We use temperature casually every day to check the weather or set an oven, but the measurement of heat also describes the physical reality of the entire universe. From the near-absolute zero of deep space to the incomprehensible heat of the Big Bang, the Kelvin scale maps the extremes of existence. This episode follows that scale upward, exploring what temperature actually is, where it reaches its absolute limits, and what those extremes tell us about the cosmos.

The journey takes us from the mild warmth of a summer day to the ancient heat trapped in Earth's core, and outward to the puzzling mystery of the Sun's corona. Further out, we encounter the violent stellar deaths that forge heavy elements like gold and platinum, the intense collisions of neutron stars, and the focused jets of gamma-ray bursts. We also look at the hottest human-made ...