The Voice of Allan Zade
We should conduct an easy "thought experiment" to eliminate that delusion (Gedankenexperiment in German). That is a double-device experiment. There are two thermometers (marked “A” and “B”) in one water tank filled with some water and two fully operable clocks (marked “A” and “B”) with pendulums on the same table. The table is exposed in the open air. A person (the experimenter and observer) begins the experiment. The person reads both thermometers' indications and writes them in the log. Suppose the thermometers show indications of 21 and 21.1 degrees centigrade. Their precision causes little difference in their indication.
After that, the person turned his attention to two clocks. Both clocks operate properly and show similar indications of eight o’clock precisely. The person writes down the indication of both clocks as 8:00 AM. It raises the first question here. The clocks do not indicate noon or midnight. As a result, there is no way to decide between 8:00 AM and 8:00 PM by indicating a pendulum clock. Hence, the person cannot take that information by indicating those devices. However, he had the decision to make AM. How was it possible? There is only one way to make such a determination. The person must look outside to estimate the Sun's location in the sky. In the case of morning (i.e., the rising Sun), he makes a decision of AM (from the Latin ante meridiem, meaning "before midday") according to the location of the Sun in the sky (before midday). Hence, the estimation of a clock indication needs some extra activity from a person to be “correct.”
Moreover, the indication itself needs to be improved because any pendulum clock shows the same indication twice daily. Obviously, a person sitting in a room below ground level has no idea about the right time because that person is unable to determine the location of the Sun in the sky and reach a conclusion about the actual part of the day—is it before or after midday? Hence, the indication of a pendulum clock is incomplete, at least relative to day and night.
The experiment continues. The person withdraws the thermometer “B” from the water tank and puts it on the table. After 10 minutes of waiting, both clocks show 8:10. The person takes the indications of both thermometers and writes down that information in the log again. Thermometers “A” and “B” show 21 and 26 degrees centigrade, respectively. Why do two identical devices show different indications? The answer is straightforward.
Both thermometers (and any other number) show matching physical properties of a measuring thing. That is temperature. In the case of the first stage of the experiment, both thermometers show indications of the thermal properties of liquid in the same tank. That property has some measurable value, as does any other physical property. Both thermometers make measurements by means of physical interaction between the measuring property of the water and the same property of their own. As a result, the thermal property of the water causes an indication of both thermometers. The same indication of each thermometer (inside level of their precision) is caused by the exact value of the comparable measuring property of the water in the tank.
As soon as thermometer “B” was withdrawn from the tank, physical interaction between the device and the measuring property of the water in the tank was broken, and that thermometer began to determine a property of a thin layer of air on the table surface, because of the sun heat that property has a different value and the device immediately begins to change its indication. As soon as thermodynamic equilibrium is established between the thermometer and surrounding air, the device stops changing its indication, and it shows the constant value of the measuring physical property.
Ten minutes later, when the clocks indicate 8:20, the person takes thermometer “B” from the table and puts it back into the water tank. After ten minutes of waiting, he writes down information on temperature in the log again. According to the indication on both clocks, it was 8:30. Thermometers “A” and “B” show temperatures of 23 and 23.1 degrees centigrade, respectively. Why did the devices change their indications?
That happened because the sun shining in the sky heats everything on the Earth's surface. In the case of the tank, it warms by the sun's rays and increases its temperature. That property changes the same property of the water (temperature) in the tank and raises its temperature too. Both thermometers have interaction with the same property of the water again. As a result, both of them have similar indications (in their precision level). Still, both indications differ from the prior indication at 8:00 AM because the measuring property has changed. Thermometers, as measuring devices, trace measuring physical properties perfectly. Moreover, they need no additional human activity to show correct indications.