Chapter 253 Flaws in the law of gravity! Why is it inverse square?
Li Qiwei looked at the people in the audience with a smile on his lips.
As expected, everyone wanted to dethrone him, the first genius in physics.
Look at the excitement on those young faces and the eager eyes.
Li Qiwei suddenly sighed, as if he had never enjoyed this feeling in his previous life.
Instead, they were drowned in the sea of questions, became victims of those test papers, and became bored with science.
Back in 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 down, then picked up the chalk and started drawing on the blackboard behind him.
He first drew a huge circle on the left and right sides, and then connected the centers of the two circles with a straight line.
Finally, he wrote a big equation on top of the diagram.
【F=G·Mm/R】
Wow!
When Ridgway finished writing the equation, the audience was in an uproar.
It’s not because I don’t understand, it’s because I understand it so well.
This formula is really famous.
Because it is Newton's law of universal gravitation.
The magnitude of the gravitational force between two interacting objects is inversely proportional to the square of the distance.
Not to mention undergraduates, even middle school students are extremely familiar with this formula.
Because this theory was taught in middle school.
It is precisely because of this formula that Newton was able to explain the motion between celestial bodies.
This formula also put Newton on the altar.
The movements of great celestial bodies must also conform to the calculation results written by humans.
Man can conquer nature!
But now, Professor Bruce said he wanted to ask a question, could it be the law of universal gravitation?
"How is it possible? Is the law of universal gravitation wrong? Professor Bruce must have made some latest discovery."
"My God, Professor Bruce just dealt with Newton's three laws of mechanics, and now he wants to deal with the law of universal gravitation. Are you ready?"
"I have perfect scores in all my physics courses. I can't imagine there is any problem with the law of gravity."
"Don't worry, Professor Bruce just wrote this formula, nothing. Said it was wrong."
"Maybe he wanted us to calculate the orbit of the celestial body."
"It is said that Professor Bruce calculated a very complex celestial problem 10 years ago. Maybe he wants to repeat the same trick."
"Then Professor Bruce will definitely lose. I have specialized in that kind of problem." Type, you can catch it."
"."
Before Li Qiwei started to ask, the audience was already talking about it.
Although the big guys in the front row are very calm, those young students are 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 don't think I need to introduce this schematic diagram and formula."
"My question is very simple."
< br>“Why in the law of universal gravitation, gravity is inversely proportional to the square of the distance.”
"Why can't the number 2 be 1.9, not 2.1, not 3 or 4."
"Everyone here, can any of you answer this question?"
Boom!
Deathly silence.
Thousands of people in the entire auditorium were all dumbfounded at this moment.
Everyone stared blankly at the formula on the blackboard.
Gravity is inversely proportional to the square of distance. Isn’t this taught in textbooks?
It seems that teachers and professors have never raised the issue of squares.
At this time, Li Qiwei added more information and said: "When you were studying the law of universal gravitation, have you ever thought about where this formula came from?"
Wow!
The students in the auditorium were even more confused.
"Yes, where did the formula of universal gravitation come from? Why can't I remember it."
"Well, it seems that the teacher didn't mention it in class at that time, so he said that Newton gave this Formula."
"My teacher said: Just remember it, don't go over it, it's useless for the exam."
"I vaguely remember that Newton got it from Kepler's three laws. Inspiration, the law of universal gravitation was proposed, but there was no derivation process. ”
"I'm good at physics. I can confirm that Newton didn't explain why it's inverse square."
"."
At this time, the students were not calm at all, and everyone was anxiously talking to the surroundings. people discuss.
They really don’t know why it must be square, not cube, or 2.1.
Is there any hidden flaw in this?
Among the crowd, there was a young man who frowned and stared at the formula on the blackboard with his deep eyes, thoughtfully.
Not to mention the students, even the bosses in the front row were confused at this moment.
However, Michelson and Millikan are obviously not included in this list.
At the same time, they sighed inwardly that Bruce was really good at teaching.
No wonder the other party can make education in their country flourish.
The private university he founded, Huangpu University of Technology, has developed rapidly.
Based on this method of mobilizing students' enthusiasm for research and learning, Bruce is a well-deserved master of education.
They, the older generation of physicists, all know about Newton's flaw in universal gravitation.
Just to facilitate teaching, the bosses deliberately omitted certain contents from the textbooks.
After all, for undergraduates, if the foundation cannot be laid in the early stage and the content is too complicated, it will be detrimental to growth.
Therefore, among the students present, unless they are the kind of people who have a very wide range of knowledge and like to dig into the corners of their heads, it is impossible for anyone to know how to answer this question.
After five minutes, no one in the audience raised their hands.
Everyone was downcast.
Before, they looked down on classical physics, thinking that they were old antiques and nothing worth studying.
As a result, Professor Bruce slapped him in the face.
The familiar law of universal gravitation actually has an unknown side.
Sure enough, ginger is still spicy.
At this moment, everyone’s admiration for Li Qiwei increased.
It turns out that the other party's achievement is not just genius, but his profound insight into classical physics.
In everything, we must think about the essence of the problem.
Li Qiwei smiled when he saw everyone's reaction, thinking that you might be more shocked later.
Brother, I came today specifically to torture you Americans.
Who makes you so arrogant in future generations?
“It seems that I have won, so after everyone goes back, let’s study classical physics conscientiously.”
“Only by thoroughly studying classical physics, Only then can you understand what the core of modern physics is.”
"However, this problem still needs to be solved."
"I think Professor Michelson will do the talking."
A burst of applause broke out from the audience.
Michelson is now president of the American Physical Society.
Basically considered the number one person in American physics, similar to Hantaro Nagaoka of Sakura Country.
"Ahem, actually, I'm not completely sure about this problem either."
"Because some phenomena have not been solved until now."
"If you have read Bohr carefully, If you take notes, you will know that Professor Bruce once firmly opposed the outdated view of classical physics."
"You have hit someone's gun."
Michelson's words shocked many people. The man laughed awkwardly.
"First of all, we can be sure that when Newton proposed the law of universal gravitation, he did not derive it from it."
"He summarized the inverse square law based on Kepler's three laws and some other theories. "
"This theory has a premise, that is, 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's theorem."
"This is a mathematical analysis method, that is, what will happen if the orbit of the planet deviates slightly from its original orbit?"
"Through complex mathematical calculations, Bertrand found that if the planet deviates from its orbit, Finally, if you want to remain stable, there are only two situations."
"Either it is consistent with the inverse square ratio, or it is consistent with the linear law."
"The former is the law of gravity, and the latter is. Hooke's Law. "Planet can move in a circle around the sun, or in a spring motion"
"This is the origin of the inverse square ratio in Newton's law of universal gravitation."
"It is supported by strict mathematical relationships."
"We have to lament the magic of nature. If the planet If it wants to remain closed and stable, it must meet this condition.”
Boom!
Michelson's explanation made all the students stunned and stunned.
What's going on!
The simple law of universal gravitation actually has such complicated reasons behind it.
That Bertrand's theorem sounds very profound as soon as you hear it. It probably requires very profound 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 questioned Li Qiwei before also drooped his face in shame, feeling a little embarrassed.
I used ignorance as courage.
Professor Bruce really can’t do it by himself.
"Hey, this is so embarrassing. I am a person with my level and still want to study modern physics?"
"Mom, I want to call the police. Why do I study physics so different from other people's?" ”
"I finally understand the meaning of an ancient Chinese proverb I read before. I know it but don't know why."
"."
However, another student in the crowd suddenly asked: "Professor Bruce, I still want to ask."
"Even if we don't know Bertrand's theorem, no matter what, the law of universal gravitation has been explained clearly."
" It’s just that we don’t know.”
"And this just shows that there is nothing left to discover in classical physics."
There are still some people who are not giving up.
This student is right.
Bruce asked why it is inverse square, we really don’t know.
But as long as we see Bertrand's theorem one day, won't we be able to figure out this problem?
After all, classical physics has been thoroughly studied.
Faced with the young man’s stalking, Li Qiwei smiled knowingly.
It seems that they still did not listen carefully to what Michelson just said.
The other party said that some phenomena cannot be explained, and also mentioned closed orbit.
Just as Michelson was about to continue speaking, Li Qiwei stopped him with a look in his eyes.
Michelson smiled helplessly, forget it, let Bruce educate you guys who don't know the heights of heaven and earth.
At this time, Li Qiwei was just about to say what phenomena could not be explained by the law of gravity.
Suddenly, another young man stood up.
He was the one who frowned before and looked at the formula thoughtfully.
The other party said very respectfully: "Hello, Professor Bruce, my name is Edwin Hubble, from the University of Chicago, majoring in astronomy."
"I just graduated this year."
Oops!
Li Qiwei was surprised, good guy, there is actually a great god hidden in the crowd.
The famous Hubble!
The Hubble Telescope 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 modern theories of the universe.
He was the first person to provide evidence for the theory of universe expansion, which is the so-called law of galaxy redshift.
He established the concept of the large-scale universe, pioneered galaxy astronomy, and is known as the "Father of Galaxy Astronomy."
Of course, Hubble at this time was just a young man who had just graduated from undergraduate school, and his speech was a bit reserved.
"About the inverse square law, I thought of a more understandable explanation."
"I hope Professor Bruce and all the professors here can give me some advice."
"I think The essence of the inverse square ratio is that we live in an isotropic three-dimensional space."
"Not only the law of gravity, but Coulomb's law is also the inverse square ratio."
"Suppose there is. A celestial body that releases gravity outwards”
"Then at the same point in time, the gravitational force will form a spherical surface."
"And since space is isotropic, the gravitational force on the spherical surface is evenly distributed."
"Every time The gravity density of each point is the same. "
"And the gravity of each point is equal to the sum of the gravity of the sphere divided by the area of the entire sphere."
"The area formula of the sphere. It’s 4πR.”
"So the gravity of each point on the sphere is naturally inversely proportional to the square of the radius."
"This is the essence of the inverse square law."
"It can not only explain universal gravitation, but also Explain any other phenomena that obey this law."
Boom!
Hubble's remarks instantly made the auditorium boil.
Everyone looked at the young man in unison.
The thin figure appears to be 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 were jumping up and down excitedly.
“It turns out that we at the University of Chicago are hiding great minds like Hubble.”
“My God, this explanation is so simple and beautiful.”
“Awesome, really. It’s amazing, and it also explains Coulomb’s law.”
Even Michelson and Millikan looked at Hubble, and they were very shocked.
"There is such a good talent at the University of Chicago. Why haven't we discovered it before?"
"Millikan, you must keep him, you can't let him run away."
Michelson With fiery eyes, this American physicist is simply his darling.
In real history, Hubble went to the UK for further study after graduating from his undergraduate degree, and he also studied law.
But later he returned to the University of Chicago to study for a Ph.D.
At this moment, the young Hubble instantly pushed the atmosphere in the venue to a climax.
Someone actually answered Professor Bruce's question, and his answer was even more subtle than Professor Michelson's.
Some students who were naughty even said jokingly: "Professor Bruce, it's time for you to apologize."
It made everyone laugh.
Li Qiwei looked at Hubble with emotion, he is indeed a future great.
Although the other party has not won the Nobel Prize in Physics, this does not affect his status in the slightest.
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 them.
Nothing!
No matter how awesome you are, you can't compare to you, Brother Li, and me, a time traveler.
In the face of the crowd's booing, Li Qiwei smiled and said: "Hubble, right? It's very good. You will definitely have a place in the future of physics."
"Will you consider becoming my doctoral student?"
Hearing Li Qiwei's praise in front of so many people, Hubble's face turned slightly red with embarrassment.
With this sentence alone, Hubble's fame instantly surpassed that of many professors, and he can be regarded as the number one figure in the world of physics.
When Michelson heard Li Qiwei's words, he almost stood up excitedly.
"This Bruce wants to rob someone in front of him."
"No, I will definitely protest to him after the meeting."
Millikan smiled and said: "Professor, don't worry, Bruce must be Just kidding."
"If Bruce dares to rob Hubble, I, Millikan, will rob the Fifth Division."
The students in the auditorium were envious.
They were annoyed that they couldn't figure out the answer, otherwise they would have been favored by Professor Bruce.
However, Li Qiwei’s next sentence caused everyone’s brains to shut down instantly.
“However, unfortunately, your explanation is wrong.”
Boom!
There was silence in the auditorium.
Countless people were shocked: Professor Bruce, you are trying to cheat!
(End of this chapter)