Absolute zero (noun, “AB-so-loot ZEE-ro”)
This is the coldest possible temperature. It is zero on the kelvin scale, which is also -273.15° Celsius (-459.67° Fahrenheit). The temperature of a sample depends on how quickly the atoms or molecules in it are moving relative to each other. What we call ice is water molecules moving very slowly, in a matrix. Water molecules moving very quickly become steam. When molecules are near absolute zero, they cease moving altogether. Nothing can be colder than absolute zero.
In a sentence
When Science News magazine reported that scientists achieved a temperature below absolute zero, the substance never got “colder.”
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absolute zero The coldest possible temperature, also known as 0 kelvin. It is equal to minus 273.15 degrees Celsius (minus 459.67 degrees Fahrenheit).
kelvin A temperature scale that has units the size of those on the Celsius scale. The difference, 0 kelvin is absolute zero. By contrast, 0 kelvin is equal to -273.15 Celsius. So 0 Celsius is equal to 273.15 kelvins. NOTE: Unlike with the Celsius and Fahrenheit scales, there is no use of the term “degrees” for numbers on the kelvin scale.