Doctor Who: The Timey-Wimiest Episodes Not By Steven Moffat
2. The Girl Who Waited (2011)
In this bitter time travel tragedy, Amy Pond finds herself separated from the Eleventh Doctor and her husband Rory and trapped in an accelerated time stream on the planet Apalapucia, a place where terminally ill patients live out long and comfortable lives contained in their final few days and hours.
By the time Rory catches up with her, a shocking 36 years have passed for Amy, during which she has grown hardened and embittered after decades of fighting for survival against misguided medical robots.
Though glad to finally be rescued, Amy is reluctant to help Rory and the Doctor save her younger self from this life, as she knows it will cause her to cease to exist. Eventually she is persuaded, leading to a series of scenes where the two Amy Ponds exist side by side.
The Doctor knows that this paradox cannot endure, and ultimately Rory and the older Amy together make the harsh decision that it is the younger Amy who will survive.