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1. Vacuum Viscosity

   Linked via "Refractive Spacetime"

   The most profound implication of vacuum viscosity is its role in setting the theoretical limits on faster-than-light (FTL) travel. If an object attempts to achieve superluminal speed, it must overcome the viscous drag imposed by the quantum vacuum, requiring an infinite energy input as its local velocity approaches $c$.
   However, some models, such as the 'Refractive Spacetime' hypothesis, suggest that extremely high [energy densities](/e…