Chapter 55: A chapter to teach you how to understand the special theory of relativity
At the Cavendish Laboratory, the four masters and apprentices finally calmed down from their excitement.
Thomson took the letter back and said in full force: "Everyone here has a chance to win this award."
“Even if you can’t be selected in the first session, you still have a great chance in the next few sessions.”
"For example, Rutherford, your results were only published this year. I guess even if the committee wants to nominate you, it's too late." Rutherford nodded, not really caring. Anyway, he was not prepared to fight in the first session.
"Bruce, it's hard to say for you. I personally am very optimistic about your achievements, but you are too young after all, and those physics veterans may be prejudiced." Li Qiwei also knew his shortcomings, but he did not give up.
“As for Wilson, don’t be discouraged. Once your cloud chamber design is mature, it will surely be a Nobel Prize-worthy achievement.”
“Perhaps in a dozen years, we at the Cavendish Laboratory will have four Nobel Prize winners in physics.”
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 laboratory's glory went far beyond this.
And he couldn't stop, so he temporarily 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, Newton's laws of mechanics still dominate, and quantum theory and Newton's mechanics only differ in the scale of research on matter.
Then the special theory of relativity denies Newton's "absolute" view of space and time, which physicists cannot accept no matter what.
The special theory of relativity completely overturned Newton's classical mechanics. It can even be said that Newtonian mechanics is wrong.
So when Einstein first proposed the theory of special relativity in 1905, no one in the physics community at the time accepted it. On the one hand, it was because of Newton's authority, and on the other hand, the theory was too bold.
Compared with the extremely complex mathematical transformations of general relativity, special relativity does not actually involve much advanced mathematical knowledge.
The difficulty of this theory actually lies in the fact that people’s concept of time and space needs to be changed counter-intuitively and abandon the inherent thinking that has been inherited from childhood to adulthood.
There are two basic principles (axioms, self-evident) of the special theory of relativity: the principle of special relativity and the principle of the constancy of the speed of light.
The principle of special relativity: All physical laws are equivalent in all inertial reference frames (reference frames at rest or in linear motion).
The principle of the constancy of the speed of light: In all inertial reference frames, the speed of light c in a vacuum remains unchanged.
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 performs uniform linear motion relative to the inertial system.
For example, although the earth is constantly moving in the universe, no matter how fast it is, it makes no difference when we do experiments on it.
Whether you do experiments in Antarctica or in the Arctic, the physical laws you come up with will 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 the constancy of the speed of light was not postulated by Einstein, but was measured through theory and experiments and is a real natural phenomenon.
When Maxwell emerged, his electromagnetic equations showed that the speed of light c is a constant value of about 30 kilometers per second.
Later, many physicists conducted various experiments and finally discovered that the speed of light c is indeed a constant, and the experiments are consistent with the theory.
Although Maxwell derived the speed of light based on the existence of a special reference system called "ether" in space.
But unfortunately, later results proved that ether did not exist, and this was the nature of the first dark cloud.
At the same time, this is also the biggest obstacle that has troubled countless physicists in this era. No one can understand that the speed of light c is constant.
In fact, if you want to understand the principle of the constancy of the speed of light, you need to consider it from two perspectives.
First, the speed of light has nothing to do with the speed of the light source.
Suppose person A runs fast on the grass (high speed) and then turns on the flashlight; then he walks slowly (low speed) and turns on the flashlight again.
When observed by another person B, the speed of light of the flashlight in these two processes is actually the same, both c, which is very strange.
Because if the flashlight is replaced with a stick, the stick will be thrown at different speeds in these two situations. According to Newton's law of inertia and intuition, the stick can be thrown farther after the run-up (assuming the throwing force is the same).
The question is, why does inertia work for the stick but not for light?
We in later generations know that, firstly, because light has no rest mass, it has no inertia; secondly, light is excited instantaneously and does not exist before the flashlight is turned on.
The moment light is produced, it has nothing to do with the light source. Not only does the speed of person A not affect the speed of light, even the orbital speed of the Earth does not affect the speed of light.
This should be well understood now.
The second point is difficult: the speed of light has nothing to do with the speed of the observer.
Suppose now there is no observer B, but A runs at a constant speed with a flashlight and observes the speed of light by himself.
At the moment the flashlight is turned on, A has three choices: first, continue running forward, second, stay still, and third, turn around and run back.
As a result, in these three cases, the speed of light observed by A is the same, equal to c.
This is again a very counter-intuitive phenomenon.
Since light has a specific speed, if we run along the light, we should observe that the speed of light slows down; if we run against the light, we should observe that the speed of light speeds up.
But the reality is not like this. Why does the velocity superposition of Newtonian mechanics no longer work?
This involves the nature of space-time and its transformation, which 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, in the Newtonian system, time and space are absolute. Measuring the length of time and the size of space are absolute, and only speed is relative.
However, 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, and speed is a constant (not just the speed of light).
The subsequent clock slow effect, length contraction effect, and mass-energy equation are all theoretical derivations based on this view of space and time.
As long as we complete this transformation of the concept of space and time and break the absolute concept of space and time in classical mechanics, we will be able to understand the special theory of relativity.
As for how to understand the relativity of space and time, that is another complex issue that cannot be elaborated here.
Now let’s go back to the second point, why speeds cannot be superimposed. To put it simply, objects moving at different speeds each have their own time and space.
Therefore, the space-time where A is located at this moment is no longer the same space-time as the space-time where light is located, and Newton's laws are naturally invalid.
Note! In this case, even if you replace the light with a stick, it cannot be superimposed.
The reason why it can be directly superimposed when studying in junior high and high school is that under low speed conditions, the calculated error is very small.
According to the Lorentz factor, the relativistic effect is greater than when the speed of an object is greater than 1 times the speed of light.
So in daily activities, there is nothing wrong with using approximate calculations based on Newtonian mechanics.
As for why the speed of light is this value, no one knows. We can only regard it as a universal truth, deliberately set by the Creator, etc.
Li Qiwei couldn't help but smile when he thought of this. The special theory of relativity was indeed too outrageous. No wonder it was not understood and recognized after it was published.
Wilson, who was standing by, saw him laughing for no reason and asked, "Bruce, what good ideas do you have? Would you like to discuss them with me?"
Li Qiwei came back to his senses and smiled: "Oh, I was imagining the speech I gave after winning the Nobel Prize in Physics this year."
Lao Wei was very angry and quickly moved away from the show-off.
The special theory of relativity is a big plot, and the academic debate that follows will be exciting and exciting, so I need to lay some groundwork to explain the core of the debate and make it easier for readers to understand. Of course, I know that all of my readers have PhDs, but for the sake of the plot being complete, I still think I have to write it.
Finally, please collect and read this article. Since everyone has cursed so harshly in the comment section, please at least give some votes as compensation.
(End of this chapter)