Hume Manipulation allows for changing the Hume level of a space. The Hume level is how much reality there is in a space, how much the laws of physics apply and how strictly. At 1 Hume, all laws of physics exist and are normal. Above 1 and it becomes much harder to break or bend these laws, stricter conditions are added, magnetic and particle effects especially become stricter which can greatly effect unprotected electronics. Below 1, and the laws of physics begin to fade. Entropy, gravity, time, physical space, 4D 3D 2D 1D it all begins to blur. At 0 Hume(entirely theoretical) there is nothing. No laws of physics to tell atoms to bind to each other, to tell subatomic particles to bind, to tell what makes up those neutrons and electrons to even exist. Nothing. This is done in small amounts(Down to 0.9 Humes is standard) to more easily induce, study, and utilize quantum states under less expensive or dangerous conditions, making it paramount in the FTL travel of the Karth empire.
Humes were studied when Karthenon's scholars realized there were a total of 3 other systems with metal based species. 2 of those had rogue metallophages and 1 of them had an offshoot of Titanium Terrors that evolved to live inside of a gas giant and consume aerosolized metal. Metal life occurring without organic interference seemed to be incredibly rare in this galaxy, so they researched what was special about their system in particular, eventually finding it: A reality sink happened to exist in 4D space very close to their star. A reality sink is a singularity of Humes, it has an incredibly high Hume level and its immediate surroundings have lower Hume levels, the effect is identical to a gravitational field. It continuously drains the surrounding space, causing Humes to flow towards these sinks, and causing a sort of flow that exists physically in 4D space. Realizing they were, by definition, impossible under normal physics, they began to worry that if they were to expand, some terrible catastrophe would befall their biology. This prompted the research of how to control the Hume level, these 4D particles, in 3D space. The short answer is you can't, and the long answer is that you can't affect higher dimensional objects except for when the tip of them is inside the 3D space you occupy, meaning that they have to build their own reality sinks, Reality Anchors as they're called, that exist partially within 4D space, and repel or attract Humes to increase or decrease the amount of reality. Any long-term living space for the Karth generally has a reality anchor in it, in case that long-feared disaster strikes.
Advancements
Any space designed to house Karths will face incredible morale difficulties without a reality anchor, even an inactive one, to keep them relatively safe.
Organic life experiences increased life expectancy and decreased metabolism under lower Hume levels, but the rate of degenerative brain disorders increases rapidly under these conditions, both their progression and spontaneous development.