Physics is essentially an experimental science. Physics experiment plays an important role in the development of physics and physics education. It can be said that physics cannot be understood without physical experiments. Because of this, in the research and teaching of physics, physical experiments have always been highly valued, and meticulous attention has been paid to the design of experiments, the manufacture and debugging of instruments, the control of experiments and the analysis of experimental results. I want to compare this kind of thinking experiment, but how much. Therefore, it is very necessary to study the history of thought experiment in physics vertically and compare it horizontally. Promote the research and teaching of physics.
A general visit to the thought experiment,
Galileo was a pioneer of modern physics. He made various contributions to physics. Among them, he discovered the law of falling body and inertia, which are the cornerstones of modern physics. Galileo's success benefited from taking the lead in using scientific physics experiments, and also from his original scientific method of combining physical experiments with ideological experiments. Galileo's outstanding work, he is a master of physics and a pioneer of thought experiments.
As we all know, for a long time, the understanding of physical phenomena and laws such as force and motion has bound Aristotle's theory. Aristotle believes that the speed, force and force of an object directly determine whether it is lowered by different ground objects with different speeds; It is also his fault that the weight is light and slow, but because there is no exact experimental and theoretical proof at present, no one pays attention. The first successful breakthrough of Aristotle's mistake was Galileo. Galileo's thought experiment was skillfully used to deny that this system was almost a wrong theory in Europe in 2000.
The speed at which an object falls is proportional. Galileo wrote in his book "On Two New Scientific and Mathematical Proves": "I suspect that Aristotle proved through experiments that when the weight of two stones is 10 times, in addition, from the same height, for example, 100 cups, the falling speed is not more than the position of the former 10." Galileo grasped this problem and designed the idea of analyzing and verifying the experiment. He pointed out: if Aristotle's statement holds, then heavy objects fall faster than light objects, so when heavy objects are slowly bound, obstacles fall faster and slower. As a result of the acceleration of slow drive, the object with linked falling speed must be the original speed between two objects, that is, less than the original falling speed of heavy objects. However, the falling speed of two objects tied together into a complex is much greater than the original weight. Aristotle asserts that the falling speed of the complex is mutually exclusive. So heavy objects don't fall faster than light objects, and two people should fall at the same speed. It is this thought experiment that strengthened Galileo's confidence and determination in the descent method.
Reject Aristotle's law of falling body, and further study Galileo's free fall quantitatively. On the basis of qualitative observation, the speed of free fall and the faster free fall are uniformly accelerated, and there are many assumptions about the method of falling from 1590 to 1592. However, under the experimental conditions, it is impossible to confirm this hypothesis immediately. Galileo will solve this problem by combining experiments with practical experiments. With the help of mathematics, he obtained the distance and time from standstill to uniform acceleration. When T: S/T 2 = constant, it does not include any speed, as long as S and T are measured directly.
However, free fall may be too fast to accurately determine the time. Galileo's falling body experiment, after repeated experiments, obtained the following results: the measured slope, not too fast movement T2 = C./> (2) The value of /2 ton changes with the change of the inclined plane, but the distance traveled by the ball is proportional to the square of time, and the only change is the proportional constant.
Galileo's thought experiment brought the use effect to the extreme-when the inclination angle was 90 degrees. The same is true of this free-falling object. He concluded that the motion of a free-falling body is uniformly accelerated.
Galileo was very satisfied with his original scientific method of combining physical experiments with ideological experiments.
With the in-depth development of Galileo's technology and consciousness activities, the thought experiments in physics are increasingly extensive, and the excellent thought experiments of physicists such as Mach and Einstein are consciously used. The branches of physics in a famous thought experiment. For example, in mechanics, Mach Newton's "rotating barrel" thought experiment. Reject Newton's absolute space and absolute motion. In quantum mechanics, the single electron diffraction experiment shows the fluctuation of particles, the potential of energy and the thought experiment, and the experiment proves the uncertain relationship between the ideal microscope and the electron beam single slit diffraction experiment. In the theory of relativity, it can be said that the development of physics is very difficult without thought experiment. At the same time, compare Einstein's "photon rocket" thought experiment. Its theoretical system cannot be established.
In this regard, Einstein once commented: "Galileo's discovery and his applied scientific reasoning method are one of the greatest achievements in the history of human thought, but they also mark the real beginning of physics.
Historical investigation of thinking experiment From the basic characteristics of thinking experiment physics, we can see that thinking experiment is a complex thinking and reasoning activity, which started in the form of real experiment. Its ideological business includes the following aspects: (1) Never or potential experiments can reach expectations; (2) the ideal abstraction or extrapolation of the real experiment, that is, the ideal experiment; (3) There is no realistic and contradictory experience, only logical abstract meaning and physical meaning. If we don't carry out this thought experiment, we can get a clear conclusion. Therefore, the thinking experiment in physics has the following basic characteristics:
Experimental operability
Thinking experiment is an unrealistic experiment, but it is called an experiment because this kind of thinking activity begins with the operation of the experiment according to the format. R. Harry pointed out that the so-called thinking experiment is the operation mode of imagination. "
According to their own understanding and thinking, the operator of thinking experiment uses the experience representation and language materials stored in his mind to imagine and operate through analysis, imagination, analogy, guess and logical reasoning.
Imagination tool of thinking experiment is the basic means of fictional interaction between subject and object. Einstein travels in a straight line at a constant speed, checks the synchronization procedure of two clocks, and determines the defined process at the same time: measure well, find their midpoint within two minutes, wait for the clock signal point of the next two observers of two clocks to be 7.5, and if the two signals intersect at the midpoint, the two clocks are synchronized. /& gt； The change of the image of the imaginary object is inevitable in the process of thinking experiment. The most important content of the imaginary subject and equipment used for this purpose, the imaginary object that plays a role in the observation process, reveals the essential things and relationships for research in order to achieve the expected purpose.
The logic is strict.
In a thought experiment, logical reasoning is his basic point. Physicists experiment with ideas and concepts, and have full freedom of imagination: rich experience and scientific knowledge, the research objects are completely related, and the directions of related hairs are random. When a lot of image materials and experiences appear in physicists' minds, expansion and connection often carry related concepts and relationships, which are related to the following logical thinking and the thinking before the predetermined goal. Logical reasoning, it even accepts the opposite empirical facts or some "physics", rather than the representation of laws by thought experiments.
Therefore, the operation of thought experiment, while imagining the process of free development, the logical movement, middle and logic of this process play a leading role, guiding and controlling imagination, and still imagining copper stink, but don't think about it. The logical movement of imagination began to operate, and the image propaganda of imagination provided a reliable material basis. Complementarity and mud are a whole.
Very creative
The purpose of the physicist's thought experiment is to reveal the internal laws of things, so there is no precedent to explore and it is very creative. Einstein and infeld pointed out in the Evolution of Physics: "The purpose of any theory is to guide us to know new situations, inspire us to do new experiments and discover new phenomena and laws. "Thought experiment box. Revelation of waterfall drop In the study of thermal efficiency and heat engine efficiency of Carcano cycle by French physicist and engineer in "thought experiment", his thought has two ideal isothermal processes and two adiabatic processes to complete an ideal thermodynamics through such an ideal thermodynamic cycle. "The highest thermal efficiency of Carnot heat engine is equal to the efficiency of T2-T 1/T 1 heat engine, which is a creative solution.
Positive effects of thinking experiment
Thought experiment plays a positive role in the development of physics, mainly as follows:
Strongly questioning the key role of using thought experiments often begins with challenging traditional theories, so as to expose the defects of the old theories vividly and accurately and refute the wrong old theories.
At that time, Aristotle summed up his mechanics in the prestige of the whole Europe: the original moving object still pushes, but it no longer pushes. This theory has a history of more than 2000 years in the minds of those in power. Galileo questioned the idea of carrying out experiments based on umbrellas. He thought that if a moving object is very long at a certain speed, it always keeps its current speed because of the external reasons that they don't increase or decrease the speed. This situation may only be possible in a horizontal plane. Moving along a slope, the acceleration of continuous downward movement, the acceleration of continuous upward movement and the deceleration of continuous movement, so the movement is the same only in the horizontal plane. If the speed is constant, the movement is not only different. Change the idea put forward? "Inertia", the new relationship between strength and speed of mechanical change, denies the relationship between strength and speed of the old theory.
A deep understanding of the application of innovation.
Thinking experiment, deepen understanding, open up new research directions and promote the development of physics.
Fifth, think that the experiment is the same as the real experiment
The relationship between thinking experiment and reality experiment is different in principle: in actual experiment, it is a scientific experimental activity, and it is a rational thinking activity that makes the reappeared thing (or process) initially higher than the actual experimental practice under the condition of excluding many external influences and highlighting the relationship between the main factors as much as possible. It is not divorced from reality and subjective imagination, but actually put into production. According to the format of experiment, practice goes deeper into the level of abstract analysis. Its reasoning process is a law based on logic, and it is a relatively independent scientific method.
Thinking experiment and real experiment are closely related and complement each other. Physical theories and laws are based on summarizing a large number of experimental facts, and physical assumptions and parameters also depend on the verification of real experiments. In a real experiment, physical equipment and other devices are used to obtain natural laws, strictly controlled objects and purposeful changes. Therefore, it is hoped that after observation, with the help of a rational thinking, the experience of materials in actual experiments and before experimental design can be analyzed and summarized. Sometimes, two real experiments provide empirical materials, which are often inextricably intertwined. Rational treatment of ideological experiments and practical experiments provides theoretical guidance. Galileo discovered the law of falling body and the law of inertia and saw it clearly.
The thought experiment in physics research also wants to be an irreplaceable scientific method experiment, and its rigorous scientific thinking and accuracy supplement lack real experiments.
In the development stage of modern physics, theoretical science, daily experience and intuitive human consciousness activities and deep feelings should all pay attention to the micro and macro fields that cannot be directly perceived, and the relationship between phenomena and essence of things is becoming more and more complicated and hidden. The equipment needed for physical research activities is more and more advanced and complex, and rational thinking is more prominent. As a scientific method, thinking experiment will be applied in a wider field.
The thinking experiment of investigation and analysis tells us that thinking experiment is one of the important ways to carry out in-depth physics research and teaching. Einstein said: "It is often more important to ask a question than to solve it. Solving a problem may be just a mathematical or experimental skill, raising new questions and new possibilities. To look at old problems from a new perspective, they need creative imagination, which marks real progress. " Therefore, on the basis of real experiments, we should strengthen our study, conduct thought-provoking experiments, and guide physics research professors to lead fascinating and fruitful lives.
refer to
[2] TS Kuhn: Thought Experiment, Tension, Fujian People's Publishing House 198 1.
[-3] WI.B. Bei Filic: "Scientific Research" by Art Science Press, 1979.
[4] Gao Wenwu: "Thought Experiment", "Dialectics Natural Communication", 1982.
[5] Seminar on Historical Physics of Beijing Physical Society, 1983.