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1. What is the final unit of matter?
In the past 100 years, physicists have discovered a series of smaller and more basic physical units. These research results are finally summarized into standard models: leptons (like electrons and neutrinos), quarks, electromagnetic forces and weak interaction forces that bind these particles together. However, the standard model is not the end of the story, because it is too complicated to explain a basic particle table that is more complicated than the periodic table of elements and their interaction.
Now, string theorists generally believe that the basic particles in the standard model are actually small closed circles of vibrating strings (called closed strings or closed strings), and all particles can be obtained through different vibrations and motions of closed strings. Essentially, all particles are chords with the same texture. This seemingly strange idea can explain many rough outlines and characteristics of the standard model, but before decisive experiments verify it, people still need to have a deeper understanding and understanding of string theory.
2. Are there any conflicts between the principles of quantum mechanics and general relativity?
Quantum mechanics and general relativity are two very successful theories in the twentieth century, but surprisingly, these two theories are in conflict under the existing framework. Simply put, quantum mechanics holds that nothing is static and everything has ups and downs (uncertainty principle). General relativity holds that space-time is curved, and curved space-time is the origin of gravity. Combining these two theories, it can be concluded that space-time itself is experiencing quantum fluctuations all the time. In most cases, these fluctuations are very small, but in some extreme cases, such as in a very short distance, near the event horizon of a black hole, at the initial moment of the Big Bang, etc. These quantum fluctuations will become very important. In these cases, our existing theories (quantum mechanics and general relativity) are not applicable, and we can only get some absurd conclusions, and the results are infinite. Obviously, we need a more complete theory.
Surprisingly, the string theory developed from particle physics provides the answer to this question. In string theory, due to the ductility of strings (one dimension instead of points), the concepts of gravity and smoothness of spacetime lose their meaning at a distance smaller than the scale of strings, and the quantum bubbles of spacetime are replaced by "string geometry". Now, some problems about quantum mechanics of black holes have been solved by string theory. How to explain the initial singularity of BIGBANG with string theory is still a big unsolved problem.
3. Do we live in 1 1 dimensional space-time?
Cosmology tells us that the three dimensions of space we see with the naked eye are expanding, so we can infer that they were once very small and highly curved. A natural possibility is; There may be other spatial dimensions perpendicular to the three spatial dimensions we observed. These extra spatial dimensions used to be, but they are still very small and highly curved. If the scales of these dimensions are small enough, our existing observation methods still can't be directly inferred, but these dimensions will still be manifested through many indirect effects.
In particular, this is a powerful unified concept: different particles observed in the low dimension may also be the same particle, and in the extra dimension space, they are all manifestations of the same particle moving in different directions. In fact, extra dimension is an inseparable part of string theory: the mathematical equation of string theory requires that the space is 9 dimensions and the total dimension of time is 10 dimension. Further research shows that the more complete understanding given by M theory reveals the 10 dimension of string theory, so the maximum dimension of the theory is 1 1 dimension. Some recent developments also show that we may live on a low-dimensional film, but the gravity is still 10. In order to get realistic three-dimensional gravity, we can introduce "shadow film" or Randall-Sunderland mechanism. Randall-Sundrum mechanism is a new method to restrain gravity. At this time, the extra dimension may not be too small. By observing some strange phenomena, such as gravity deviating from inverse square law at a small distance, or particles accelerating or particles produced in supernova explosions scattering into extra dimensions, it seems that they have disappeared, and so on, we may be able to detect these extra dimensions now. String theory not only greatly expands people's thinking space, but also greatly expands people's activity space.
Basic principle: reveal the mystery of micro and macro.
In the last 30 years of his life, Einstein has been looking for the unified field theory-a theory that can describe all the forces in nature under a single all-encompassing and harmonious mathematical framework. Einstein's motivation for doing this is not closely related to scientific research as we usually think, for example, explaining known phenomena or experimental data of one kind or another. In fact, what drives him is a belief in the inherent beauty of the basic laws of nature: the deepest understanding of the universe will reveal its truest secret, that is, the principles it relies on are simple and powerful. Einstein is eager to reveal the mystery of cosmic activities with unprecedented clarity, and the moving beauty and elegance of nature displayed from this will make everyone who knows it for the first time feel the strongest awe, surprise and shock in his life.
Einstein never realized his dream, mainly because many basic features of nature at that time were unknown or little known. But in the past half century, people have established more and more complete theories about nature. At that time, Einstein enthusiastically pursued the unified theory, but returned empty-handed. Now, quite a few physicists believe that they have finally found a framework, and it is possible to sew this knowledge into a seamless whole-a single theory, a theory that can describe all phenomena. This is the theme of superstring theory "2006 International Conference on String Theory".
String theory or superstring theory is one of many new scientific terms such as quantum and quark, which has been included in popular dictionaries, but it is rarely explained clearly. Even people attending the meeting will tell you that superstring theory, like many emerging scientific research fields, involves many advanced mathematics fields and is not easy to master. What exactly is superstring theory? First of all, we find that string theory does have some elements of scientific fantasy when describing the activities in nature. For example, the world described by string theory is not the three-dimensional space and one-dimensional time that we see with our naked eyes. The reasonable explanation is that those extra spatial dimensions are not observed because they are very small. The high-dimensional nature of string theory is not difficult to understand. (see cosmic string p. 180 ~ 18 1).
There are many tiny extra dimensions in string theory, so the microscopic world is not as simple as the world we generally feel. On the macro scale, string theory may also be used to explain the beginning of the Big Bang and the internal behavior of black holes, and these problems are exactly where previous physical theories, including Einstein's general theory of relativity, failed. The string theory developed now is a quantum theory about time and space, so this theory looks strange.
A basic view of string theory is that the basic units of nature are not particles such as electrons, photons, neutrinos and quarks. These seemingly particles are actually closed circles of tiny chords (called closed chords or closed chords), and the different vibrations and motions of closed chords endow these different basic particles. So string theory can get the infinite change and complexity of the universe from some very basic and simple units. In string theory, people can naturally get gauge symmetry, supersymmetry and gravity, and these principles are either imposed in the original standard model or conflict with quantum theory. In string theory, they are all harmonious and unified, need each other and have their own characteristics.
So far, no one has observed the basic string. But as most people attending the 2006 international conference on string theory think, if strings are real, then the perfect combination of general relativity and quantum theory initiated by Einstein is not an unreachable hope.
The latest development of string theory: the second revolution
If the first revolution of superstring theory unified quantum mechanics and general relativity, then the second revolution of string theory in recent years unified five different string theories and eleven-dimensional supergravity, predicted the existence of a larger M theory, revealed some essence of interaction and space-time, and implied that time and space were not the most basic, but derived or evolved from some more basic quantities. If M theory is successful, it will be a revolution in human understanding of the concept and dimension of time and space, which is as profound as the two physical revolutions in the last century.
From the point of view of scientific research itself, it is the dream of international famous physicists since Einstein to study the quantization of gravity and its unity with other interaction forces, but it cannot be directly verified by experiments because of the extremely high energy involved. Nevertheless, the development of some technologies and methods has inspired many new physical ideas, such as Randall-Sundrum model and gravitational localization for solving energy level problems, the image idea and anthropic principle of huge possible vacuum in string theory and so on.
The latest progress in astronomy and cosmological observation will play a positive role in promoting the development of string theory. For example, a small cosmic constant (or dark energy) implied by the recently observed accelerated expansion of the universe provides guidance for the current development of string theory. On the other hand, to understand recent astrophysical observations and dark energy at a deeper level, there is no basic quantum gravity theory, and string theory is the only ideal candidate for quantum gravity theory at present. Their combination not only plays a guiding role in the development of string theory itself, but also greatly promotes the understanding and interpretation of cosmic observation.
String Theory in China: Preparing for the Third Revolution
In the first and second revolutions of superstring and its subsequent rapid development, China failed to play its due role in the international arena. On the whole research level, we still have a certain gap compared with international and neighboring countries such as Indian, Japanese, Korean and even Taiwan Province Province. There are great differences in understanding string theory in mainland academic circles. Some influential physicists, based on some judgments, openly express the view that string theory is not physics. Influenced by their status, this view is more easily accepted by most people in China, which restricts the research and development of string theory in China to some extent.
From the perspective of education and personnel training, the world-class universities in China, such as Peking University and Tsinghua, have long been seriously short of talents mainly engaged in string theory research, which indirectly restricts the professional choice of young graduate students and directly leads to the shortage of domestic research teams.
Fortunately, under the direct promotion of Professor Qiu Chengtong, with the establishment of the Mathematical Science Center of Zhejiang University, the annual high-level professional meetings held by the Center and Morningside Mathematical Center of Chinese Academy of Sciences, and the first-class scholars like Andy Strominger being invited to work in the Center, the research on string theory in China has been greatly promoted.
At the end of 2002, the interdisciplinary theoretical research center established in China University of Science and Technology has developed into a very active and attractive research center. Since its establishment four years ago, it has done a lot of basic work in the training and research of superstring theory by holding several working weeks and summer schools. Prior to this international conference on string theory, the International Center for Theoretical Physics and the Interdisciplinary Theoretical Research Center of China Academy of Sciences also held the Summer School of String Theory in Asia-Pacific region, which attracted more than 100 participants.
All these phenomena indicate that China's research on superstring theory is accumulating strong explosive potential under the calm appearance. Obviously, the overall level of a country or a research group is directly proportional to the probability of a breakthrough in scientific research in this country. This is the truth that "the East is not bright and the West is bright", and it is also the importance of the so-called scientific research culture construction. Ignoring the construction of scientific research culture and simply pursuing the Nobel Prize is an attitude of quick success and instant benefit, and the result is often "haste makes waste".
In front of the research of superstring theory, the prospect is broad and the road is difficult. It is a lively and lonely journey. The problems involved have a strong charm for young students and scholars, and at the same time have high requirements for the professionalism of researchers. The 2006 International Conference on String Theory is an opportunity for us-to expand the team, improve the level, and occupy a place in the world with the continuous improvement of the overall level. We are preparing for the third revolution of string theory and look forward to her early arrival.
Background link: three basic physical problems to be solved by string theory
What is the ultimate unit of matter?
In the past 100 years, physicists have discovered a series of smaller and more basic physical units. These research results are finally summarized into standard models: leptons (like electrons and neutrinos), quarks, electromagnetic forces and weak interaction forces that bind these particles together. However, the standard model is not the end of the story, because it is too complicated to explain a basic particle table that is more complicated than the periodic table of elements and their interaction.
Now, string theorists generally believe that the basic particles in the standard model are actually small closed circles of vibrating strings (called closed strings or closed strings), and all particles can be obtained through different vibrations and motions of closed strings. Essentially, all particles are chords with the same texture. This strange idea can explain many rough outlines and characteristics of the standard model, but before decisive experiments verify it, people still need to have a deeper understanding and understanding of string theory. Recently, people's understanding of the mathematical structure of string theory has made rapid progress, and many new components ("film") and new concepts (duality, holographic principle, noncommutative geometry) in string theory have been discovered. Now people call string theory and these newly introduced things M theory.
Do the principles of quantum mechanics conflict with general relativity?
Quantum mechanics and general relativity are two very successful theories in the 20th century, but surprisingly, they are in conflict under the existing framework. Simply put, quantum mechanics holds that nothing is static and everything has ups and downs (uncertainty principle). General relativity holds that space-time is curved, and curved space-time is the origin of gravity. Combining these two theories, it can be concluded that space-time itself is experiencing quantum fluctuations all the time. In most cases, these fluctuations are very small, but in some extreme cases, such as in a very short distance, near the horizon of a black hole, at the initial moment of the Big Bang, etc. These quantum fluctuations will become very important. In these cases, our existing theories (quantum mechanics and general relativity) are not applicable, and we can only get some absurd conclusions, and the results are infinite. Obviously, we need a more complete theory.
Surprisingly, the string theory developed from particle physics provides the answer to this question. In string theory, due to the ductility of strings (one dimension instead of points), the concepts of gravity and smoothness of spacetime lose their meaning at a distance smaller than the scale of strings, and the quantum bubbles of spacetime are replaced by "string geometry". Now, some problems about quantum mechanics of black holes have been solved by string theory. How to explain the initial singularity of BIGBANG with string theory is still a big unsolved problem.
Do we live in 1 1 dimensional space-time?
Cosmology tells us that the three dimensions of space we see with the naked eye are expanding, so we can infer that they were once very small and highly curved. A natural possibility is; There may be other spatial dimensions perpendicular to the three spatial dimensions we observed. These extra spatial dimensions used to be, but they are still very small and highly curved. If the scales of these dimensions are small enough, our existing observation methods still can't be directly inferred, but these dimensions will still be manifested through many indirect effects.
In particular, this is a powerful unified concept: different particles observed in the low dimension may also be the same particle, and in the extra dimension space, they are all manifestations of the same particle moving in different directions. In fact, extra dimension is an inseparable part of string theory: the mathematical equation of string theory requires that the space is 9 dimensions and the total dimension of time is 10 dimension. Further research shows that the more complete understanding given by M theory reveals the 10 dimension of string theory, so the maximum dimension of the theory is 1 1 dimension. Some recent developments also show that we may live on a low-dimensional film, but the gravity is still 10. In order to get realistic three-dimensional gravity, we can introduce "shadow film" or Randall-Sunderland mechanism. Randall-Sundrum mechanism is a new method to restrain gravity. At this time, the extra dimension may not be too small. We may now be able to detect these extra dimensions by observing some strange phenomena, such as gravity deviating from inverse square law at a small distance, or the acceleration of particles, or the particles generated in supernova explosions are scattered to the extra dimensions, so that they seem to disappear. String theory not only greatly expands people's thinking space, but also greatly expands people's activity space.
2006 international conference on string theory: the star of science shines
The conference was sponsored by Morningside Mathematics Center of China Academy of Sciences, Institute of Mathematics and System Science, Institute of Theoretical Physics, Mathematical Science Center of Zhejiang University and American Natural Science Foundation at the suggestion of the International Committee of String Theory Series Conference. More than 600 experts from all over the world attended the conference, and many famous theoretical physicists, such as Professor Hawking, Professor Gross, Professor Witten and Professor Strominger, will be invited to attend and give speeches at the conference.
Professor David David Gross.
Winner of the 2004 Nobel Prize in Physics, Chairman of the 2006 International Conference on String Theory. He is currently a professor of physics at the University of California, Santa Barbara, director of the Cabili Institute of Theoretical Physics, and chairman of the International Advisory Committee of the Institute of Theoretical Physics of the Chinese Academy of Sciences. Professor Gross has made a series of outstanding research achievements in theoretical physics, especially in gauge field, particle physics and superstring theory. He is one of the founders of quantum chromodynamics, the basic theory of strong interaction. He is also one of the inventors of "mixed string theory". 1985 was elected as an academician of the American Academy of Science and Arts, and 1986 was elected as an academician of the American National Academy of Sciences.
Professor edward witten.
An internationally renowned theoretical physicist, he is currently a professor at Princeton Institute for Advanced Studies and a professor at Charles Simonyi. His research covers many directions of high-energy physics and mathematical physics, and he is best at combining modern mathematics with the frontier problems of physics research. Typical examples of his application are Wess-Zumino-Witten term and topological term, anomaly and exponential theorem, Dirac operator and positive energy theorem, supersymmetry and Morse theory. His two-volume Superstring Theory, co-authored with Professor Green and Professor Schwartz, has been the Bible of string theorists since its publication.
Professor Stephen Hawking
A great man with a high reputation is called "Einstein alive". He took an important step to solve the conflict between two very successful physics theories in the 20th century-general relativity and quantum theory.
On March 1973 and 1 Sunday, Professor Hawking published a paper in Nature, expounding his new discovery that black holes have radiation (Hawking radiation). Hawking's new discovery is regarded as the most important progress in the field of theoretical physics for many years. This paper is called "one of the most profound papers in the history of physics".
Professor Andrew Strominger.
incumbent
Professor of Harvard University, academician of American Academy of Science and Art, mainly studying quantum gravity, string theory and quantum field theory. In the study of string theory, Strominger and his collaborators successfully described the phase transition process of spatio-temporal topological changes by using the luminescence and condensation of microscopic black holes. In addition, Strominger and his colleague C. Vafa successfully derived the Bekerstein-Hawking entropy formula of black holes by using string theory and statistical mechanics. This result shows that string theory may finally solve the problem of information loss of black holes proposed by Hawking.
Professor Cheng Qiu Chengtong
An internationally renowned mathematician, President of the 2006 International Conference on String Theory. He is currently a professor at Harvard University, a member of the American Academy of Sciences and a foreign member of the China Academy of Sciences. Professor Qiu Chengtong has made outstanding achievements in scientific research and won many honors. More importantly, he paid close attention to the development of basic research in China and closely linked it with his own scientific research development. Over the years, he has been using his international influence and activity ability to cooperate with various forces, and has done a lot of work for the development of mathematics in China.