Scientists Say: Absolute zero

This temperature is the coldest possible


The thermometer on the left might show us that it’s cold. But that cold is nothing compared to absolute zero.


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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Power Words

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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.

Bethany Brookshire was a longtime staff writer at Science News Explores and is the author of the book Pests: How Humans Create Animal Villains. She has a Ph.D. in physiology and pharmacology and likes to write about neuroscience, biology, climate and more. She thinks Porgs are an invasive species.

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