Quantum mechanics explains the microscopic universe. It gives a mathematical description of atoms, electrons and other subatomic particles and how they interact. Unlike the large-scale world which can be described as smooth and predictable, the quantum world is very strange and chaotic.
Scientists have been trying to combine these two theories for a long time, because there will be problems and inconsistencies in some cases, which shows that both theories have not got all the answers. Take a black hole for example. Black holes are very dense and huge, but very small. Due to extreme gravity, all the mass is compressed into a small volume called singularity. Do we explain the black hole by relativity because it contains too much mass or by quantum mechanics because it is too small?
This is the problem. Scientists cannot avoid using general relativity and quantum mechanics at the same time. But when they try to do so, they can't get the answer. They began to provide meaningless predictions and answers. The laws of physics have just been broken.
String theory-originally called "superstring theory"-is a term used to describe a group of very closely related elementary particles and the mathematical model of their interaction. String theory attempts to unify the four forces in the universe-electromagnetic force, strong nuclear force, weak nuclear force and gravity-into a unified theory. This theory attempts to combine quantum mechanics with general relativity, so that scientists can understand the universe at all scales in any place or time without being destroyed.
String theory does this by rejecting the view that subatomic particles are point-shaped; On the contrary, they are tiny vibration energy called strings. The strings of string theory are very small. The average string is estimated to be about 10-33 cm long. The size of a single string is so small that any experiment we may carry out on elementary particles will not show its string-like nature-it looks like a point particle that scientists are familiar with.
In string theory, the known elementary particles are no longer described as dimensionless mathematical point objects, but as extended one-dimensional objects (hence the name "string"). These objects can be open rows or closed loops.
These strings are not "made of": they are the basic components of matter. Because the size of strings is limited, they can vibrate. It is said that these strings vibrate at different rates. These "notes" or vibration frequencies are the reasons for the different characteristics of quarks and atoms. According to this theory, all known natural particles are just different vibration modes of strings. Therefore, the string is the only truly "elementary" particle. One special type of vibration can produce muons, while the other represents electrons. By changing the vibration of the string, different particles can be produced.
By replacing those dotted subatomic particles with tiny vibration energy, scientists have opened a window to the universe, which relativity and quantum mechanics cannot do; A window can give us a deep understanding of gravity on the quantum scale, black holes and even the birth of the universe itself.
There is a problem. String theory is consistent in mathematics, and they need to describe strings beyond the familiar four dimensions. Assuming that string theory is a correct natural theory, these extra dimensions are obviously hidden outside our ability to detect them. The general assumption is that they are "compact"-so small that our daily experience can only reveal four big ones in our lives (three in space and one in time). This is a ten-dimensional world. Some people are curled up at the micro level, and some "big" dimensions are considered "real" by us.
Several theorists participated in the development of string theory. Some of the earliest and most important theorists are Gabriel Veneno (Italian physicist), Andre Neve and Joel Scheck (French physicist), John Schwartz and Pierre Raymond (American physicist).
Thank you very much for your trust and invitation.
Although your question is beyond the ability of an undergraduate majoring in physics, I still hope to answer it with my own knowledge.
First, the previous life of string theory
Quantum mechanics and relativity are two cornerstones of modern physics. Among them, the fastest development is quantum mechanics. However, one of the biggest problems encountered in the development of quantum mechanics is gravity. So far, the quantization of gravity has not been completed. As we all know, the grand unified theory or grand unified model has not been established. Countless cows in the field of science are on the way forward, and until today it is only a semi-classical formula.
Second, the dilemma of gravity quantization.
Anyone who knows quantum mechanics knows that quantum mechanics is described by operators. The so-called gravitational quantization means that the metric is regarded as an operator, and then they are determined by the reciprocity of the momentum operator of the metric and its yoke. In quantum mechanics and quantum field theory, reciprocity is simultaneous, so the quantization operator of gravitational field must be defined in the space-like division of time and space. But if we want to know whether the interval between two points is empty, we must first know that the vacuum expectation operator of the gauge tensor here should be determined by the quantum gravity operator, and the gauge expectation must be known before establishing this operator, so the theory falls into a logical cycle.
The second difficulty of gravitational quantization is that the gravitational field cannot be reorganized after quantization and becomes a "divergent" theory.
Third, the quantum field theory of curved spacetime.
Before solving the dilemma of gravity quantization, scientists are not powerless. The theory that physicists can use now is "quantum field theory of curved spacetime". This theory is a transition theory from classical gravity to quantum gravity. In theory, the gravitational field is not quantized and is still regarded as a continuous curved space-time, while the material field (electromagnetic field and electron field) is quantized. It can be said that this theory is still very reliable. It is a combination of general relativity and quantum field theory. Of course, this combination is unnatural. This theory is a bit like Bohr's quantum theory, or quantum mechanics before the second quantization; Matter is quantized, but electromagnetic field is not. The electromagnetic field is still regarded as a continuous field, not a photon. But before the quantization of gravity is completed, this theory can also solve many problems. For example, the research results about black holes and the early universe are based on this theory.
Fourthly, the birth of string theory.
As we said before, the quantized gravitational field can't be reorganized and become a "divergent" theory. Scientists have designed various schemes to solve this problem, and string theory was born under this background. Such as supergravity, loop quantum gravity, superstring and so on. Actually, it stems from the difficulty of customer service. 1968, Gabriele Veneziano hoped to find a mathematical formula that could describe the strength in the nucleus, and then found the Euler function with a history of 200 years in an old math book. This formula can successfully describe the strength he asked for. However, shortly after this formula was further understood as a small elastic "line segment" that can be twisted and shaken like a rubber band, Leonard Susskind (Leonard Susskind) discovered it, which developed the "string theory" in the future.
5. Why do scientists attach great importance to string theory and place high hopes on it?
Friends who are familiar with and concerned about scientific development know that the theory of string theory is difficult to test now, and there is still a lack of real experimental evidence to support it. And we need to make some adjustments to the universe we describe, that is, the space-time dimension in the universe must be more than the four-dimensional space we know. Scientists believe that these hidden dimensions may be so small that we don't find them. However, this has not dampened physicists' enthusiasm for string theory, mainly because string theory mainly tries to solve two seemingly incompatible physical theories-quantum mechanics and general relativity-and wants to create a "theory of everything" that describes the whole universe. Of course, the discovery of the God particle (Higgs particle) is a great benefit to string theory.
1968, physicist Venice thought that the ultimate part of the universe was not particles. Inverted chord structure, infinitely slender.
198 1 year, physicist Wei Lianjin proposed that open string linearity can be connected and sealed; Close the chord ring, which can be broken and extended.
The current cosmic string theory holds that if energy is absorbed, the string will stretch and stretch; If energy is released, the rope will curl and contract. Even, following the string law, the continuous space-time area is the smallest.
Cosmic string theory holds that, on the one hand, it can be described as particles that transmit energy fields when strings oscillate and fluctuate. Therefore, the ultimate composition of the universe should be formed by the fluctuation of strings. After all, it includes real fermions. Like quarks and leptons. Of course, it also includes virtual bosons. For example, like W+, Z0 and photons. On the one hand, it can be said that the string is broken and collided, and the interaction force is transmitted. So, when the string breaks, imagine that the charge pair is a positive particle and a negative particle. When disconnected, the electromagnetic force is transmitted. Then at the closed chord collision point, imagine particle pairs, which are positive and negative waves respectively. In annihilation, attraction is transmitted.
After all, cosmic string theory holds that no matter whether particles are virtual or real, no matter how they interact, they can eventually be unified.
However, the string theory of the universe depends on the height of time and space. Perhaps, at least 10 dimensions. Although, Einstein thought that four-dimensional space-time body. Moreover, according to the cosmic string theory, in the Planck range of 10ˉ33 cm, most of them are just hidden entanglements. Even any extra dimension that can be described as winding and curling is uncertain. Finally, the vibration and collision forms of strings are infinitely diverse.
Therefore, cosmic string theory allows interaction, virtual and real particles, and infinite changes.
In addition, following the string law, the area of continuous space-time is the smallest. So there is no extra energy to pander. Then, it is not difficult to imagine that the structure of the string, within the Planck range of 10ˉ33 cm, should be spherical. According to the view of string theory, the string ball is pulled by powerful extra energy. Although, an extra energy is infinitely powerful. However, like a black hole. In an infinitely strong energy field, it is not difficult to imagine a string ball, but it is limited. In the final analysis, the area of a continuous sphere is the smallest, and it can't be thinned and elongated.
Obviously, in cosmic string theory, there are no interactions and virtual and real particles. Because the infinitely strong extra energy binds the string to vibrate and cannot radiate particles. Moreover, the infinite extra energy binds the strings together to collide and cannot interact with each other.
Therefore, scientists put forward the theory of quantum mechanics, hoping to unify the interaction and the basic particles of the universe in one theory.
Now we can only wait and see!
Thanks for inviting me. The big boss downstairs has made it very clear. Supermodel Jun, please tell me more about your understanding of string theory.
String theory (and its upgraded superstring theory) can be used to describe gravity and all elementary particles. One of its basic ideas is that the basic units of nature, such as electrons, photons, neutrinos and quarks, look like particles, but in fact they are all different vibration modes of a small one-dimensional string.
String theory mainly tries to solve two seemingly incompatible main physical theories:
However, this theory is difficult to test, and we need to make some adjustments to the universe we currently describe, that is, the universe must have more space-time dimensions than the thinking space we know. Scientists believe that these hidden dimensions may be so small that we don't find them.
But string theory, as our most promising candidate theory of all things, is meaningless in the space-time below 10 dimension.
String theory, usually called "The Theory of Everything", is a relatively young science, including superstring, membrane, extra dimension and other unusual concepts. Scientists hope that string theory can solve one of the biggest mysteries in the universe, that is, how gravity and quantum physics combine.
String theory is an ongoing research work, so it may be a bit tricky to try to determine what science is or what its basic elements are. The main features of string theory include:
All objects in our universe are composed of vibrating filaments (strings) and energy membranes (membranes).
String theory tries to reconcile general relativity (gravity) with quantum physics.
There is a new connection (called supersymmetry) between boson and fermion, two fundamentally different types of particles.
The universe must have several extra (usually unobservable) dimensions.
According to which theories are proved to be valuable in the future, string theory has other possible characteristics. Possibilities include:
The string theory solution of landscape allows possible parallel universes.
The principle of holography explains how the information in space is related to the information on the surface of space.
Anthropic principle, that is, scientists can explain some physical properties of our universe with the fact that human beings exist.
Our universe may be "glued" to a thin film, allowing a new interpretation of string theory.
Other principles or features, waiting to be discovered.
Although string theory is a young science, it has made many remarkable achievements. The following are some milestones in the history of string theory:
1968: Gabriele Winnie Ciano first proposed a double * * * vibration model.
1970: String theory was born when physicists interpreted Winnie Siano's model as describing a universe of vibrating strings.
197 1 year: Incorporate supersymmetry and establish superstring theory.
1974: String theory proved to need extra dimensions. A graviton-like object was found in superstring theory.
1984: When there is no abnormality in superstring theory, the first superstring revolution begins.
1985: The theory of heterogenous strings is developed. The Calabi-Yoo manifold is shown compressed to an extra size.
1995: edward witten put forward the unified theory of motion as superstring theory, which started the second superstring revolution.
1996: string theory is used to analyze the thermodynamics of black holes, which is consistent with the early predictions of other methods.
The main problems of string theory may have the following two difficulties. First, it is difficult to explain how the string itself is expressed (or transformed) into real particles, such as how the energy string becomes a mass string. The key is the lack of a (mathematical) mediator with physical transformation function (such as the so-called Higgs field); Second, it is difficult to explain that more dimensions are transformed into three dimensions of space, such as why the redundant dimensions should be rolled up and why? The key to the problem may be that it is too dependent on mathematical derivation to find the answer, which is divorced from the physical essence.
Let's start with the definition of string theory: the basic view of string theory is that the basic unit of nature is not point particles such as electrons, photons, neutrinos and quarks, but tiny linear "strings" (including "open strings" and "closed strings" with endpoints or closed strings in a circle), and different vibrations and movements of strings produce various basic particles.
Although string theory has the advantages of intuition and universality, it is powerless to study solid space, high temperature and high pressure quantum space, sparse quantum space and large space outside the universe, and it is not helpful to establish the grand unified theory of the macro-micro world of the universe.
Quantum mechanics is a scientific theory that has been proved, and now it has entered the stage of theoretical transformation. There is no doubt about the correctness of its theory, and the research results and experiments in the last 50 years are also very sufficient. However, string theory is only a mathematical model at present. Different string theories have their own mathematical models, and M theory is a set of theories compatible with all string theories, but these theories are only mathematically self-consistent and have not proved the correctness of the theories. The universe derived from string theory has ten dimensions, while M theory needs eleven dimensions.
Who put forward string theory?
1968, an accidental discovery, solved the mystery of the physical world.
Gabriele Veneziano accidentally found something called "Euler β function" in a math book.
This function can accurately describe the four-particle scattering model of strong nuclear force, which was later called Veneziano model.
But he doesn't know what this mathematical equation really means. After him, Leonard Susskind and holger Nelson analyzed this mathematical equation in detail, and they found that this equation can describe the vibrating string. Therefore, string theory is an unexpected discovery in studying strong nuclear forces.
String theory predicts that the universe is 26-dimensional, which directly leads to the stillbirth of string theory. (26 dimensions, not to mention scientists, it is hard for most people to believe. )
Until the appearance of superstring theory (previously called Bose string theory), the universe dimension was successfully reduced to 10 dimension, and the "graviton" was predicted, which triggered a research upsurge of theoretical physics!
After crazy exploration, people left five kinds of string theories.
Can justify themselves, but they are independent of each other. Physicists don't know which of these theories is correct.
Soon, most people returned to their jobs, and superstring theory was put aside. ...
1995, the University of Southern California held a superstring conference, and Witten's speech awakened the superstring theory that had been sleeping for more than ten years. He unified five string theories with duality, and proved that the remaining five string theories are essentially the same!
In Witten's theory, the original chord of 10 dimension has one more dimension, and it becomes 1 1 dimension.
Simply put, it's like a piece of paper has only two dimensions, but when many pieces of paper are stacked together, a new dimension appears. So is Witten's theory. When many strings are stacked together, the 1 1 dimension appears.
Witten's report suddenly dispelled the haze of superstring theory. Superstring theory, which has been neglected for more than ten years, has been hit by the altar again and become the best tool to explain nature at present!
In addition, Witten speculated a theory.
He believes that there is still a unified theory that has not yet been discovered. He named this theory M theory, which may be the most fundamental basis of the theory of cosmic physics. Hawking, a British physicist, thinks that M theory may be the ultimate theory of the universe in his book The Grand Design!
At present, quantum theory is a new field that human beings are most likely to discover. At present, human beings can realize commercialization through quantum theory, such as quantum communication and microchip, which is a scientific field closely related to the next generation of industrial revolution.
String theory is the ultimate theory. At present, human ability is far from enough to prove, and experimental verification is still far from us. At present, it can only be demonstrated by mathematical methods, and the multi-dimensional space guided by string theory has not been discovered. Therefore, string theory can only stay in mathematics, but not in physics. Therefore, this is also the reason why string theory has no fire in quantum theory.