The "other side"
So to my understanding the people stuck in this "hellish dimension" are being controlled by an unseen entity to do horrible, unspeakable things to each other.
And since this is taking place in an alternate reality. Our own laws of reality don't necessarily apply here. Which explains why the crew is capable of endlessly torturing each other in the most horrible ways imaginable and not die.
But my question is this. Why is this entity doing this? What's the purpose? Maybe it's best not to know.