- It worked.— first words of 10,000 year old Dr. Weir
The team discovers a ten thousand year old Dr. Weir from another timeline in which Atlantis' never had the fail-safes which caused it to rise from the ocean.
- Black Comedy: Sheppard and Rodney's hits against the other on how their alternate selves died.
- Continuity Cameo: Merlin, who will show up in a later season of SG-1, is on the Lantean high council. Also counts as an Early-Bird Cameo, since at this point the Arthurian plotline hasn't even started on SG-1 and he's referred to by his original Lantean name of Moros. He also apparently underwent some Character Development after he left Atlantis, since he comes across here as a bit of a jerkass, although his reasons for not wanting to meddle with time travel are understandable.
- Face Death with Dignity: Alt!McKay doesn't panic as the gate room floods, he just keeps trying to save as many people as he can in his last minutes of life.
- Gallows Humour: Sheppard snarking at Alternate!McKay's death, which turns into somewhat of a competition when McKay scornfully mocks Alternate!Sheppard's death using the same line later in Old!Weir's story.McKay: A man wonders how he would choose to go out, given such dire circumstances. Now I know.
Old!Weir: *Reverently* Trying to save the lives of others!
Sheppard: But, ultimately failing
- Human Popsicle: No, Old!Dr. Weir is not an immortal, just frozen.
- Literary Allusion Title: to Stopping By Woods On A Snowy Evening by Robert Frost
- Meaningful Name: The Ancient working on time-travel is named Janus — Roman god of Time.
- Ripple Effect-Proof Memory: Old!Weir doesn't have any of her memories changed after arriving the very long path to what she once considered the present.
- Set Right What Once Went Wrong: After meeting Janus 10,000 years in the past, Weir works with him to figure out a way to prevent the flooding that doomed her team in the 'original' timeline.
- Shout-Out: Sheppard makes several references to Back to the Future, which McKay does his best to quash.
- The Slow Path: Weir's return to Atlantis - a bit of a subversion, however, in that she had to leave stasis every once in awhile to rotate her power source and make sure everything was working.
- Time and Relative Dimensions in Space: This episode uses the "you end up in outer space" model — which is curious, because the SG-1 episode using the same technology doesn't.
- Of course, the Jumper uses a mental component in its controls and Sheppard was desperate to escape from under the ocean, so it makes some sense why it moved the vessel through time and space. When SG-1 use the similar Jumper in "Moebius", they were merely focusing on travelling through time and presumably didn't even know it could move through space as well.
- Alternatively, it was a less refined, earlier model than the Milky Way version (that Janus is implied to build after returning) and it was dumb luck that Sheppard didn't cause them to be embedded inside of the planet.
- Writers Cannot Do Math: Assuming the power requirement is not changed, there should be no advantage to powering the city's systems off of one ZPM at a time rather than all three in parallel; Kirchoff's Current Law just doesn't work that way.