Science Puzzle
How Cold Can Anything Get?
There seems to be no upper limit to how hot things can get: the centre of the Sun is about 15 million degrees. The coldest temperature ever measured on Earth's surface was -89 °C, in Antarctica, and deep space is colder still.
Is there a limit to how cold anything can get?
The Answer
Yes. Nothing can be colder than -273.15 °C, known as absolute zero. At that temperature the particles in a substance have the least movement they possibly can, so there's no more heat to take away.
Temperature measures how vigorously the atoms and molecules in something are jiggling about. Heat something and they jiggle faster, with no obvious upper limit. Cool it and they slow down. But you can't slow a particle down below the least movement there is, so there has to be a bottom to the scale. Scientists measure from there on the Kelvin scale, which starts at zero at absolute zero: water freezes at 273.15 kelvin.
You can get close to absolute zero but never quite reach it; each step of cooling takes away a smaller share of what's left. In 2021 a team in Bremen, Germany, cooled a cloud of atoms to 38 trillionths of a degree above absolute zero. Deep space is about -270 °C, warmed slightly by the faint glow left over from the Big Bang.
Very near absolute zero, materials behave strangely. Some metals lose all resistance to electricity, and liquid helium can creep up the sides of its container and escape over the rim.
The principle: Absolute zero. Temperature measures how much particles jiggle, and that can't fall below a minimum, so nothing can be colder than -273.15 °C, the zero of the Kelvin scale.