Earth Uninterrupted: 1977
Planar study is more art than science. Certainly, there are guidelines that aid in the small success that sentients have made in planar travel. However, much of the progress was attained by those whose are able to work within those guidelines to manipulate them into works of intuition; beautiful or terrible.
As discovered by the ancient Daedalus, the planes are arranged in a honeycomb-like structure. Each plane is slightly offset from the next and, like honeycomb, increase the integrity of the cosmos efficiently using the present energy/matter. All planes have ten defining omens (the Ten Omens) that can be keyed much as hands on a musical instrument. This arrangement can be molded to create portals, but such a working is always temporary. Like a river must flow towards the sea, the planes will make corrections to maintain universal equilibrium.
Achievements in this field of study have been the sole territory of priests and magi. To date, conventional science has yet to make headway in this realm of study. However, given the rapid progress in other fields, it may simply be a matter of time.