Absolute Zero — Definition & Importance

Absolute zero is the lowest possible temperature, when no heat remains. As the temperature of a substance decreases, its molecules move slower, including electrons, protons, and neutrons.

At absolute zero, molecules move the slowest they possibly could, though particles never stop moving completely and there is internal energy. In reality, objects can never achieve absolute zero, but rather stop at a degree above absolute zero. Out of the three temperature scales/temperature measurements, Kelvin is always positive, whereas the other two scales can go into negative numbers. Thus, absolute zero is 0 K.

Right now, absolute zero is simply theoretical. The Laws of Thermodynamics say that we cannot reach absolute zero (which we learned from a Nobel Prize winner!). Scientists have not managed to create absolute zero in a lab setting, but through quantum computing, they've gotten a better understanding of what absolute zero is and why it's important. Remember, even a billionths of a degree above $0$ K is still not absolute zero.

Application

There are an abundance of applications for absolute value!

First, we will talk about the Bose Einstein Condensate. It sounds complicated, and it is, so we will just touch on it. The Bose Einstein Condensate is when any state of matter is cooled so much that when it reaches absolute zero, all of the matter can be described as a single piece of matter. You will learn more about this concept when you learn about quantum mechanics!

Out in the galaxy, scientists have discovered a place where absolute zero nearly exists: The Boomerang Nebula. In this chilly place, the temperature reaches one degree above absolute zero.

Imagine heating and cooling a balloon full of air. As you heat the balloon it expands, and when you cool it, it contracts. Now lets say you want to quantify this physical change. Well, all we're changing about the balloon is temperature, $T$, and the only change we observe is is the volume, $V$. So for now, lets write the following relationship, $$V=\alpha T$$ Where $\alpha$ is a constant. This is fine and all, but we run into a bit of an issue. What happens when $T$ is $0$? What happens when $T$ is negative?

Obviously the volume cannot be negative, and it doesn't even make sense for volume to be $0$. To make matters worse, where even is $0$? $0$ Celsius is $32$ Fahrenheit. To solve these issues, lets introduce a new temperature scale, Kelvin. In the Kelvin scale, each tick is equivalent to a tick on the celsius scale, but $0$ is the lowest possible temperature, and is often called absolute zero. $0$ kelvin is equivalent to $-273.15^{\circ}\text{ C}$

So what is the significance of $0$ kelvin? It turns out that this is the temperature that both thermal kinetic energy, and entropy, are minimized. Written more mathematically, $$\lim_{T\rightarrow 0} S=0$$

Where S is entropy. All substances are solid at absolute zero.

It turns out, partially because of the significance, that absolute zero is impossible to reach. Reaching absolute zero would require an infinite amount of work to remove the heat. That doesn't mean scientists aren't working to try to reach it, often applying the scientific method to design experiments that can reach temperatures very near absolute zero. As of 2017, the coldest temperature we have been able to reach is $\text{~}10^{-12}\text{ k}$.

(Video) Absolute Zero: Absolute Awesome

by SciShow

Is it possible to stop particle motion completely? Not quite, but absolute zero is the closest we'll ever get. This point, measured in Kelvin, is where the kinetic energy of a material is the lowest it can possibly be. Watch the video above to find out more.

Some key points to takeaway from the video are, as explained by Hank Green, at absolute zero the actual particles (e.g. electrons) don't stop moving. Due to the Heisenberg Uncertainty Principle, we can't know both an electrons momentum and location.

Absolute Zero Preview