To humans, the difference between hot and cold is simply switching a winter coat for shorts and sandals. In reality, our universe can get much, much hotter than an Earthly summer, like the scorching temperatures found during a supernova. It can also get much colder, like the frigid Boomerang Nebula, which is chillier than empty space. Scientists measure these temperatures on what’s called the Kelvin scale, which starts at a theoretical absolute zero, the point at which all molecular movement stops. These extreme temperatures result in fascinating physical and chemical changes, like the nuclear fusion that powers the sun. But can we take these intense temperatures further? Physicists at the Large Hadron Collider (LHC) at CERN have smashed lead ions together to achieve the hottest man-made temperatures ever recorded – around 5.5 trillion Kelvin. And scientists at MIT have cooled sodium gas with lasers to half a billionth of a degree above absolute zero. Experimenting with extreme temperatures could be a promising window into solving many of our universe’s lingering mysteries, perhaps even giving clues to the earliest moments of its existence.