We experience extreme hot and cold temperatures on Earth, but they're nothing compared to the temperature extremes we've created in labs, not to mention the Universe at large. Do these hot and cold extremes have a limit?
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 coldest natural temperature on Earth is much warmer and recorded at -98 degrees Celsius (which is -44 degrees Fahrenheit) in Antarctica. Clear skies, light winds, and low humidity all contribute to getting this temperature as low as possible.
We humans like to tempt fate.
But we humans like to tempt fate. Scientists working with sodium gas in a laboratory were able to cool the gas to one-half of one billionth of a degree above absolute zero. That is one half of a nanokelvin and a fraction with a lot of zeros. Why would we do this, you might be thinking? Besides our consistent interest in pushing the limits, such low temperatures can be used to cool instruments that need to take incredibly precise measurements like atomic clocks and gravity sensors.
Is there an absolute hot?
So, if there’s an absolute zero, is there an absolute … hot? The laws of physics once again say that there should be a hottest possible temperature.
Our universe is expanding, and things generally cool down as they expand. To picture this, you can think of the particles in a gas as being a crowd of joggers headed in all different directions. Confine the joggers in a small space and there will be lots of collisions as they move around and transfer energy. But spread them out and suddenly they have more room to move around without running into each other.
So if the universe is expanding, then it was denser and hotter in the past. We can’t go back in time and measure the very earliest temperature, but our models suggest it was somewhere around 1032 Kelvin (that’s 1 followed by 32 zeroes).
What is the Planck temperature?
Since that number is completely mind-boggling, let’s look at the physics it describes. At this temperature, also known as the Planck temperature (after the German physicist Max Planc), particle energies are so high that the normally weak gravitational force starts to rival the strength of other, shorter-range forces. At that point, we run into the same problem we have in explaining what goes on in a black hole or in the very first fractions of a second after the Big Bang—we don’t have a theory of quantum gravity that meshes the physics of the really small with the really large.
We don’t have a theory of quantum gravity that meshes the physics of the really small with the really large.
How hot does it get on Earth?
And here on Earth, the highest naturally occurring temperature recorded, according to the Guinness Book of World Records, was recorded in 1913 in Death Valley, California. The temperature was 134 degrees Fahrenheit (almost 57 degrees Celsius). This record has stood for over 100 years, but as global average temperatures continue to rise, our yearly averages are quickly approaching it.
The resulting temperature was around 5.5 trillion Kelvin. That’s 55 followed by 11 zeroes.
Scientists have also yet again tested how high human-made temperatures can get. Physicists at the Large Hadron Collider—that enormous underground particle accelerator looking for antimatter, dark matter, and even other dimensions—accelerated two lead ions until they were whipping around at 99% the speed of light and then smashed them into each other. The resulting temperature was around 5.5 trillion Kelvin. That’s 55 followed by 11 zeroes. For reference, the center of the Sun is only about 15 million Kelvin, or 15 followed by 6 zeroes.