1900: A physics genius wandering around Europe

Chapter 253: The flaw in the law of universal gravitation! Why is it inverse square proportion?

Li Qiwei looked at the people in the audience with a smile on his face.

Sure enough, everyone wanted to bring him down as the top genius in physics.

Look at the excitement on those young faces and their eager eyes.

Li Qiwei suddenly felt emotional, as if he had never enjoyed this feeling in his previous life.

Instead, they are buried in a sea of ​​questions, become victims of those test papers, and develop a dislike for science.

Returning to this era, he finally realized the charm of science.

There is a world of difference between learning from books and experiencing it in person.

Li Qiwei calmed himself down, then picked up the chalk and began to draw on the blackboard behind him.

He first drew a huge circle on each side, and then connected the centers of the two circles with a straight line.

Finally, he wrote a large equation above the diagram.

【F=G·Mm/R】

Wow!
When Li Qiwei finished writing the equation, there was an uproar in the audience.

It’s not because I don’t understand, but because I understand it too well.

This formula is really famous.

Because it is Newton's law of universal gravitation.

For two interacting objects, the magnitude of the gravitational force between them is inversely proportional to the square of the distance between them.

Not to mention undergraduates, even middle school students are extremely familiar with this formula.

Because this theory is taught in middle school.

It was because of this formula that Newton was able to explain the movement of celestial bodies.

This formula also made Newton a god.

The movements of great celestial bodies must also conform to the calculations made by humans.

Man can conquer heaven!

However, now, Professor Bruce said he wanted to ask a question, is it the law of universal gravitation?
"How is that possible? Is the law of gravity wrong? Could it be that Professor Bruce has made some new discovery?"

"Oh my God, Professor Bruce just started working on Newton's three laws of mechanics, and now he's going to work on the law of universal gravitation?"

"I got full marks in all my physics courses, and I couldn't imagine there would be any problem with the law of gravity."

"Don't worry, Professor Bruce just wrote down the formula, he didn't say it was wrong."

"Maybe he wants us to calculate the orbits of celestial bodies."

"It is said that Professor Bruce calculated a very complicated celestial problem 10 years ago. Maybe he wants to repeat the same trick."

"Then Professor Bruce is doomed to fail. I have studied that type of question before, so I can handle it easily."

"."

Before Li Qiwei started asking, the audience had already started talking.

Although the big guys in the front row were very calm, the young students were very active.

Because the law of universal gravitation is so famous.

All students are very confident.

At this time, Li Qiwei smiled and said, "Looking at everyone's expressions, I think I don't need to introduce this diagram and formula."

"My question is simple."

"Why in the law of universal gravitation, the gravitational force is inversely proportional to the square of the distance."

“数字2为什么不能是1.9，不是2.1，也不是3或者4。”

"Everyone here, can anyone answer this question?"

boom!
Deathly silence.

Thousands of people in the auditorium were all dumbfounded at this moment.

Everyone stared blankly at the formula on the blackboard.

The force of gravity is inversely proportional to the square of the distance. Isn't this what we learn in textbooks?

It seems that teachers and professors have never mentioned the problem of square.

At this time, Li Qiwei added more information and said, "When you were studying the law of universal gravitation, did you ever think about where this formula came from?"

Wow!
The students in the auditorium were even more confused.

"Yeah, where did the formula for universal gravitation come from? I can't remember it."

"Well, it seems that the teacher didn't mention it in class at that time, and just said that Newton gave this formula."

"My teacher said: Just remember it, don't dwell on it, it won't help you on the exam."

"I vaguely remember that Newton was inspired by Kepler's three laws and proposed the law of universal gravitation, but there is indeed no derivation process."

"I'm good at physics, and I'm sure Newton didn't explain why it's an inverse square ratio."

"."

At this point, the students were completely uneasy, and everyone was anxiously discussing the issue with the people around them.

They really don't know why it has to be a square, not a cube, not 2.1.

Is there some hidden flaw here?
Among the crowd, there was a young man with a frown on his face, his deep eyes fixed on the formula on the blackboard, as if he was thinking about something.

Not to mention the students, even many of the big guys in the front row were confused at this moment.

However, Michelson, Millikan and others are obviously not among them.

At the same time, they secretly sighed that Bruce was such a great teacher.

No wonder the other party can run his country's education so successfully.

The private university he founded, Huangpu Polytechnic University, has developed rapidly.

Just based on this method of motivating students to study and research, Bruce is a well-deserved master of education.

The older generation of physicists all knew about the flaws in Newton's law of universal gravitation.

It’s just that in order to facilitate teaching, the big guys deliberately omitted some content in the textbooks.

After all, for undergraduates, if they fail to lay a solid foundation in the early stages and the content is too complicated, it will be detrimental to their growth.

Therefore, unless the students present here are the kind of people who have a wide range of interests and like to get stuck in a rut, it is impossible for anyone to know how to answer this question.

After 5 minutes, no student in the audience raised their hand.

Everyone was dejected.

Before, they looked down on classical physics, thinking that it was all old-fashioned and not worth studying.

As a result, Professor Bruce slapped him in the face.

The law of universal gravitation, which is so familiar that it cannot be more familiar, actually has a side that is unknown to the public.

Sure enough, ginger is still spicy.

At this moment, everyone's admiration for Li Qiwei increased even more.

It turns out that the other party's achievement is not just his genius, but his profound insight into classical physics.

In everything, we should think about the essence of the problem.

Li Qiwei smiled when he saw everyone's reactions, and thought to himself that you will be even more shocked later.

Brother, I am here today just to beat up you Americans.

Who made you, the later generations, so arrogant?

"It seems that I have won, so everyone should go back and study classical physics seriously."

“Only by thoroughly studying classical physics can you understand the core of modern physics.”

“However, this problem still needs to be solved.”

"I think it's Professor Michelson who'll do the talking."

There was a sudden burst of applause from the audience.

Michelson is now president of the American Physical Society.

He is basically the number one person in the American physics community, similar to Nagaoka Hantaro in the Land of Sakura.

"Ahem, actually, I'm not completely sure about this question."

"Because some phenomena have not been resolved until now."

"If you have read Bohr's notes carefully, you will know that Professor Bruce once firmly opposed the view that classical physics is outdated."

"You guys have run into someone's gun."

Michelson's words made many people laugh awkwardly.

"First of all, we can be sure that when Newton proposed the law of universal gravitation, it was not derived."

"He derived the inverse square law based on Kepler's three laws and some other theories."

"This theory has a premise, which is that the orbit of the planet around the sun must be closed."

"Otherwise, the law of gravity cannot be explained."

"Based on this principle, in 1873, French mathematician Joseph Bertrand published the famous Bertrand theorem."

"It's a way of doing mathematical analysis, which is to say, what happens if the orbit of a planet deviates slightly from its original orbit?"

"Bertrand used complex mathematical calculations to find that if a planet deviates from its orbit, there are only two ways to remain stable."

"Either it conforms to the inverse square law or it conforms to the linear law."

"The former is the law of universal gravitation, and the latter is Hooke's law." "Planets can move in a circle around the sun, or they can move like a spring."

"This is the origin of the inverse square law in Newton's law of universal gravitation."

"There is a strict mathematical relationship behind it."

"We have to admire the magic of nature. If a planet wants to remain closed and stable, it must meet this condition."

boom!
Michelson's explanation stunned all the students.

What's going on!

The simple law of universal gravitation actually has such a complicated reason behind it.

That Bertrand theorem sounds extremely profound and probably requires very deep mathematical knowledge.

At this moment, the students realized that the little physics knowledge they had learned was far from classical physics.

I didn't even touch the door.

The student who had questioned Li Qiwei before also hung his face in shame, feeling a little embarrassed.

I took ignorance as courage.

It turns out that Professor Bruce is not someone he can mess with.

"Oh, this is so embarrassing. With my level, I still want to study modern physics?"

"Mom, I want to call the police. Why is the physics I learned different from others?"

"I finally understand the meaning of an ancient Chinese saying I read before: I know the result but not the reason."

"."

However, another student suddenly asked in the crowd: "Professor Bruce, I still want to ask a question."

"Even if we don't know Bertrand's theorem, the law of gravity has been explained anyway."

“We just don’t know.”

"And this just shows that there is something that classical physics has not explored."

Some people still refuse to give up.

This student is right.

Bruce asked why it is inverse square proportion, we really don't know.

But as long as we see Bertrand's theorem one day, we will be able to figure out this problem.

After all, classical physics has been thoroughly studied.

Faced with the young man's persistence, Li Qiwei smiled knowingly.

It seems that they still didn't listen carefully to what Michelson just said.

The other party said that some phenomena could not be explained and also mentioned closed orbits.

Just as Michelson was about to continue speaking, Li Qiwei stopped him with his eyes.

Michelson smiled helplessly and said, "Well, let Bruce teach you guys a lesson."

At this time, Li Qiwei was just about to say what phenomenon the law of universal gravitation could not explain.

Suddenly, another young man stood up.

He was the one who had frowned and looked at the formula thoughtfully.

The other party said very respectfully: "Hello, Professor Bruce, my name is Edwin Hubble, and I am from the University of Chicago majoring in astronomy."

“I just graduated this year.”

Hey!
Li Qiwei was shocked. Wow, there was actually a great man hidden in the crowd.

The famous Hubble!
The Hubble telescope, which was later named after him, is a household name.

It allows physicists to understand the mystery and vastness of the deep universe.

Hubble is one of the most famous figures in the study of modern cosmological theory.

He was the first person to provide evidence for the theory of cosmic expansion, also known as the law of galaxy redshift.

He established the concept of the large-scale universe, pioneered galactic astronomy, and is known as the "Father of Galactic Astronomy."

Of course, at this time Hubble was just a young man who had just graduated from college, and he was still a little reserved in his speech.

"I've come up with a more accessible explanation for the inverse square law."

"I hope Professor Bruce and the professors here can give me some advice."

"I think the inverse square law is because we live in an isotropic three-dimensional space."

"Not only the law of gravity, but Coulomb's law is also inverse square."

"Suppose there is a celestial body that releases gravity outward."

"Then at the same point in time, gravity will form a spherical surface."

"And because space is isotropic, the gravitational force on the sphere is evenly distributed."

"The gravitational density is the same at every point."

"And the gravitational force at each point is equal to the sum of the gravitational forces on the sphere divided by the area of ​​the entire sphere."

"The area formula for a sphere is 4πR."

"So the gravitational force at every point on the sphere is naturally inversely proportional to the square of the radius."

"That's the nature of the inverse square law."

"It would explain not only gravity, but everything else that obeys this law."

boom!
Hubble's remarks instantly caused an uproar in the auditorium.

Everyone looked at the young man at the same time.

The thin figure appears extremely tall.

He actually thought of such an explanation.

Even middle school students can understand it.

Unlike Bertrand's theorem, which requires complex mathematical knowledge, Hubble's explanation can even be imagined intuitively.

All the students jumped up and down excitedly.

"It turns out that our University of Chicago still has a great man like Hubble."

"My God, this explanation is so simple and beautiful."

"Amazing! Really amazing! It also explains Coulomb's law."

Even Michelson and Millikan looked toward Hubble and were both shocked.

"The University of Chicago actually has such a talented person. How come I didn't discover it before?"

"Millikan, you have to keep him here. Don't let him run away."

Michelson's eyes were filled with enthusiasm. This talented physics student from the United States was simply his sweetheart.

In real history, after graduating from college, Hubble went to study law in the UK.

But later he returned to the University of Chicago to pursue a doctorate.

At this moment, the young Hubble instantly brought the atmosphere in the venue to a climax.

Surprisingly, someone was able to answer Professor Bruce's question, and his answer was even more ingenious than Professor Michelson's.

Some students even said jokingly, "Professor Bruce, you should apologize."

It made everyone laugh.

Li Qiwei looked at Hubble with emotion, he is indeed the great god of the future.

Although he has never won the Nobel Prize in Physics, this does not affect his status at all.

The boss was already so sharp when he was young.

Li Qiwei thought of Einstein, Laue and others again. If they were here, they would probably be able to think of the same thing.

But that’s it!
No matter how awesome you are, you can't compare to me, your brother Li, a time traveler.

Facing the crowd's booing, Li Qiwei smiled and said, "Hubble, right? Very good. You will definitely have a place in the future of physics."

"Would you consider becoming my doctoral student?"

Hearing Li Qiwei praising him in front of so many people, Hubble's face turned slightly red with shyness.

With just this one sentence, Hubble's fame instantly surpassed that of many professors, and he could be considered the number one figure in the world of physics.

When Michelson heard what Li Qiwei said, he almost stood up with excitement.

"This Bruce is trying to snatch someone in front of me."

"No, I must protest to him after the meeting."

Millikan smiled and said, "Don't worry, Professor. Bruce is definitely joking."

"If Bruce dares to rob Hubble, I, Millikan, will rob Qian Wushi."

The students in the auditorium were envious.

They were upset that they couldn't come up with the answer, otherwise they would have won the favor of Professor Bruce.

However, Li Qiwei's next sentence made everyone's brain crash instantly.

"But, unfortunately, your explanation is wrong."

boom!
The auditorium was completely silent.

Countless people were shocked: Professor Bruce, are you trying to cheat?
(End of this chapter)