Why the universe has the lowest temperature, but the high temperature can be infinite?

Speaking of object temperature, it is the most familiar but unfamiliar concept. Everyone is familiar with the fact that we look at the weather forecast every day, the highest and lowest temperatures in one day, and then decide what kind of clothes to wear the next day. During this epidemic, we need to measure our body temperature when we go in and out of the community, and we also know clearly within what range our body temperature is qualified.

In most people's conventional understanding, the temperature should be infinite, the highest and lowest can be infinite, but the actual situation is far from it. The universe has a temperature limit, and the lowest temperature is absolute zero (0k), which is -273.438+05 degrees Celsius. According to the current scientific system, the maximum temperature is also limited. We can call it Planck temperature, which is about 1.42x 10 32 degrees, which is the data of14.2 billion degrees that often appears.

In order to understand the high and low temperature limit of the universe, we must first clearly know the concept of temperature. Macroscopically, temperature is a physical quantity to measure the hot and cold state of an object. Microscopically, it represents the intensity of molecular thermal motion of an object, or more accurately, the average kinetic energy of molecular motion. The more intense the micro-molecular movement, the higher the temperature value displayed by the object.

Then the temperature limit of the next room is easy to understand. The average kinetic energy of molecular motion can be seen from another angle, which is the speed of molecular motion. Under normal understanding, molecules can be at rest, and the fastest speed is the speed of light, so according to this definition, temperature limits can appear. But this is not true, because molecules can't be static, and it can't be the speed of light. According to Einstein's special theory of relativity, objects with static mass can never reach the speed of light. Although molecules are microscopic particles with small mass, they still have static mass.

Secondly, molecules cannot be completely at rest, which can be cut in from the perspective of quantum mechanics. A very core concept in quantum mechanics is uncertainty principle or uncertainty principle. The simple understanding is that we can't grasp the position and momentum of the quantum at the same time, and we can only express it by probability. For example, we can't say that a quantum is at point A, only what its probability is. Then the same microscopic particle can't be completely at rest, and then the position and momentum can be determined, which directly overturns quantum mechanics.

Therefore, from the thermodynamic point of view, when the average kinetic energy of microscopic particles is reduced to the lowest point allowed by quantum mechanics, the temperature of the object reaches absolute zero, that is, -273.6438+05 degrees Celsius (0k). But the lowest point of this theory is unattainable, so absolute zero is also a theoretical value, which can only be infinitely close, but can not reach absolute zero.

I see the lowest temperature limit of the universe, so let's continue to look at the highest temperature limit of the universe. As I said before, the speed of microscopic particles and the speed of light are the temperature limits, but we can't understand them like this here. There should be no limit to the highest temperature in the universe, but beyond a certain value it becomes meaningless.

At present, it is believed that the origin of the universe was the Singularity Big Bang 65.438+038 billion years ago, and then the universe expanded continuously to form what it is today. Theoretically, with the expansion of the universe, the temperature gradually decreases, so the temperature at the moment after the Big Bang should be the highest. We call it Planck temperature, and the value calculated by scientists is 65.438+0.4 billion degrees Celsius.

Why is it called Planck temperature? According to the viewpoint of quantum mechanics, at the moment of the Big Bang, we can make the time accurate to 10-43 seconds, which is the minimum span of time. We call it Planck time, so the temperature after this time span is the highest temperature limit Planck temperature. Actually, we can think about it from another angle. If the temperature of an object is higher than Planck's temperature, it will radiate electromagnetic waves with a wavelength less than Planck's length, but at present Planck's length is the minimum length with practical significance, and it is meaningless to be lower than this length under the current scientific system.

So far, we have not found the phenomenon of breaking through the highest and lowest temperature limits of the universe. The lowest temperature found by scientists in the universe is 1k(-272. 15 degrees Celsius), which comes from the pull back rod nebula, located in Centauri, 5000 light years away from the earth. Scientists have analyzed that the reason for this low temperature is that the nebula expands adiabatically in the early stage, and the gas expands rapidly to do work, so the temperature drops sharply.

It can be said that the current altitude temperature limit of the universe is not stipulated by anyone, but is only deduced under our current scientific system. Under the current scientific system, it is meaningless to be below absolute zero and above Planck temperature, and such a situation has not been found in real life.

Text/science black hole, image source network intrusion.