After reading 10 _ After reading _ What is gravity?

What is Gravity is a paperback book published by People's Posts and Telecommunications Publishing House. The author is Dr. Li Bo (Japan). The price of this book is 39.00 yuan and the number of pages is 292. The article gives some readers' thoughts after reading, hoping to help everyone.

What is gravity? (1): The content is good, but the translation is poor.

The things in the book are very basic and detailed, and there are many interesting places. The author uses some small examples to make some Dali theories smaller. From this small version of the story, readers may not know much about this theory. After all, some theories can't be explained clearly without a long speech, and which one can be finished with an example. But this little example is like a sharp knife. When you face a big piece of meat and you can't eat it, it will cut a small piece from the meat for you to taste. If you think it is delicious, you might as well read it. If you don't think it tastes good, don't watch it.

In addition to the content, there are also some problems in the translation of this book, and some places are confusing. I don't believe this is the author's intention. No matter how good a work is, it can't be spread all over the world without a good translation. In terms of communication, translation is as important as content.

What is gravity (2): approaching gravity in ignorance.

Approaching gravity in ignorance-what is gravity?

This is a book of semi-physics history and semi-frontier theory science popularization. It tells classical mechanics (Newtonian mechanics), electrodynamics-Einstein's theory of relativity, quantum mechanics and superstring theory in a very popular way. The reason why this writing method is adopted, as the author said at the end of the book, is because understanding the history of science can make people realize that today's theory is still in the general trend. In other words, the frontier theory, like the historical theory, contains many wrong views. Therefore, you cannot bind to it.

The author of this book is a Japanese physicist. Probably because the author is Japanese, he expressed such a meaning from time to time when writing: Look at this book, it's really troublesome! I'm sorry that some content didn't satisfy you! I don't think it's necessary to be polite.

When he wrote this book, he presupposed that he knew little about gravity and related theories. Therefore, the content of this book is almost to let readers understand the theory of gravity with almost ignorance. In this case, the content of this book is the most concise even among popular science books. Then for readers who have read relevant popular science books, the value of this book is relatively small, and many contents can be ignored, and there is not much valuable new content after ignoring it.

Probably because the author is a physicist, or he may have borrowed from Hawking's attitude in writing popular science books such as A Brief History of Time. As a result, it not only talks about gravity in combination with the history of physics, but also tells you what physics is and how to treat its development. For example, the second chapter 1 section of this book says that physicists are radical conservatives. It first says what physics is, and then says how to look at the development of physics:

"The progress of physics does not mean denying past theories and then establishing new ones. Of course, there are also many theories that are denied and disappeared in the hypothesis stage, but once the theory is verified by experiments and observations, it will be preserved as the basis of the next theory. "

At the end of chapter 8, the book talks about how to look at science:

"The so-called science is the work of establishing a new theory for understanding nature. Although the verification of the experiment is an important step, the progress of science is not only evaluated by this point. In my opinion, the extent to which new ideas conceived in a certain field are accepted by scientists and how many new studies have been triggered is also an important benchmark to measure the progress in this field.

In other words, science is a free market for ideas. Strong and beautiful views will naturally gather many researchers, thus promoting the continuous development of this field. ……"

This kind of content should not be common in popular science books, which makes this book appear more sincere, unlike some popular science books. But as far as physical knowledge is concerned, there is still too little valuable content in this book.

What is gravity? (3): Introduction to the physical world.

It is often said that there is no right to speak without comparison, so I should belong to the category of no right to speak. But from the most intuitive feeling of reading this book, it should not be misleading. After finishing the undergraduate course, I know E=mc except the name, and I know nothing about relativity and quantum self-study. This book not only vividly explains these theories and their development and dialectical process, omits the obscure derivation process, but also leads us to some interesting things in the history of science, such as the story of Hawking's bet and Newton's being hit by an apple. Generally speaking, it is a very good physics popular science book, written in 12. During this period, some changes have taken place in the physical world. The book points out the prediction of gravitational waves, emphasizing that XXX will be verified once gravitational waves are discovered. 16 years, gravitational waves have really been discovered by us. I wonder if the author is working overtime to study them at this time. Finally, I want to feel how long the brain holes of these physicists are, which is really awesome. I deeply admire it.

What is gravity (4): Gravity is the key to the mystery of the universe?

Gravity is the key to solving the mystery of the universe?

What is gravity? This is a great popular science book, without obscure theories and annoying formulas, but simply tells the history of gravity. This question reveals the historical process of human understanding of the world through what gravity is, looking up at the starry sky and overlooking the particle world as vast as the starry sky. Gravity is ether? Gravity is everything? Does gravity really exist? Great scientists Aristotle, Newton, Maxwell and Einstein all used their genius inspiration to let people know the space of the universe at the level of 65.438+0 billion meters (or 65.438+0 billion meters), and later scientists followed in the footsteps of giants.

Things are never what you do, and what you think is always what you think. The history of gravity has also verified a truth, "The only thing eternal in this world is change!" What is gravity? This will be the ultimate question? Will this question be the mysterious key to unlock everything in the universe?

This book was published by Turing. The author is a Japanese physicist (born in 1962), doctor of science (University of Tokyo, 1989), professor of theoretical physics at California Institute of Technology, director of the Institute of Theoretical Physics, and director of the Joint Institute of Mathematical Physics at the University of Tokyo, Japan. His major is elementary particle theory. His works include the trilogy of frontier physics, what is gravity, strength and weakness, and superstring theory.

Key words: force, ether, gravity, relativity, tidal force, GPS satellite positioning, wave-particle duality of light, quantum mechanics (Schrodinger's cat, everything is uncertain), string theory, superstring theory (supersymmetry "supersymmetry").

First, the theory of physics is developing at the speed of "1 100 million" meters.

1 100 million * 1 100 million * 1 100 million meters (the end of the universe seen through light energy) Perhaps Einstein's language "gravitational wave" can unlock the veil of such a big world.

1 100 million * 1 100 million meters (the size of a galaxy) Einstein's theory of relativity.

10 billion meters (lunar orbit) newtonian gravity

1 ~ 2m (the height of a person) is macroscopic upward and microscopic downward.

1 100 millionth of a meter nanoscience Maxwell electromagnetics

Standard model of elementary particles 65438+ billionth * 65438+ billionth quantum mechanics, superstring theory.

Second, the macro direction of the universe.

1, gravitational force and incredible properties

1. 1 gravity is "force"

First, gravity is "force". What is force? In Aristotle's time, people thought that matter was divided into four elements: water, fire, earth and air. In order to explain the motion of celestial bodies, people classify objects in the sky as ether (the fifth element). Newton subverted this view and clearly defined "force", that is, everything that can change the motion state of an object is "force". According to Newton's definition of mechanics, physics is established as a knowledge to describe the phenomena produced by the action of "objects" and "forces" on physics. The free-falling motion of an object is bound to be influenced by a kind of "force" called gravity, which changes the motion state of the object.

1.2 the strength of gravity (that is, what is the size? )

Very weak. Henry cavendish proved that there is universal and weak gravity between objects by torsion balance experiment.

1.3 gravity can work even if it is separated.

Gravity can act even if it is separated, and the theory of gravitational field is deduced. In a magnetic field, when magnets are attracted, particles with conductive power come and go between them, and so does gravity. There are also invisible particles that conduct gravity between the apple and the ground and between the moon and the earth. Let's call this particle a graviton, but it has been found so far.

1.4 gravity has the same effect on all objects.

Mass indicates the difficulty of changing the motion state of an object, and weight indicates the strength of gravity. Why did the apple and the shot put land at the same time? Why do "the difficulty of moving" and "the strength of gravity" just cancel each other out?

1.5 gravity is "fantasy"

Although gravity can't be shielded like electromagnetic force, it can make people feel the function of gravity (people who fall freely can't feel gravity, and Einstein himself said it is "the best inspiration for life"). Gravity has an incredible property, which will change because of different viewpoints.

1.6 gravity is just right.

The reason why the universe can give birth to celestial bodies and galaxies after a long time and give birth to life like ours is because gravity is "just right". What is the inevitable principle of chance or existence? Of course?

1.7 The theory of gravity is not perfect.

The progress of learning is like digging. Hidden behind the front rock wall is the unknown world, and digging here will increase your knowledge. However, the unknown world we can understand is only a part hidden inside the rock wall. There should be a wider unknown world in the deeper place, but we don't even realize that there is a wider existence. It was not until I got there that I began to face the unknown world and encountered puzzles that I had never thought of before.

2. Einstein's Theory of Relativity

2. 1 Einstein's special theory of relativity (one-dimensional, flat space) and e = MC * C.

The two theories of physics, Newtonian mechanics and Maxwell electromagnetism, have great contradictions on the issue of the speed of light. Radio waves, light and radiation are all electromagnetic waves. When the speed of an object is much slower than the speed of light, Newton's speed synthesis theorem can calculate a basically correct "approximate value", while in the "limit state" of the speed of light, a more accurate "ruler" than Newton is needed. Einstein's special theory of relativity published in 1905 holds that the observed speed of light is fixed in any state, and simple addition and subtraction are not valid for it. The change of time and space replaced the fixed speed of light. The closer we get to the speed of light, the slower time passes and the smaller the space shrinks. What is the time? Einstein thought that the flow of time is something that changes with different observers, and there is no "absolute time" that people generally think.

For thinking about the motion of objects, Newtonian mechanics is based on the premise that time and space remain unchanged. While that speed of light is constant, which contradict Newton's mechanical theorem. Einstein believed that if the speed of light is constant, then time and space only need to expand and contract.

E=m*c*c, the conversion of mass and energy becomes possible, and atomic bombs and nuclear energy become possible.

The derivation and proof of the formula show that the important property of the center of gravity is that its position will not change as long as there is no external force. Photons, light is composed of particles, that is, photons, photons have no mass (if they have mass, they cannot move at the speed of light). Xiaoming and Xiaohua throw the ball instead of shining. According to Maxwell's equation, the pressure of light is directly proportional to energy, and the calculated result is e = m * c * c The experiment of proton hitting lithium nucleus shows that the total mass is only reduced by 0.2% when it is transformed into two helium nuclei. The correctness of the formula is proved.

So Einstein's special theory of relativity connects Maxwell's electromagnetic theory with Newton's mechanical theory.

2.2 Einstein's general theory of relativity explains the theory of gravity. Why does gravity happen? Without gravity, gravity is a purely geometric phenomenon.

2.2. 1 gravitational force that can disappear and gravitational force that cannot disappear.

The gravitational force that can disappear can't be felt in the elevator of free fall; Inevitable gravity, the influence of the moon's gravity on the earth makes the earth stretch in the longitudinal direction and squeeze in the lateral direction. Therefore, the sea water on the earth's surface will gradually fill up along the direction of the moon and recede in the direction perpendicular to the moon, which is called tidal force.

general theory of relativity

General relativity holds that the "mass" of an object will also distort space and stretch time. Therefore, according to Einstein's theoretical thinking, gravity is just a kind of "fantasy". As long as there seems to be gravity, the true face of this phenomenon is "lack of angle" and the resulting "space distortion". The true face of gravity is the distortion of time and space. In our three-dimensional space, the earth revolves around the sun and the moon revolves around the earth because the distortion of time and space changes their direction of motion.

As long as there is an object, time and space will change, and the change of time and space will affect the movement of the object. The questions are "How does the existence of an object change time and space" and "How does an object move in changing time and space".

2.2.3 Verification of General Relativity

1) The Mystery of Mercury Orbit

The discovery of Neptune proved the victory of Newton's theory. Newton's theory of gravity also holds that if there are no other unknown planets inside Mercury (near the sun), its orbit cannot be explained, and this planet named Vulcan has never been discovered. The flaw of Newton's theory and the equation of general relativity are completely applicable to the movement of mercury, and Einstein won.

2) Eddington's observation of light bending

Einstein's theory predicts that gravity will bend light. 19 18 arthur eddington, England, through the experiment of observing the total solar eclipse, verified that the gravity of the sun made the light bend. This phenomenon is widely used in astronomy, especially in the study of dark matter, which is a "mysterious source of gravity" in the universe.

3) the existence of gravitational waves

Einstein's other prediction that the distortion of time and space should also produce waves and propagate in space at the speed of light has not been confirmed.

4)GPS navigation

According to the special theory of relativity, the time of a high-speed moving object is slower than that of a stationary object. The speed of each GPS satellite is 14000 km per hour. According to the special theory of relativity, its on-board atomic clock is 7 microseconds slower than the clock on earth every day. On the other hand, the general theory of relativity holds that gravity has a greater influence on time (the stronger the gravity, the slower the time, and it seems that the satellite will get faster when it looks at the place with strong gravity, that is, the earth, because of its high-speed rotation). GPS satellites are located in space about 20,000 kilometers above the ground. Because the atomic clock of GPS satellite has a higher gravity level than the atomic clock on the surface of the earth, the clock on the satellite is 45 microseconds faster every day. As a result of the combination of the two, the satellite clock is about 38 microseconds faster than the ground clock every day.

3. Einstein's Limit-Black Hole and the Birth of the Universe

The limit of Newton's theory, the "velocity synthesis theorem" of Newton's mechanics is fixed at the speed of light or transmitted to the limit. Starting from this defect, Einstein's special theory of relativity was born. On the other hand, the failure of Newton's mechanical theory in the mystery of Mercury's orbit was successfully explained by Einstein's general theory of relativity.

Similarly, Einstein's theory also has an unexplained "limit state". One of them is a "black hole". A black hole is a star from which even light cannot escape. Before explaining a black hole, let's understand the "escape velocity", which refers to the minimum speed required to escape the gravity of a planet. The astrophysicist Schwarzschild pushed down the radius of the celestial body whose escape speed is the speed of light, that is, the "schwarzschild radius". The size of this radius depends on the mass of celestial bodies, for example, the schwarzschild radius of the earth is 9mm. Nowadays, we find that there are many black holes everywhere in the universe, and quasars are supermassive black holes located in the center of galaxies.

Singularity of space-time, the point at which tidal force becomes infinite in finite time. The singularity of time and space involves the origin of the universe that we have been thinking about. Hubble's Law: The farther a galaxy is from the Earth, the farther it is from the Earth. Hubble's discovery clarified the expansion of the universe. The universe is happening strangely. The addition of some energy accelerates the expansion of the universe, which is "dark energy", which is as mysterious as dark matter.

The defects of Einstein's equation, Penrose and Hawking published their co-authored paper. If Einstein's equation is used to trace the past of the universe on the premise of observed mass and Hubble's law, then the initial universe will inevitably produce singularities. Hawking's scientific career began with proving that Einstein's theory was not perfect.

Third, particles in the microscopic world.

1. Is the true face of light a particle or a wave?

Newton thought that light was composed of tiny "particles", Huygens put forward the view that light was a "wave", and Thomas Young's double-slit experiment in19th century ended this debate. This experiment proves that light is a kind of "wave". Maxwell's electromagnetic theory further shows that light is an "electromagnetic wave". 1905, Einstein expounded in his paper that light has the property of "particle", which is the famous "light quantum hypothesis". This property unlocks the photoelectric effect that light is an unexplained "wave". Light consists of particles, and the energy of each particle is inversely proportional to its wavelength. Such as infrared rays, ultraviolet rays, X rays and gamma rays of radioactive substances.

Particles have both the properties of "particles" and "waves" (Rubin's pot).

2. Quantum mechanics (the theory that supports modern physics together with relativity).

Feynman's path summation and Schrodinger's thought experiment tell us that all kinds of physical quantities are "uncertainties" in quantum mechanics. Particles that stack all possible paths are called "quantum mechanical particles". Liu's early sci-fi novel "Ball Lightning" tells the sci-fi story that human beings capture macroscopic electrons, make objects (such as chips and people) in quantum state by using macroscopic electrons with different wavelengths, further study macroscopic atoms, and trigger a macroscopic nuclear war similar to an atomic bomb. The so-called macro electrons in science fiction refer to the electrons in quantum state (that is, using the uncertainty principle of quantum mechanics), which may or may not exist, but when the observer appears, the state of the electrons collapses to the basic state.

3. Combine quantum mechanics with special relativity to predict "antiparticles".

This is a puzzling thinking problem. Anyway, it is good to know the conclusion. As long as all particles combine special relativity with quantum mechanics, they can be pushed on, and any particle has a corresponding antiparticle. An uncharged particle like a photon also has antiparticles, but its antiparticle is itself. The combination of quantum mechanics and special relativity is quantum field theory, and the combination of quantum mechanics and Maxwell electromagnetism is "quantum electromagnetism".

4. Peel off the core of onion-superstring theory.

The book Onion in the Universe points out that the outermost skin of onion is the world we experience every day. After peeling off this layer of skin, we found that everything is made up of "atoms". But this layer is just "skin". After peeling off this layer of skin again, a "nucleus" appeared inside. Continue to peel off this skin, and the nucleus can decompose protons and neutrons. Now we find that protons and neutrons are just "skins", and they are filled with particles called quarks. Planck discovered the Planck length according to his own theory and gravity theory. Combining quantum mechanics with general relativity, the "superstring theory" appeared. The so-called chord here refers to the smallest unit of elementary particles as the root of matter. The superstring theory holds that all particles are composed of the same "string". The "string" mentioned here will also form quarks or neutrinos through different vibration modes.

Fourth, the end.

Light means warmth, food, safety and life, and human history is the history of chasing light. In the long process of exploring the essence of light, human beings have gradually revealed the mysteries of nature and the universe. The ancient Greek philosopher Anbi Dulles put forward a theory about the vision of light, which produced Euclid's Principles of Geometry. 1000 years later, the great Islamic scholar Ale? Hassan wrote an optical encyclopedia, explained the laws of light reflection and refraction, and made accurate calculations, thus overthrowing the theory of light vision. Countries and religions also study light and astronomy, authoritatively promulgate calendars, and Christian bronze calendars. Descartes proved the inverted image method by dissecting the bull's eye. The convex lens and concave lens made of glass enable human beings to explore the vast starry sky and the microscopic world so similar to the vast starry sky with better "eyes" (astronomical telescope and microscope invented by robert hooke).

Gravity and light, is gravity really the mysterious key to unlock the universe at the end of light? Newton, who discovered gravity, accurately measured the color of light with a prism and invented the spectrum. Starting from Maxwell's four equations, the equations relate electricity, magnetism and light to each other and reveal the essence of light. Light is electromagnetic wave, which spreads in the form of waves and sets off a new revolution in physical science. Humans find more light with different frequencies, visible spectrum, invisible light, ultraviolet light and infrared light (and the heat source of light). After 1600 failed experiments, the inventor Edison finally invented the tungsten filament incandescent lamp, which lit up the whole world. Newton's mechanical theory reached its limit at the speed of light, which contradicted Maxwell's equation. Einstein's special theory of relativity proves that the speed of light is eternal, the flow of time changes with different observers, and space will expand and contract. Newton's theory of gravity met with defects in proving the trajectory of mercury, and Einstein's general theory of relativity perfectly explained the trajectory of mercury. Relativity also meets the same limit conditions in black holes and dark matter. The big bang theory and the end of the universe are the end of light? The combination of quantum mechanics and special relativity is quantum field theory, and the combination of quantum mechanics and Maxwell electromagnetism is "quantum electromagnetism". Combining quantum mechanics with general relativity, superstring theory came into being.

Science and exploration, although scientific discovery stems from the curiosity of researchers, in the long run, many achievements have finally played a role in practical application. Mori Chongwen, a Japanese Fields Prize winner, commented on the basic mathematics he studied: "Although it can't play a role now, it will play an unknown role in 50 years or 100 years. Therefore, an inquiring heart is the best compass. "