In Expanding de Sitter Space, Quantum Mechanics Gets More Elusive (quantamagazine.org)

The article explains why quantum mechanics is especially difficult to formulate in de Sitter space, a model for an exponentially expanding universe driven by dark energy. Unlike in flat or anti–de Sitter space, de Sitter space has no accessible boundary to shield observers from quantum fluctuations, making standard measurement concepts break down. Researchers are using insights from black holes and recent theoretical calculations—such as how photons can behave in expanding space—to clarify what can and can’t be meaningfully computed.