Hollydeva lives in a world similar to our world, to Earth ( at least at the beginning of the series). It, however, is happening on a parrallel world.

This (parallel world, not ours) is indicated by ypsilons in the geographical names, like Eyrope, Ameryka, Yrth, Londynium.

The incidents yet are possible in our world as well. So the learnings and conclusions from these inciidents and processes have significance for our world as well.

Modern physics assumes a multitude of parrallel worlds.

It will be similar in all these worlds and yet significantly different as well.