[general_re]

Imagine you have a total vacuum in your room, but instead of opening a window, you remove an entire wall. Now, at t₀, you have a room at 0 atmospheres, with an "outside" pressure of 1 atmosphere, but that's not going to last. The atmosphere will move from high pressure to low pressure, and it's not going to slow down three inches inside the room and decide to take a leisurely pace the rest of the way - your leading edge is going to keep on trucking right on into the rest of the room, because the rest of the room, minus the first three inches, is lower pressure than everything else. And in a tube 100 miles (160,000 meters) long, there's pretty much only one direction for it to go - down the tube, and tout suite at that. ;)

[SampleMan]

Fascinating, can you fix the water pressure in my neighborhood? Because I live on earth, where a gas or liquid filling vacuum or area of lower pressure decreases in pressure until it completely fills the area and meets itself trying to come back out.

Your assumption is that air molecules would all be traveling perfectly straight down the opening and not interacting with each other. This interaction is what prevents the rising water scenario you describe.

However, this could be even more distributed by putting an inverted cone muzzle on the tube, when the small end opened the entering air would decrease even more greatly.

As any method is just a delaying action anyway though, why not do as I suggested and allow pressure into the tubes terminus from its sides just before vessel passage. I'm sure you would agree that this could be done gradually, as air cannot possibly reach equilibrium within seconds, let alone the thousands of second we're talking about over a length of several miles.