There are concepts of infinity and infinitesimal in the mathematical world, yet there are limits to the vast majority of physical indicators in the objective world. Taking temperature as an example, there is an upper and lower limit for temperature.
The upper limit of temperature is the Planck temperature, which is about 1.4 × 10^32 degrees Celsius, a temperature that existed only in the first moments of the universe's birth. In everyday life, a few thousand degrees Celsius is already a very high temperature, and the Planck temperature is definitely the highest temperature that has ever existed in the universe. It should be noted that this temperature is derived from theory.
As for the lower limit of temperature, it is absolute zero, and the value is minus 273.15 degrees Celsius. This is the theoretical lowest temperature in the universe. The Earth's average temperature is 15 degrees Celsius, and the coldest place is in the South Pole, where it has been recorded to have reached minus 90 degrees Celsius, and absolute zero is only about 180 degrees Celsius lower than this.
However, such a low temperature is common in the universe, because the average temperature of the universe is minus 270.42 degrees Celsius, which is only 2.73 degrees Celsius higher than absolute zero.
Don't underestimate the difference between one or two hundred degrees, when the temperature is close to or reaches absolute zero, there will be a lot of strange phenomena that cannot be seen before. For example, when the temperature of some substances is close to this temperature, it will show superfluability, superconductivity and other characteristics.
Minus 273.15 degrees Celsius, this is not a direct measurement, but a derivation. Scientists first introduced it by using the Guy-Lusack law in thermodynamics. For an ideal gas, when the air pressure is constant and the temperature is lowered, its volume will shrink linearly with the change of temperature. Simply measure the law of volume with temperature over a certain temperature range and extend it to the case when the volume is zero, and the theoretical value of the lowest temperature in the universe can be derived.
Macroscopically, temperature is a physical quantity that represents the degree of heat and cold of an object. From a microscopic point of view, the degree of cold and heat of an object is expressed as the intensity of the thermal motion of the various large numbers of particles (such as molecules, atoms, etc.) that make up the object. The more intense the movement of particles in the system, the higher the temperature. Temperature is statistically significant and is the embodiment of the average kinetic energy during the thermal motion of a large number of particles, so for individual particles, temperature is meaningless.
The so-called thermal motion is that the particles that make up the object are doing irregular motion without stopping. Everything in the universe is in motion, motion is absolute, while stationary is relative. Since the thermal motion of particles cannot be completely stopped, minus 273.15 degrees Celsius in the objective world is never possible. This conclusion is called the third law of thermodynamics in thermodynamics.
What happens assuming the temperature reaches minus 273.15 degrees Celsius?
According to the thermodynamic point of view, if the temperature does reach absolute zero, the particles that make up the object must be in an absolutely static state, and the particle kinetic energy will be 0. Scientists used to think so, until the advent of quantum mechanics.
According to the view of quantum mechanics, when an object is in an absolute zero state, the kinetic energy of the particles inside it is not 0, but the lowest energy state in the quantum system, and these particles will still maintain the lowest energy level of motion in the entire system, not in an absolutely static state. However, from a macroscopic point of view, the object should be very close to absolute rest.
Usually any object with a temperature above absolute zero will continuously radiate electromagnetic waves outward. If the temperature of the object reaches absolute zero, because the particles in the entire system are in the lowest energy state, then these particles will not radiate electromagnetic waves or photons, in layman's terms, even the photons are frozen.
If the temperature of the entire universe reaches absolute zero, then the world will become pitch black. Now the average temperature of the entire universe is only 2 kai, which is close to absolute zero. If you reach outer space and stay away from the sun, you'll find that the entire universe is pitch black with only starlight. As the universe accelerates and expands, the temperature of the future universe will only get closer and closer to absolute zero, and the entire universe will become darker.
At this point, everything will fall into a cold silence, and there will only be extremely weak changes in motion in the whole of space-time, then time and space will have no meaning of existence, and all things will return to nothingness.
A digression. Some may ask, why is this minimum temperature minus 273.15 degrees Celsius instead of 0 degrees Celsius?
In fact, this is related to the setting of the temperature scale. The Celsius temperature scale is based on the temperature of the ice-water mixture at standard atmospheric pressure, not the minimum temperature. If the thermodynamic temperature scale is used, the value of the temperature cannot be negative. Because the thermodynamic temperature scale is based on the theoretical minimum temperature "absolute zero". In the thermodynamic temperature scale, the temperature of the ice-water mixture at standard atmospheric pressure is 273.15 kai.
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