At the edge of what is seen and what is known, a researcher has built a device to illuminate one of science's most consequential blind spots: how clouds are born. Mayur Sapkal, a Pioneer Fellow at ETH Zurich, has developed RepliClouds, an instrument that recreates in the laboratory the precise conditions under which water vapor condenses onto microscopic particles to form cloud droplets. Because clouds remain the largest source of uncertainty in climate modeling, this work carries weight far beyond the lab — it is an attempt to sharpen humanity's vision of its own future, at a moment when that