Normally, if you have a collection of atoms that are moving around quickly, with lots of kinetic energy, then the temperature is high. In contrast, slow-moving atoms with little kinetic energy have a low temperature. When all atoms are perfectly still, the Kelvin scale – used by scientists to measure temperature – hits absolute zero, the lowest value possible.

But physicists also have a more precise definition of temperature that reflects how energy is distributed among the atoms, a property related to a system’s entropy, or how disordered it is.

For a collection of atoms with a positive absolute temperature, only a few of them have lots of energy, while most have lower energy levels. At absolute zero, all atoms have the same, minimal energy. But at negative absolute temperatures the distribution flips so that higher-energy atoms become the majority, and those with lower energy become outliers.

This leads to one of the biggest oddities about negative absolute temperatures – they are technically hotter than all positive temperatures. This is because a negative absolute temperature object will always have more energy, so putting it together with a positive temperature object would make heat flow into the latter, as from a warm room into a cold glass of water.