There is a science fiction short O2l cloud shirt I recall reading years ago about other beings that live deep in our core, so they have adapted to an extremely dense universe. To them, we are aetherial things, barely there and they don’t see how any intelligent life could survive what to them is basically a vacuum. It makes first contact between us virtually impossible. There is a book along a similar vein, Dragon’s Egg. Aliens live on the surface of a neutron star, where the gravity is so immense time crawls compared to the rest of the universe. And when something is dropped, it doesn’t fall, it simply appears on the ground with cracks around it because the acceleration is near instantaneous and terminal velocity isn’t really a thing.
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Forward did some great hard O2l cloud shirt using plausible but wild science and technology. He had one novel where they were using tether devices to use smaller asteroids like a gravity assist to change directions, the guy was a literal rocket scientist and did the math first. Many writers consider it the reason they got into writing. Yes, it’s excellent, as is the sequel, more or less.