Cosmic string

Theoretically possible space-time

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Cosmic string is hypothetical and theoretically possible space-time 。

Assuming that the cosmic string is valid, the "string" between the two regions obtained at the boundary of the domain when the first phase changes occur in different space-time.

This is a bit similar to the formation of crystal particles between the boundaries liquid , or when cracks are formed, water frozen into ice (ρ ＜ water). In our universe Such phase changes may have occurred in the early days as the formation of the universe. It should appear in the very early time of the universe big bang At the beginning, it is a very short moment between 0 seconds and 1 second.

Chinese name: Cosmic string
Foreign name: Cosmic string

Interpretation: Hypothetical and theoretically possible space-time
Name reason: It may be a closed ring and can be used for string oscillation

catalog

▪ Research
▪ Supersymmetry
two explain
three cause
four ruins

ten Physics or Philosophy
eleven Issue dispute

Basic Introduction

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concept

The physical concept of cosmic strings was put forward by Verenkin and others in 1981. They believe that the power of the Big Bang should form numerous thin and long pipes with highly concentrated energy, which are called cosmic strings. As we all know, when the pool water freezes in winter, at first, the liquid on the water surface.^[1]

form

Cosmic string

The shape of this material may be a closed ring, which can be used for string oscillation, so it is called cosmic string. The physical concept of cosmic strings was in 1981 Verenkin They believe that, Big Bang The generated power should form numerous thin and long Energy altitude Clustered tubes. These tubes are called cosmic strings. The nature of cosmic strings given by theorists is extraordinary. It's a bit like spider silk, but it's much thinner than atoms. You can walk through it without ever finding it. However, the cosmic string of one centimeter is larger than that of the whole the himalayas The quality of is larger, and the quality is variable, depending on its tension: the longer the tension, the tighter the tension, the greater the quality. It is also very strong. The activities of cosmic strings and their adjacent celestial bodies Cosmic expansion Closely related.

nature

Related books

Cosmic string is a hypothetical one-dimensional topology (Tu òòòòòòòòòòò) defects, in the fabric of time and space. When the hypothesis is established, the cosmic string space-time In the first stage of the change, the boundary between the two regions of the domain was obtained when they met. Another peculiar property that theorists endow with cosmic strings is that they either extend to infinity or form closed and endless Ring 。

viewpoint

It is always believed that nature has symmetry, such as Deficit And Lepton They are also three groups, or Antiparticle ， CPT conservation wait. But the physical world is not as symmetric as we think, such as CP is not conservative, but the largest asymmetry（ asymmetry ）Yes Fermion and Boson of Spin property Fermio wants spin Only two circles can return to the original scene, while the boson only needs to spin one circle.

theory

Cosmic string

Physicists established N=8“ Supersymmetry theory ”(Supersymmetry/SUSY) unified Fermion And Boson That is to say that the universe has eight dimensions besides four. The eight dimensional universe is called Hyperspace However, the extra four dimensions cannot be understood as time or space. The eight dimensional universe is inhabited by fermions, and matter can pass through spin from Four-dimensional space When transferred to Fermion to live in eight dimensions, it can be transferred from eight dimensions to four dimensions, that is, the boson can be replaced by Fermion Fermions can be converted into bosons. They are not different. The reason why we see their different spins is just an illusion that we are limited to four dimensions and cannot see eight dimensions.

Let me make a metaphor. If you can only feel three dimensions (up, down, back, left, right) on the earth, although we know the existence of time, our eyes can't see it. Our eyes only help us analyze the three-dimensional system. However, it is possible that the world is eight dimensions, and because the eyes can only distinguish three dimensions, you can't know.

Research

Cosmic string

Scientists particle be called Supersymmetry Supersymmetric partner, such as Gravitational neutrino （gravitino）， Photoneutrino （photino）， Gluon (gluino), while Fermion Our partner is called a particle, which is just an s in front of the fermion, such as a selectron. But we know that fermions can't spin out no matter how Boson And no fermions or bosons are found Supersymmetric partner For example, electrons are not transferred from any known boson. If every boson or fermion has its supersymmetric partner Number of particles It will be twice as big as 2012.

Supersymmetry

It is believed that Supersymmetry Partner quality is better than original particle It is many times higher and only exists in the state of high energy. We cannot be seen when we are in a quiet universe. Only in rare cases, Supersymmetric partner Will fade into ordinary Fermion and Boson Of course, we haven't detected the supersymmetric partner, otherwise it will be a sensation!

However, in the Supersymmetry theory Behind the scenes, String theory (strange theory) is slowly rising, which is also to unify the fermion boson. String theory believes that the world, whether bosons or fermions, is composed of one thing string. Strings are like a rope, but in fact they are really too small to move forward, so they form granular particles.

Some stars generate gravity and other huge attraction or repulsion, which may distort space and generate space-time fluctuations, that is, cosmic strings may appear.

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Spacecraft Virtual

At first physicists thought that String theory It must be ten dimensions, because only ten dimensional closed string theory can be repeated Regularization (Renormalization), re regularization is a solution for physicists Quantum electrodynamics An ingenious technique used in the emergence of 'infinity' in, in which many infinity problems are related to self interaction. Let me give an example of the infinity of electrons and electromagnetic fields:

Electromagnetic force Scope of influence Compliance Inverse square law , that is, 1 divides the square of the distance, and the distance between the electron and itself is 0, so the range affecting itself is 1 divided by 0, which is infinite, because E=mc2 , so Electronic quality Isn't it infinite! That is not consistent with the observation. The re regularization uses the method of infinite minus infinite to calculate the electron mass (because finite plus infinite is also infinite).

Dutch physicist Hendrik Kramers believes that the mass of an electron is composed of two masses -bare mass and infinite mass Composition, another electron mass is calculated by Maxwell Equation, which is infinite. Use the second mass to subtract the first mass, and the rest is the bare mass, which is the normal mass of the electron.

Of course, not everything can be re regularized. You'd better skillfully define the formula as: (infinite) - (infinite+less)=(less), otherwise the answer will be zero, or the answer is still infinite. The most successful example is to use heavy Regularization explain Lamb shift Lamb Shift particle (Spinning up and down) There is a little difference in energy, so the spin on electrons will release 21.11cm when they become spin off electrons microwave radiation 。

In fact, the feasibility of a theory in modern physics depends entirely on whether it can be re emphasized Regularization 。

cause

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one Big Bang Can't solve the "uneven" problem

Wormhole

In the remote ancient times, human beings were trying to understand the mystery of "the dark and yellow heaven and earth, the flood and famine of the universe". In modern times, what can explain the evolution of the universe relatively successfully is Big Bang Cosmic Model 。

Big Bang Theory In the 1940s, American physicists George Gamov (1904-1968). It believes that all matter and energy in the universe were once concentrated in one space-time At some point between 10 and 20 billion years ago, Primitive fireball For some reason, our universe was born and expanded to the state of this century.

However, the Big Bang model did not solve all the problems, for example, it could not explain Cosmic structure Local of Nonuniformity 。 this Big Bang Model The material of the whole universe should uniform distribution However, the matter in the universe is not like this, but is in a "lumpy" structure, even including galaxies Galaxy cluster 、 Supercluster 。 In this way, we have to find another way to solve this contradiction. This is exactly what astrophysicists came up with Cosmic string theory Reason for.

2. New discoveries of cosmic observation

Big Bang According to the theory, although most stars in the universe form clusters called "galaxies", galaxies form larger galaxy clusters; However, from the perspective of cosmology, the whole space is isotropic. However, with the rapid development of astronomical observation technology, new discoveries have forced people to reconsider this problem.

In the 1980s, the United States California Carnegie College Observatory Infrared optical telescope It is found that the galaxies are arranged in a very complicated way, "these galaxies look like carved ones, rather than exploded and sputtered ones". The more unusual discovery is the huge void and huge Galaxy chain 。 Discovered in 1986 the galaxy And its neighbors are moving towards Virgo Operation, which indicates that there is a strong gravitational source whose mass is equivalent to Solar mass 1019 times. Observations in 1989 confirmed the existence of this "galaxy continent" and found that it has a stable attraction to millions of other galaxies around it. Scientists from a scientific group (cfA) of Harvard Smithsonian Center for Astrophysics are doing red shift Celestial survey It is found that there is a foam like structure in the universe, that is, some regions of the universe are almost empty, which is called“ cosmic voids ”。 In 1989, the cfA scientific team surveyed thousands of galaxies and found that there is a galaxy about 500 million light years long, 200 million light years high and 15 million light years thick Supercluster "Giant Wall". This is the largest celestial galaxy chain in the known universe. They are like "pearl necklaces", crossed in the vast universe, like the magnificent Great Wall, so astronomers call it "cosmic chain" or“ The Great Wall of the Universe ”。 This shows that the apparent scale of cosmic objects is not galaxies or Galaxy cluster It may be something bigger. Their huge and ancient structure challenges the Big Bang model. For this reason, physicists began to consider modifying the relevant theory of the universe and introduced the "cosmic string model".

ruins

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Physicists can Cosmic string theory Infer current Cosmic structure How did it evolve. This theory enables physicists to explain the universe's Large-scale structure And propose accurate predictions that can be verified. If the cosmic string theory is proved to be correct, human beings Large scale structure of the universe Our understanding can be based on a solid foundation. So how did cosmic strings come into being?

According to the unified theory of "weak electricity" or Grand unified theory , physicists believe that cosmic strings appeared in the 10th to 35th seconds after the Big Bang. The closer to the Big Bang, the higher the temperature of the universe. Let's go against it Time arrow Look at this: the universe reached enough temperature 30 minutes after the big bang photon Generate a pair of "electrons"—— positron ”； In the third minute, the temperature is high enough to split the atomic nucleus into proton and neutron ； The first second, weak interaction Start to work; At 0.01 second, the temperature is high enough to split protons and neutrons into quarks, which pass through Strong interaction And combine. What was matter like before that?

In the extremely high energy state at the initial stage after the big bang, gravity Electromagnetic force 、 weak force There is no difference between power and strength. It only exists in one Unified field in However, at that time Ultrahigh temperature phase transition The cosmic string is the vestige of this ultrahigh temperature phase transition, which is a linear defect of phase transition. These defects contain the high-energy remnants of the Big Bang - extremely thin and heavy unified field. The existence of cosmic strings is based on Grand unified theory Extrapolated.

Characteristics

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The cosmic string formed by the above mechanism can be said to be an extremely dense energy line, which is very thin, with a diameter of only 10-29 cm (equivalent to Hydrogen nucleus 10 times the radius), and it is exceptionally heavy, with a density of 10 tons per cubic centimeter. After the formation of cosmic strings, a series of "reconnection" will take place (the two ends of each string are connected with each other or with the two ends of other strings) to develop into annular strings of different sizes or long strings across the universe. Because the density of this string is very high, the gravity is very strong. A finite (short) chord with two endpoints will quickly shrink to form a point and disappear. Therefore, there are only two kinds of strings in the universe: one is the infinite long straight string that runs across the universe, and the other is the annular string of various sizes.

According to the calculation, about 20% of the cosmic strings are circular, and other strings traverse the entire universe. The infinite cosmic string is not straight, but crooked. The collection of all strings forms a net full of space. Although the quality of the strings is very large, the bent strings are extremely tight, and their tension is greater, making them vibrate at a speed close to the speed of light, and sometimes collide with each other.

In the cosmic string network composed of ring strings and infinite strings, only ring strings can attract the surrounding matter to form various celestial structures, while the infinite strings do not attract matter. The entire cosmic string network is based on“ Self replication ”The way of evolution. That is to say, the whole structure of the universe does not change in the development process, but is magnified in the expansion of the universe. If the cosmic string is photographed at two different times, and then the previous photo is magnified at a certain ratio, the two photos will be very similar.

The universe is really made up of Reticular structure Is there any evidence?

It may be extremely difficult to observe the cosmic strings directly, because the annular strings have decayed due to gravitational radiation during the generation of galaxies. It is unknown whether long strings exist in the universe more or less. Moreover, this extremely fine structure does not emit visible light and any electromagnetic radiation 。 All these make it difficult to observe the cosmic strings. The difficult conditions for the generation of cosmic strings also make it almost impossible to simulate them in the laboratory. But even so, we can find out whether there really exists such a magical structure as cosmic strings through other methods.

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Whether the cosmic string exists or not, use it to Cosmic structure The presentation was very successful. It seems that all the newly discovered complex celestial structures, which are extremely troublesome for physicists and astronomers, can be explained at once. I'm afraid this is one of the reasons why physicists are so enthusiastic about cosmic strings.

Cosmic strings were born from the high-temperature phase transition at the time of the Big Bang. In the early days of the Big Bang, the pressure was too high for matter to gather. Ten thousand years after the Big Bang, the universe still consists of the cosmic string network and uniform distribution The ring string is not enough to attract matter to its surroundings. However, ten thousand years later, the pressure dropped sharply, and the matter began to gather. At this time, the energy of the cosmic string was less than when it was first formed, because of radiation Gravitational wave And lose some energy, but the string Density ratio Other substances fall much more slowly.

Cosmic chords Imbibition The mass of a substance is proportional to its own mass, so smaller chords attract relatively less substance; The larger chord not only attracts more material, but also attracts the smaller chord to its surroundings. In this way, smaller chords form galaxies, and larger chords form galaxies Galaxy cluster , even larger scale group structure.

This is based on cosmic strings Cosmic model Can predict the number and structure of galaxies and galaxy clusters. The cosmic string is at the high temperature of the Big Bang phase transition The layout structure of the cosmic string network should be reflected in various structures of cosmic celestial bodies. It can easily explain the holes, galaxy chains and Flaky structure Wait, and these are Big Bang Cosmic Model Difficult to explain.

probe

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The cosmic string is based on Gravitational radiation Having lost most of its energy, thus producing Gravitational wave It should be observed. However, the effect of this gravitational wave has not been measured (although astronomers believe that this is due to insufficient observation technology). In addition, cosmic strings should cause 2.7K Background radiation This kind of mutation has not been observed.

But there is also evidence of cosmic strings. Because cosmic strings can deflect light, quasars behind cosmic strings will present double images. If the light deflection is caused by a point like gravitational source, the resulting "multi images" will be odd; If it is caused by cosmic strings, then double images will be observed. In 1987, two American astronomers had observed four double images a quasar This may be the first time that humans have observed cosmic strings.

Australian astronomers claim to have clear evidence of the existence of cosmic strings. They observed a gravitational body with huge mass Galaxy And its neighboring galaxies converge at a speed of 1000 kilometers per second. Research has proved that the shape of this huge gravitational body is not spherical, but a long cylinder with a length of 2.4 million light years. They reasoned that this Gravitator It is a huge cosmic string ring.

It may take a long time to finally solve the mystery of cosmic strings.

Scalability

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Cosmic strings are long objects with small weight. They may be formed in the early stage of the universe, and they will be extended once due to the expansion of the universe. Moreover, a single cosmic string can cross the entire scale of the universe we observe at this moment.

The cosmic string should not String theory Although they are not completely unrelated, they are all objects with length and only small cross section.

The cosmic string has very large flexibility, and its tension is about 100 billion tons. If a cosmic string system is on the earth, it can accelerate the earth to 2899Km/h in one second.

Time travel

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Cosmic strings are interwoven in the whole universe, thinner than a particle of atoms, and have great density (under great pressure). This means that they will generate considerable gravity on anything passing by, so that things on the cosmic string can travel at a speed of over speed. Therefore, it is proposed that drawing two cosmic strings together or one cosmic string close to the black hole may Space and time Compress to a sufficient limit to produce closed timelike curve , realize time travel.^[2-3]

Physics or Philosophy

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Before experimental confirmation, String theory It belongs to the category of philosophy and cannot be regarded as physics completely. One of the reasons why experimental proof cannot be obtained is that no one has enough knowledge of string theory to make correct predictions, and the other is the current High-speed particle accelerator Not strong enough.

Scientists use the current and the new generation of high-speed particle accelerators under preparation to try to find the main Supersymmetry Predicted by the theory Superparticle 。 But even if it's super particle It is really found, which is still not strong evidence to confirm string theory, because it is just to find a particle that originally exists in this universe, but this at least indicates that the research direction is not wrong.

Issue dispute

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Although historically, String theory It is one of the branches of physics, but some people still hold that string theory cannot be tested at present, which means that it should (strictly speaking) be more classified as one Mathematical framework Not science. An effective theory must be proved empirically through experiment and observation. Many physicists advocate that string theory should be verified through some experimental ways. Some scientists hope to use European Organization for Nuclear Research （CERN， CONSEIL European Pour Retrieves Nucleaires) Large Hadron Collider , in order to obtain the corresponding experimental data - although many people believe that any theory of quantum gravity needs to be higher Order of magnitude To explore directly. In addition, although string theory is widely accepted（ Note: To be confirmed ）, but it has a lot of Equipotential Solution for. Therefore, some scientists claim that String theory Maybe not Falsification And has no power of prophecy.

Since the predictions made by any string theory that are different from those of other theories have not been verified by experiments, the correctness of this theory remains to be verified. To see the nature of strings in particles Energy level , which is much higher than the current experiment can achieve. String theory has many features of mathematical interest and naturally includes Standard model Most features of, such as non Abelian group And chiral fermions （chiral fermions）。 Because string theory may be difficult to prove experimentally in the foreseeable future, some scientists ask whether string theory should even be called a scientific theory. It is not available yet Popper Is falsified in its philosophical meaning. But it also implies that String theory More often seen as a framework for building models. In the same form, quantum field theory is a framework.

The idea of string theory has brought a huge impact on physics that exceeds the standard model in terms of suggestions. For example, although Supersymmetry It is an important part of string theory, but those that have no obvious connection with string theory Supersymmetry Models, scientists have also studied. Therefore, if the supersymmetry Large Hadron Collider It will not be seen as a direct proof of string theory. However, if the supersymmetry is not detected, the supersymmetry can only be seen with higher energy vacuum So its lack will not prove string theory wrong. Conversely, if solar eclipse During this period, it was observed that the gravity of the sun did not deflect the light according to the predicted angle, then Einstein's general theory of relativity would be proved wrong. General relativity has certainly been proved correct

On a more mathematical level, another problem is that, like many quantum field theories, String theory A large part of Perturbation It is expressed by formula (that is, it is an approximation to continuity rather than an exact solution). Although non perturbative technology has made considerable progress - including speculation space-time A complete definition satisfying some gradualness in Nonperturbative Sufficient theoretical definitions are still lacking.

In physics, a central problem in the application of string theory is that the best understanding background of string theory preserves most of the underlying theories of supersymmetry derived from "time invariant space-time": at present, string theory cannot deal with time dependence and Cosmology Background.

The two points mentioned above involve a more profound problem: in the current conception of string theory, because string theory depends on the background - it describes the perturbation expansion of fixed space-time background, it may not be the real foundation. Some people put Independent background (background independence) Quantum gravity theory Basic requirements of; This is especially true since general relativity has been background independent.

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