The angels provide the advanced technology. Ordinary humans (mortals) can make use of it, but are not allowed to build their own. That would be heresy, and the angels have their own contingent devoted to rooting out and destroying any and all forms of heresy. Humans are not allowed to have 'real' computers. The computer our heroine is using at least partly depends on vacuum tubes. But she carries a pocket calculator with her, so there is some kind of line between what is allowed and what is not. I think the gating factor is that humans are not allowed any computers that would be powerful enough to run an ansible or a portal as those evidently take an enormous amount of processing power.
|The classic wheel-shaped space station concept of the 1950s. (NASA)|
There is one theory of reality that's been kicking around for a while that says everything is a construct of our minds. Everything in our lives, our world, our reality, is there only because we collectively agree on what we imagine. For instance, back in the stone age, the universe was only a few million miles in diameter. Stars were just dots of light. When people started messing about with telescopes and started measuring things they found they needed a bigger universe to explain what they saw, so they imagined it and the universe reacted by expanding to accommodate their imaginings.
|"Digital Rain" from The Matrix - ANIMAL LOGIC/WARNER BROS|
Or maybe the very fabric of reality has somehow collapsed, and The Outside has wandered in.