newton
Einstein's description of gravity
Before 1905, Einstein was an unknown civil servant in the patent office. Speaking of 1905, I wonder if Einstein accumulated a lot of money or was inspired. Einstein published several Nobel Prize-level papers in this year, which was called Einstein's "miracle year". One of them is the epoch-making special theory of relativity.
[Name] Albert Einstein (Jewish theoretical physicist)
Einstein derived the special theory of relativity through mathematical deduction under the condition that all inertial systems satisfy the principle of relativity and predicted that the speed of light would never change. From the framework of special relativity, time and space are integrated, and the formation of a space-time (Minkowski's four-dimensional space-time) must be considered in a unified way. Generally speaking, the same event may happen to different people at different times. However, the special theory of relativity has a fatal flaw, that is, it only obeys the inertial system and does not obey the non-inertial system.
Inertial system and non-inertial system
So what's the difference between inertial system and non-inertial system? To give a practical example, please see the following picture: in a closed car, there is an object M, which is in smooth contact with the car, that is, ignoring the influence of friction, the acceleration of the car is A, but no matter what the motion state of the car is, the object M always stays still or moves in a straight line at a constant speed, so we say that the car is an inertial reference system, and on the contrary, M accelerates with the acceleration of A, so the reference system at this time is a non-inertial reference system.
To sum up:
1. If in a reference system, a free object stays still or keeps moving in a straight line at a constant speed relative to the reference system, then this reference system is an inertial system, and Newton's law holds.
2. On the other hand, if a free body keeps moving with constant acceleration or variable acceleration in a reference system, this reference system is non-inertial and Newton's law of motion is not valid.
The difference between inertial system and non-inertial system
We know that the real inertial system is hard to exist in reality, and most inertial systems are hypothetical. Therefore, after the publication of the special theory of relativity, Einstein thought that the special theory of relativity could only be satisfied under the condition of inertial system, and could not be extended to non-inertial system. After 10 years of painstaking research, Einstein finally published his general theory of relativity in 19 15.
Einstein's Unity of Time and Space
The same general theory of relativity also makes a fuss about time and space. The gravity described by general relativity is that the existence of matter will deviate time and space and cause bending. The distribution of matter determines the curvature of time and space and the curvature of time and space, which in turn restricts the trajectory of matter. Its mathematical expression is Riemann geometry proposed by mathematician Riemann. Riemannian geometry is a non-Euclidean geometry. It can be said that Riemannian geometry provides an important mathematical basis for the formation of general relativity.
The mass of the sun causes space-time to bend.
Interpretation of Maxwell's electromagnetic equation
In addition to gravity, another basic force that is ubiquitous in life is electromagnetic force. When it comes to electromagnetic force, the first thing we think of is that electricity can drive the motor to rotate, magnets can absorb iron filings, and both the stator and iron filings of the motor are stressed.
electromagnetic force
1785, the French physicist Coulomb found that the interaction between charges at two stationary points in vacuum is inversely proportional to the square of the distance and directly proportional to the product of the electric quantity. The direction of the interaction between the two points can be summarized as like charges repel and opposite charges attract, and along the straight line between them. F = k (QQ/R 2) (k is the electrostatic force constant) can be used to calculate the force quantitatively.
Coulomb law
At first, electricity and magnetism seemed to have nothing to do. Oster found that the outside of the electrified wire can cause the rotation of the small magnetic needle. A few years later, Faraday's excellent scientific intuition made him think that there seemed to be some subtle relationship between electricity and magnetism. Faraday is good at doing experiments. After an unintentional behavior, Faraday finally discovered that the magnet can light the bulb after passing through the electrified coil, and put forward the electromagnetic induction phenomenon. Later, on the basis of summarizing the previous research results, Maxwell finally unified electricity and magnetism, and gave the most perfect equations in human history-Maxwell equations, and Maxwell also became a master of electromagnetism.
Faraday
At first, Maxwell's equations were composed of more than 20 equations, but due to the conflict with classical mechanics, Maxwell's theory has not been paid enough attention. Maxwell died of overwork in order to popularize his theory. In addition, coupled with the limitations of mathematical development, Maxwell finally failed to give a simplified version of Maxwell's equations.
maxwell
1884, oliver heaviside and Josiah Gibbs restated in the form of vector analysis, and Maxwell's equations with only four equations in our textbook were thus produced! It can be seen from Maxwell's equations that Maxwell uses the concept of field to reflect the properties of a specific electric field through the relationship between the electromagnetic field (D, E, B, H) and the field source (charge Q, current I) in a certain area of space, and summarizes the properties of magnetic field, electric field, electromagnetism and electromagnetism.
Maxwell equations
Since Maxwell unified electricity and magnetism, electromagnetic force has been regarded as a basic force, and all its quantitative calculations can be covered by Maxwell equations. Different from other advanced scientific theories, Maxwell's equations have made great contributions to the real life of human society since their publication.
Einstein set out to unify gravity and electromagnetic force.
1915438+01June, 2008, mathematician Hilbert wrote a letter to Einstein after seeing the successful application of Riemann geometry in general relativity, in which he wrote: "Mathematically universal Maxwell equations can be regarded as the generalization of gravitational field equations, and gravity and electromagnetic force are actually a kind of force". After reading this letter, Einstein wrote back and said, "Your letter gave me great expectations. I have always wanted to build a bridge between gravity and electromagnetic force. "
Electromagnetic force and gravity
From 1922, inspired by his sage Maxwell's unified theory of electricity, magnetism and light, Einstein tried to describe gravity and electromagnetic force by establishing a unified theory, but unfortunately, he failed to make a breakthrough until 1955 died. Einstein has always unified electromagnetic force and gravity in a geometric way like general relativity. He put the four-dimensional space-time of Riemannian geometry and electromagnetic field together, and created the five-dimensional space-time thought, but every time it seems successful, Einstein will find the difference that goes against common sense.
Five-dimensional space-time
When Einstein tried to construct the unity of gravity and electromagnetic force, physicists discovered the strong interaction force and weak interaction force in the nucleus one after another, and people finally made a new breakthrough in unifying other basic forces. Since 1950s, American physicist glashow, inspired by Yang Zhenning and Li Zhengdao's parity non-conservation theory, predicted that electromagnetic force and weak interaction force are different manifestations of the same force. With the development of quantum mechanics, physicists believe that the function of transmitting force is accomplished by a vector boson, while photons are used to transmit electromagnetic force, and W-, W+ and Z0 transmit weak force. This was confirmed for the first time in the CERN super proton synchrotron of 1983.
The unification of electromagnetic force and weak force has also found a new way through quantum mechanics-quantum field theory.
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With the development of physics today, human beings have discovered the mechanisms of electromagnetic force, strong interaction force and weak interaction force. And a unified theory is compiled to describe it, which is called the standard model, but gravity has not been brought into this system.
But scientists seem to have found a way to explain it with quantum field theory, because in the standard model, every fundamental force will have a dielectric particle. For gravity, physicists have proposed that there will be gravitons as medium particles to transmit gravity, but so far, no gravitons have been found.