargate (radio) is bi-directional, matter can only travel from the dialing gate to the dialed gate. This is always respected throughout the series.

In order to return home, Carter's expedition had to dial Earth. There was no other option.

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