Dec 19 2019
From the end of the 19th century, physicists have been aware that energy transfer from one body to another is related to entropy. Soon it became evident that this entity is of primary significance. Therefore, it became a successful emergence as a useful theoretical entity in the fields of physics, engineering, and chemistry.
In their experiments, the Kiel physicists used a laser to transfer energy into thermal motion of microparticles embedded in a plasma. Their diagnostic allows observing the dynamical behavior of all particles at once and in real time. Image Credit: Frank Wieben.
But in general, this entity is quite challenging to measure. At present, Professor Dietmar Block and Frank Wieben of Kiel University (CAU) have successfully measured entropy in complex plasmas. The study was recently published in the leading scientific journal Physical Review Letters.
In a charged microparticle system within the ionized gas, the scientists could quantify the velocities and positions of all the particles at the same time. Thus, they were able to quantify the entropy, as it was already theoretically explained around 1880 by the physicist Ludwig Boltzmann.
Surprising Thermodynamic Equilibrium in Plasma
With our experiments, we were able to prove that in the important model system of complex plasma, the thermodynamic fundamentals are fulfilled. What is surprising is that this applies to microparticles in a plasma, which is far away from thermodynamic equilibrium.
Frank Wieben, PhD Student, Kiel University
As part of his experiments, Wieben was able to tweak the microparticles’ thermal motion by using a laser beam. With the help of video microscopy, he can view the particles’ dynamic behavior in real-time, and quantify the entropy using the collected data.
We thus lay the foundation for future fundamental studies on thermodynamics in strongly coupled systems. These are applicable to other systems as well.
Dietmar Block, Professor, Institute of Experimental and Applied Physics, Kiel University
This success was mainly possible due to the outcomes and diagnostic methods developed in Kiel as part of the Collaborative Research Center Transregio 24 “Fundamentals of Complex Plasmas” (2005–2017).
Explaining Entropy with a Water Experiment
Entropy can be demonstrated by an everyday experiment: upon pouring a container of hot water into a container of cold water, the mixture is warmer than the cold water, and cooler than the hot water. But this process cannot be undone; in other words, it is irreversible: at medium temperature, it is not possible to split water into a container of hot water and a container of cold water.
Entropy is the reason behind the irreversibility of this process. According to the second law of thermodynamics, in a closed system, there is no decrease in entropy over time. Hence, the mixing of cold and hot water must lead to an increase in entropy.
On the other hand, it is also possible to associate entropy with the degree of randomness or disorder. To be very specific, it can be said that systems as such do not change into a highly ordered state. Order must be created by someone; however, disorder can appear on its own.