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Samantha Carter explains in the pilot that because of the expansion of the universe, stars are moving away from each other and a correction needs to be made to the dialing protocol to account for this. She further states that dialing for nearby gates (such as Abydos, and later we learn also Heliopolis) is unaffected since stars further away are receding from earth more rapidly than nearby stars. However, isn't the expansion of the universe observed between galaxies clusters and not between individual stars within a galaxy? The stars of the milky way are not receding from each other, they are all at a (roughly) fixed position relative to each other as they orbit the supermassive blackhole at the center of our galaxy. So why would any correction need to be made for dialing between gates in the milky way?

(And further, the expansion of the universe is an effect seen at even larger distances than galactic clusters, so one wouldn't think this effect impacts dialing within the local group; therefore, not meaningful even for dialing to Pegasus. Though, of course, galaxies in the local group are moving relative to each other... a fact we will be painfully aware of in 2.5 billion years when the Adromeda and Milky Way galaxies collide.)

Edited to Add: Certainly stars in the galaxy are moving relative to each other, and this might well account for some of the addresses not working. However, Carter and Daniel Jackson explicitly state that it is the expanding universe causing the dialing to be off, which is why they can (relatively) easily correct for it:

Carter: According to the expanding universe model, all bodies in the universe are constantly moving apart.
...
Jackson: But why does it still work between Abydos and Earth?
Carter: Abydos is probably the closest planet in the network to Earth. I mean, the closer they are, the less the difference in the relative position due to expansion. The further away, the greater the difference.

If the adjustment had to do with intragalactic stellar movement, then closeness to Earth would not be as relevant. (Though, of course, the closer to Earth the less likely some other massive body has passed into the path between Earth and the other planet which might make it less likely that an adjustment is needed in dialing).

Also, I discount things like the motion of the planet around it's star since this would have impacted dialing Abydos and Heliopolis as much as anywhere else over thousands of years (presuming they orbit their stars at speeds at least comparable to that of earth, which seems reasonable given that their environmental conditions are very similar to earth).

  • What episode was this in? It took a few before they switched all the way from the movie's "across the universe" to "within this galaxy" for the Stargate network's range. – Izkata Apr 8 '12 at 2:30
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    @Izkata This was in the pilot. When Daniel is first showing them the room on Abydos with all of the gate addresses (that form the entire basis for their dialing until Jack adds the ancient addresses to the database). – user5730 Apr 8 '12 at 2:31
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    Then, out of universe, I'd attribute it to the writers not yet having defined what the Stargate network's range is. In the original movie, Abydos was in another (nearby) galaxy, so when they wrote Carter's explanation they probably used that as the basis. Abydos being nearby in our galaxy is a retcon that happened later. Did you want a specifically in-universe answer? – Izkata Apr 8 '12 at 2:35
  • @Izkata Ah, I didn't realize that was the case in the movie. (I only saw the movie in the theatres many years ago and don't have it on my DVD shelf like the series.) Thanks, that makes Carter's explanation perfectly sensible. – user5730 Apr 8 '12 at 2:40
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Despite their apparently fixed location in the night sky, stars are actually moving fantastically fast. Our sun is moving 10 miles per second toward the constellation Hercules. Targeting our sun at a distance would be quite a feat after a light year or two of distance begins to separate us.

Stars are actually moving not only in rotation with galactic movement, they are also moving in relationship to each other, depending on how they formed, where they formed, how they have been affected by gravitational influences of other stellar bodies, including black holes, dark matter and other high mass stars. The study of stellar movement is called kinematics

enter image description here

For reference, a galactic year is estimated to be 225–250 million (solar) years, but as the galaxy is big this is still fast. The Sun's velocity in the galaxy is around 220km/s (kind of a average with everything else moving). Compare to Earth's orbital velocity ~30km/s.

Stellar movement can be affected by their planetary bodies as well, depending on how close an orbit they have, whether they are double stellar units and how close they are to the galactic core. Any system that was designed to deal with linking two places together by analyzing the gravity wells of stars, creating synchronized, dedicated wormholes between those two stars to tiny receivers on planets within that gravity well would need to compensate for:

  • double star systems (there are more of these than you think)
  • planetary movement around the star
  • planetary rotation stellar
  • movement of the star through the galaxy
  • stellar movement in relationship to other gravity wells

In addition, the wormhole or Einstein-Rosen bridge has to be able to negotiate any ripples or gravitational anomalies between the two locations. It can be assumed the Stargate technology compensates for black holes or other gravitational bodies that could disrupt the wormhole bridge between the two locations due to stellar drift.

  • Good point. Stars are certainly moving relative to other gravity wells, and this may well account for the needed adjustments, but Sam suggests it is universal expansion. Also, it would be nearly impossible to adjust for movement relative to other gravity wells since we can't observe many (most?) of those. I edited my question to quote the statement about universal expansion that Sam made. – user5730 Apr 8 '12 at 2:15
  • I would assume the Stargate technology would make that possible as part of its initial programming. Gates would need to talk to each other and ping their relative locations at faster than light speeds, likely creating tiny wormholes to send information updating gate movement, relative to other bodies in their vicinity. Such a complex technology would leave NOTHING to chance. – Thaddeus Howze Apr 8 '12 at 2:37
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    @ThaddeusHowze And indeed the gates do: as seen in the episode where the whole network is disabled due to the introduction of a malicious update. And, for reference, a galactic year is estimated to be 225–250 million (solar) years, but as the galaxy is big this is still fast. The Sun's velocity in the galaxy is around 220km/s (kind of a average with everything else moving). Compare to Earth's orbital velocity ~30km/s. – Richard Apr 8 '12 at 7:58
  • It's worth noting that the problem is far more noticable to astronomers. If you want to point a telescope at any particular point in the sky, you have to keep your star charts (and the coordinates for those particular stars and nebulae) updated on a regular basis. Print charts are updated every 50 years, so if your coordinates are 3 or 4 thousand years out of date (like the addresses from Egypt were), the difference is going to be quite large. The ancient Egyptians literally had different constellations in the sky than we do today. – Ernie Jul 8 '15 at 23:32
2

From the Wikipedia article on stellar drift:

Nothing in space stands still—more precisely, standing still is meaningless without defining what "still" means. Most galaxies have been moving away ever since the Big Bang, as explained by the metric expansion of space. Galaxy motion is also influenced by galaxy groups and clusters. Stars orbit moving galaxies, and they also orbit moving star clusters and companion stars. Planets orbit their moving stars.

(Bolding is mine)

Basically, galaxies aren't a static object - everything is shifting around. It's slow enough that Earth dialing computer could still dial most planets without accounting for the stellar drift since Ra left earth, but travel through the resulting wormholes wasn't exactly comfortable.

  • I don't think the Earth dialing computer could still dial most planets without accounting for Stellar drift. Sam specifically states they had the computer dial "hundreds" of other addresses after the original mission and couldn't establish a connection. Though, you're certainly right that everything is shifting around even inside the galaxy. But near objects are not necessarily shifting less than far objects. – user5730 Apr 8 '12 at 2:13
  • @rar There are 3010936384 possible combinations of glyphs, even knowing what the point of origin is. It's amazing that addresses are ever hit with random dialing. I'd guess that the near/far thing as to do more with percent offset from the dialing point. A 3 degree shift is a much larger distance when you're further away. – Izkata Apr 8 '12 at 2:18
  • Yeah, there are many possible combinations. I was surprised at Sam's statement that they had dialed "hundreds," as if that were a lot. They could have just left the computer dialing. Good theory on the small degree shift getting extrapolated over a larger distance causing far planets to need more correction. I think that makes a lot of sense. – user5730 Apr 8 '12 at 2:20
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It's worth noting that stellar body are moving apart for a variety of reasons. In fact the moon is moving away from the Earth at a rate of 3.8 cm per year, And the Earth is moving away from the Sun at a rate of 15cm per year. It wouldn't be just a matter of adjusting for the expansion of the Universe. Stargates would need some pretty broad parameters for getting a lock....The margin of error would have to include the maximum distance between 2 given planets at any point in there orbital path.

  • The trick is that the stargates only have to get their general vicinity correct, probably to an accuracy of around 8 light hours, and once they connect they take care of the rest of the calculations. This is made more obvious in episodes that discuss multiple stargates in close proximity. For example, the three (!) that exist on Earth, or stargates that connect to ships instead of ground-based stargates. – Ernie Jul 8 '15 at 23:25

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