Conventional thermodynamics states that heating and cooling are essentially opposite phenomena. However, the latest experiment with a small silica ball suggests something else entirely. Details are provided by New Scientist magazine.
According to the new principle of thermodynamics heating on a microscopic scale is always faster than cooling. The two processes, long regarded by physicists as two sides of the same coin, appear to be fundamentally different in light of the latest research.
Heating and cooling are not opposites
While most people have an intuitive idea of what temperature is, physicists have been arguing over the exact definition for centuries. The textbooks say it’s about how much the atoms move around in the system. However, thermodynamics, which deals with the relationship between heat and other forms of energy, describes temperature as a measure of how many different arrangements of values—for example, speed or energy—all atoms in a system can have. These arrangements are called microstates.
Based on these findings conventional thermodynamics holds that heating and cooling are essentially mirror images of the same process. However, this theory assumes that temperature changes occur either slowly or at small intervals.
When systems heat up or cool down over very long intervals, the physics becomes harder to understand—and the results can be quite counterintuitive. For example, hot water freezes faster than cold water – a paradox known as the Mpemba phenomenon.
The silica ball proved the truth
Aljaz Godec of the Max Planck Institute for Multidisciplinary Sciences in Göttingen, Germany, and his colleagues found that a microscopic sphere of silica that is rapidly heated or cooled by an electric field heats up faster than it cools down. “That is very surprising,” says Godec. “So far we know it is because we have proven it, but I don’t think we can claim to understand why it is.”
The researchers placed a small ball in water and captured it in place with a laser. They then heated or cooled it with an electric field and measured how much the particle vibrated and moved. They repeated this process ten thousand times. Measuring a single particle in this way corresponds to measuring a single microstate.
This is impossible for a material composed of many particles, because they can take on a huge number of possible configurations. But through many measurements of a single microscopic particle the science team was able to map the possible number of microstates it can acquire.
The scientists then measured how many different microstates the particles had to go through when transitioning between two temperatures due to heating or cooling. They found that it had to pass through fewer possible microstates when heating than when cooling, which was reflected in a faster heating rate.
It is not yet clear why
“Although it is not obvious why this fundamental difference should existshould be present in any system that is heated or cooled,” says Godec, noting that it would usually be difficult to observe. The reason for this is the fact that such large changes in temperature usually induce phenomena in the system itself, such as freezing or boiling, which obscure this newly discovered effect.
“It’s really interesting work,” says Janet Anders of the University of Exeter in the UK. “It’s important to think about what might explain it in nature.” The results of the scientific research were published on January 3, 2024 in the scientific journal Nature Physics.
“The effect that Godec and his team discovered could be considered an additional law of thermodynamics,” says Anders. It extends the second law of thermodynamicswhich says that hot things will always cool unless we prevent them in some way.
“The second law says nothing about speed, but about possibility,” clarifies Andres. “This second and a half law, as I call it, says that you can do these things, but some of them will take much longer than the opposite processes.”