Chapter 55: Chapter 1 teaches you about the special theory of relativity
Cavendish Laboratory, the four masters and apprentices finally calmed down from their excitement.
Thomson received the letter and said with great enthusiasm: "Everyone here has the opportunity to compete for this award."
"Even if you are not selected for the first session, you will be selected for the following ones. There is still a big chance.”
“For example, Rutherford, your results were only published this year. It is estimated that even if the committee wants to nominate, it will be too late.” Rutherford nodded, not really caring, anyway. We weren’t prepared to fight in the first session either.
"Bruce, it's hard for you to say. I personally am very optimistic about your achievements, but you are too young after all, and those physics veterans may be biased." Li Qiwei also knew his shortcomings, but he did not give up.
“As for Wilson, don’t be discouraged. When your cloud chamber design matures, it will definitely be a Nobel Prize-level achievement.”
“Perhaps in more than ten years, we will be able to There will be four Nobel Prize winners in physics in the Disch Laboratory.”
Thomson was in high spirits, and the three of them were infected by his confidence, and the room was filled with hearty laughter.
Only Li Qiwei knew that the glory of the laboratory was far more than this.
And he himself couldn't stop, so he tentatively set a small goal: the special theory of relativity.
If quantum theory denies Newton's "continuous" view of space and time, physicists can still accept it intuitively.
After all, in the macroscopic world, Newtonian mechanical laws still play a dominant role. Quantum theory and Newtonian mechanics only study matter on different scales.
Then the special theory of relativity denies Newton's "absolute" view of space and time, and physicists cannot accept it no matter what.
The special theory of relativity has completely subverted Newton's classical mechanics. It can even be directly said that Newton's mechanics is wrong.
So when Einstein first proposed the special theory of relativity in 1905, no one in the physics community recognized it. On the one hand, it was Newton's authority, and on the other hand, the theory was too bold.
Compared with the extremely complex mathematical transformations of the general theory of relativity, the special theory of relativity actually does not have much advanced mathematical knowledge.
The difficulty of this theory actually lies in the fact that people need to be counter-intuitive and abandon their inherent thinking from small to large when it comes to changing their concepts of time and space.
The special theory of relativity has two basic principles (axioms, self-evident): the principle of special relativity and the principle of the invariance of the speed of light.
Principle of special relativity: In all inertial reference systems (reference systems at rest or linear motion), all physical laws are equivalent.
The principle of constant speed of light: In all inertial reference systems, the speed c of light in vacuum never changes.
The first principle is easy to understand because it is completely consistent with human intuition.
In fact, as early as 1632, Galileo proposed this principle: the laws of mechanics are the same for any inertial system that moves in a straight line at a uniform speed relative to the inertial system.
For example, although the earth is constantly moving in the universe, no matter what its speed is, there is no difference when we conduct experiments on it.
Whether you do experiments in the Antarctic or the Arctic, the physical laws you get must be the same.
As for the second principle, it is the biggest obstacle to understanding the special theory of relativity.
First of all, we must understand that the principle of constant speed of light is not hypothesized by Einstein, but measured through theory and experiment. It is a real natural phenomenon.
When Maxwell was born, his electromagnetic equations resulted in the discovery that the speed of light c is a constant value, about 300,000 kilometers per second.
Later, many physicists conducted various experiments, and finally found that the speed of light c is indeed a constant, and the experiments are consistent with the theory.
Although Maxwell originally derived the speed of light based on the existence of the special reference system "ether" in space.
But unfortunately, it later turned out that the ether did not exist, and this was the nature of the first dark cloud.
At the same time, the biggest obstacle that troubles countless physicists in this era is that no one can understand that the speed of light c is constant.
In fact, if you want to understand the principle of the constant speed of light, you need to consider it from two angles.
First, the speed of light has nothing to do with the speed of the light source.
Suppose a person A runs fast on the grass (high speed), then turns on the flashlight; then walks slowly (low speed), and turns on the flashlight again.
When another person B observes these two processes, the speed of light in the flashlight is actually the same, c, which is very strange.
Because if the flashlight is replaced by a wooden stick, and the wooden stick is thrown out in these two situations, the flying speed of the wooden stick observed by B will definitely be different. According to Newton's law of inertia and intuition, the stick can be thrown further after a person takes a running start (assuming the throwing force is the same).
The question is, why does inertia work on sticks but not on light?
We know in later generations that, first, because light has no rest mass, it has no inertia; second, light is excited instantaneously, and light does not exist before turning on the flashlight.
The moment light is generated, it has nothing to do with the light source. Not only does the speed of person A not affect the speed of light, but even the revolution speed of the earth does not affect the speed of light.
This should be easy to understand now.
The difficult thing is the second point, the speed of light has nothing to do with the speed of the observer.
Suppose there is no observer B now, but A is running at a constant speed with a flashlight and observing the speed of light by himself.
At the moment when he turns on the flashlight, A has three choices. The first is to continue running forward, the second is to stand still, and the third is to turn around and run back.
As a result, in these three cases, the speed of light observed by A is all the same, equal to c.
This is again a very counter-intuitive phenomenon.
Since light has a specific speed, if you run along the light, you should observe that the speed of light becomes slower; if you run against the light, you will observe that the speed of light becomes faster.
But reality is not like this. Why does the velocity superposition of Newtonian mechanics no longer work?
This involves the nature of space and time and the transformation of space and time. It is also the most difficult point to understand in the special theory of relativity.
Ordinary people and physicists at that time had almost the same understanding on this point.
That is, under the Newtonian system, time and space are absolute. The length of measurement time and the size of measurement space are absolute, only the speed is relative.
But the special theory of relativity points out that time and space are relative, and speed is absolute. Measuring time and space requires a reference frame, but measuring speed does not. Speed is a constant (not just the speed of light).
The following clock slowness effect, ruler shrinkage effect, and mass-energy equation are all based on theoretical derivation under this space-time view.
As long as this transformation of the concept of space and time is completed and the absolute concept of space and time of classical mechanics is broken, the special theory of relativity can be understood.
As for how to understand the relativity of space and time, that is another complex issue that cannot be discussed here.
Now let’s go back to the second point, why speeds cannot be superimposed. In layman’s terms, objects moving at different speeds each have their own time and space.
So at this moment, the space-time where A is located and the space-time where the light is located are no longer the same space-time, and Newton's laws naturally become invalid.
Attention! In this case, even if the light is replaced by a wooden stick, it cannot actually be superimposed.
The reason why later generations of middle and high school students can directly superpose is because at low speeds, the calculated error is very small.
According to Lorentz factor calculation, when the object speed is greater than 0.14 times the speed of light, the relativistic effect is greater than 1%.
So in daily activities, there is no problem in using approximate calculations of Newtonian mechanics.
As for why the speed of light is this value, no one knows. It can only be regarded as the truth of the universe, deliberately set by the Creator, etc.
Li Qiwei couldn't help but smile when he thought of this. The special theory of relativity is indeed too outrageous. No wonder it was not understood and recognized after it was published.
Wilson on the side saw him laughing for no reason, and asked: "Bruce, do you have any good ideas? Why don't you discuss it with me?"
Li Qiwei came back to his senses and said with a smile: "Oh, I was imagining the speech I gave after winning this year's Nobel Prize in Physics."
Old Wei was very angry and quickly moved away from the pretender.
The special theory of relativity is a big plot, and the academic debates that follow will be exciting and exciting, so Lao Xu needs some foreshadowing to explain the core points of the debate to facilitate readers' understanding. Of course, I know that all the book friends started out with Ph.D.s, but for the sake of a complete plot, I think I still have to write it.
Finally, please collect and read it. Everyone scolded me so harshly in the comment area. At least I should compensate you with the votes.
(End of this chapter)