Based on these two conclusions, Einstein then extended Galileo's theory of relativity and established his own new theory-special relativity. The so-called "narrow sense" refers to the situation that is limited to uniform motion.
The special theory of relativity points out that no matter mechanical phenomena, optical phenomena and electromagnetic phenomena, the laws they follow have nothing to do with the motion state of inertial system.
In this way, Einstein completely solved the contradiction between Maxwell's electromagnetic wave theory and other parts of physics based on Newton's laws of mechanics, thus creating a new era of physics.
The special theory of relativity was published in 1905, and the topic of the paper was "On Electrodynamics of Moving Objects". From this article, we can see that Einstein solved this problem by analyzing the concept of time, and also made a breakthrough on the issue of "relativity of simultaneity". He realized that time was suspicious, thought that time could not be defined absolutely, and pointed out that the measurement of elbow depended on people's understanding of "simultaneity". That is to say, the measurement of time interval must involve the judgment of simultaneity, that is, the coincidence of one event with another event in time. In his article on electrodynamics of moving objects, he made a wonderful statement on this point:
"If we want to describe the motion of a particle, we will give its coordinate values as a function of time. Now we must remember that such a mathematical description has physical significance only after we know exactly what "time" means here. We should take into account that all our judgments that work all the time are always about simultaneous events. For example, when I say,' That train arrived here at 7 o'clock', it may mean,' The short hand of my watch points to 7 and the arrival of the train is the same event.' "
Some people may think that it is possible to overcome all the difficulties in defining "time" by replacing "time" with "the position of the short hand of my watch". In fact, if the problem is only to define a time where this watch is located, then such a definition is enough. However, if the problem is to connect a series of events in different places in time, or-the result is still the same-to determine the time when those events occurred far away from this table, then such a definition is not enough.
Einstein realized that there is an inseparable relationship between time and signal speed, and the simultaneity of two events at different distances is related to the relative position of events and the way observers perceive their connection. If the distance of the event and the speed of the signal connecting it with the observer are known, the observer can calculate the time of the event and relate it to a certain moment he has experienced before. This calculation is different for different observers. However, before Einstein put forward this question, people always adhered to the principle that the time when an event is perceived only depends on the time when it occurs, which is the same for all observers. Einstein pointed out that the premise of the above principle is that if all observers' calculations are correct, they should get the same time for the same given event. However, Einstein convincingly proved that this premise is generally not established. He found that different observers with uniform relative motion generally measured different times for the same event. If two clocks move relatively at a constant speed, they will keep different times. You can't say which clock is accurate. A moving clock is always slower than a relatively stationary clock. For the speed of our daily movement, this effect can be ignored, but the closer the speed of the clock is to the speed of light, the more obvious the effect of clock slowing down.
To further illustrate this problem, let's do a "thought experiment". This is an "experiment" that doesn't need to be carried out in the laboratory, but only needs the mind to imagine. It is also a form of scientific experiment, which is favored by physicists. In fact, even middle school students often use it when doing exercises in physics class.
This experiment is like this:
Suppose there are two clocks A and B with the same mass in the satellite building of the Capital Airport. After calibration and synchronization, clock A is left in the satellite building and clock B is placed on the plane. When the plane flies from Beijing to Shanghai and returns to the Capital Airport, compare clock B with clock A, will their hands indicate the same time?
Some readers may blurt out: the same. But this is not the case. If these two clocks are accurate enough, we will find that clock B is slower than clock A. ..
This is the "clock contradiction" predicted by Einstein's theory of relativity. The contradiction mentioned here is not a contradiction in the logical sense, but a way of thinking contrary to common sense, the so-called "paradox".
According to the special theory of relativity, two synchronous clocks, one of which moves along ten closed curves at the speed v, return to the original position after one second, which is (V/c)2 slower than the clock that has never moved, where c is the speed of light. It can be concluded that for the same experience, the time interval measured by the clock B on the plane is △τ, and the time interval measured by the static clock 4 in the satellite building is △t, so
Because the speed of any object (in this case, an airplane) will never exceed the speed of light, and the value of √ 1-(V/c)2 is always less than 1, so clock B is slower than clock A ... When clock A passes 1 s, clock B only passes for seconds.
Under normal circumstances, the value of V/c is much less than 1 and about equal to 1, and the clock slows down very little. However, if we can launch a spaceship and make it fly relative to the earth at 0.98 times the speed of light, the speed of the clock in the spaceship will only be 1/5 of that on the ground. In this case, if we let the elder of the 25-year-old and 28-year-old brothers fly by spaceship for five years, then when he returns to the ground, the younger brother will find that he is older than his elder brother 1 year. Because these five years mean five years on the ground, my brother is 30 years old. However, during this time, the clock in the spaceship only passed 1 year, and my brother only grew 1 year, only 29 years old. Some physics books also call this phenomenon "twin paradox".
This wonderful phenomenon predicted by relativity has long been a hot topic for physicists. However, it was not until the atomic clock came out that it was possible to make a definite experimental verification.
197 1 year, the U.S. naval observatory put four cesium atomic clocks on a plane, set out from Washington, D.C., and flew around the world to the east and west respectively. The results show that the reading difference between the cesium atomic clock flying eastward and the cesium atomic clock parked at the observatory is one nanosecond. When flying west, the difference is 273 microseconds. Although the influence caused by the gravity of the earth is not deducted in this experiment, the measurement results show that the "twin paradox" does exist.