Theories that seek to explain the outstanding puzzles of the Standard Model of particle physics often predict new, light, feebly-interacting particles. In this talk, I will outline a range of novel search strategies that are required for their discovery, from the laboratory to the sky. I will focus on the early universe, where even a small trace of hyperlight scalar fields can be observed through the power of the cosmic microwave background. Scalar fields which interact with photons and electrons provide concrete microphysical models of varying-constant scenarios, invoked as a potential resolution of discrepant measurements of the universe's expansion rate. I will discuss cosmological and laboratory constraints on these models, including measurements of quasar absorption lines, abundances of light elements, and universality of free fall, as well as their dynamics and signatures in the early universe and their effect on the cosmic microwave background and inferred cosmological parameters.