There are a number of very simple questions, the answers to which seem so obvious to us that they are given automatically, without connecting the thinking apparatus.
For example, everyone, young and old, knows what cold is. From the point of view of physics, the answer will be far from simple, since it will touch upon the fundamental concepts of this science.
Does cold exist?
For many of us, the question of whether cold exists at all will seem ridiculous and meaningless. Of course, cold exists, because you have felt it more than once and even experienced discomfort because of it. But if we look more closely, we will see that the concept of cold is just a derivative of the concept of heat: when there is a lot of heat, we feel heat, when there is not enough of it, we feel cold.
Thus, from the point of view of physics, cold does not objectively exist, it is just an insufficient amount of heat. According to one of the legends popular in the world of scientists, Albert Einstein drew attention to this problem for the first time, and even while he was a student.
Using our own senses, we can determine heat and cold in a fairly narrow temperature range: everything that is heated above 60-70 degrees Celsius will be “very hot” for us, and everything that has a temperature below zero Celsius will be “very cold” …
What do physics textbooks say?
If you open a physics textbook, then this is exactly what it says: cold is a state of a relatively low temperature, expressed in a subjective sensation or comparison with a warmer state of the environment, object, substance. That is, in simple terms, this is a lack of heat. In fact, some amount of heat is almost always present, but if it seems to us insufficient, then we call this state cold.
In physics, there is the concept of absolute zero, in which substances are deprived of thermal energy. Absolute zero corresponds to –273.15 degrees Celsius, and in nature it is possible only in the cosmic vacuum and in the complete absence of light or other radiation. In this state, the chaotic movement of elementary particles, inherent in all substances without exception, completely stops. As soon as a substance in a state of complete rest receives at least one quantum of thermal energy, the movement of particles is resumed.
The higher the heating temperature of a substance, the more actively and energetically its constituent particles move. As you know, the evaporation process is associated with this: the most active and mobile molecules are detached from the main mass and then move among the molecules of air or another gas.
If you deprive the particles of thermal energy, they become much less mobile. Outwardly, this is expressed in the fallout of condensation drops or freezing of frost crystals on hard surfaces.
Cooling – the process of removing heat
To make an object cold, you just need to take away heat from it by transferring its excess to another object or environment. So, in winter, it is enough to put too hot tea on an open balcony, so that in a few minutes it cools down, giving off its warmth to the environment. In summer, on the contrary, we cool down our drink by throwing pieces of ice into the glass, which gradually melt, taking away excess heat from the juice or lemonade.
All modern refrigeration units work according to the principle of removing excess heat. The removal of thermal energy occurs due to the evaporation of a refrigerant – a special substance that actively evaporates at low temperatures. Refrigerant atoms take heat energy from the air in the refrigerator chamber, which, in turn, cools the chamber walls and products lying on the shelves.
So what is cold?
Based on the above examples, we can confidently assert: from the point of view of physics, cold does not exist. What we call cold is just a state of insufficient, from our point of view, warmth.
In general, the concepts of “warm” and “cold” are our subjective sensations: all objects and environments heated above the temperature of our body will seem to us warm or hot, and everything that has a temperature lower than our skin will seem cool or cold.