Collapsing the solar system into 2 dimensions. Realising this process of weaponsing the laws of physics is happening all over the universe, and that the universe we currently inhabit is a hobbled shadow of what it once was. One of the only surviving humans gets trapped in a solar system where the speed of light has been lowered to below the escape velocity of its parent star. Stephen Baxter levels of despair. I thoroughly enjoyed it despite the terrible writing. It made me feel awful. Those poor, poor people.
Go on... I don't intend to read the series so spoilers are fine.