How is fire formed?

Simply put, fire is a plasma state. The detailed explanation is as follows:

Although our earth is a member of the universe, it looks aloof in the vast universe, just like an island. Don't say that it gave birth to an extremely rare intelligent life in the universe (this kind of life is difficult to survive in other parts of the universe), but the material form on it is particularly different. The three common states of matter on earth-solid, liquid and gas-are extremely rare in the universe, while the fourth state of matter-plasma state is a lot of states in the universe. This is really a strange phenomenon.

What's more interesting is that when we let this matter cool down ... incredible new material forms reappear. Will this form of matter, which can only appear in a strict laboratory on earth, wander around a corner of the universe at will?

From the three states of matter to the fourth state.

Stone, iron and other objects are hard and not volatile, which is one of the basic characteristics of solid matter. We humans live in a world mainly composed of these solid substances. Of course, we can't live without water and air. They belong to liquid and gaseous substances respectively. Comparatively speaking, these soft and volatile substances occupy a larger proportion in our living environment and have a greater impact on our lives. In science fiction stories, human beings can still live in the future water world, but they can't live in a world composed entirely of rocks.

The transition between the three states of matter has long been recognized by human beings. They are at different temperatures, and the so-called freezing point and melting point determine the temperature at which the transition occurs. 100 years ago, people's understanding of the state of things was basically limited to this. Although Aristotle discovered more than 2000 years ago that the composition of the world includes fire in addition to these three states, he did not know what kind of substance fire is. In fact, this is the fourth state of matter-a manifestation of plasma.

If the gas is heated to thousands or even tens of thousands of degrees, what state will the substance take? At this time, the outer electrons of the gas atom will get rid of the shackles of the nucleus and become free electrons, and the atoms that lose the outer electrons will become charged ions. This process is called ionization. The so-called "ionization" actually means that electrons leave the nucleus. Besides heating can ionize atoms (thermal ionization), electrons can also absorb photon energy to ionize (photoionization), or charged particles can accelerate energy acquisition in electric field and exchange energy with gas atoms, thus ionizing gas (collision ionization). Ionized gas (whether partially ionized or completely ionized) is called plasma (or plasma state). The unique behavior of plasma is completely different from that of solid, liquid and gas, so it is called the fourth state of matter.

What is the existence mechanism of plasma? Matter is composed of molecules or atoms, and molecules are also composed of atoms. Atoms are made up of nuclei and electrons moving around them at high speed. The nucleus is positively charged, the electrons are negatively charged, and the positive and negative charges are equal, so the whole atom is not conductive to the outside world. The reason why electrons move around the nucleus is because its energy is not enough to break away from the binding force of the nucleus. If the material is heated continuously, when the temperature rises to several hundred thousand degrees or even higher, or when it is excited by a higher voltage, electrons can get enough energy to escape from the nucleus and be stripped off, becoming free-moving electrons. It's like a group of students running to the playground after class to play at will. At this point, the substance becomes a homogenate composed of positively charged nuclei and negatively charged electrons, which is dubbed "ionic slurry". The total amount of positive and negative charges in these plasmas is equal, so they are also called plasmas.

The material density of plasma spans a wide range, from the cubic rarefied interstellar plasma of 65,438 to the 22nd arc discharge plasma of 65,438, spanning nearly 20 orders of magnitude. The temperature distribution ranges from low temperature 100k (-10/73.15 C) to the 8th power of10-9th power k of ultra-high temperature nuclear fusion plasma.

Plasma is very abundant in our universe, from the flame lit by candles to the sun that breeds everything, from twinkling stars to brilliant galaxies. It can be found around us, in fluorescent lights and neon lights, in the dazzling incandescent arc; In addition, in the ionosphere of the earth's atmosphere, in the beautiful aurora and the tail of a meteor, wonderful plasma states can also be found. Looking at the universe, especially the plasma world, the temperature and pressure inside most luminous stars in the universe are very high, and almost all the substances inside these stars are in the plasma state. A hot star like the sun is a huge plasma. Solid, liquid and gaseous matter can only be found in dim planets and scattered interstellar matter. According to the calculation of Indian astrophysicist Shaha, 99% of the matter in the universe is in plasma state, but the common material state on the earth has become a rare treasure in the universe.

Why is this? It turns out that today's earth has evolved into a cold planet. In fact, the ionized composition of a substance at room temperature can be completely ignored. Even if the temperature rises to 10000 degrees, the ionization component is only one in ten million!

The research of plasma is mainly divided into two aspects: high temperature plasma and low temperature plasma.

The temperature of particles in high temperature plasma is as high as tens of millions or even hundreds of millions of degrees, which can make particles have enough energy to collide with each other and realize nuclear fusion reaction. The hydrogen bomb is the product of the first successful application of high temperature plasma in human history. The hydrogen bomb uses the atomic bomb as a "fuse" to emit high heat, thus producing high-temperature plasma, triggering intense nuclear fusion and releasing great destructive power.

If nuclear fusion is used for peaceful purposes and becomes a new energy source, it must be carried out slowly, continuously and controllably, which has been the focus of high temperature plasma physics research for half a century.

Space plasma research is also an important part of high temperature plasma research. More than 99% of the matter in the universe is plasma, and our sun is a huge plasma, so the study of space plasma plays an extremely important role in the aerospace era.

Generally speaking, the plasma whose temperature is below 654.38+ 1 100 million degrees is called low temperature plasma, which is mostly weakly ionized, multi-component and has strong interaction with other substances. Low temperature plasma can be produced by human technology, so it is widely used in many scientific and industrial fields. Now, low temperature plasma technology has become a very advanced industrial processing technology, for example, all future VLSI will rely on plasma processing; Low temperature plasma technology is needed in aerospace, smelting, cutting, spraying and other fields.

Superlarge Atoms —— The Fifth State of Matter

If the material continues to cool, cool ... until it can no longer be cooled, for example, it is close to absolute zero (-273.438+06℃). What strange state will the material appear at such an extremely low temperature?

At this time, a miracle appeared-all the atoms seem to have become the same atom, and you, me and him can no longer be separated! This is the fifth state of matter-Bose-Einstein condensate (hereinafter referred to as Bose condensate).

The discovery of this new fifth state has to start with 1924. That year, the young Indian physicist Bose sent Einstein a paper and put forward a new theory about atoms. In traditional theory, people assume that all atoms (or molecules) in a system can be distinguished. We can name one atom Zhang San and the other atom Li Si ... we won't admit that Zhang San is. However, Bose challenges the above assumption, that is, it is impossible for us to distinguish two atoms of the same kind (for example, two oxygen atoms) on the atomic scale.

Einstein attached great importance to Bose's papers. He applied Bose theory to atomic gas, and further speculated that at room temperature, atoms can be at any energy level (energy level means that the energy of atoms is arranged from low to high like a step), but at extremely low temperature, most atoms will suddenly drop to the lowest energy level, just like a building that suddenly collapses. A large number of atoms in this state behave like a big super atom. For example, the scattered soldiers on the training ground suddenly received the command of the commander to "March forward in a hurry", so they quickly gathered together and walked forward neatly like soldiers. Later, physics called this state of matter Bose-Einstein condensed state (BEC), which meant that atoms in different states suddenly "condensed" into the same state. This is a brand-new concentrated state of Bohai Sea.

However, the conditions for realizing the condensed state of Bohai Sea are extremely harsh and contradictory: on the one hand, it needs to reach extremely low temperature, on the other hand, it needs the atomic system to be in gas state. How does a substance remain gaseous at extremely low temperatures? This is really a headache for countless scientists.

Later, physicists used thin metal atomic gas, which has a good characteristic: it will not be liquid due to refrigeration, nor will it be highly aggregated to form conventional solids. The experimental object has been found, and the next step is to create conditions that can be cooled to a sufficiently low temperature. Due to the development of laser cooling technology, people can create a low temperature that is only one billionth of a degree different from absolute zero. In addition, any metal object can be moved without contact by using the electromagnetically operated magnetic trap technology. After continuous improvement of this experimental system, finally1June, 995, 7/kloc-0 years after the Bose-Einstein condensation theory was put forward, two American scientists Cornell, Weiman and German scientist kettler directly observed the Bose condensate in rubidium atomic vapor for the first time. These three scientists were awarded the 200 1 Nobel Prize in Physics. Since then, this field has experienced explosive development. At present, nearly 30 research groups in the world have realized the Bohai Sea condensed state in rare atomic gases.

The condensed matter in Bohai Sea has many peculiar properties, please see the following aspects:

The collective pace of these atoms is very consistent, so there is no resistance inside. Laser is the love condensation of photons, and a tiny laser beam is crowded with many photon streams with the same color and direction. Superconductivity and superfluidity are also the results of condensation in Bohai Sea.

The condensation effect of Bohai condensate can form a macroscopic electron pair wave propagating in a certain direction, which is charged and forms a macroscopic current without voltage.

The atoms in the atomic condensate are almost motionless, which can be used to design atomic clocks with higher accuracy for space navigation and precise positioning.

The condensed atomic matter in Bohai Sea shows photon-like characteristics. It is by using this characteristic that two research teams of Harvard University used Bose-Einstein condensate to reduce the speed of light to zero and store it.

The research of Bohai condensate oil can also be extended to other fields. For example, the interaction between atoms can be controlled by magnetic field, which can produce a phenomenon similar to supernova explosion in the fifth state of matter, and even use Bose-Einstein condensate to simulate black holes.

With the in-depth study of condensed matter in Bohai Sea, the horn of another thorough technological revolution has sounded.

Break through the fifth state and create the sixth state.

Is this the end of the material form? Not yet.

In the past few years, Bohemian condensed matter can only be formed by one kind of atoms, namely bosons, but fermions cannot be formed. What is a fermion? What is a boson? We need to enter the atomic world composed of elementary particles first.

It has long been known that atoms are composed of electrons and nuclei, and nuclei are composed of protons and neutrons. At the beginning of the 20th century, physicists discovered positrons and photons, and began to look for smaller particles. They found that the nucleus can be divided into smaller "tiny nuclei": neutrinos, mesons, hyperons, variants and so on. Physicists collectively refer to them as "elementary particles". The elementary particles discovered in the early days can be divided into four categories according to the "forces" they encounter: photons, leptons, mesons and baryons. In 1980s, gluons, W bosons and Z bosons were discovered. The "uses" of these elementary particles in the universe can be expressed as: particles that constitute physical objects (leptons and baryons) and particles that transmit force (photons, mesons, gluons, W and Z bosons). In such a quantum world, all members have four quantum properties: mass, energy, magnetic moment and spin.

Among these four properties, the nature of spin is the most important, which divides the particle kingdom into two distinct categories, just as it is as significant to divide human beings into men and women because of gender in this world. The spin of particles is not continuous like the earth's rotation, but rotates hop by hop. Scientists divide elementary particles into bosons and fermions according to different spin multiples. Fermions are electron-like particles with semi-integer spins (e.g. 1/2, 3/2, 5/2, etc. ). Bosons are photon-like particles with integer spins (such as 0, 1, 2, etc.). ). This spin difference makes fermions and bosons have completely different characteristics. No two fermions can have the same quantum state: they do not have the same characteristics and cannot be in the same position at the same time; Bosons can have the same characteristics.

All matter particles in elementary particles are fermions, which are the raw materials of matter (such as leptons, quarks and electrons in neutrinos that make up protons and neutrons); Particles that transfer force (photons, mesons, gluons, W and Z bosons) are all bosons.

Bosons account for only half of our universe, and the rest is the material world composed of fermions. Unfortunately, the condensed matter in Bohai Sea can only be formed by bosons. So why can't fermions form condensed state in Bohai Sea?

Enrico Fermi, an Italian physicist, and Dirac, an American physicist, pointed out that since fermions have semi-integer spins, their interaction will follow the Pauli exclusion principle (this rule does not apply to bosons). This principle points out that no two fermions can have the same quantum state, so they can't be in the same position in the spatial arrangement. When one fermion occupies the lowest energy level, the other fermions can only be arranged outward in turn. This very important principle excludes the possibility of tightly packed fermions, so even at absolute zero, these fermions cannot be the same and condensed. These subtle differences lead to a phenomenon: when they walk together, they always come first, and those who come later line up outside.

But fermions occupy a very important position in our universe, which is the cornerstone of the material world. In addition, the dream of high-temperature superconductivity pursued by human beings for a long time still cannot be broken in theory, and so far human beings still cannot break through the upper boundary-135 C to make superconductivity happen. As a kind of fermion, if we understand the mechanism of atomic fermion condensation, the secret of electron fermion condensation will be completely revealed. Moreover, the visible physical atom pairs in Fermi condensate simulate the composition of electron pairs in superconductors very similarly and become a visible tool, so people no longer need to look for the secret tunnel of superconductivity from pure imagination.

Rhapsodies more bizarre than dreams

At present, the top physicists in the field of particle and condensed matter physics dream of calling this state of matter the so-called "fermion condensed state". Semantically, the physical meaning of fermions means that particles cannot gather in the quantum ground state, while condensed state means that particles are deposited at an energy level. The term itself is a pair of contradictions, but it is wonderful that the contradiction between reality and theory has been calmed down by the skill of genius.

Solving this contradiction first comes from the inspiration of superconductivity. Badin, Cooper and schrieffer (both of whom won the Nobel Prize in Physics in 1972) put forward a theory to explain the superconductivity of metals-BCS theory. The basic idea is that electron fermions in metals will combine with each other in pairs at extremely low temperature, and this electron pair is called Cooper pair. The electron fermions combined into Cooper pairs show the characteristics of bosons, so physicists have found a way to make "fermion condensed state". They turned fermions into bosons in pairs, and two semi-integer spins formed an integer spin, so fermions acted as bosons, and all gases suddenly condensed into Abreu condensate.

If electrons can do this, why can't atoms? Using this theory, scientists began to experiment with another fermion 3He isotope. Later, people discovered the superfluid phenomenon caused by the condensed state of 3He‘s glass love: when superfluid liquid helium is carefully injected into the center of the beaker, it will immediately "climb out" of the cup mouth along the beaker wall from the bottom and overflow! But the mechanism of this condensation is very complicated.

After all, this is a successful start. Deborah Jean firmly believes that this method can achieve her goal. They first successfully realized the Fermi condensation of potassium -40 atomic gas, and these condensed gases have a special name-degenerate Fermi gas. Degenerate Fermi gas contains two kinds of fermions with different spin directions, which can be used to form atomic pairs and become boson-like binaries. This is a quantum gaseous substance in an unconventional sense, and it is also the only way for Fermi condensed state. Making them is also a difficult concentration process. When the temperature drops below 65.438+0.1 billion k, these atoms still do not form condensed state due to too strong atomic action.

How to persuade these fermions who believe in "lifelong independence" to form Cooper pairs, and then form condensed states? They used a magical magnetic field. At the temperature of 50 Kelvin (only 0.00000005K away from the absolute temperature), when the magnetic field reaches a certain frequency, the ultra-cold fermion gas begins to vibrate in the magnetic field of nuclear magnetic resonance, just like slowly finding one's partner in ballroom dancing. At this time, the magnetic field quickly withdrew, and the unpaired fermions at the periphery quickly dispersed due to the loss of constraints, taking away heat and further condensing at the center. A wonderful phenomenon has finally happened: the probe light wave passing through the center of Fermi gas is diffracted like hitting a crystal, but the gas will not diffract the light wave. Deborah Jean thinks that a magical solid substance must have been born. Later, it was observed by atomic array microscope that about 500 thousand potassium fermions in the condensate did form Cooper pairs.

Fermion condensation is different from electron fermion condensation in superconductivity. The former is a real atomic condensation, while the latter is a massless hole electron condensation. The former is visible atomic superfluid, and the latter is electronic superfluid in metal. Scientists call this state of matter an intermediate state between superconductors and Bohai condensate.

What is the difference between fermion condensate and superconductor? Firstly, atoms used in Fermi condensate are much heavier than electrons, and secondly, the attraction between atom pairs is much stronger than that of electron pairs in superconductors. At the same density, if the attraction of electron pairs in superconductors reaches the level of atom pairs in Fermi condensate, superconductors can be manufactured at room temperature immediately. Fermi body formed in ultra-cold gas provides a new material tool for studying superconducting mechanism, so this achievement is helpful to the birth of the next generation of new superconductors. The next generation superconductor technology can be applied to many fields and disciplines, such as power transmission, superconducting maglev train, superconducting computer, geophysical exploration, biomagnetism, high-energy physics research and so on.

Of course, the current technology can't make all fermions undergo Fermi condensation, and the obtained condensate is quite fragile-more brittle than glass! But this is only a technical problem.

[information]

Scientists who won the "Genius Award" in 2003.

There are new discoveries and inventions every day in the world, but our eyes are most concerned about those great discoveries that will completely change human understanding and creativity. On June 28th, 2004, a scientist announced such a revolutionary pioneering work to the world and created a brand-new substance in the world. This substance is a challenge to a basic theory and the eve of the complete realization of the macro quantum world. She's-

In 2003, Deborah Jean, a 34-year-old American female scientist, won the MacArthur Award, because she led her research team to create a new quantum gas substance-degenerate Fermi gas in 1999, which is generally regarded as a genius by scientists all over the world. The winner of this award has three harsh conditions: extraordinary creativity; Great achievements have been made and greater breakthroughs are promised; Its work will promote a series of highly creative work.

What are the characteristics of this mysterious quantum gas-fermion, which is on the edge of condensation at one millionth absolute temperature? This is the first time that mankind has made a theoretically predicted non-condensable atom extremely close to solidification and become like a light wave that can be emitted, which has taken a big step to break through the theoretical limit. It is roughly predicted that in the next few years, an extremely accurate atomic clock and a laser composed of solid atomic substances that have never been manufactured will be invented. Just entering 2004, this scientific feat, which has been at the forefront of the world, has taken an amazing step forward with the efforts of this talented scientist: human beings have created Fermi condensed solid matter for the first time, which is theoretically impossible to predict. This is the sixth material form created by human beings after 1995 created the fifth material form-Bose-Einstein condensate (BEC for short). Room temperature superconductors, which human beings have long dreamed of, will soon be manufactured in the direction indicated by this work. While marveling at the birth of a new world, we are once again convinced that the "genius bonus" is well deserved.

Source: big technology