1900: A physics genius wandering around Europe

Chapter 668 Conservation of Isospin! The Nuclear Drop Model! The Core of Uranium Fission Theory! A Shocking Entire Audience!
Pauli's neutrino conjecture immediately demonstrated the supreme status of the Bruce Conference!
This is yet another discovery that will shake the physics community!
But the bigwigs gave a wry smile.

The complexity of weak forces far exceeds people's imagination.

The strong force involves only two particles, protons and neutrons, but the weak force involves four particles.

Therefore, people subconsciously believe that weak force is definitely more difficult than strong force.

After all, the three-body problem is infinitely more complex than the two-body problem.

However, the truth is that the strong force is more unpredictable than the weak force.

After some discussion, Pauli happily returned to his seat.

The questions from the experts just now gave him new insights, and he can further refine his neutrino hypothesis when he gets back.

At this moment, Langevin said:

"Next up, please welcome Professor Heisenberg from the University of Leipzig, Germany."

Heisenberg stood up, walked to the stage, nodded to the crowd, and then said:

"My report today is about power."

"Since Professor Bruce predicted the existence of the strong and weak forces, there have been many experiments that have indirectly shown that these two forces are real."

"But we know nothing about their mechanisms of action at present."

"My research focuses on a small problem within power."

"We know that the strong force is the force that binds protons and neutrons together."

"But protons are positively charged and neutrons are uncharged. Why can two particles with such different properties be affected by the same force?"

"Electromagnetic force can only act on charged particles, but not on neutral particles."

"But power broke that."

"Therefore, I boldly speculate that there must be an unknown property in protons and neutrons."

"This property can ignore differences in charge and mass, allowing two particles to be subjected to strong forces simultaneously."

"Based on theoretical derivation, I found a property that I named 'isospin'."

Wow!
Everyone was shocked!
Although Heisenberg's research is not easy to understand, its importance is self-evident.

This isospin might reveal part of the nature of the powerful force.

Moreover, he actually derived this property purely from theory.

This is exactly the same as the other party's derivation of matrix mechanics back then.

"too strong!"

Pauli and Heisenberg, these two brothers, are the unparalleled geniuses of quantum mechanics.

The praise from everyone made Heisenberg a little smug.

He continued:
"The specific process is as follows."

"Everyone please look at the screen."

Heisenberg performed the calculations while explaining:
"According to the ideas of quantum mechanics, isospin is also a quantum number, similar to spin, and is an inherent property of particles."

"Actually, I named it isospin precisely because I took spin as a reference."

"Particles with different charges but the same strength can be regarded as the same particles in different charge states."

"for example."

"Now there is a particle A, whose isospin changes when it is subjected to a strong force."

"One change turned particle A into a proton, and another change turned particle A into a neutron."

"This explains why both neutrons and protons are affected by the strong force."

"There is one thing to note."

"Isospin is a mathematical representation that has no direct relation to a particle's charge, mass, or other quantum properties."

"It can be understood figuratively that isospin is a kind of symmetry inside a particle, which reflects that the particle can undergo certain transformations without changing its properties."

Wow!
The whole audience was shocked!

Heisenberg's work is very beautiful.

He combined ideas from quantum mechanics to study particles from the perspective of quantum number conservation or symmetry.

Based on our current understanding of the power, if it truly exists, then isospin must be conserved.

This is rigorously proven mathematically.

At this moment, Fermi suddenly asked a question:
"Professor Heisenberg, according to your definition of isospin, it should also be related to the weak force."

"Isospin changes alter the properties of protons and neutrons, which is also the phenomenon of beta decay."

"Do you have any research experience in this area?"

Heisenberg was immediately startled!
He hadn't really considered that aspect.

He originally introduced the concept of isospin to explain why the strong energy can simultaneously bind protons and neutrons.

But after Fermi's reminder, he suddenly realized that isospin might indeed be related to the weak force.

Then, he excitedly said:
“I’m sorry, Professor Fermi, I haven’t considered it yet.”

"But your question is very useful to me. Perhaps I should consider introducing isospin into the weak force."

Planck, Sommerfeld, and other older generation physicists smiled with great satisfaction.

Pauli, Heisenberg, Fermi and others delivered truly brilliant performances.

These young people are already at the forefront of physics, pushing their limits to explore the unknown forces of strength and weakness.

"The Bruce Conference is now dominated by young people!"

Li Qiwei smiled slightly as he watched the two discussing.

In reality, Fermi ultimately established the four-fermion theory based on the work of three other people.

These are Pauli's neutrino, Dirac's quantum electrodynamics, and Heisenberg's isospin conservation.

Furthermore, Fermi developed the isospin theory.

Isorotation has three components, much like the xyz axis projection of a coordinate system.

In the strong force, isospin is conserved; however, in the weak force, isospin is not conserved.

Furthermore, isospin under weak force is called "weak isospin".

Therefore, it is clear that compared to gravity and electromagnetism, the strong and weak forces are indeed a bit too complex.

At this moment, Heisenberg and Fermi had a heated discussion about the concept of isospin.

Rutherford said with a smile:

"Although Fermi was physically involved in experimental physics, his heart was still in theoretical physics."

The bigwigs burst into laughter after hearing this.

The meeting continues.

"Next, please welcome Professor Bohr from the University of Copenhagen, Denmark."

Wow!
Everyone immediately turned to look at him.

Bohr's name seems to have been absent from the physics community for a long time.

As Professor Bruce's top disciple, Bohr's name was once at its zenith, inspiring a generation of young people.

Heisenberg, Pauli, Dirac and others all idolized him.

Because the other party was not afraid of the teacher's authority, they proposed a quantized orbital model based on the planetary model, thus officially ushering in the era of quantum theory.

Although quantum theory has now become the old quantum theory, and quantized orbitals have been replaced by electron probability clouds.

But no one would deny Bohr's achievements because of this.

He remains a recognized leading figure in quantum mechanics.

What research findings will they bring today?

Bohr was equally excited.

He did not stand out in the previous two Bruce conferences.

Quantum mechanics has been almost entirely dominated by those young guys, leaving him, the older brother, no chance to get involved.

And now, he has finally achieved what he considers to be a decent result.

"Today, I'm going to share something about nuclear models."

"We know that atoms are composed of a nucleus and electrons, with electrons appearing randomly at any point in the atom as a probability cloud." "But what is the structure of the nucleus itself?"

What properties would a combination of protons and neutrons produce?

"Therefore, I proposed the droplet model."

Having said that, Bohr turned on the prepared projector and said:

"Everyone, please take a look."

"The droplet model is a nuclear model that I developed based on the property of strong nucleon-nucleon coupling in the atomic nucleus."

"I consider the atomic nucleus as an ideal liquid droplet with a charge, and describe the atomic nucleus based on the laws of motion of the droplet."

"In this process, I combined the theories of quantum mechanics with those of classical mechanics and electromagnetism."

"The droplet model can explain the static properties and dynamic laws of the atomic nucleus."

"For example, the laws of mass, surface vibrations, the rotation of deformable nuclei, and even nuclear fission!"

Wow!
The whole audience was shocked!

Professor Bohr was indeed a man of action; when he did act, it was earth-shattering.

He actually used his own created droplet model to theoretically describe the process of nuclear fission.

That's absolutely amazing!
However, that wasn't all. Bohr continued:
"To get closer to the real situation of the atomic nucleus, I added a few more degrees of freedom."

"For example, we can consider protons and neutrons as two different fluids, and even consider spin orientation as a different fluid."

"This explains properties such as compressibility."

"The droplet model mainly includes two main components."

"One is the surface vibration of the spherical nucleus, and the other is the nuclear fission mechanism."

The derivation formula is shown below.

"Nuclear fission can be viewed as a droplet splitting into two."

"We know that liquids have surface tension, which prevents them from breaking down."

"The same applies to nuclear droplets."

"To split an atomic nucleus, additional energy is needed to break this tension."

"When high-energy particles collide with atomic nuclei, they merge with them to form excited semi-stable complex nuclei."

"This composite nucleus wobbles like a droplet until the final impact effect ends."

"And there are only two possible outcomes."

"Either release energy or release very small particles."

"The latter is the experimental basis for the phenomenon of nuclear fission today."

boom!
The entire audience was stunned!

Bohr's theory, in terms of difficulty, may seem less complex than Pauli's neutrino or Heisenberg's isospin.

However, in terms of innovation, they are definitely on the same level.

He used the simplest theories to theoretically establish a framework for the properties of the atomic nucleus.

It can even explain many experimental phenomena.

Everyone was amazed:

"That's amazing!"

"Professor Bohr is indeed as sharp as ever!"

Those involved in experimental physics, in particular, remarked with deep feeling:
"Theory doesn't necessarily require very complex mathematical knowledge."

The greatest truths are the simplest.

Bohr did not use any sophisticated mathematical or physical techniques in his droplet model.

It starts from the idea of ​​liquid surface tension and combines physical concepts such as surface energy, binding energy, and volume energy.

But the result was a pleasant surprise.

At this moment, Rutherford suddenly asked:

“Bohr, according to your theory, large-scale fission of the atomic nucleus should be impossible.”

Bohr said:

"Is such that."

"If you want to split a droplet in two, you need to overcome a huge binding energy."

"The energy carried by the particle itself cannot satisfy this requirement, which can be proven theoretically."

After saying that, he immediately began to calculate, proving that it was impossible.

Everyone suddenly realized.

That makes sense.

Current nuclear fission methods only reduce the number of protons by a few, producing only very small fragments.

That's because the smaller the fragment, the lower the energy required to escape the atomic nucleus, and the easier it is for it to happen.

The theory and experiment match perfectly!
Bohr was awesome!
However, only Ridgway, after reading Bohr's content, felt both amused and exasperated.

In real history, the droplet model proposed by Niels Bohr, a leader of his generation, has misled countless people.

Because of this theory, everyone believed that large-scale nuclear fission was impossible.

Except for one person, she is Maitner.

At the time, Meitner was persecuted by the Nazis and fled to Sweden.

However, she continued to study the nuclear fission phenomenon of uranium.

At the time, according to Bohr's droplet model, uranium nuclear fission would only produce new atomic nuclei with atomic numbers a few smaller.

However, physicists discovered a new atomic nucleus with only half the atomic number of uranium in the products of nuclear fission.

This is incredible.

At one point, Meitner had a flash of inspiration, imagining a giant atomic nucleus suddenly splitting in two, creating two roughly equal fragments.

This explains the experimental phenomena.

However, Meitner was also aware of Bohr's droplet model.

That seems impossible.

Theoretically, uranium nuclei are too large; to split them in two, at least 200 MeV of energy would be required.

It's simply impossible with just the impact of a single neutron.

Even the most advanced particle accelerators at the time could not produce particles with such high kinetic energy.

Where does this energy come from?
At that moment, Meitner thought of a crucial detail.

That is: if a uranium nucleus is split in two, its mass will decrease by 1/5 of the proton's mass.

According to the mass-energy equivalence equation, this missing mass will be converted into energy and released.

Meitner did some calculations and was pleasantly surprised to find that 1/15 of the proton's mass, when converted into energy, was exactly 200 MeV.

In this way, everything can be explained.

The atomic nucleus can be split in two!

Bohr's droplet model, while misleading many, also provided a rigorous theoretical basis for this heavy nucleus fission.

Thus, the story of uranium nuclear fission officially began.

At that moment, Bohr was still eloquently explaining his droplet model.

He was completely unaware of how his theory would influence the great discovery of uranium nuclear fission.

Li Qiwei looked at everything with a deep gaze.

With Bohr's development of the droplet model, which paved the way for the theoretical possibility of nuclear fission, the Pangu Project drew ever closer.

In later generations, many people, upon hearing about the atomic bomb, attributed it to the mass-energy equivalence equation.

They even equated the mass-energy equivalence equation with the atomic bomb.

However, Ridgway only truly understood after personally experiencing the journey that it was so difficult for humanity to master the power of nuclear weapons.

The meeting continues.

(End of this chapter)