[Mortal slang is amusing, it truly is. And it does achieve a desired effect on Loki's part. Since he's decided he is going to give Tony a ride in to town (you know, unless Tony annoys him and then just gets dumped off the horse) better to make it a bit friendlier. He doesn't like having people at his back. It's the principle of the thing.]

Then there you have your answer. We were brought here by some means. I haven't seen convincing proof yet that there is such a creature as a one-way spatial door.

So then it is a question of finding the appropriate theory and then manufacturing the necessary devices.