After a multi-decade-year mission to understand the nature of the universe, a telescope perched in the mountain plateaus of northern Chile said goodbye in 2022. Now, its final data release is revealing the telescope's legacy: a field in tension.
In October 2007, the Atacama Cosmology Telescope (ACT) saw its first light. But it was not light from a star, or even a distant galaxy. Instead, ACT was designed to hunt for microwaves, especially the kind of microwaves left over from some of the earliest epochs of the universe. This "fossil" light, known as the cosmic microwave background (CMB), was emitted when the universe was just 380,000 years old.
