The destination of Time Travel
Space-Time
In Roberta Sparrow's philosophy of time travel, the dimension of past-present-future, as well as space-time continuum as a two-dimensional logical plane require to be framed within the context of the Primary Universe - Tangent Universe nomenclature.
While the Fourth Dimension of Time is assumed to be a stable construct, it may be corrupted on rare occasions. It is not explained how the phenomenon may occur. Any attempts at providing an explanation are speculative.
Considering the seemingly truly random nature of the election of each Living Receiver in addition to the extreme rarity of a tear in the Fourth Dimension of Time, as well as finally computing the highly irregular circumstance of the two Living Receivers in the same lifetime in the same exact geographical location occurred in the events depicted in the movie, hopes for such an event are reasonably assumed to be statistically insignificant.