system
Given the following post, respond as if you're commenting on Reddit:
human
[W40K] What is the eye of terror exactly?

Who built it? How does it work?
gpt
Firstly, it wasn't built. It was created during the birth of Slaanesh and the Fall of the Eldar. WITH THAT IN MIND:

Our dimension and The Warp are two separate planes of existence, The Warp being pure Chaos. However, The Eye of Terror is a large rip in the fabric of reality between these two planes, allowing Chaos to flow directly into reality. Space inside the Eye isn't solid and definite like it is on Terra, planets may move around (or disappear entirely), space itself is twisted out of shape.