Stargate SG-1/WMG

The movie Stargate occurred in an Alternate Universe in relation to the SG-1 universe.
Well, it just makes a sort of sense. The alternate Samantha Carter says in "There But For the Grace of God" that alternate universes differ in their degrees of likeness to each other. It's not inconceivable that there's an alternate universe in which everyone looked different, O'Neill had only one L in his name, and Sha're was called Sha'uri.
 * And Lucius Lavin somehow ended up being an Earthling scientist. See here.

Daniel Jackson is a Timelord.
It's the reason he has come back from death so many times.

Glasses in Stargate are the opposite of goatees in Star Trek.
Daniel's incident with the sarcophagus that chewed up his soul, or whatever, progressively corrected his vision. If his vision was considered normal for him (so the sarcophagi didn't bother "fixing" it), his vision should have stayed bad every time he used the sarcophagus. But when he went all Dark Daniel from abusing the healing powers, he didn't need his glasses. Their loss must have been a visual representation of his soullessness, or whatever, just like Mirror Spock's goatee and the beards in the Middleman alt-world special.
 * Later, Daniel gets given a vision of what would happen if he had the knowledge of the Goa'uld. Among other things, he loses his glasses. Coincidence? I think not...

O'Neill is a Troper
Think about it.

The SG 1 team ran out of helmets that fit them
In early episodes they have helmets but later on budget cuts mean that they can't afford helmets for everybody. So the old helmets got used up and the remaining can't fit SG 1.

Naqida is an element in the island of stability.
It's a superheavy element with a very long half-life, but it is extremely unstable to explosions- the slightest explosion will make it go supercritical and cause a nuclear explosion. These are properties we would anticipate for elements in the island of stability (which has not, as of yet, been observed).
 * Then the Naquadah that stargates are made of must be very resilient/refined, considering how often very explosive firefights are fought near a chappa'ai. Otherwise, every stargate could be a potential ground-zero for an Earthshattering Kaboom.

The ship encountered in Grace belongs to the guys from Foothold, AKA the Stragoth.

 * To paraphrase Rodney: otherwise they've discovered yet another technologically advanced species capable of posing a threat to earth. It would also explain why they fire on the Prometheus right away.
 * The Stragoth by the way are named as such in the SG-1 roleplaying game.

The planet of the feral Goa'uld is not the Goa'uld homeworld. Or it is, but it isn't, really.
Thousands of years ago, an "older, wiser" species stumbled across a planet inhabited by a large, sentient, bipedal, reptilian species that was infested by a horrible brain-eating parasite. Being merciful and kind, they removed some of the unfortunate creatures from their homeworld to an experimental station on an uninhabited planet. However, they discovered that the two species had a symbiotic relationship. Without the weird worm-like creatures, the reptilians were reduced to animal intelligence and near-total amnesia. They also became sterile. The symbiote, meanwhile, slowly lost its intelligence and wasted away. Still creeped out by the idea of two species being linked that way, the scientists working on the project tried to make it possible for them to live separately. The result: the first Unas--intelligent, but forced to rediscover everything from firebuilding on up--and the first Goa'uld--ironically, true parasites, no longer dependent on their hosts for a brain boost and able to take control in a way that their ancestors could not. The scientists gave up and left and some of the feral Goa'uld later managed to kidnap Unas hosts and escape. The actual homeworld of the original, unmodified species is still out there somewhere.

Tealc lost his staff and had to grow his hair after he lost a bet.
He did have experience playing poker.

General Hammond is Jewish.
In "The Serpent's Lair" he uses the Yiddish expression "From your mouth to God's ears."

Stargate personnel use armor-piercing bullets.
When Apophis attacks Cheyenne Mountain in "Children of the Gods", Jaffa armor proves mostly bulletproof, with only one killed by a lucky shot. But later in the episode, and in all subsequent episodes, Tau'ri bullets do quite well. What happened was that they used Cheyenne Mountain's supply of armor-piercing bullets for the mission to Chulak, and all subsequent requisition orders have included plenty of armor-piercing bullets.
 * Confirmed in "The Tomb" - O'Neill mentions that the P-90s are loaded with armor-piercing bullets.
 * The standard round is armor-piercing. Part of the design objective for the P90 was countering the increasing use of body armour by modern armies.
 * The SGC is probably the largest consumer of armor-piercing bullets in the world by now.

The entire series is Teal'c's dream. The only real part is the "normal world" in "The Changeling".
Come on, somebody had to propose it. (It's the basis for one fanfic community as well.)

Some of the things Teal'c and O'Neill did when stuck in the loop in "Window of Opportunity"

 * Set the auto-destruct to go off
 * Take out Teal'c's symbiote
 * Teal'c went into a dangerous, deadly Kel'no'reem to talk to his symbiote
 * Tell everybody else to take the loop off, too
 * Watch every single episode of The Simpsons that had aired by that point.
 * Finally get Jack to watch Star Wars.

Merlin's tablet was encrypted with his public key

 * What, you think Ancients are going to go for a substitution cipher?

The alliance of four great races were of races that inspired one another
Yet another alternative to the above theory. The cycle starts with the furlings, who are an ancient and powerful race. When they felt their end coming and retreated far away (possibly integrating with background radiation from the big bang, just to integrate SGU) they passed on their knowledge to the race they saw most worthy, the nox. The Nox, inspired by the furling ideas, develop even further, integrating various ideas into their society. But when the Nox felt that they had grown stagnant and complacent, they gave their legacy to a race that had recently fled to their galaxy; the Ancients. What happened to the ancients is pretty well known to all by now, and they passed their knowledge down to a race that had just created their first hyperdrive, yet were already capable of reaching another galaxy; the asgard. The asgard, inspired by their predeccesors, protected the children of the ancients, the tau'ri, and built the Heliopolis complex so that none of the four great races would be lost to history. And when their history was over, they passed on all their knowledge once again.
 * Furlings being the aliens Destiny is looking for would be a Crowning Chekhov's Gun Of Funny.

Laura Cadman is gay.
When Laura Cadman's mind is stuck inside Rodney McKay's brain, she insists he turn up to a dinner date, keeps giving him advice on romance, and eventually takes over his body and passionately kisses his date. That seems to suggest that she's attracted to his date herself. Her pursuit of Carson is done purely to annoy McKay -- Carson's later relationship with her doesn't go beyond a couple of dinner dates. Even McKay seems to recognize this. He irritably says that he doesn't need her to be his "Cyrano". The Cyrano from the play was in love with Roxanne himself.

In "It's Good to be King", Garan (the woman who supports Maybourne by listing all the good things he's done) is actually the Ancient who built the Prophecy Wall.
Well, the Ancient had to be there somewhere, right?
 * No, because the Ancient who built it was Janus, who created the time-traveling Puddle Jumper and was the only Ancient who ever used it.

They use the guoald hand healing device off screen to heal away all their injuries
Lets face it their medical insurance would probably bankrupt the programme anyways and they do manage to heal away some injuries which should leave some scarring. Aside form Col O'Niell's scar on his eyebrow probably because he wanted to out do Quatrich.

The Stargate Program is the worst-kept secret in the armed forces.
Maybe they're keeping the information quiet from civilians, but there is no way they can be keeping something of this magnitude quiet anymore. Everyone has undoubtedly heard the rumors.
 * Over the decade-plus or so that the program has been in existence, thousands, if not tens of thousands, of personnel have to have been assigned either directly or in support, and all of them have civilian relatives and friends; several of them had to have talked, even if they swore their loved ones/friends to silence. There's simply no way that something this big can be kept secret indefinitely with so many people that have to be involved, especially now that the world's other major powers are involved in helping to oversee the program, have sent personnel of their own to liaise with the SGC, etc. It's really only a matter of time before the civilian population at large learns what's been happening.

The sticking point on the revelation of the Stargate Program isn't technology or science, it's religion.
All the upper echelons of every major established world religion have already been briefed. They're just still bickering a bit on how to explain things to the faithful.

By all accounts, the Ancients seem to massively outpace the Asgard and possible the Nox? But how true is that?

 * I mean, let's take a look at what we see from Ye Old Gooden Times. We see in "The Lost Tribe" that the Asgard are capable of intergalactic travel even ten thousand years ago, hence the fact that they able to even get into the Pegasus Galaxy. Given that modern Wraith or Goa'uld (or other one note alien races) aren't even capable of that already makes them pretty damn notable. Now, the Ancients were no doubt the most advanced, but they hardly had the Asgard outpaced. And frankly, the Asgard had no reason to try and compete. After all, they had no enemies! The Ancients had to develop all kinds of weapons and technology to fight off the Wraith. But the Asgard (or the Vanir counterparts) stuck around in the Pegasus Galaxy waiting for the Ancients to win. And frankly they're not a warlike race to begin with, otherwise they would have helped eliminate the Wraith or more seriously dealt with the Goa'uld long before the replicators became an issue. It's why they never had combustion-based weapons like Earth. Why? Because war is not the Asgard way. Consequently, in the ten thousand ensuing years, the Asgard focused all their research on improving themselves by conquering old age and diseases - something the Ancients never did. They only got caught up in the downside of cloning that ultimately destroyed them. The only reason the Asgard started becoming warlike was because the Replicators were an unstoppable force that couldn't be reasoned with or outmatched in technology. So because of their own cloning issues, the Asgard never had to worry about improving their military technology because up until the replicators showed up, their technology was vastly superior to anything in the Milky Way galaxy. Given they lack our warlike tendencies, why would they spend ten thousand years constantly improving their military might when their technology was already more than enough? They had no desire to fight the Wraith or Goa'uld or any other lingering enemies. They just needed to have ships sufficiently advanced that they could go around doing whatever they want unchecked.
 * On the flip side, you have the Nox. We don't get to see much, but they seem sufficiently advanced in modern times. This is despite the fact they're living in trees and huts. Rather than keep advancing their technology, they decided to embrace nature. All of their special tricks they are able to perform are fairly consistent with what near-ascension humans are shown to do, just with a different skillset since they are of a different species. They probably just chose not to ascend because they were more interested in exploring the simplicity of existence and not moving forward. It's likely that their technology remained unchanged for the ten thousand years since the Great Alliance.
 * As for the Furlings... given both the Asgard and Ancients were intergalactic travelers back in those times (and the Nox probably were too), they probably are off in some other galaxy. After all, the Asgard hail from the Ida Galaxy, the Ancients from the Ori Galaxy, and only the Nox seem to come from our galaxy. It's pretty likely the the Furlings are from some other galaxy too. (I'm kind of partial to the theory that they're the aliens from Stargate Universe).

Daniel never actually decended
According to a somewhat crackish theory that this troper read he ascended that first time and never actually came back. He just raised a homunculus with his non-ascended memories to act as his pawn in the material universe via some sort of ascended loophole. Each time one homunculus gets itself killed, he manufactures another one.

The point of origin symbol is the equivalent of the Enter key.
Since the POO symbol is always the last one in a sequence, and since it stays the same for every address dialed, its only meaning can be to signal that the address is complete -- thus allowing the dialing program to distinguish between situations where seven, eight, or all nine chevrons are used.

Explaining why it's different for every Stargate is trickier. In Stargate the movie, the Earth and Abydos Stargates had completely different symbol sets -- an aspect that SG-1 quietly retconned away. Since all Stargates are now identical except for the POO symbol, the idea is probably to tell Stargates apart even if they are moved between planets.

"Ancient 1: So, where are you going this year?
 * Alternatively, the POO symbol could have been used as a shorthand by the ancients for talking about their destination.

Ancient 2: I was thinking of going to Circle over Pyramid.

Ancient 1: Nice."


 * Actually, they would've probably referred to the planets by their seven-to-nine-syllable Ancient name as derived from the planet's gate address. ("Lost City, Part 2")
 * The syllable for the Earth's POO in Ancient is "At".
 * Since "Lost City" showed that the symbols are assigned corresponding syllables, this alternative is probably confirmed. Earth is 'At', by the way. Whole addresses form phrases that are used as planet names ('Prok-la-rush Tay-o-nas' for the only in-universe example), but these may be more "formal" or official names than that represented by the POO.
 * Couldn't it just as likely be a serial number, the ancients equivalent of going to planet 831547?
 * In the Pegasus galaxy, the POO and enter keys seem to be the same, suggesting that the use of two separate keys for POO and enter became obsolete some time between the creation of the stargate system in the Milky Way and that in Pegasus. Perhaps related to the obsolescence of manual dial?
 * Would make sense as far as dialing out of the galaxy goes. If you didn't have an 'enter' command, you'd connect as soon as you had seven, wouldn't you?
 * (This idea was copied from the SGU WMG) Alternatively, the origin symbol is actually an "orientation" symbol, added to keep version 1.0 gates (such as those used by Destiny) upright when they connect. Since they spin their entire ring, they would have to have some mechanism keeping the cargo from coming through upside-down. The answer is the final symbol, which isn't actually part of the address, but sets the gate's orientation to a known value. Version 2.0 gates (such as those used in the Milky Way) didn't really need it, but by that point, people were so used to dialing an orientation symbol every time that the designers kept it around.
 * It would actually make a lot more sense if the Point of Origin is actually the starting point of the dialing process. It doesn't mean a "point of origin" in the sense of where you start your travel, but rather, it's the start and end point of the dialing process. The gate only dials when it has been returned to its Point of Origin. As such, the symbol used is entirely up to the creator of that specific stargate. The Milky Way stargates were one of the earlier versions, and were made to order - as such, each one had a symbol, possibly indicating who created that stargate. The newer Pegasus stargates were mass-created for quicker distribution to replace the older units, while the ones being placed by the ships that went before Destiny had to be standardised and produced automatically. So really, the unique symbol used on some Milky Way stargates might be considered to be a maker's mark.

DHDs were invented between the colonization of the Milky Way galaxy and the colonization of the Pegasus galaxy. Before, only manual dial was used.
This is based solely on the fact that Pegasus Stargates don't have moving parts, not allowing manual dial at all, unlike Milky Way Stargates. Presumably, once the Ancients invented DHDs and installed them everywhere in the Milky Way, they declared manual dial obsolete; its possibility was only retained for already existing Stargates.
 * Alternatively, DHDs have existed as long as Stargates; what happened between the colonization of the Milky Way and Pegasus was that some mechanical problem with DHDs was solved, rendering manual dial unnecessary as an emergency backup procedure.
 * Note how often we encountered "broken" DHDs in SG-1 compared to Atlantis.

The Milky Way, Othalla, and Ori home galaxies' Stargates have three junk symbols.
Consider: Both the 'newer'/more advanced Pegasus Galaxy Stargates have 36 glyph spaces. The new 'proto-Stargate' seen on the Gateship Destiny and in some episode previews on distant planets also have 36 glyphs. The Milky Way, Ida Othalla, and Ori/Ancient/Alteran home galaxies' Stargates each have 39 glyphs. Therefore, three of those 38 glyphs + one point of origin glyph are 'useless' glyphs which are either never used, or specific eighth-chevron/ninth-chevron glyphs. Or possibly maintenance/'dry-dial' glyphs.
 * Alternatively, since we know at least as far as The Milky Way goes, the stargates are older. At that point in time the ancients thought there would be far more Gates and those extra symbols would be needed, (IE, I Pv 6 versus I Pv 4). At some point when the new gates were rolled out, the Ancients realized they'd never possibly need that many gates and cut down on the symbols.

The SGC uses the dialing computer instead of a DHD intentionally.
They could get a DHD if they really wanted one. The dialing computer is far more secure.
 * They can lock out dangerous addresses (black holes, for instance) so nobody can dial them, intentionally or otherwise.
 * They can employ user IDs, passwords (changed at need), palmprints and so forth to prevent unauthorized access even if someone gets to sub-level 26 undetected.
 * It can ignore a lot of nitpicky dialing protocols (admittedly, not always a feature, sometimes a bug).
 * It's only real drawback is that it's slower than a DHD, as they've learned to their cost on more than one occasion.
 * I'm pretty sure this one is confirmed in the show -- they say that they keep the dialing computer for security reasons.

Stargate addresses map to real coordinates differently from Daniel's explanation in Stargate.
First, having three lines intersecting in 3D space is redundant: if a set of fixed points is enough to cover all addresses, then addresses only need to have four components, not six, to get two intersecting lines.

Second, Daniel's model would imply that addresses allow a number of permutations: for example, 2-1-3-4-6-5, 4-3-2-1-5-6, or even backwards, as the three intersecting lines would stay the same. However, in Stargate SG-1, it's implied that addresses are unique and strictly order-dependent.

Third, constellations are not fixed points in space: they're areas of the imaginary sky sphere created by projecting stars of varying distance from Earth onto a single sphere.

Fourth, there are addresses differing in only one symbol. In Daniel's model, it would result (at best) in two intersecting lines and one line not passing through their intersection point.

What do the addresses mean, then? Well, in 3D space, you need at least three coordinates, although the coordinate system itself can vary (Cartesian, cylindrical, spherical, etc.) It's possible that the "constellations" do not correspond to real constellations (as Daniel assumed) and instead only serve as digits in base 38, and the mapping between "constellations" and digits was arbitrarily chosen. They translate into some coordinate system, and each of the three coordinates uses two "constellation" digits (and thus each coordinate has 1444 possible values -- presumably, in some coordinate system, this gives sufficient resolution to address the entire galaxy).

What about the SGC address correction program, then? Well, presumably, Samantha came up with her own (correct) explanation of the addresses, independently, and probably never learned about Daniel's erroneous guess because she wasn't present when he explained it.
 * In one episode, Sam explains that once in a while, each Stargate autodials each other one to update their coordinates. This evidence supports the above theory.
 * This theory also explains why dialing the Asgard galaxy requires eight symbols rather than the usual seven.
 * They live in a different area code?
 * That is literally the in-universe explanation.
 * The address correction program, we may assume, is necessary only because the SGC does not use a proper DHD and therefore does not receive updates.
 * To the third point, the Abydos Stargate in the movie has unique symbols which would correlate to its own constellations. It can be guessed that the symbols only correlate to a general area, and that the Stargates never get close enough together to overlap.
 * In the movie, Abydos was in a different galaxy "at the other side of the known universe". SG-1 retconned quite a few things; all the other Milky Way Stargates have the same glyph sets, so it's logical to assume that so does the Abydos Stargate.
 * The Abydos DHD may be damaged (it does not appear that Ra kept it in regular use in the movie, perhaps having one on his ship instead), explaining its unusual symbols and its only being able to dial Earth. (The on-screen explanation implies that address correction had to be done manually and that they could only dial Earth because only Earth's address was still current; but this does not mesh with much of anything else we know about the working of the Stargate).
 * Apophis uses the Abydos DHD to dial Chulak. It is an outrageous plot device: he had the hand-dialer, which he previously used to dial the SGC's Stargate, and the only purpose was to allow Ferretti to learn Chulak's address by looking at the highlighted keys. What ever happened to the glyph order being significant? As for the movie, no DHDs were shown in it; for all we know, they may not even exist in the movie-only continuity.
 * Even if the glyph order is significant, the SGC's dialing computer is more than capable of spam-dialing all 720 possible combinations of the glyphs until it found one that works. t SGC already knew which six symbols they needed, but didn't know the order for them (Ferretti saw the proper symbols glowing on the hand-dialer, but didn't see them actually entered). Six symbols chosen 6 at a time give 720 permutation.
 * Here is a screenshot of an Ancient's notebook from Ark of Truth. As you can see, there's a drawing like the one Daniel used in the movie to describe the coordinate system.
 * It was just a sketch, not a blueprint or a formal technical paper. Perhaps the original concept for the system was exactly like Daniel suggested. But when the system was being built, they hit the same issues that were mentioned here and decided to scrap the constellations idea, reverting to an address system more like a phone-number. Keeping the constellation symbols on the DH Ds would make sense, seeing as every race that used the system would have their own language. As was shown in an earlier episode, The Four Races used a joint language based on the table of elements for communication. Using constellations isn't a far reach...
 * Except that constellations are Earth-specific, so for anyone not from Earth they would simply be arbitrary pictograms.
 * This disposes nicely of the Fridge Logic behind eight-chevron addresses - a number in base 38 corresponding to an alternate galaxy makes a lot more sense than a random constellation does.
 * It is possible that Daniel's explanation is simply inadequate due to his lack of in-depth mathematical knowledge. Assuming that each symbol represents an unique point in the galaxy, it is possible that a more accurate description of its mechanism for determining an unique point within the galaxy involves using a formula that uses planes created according to some rule - the intersection of three distinct, non-parallel planes (whose normals aren't coplanar) will identify a single location in space. Perhaps the order is part of the process used to define the orientations of the planes.

Having a symbiote in you increases your inteligence
Okay we know that knowledge gets blended over but when faced with new situations like the sg team face it requires much more intuitive thinking. Vala was able to learn how to operate the prometheus despite bing just a common thief. Major Carter often complained about how we couldn't operate or understand alien technology but after having jolinar, new technologies happen to be as challenging as a newspaper soduku.

The Furlings are the Goa'uld or the Goa'uld's predecessors.
Who are the most advanced aliens who aren't in the four great races? That's right, the Goa'uld. Genetic memory can't occur naturally; it just doesn't work that way. The Furlings ascended, leaving behind their petty descendants who were more interested in conquering; this, using their genetic memory technology, evolved into a species-wide god complex.
 * So there are three tiers of Goa'uld, then? The Furlings, the galaxy-wide Goa'uld we know well, and the wild Goa'uld on P 3 X-888 with no blood naquadah?
 * Genetic memory could evolve naturally (starting with offspring inheriting fundamental instincts, then more complex memories) and would present a significant advantage in selection (offspring matures faster, knowledge is retained better, etc).

Alternatively, the Furlings did not ascend, but were wiped out by the Goa'uld. Either way, the Goa'uld fractured time and again due to their developing god complex and lost most of their technology.
 * In a universe with Psychic Powers, Time Travel and non-corporeal beings, how can you say "it doesn't work that way"? Their way is clearly not our way. Memory and mind in the Stargate Verse can transcend the physical.
 * Actually, genetic memory DOES exist in our world...the Goa'uld've simply fount a way to break it and make it ridiculous.

Anise/Freya was a Goa'uld, and she alone was responsible for the supposed za'tark problem
Anise/Freya created the supposed za'tark detector as a means to create za'tarks. The first thing she did on Earth was to make Astor kill herself to create paranoia. She then made sure that Carter and O'Neill came out positive so that they would be locked up and unable to stop the real za'tark,, from assassinating the President.

The za'tark "detector" only works if it can find a memory gap to exploit, possibly taking advantage of the mind's possibly vulnerable state as it tries to fill in missing blanks from a given situation. (Nobody's memory is perfect, especially in a stressful situation.) Daniel and Teal'c had been lucky.

When Anise/Freya retested O'Neill and Carter, she didn't expect that they could fill in the blanks. She didn't 'trigger' them because she wanted O'Neill's DNA to start her own Goa'uld (hence, her trying to seduce him), and she likely knew that O'Neill would certainly not be in the 'mood' if anything happened to Sam.

The "nikta" is not the ass, but a part of the Goa'uld anatomy
Wouldn't be out of place.
 * Goa'uld take humans (or human-decendants) as hosts. Why would they make a comment like that based on their symbiont bodies rather than their hosts'? Also, a Goa'uld didn't say that line, Aris Boch, a human, did. ("Deadman Switch")

System Lord Ba'al = Baal, Lord of Terror
Consider. Overlord Baal is capable of body surfing every time his current body is destroyed and can even hijack multiple bodies at once! Therefore, somewhere along the lines, one of the Ba'al clones went through a Stargate that had Phlebotinum liberally applied to it and ended up in one of the Netherworlds. Through the same explanation that gave us Overlord Prier{e}, Lord of Terror Baal was born.

System Lord Ba'al = Baal, Lord of Destruction
The Soulstone and Goa'uld itself are related.
 * Alternatively the Soul Stones ARE the Goa'Uld, and Diablo is simply a heavily fictionalized myth version of an actual alliance in ancient time between Sokar, Baal, and a now-dead Goa'uld named Mephisto.

Hades is/was a Tok'ra (or at least allied)
Kronos and Ares existence indicate the Greek pantheon were Goa'uld. Hades was pretty much the only guy there who didn't make a hobby of being a dick to mortals.
 * What about Athena? If I recall correctly she was one of the nicer gods. Certainly up there with Hades, anyway. She's not particularly nice on the show though, what with running the trust for Ba'al and all.
 * Hades kidnapped and married Persephone against her will, causing her mother Demeter to be so disheartened that it caused winter. He was also allies with/brother of Zeus and Poseidon, not two of the nicest fellows when it comes to humanity. Also, he specialized in Cold-Blooded Torture against people who dared offend the gods (as well as those who actually did something wrong). And allowing somebody his wife to come back from the dead as long as he doesn't look at her to see if she's following him, and then making her footsteps inaudible? Dick move. Still less bad than the Asgard Loki, who raped a horse in mythology.

The Tok'ra exist as the result of covert manipulation by the Ancients.
Egeria, the queen who founded the Tok'ra, is also the only Goa'uld we've seen to take on a role from a specifically Roman myth. The Ancients are explicitly associated with Rome (both in language and in their role as "road-builders"). Obviously when they communicated with Rome, they discovered Egeria attempting to set up a power base in Italy, convinced her of the immorality of the Goa'uld methods, and got her to go into hiding to try to stop them.

(Incidentally, this is also the Stargate 'verse's explanation for why Roman mythology is mostly cribbed from Greek mythology--the Ancients stopped any Goa'uld from gaining any foothold in the Italian peninsula, but they weren't willing to go so far as to prevent its inhabitants from worshipping the next nearest "gods".)

Ba'al has a symbiotic relationship with his host, much as the Tok'ra do.
This is why he's so much less of a Large Ham Card-Carrying Villain than your standard Goa'uld--their personalities have blended considerably over the 2000 years they've been together. (It also means that Vala is about to get a big shock at the end of Stargate: Continuum--she's expecting to help support someone who like her was a passive observer of Goa'uld tyranny, when in reality she's going to end up having to deal with a man who was entirely complicit in it.)
 * Ba'al's host may in fact be the genius of the operation, which is why Ba'al never tried swapping hosts, and why he went to the trouble of cloning his host as well as himself.

Ba'al's host is his own Harcesis.
We already know that a Goa'uld queen can choose what they pass on to their spawn, so logically they could do the same with normal kids, since they also get the Goa'uld genetic memory. We know Apophis tried to pull it off, and given how terrible unoriginal he was, there's no way he thought of it on his own. He had to get the idea somewhere, and given how innovative Ba'al is, he probably thought of it first and, some time ago, pulled it off, probably with Anat if you go by the RPG's books. This is why he's so much better at everything than the other Goa'uld: there are effectively two of him in each body. It also gives a good excuse to reuse him post-continuum. So what if the Symbiote is gone, Ba'al's still there.

Before his exile, Anubis was in the entertainment industry.
He wrote teleball dramas, mostly made for Goa'uld audiences. He was exiled after writing one too many cliffhanger season finales.
 * Talk about getting Screwed by the Network
 * now I finally understand what "crimes unspeakable even to the Goa'uld" means
 * His ultimate plot was not to conquer the galaxy but to continue his reign of cliffhanger finales. He succeeded in season 6 but barely failed in seasons 5,7, and 8, after which he was put on a bus to ensure that he never did it again, only to sneak past Oma to trick the Ori into doing it for season 9. The series was canceled after season 10 to insure he couldn't repeat that.

Most SGC personnel are at least minimally-proficient in Goa'uld
Jackson had to provide the translation early on, but over the years, most SGC personnel picked up the language, and eventually it became part of the training program. It explains why no one seems to have any trouble communicating with displaced human populations throughout the galaxy (even if Goa'uld isn't their native tongue, it's probably a lingua franca of sorts.) By now, Jackson has proven himself indispensable in far more ways than just as a walking Universal Translator, so of course they keep him around.

The Goa'uld are capable of sexual reproduction
The powerful males seem to keep Queens as "mates" and Heru'ur has two Goa'uld parents apparently. It also seems very odd for the "drones" to be the ones who hold more political power than the average Queen. Instead the Goa'uld are quite capable of sexual reproduction but they prefer to use parthenogenesis to reproduce instead for whatever reason, perhaps they can't incorporate the host species' DNA to ensure host compatibility unless it's done asexually

Ba'al's clones have no consciousness in the hosts

 * Ba'al copied the cloning technology from a group of humans who had previously cloned an Asgard. That Asgard had no consciousness, because nothing had ever been added to it. These same humans never received that technology to fix that. Later Ba'al uses that same technology, but he never needs to be able to copy the consciousness. Why? Goa'uld have their own built genetic memory, so any clone Ba'al makes of himself already is him. He copied his hosts too, but since there's absolutely no reason for it to contain the memories of his past hosts, why bother inventing the technology to copy a human consciousness to a clone? There isn't!
 * Of course, this means that the Ba'al getting extracted at the end of Continuum is completely pointless. They're going to end up with a vegetable Ba'al clone that has no mind of his own. Or if he does have a mind of his own, it's just a human copy of the symbiote.
 * Except that a Goa'uld gains the memories of its host. Which means that even if the clones Ba'al's host were blank slates, they'd still end up with the original host's memories on a secondhand basis. Of course, if Ba'al is like most Goa'uld and keeps the same host for as long as possible, that would mean that the host has thousands of years of Ba'al's memories to sort through. Thus, quite a bit more to deal with than Vala's brief time as Qetesh's host. Even with the memories of the host intact, he might still think of himself as being Ba'al.

Jaffa helmets have built-in Universal Translators. That is why everyone seems to speak in English.
In the first seasons SG-1 used the translators that were salvaged from dead Jaffa, and later they managed to reverse engineer the technology.
 * Make sense if you think about the first episode. They go to Abydos, where everyone speak the heavy accented English Daniel taught them. Then they go to Chulak where nobody speaks in English except for the Goa'uld and the jaffa. in later episodes the language problem disappear and everybody seems to speak perfect English except for the people of Abydos who still have the same accent because unlike anybody else the team meet, they actually speak in English.

The sodan eat their goauld symbiotes after they mature.
Well why not, a warrior's gotta eat. And if the system lords do it, why not their slaves?

Trenonin allows Jaffa to live far longer and slows down aging
Take Teal'c for example who should now be older than Bratac but all he got was a patch of white.
 * This helps explain
 * That would nicely handle the potential plot hole, anyway.
 * Tretonin gives him the same life span he would have had if he still had his goa'uld.
 * It can't possibly. In "Maternal Instinct" Bra'tac is in his mid-130s. He says in that episode that he's within a couple years of his symbiote outgrowing him, but that he's too old to take another symbiote. That puts the Goa'ulded Jaffa lifespan somewhere below 140.

Jenny from "1969" is Jenny from Stargate
The young female hippie from the episode "1969" and the Chevron Gal in Stargate are the same person. Both are named "Jenny" (the latter according to the credits), their appearance is similar (aside from hair color), and the Stargate Jenny is just about the right number of years older.

You see, after SG-1 escaped through the Stargate back to 1999, the military searched the area, found the hippies, questioned them about SG-1, and then sent Michael to Vietnam, where he died. The Stargate Program was then started to investigate what happened (creating a Stable Time Loop), and Jenny somehow became involved, possibly since the military didn't want to bring any more civilians into the fold.

Jenny eventually ended up being the Chevron Gal at the time of the first Abydos mission. She was fired after the project got mothballed and was not brought back when the program was restarted; hence the reason there are civilian technicians in the film and military technicians in the series.
 * Time travel in Stargate doesn't seem to work that way. "2010/2001", "Moebius", etc. clearly show that it works under the "mutable history" model. "1969" can be interpreted under the mutable model as well. See this. However, the only aspect that needs to be changed due to this is the reason for the Stargate Program's creation. After all, a mutated mutable timeline can resemble a Stable Time Loop if the past isn't changed much.
 * Time Travel in the Stargate Universe seems to work both ways; 1969 requires a Stable Time Loop. Perhaps you can trigger one if you work hard enough.
 * The time loop in "1969" is stable because the resolution of the loop does not prevent the creation of the loop. They don't tell past-Hammond not to let them go on the current mission. Even if time is mutable, since nothing critical to the loop changes when the loop is formed, it never goes away.

Cam Mitchell didn't exist until the end of season eight
Season eight ends on time travel, and it's implied that SG-1 managed to change a little more than they thought they did during that particular adventure. (Jack's fish, for example.) Mitchell had never been so much as alluded to before the premiere of season nine, despite apparently having been involved in events before that. Obviously, seasons 1-8 were one timeline, in which Mitchell was never born. After season eight, the timeline we'd been watching stopped existing, we caught a glimpse into another timeline where the Stargate program was never created at all, and then switched permanently over to a timeline where there were fish in Jack's pond and Cam Mitchell existed.
 * Since when has it been though otherwise?

The alternate universe from "The Road Not Taken" is one of the ones Daniel finds in the Quantum Mirror in "Point of View".
In "Point of View", while they're in Kowalski's universe, Daniel has to scan through a bunch of other alternate universes to find the one they came from. There's a near miss that looks almost exactly like the right universe, except that Carter is a captain rather than a major. Seven years later, in "The Road Not Taken", Carter finds herself in a universe that again looks superficially similar to hers (though the longer she stays the more different it looks), except that she's a major instead of a lieutenant colonel.

The ancients got their knowledge from an even older race
Like the Precursors in halo

The ancients are actually humans gone back in time
Well even the ancients have to come from somewhere. The ori are probable anti-evolutionist anyway.
 * So where did these humans come from originally? And how is it that nothing the "time-traveling Ancients" do screws with their future Ascension in the first place (see "The Grandfather Paradox")

Macgyver is an ancient
He could build anything out of anything after all.

The ori are the pah-wraith and the ascended are the wormhole aliens
Wormholes exist in other realities so the ones from star trek and stargate are one and the same.

The Ori spread the use of English
It would be timewasting to estabilish a common dialogue so the ori secretly sent a means of teching english.
 * It seems their "teching" did not reach everyone.

Near-Ascended Beings Can't Directly Kill People
There is something about the super-advanced human brain that prevents you from going around killing people. Telekinesis would make killing people easy, just choke them or break their necks or even just damage the heart or brain. But the only times I have seen near ascended beings kill people with telekinesis is indirectly. For example, pulling them onto a 50,000 volt metal plate or throwing them long distances. Even Kalek, homicidal maniac that he was didn't kill any of the SGC soldiers he was fighting by choking them, throwing their bullets back at them or just crushing them against a wall. Adria never killed anyone either (directly). The only times a direct kill has been done is but one of Nirrti's experiments (and he wasn't really near ascended) or by a Prior, who the Ori probably reprogramed to allow that, since he wasn't close to ascension anyway.
 * Did you miss the part in "Counterstrike" where Adria choked a Jaffa to death with telekineses, brought him back to life, and then snapped his neck, again using telekineses? I'm pretty sure that counts as "killing people".

It was the post ascension ancients that were part of the alliance of four great races
Mostly a way to reconcile all the weird stuff going on with the timeline. The timeline for the ancients would basically go like this: 1) Ancients flee from Ori galaxy 2) Ancients seed humanity 3) Ancients flee to Pegasus 4) Ancients build up a civilization/the Asgard quickly develop new technology/the nox something something/ the furlings something something 5) Ancients get their collective asses kicked by the wraith/The asgard travel to the milky way/the nox something something/ the furlings something something 6) The post-ascension ancients ally themselves with these dudes to discuss philosophy all day. 7) After a profound argument by Nox philosopher Telan, the ancients realize that, from a universal standpoint, a policy of non-interference would be the most logical according to their core beliefs. 8) Ancients and Nox stop talking to everyone and the alliance members don't really have any reason to contact one another anymore.

Alternate 4,5 and 6 from the previous theory
4) Ancients build up a civilization 5) Ancients get their collective asses kicked by the wraith 6) The ascended ancients artificially enhance the three races as to leave behind a legacy, teaching them stuff like the universal alphabet. This version possibly includes the four races never really meeting very often, with heliopolis being built by the furlings as a museum, rather than a meeting place.

The remaining three of the four great races (Furling, Asgard, Nox), realized that ascending doesn't solve any problems.
They realized that ascending is really a bit of a wash after seeing it didn't really improve on the quality of life.
 * Who's to say the Nox haven't ascended? They're able to hide cities, resurrect their dead, etc. Perhaps the form that is manifested in the series is what we see in our reality, even though they're already ascended?

The Ori have non-believers killed because otherwise they could used to weaken their power.
When people worship the Ori in the matter as set by the rules of Origin, the worshipers somehow create a "positive energy" which increases the Ori's power.

The reason the Ori have zero tolerance for non-believers is that, if enough non-believers were ever to get organised and work as one, then they could focus their anti-Ori beliefs to create a "negative energy" which would weaken the Ori enough that they could be defeated or even killed by mere mortals.

This is why they destroy worlds that do not bow to the Ori. They want to prevent that possibility of non-believers working together from ever happening.

The Ancients are actually human
Via time travel, future humans arrive to the Ori galaxy several hundred million years ago. After a while they forgot their origins. The Ancients arriving to the Milky Way (and Earth, specifically) witnessed the evolution of humans, and being the haughty bunch they are, they assumed that the universe revolves around them and they are their second evolution.

Repli!Carter survived
When her ship was hit by the energy weapon of Dakara, we see the ship disintegrate and we see both her and Daniel disappear in a flash of light. Daniel survived because Oma ascended him just before he would have died. However, Daniel had ascended before, and would presumably know quite a lot about the process as a result of being ascended and from studying the process independently. When Repli!Carter fought Daniel, they both gained each other's knowledge. Perhaps Repli!Carter figured out a way to ascend a split second before the weapon destroyed her ship.

The Ancients are Jedi and Elves
Star Wars occurred 'a long time ago in a galaxy far, far away' and the 'advanced humans', aka Jedi, were part of an evolutionary process towards ascension. Eventually they came to earth as 'the oldest race' but when they got old they didn't die but 'went to the gray havens.' All three groups wear similar clothing and have a deep reverence for the natural world and try not to interfere with humanity as much as they can.

The Furling were/are dragons.

 * Because how epic would that be? Also, Asian legends usually paint dragons as wise, ancient creatures that while benevolent were totally capable of ruining your day if they felt it was necessary - doesn't that sound like a people each of the three Great Races already encountered would get along with?

The Furlings are the Aliens who crewed the ship in "Grace"
Personally, I'd just find it amusing to find out that the Furlings are a bunch of A**holes who cruise around the galaxy shooting at everything that moves.
 * No real evidence to back this one up beyond the fact that the unknown aliens from grace were considerably advanced (Sizable ship, teleport technology, advanced weapons, etc) and that they understood English (POSSIBLY indicating involvement with either a human group or the ancients/asgard, or just really, really good translators). The alien ship appeared to be comparable in some ways to Asgard tech (Asgard style teleports as opposed to rings, energy weapons that didn't appear to be similar to Goa'uld weapons or Ori Beam weapons) so it is not entirely inconcievable that the Furlings, as part of the alliance, shared aspects of technological development with the Asgard, or at least influenced eachother in that regard.

The Furling are humans from the far future.

 * Their many time-travel experiments nearly destroyed history as we know it, so they communicated with the other three Great Races from the future and guided them along to ensure history happened the way it did originally.

The Furlings were Replicators, before they became evil.
Bit of explaining to do, bear with me. Reese, the robot girl who created the Replicators, was created by a priest of the Furlings, who (much like the Goa'uld) pretended to be gods on many planets. She was able to create Replicators because she was programmed to do so by the priest, who got the coding directly from his gods. The Furlings, in the meantime, were suffering from errors that were passed down into all existing members of their species (similar to the Asgard terminal illness, perhaps) and needed new ways to reproduce indirectly, so that the new Furlings wouldn't have the same fatal errors they were having. The plan was going smoothly, Reese had the programming, but when she turned out to be child-like, acting on whims and emotions, they realized they had made a great mistake, as she passed down her emotional control to the new Furlings. In their attempt to wipe the slate and get rid of Reese, the turned her entire planet against her, only to have her and her Furling army win. Having failed, the Furlings left, refusing to acknowledge the new Furlings as members of their species as they themselves either died out or became as feral as the other Replicators due to their errors. And so the Replicators became a great galactic power as the Furlings disappeared entirely, forgotten by members of the Four Races to distance themselves from the new galactic scourge.

The Furlings are the "giant aliens" from Crystal Skull.
The ones with whom Daniel's grandfather was left at the end of the episode. They seem super-powerful, they have very advanced technology, they are shrouded in myth and awe... sounds like one of the Four Great Races to me.
 * Alternatively, they're failed Ancient experiments for ascension. They got trapped in their current limited form, but require a high level of radiation to stay intact/alive. The giant pyramid was designed as a place where they could live. We know the Ancients have the technology for shifting dimensions and building a sufficiently large structure. The crystal skull is a symbol for ascension, meaning clarity of mind or some other philosophical Ancient thing. Or maybe, ascension was a success, and the pyramid is what the hall of fire is to the Ori - the place where their energy bodies are located by default. They choose to manifest themselves as giant aliens rather than a raging inferno, and aren't active enough to warrant a priesthood. The skull itself is meant as a way to ask for an audience without having to invade one's body.
 * Expanded Universe materials call the smoke aliens Omeyocans. It seems the Furlings are doomed to be the series' ultimate Noodle Incident forever.

The Furlings did not call themselves that
The Ancients, Asgard, and Nox came up with that name, on the basis that the Furlings' own name for themselves was way too pretentious. I mean, seriously, "the Time Lords"?
 * *looks at her SG/DW crossover* That is now my personal canon. And it explains why you never see the Furlings- they all got time-locked on Gallifrey after the Last Great Time War, except the Doctor and the Master.
 * Picturing the Doctor as a giant teddy bear: Awesome.

The Asgard naming the ship from the Season 4 opener the "O'Neill" wasn't a compliment.
It may have been of the highest technology, but it was a finicky, troublesome prototype only designed to get the job done - possibly destroying itself in the process.
 * Finicky, troublesome, gets the job done, possibly self-destructive...

Asgard computer interfaces are the pinnacle of user-friendly.
In "Nemesis" O'Neill was able to operate an Asgard computer with no instructions, no real tech skills, or any knowledge of the Asgard language. There is only one explanation - over the millenia, the Asgard have made multiple breakthroughs in computer interface design, resulting in systems that are incredibly intuitive, efficient, and user-friendly.
 * Further evidence comes from the ability of Wraith to operate the Daedalus. The human engineers designing the Daedalus would have incorporated the superior Asgard interfaces into their own technology. Unfortunately, that means that just about anyone could operate the Daedalus - including the Wraith.

Over the course of the series, the amount of Asgard alive drops to the single digits. (warning, ending spoilers)
Almost all Asgard died out in the replicator wars. The only slightly densely populated area was the Asgard homeworld, which was conquered, and even that had only a few hundred or thousand running around. The amount of Asgard living on other planets ranked in the mere dozens. Remember they haven't been capable of sexual reproduction for the last 50 million years. Most of these were killed when the replicators escaped the black hole and started spreading again. Each Asgard ship is piloted by only one Asgard, but there are only a few ever shown. By the 10th season, most Asgard have become depressed by their cities being overwhelmingly empty and slowly decaying, most of their loved ones having died, and even having become obsolete in the defense of other people. They have become unnecessary, are unhappy, have no hope of ever rebuilding their civilization (they're infertile, and all the scientists who were researching improved cloning technology were slaughtered). In the last episode, the last two or three Asgard left alive decide to just quit. Their hopes have been shattered, their work undone, their friends and family brutally killed, their very species out-thought and outfought by any who chose to ally or attack them. It's not an Idiot Ball that caused them to blow themselves up, it's just the suicide following the depression from being the Cosmic Plaything subject to every Diabolus Ex Machina the writers could throw at them.
 * In one episode, O'Neill is summoned to the Asgard counsel chambers, which is cavernous and full of empty seats.

The reason the Asgard were in our galaxy in the first place was the study of the Gou'uld as a means of stopping their genetic problem
If they could transplant their consciousness into one it may have solved a lot of their issues. Unfortunately it didn't work and the Asgard just ended up in a picky relationship with a frustrating alien race.

The Star Wars galaxy was colonized by the Ancients, who go by the name "Whills" there.
This explains the apparently-independent evolution of humans in the Star Wars galaxy: the Ancients seeded humans and near-humans there before ascending, like they did with the Tau'ri. Powers attributed to "the Force" stem from residual Ancient genes (screw midichlorians); and Force ghosts are ascended beings. Qui-Gon, self-admittedly, received the knowledge of ascension from the Whills, who are already-ascended beings (ergo, the Ancients). Oh, and Stargates? They exist, albeit in more limited quantities and less compact form; presumably, that galaxy was colonized long before the Milky Way, before the technology was perfected.
 * Star Wars exists in the Stargate Verse as fiction, but it could fall under the Literary Agent Hypothesis. In early drafts of the SW screenplay, the story was framed as being told from the "Journal of the Whills". Perhaps this exists as a document in the Stargate Verse.
 * Alternatively, George Lucas is an alien, much like Martin Lloyd of Wormhole X-Treme.
 * Even more alternatively, Star Wars is a highly fictionalized version of a real war fought between different factions of Ancients in the Milky Way galaxy. It's referred to as being "A long time ago in a galaxy far, far away..." because it's being told to the modern inhabitants of Atlantis. It exists as fiction because someone told the story to Lucas on one of their unintentional time-traveling trips.

Sylar from Heroes is the Father of the Shadows, and Peter Petrelli is the Father of the Vorlons of ''Babylon 5, after they encounter Dr. Jackson and/or O'Neil
At some point, Sylar will kill and "examine" either Daniel Jackson's or Jack O'Neill's mind, gain the Ancient knowledge, and ascend. Sylar decides to force his evolutionary theory upon the rest of the universe by creating the Shadows and "kicking over the anthills" to force the races to evolve. Peter, who at some point walked past the Stargate character that Sylar didn't kill, also ascends and tries to stop Sylar by creating the Vorlons.

Lt. Mitchell and Vala are John Crichton and Aeryn Sun on a deep undercover mission.
They managed to find a wormhole after all, and it eventually brought them back to Earth. John is interested in wormholes and their possible uses (including as doomsday weapons), so naturally he and his wife will be all over the Stargate project. They have been assigned by a deep, secretive Terran organization to monitor the SG-1 operation. Sadly, Scorpius attempted to come through the gate once to warn them of some Scarran shenanigans, but he got accidentally shunted off to the Ewoks' planet, which is why he never made a crossover to SG-1.
 * Fortunately, if Scorpius ended up on Endor after the final battle in Return of the Jedi, then... oh joy, Endor Holocaust!
 * And if before, then we can safely discout Palpatine's story about his Master's name being Darth Plagueis.
 * Well, obviously this is another Aeryn Sun who was "thrown into a blender" with Chiana, like in that unrealized reality--her personality is 90% Chiana, her physiology 90% Aeryn.

Variation: Cameron Mitchell and Vala are actually John Crichton and Aeryn Sun

 * Seeing as wornholes are a common feature in both universes they both tried to escape together but with realitiy differences the universe has to reset itself to allow them both to exist there hence they lived completely different lives from day one.

The Carters are descended from the Cartwrights of Bonanza fame.
They changed the name to try to avoid the curse. But all in all, Sam's mother was lucky to live long enough to have two kids; and that was only because her husband, being in the military, was away a lot. Carter figured it out and joined the military for that reason. Her involvement with O'Neill was a sneaky way to fast-track to head of the team, but he stubbornly kept coming back to life.

We may or may not be safe from the Great Old Ones.
Facts: Carter blew up a star. The Ori and priors have done some nasty things, too. So, there is a possibility that the stars may never be right from now on. Of course, there is also the possibility that the Old Ones planned it all and needed that star destroyed to rise again...

DANIEL JACKSON IS THE FINAL CYLON!!!
What? They even say that the last one is named Daniel. That could explain why he never dies. He's not coming back in a new and creative way every time. He's resurrecting!

Hammond was killed by Kira
He died of a heart attack.
 * Um, what possible reason would Kira have for killing Hammond? He kills criminals (and people who try to stop him, when he can get away with it). Hammond definitely wasn't a criminal, and would have no reason to try to stop him since it's not his jurisdiction and he's got bigger problems than a Serial Killer (i.e. keeping the entire planet from being overrun by aliens).

The aliens out of Assasin's Creed 2 are ancients
Latin sounding names and advanced technology coupled with creating humans.

Merlin created the Wizards of Waverly Place wizards
One of Merlin's early efforts to combat the Ori was to create his own version of the Priors. These were the first human wizards. Upon discovering their ability to access the Wizard World, however, they lost interest in fighting the Ori, and Merlin instead set about building his superweapon.

The wizards of Harry Potter are descended from Ancients stranded on Earth.
Think about it. Of all the pop culture references made in the Stargate Verse, Harry Potter isn't mentioned once. In the Potter Verse, we have no idea where wizards came from; but it seems to be genetic, and the oldest era we know they existed in is... Ancient Egypt. Yes, several Stargate characters have the Ancient Gene and never went to Hogwarts, but they could be Squibs that were given to Muggle families by disgusted wizarding parents.
 * Dumbledore's body was never shown after his death because he Ascended to A Higher Plane of Existence. After  in book 7, Dumbledore attempted to ascend him as well. (Compare the "celestial train station" scene in Deathly Hallows to what Daniel experienced prior to his ascension.)
 * Harry Potter Comics may embrace this idea, with members of the SGC being involved with a Christmas Eve plot of Voldemort. First seen in this comic
 * OOOO!!! Diagon Alley is out of phase!!!!!
 * Wizards and Muggles could be the second evolution's version of the Ori and the Altereans, only with the the mystical ones outranking the science-y ones this time.

The film Inception takes place in the Stargate universe
This one is actually pretty cut and dry, in Stargate: Atlantis they reveal that the military has reverse engineered alien shared dreaming technology, and military research is the only origin ever given for the shared dreaming tech in Inception. In Stargate SG 1 they're even testing similar stuff with Tealc. There is nothing in Inception that would go against this.