The Wraith have ships with sensors, once they found one of the gates in the gate bridge couldn't they just scan for the next one. Essentially following the gates to get to the Milky Way galaxy.

I've been wondering this for years as onscreen the bridge is shown to be a straight line between Earth and Atlantis. Even assuming McKay was right that the Wraith couldn't connect to the bridge, the gates are essentially like arrows pointing to Earth.

Even space gates are in orbit of a planet, and a gate in open space would be obvious. Unless I'm missing something the gate bridge is like a sign saying 'Earth this way, follow us'. Also the gate address is also its location, so finding ANY gate in the bridge shouldn't be too hard.

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    Because the travel times are non-trivial
    – Valorum
    Nov 3, 2017 at 16:03
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    The distance is vast I agree, but they are very careful not to tell the Wraith where Earth is. So obviously them getting there is a big concern, so they instead build a bridge saying 'this way guys'. It makes no sense
    – Matt
    Nov 3, 2017 at 16:08
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    Very small objects someplace in space, thousands of light years apart. What exactly do you do with sensors in that case? Very safe I believe, it would take them millions of years. And then it's just to the galaxy. Finding earth there ...
    – Raditz_35
    Nov 3, 2017 at 16:10
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    The Wraith ships had a significantly slower FTL drive than Tau'ri, Asgardian, and Ancient vessels (unless they stole a ZPM to boost the hyperdrive power).
    – RobertF
    Nov 3, 2017 at 16:14

4 Answers 4


The gate bridge is composed of 34 Stargates. The distance between the Pegasus Galaxy and Milky Way is 2.7 million light years.

That means each gate is roughly 79412 light years apart (by comparison, the entire diameter of the Milky way is only 100,000 light years). Detecting a Stargate is difficult enough that using Asgard-sensor-boosted ships, Stargate teams have sometimes had to look for a long time on a planet they believed one should be (due to the location corresponding to a known address), so the odds that the first outside-of-the-Pegaus-galaxy gate can be detected at such distances is exceedingly small, almost equivalent to detecting a stargate from one side of the galaxy to another. If you even knew in which direction to look you probably already have enough information to narrow down what galaxy humans come from.

Stargate addresses only generally correspond to their location in space, there's a deeper addressing system that correlative updates use to make sure gate addresses go to the right actual location. Several episodes have mentioned encrypted or scrambling gate addresses so those who don't know the new coding can't access them, and in one occasion (the episode "Avenger") this left Earth's Stargate as one of the only ones left that could use the old addresses, which suggests that it can be altered on a gate-by-gate basis. So, considering McKay and Carter are geniuses, it's likely the address to the next gate in the bridge is only available in the previous gate, and most likely encrypted in a way that it's not easy to figure out.

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    I think the issue is that once you find two, it's trivially simple to work out which direction to travel in. And all you need to do is find one, then travel in the direction of a few of the nearest galaxies and you'll find the second gate and can then set course for the Milky Way
    – Valorum
    Nov 3, 2017 at 16:29
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    @Valorum if they are arranged in a perfect line. You might be underestimating just how difficult all of this would be and how long that would take. You won't Just find an object smaller than a house in space when roughly travelling for 80k light years. Just look at the next few galaxies? Well, they spend in hybernation forever, but they need food now and are territorial. No ship would go on a thousand year mission just to find earth for a bit of food. And even if, I doubt earth cares about what happens after that time
    – Raditz_35
    Nov 3, 2017 at 16:38
  • @Valorum, how would they even find one, never mind two? We're talking about an object a few meters across in an area larger than a galaxy. Nov 3, 2017 at 21:10
  • @HarryJohnston - Dunno. They have scanners and know its approximate direction. Assuming it's (nearly) arrow straight, the range would be less than a few light years.
    – Valorum
    Nov 3, 2017 at 21:12
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    I agree with your answer in general, but I also disagree with your assessment of what happens to gate addresses. To connect to a gate, you have to know where it is, which is its address. You can't scramble/encrypt it - it has a physical address, i.e. where it is, and you either know it or you don't. In Avenger 2.0 gates lost the [accurate] knowledge of where other gates where; no gate's own address was "scrambled", it's just no other gate had it properly recorded any more. Nov 13, 2018 at 11:30

In order for a Wraith ship (or any ship for that matter) to cross intergalactic distances in any sort of workable time frame, they must have a ZPM. This is what happens in Enemy at the Gate, the last episode. Prior to the Wraith stealing a ZPM from the Asurans, the Wraith would have had to put their ship on a trajectory for Earth and gone into hibernation; certainly an option but it would've taken them (probably) centuries. Early in the series the Atlantis team didn't even know that the Wraith weren't capable of interstellar travel, so preventing them from finding Earth is really a "better safe then sorry".

By the time they built the bridge, they had a much better idea of what the Wraith were capable of. Gates are tiny at interstellar distances, let alone intergalactic ones, and don't use power until they are opened, so are likely to be missed by sensors. Remember around the same time when they detected the (much larger and more powerful signature) Aurora-class ancient ship, the Tria, they specifically say it was because they were in the right place at the right time.

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    If they can cross a galaxy in 2 weeks, crossing intergalactic distances should only take them a few years at most
    – Valorum
    Nov 3, 2017 at 16:17
  • I don't recall them crossing the galaxy in 2 weeks, but considering the limitations of Wraith hyperdrive in general (having limited range per jump and requiring a significant cooldown before they can jump again) intergalactic travel was certainly a challenge for Wraith ships.
    – Kevin Fee
    Nov 3, 2017 at 16:26
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    They do it with 2 regular hive ships in s3:e1 when Todd find out where earth is. The whole episode is about stopping them before they get to earth
    – Matt
    Nov 3, 2017 at 16:29
  • @Valorum Wraith hyperdrives aren't very advanced, and are only capable of small jumps before requiring repair period due to radiation buildup. They can handle a galaxy, but not intergalactic travel.
    – Izkata
    Nov 4, 2017 at 2:12
  • @Matt Zelenka mentions at the start of 3x01 that the Wraith upgraded their hyperdrives with what they took from the Atlantis database
    – Izkata
    Nov 4, 2017 at 2:27


  • They could have, but I do not think it would have been worth the risks.
  • There are a lot of unknowns here, but I do not think that matters. The only way their plan really can work is if they subtly sneak in. Even still, I do not understand the end goal... It is possible, but I think such a plan is doomed to failure.
  • The real question is why didn't the majority of the Wraith land their ships at the bottom of random planet oceans and go back to sleep after they found out Earth was inaccessible?

For the Wraith, there are a lot of unknowns here. What we do know is how specific the information they knew was. They knew they needed to be "looking" when the Atlantis gate was activated to go to the bridge, to hack the code to gate in, secure the station of course, and that they would need to bypass Earth's extensive defenses. How did they know all of this? It must have come from a captured team member that was taken AFTER or maybe DURING the bridge's construction. Given this, how much else did the aforementioned prisoner tell them?

Given they have some information, let's say that they know the Milky Way situation entirely and every possible Wraith cruiser left together for the promised land; knowing full well the war with the Ori was ended and they may need their combined force to defeat a (nearly) unified Milky Way galaxy.

So they all travel along the gate path with nearly everyone but the care takers back in stasis for the journey. They bring a bunch of "snacks" with them given that this trip will take a while for them. Wikis online state that it takes them weeks to travel across Pegasus, let alone the time between galaxies, without ZPM power. The Daedalus in Season 5 , Episode 2 "The Seed" is said to be out of contact for three weeks, but I have also read 18 days for the trip as well; these are relatively the same and either of these is significantly less than the Wraith. In addition, given the ease of travel between the galaxies the daily or weekly check-ins are happening from one side or the other, thanks to the bridge to at least send reports back home for review.


Now, let's say that Atlantis never catches on to the fact that they have all the sudden stopped seeing the Wraith and that no other planet they have communication with has not mentioned it either, so they never think to put it in a report.

Once the Wraith fleet is detected by the bridge station, they are outed and Earth knows what is coming and has time to prepare. Considering the Wraith were detected, whether it is one ship, all ships, or somewhere in between that has decided to make the trip there is a good chance that as soon as they drop out of light-speed in the Milky Way they will have an armada waiting for them.

But let's say the bridge station doesn't have a chance to get the word out for some reason. Destroyed or whatever. When they miss check in, Earth sends the Daedalus (or another ship) to find out why. This is really the only saving grace in this entire plan, in the beginning at least. I can not remember how many ships the Milky Way has at this point, but if the Daedalus was unable to relay the invasion for whatever reason the Wraith may be able to make it unannounced. Otherwise, if the status of Midway was sent, Earth has time to prepare again.

Once again, let's say that they out smart everyone. The Wraith dodge all the defense ships initially, no one believes Earth about the approaching danger, they were able to destroy the Daedalus, etc. The Wraith start culling and eating after their long trip. Even if it takes the Milky Way time to discover, years even that they have made it to the Milky Way and even if Wraith that are made the old fashioned way (assuming that is still possible) grow in both large numbers and mature quickly, once the war starts they will need at least a generation to begin replenishing their numbers.

Judging by human standards this would mean that the replacements would need to be at least ?10? to be able to operate the vessels and/or become efficient soldiers. We know that they do grow similarly to humans thanks to Season 2, Episode 7 "Instinct" when we see a pre-teen adolescent Wraith. It is possible there was heavy influence by her father, or that the soldiers grow differently, but we do not know that for sure.

At that point, under the best circumstances you have (however numerous) a limited number of Wraith against the entire combined forces of the Milky Way that has numerous abilities to manufacture more soldiers and ships. Unless the Wraith are lucky enough to get someone to ally with them or there is some serious infighting between the Milky Way factions, they are doomed to failure.

Without the guarantee of success I think that the Wraith would prefer to maintain the status-quo in Pegasus. Sure they may eat really well for a bit and have the ability to go out in a blaze of glory, but they want to survive as a species. That is why they all went to sleep after the war with Atlantis. The situation in Pegasus is survivable compared to the slim chance they would have assuming they survived the trip to the Milky Way.


The gate bridge connects the Milky Way to the Pegasus galaxy. It doesn't go from the Pegasus galaxy to Earth. Once you get back to the Milky Way galaxy, the Milky Way gate system takes over to deliver you to Earth.

The Wraith have already figured out which galaxy Earth is in. They need to know where in the galaxy Earth actually is. Following the bridge to the edge of the Milky Way doesn't get them that information.

So, in addition to the problems that exist in actually following the gate bridge, there isn't actually any benefit in doing so.

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    I don't recall any mention that they know earth is in the milky way, only that its in another galaxy. Do you have a reference for that? Also they know that 'whatever galaxy earth is in' its a much better feeding ground than Pegasus at that time: thus even if the bridge only went to the Milky Way (and not earth) they would have a new food source in a time of famine. Its win-win for the Wraith even if it doesn't lead to earths doorstep
    – Matt
    Nov 3, 2017 at 21:46
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    Even finding out which galaxy (out of potentially dozens) would be a massive win for the Wraith
    – Valorum
    Dec 30, 2017 at 19:58

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