1900: A physics genius wandering around Europe

Chapter 563: Mirror Symmetry of Space! Parity Violation! China's Peerless Prodigies!
When Ridgwell proposed that "the universe originated from asymmetry", everyone found it incredible.

There are indeed many asymmetric phenomena in this world.

For example, although the human appearance is symmetrical, the internal organs are asymmetrical. People have only one heart, which is located in the left half of the body.

The planet is not a standard sphere, but a bit "elliptical".

But in the field of physics, the concept of symmetry is not as simple as "folding in half".

What physicists care about is the more essential and underlying symmetry.

Time symmetry, space symmetry, etc.

Symmetry is the framework, asymmetry is the detail!

As long as the framework is right, the details don't matter.

Therefore, although Noether's paper does not seem worth discussing in the eyes of physics giants, its correctness is beyond doubt.

Moreover, Noether also linked conservation with symmetry, which can be regarded as a pioneering innovation.

But that's all.

But if you really want to shock the academic community and the bigwigs, what should you do?

Scarcity makes things valuable, and this also applies to the field of physics research.

Physicists take symmetry and conservation for granted because that is how nature works.

But if you propose "asymmetry and non-conservation", it will definitely be eye-popping!

When everyone was shouting that the universe was symmetrical, Li Qiwei suddenly said "asymmetric".

You can imagine the sensation it caused!

At this moment, the venue was boiling!

Everyone was shocked and discussed it intensely.

"I think Professor Bruce's conjecture is too bold!"

“Without symmetry, the world would have been in chaos.”

"Compared to the second conjecture, I still think the first conjecture is more reasonable."

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Planck, Einstein and other great men were also communicating excitedly.

However, they did not object at the first sight, but maintained a cautious attitude.

After all, the development of quantum mechanics has overturned too much so-called common sense and intuition.

No one can guarantee what the true nature of this world is.

“Maybe the universe is just asymmetric about something.”

Li Qiwei looked at the various expressions on everyone's faces and felt emotional.

Developed from Noether's theorem, there is a famous concept: parity non-conservation!

In later generations, many people have heard of this term, but probably not one out of 100 people can clearly know what it is.

Because most of the popular science content about it is wrong.

When talking about the violation of parity conservation, we have to mention two unparalleled geniuses of China: Yang Zhenning and Li Zhengdao.

In real history, after Noether published Noether's theorem and proposed the relationship between conservation quantities and symmetry, his influence in the physics community was not very great.

Because quantum mechanics had not yet developed at that time, physicists could not find the effect of this law.

However, there is still a small number of physicists willing to study this niche field.

Wigner is one of them.

After witnessing the extraordinary talent of his brother-in-law Dirac, Wigner realized that the mainstream content of quantum mechanics had been monopolized by those perverts.

Ordinary physicists can only squat below and drink the soup pitifully.

So he decided to take a different approach.

Noether's theorem has proved that conservation must come from symmetry.

And Noether also gave three examples.

Time translation symmetry → energy conservation;
Spatial translation symmetry → momentum conservation;
Rotational symmetry of space → conservation of angular momentum.

So, Wigner thought, if he could discover a completely new symmetry, wouldn't he be able to propose a completely new conservation law?

This is definitely a result that will shock the physics community!

Just do it!

He also wanted to shock von Neumann!

However, symmetry is not so easy to find.

Noether's theorem already involves time and space. Are there any other symmetries?

Wigner does have a talent for physics, and he is also very lucky.

One day, when he was looking in the mirror, he saw his handsome face and suddenly had an idea:

"Hey, isn't the me in the mirror and the me outside the mirror also a kind of symmetry?"

"Mirror symmetry!"

Wow!
As if he had suddenly been enlightened, Wigner danced with excitement.

He discovered a new symmetry of space!
No, it should be said that he did not discover it, but he thought of it.

After all, mirror symmetry is nothing new and is very common in the field of chemical molecules.

Even so, no one has studied what this symmetry means in physics, at least not yet.

Wigner seemed to have seen the Nobel Prize beckoning him, and a bright future ahead with various universities vying to invite him to become professors.

How do you understand mirror symmetry?
If there is a mirror and a physical process occurs outside the mirror, then the process inside the mirror should have the same result.

For example, if you throw an apple outside the mirror and it falls to the ground, the apple inside the mirror will also fall to the ground instead of flying into the sky.

In later generations, many popular science accounts used examples similar to the above to explain the "non-conservation of parity".

It sounds particularly vivid and easy to understand.

For example, you are playing rock-paper-scissors with yourself in the mirror. You play punch, but the you in the mirror plays paper.

This is called parity violation.

At this point, you will definitely feel:
"Wow, this is amazing! I actually understood it!"

Unfortunately, this analogy is wrong!

The connotation is also wrong!
Wigner was a rigorous and talented physicist, and he immediately realized that mirror symmetry was just a figurative metaphor.

Because the world in the mirror is not the real world!

Whether it is time translation, space translation, or space rotation, these processes all occur in the real world.

You did experiments on the third floor on the first day, and you did experiments on the third floor again on the second day. Both times were in the same world.

But the inside and outside of the mirror are completely different!

Therefore, Wigner had to find a way to convert the form of mirror symmetry into strict physical language.

That is, let this symmetric process happen in the real world.

After careful study, he found that the so-called mirror symmetry can be understood as follows:

"In a physical system, the directions of all vectors are reversed according to mirror symmetry."

"Then at this point, the entire physical system is reversed."

“All processes in the system are reversed left to right, but everything else remains the same.”

It's like a person's left and right hands, which are mirror images.

For example, a rotating ball, rotating clockwise and counterclockwise, is also a mirror image.

Moreover, they all take place in real space, not in a mirror.

At this point, Wigner finally sorted out this new symmetry using the language of physics.

He defined it as "mirror symmetry in space".

But then, the rigorous Wigner discovered a fatal problem.

The mirror symmetry of space does not conform to the definition of Noether's theorem!
Remember the original words of Noether's theorem?
[In a system, each continuous symmetry corresponds to a conserved quantity. ]

Note the word “continuous”.

Time translation is continuous, space translation is continuous, and space rotation is also continuous.

But space mirroring is not a continuous process!
Mirror symmetry is when one side is directly switched to the other side without any intermediate process, and it is discontinuous.

Therefore, it does not conform to the description and proof of Noether's theorem.

Wigner suddenly felt a little discouraged.

But having come this far, he didn't want to give up halfway.

So, he just decided to give it a try.

"Perhaps this discontinuous symmetry can also have a corresponding conservation law?"

"You have to give it a try anyway."

So, what quantity does the mirror symmetry of space correspond to?

After in-depth research, Wigner proposed:

"Mirror symmetry of space [parity conservation]!"

The word parity is very misleading and is not a very good translation.

In Chinese, the up and down and the four directions are called "Yu", and the past and the present are called "Zhou", so "Yu" means space.

So parity, as the name suggests, refers to spatial symmetry.

But this connotation obviously does not conform to Wigner's original intention.

Parity conservation, parity should be a physical representation similar to energy, momentum, etc.

But the term "spatial symmetry" obviously doesn't fit in with energy.

The conservation of "spatial symmetry" sounds weird.

At this point, if you look at the English name of parity, it will be very easy to understand.

The original English name of parity conservation is “Parity conservation”.

Among them, conservation means conservation, and Parity is translated into parity.

But its original meaning is actually "equality, equality", which is extended to "parity" in physics.

Therefore, parity conservation is actually parity conservation.

So what does conservation of parity mean?

This requires the use of mathematical concepts.

We learned in the third grade of elementary school that there are odd functions and even functions.

If f(-x)=f(x), then the function f(x) is an even function.

If f(-x) = -f(x), then the function f(x) is an odd function.

In quantum mechanics, the wave function is also a mathematical function.

Although it is not an odd or even function in the conventional sense, it has similar "oddity".

The types of wave functions can be defined by odd and even.

As mentioned earlier, the mirror symmetry of space is discontinuous, so it does not conform to Noether's theorem.

But Wigner had an idea: since this symmetry is discontinuous, perhaps it applies to quantum mechanics.

After all, quantum mechanics is a theory that specializes in the study of discontinuities.

Therefore, after rigorous mathematical proof, Wigner boldly proposed:
For any two physical systems that are mirror-symmetric to each other, the parity of the quantum wave functions they contain is conserved.

That is, if the wave function in system A is even, then after being transformed into system B through spatial mirror symmetry, the wave function of the quantum in B will also be even.

This conservation is the so-called parity conservation, also known as parity conservation.

Once the concept of parity conservation was proposed, it immediately caused a sensation in the physics community and Wigner became famous.

Physicists accepted this theory almost without thinking twice, without even verifying it experimentally, for a simple and plain reason.

“Nature loves symmetry!”

"Symmetry is the most harmonious and beautiful!"

Later, with the development of quantum mechanics and particle physics, physicists' experimental methods became increasingly powerful.

As expected, the conservation of parity was indeed proven to be correct.

Physicists have verified the phenomenon of parity conservation in gravity, electromagnetism, and strong force.

At this time, everyone was very excited.

Although the conservation of parity in the weak force has not yet been verified, it is undoubtedly correct.

If the story ended here, it would indeed be a happy ending. Our universe is symmetrical and harmonious.

Unfortunately, no.

Soon, a small problem arose that troubled everyone.

That is the famous [θ-τ mystery].

At that time, physicists discovered two new particles through the collider: theta particles and tau particles.

The study found that the physical properties of the two particles are very similar, almost identical.

They have the same mass, the same charge, and even the same lifespan.

Therefore, some people believe that theta particles and tau particles are actually the same particle.

But soon, a strange experimental result disproved this view.

Physicists have discovered that the decay products of theta particles and tau particles are different!

The theta particle decays into 2 particles, while the tau particle decays into 3 particles.

Obviously, this experiment fully demonstrates that theta particles and tau particles are not the same particles!
In addition, physicists have verified that the parity of the two particles is different.

The wave function of the decay product of the theta particle is even, so according to the conservation of parity, the wave function of the theta particle should be even.

The wave function of the decay product of the tau particle is singular, therefore, the wave function of the tau particle is singular.

Now the problem is that not only do the two particles have different decay products, but their parity is also different.

Logically, they are obviously different particles.

However, the measurement results show that the properties of the two particles are completely consistent, with only some measurement errors.

Such an incredible phenomenon left all physicists at the time puzzled and unbelievable.

This is the so-called "θ-τ mystery".

Until two young Chinese physicists became interested in this problem.

They are the famous Yang Zhenning and Li Zhengdao.

The two systematically reviewed the entire experiment and found a strange point.

That is, decay is governed by the weak force.

According to known experiments, the conservation of parity has been verified in gravity, electromagnetic force, and strong force, but not in weak force.

Because physicists all assume that parity conservation must be correct in the weak force as well.

It’s really good to be young!

bold!

After searching a large amount of information, Yang and Li came up with a surprising conjecture:

"What if parity is not conserved in the weak force?"

boom!
This shocking conjecture shocked both of them. It was really too bold!

But if we really admit that parity is not conserved, then the θ-τ mystery can be perfectly explained.

Theta particles and tau particles are actually the same kind of particle, let's call it x particle.

Because parity is not conserved under the weak force, when the x-particle decays, different mirror changes occur, resulting in two decay processes.

If the x particle decays into 2 particles, then it is a theta particle, and if it decays into 3 particles, it is a tau particle.

The logic is perfect!
When Yang and Li published their paper, it caused a huge wave in the physics community!
Everyone thought they were both crazy.

"Impossible! Absolutely impossible!"

Even many of the world's top bosses do not agree with it.

They thought this was as ridiculous as overturning the law of conservation of energy.

Yes, in the physics community at that time, the conservation of parity and the conservation of energy were both unbreakable truths.

Who are Chen Ning Yang and Tsung Dao Lee?

Sensational!

Pauli even publicly made a bet with someone that if parity was not conserved, he would give the other person a thousand dollars.

I have to say that Pauli is really thick-skinned. I don't know how many times he has been beaten.

In order to verify their conjecture, Yang and Li hope to find a great experimental physicist to help them verify it through experiments.

Unfortunately, no one was willing to help the two whimsical Chinese people.

At this moment, a woman of Chinese descent took action!

She is the famous Wu Jianxiong!
As both were of Chinese descent, Wu Jianxiong naturally had a good impression of Yang and Li and gave them all her help.

Coincidentally, Wu Jianxiong was an experimental physicist studying β decay at the time, and she was very familiar with this experiment.

So, the three of them worked together to come up with a feasible experimental plan.

The wheel of scientific history has finally been turned by the Chinese!

The experimental plan sounds very simple:
First, find a radioactive particle, then split it into two parts, making one part spin to the left and the other part spin to the right.

In this way, the two parts of particles satisfy spatial mirror symmetry.

At this time, observe and record whether the properties of the radiation produced by the particles on both sides when β decay occurs satisfy the law of conservation of parity.

Finally, based on her own experience, Wu Jianxiong chose cobalt as the radiation source.

When cobalt decays, it turns into nickel, releasing electrons, neutrinos, and gamma rays.

Among them, electrons are very friendly particles and are easy to observe.

Therefore, the experiment can be completed by simply detecting the conditions of the emitted electrons.

Now that the plan is done, let’s start the experiment!
The most difficult step in the experiment is to create two types of cobalt atoms with different spins.

To this end, Wu Jianxiong used all his connections to borrow the most advanced cryogenic equipment in the United States at that time.

It can freeze cobalt atoms to temperatures as close to absolute zero as possible.

At this time, the cobalt atoms are very stable.

Then, Wu Jianxiong used a strong magnetic field to polarize the spin direction of some of the cobalt atoms, making their spins opposite, thus satisfying the mirror symmetry relationship.

The experiment officially begins!
At this point, there are two possible outcomes.

The first type is that the electrons emitted by the cobalt atom with left-spin are spin-right; the electrons emitted by the cobalt atom with right-spin are spin-left.

This shows that the decay behavior of the two is the same, and parity is conserved.

The second type is that the electrons emitted by the cobalt atom with left-spin are spin-right; but the electrons emitted by the cobalt atom with right-spin are also spin-right.

This shows that the decay behaviors of the two are different and parity is not conserved.

(You don’t need to understand the relationship between parity and spin)

One can imagine how Yang Zhenning, Li Zhengdao and Wu Jianxiong felt when they were waiting for the experimental results.

The experimental results are out!
It’s the second one!

The emperor pays off!
They proved that parity is not conserved!

At that moment, the three of them cried with joy!

When the paper was published, it caused a huge earthquake in the physics community.

Soon, other teams continued to repeat Wu Jianxiong's experiment.

All experimental results prove that parity is not conserved under the weak force!

The physics community is boiling!
Just the following year, in 1957, Yang Zhenning and Li Zhengdao won the Nobel Prize in Physics for this.

This is an extremely rare speed in the entire history of the Nobel Prize, which shows how shocking it is!
The two young men who were looked down upon by everyone suddenly became the world's top physics masters, standing tall among their peers!

Pauli's face was also swollen.

At that time, Yang and Li were still Chinese citizens, so this was a breakthrough for China in the field of physics!

But unfortunately, Wu Jianxiong, a heroine known as the "Oriental Madame Curie", did not win the Nobel Prize.

Soon, the entire physics community gradually accepted the fact that parity is not conserved.

The violation of parity conservation actually means that the mirror image of space is not symmetrical.

At least under the weak force in physics, spatial mirrors are not symmetrical.

This asymmetry destroys the beauty of nature.

It's like God is a bad painter, or the creator of the universe is a bad programmer.

Why should such a "Bug" be inserted into such a harmonious and perfect universe system?

Therefore, some big guys are still unwilling to give up and want to patch this bug.

Landau was one of them, and he put forward an extremely clever point of view.

But that’s another story.

Now, let's go back to the description of the mirror.

At this point, everyone should know that parity violation and mirrors actually have nothing to do with each other.

It is also wrong to explain it by the act of rock-paper-scissors.

If you must use the mirror and rock-paper-scissors analogy to explain it to elementary school students, you can say this:
"Parity violation means that the motion characteristics of particles inside and outside the mirror are different!"

“For example, if you punch, the you in the mirror also punches, but its fist is smaller than yours.”

"Instead of you punching, the mirror comes out with a cloth."

It is the [characteristics of the same movement] that are asymmetric, not [different modes of movement] that are asymmetric.

Another common story is how to explain to aliens what "left" and "right" are.

You definitely can't do it with your left hand or your right hand.

Some say that parity violation proves that humans can precisely define left and right.

Well, this is actually a misunderstanding, just a pure word game.

Parity violation does break the symmetry, but it has nothing to do with left and right, you can define it however you want.

You conduct a cobalt decay radiation experiment in front of aliens, and choose the direction of half of the spins, naming it left or right.

Later, physicists applied the violation of parity conservation to the Big Bang theory, and thus proposed the hypothesis that there is more matter than antimatter.

And this is the principle behind Li Qiwei's current proposal that "the universe comes from asymmetry."

It can be said that this conjecture was decades ahead of its time.

Only after several years will people understand what a shocking prophecy this is!

It was ahead of its time!
At this moment, it is obviously impossible for Li Qiwei to directly propose that parity is not conserved, as that would be too big a step.

For now, he just needs to put forward a hypothesis and open up a field.

Finally, he highly praised Noether's theory, believing that it represented a new direction for the future development of physics.

"From a more macroscopic perspective, from the perspective of symmetry and conservation, we can re-examine physics and the world."

"Symmetry is beautiful, asymmetry is even more beautiful!"

Everyone was filled with emotion:

"Professor Bruce respects women too much."

I am worried that this book may not be able to cover the era of Yang Zhenning, so I will give a brief overview of parity non-conservation in advance. After all, it is too famous and is also Yang's masterpiece.

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(End of this chapter)