In the entire history of science, there is a rare period that matches the development of astronomy and physics from Copernicus to Newton . During this rather short period of time, scientific progress was both continuous and complete, fully demonstrating the natural development of event logic. Copernicus regarded the earth as a planet, and started with this revolutionary idea. After the work of Galileo, Tycho, Kepler, and others, he finally reached Newton's great synthesis of the physical world.
(I) Newton's life
1642 is destined to be an extraordinary year. The great genius Galileo passed away this year, and a greater genius Newton was born this year.
On Christmas this year ( Julian ), Issac Newton was born in a middle peasant family in Lincolnshire, England. He is a posthumous son and a premature baby. At the age of 12, he entered a local liberal arts middle school. In 1656, Newton's second marriage mother became a widow again and was recalled to help with the farm. Obviously Newton was a very crappy farmer, so he was sent back to school. However, his uncle found that Newton was very knowledgeable and strongly advocated sending him to Cambridge University for further studies. In June 1661, Newton entered , Cambridge Trinity College, . He graduated in early 1665 and obtained a bachelor's degree in in Literature.
1665 and 1666, in order to escape from the plague in London, Newton spent most of his time in his mother's farm. During this period, in addition to making some mathematical discoveries, he also conducted some experiments on color. Newton, who had been preaching to people, saw an apple falling to the ground, which inspired him to discover the law of universal gravitation. However, because some mathematical preparations were not done yet, Newton did not strictly deduce the mathematical expression of gravity at that time.
1667 After Newton returned to Cambridge, he was elected as a researcher at Trinity College , and obtained a master's degree in arts the following year. In 1669, at the age of 27, he became a professor of mathematics Lucas. During this period, Newton restored optical research and built the first reflective telescope , and also discovered the synthetic properties of white light. In 1672, Newton was elected to the Royal Society and reported his spectroscopic experiments on sunlight to the Society. Since then, Newton has done some research in mathematics and chemistry.
Newton's conversation and communication with his friends in the scientific community brought his attention back to the issue of gravity from time to time. In August 1684, Harley visited Newton, prompting Newton to enter a tense study of gravity problems. After 18 months, he wrote "HTM1 Mathematical Principles of Natural Philosophy ", which was published in July 1687.
was also in early 1687. Newton, as one of the representatives of Cambridge University, went to Congress to debate with James II on the issue of Cambridge University's privilege. From this event on, Newton gradually participated in public affairs and social activities. In 1689, he was elected as a member of Congress on behalf of the University of Cambridge, but he is said to never speak in Congress. Once he stood up, and the parliamentary hall suddenly became silent, waiting for the great man to speak. But Newton only said, "The window should be closed because there is through the hall ." After the disbandment of Congress in 1690, Newton returned to Cambridge and spent many years devoted himself to the study and interpretation of the Scriptures of " Bible ". He wrote a 1.5 million-word verification article on the most mysterious chapters of the Bible, and also calculated the age of "creating the world", which was around 3500 BC.
1692, Newton's busy brain finally failed. He suffered from mental breakdown and rested for nearly two years. Since then, Newton's physical condition has not recovered as before, but his thinking agility is still comparable to ten ordinary people. For example, in 1696, a Swiss mathematician challenged European scholars to solve two problems. After reading these two questions, Newton sent the answer anonymously the next day. The challenger saw through it at a glance and said, "I recognized the claws of the lion." When Newton was 75 years old in 1716, Leibniz asked another question, aiming to stump Newton. Newton solved it in one afternoon.
1695 Newton was appointed as the supervisor of the Mint, and he worked diligently to take charge of this new position.At that time, the quality of silver coins was greatly reduced, and the responsibility of supervision was to supervise the recast of the silver coins, which was of great importance. In 1699, after successfully completing this task, he was appointed director of the Mint and held this position until his death.
1699 he was also elected as a foreign academician of the French Academy of Sciences . In 1701, he resigned from his position as a researcher at Trinity College and Professor Lucas, but he also studied minor scientific issues from time to time, as well as preparing for the publication of Optics and the reprint of Principles. In 1703, Newton was elected president of the Royal Society and was re-elected year by year until his death. In 1705, Queen Anne was awarded the title of Newton as a jazz. In 1727, Newton suddenly fell ill while presiding on a meeting of the Royal Society. He died two weeks later on March 20 at the age of 85. Newton was buried in Westminster Abbey , with British heroes. In general, in the early history of science, there were very few geniuses like Newton who were quickly recognized at home and abroad. Newton's luck and Galileo's luck are in sharp contrast.
Newton has the virtue of modesty, and his two famous sayings are passed down by the world. In a letter to Hook in 1676, Newton wrote: "If I see farther than others, it is because I stand on the shoulders of giants." It is said that he also said: "I don't know what the world thinks of me, but I myself think I am just a child playing on the beach, and I am happy to find a smoother pebble or a more beautiful shell than others. The vast ocean of truth before me is still a complete mystery." But other people of Newton's contemporary era also stood on the shoulders of the same giants, and were also children playing on the same beach, but Newton alone looked farther and got smoother pebble and more beautiful shells.
(II) Discovery of universal gravity
Galileo's experiments show that it is not to maintain a uniform linear motion of an object, but to change this movement, an external force is required. This means that the problem that astronomers need to explain is not why planets move continuously, nor why planets do not move in strict circumferential orbits, but why they always move around the sun in a closed curve without moving in a straight line to run to external space. Newton's great contribution to astronomy was made in his thinking and answering this question.
According to some reliable information, the "Apple incident" is likely to be real. But there are still many problems to be solved from the landing of the apple to the discovery of the law of gravity. According to Galileo's law of projectile, Newton initially believed that the orbital motion of the moon and other planets was similar to that of the projectile , or it was a limit of the movement of the projectile: "A stone being ejected had to deviate from the straight path due to its own weight, and drew a curve in the air; finally landed on the ground. The larger the initial velocity of the projectile, the longer the distance before the stone landed. Therefore, we can imagine that as the initial velocity of the projectile increases, the longer the arc drawn in the air before the stone landed, until it finally crossed the boundary of the earth, and it could fly in the air without contacting the earth."
Newton was inspired by the landing of the apple, thinking that the force pulling the apple to the ground may be the same as the force that the earth controls the moon. In order to test the possible relationship between the force that makes the apple fall and the force that maintains the moon's movement in its closed orbit, it is necessary to figure out: (1) According to what law, gravity decreases with the increase of distance from the earth; (2) Calculate how much gravity will be at the moon's orbit based on this law and the measured acceleration of objects on the earth's surface; (3) Assuming that the moon's orbit is a circle centered on the earth, calculate the actual centripetal acceleration of the moon ; (4) Determine whether the accelerations derived from (2) and (3) are numerically equal, so it can be considered whether the two are caused by the action of the same force.
Newton's research was basically carried out according to this idea.If the linear velocity of an object moving in a constant circumference is v, the period is T, the radius is r, and the centripetal acceleration is a, then:
a=v2/r
v=2πr/Th
and according to Kepler's third law has:
T2/r3=k
k is the Kepler constant. It is not difficult to obtain:
a=4π2/kr2
This is the mathematical description of this force given: the rate of change of the object's falling speed is inversely proportional to the square of the object's distance from the center of the earth. Newton calculated the lunar acceleration determined by the gravity of the lunar distance from to according to the inverse square law. However, this value is too different from the actual measured results, and Newton was very disappointed.
Some people believe that because Newton used a smaller value for the earth's radius, it led to a deduction difference. But the more likely reason is that Newton had difficulty determining the effective distance between the Earth and the attracted object. Can the gravity of the earth, a large sphere, be regarded as just emitted from the center of the earth? A positive answer to this question will not be made until Newton founded the mathematical tool of calculus in 1685. Whatever the reason, Newton put the gravity problem on hold for 15 years.
1680 Hook wrote to Newton, suggesting that he study the problem of determining the path of the particle moving in the area near a gravity center that changes according to the inverse square law of square. Newton did not seem to reply to the letter, but did restart his early calculations and calculate that the orbit under the force of the inverse squared rule is an ellipse with the attraction body as the focus. In this way, the planet's elliptical orbit is a reasonable explanation. Then Newton further proved that if the motion around the center of gravity is an elliptical motion, and the center of gravity is a focal point of the ellipse, then the force must be a force with the inverse proportion of square.
Like Newton, Harley also derived the inverse square proportional law based on Kepler's third law, but failed to go further. Another scientist, Renn, also derived the law of inverse square proportion. But Hook claims that he has made a perfect explanation of planetary motion based on this law. Renn offered a bonus to see who of his two friends could make such an explanation in two months. Harley did not do it; and Hooker made an excuse for not giving out a timely explanation, and never took it out again. In August 1684, Halley visited Newton and asked him how the celestial bodies would move under the action of inverse square gravity. Newton immediately replied that he would move in an elliptical orbit. When Harley asked him how he learned, Newton told about the calculations in the farm in 1666, but the manuscript was lost at that time. Halley was very happy and encouraged Newton to continue the research and asked Newton to agree to send the research results to the Royal Society for registration and establishment of its priority.
This time the calculation was very smooth, because the relatively accurate earth radius value had been obtained at that time, and the calculus created by Newton allowed him to prove that a sphere with equal density at points equal to the center of the sphere when attracting an external particle, all its mass is concentrated in the center of the sphere. Therefore, Newton had every reason to regard the various objects in the solar system as particles with mass but without volume. It is said that in the face of an increasingly strong sense of success, Newton was so excited that he couldn't count it, so he had to let a friend continue to count it for him. In order to elaborate on all this, Newton began to write a book, which was completed 18 months later, called "The Principles of Mathematical Philosophy" (hereinafter referred to as "Principles").
(III) "Mathematical Principles of Natural Philosophy"
"Principles" was first published in Latin and was published in July 1687. Harley made an indelible contribution to the publication of "Principles". At first, the Royal Society was preparing to publish Newton's research results in the Journal of Philosophy, but after studying the previous parts, it decided to invest in the printing of this work. But at that time, the Royal Society was in a long-term financial difficulties and lacked enough funds to publish the book. In addition, Hook claimed priority for discovery, the Royal Society gave up its original plan. So Harley took on the publication of the book at his own expense. He also collected necessary astronomical materials for Newton, proofreaded samples, pointed out the ambiguity in the text, arranged printing and illustrations, etc.
"Principles" are divided into three articles, plus a very important introduction.The book defines various basic concepts in mechanics at the beginning, including mass, momentum, force, etc. Newton was the first to use these concepts accurately. In a note following these definitions, Newton assumes that there are absolute, real and mathematical time and absolute space and absolute motion. Absolute time passes evenly without any external thing; absolute space always remains the same and immobile; absolute motion is the translation of an object from one absolute position to another. The fundamental break between physics and Newtonian physics in the 20th century lies in the abandonment of these absolute and independent concepts of space and time.
"Principle" then describes the famous three laws of Newton's motion: (1) Each object maintains its static state or a linear uniform motion state, unless it is forced to change this state by external forces; (2) The acceleration of the object is proportional to the external force, and the direction of acceleration is the same as the direction of the external force; (3) For each action, there is always a reaction of equal magnitude and opposite direction. First, the second law of is directly deduced from Galileo's results, and the first law was clearly proposed by Descartes . The third law is Newton's discovery, which is what makes rockets' flight possible.
Principles After making the necessary mathematical preparations, the first article of "Principles" focused on the motion law of two particles under the action of square inverse gravity. On this basis, the influence of the sun as a perturbed celestial body on the moon's movement around the earth was discussed, thus theoretically explaining the various differences that have been observed in the moon's movement, and laying a theoretical foundation for the successful explanation of the -year-old difference and tidal phenomena. In this article, Newton also perfectly solved the problem that how the universal gravity of an extended object depends on its shape.
"Principle" The second article mainly discusses the motion law of objects in damped medium, and uses a section to specifically discuss the fluctuations in elastic fluids and the propagation speed of waves, further trying to calculate the propagation speed of sound in the air.
The third chapter of "Principle" mainly discusses the application of mechanical laws given in the previous two chapters in astronomy. At the beginning of this article, Newton gave evidence that the celestial bodies in the solar system move according to Copernicus' doctrine and Kepler's laws, and the orbits of celestial bodies depend on the gravitational force between them. Newton also theoretically calculated the degree of the equatorial uplift of the Earth, and pointed out that the attraction of the moon and the sun's gravity to the equatorial uplift of the Earth is the cause of the precession. This article also calculates various differences in the moon's motion from numerical values.
Newton's "Principles" is recognized as the greatest work in the history of science. In terms of its influence on contemporary and future generations, no other masterpiece can be compared with "Principles". It has been the basis of all astronomy and cosmological thoughts for more than 200 years after its publication. The movement of celestial bodies, the fluctuations of tides, and the appearance of comets of and , all of which can be explained by the same mechanical law. This really impressed people so much that its influence went beyond the scope of astronomy and physics. In various fields such as society, economy, and thought, people hope to imitate the principles of Newtonian mechanics , obtain several principles through observation of phenomena, and then use mathematical means to answer all questions. The facts may not be as good as they wish, but in this rational era pioneered by Newton, people did experience an unprecedented intellectual confidence.
(IV) Optical Research
Newton began to become interested in optical issues when he was still in college. At that time, he tried to build a telescope to eliminate the defects of the telescope. Refraction telescope will produce colored edges around the icons formed by the image, which is called color difference. In order to find a way to eliminate color aberrations, he decided to study color phenomena. In 1666 he bought an prism , until in 1672 he published a report on his prism experiment in the Journal of Philosophy, his first scientific paper. It reads: "Dark my room and drill a small hole in the window panel to allow the proper sunlight to come in. I put the prism at the sunlight entrance, and the sunlight is refracted to the opposite wall.When I saw the bright and strong colors that resulted from it, I felt it was a pleasing pleasure at first; but when I looked more closely, I was surprised that they were oblong; according to the accepted law of refraction of , , I expected them to be round. "
Newton conceived various possible explanations of his discovery and conducted various experiments. Finally, he concluded that sunlight and general white light are composed of various colors of light, which are the original innate properties of these light, not caused by prisms. What color will always belong to what kind of refractive index, and what kind of refractive index will always belong to what kind of color.
Newton's paper provoked him with Hooker, Paddy, Linus, Lucas and other contemporaries of physicists. Their questioning and Newton's answers were found in the Journal of Philosophy years after 1672. Through these discussions, Newton's thoughts on the nature of light gradually became concrete.
At first, Newton tended to combine the particle theory with the fluctuation theory to explain light. He believed that the universe was filled with a medium called ether , in which light traveled and stimulated vibration. However, he refused to be pure fluctuation theory , because it cannot be harmonized with the linear propagation of light. Newton's concept of ether mainly provides an explanation for gravity attraction. However, when this explanation was quickly replaced by the descriptive inverse square law of gravitation, Newton's interest in ether theory greatly decreased, especially because it is difficult to make the existence of ether medium parallel with the apparently unhindered movement of the planet. In addition, the discovery of polarization seems to only compare light to some kind of particles It can be explained. Therefore, Newton is increasingly inclined to the particle hypothesis.
1704 Newton's book "Opthalmology" was published. In the first article of "Opthalmology", some basic experiments by Newton about spectra : the formation of the spectrum, the measurement of spectral length, and the relationship between color and refractive index. After a series of experiments, Newton was able to explain the chromatic aberration of the refractive telescope. The reason for the chromatic aberration is that the objective lens focuses on a piece at different points on its axis. The different color components of the incident beam, and the eyepiece can only focus on one color component at a time, so other lights create ribbons. Newton further concluded that the chromatic aberration cannot be corrected, that is, the lens cannot eliminate chromatic aberration unless it is no longer a lens. Because he lost all confidence in eliminating chromatic aberration, Newton simply gave up the refractive telescope and advocated a reflective telescope. He may also be the first to create a reflective telescope.
Newton Experiments were also conducted to synthesize various colors of light into white light, and experiments were used to examine the causes of the color of the object: the color of the object is caused by the various light incident on it being reflected by the surface of different objects in different proportions, and these proportions depend on the thickness of the films that make up the surface of the object.
"Optics" second article discusses the color of the film. Among them, the central topic is the phenomenon called "Newton's ring".
"Optics" third article and the last article discusses the pattern diffraction phenomenon discovered by Limaerdi (1618-1663). Newton personally observed the diffraction phenomenon under different conditions, attributed it to the "turning" of light passing near the diffraction edge. In the last part, Newton gave 31 questions, they raised various explanations of light phenomena and gravity hypotheses, and pointed out the route of further exploration.
Looking at Newton's life's work, his contributions to the history of scientific development can be summarized as follows: (1) By laying the axiomatic foundation of mechanics itself, mechanics was established as an independent science; (2) He explained how to apply mechanics to various fields of natural science; (3) He established a clear synthesis of earthly and astrological physics by connecting mechanics with theoretical astronomy; (4) He opened up a new foundation for the theory and practice of optics; (5) He gave new meaning to the concept of natural science in mechanics; (6) Through all this, he created new prospects for the entire field of natural science.
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