When most of us think about temperature, the first thing that comes to mind is an outdoor thermometer. When it’s cold out, the mercury drops. When it’s hot out, it rises. Aside from the mental imagery associated with it, temperature is a somewhat nebulous concept, and its extremes are even more far-fetched to the imagination.

Colder than cold, hotter than hot

Temperature is defined by several different variables, all taking place on the atomic level. First, there’s atomic motion. At all times, everything around us is wiggling, shimmying, and vibrating at its own speed. Hot things vibrate faster than cold things, and other factors like state of matter dictate how fast or slow an object’s atoms are moving. Entropy, or the universal rule of chaos, also comes into play. Hot objects warm colder objects and cold objects cool warmer objects. On the atomic level, energy is exchanged between fast and slow-moving atoms to reach a balanced state.

Following the notion that cooling objects vibrate at progressively slower rates, it would reason to believe that at a point, all movement would stop if it became cold enough. Reaching that point, even in a lab, would be impossible due to external influences and limitations of technology. Previously, scientists believed that the coldest we could get was absolute zero, and even then, only theoretically. Zero Kelvin or -459.67 Fahrenheit has long been held as the coldest things could get, but recent research implies we may have had the wrong idea all along.

The rise and fall of the temperature scale

Recent studies have shown that it is possible to go below absolute zero without breaking the laws of physics or using a simulation. To do so, scientists have had to completely redefine how we look at temperature, taking the old linear model and throwing it out the window. Instead, they’ve suggested adopting a cyclical model where temperatures that feature atoms in motion are registered on the positive end of the scale while temperatures, where particles are effectively held in stasis, are expressed on the negative end of the scale. The point where it becomes a cycle and not a linear progression happens on the field of energy exchange between particles.

Earlier, we mentioned that entropy was one of the governing factors of temperature. The scientists running the experiment controlled the energy levels of the atoms in the test chamber by first lowering them to a few nanodegrees Kelvin through conventional methods. From there, they began tweaking individual variables, including pressure, mobility (kinetic energy), and potential energy. Via those adjustments, the research team was able to effectively achieve a temperature of several nanodegrees¬†negative Kelvin, breaking the previous boundary of the world’s coldest temperature.

On the other end of the scale, the hottest theoretically attainable temperature is 2.556 decillion degrees. It’s a ludicrously high number, far surpassing the highest ever measured temperature of matter, which is 5.5 trillion degrees, created by the collision of two lead ions in the Large Hadron Collider. With the redefined temperature scale, higher temperatures are likely possible, but the key to furthering technology in the near future lies with supercooled particles. These negative-Kelvin atoms absorb entropy, making them appealing candidates for future heat engine technology. The negative-Kelvin atoms would be able to absorb energy from both hotter and colder substances, allowing it to run at greater than 100% efficiency. Additionally, these new particles might finally shed light on one of the universe’s greatest mysteries: The Big Bang. This latest research has opened our eyes to the potential of previously-unimagined states of matter that could account for gravitational and material anomalies during the creation of the universe, opening endless doors for future study.