What Are the Absolute Coldest and Hottest Temperatures Possible?

What is absolute zero?

The laws of physics say there is an absolute rock bottom coldest temperature possible. We even define a temperature scale, Kelvins, where this lower limit is defined as 0 Kelvin, otherwise known as absolute zero. At a temperature of absolute zero, the motions of particles are at a minimum since almost all of their energy is removed. (But they are not completely devoid of energy as there is always some energy associated with their resting ground state.) And in case you don’t work in Kelvins every day, 0 Kelvin (or 0 K) is about -273 degrees Celsius and roughly -460 degrees Fahrenheit. 

At a temperature of absolute zero, the motions of particles are at a minimum since almost all of their energy is removed.

Absolute zero is a theoretical temperature. In other words, our mathematical calculations tell us it must exist when we dial the heat energy all the way down. But how cold can we actually get? 

At a temperature of 1 K, the Boomerang Nebula is rumored to be the coldest place in the universe, at least from what we’ve found so far. It’s a young planetary nebula, gaseous debris hurled out into space by the last gasps of a dying star. Initial observations of the gas made the nebula appear lopsided like a boomerang—hence the name. But more detailed imaging from the Hubble Space Telescope shows it actually looks more like a bowtie. Planetary nebulae are known to come in a wide variety of shapes—an unusual characteristic astronomers are still trying to understand—but even among these funky-shaped clouds of debris, the Boomerang Nebula stands out. 

The unique shape of the Boomerang appears linked to the reason for its uniquely low temperature as well. The Boomerang is losing 10-100 times more material each year than is standard for such planetary nebula due to very strong (over 300,000 mile-per-hour) winds forcing ultracold gas away from the star. This fast-moving gas forms the bowtie shape as it quickly expands and thus cools.  

How cold does it get on Earth?

Remember the tardigrade? Those extreme little water bears are known to be able to survive temperatures as cold as ~-270 degrees Celsius or just above absolute zero. Lucky for the rest of us, the ...

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