How is absolute zero calculated?

Absolute zero is obtained through complicated calculation, and it is not "absolute" zero.

1, approximate technical temperature record:

Compared with the 3K temperature of cosmic background radiation in outer space, the temperature of Bose-Einstein condensation is 170 * 10 (-9) K, which shows that it is very difficult to realize Bose-Einstein condensation in experiments. To create such an extremely low temperature environment, the main technologies are laser cooling and evaporative cooling.

An international research team composed of scientists from Germany, the United States, Austria and other countries created a temperature record in the laboratory that was only 0.5 Kelvin higher than absolute zero, while the previous record was 3 Kelvin higher than absolute zero. This is the first time in human history that the extreme low temperature has reached above absolute zero and within 1 femtogram.

The research team published a paper in the American journal Science, saying that they created this record in the process of realizing Bose-Einstein condensed state (BEC) of cesium atom by using magnetic trap technology. David prichard, a scientist who participated in the research, said that cooling the gas to extremely close to absolute zero is of great significance for accurate measurement, and their experimental results are helpful for making more accurate atomic clocks and measuring gravity more accurately.

Bose-Einstein condensation is a peculiar state of matter, in which a large number of atoms behave like a single particle. The "condensation" here is different from the condensation in daily life, which means that atoms in different States suddenly "condense" into the same state. To achieve this material state, on the one hand, it needs to reach extremely low temperature, on the other hand, it also requires the atomic system to be in a gaseous state. Chinese physicist Steven Chu once shared the 1997 Nobel Prize in Physics with two other scientists for inventing laser cooling and magnetic trap refrigeration.

Scientists said that they hope to use the newly reached lowest temperature to discover new phenomena of some substances, such as the state of atoms on the surface of the same object at this low temperature and the state of motion when the area of the motion channel is limited. German scientists who won the 200 1 year Nobel Prize in physics for discovering the new state of matter "Bose-Einstein condensation of rare gases of alkali metal atoms" commented that it was a milestone in human history to reach the temperature above absolute zero and within 1 Nakkelvin for the first time.

Ulrici Schneider, a physicist at Ludwig maximilian University in Munich, explained that technically, people can read a series of temperature numbers from a temperature curve, but these numbers only represent the probability that the particles contained in it are in a certain energy state. Generally speaking, the energy state of most particles is at or near the average energy level, and only a few particles are at a higher energy level. Theoretically, if this position is reversed, so that most particles are in high energy state and a few particles are in low energy state, the temperature curve will be reversed, and the temperature will go from positive to negative, below absolute zero. Wolfgang kettler, winner of the 200 1 Nobel Prize in Physics, also proved that there is a negative absolute temperature in the magnetic field system.

Schneider and his colleagues achieved this negative absolute zero with ultra-cold quantum gas of potassium atom. They use lasers and magnetic fields to keep individual atoms in a lattice arrangement. At positive temperature, the repulsive force between atoms keeps the lattice structure stable. Then they quickly changed the magnetic field so that the atoms attracted each other instead of repelling each other. Schneider said: "This sudden change makes atoms jump from their most stable state, that is, the lowest energy state, to the highest energy state they can reach before they can react. It's like walking through a valley and suddenly finding yourself standing on a mountain peak. "

At positive temperature, this inversion is unstable and atoms will collapse inward. At the same time, they also adjusted the laser field of the potential well to enhance the energy and stabilize the atom in its original position. Result. In this way, the gas changes from above absolute zero to below absolute zero, which is about a few parts per billion kelvin.

This research, published in many natural science journals, is a major breakthrough in human physics. Many scientists say that this will provide a path for discovering a new substance-dark matter.

2. In1877, Boltzmann discovered the relationship between the macroscopic entropy of the system and the thermodynamic probability, where k is Boltzmann constant. 1906, Nernst proposed that when the temperature is close to absolute zero? When T→0, △S/O = 0, which is the Nernst heat principle. On the basis of Nernst's research, Planck pointed out that the perfect crystal of various substances has zero entropy (S 0 = 0) at absolute zero, which is the third law of thermodynamics.

Extended data:

1, coldest place:

Astronomers in Chile have discovered the coldest place in the universe. The coldest place in the universe is called "boomerang nebula", where the temperature is MINUS 272 degrees Celsius, which is the coldest place in nature known at present and is called "cosmic ice box". In fact, the temperature of the Boumorang Nebula is only about 1 degree higher than absolute zero (-273. 15℃). This "heat" (because in fact, the temperature we are talking about is always above absolute zero) is the heat that has survived since the Big Bang as the origin of the universe. In fact, this is one of the most remarkable and effective evidences to prove the Big Bang theory.

2, vacuum energy:

At absolute zero, any energy should disappear. But even at absolute zero, there is another kind of energy, that is, vacuum zero-point energy.

The vacuum zero-point energy is named because the vibration of particles is found at absolute zero. This is the huge background energy contained in the quantum vacuum. Heisenberg's uncertainty principle points out that it is impossible to know the position and momentum of a particle with high accuracy at the same time. Therefore, when the temperature drops to absolute zero, the particles must still be vibrating; Otherwise, if the particle stops completely, its momentum and position can be measured accurately at the same time, which violates the uncertainty principle. The energy possessed by this particle at absolute zero vibration (zero vibration) is zero point energy.

Quantum vacuum is a state of matter without any physical particles, and the total energy of its field is at the lowest, which is the initial state of all material movements and energy fields, and its temperature is naturally at absolute zero. Such a state has unlimited potential for change. Zero point energy is produced by the appearance and annihilation of a pair of antiparticles produced by virtual particles (in quantum vacuum). It is inferred that the energy density per cubic centimeter in quantum vacuum is 10 13 joules.

Theoretically, vacuum energy appears in the form of particles, which constantly forms and disappears on a tiny scale. The vacuum is full of particles with almost various wavelengths, but casimir thinks that if two uncharged metal thin disks are close together, the longer wavelength will be excluded. Then, other waves outside the metal disk will produce a force that tends to bring them together. The closer the metal disks are, the stronger the attraction between them. 1996, physicists first measured this so-called casimir effect. This is conclusive evidence that vacuum zero point can exist.

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