Now let us introduce a party of visitors in a hyperspace vehicle (V). They have arrived at Mary's location by navigating to coordinates (S,T,U), where S and U each represent a set of coordinates in 3-space and n-dimensional hyperspace respectively.
Mary looks up and sees V as a UFO or "flying saucer". Now at this moment a decision is made aboard V. (For the purposes of this thought experiment, it does not matter whether the crew of V are futuristic humans or extraterrestrial "aliens".)
The crew of V must decide whether to initiate contact with the local population at (S,T,U), that is, Apple Tree, Oregon, on a summer night in 1958. Perhaps they debate, or their commander makes the decision, or perhaps, like Lovejoy and Pettigrove, they toss a coin.
From this moment on, we will now consider the system as two universes, U1 and U2. In u1, the crew of the vehicle (now V1) decide not to make contact, and move on. Mary (now Mary1) sees the UFO fly off and disappear. She runs into her house to tell her mother, but there's no trace of anything unusual in the sky, and life in Apple Tree continues in normal fashion.
Meanwhile, in universe U2, the crew of V2 have decided to initiate contact and are making preparations to meet the locals. Here - at coordinates (S2, U2, V2) - Mary's mother comes running out to see what Mary is so excited about. Sure enough, there's a real honest-to-gosh flying saucer sitting in the back yard.
From this point on, it's just like in the science-fiction movies. Soon, news reporters will arrive, flashbulbs will start popping, the President will make speeches, and life in Apple Tree will be changed forever.
(In yet another universe, U3, an officer at NORAD spots an unusual blip over Oregon and suspects a Soviet missile attack ... but I like happy endings.)
The crew of V2 will radio the coordinates of (S2, T2, U2) back to their home base (via hyperspace radio, of course) and announce that they've had a successful contact and have established friendly relations with the local population. Soon, V2 is followed by more spacecraft, and trade negotiations begin. By now, the town of Apple Tree is the subject of worldwide interest, and it becomes, almost overnight, the site of Earth's first spaceport - a 'node'.
Spacecraft navigating to the spaceport will use the coordinates (S2, Tn, U2), to ensure that they arrive in the correct location. Occasionally a navigational error will put one of the visiting spacecraft at Apple Tree in U1 - the analog of Apple Tree in which spacecraft V never made contact and the spaceport was never built. When this happens, the crew will re-check their calculations and find their way back to the spaceport at Apple Tree in U2. The residents of Apple Tree in U1 might see somethign in the sky for a few moments, but by the time they look again, it'll be gone.