I feel that the issues you raised present the serious barriers to such an implementation of gateways. The, shall we say "practical" issues raised by Fionwe are minor details for which there can be many different potential solutions.

For example, if channelers can planet hop across solar systems, it is obvious that some planets would have very different atmoshperes. Perhaps atmospheres so miniscule that you have close to a 1 atmosphere pressure differential. Some other planets may have atmospheres so dense that you may have pressure differentials of MANY atmospheres, but in the opposite direction.

So clearly, channelers were able to counter these effects when making gateways to Travel across the galaxy.

So the practicalities are not of consequence.

What IS of consequence, is whether there are fundamental problems with using the greater pressure on two sides of a gateway to generate some kind of movement of fluid/gas or even solid matter.

Your suggestion that inanimate matter cannot move across a gateway on its own might well be the likely answer. I think we don't have enough information yet to prove it one way or another, but your proposal seems likely in order to avoid all kinds of weird scenarios, not to mention perpetual motion energy generators (if you create horizontal gateways above one another and have an object perpetually falling through the bottom one only to come out of the top one again, in an endless cycle).

These are the issues that I was interested in discussing. And that's why I got somewhat irritated in the discussion with Fionwe, where lame stuff like "the channeler creating the gateway will be sucked through it and be lost in space" kept being raised.

With all the abilities so far demonstrated with the Power, and all the unknown abilities yet unrevealed, it seems virtually assured that safety measures exist that can protect a channeler from virtually every physical danger.

The fundamental issues, though, cannot be circumvented so easily.

Thanks for your thought provoking response to my original question.