1900: A physics genius wandering around Europe

Chapter 594: The third form of quantum mechanics! Path integral! Brute force cracking! Proving the truth with force! The whole audience was shocked!

1924 10 Month 31 Day.

Day 2 of the Fourth Bruce Conference.

Today's process is still personal reporting.

In the morning, Rutherford, Bohr, Born, Sommerfeld and others shared their research results in turn.

In the afternoon, it was the turn of the younger generation including Pauli, Compton, Yu Yin, Dirac, and Fermi.

With yesterday's opening, the atmosphere of today's meeting was more lively.

Everyone shared the latest research on quantum mechanics from various perspectives.

Fermi introduced quantum mechanics into nuclear physics in an attempt to explain the mechanism of β decay, which caused a sensation.

β decay has always been a key problem in nuclear physics.

It is not only related to the undiscovered neutron, but also to the weak force predicted by Professor Bruce.

Once a breakthrough is made in this direction, it will definitely be a shocking event that will shock the physics community!

Fermi's current research has not yet achieved a breakthrough, but has only provided some directions.

But for his age, it is already amazing enough.

Ridgway personally praised him:

“Fermi is great.”

Fermi was thrilled.

By chance, Compton discovered the "reverse Wu-Compton effect".

The normal Wu-Compton effect states that after an elastic collision between a photon and an electron, part of the photon's energy is transferred to the electron, causing the photon's energy to decrease.

According to E=hv, as the energy of a photon decreases, its frequency decreases, so its wavelength becomes longer.

The inverse Wu-Compton effect occurs when a low-energy photon collides with a high-energy electron, and the situation is reversed, with the electron transferring part of its energy to the photon.

Therefore, the energy of the photon increases and the wavelength becomes shorter.

Compton said confidently:

"I discovered the inverse Wu-Compton effect by accident when I was studying high-energy cosmic rays."

"I think it has something to do with the production of high-energy X-rays and gamma rays in the universe."

"This is yet another application of quantum mechanics in astrophysics."

Everyone was shocked!
Compton's discovery is very important!

Especially for astronomy, it provides an additional theoretical measurement method.

By studying the abnormal frequency shifts in the radiation spectrum of celestial bodies, we can learn a lot of information.

Compton went on to say:

"In addition, after the electron transfers energy to the photon, the classical theory cannot describe its state, and Fermi-Dirac statistics must be used to explain the energy state of the electron."

"Everyone, please look at this. This is the electronic state function I developed."

The speeches by these young physicists were very interesting.

They don’t care whether quantum mechanics is complete or whether its explanation of the world is counterintuitive.

Anyway, quantum mechanics has played an important role in all fields of physics.

Therefore, Einstein’s doubts yesterday did not reduce everyone’s enthusiasm for studying quantum mechanics.

On the contrary, his successive failures made quantum mechanics more popular.

In this life, Einstein gradually changed his view on quantum mechanics due to the influence of Ridgway.

He was no longer so stubbornly prejudiced against the theory.

Quantum mechanics and relativity both have their own unique features.

However, he had come up with a brilliant idea last night and was ready to ask one last question.

Before we knew it, the second day's meeting was over.

Moderator Lorenz explained:
"Professor Bruce and I discussed yesterday that the duration of this meeting will be appropriately extended."

"So, for those who still have their turn to speak on stage, don't worry and continue tomorrow morning."

"Tomorrow afternoon and the day after tomorrow are free discussion days."

“Everyone had a more in-depth exchange on the research results of the past few days.”

“Perhaps some completely new theories and ideas will emerge.”

Everyone looked excited when they heard this.

This time, at the invitation of Professor Bruce, almost two-thirds of the people gave reports, which were quite brilliant.

The collision of so many ideas will definitely produce different sparks.

On the afternoon of June 11th.

The free discussion will begin.

People walked around the room in groups of two or three, or sat down and discussed topics of interest to each other.

Hearty laughter could be heard from time to time in the room.

"The edifice of quantum mechanics has been completed!"

This is what many people think in their hearts.

With the proposal of concepts such as the complementarity principle, the superposition principle, and the collapse of wave function by Li Qiwei, the theoretical basis of quantum mechanics has been completely perfected.

Suddenly someone sighed:
“I feel like theoretical physics has reached its end.”

"The two pillars of modern physics, relativity and quantum mechanics, have become mature theories."

Everyone agreed silently when they heard this.

Perhaps from today onwards, no more basic theories will be born.

All physicists can do is to apply quantum mechanics to unknown experimental phenomena and explain its principles, just like Fermi and Compton did.

They don't need to create any more theories.

“Has the edifice of physics really been completed?”

At this time, Ridgway and Bohr were sitting together.

After hearing the discussions around him, Bohr smiled slightly.

"Teacher, do you think this view is correct?"

Li Qiwei's eyes were deep, and he said quietly:
"Of course not!"

“It’s only quantum mechanics that is perfected, not physics.”

"At least now I can think of a direction that quantum mechanics cannot help me with."

Bohr was startled and asked:
"What is it?"

Li Qiwei smiled and asked back:
"Bohr, what do you think is the most important concept in classical electromagnetism?"

Bohr frowned slightly when he heard this.

Many theories flashed through his mind in an instant: electric current, electromagnetic induction, Coulomb's law, Maxwell's equations.
But these seem to have nothing to do with quantum mechanics.

wrong!

Bohr suddenly thought of the content of the first Bruce Conference.

He said excitedly:

"Teacher, it's a field!"

Li Qiwei nodded with satisfaction and said:

"Yes, that's the concept of the classic field!"

"Matter and energy have all been quantized."

"Can we quantize the field as well?"

"What would happen then?"

"One of my current research directions is the quantization of electromagnetic fields."

"There has been no results so far, so I did not bring it up at this meeting."

Wow!
Bohr was extremely shocked when he heard this!

"My God!"

"The field is clearly a continuous entity, how can it be quantized?"

“This idea is so advanced!”

At this moment, he felt that he had heard something extraordinary.

The teacher's inspiration is endless!
Bohr suddenly felt that quantum mechanics might be far from over.

In real history, what Ridgwell meant by quantizing the field was to regard the continuous field as an infinite-dimensional oscillator, and to decompose the field into individual quanta through the method of canonical quantization.

One advantage of quantizing the field is that it becomes the same state as the quantized particles and energy, making it easier to explain the relationship between them theoretically.

This is the famous "quantum field theory".

Within the framework of quantum field theory, there is no matter or energy in the universe, only various fields.

The excitation of the field produces matter and energy.

Every microscopic particle has a corresponding field.

The field that produces photons is the electromagnetic field, and the quantum field theory that studies the interaction between the electromagnetic field and photons is called "quantum electrodynamics (QED)".

The field that produces quarks is the quark field, and the quantum field theory that studies the quarks that make up the strong force particles is called "quantum chromodynamics (QCD)".

And these theories were finally combined together to form the most cutting-edge and important theory of later generations: the Standard Model of Particle Physics!

Bohr could never have imagined how brilliant the future of quantum mechanics would be!
At this moment, Li Qiwei suddenly smiled. He wanted to add fuel to the fire of quantum mechanics.

He smiled and said:

"Didn't someone just say that theoretical physics has reached its end?"

"Now, I'm going to show them what it means to never stop!"

Wow!
Bohr was shocked!

Is the teacher going to come up with another shocking theory?
To everyone's shock, Li Qiwei stood up, walked to the front, and said:

"When I was chatting with Bohr just now, I recalled the double-slit interference experiment the day before yesterday."

"I thought of restating quantum mechanics from another perspective."

Wow!
Everyone was shocked!
"My God!"

"I just said that quantum mechanics is complete and theoretical physics is over."

"I didn't expect to be slapped in the face by Professor Bruce in the blink of an eye."

Ridgeway continued:
"In classical mechanics, the motion of a particle can be predicted exactly by Newton's laws of motion."

"But in quantum mechanics, we can only predict the probability of a particle being somewhere."

"The numerical value of the probability is obtained by calculating the wave function of the Schrödinger equation."

"So, is it possible to find a new way to calculate it?"

"I found inspiration from the double-slit interference experiment of electrons."

"From a holistic perspective, after the electron is emitted, it has to pass through the double slits and the display screen before it eventually becomes a certain state."

"There are only a few ways to go about it: either it goes through the left slit alone, the right slit alone, or both slits at the same time."

"We know these paths qualitatively without having to calculate them."

“But if we change the double seams to triple seams, or even five or eight seams, and add more gap panels at the front and back.”

"How can we study the path of electrons at this time?"

"Will it interfere again?"

"In this case, existing quantum theory is powerless."

Everyone looked confused and didn't know what was going on.

This is no longer a double-slit experiment, but an N-slit experiment.

"There are many different paths that electrons can take through these slits."

"It is completely impossible to tell by qualitative analysis which path the electron took."

“So I thought of a solution.”

"I add up all these possible paths and determine which specific path the electron will take."

"In this way, I don't need to know what the wave-particle duality of electrons is specifically."

“All I have to worry about is the state of the electron’s starting point and ending point.”

"There's no wave, there's no particle, the electron just moves from A to B."

"Suppose it has 100 different paths, I will overlap and add up the 100 paths with probability ratios, and calculate which path will be taken in the end by integration."

Click, click, click!
As Li Qiwei was talking, he started calculating directly on the blackboard.

The various points are dizzying.

A full twenty minutes later.

He smiled and said:

"Look, everyone. This is the result of my calculation using a new method for electrons passing through a double slit."

"I proved theoretically that individual electrons must interfere with each other."

"Similarly, if we replace the double slits with three or eight slits, we can get different results."

"I will temporarily call this theory the Path Integral."

"With the path integral, we don't have to consider the quantum situation itself at all, and can directly consider all possibilities."

quiet!
Deathly silence!

Everyone widened their eyes and were shocked!
"Oh my God! Professor Bruce is so outrageous!"

"How on earth did he come up with this theory?"

"This is simply a miracle of great strength, proving the truth with strength!"

In matrix mechanics, transition is used to represent the state change of electrons.

In wave mechanics, probability tables are used to represent changes in the state of electrons.

Both of these two mechanics describe the changes of electrons from A to B from a certain perspective through indirect means.

Because the characteristics of quantum mechanics dictate that everything about microscopic particles is uncertain and there are countless possible states.

It is impossible for physicists to take every possible state into account.

But today, everyone seemed to have seen a miracle!

Just because others can't do it doesn't mean Professor Bruce can't do it!
That man just didn't follow the beaten path. He actually used brute force to calculate all possible paths for the electron.

Then add all these paths together to calculate the final path.

The idea of ​​path integral is so fantastic and shocking!

There were sudden exclamations in the room.

"This is literally the third form of quantum mechanics!"

Everyone was shocked!

In real history, the path integral form of quantum mechanics was proposed by the famous Feynman in 1942.

Its appearance brings quantum mechanics to a higher level.

So Yang Zhenning once said: Feynman created the real quantum mechanics.

Path integral builds a bridge between classical and quantum.

Through the calculation of this theory, F=ma can be directly derived.

The determined path in the macroscopic world is actually the superposition of countless microscopic quantum paths.

The reason why a single electron is uncertain is that each path has the same impact on the final outcome.

So, they all have the potential to be the final path.

In addition, based on the path integral form, Feynman also proposed the concept of "Feynman diagram".

Of course, I will become "Brustu" in this life.

It helps physicists deal with the interactions of various particles in quantum field theory in a more visual way.

The path integral form is closely related to later quantum field theory.

At this moment, Heisenberg and Schrödinger both looked fanatical!

Their respective theories were completed under the guidance of Professor Bruce.

I didn't expect that the other party could come up with the third form of quantum mechanics.

And this form seems to be more profound than matrix mechanics and wave mechanics.

It is not only a physical theory, but also a mathematical idea and method!
Looking at quantum from a whole new perspective.

The two of them were immediately filled with admiration!
"Professor Bruce is never on the same level as us!"

Bohr looked at his teacher with admiration.

His mind was still replaying the conversation just now.

“Path integrals may not be the end of quantum mechanics.”

"I really look forward to your research on field quantization. It will surely make a sensation in the physics community again."

Li Qiwei looked at the shocked expressions of the crowd with a calm face.

At this point, quantum mechanics has been completed, and the next step is the emergence of quantum field theory!
(End of this chapter)