Winter is around the corner, and a new experiment out of a lab in Germany has scientists setting a record for the coldest temperature on Earth—an intergalactically bone-chilling 38 trillionths of a Kelvin (or .000000000038 K).
Okay, we can already see the confused looks out there. What's a Kelvin? How did they do it? How cold is that anyway?
All great questions! Let's begin with Kelvin.
C, F, or K?
When we talk temperature, we generally use the Celsius scale. Why? Because this scale is based on the chemical reactions of something that we use everyday and rely upon to live. Water. At 0°C, water freezes into ice. At 100°C, water boils turning into gas.
Another scale commonly used across the United States—Fahrenheit—was actually the first-ever temperature scale. Though it revolutionized science in the early 18th century, it is less popular now because its scale is based around the lowest temperature that salt and water will mix and other things that aren't as useful to us. Celsius makes more sense for life on Earth.
But see, that's the thing. Celsius is amazing here. But the moment you step off the planet, it stops being useful. Water only freezes and boils on Earth at those exact temperatures because of the conditions on Earth. And what use is a scale based on boiling water on a planet like Neptune where water—and ammonia and methane—are always frozen?
Enter Kelvin. This scale doesn't use degrees and is set to something far more universal. Zero Kelvin, a.k.a. absolute zero, is the temperature where all 'molecule motion' stops. And if that sounds like a weird way to measure temperature, then let's talk about that!
Temperature isn't quite what you think
Here on Earth, we know temperature as a measure of heat. But it's not actually that. Temperature is a measurement of molecular motion—this is how quickly the particles inside atoms are moving/vibrating. The colder something is, the slower its atoms are moving. And when you think about it like this, it makes a lot of sense.
Very cold matter is generally hard and tightly packed together because its atoms aren't moving very much. Whereas hot matter is either very active and flowing or a gas because its atoms are moving a lot—bouncing off each other and expanding outward.
So what about heat? Heat is just the energy that is created by all of this molecular motion. In most cases, when the temperature rises or falls, we sense it as a change in the amount of heat in an area. This is why temperature to us means heat!
The lowest temperature
If we go back to the Kelvin scale, you can see why it's so used by quantum (molecular) scientists and astrophysicists. It is based on something that is the same from planet to planet, star to star, galaxy to galaxy. The movement of atoms.
It also gives scientists a mark to shoot for: absolute zero. There is no "minus Kelvin". Once you hit absolute zero, you've reached the bottom limit of temperature. In fact, it is so cold that scientists have never observed it occurring naturally in space. Even in the emptiest vacuum of space—where the average temperature is 2.7 Kelvin—there is some teensy tiny molecular motion. The coldest known place in the universe—the Boomerang Nebula—is about one Kelvin (-272°C).
That is cold!
Which finally brings us to what those scientists achieved in Germany. By hitting .000000000038 Kelvin, they not only hit the lowest temperature ever on Earth. They hit the lowest known temperature in the universe.
They did this by placing atoms of an element called rubidium inside a special magnetic field—itself inside a vacuum (or space without other particles)—and creating an environment where the rubidium felt no gravity. With nothing acting upon it, the atoms essentially went to sleep for a few seconds. A cold, cold sleep.