Artificial gravity is considered one of the holy grails of technology… replicating one of the fundamental forces of the universe while ignoring mass. We often imitate it through spinning habitats, but there are issues with that for long range travel… issues that the Kthid are very aware of. No one has found a way to artificially create gravity without mass, however… but there are ways around this.
Acceleration and gravity are functionally interchangeable… and that creates ways to mimic gravity through electromagnetism and nanomachines. This is how Kthid artificial gravity works. Their atmosphere is not merely air – it is a gelatin-like chain of nanomachines, configured one and all to link together in an electomagnetic chain and accelerate “down,” towards the deck of the ship. This mimics the gravity of the Kthid homeworld, about 1.1g.
Functionally, there is no difference between this and gravity. It makes the air feel human and thick, but not any more so than naturally humid air, and the nanomachines lack receptors that could cause them to interact with the inside of the lungs – they just get breathed out, the same way they get breathed in. The main limitation of this, then, is that these chains need to be manufactured and repaired. It is unknown at this time how the Kthid do this, but they much have access to a far more detailed nanoforge than humanity has been able to conceive of or build.
This technology is referred to as Clarketech – Technology that we have a theoretical understanding of how it would work and how it would be possible, but have no idea of how we’d go about building it in the real world.