# Is there a maximum temperature Planck temperature

### Question:

What is the lowest temperature that is possible?

The coldest natural place in the universe discovered so far is the Boomerang Nebula, 5000 light-years away. The temperature here is -272.15 degrees Celsius. But is this the coldest temperature possible?

Let us first consider what is actually meant by “temperature”. The temperature is a measure of the average kinetic energy of molecules. What does that mean? Solids as well as liquids and gases are made up of molecules that can perform various movements. In gases, the molecules move largely independently of one another. In a solid, on the other hand, the molecules are closely linked. If a molecule moves, it pulls the others along with it, so to speak: This is how sound waves propagate in the solid. For example, if you hold your hand against a hot object, energy is transmitted in the form of collisions of the molecules against our skin. We record the movement of the molecules as heat.

From all this it follows that the state in which all molecules are at rest corresponds to the lowest theoretically possible temperature - i.e. the state in which the average kinetic energy of the molecules is zero.

We usually use a thermometer to measure temperature, which is filled with a liquid (mercury, alcohol). This expands with increasing kinetic energy of the molecules. In physics, temperature is measured in Kelvin. On this scale, the absolute temperature zero point is 0 degrees Kelvin. On the Celsius scale, this corresponds to -273.2 degrees Celsius. The unit 1 ° C corresponds to 1 degree Kelvin.

Can absolute temperature zero be reached? According to the third law of thermodynamics, one can approach absolute zero as closely as desired, but it can never be reached exactly. The reason for this arises from the laws of quantum mechanics, according to which there is always a residual quantum mechanical movement, which is referred to as zero-point energy. In the laboratory, it has already been possible to cool small samples of gases and metals to a few billionths of a Kelvin.