1900: A physics genius wandering around Europe

Chapter 674 The Great Particle Explosion! Elementary Particles! Peeking into the Heavenly Secrets through the Eight Trigrams! A Single Enlightenment Leads to Quark Success!

Humanity has never ceased its exploration of the nature of the world since ancient times.

More than two thousand years ago, the ancient Greek philosopher Democritus proposed the famous "atomism".

This theory holds that:
1. All things in the world are composed of extremely small atomic particles;
2. Atoms are solid matter and cannot be further divided;
3. The origin of the universe is atoms and void. Atoms make up matter, and void is the place where atoms move.

Even from today's perspective, Democritus's theory remains astounding.

He conceived of the atom as a fundamental particle, which, through arrangement and combination, forms all things, conforming to the simple beauty of nature.

Therefore, atomic theory has dominated the academic world for more than a thousand years.

It wasn't until 1803 that British chemist John Dalton, inheriting the atomic theory of ancient Greece and Newton's corpuscular theory, published his magnum opus, the modern atomic theory.

Its core idea is:
1. The atoms that make up different substances are different;

2. Different atoms can form new substances through chemical reactions.

It is clear that Dalton's atomic theory is far more profound than Democritus's atomic theory.

Moreover, Dalton arrived at this conclusion through extensive chemical experiments and measurements.

Therefore, his atomic theory replaced the ancient Greek atomic theory and continued to dominate the academic world for nearly 100 years.

It wasn't until 1897, when Thomson discovered the electron, that humanity finally uncovered the mysteries of the atom's interior.

It turns out that atoms are not fundamental particles!

Therefore, research on atomic structure became a focus.

Soon, protons and neutrons were discovered, and the concept of neutrinos was proposed.

As mentioned earlier, Anderson discovered muons in cosmic rays in 1936.

Physicists at the time were delighted, but also very puzzled.

The presence of muons disrupts the "simplicity and beauty of the universe".

Muons are essentially enlarged versions of electrons. Except for mass, they have all the same properties as electrons, such as spin and isospin.

Therefore, physicists are puzzled:
"The universe has already created electrons, so why create muons?"

"That's completely unnecessary."

No one can explain this problem.

Then, in 1947, Powell discovered the π meson, which transmits the strong force.

The current particle family consists of: proton, neutron, electron, neutrino, muon, pi meson, and photon.

It is worth mentioning here that, according to Heisenberg's isospin theory, the π meson has three spatial projections, representing three charge states.

They are: π+/π-/π0.

Physicists at the time believed that these particles were elementary particles and could not be further divided.

Soon, the field of cosmic rays experienced a super explosion.

In the late 40s and early 50s, physicists were able to discover new particles in cosmic rays almost every week.

In just a few years, seventy or eighty new particles have been discovered.

Most importantly, a batch of new particles were discovered by American physicists Rochester and Butler.

They can be divided into two categories:

The first type is called the K meson. (Note that this letter is not pronounced Kei, but rather the Greek letter Kappa.)
Including K+, K-, K0, anti-K0.

Like the π meson, the K meson also transmits the strong force, but the K meson has a greater mass than the π meson.

The second type is called "hyperson".

In essence, hyperons are baryons similar to protons and neutrons (all composed of quarks).
However, because their mass is much greater than that of protons and neutrons, they are called "baryons that are beyond the ordinary baryon", or simply "hyperons".

Hyperons include: Λ, Σ+, Σ0, Σ-, ≡0, ≡-. (Hmm, I can't pronounce them either.)
Both of these types of particles are related to the strong force.

At this point, you might have noticed a small problem.

As the number of particles increases, the classification of baryons and leptons solely based on weight is no longer appropriate.

Therefore, physicists collectively refer to all forces related to the strong force as "hadrons".

The aim is to analyze the properties of particles from the perspective of their interactions.

Hadrons include baryons and mesons.

Here comes the point!

Physicists discovered a very strange phenomenon while studying hadrons.

Take the Λ particle as an example. It is a product of the strong force and is unstable and will decay.

The Λ-ion decays into the π-meson and the proton.

So obviously, physicists thought that π- and protons would also become Λ- under the influence of the strong force.

However, the experimental results showed that π- and protons were transformed into Λ- under the control of the weak force.

Here, I'd like to mention how we can determine what force controls particle decay.
The interaction between two particles can be likened to the collision of two target surfaces.

The larger the collision area, the more likely a collision will occur.

Physicists have discovered that the stronger the force, the larger the collision area.

The four great forces, ranked by strength, are: strong force > electromagnetic force > weak force > gravity.

Therefore, by measuring the collision cross-section, physicists can determine which force controls the particle's interaction.

Going back to the point above, how do we explain the problem with Λ子?
At this time, American physicist Gell-Mann proposed a new quantum number: "singular number".

This is a quantum number similar to isospin, a hypothetical quantum number conceived by Gell-Mann after studying a large number of particle properties.

The thought process was very simple; it was just a matter of adding, subtracting, multiplying, and dividing to get the result.

比如一个粒子衰变中，有重子数1、轻子数1、电荷数+1、自旋1/2、同位旋2/3等等量子数。

According to the rules, the values ​​of these quantum numbers need to be conserved before and after the interaction.

But now the Λ particle is no longer conserved.

Easy, just add a new singular number to achieve conservation.

It's such a simple and unpretentious theory.

This also highlights the difference between amateur scientists and genuine physicists.

The former approach is a mere guesswork, devoid of any reason or basis; while the latter approach is a perfect solution based on in-depth research into existing results.

The two should not be confused.

After solving the problem of non-conservation, physicists began to systematically study these new particles.

Soon, people discovered that by colliding these known particles, they could obtain many new artificial particles.

(There are corresponding theories to prove that collisions produce new particles, which will not be discussed here.)
As a result, by the 60s, the particle family had grown to more than 300 members, and there were almost not enough Greek letters to go around.

The vast majority of them are various kinds of hadrons.

Most importantly, there are nine mesons and nine baryons.

Nine mesons: ρ+, ρ0, ρ-, K*+, K*0, anti-K*0, K*-, ω, ф.

Nine types of baryons: Σ*-, Σ*0, Σ*+, ≡*-, ≡*0, Δ++, Δ+, Δ0, Δ-.

These particles also possess their own quantum numbers such as charge number, baryon number, isospin number, and singularity.

By this time, physicists were already tormented by more than 300 kinds of particles.

For example, the Lamb who discovered Lamb's displacement once said helplessly:
"If anyone discovers a new particle in the future, they will be fined $1000 first."

It's clear that the increasing number of particles is driving everyone crazy.

In the past, the discovery of a new particle would have been a tremendous honor, shocking the entire academic community and causing widespread celebration.

But now, there are so many new particles that physicists are sick of them.

Sure enough, once you get tired of something, it loses its appeal.

Moreover, people don't need to remember these particles so clearly.

Because Fermi couldn't remember either.
He joked, "Anyone who can remember all the particle names can become a biologist."

What a hierarchical system of contempt!

Jokes are jokes.

At this point, a most pressing question confronted physicists: "Are these particles all indivisible fundamental particles?"

At that time, all physicists would have answered in unison:

"impossible!"

"Absolutely impossible!"

"There are too many and too varied particles."

"Our universe is so beautiful and symmetrical, it is absolutely impossible for it to have such bloated and garbage underlying code."

Physicists also deeply abhor the so-called "shit mountain code".

Thus, particle physics has a new goal: to unravel the mystery of the hadron's interior.

Physicists firmly believe that these different hadrons must be composed of more fundamental particles.

Just like how there are only a few dozen elements, yet they can combine to form thousands of compounds.

Anyone can propose more fundamental particles, but the key question is: what evidence is there? How can it be proven?

Many physicists have proposed various models.

But in the end, they all failed.

At this point, Gell-Mann, who proposed the concept of singular numbers, stepped in again.

His ideas differed from everyone else's.

"Let's not worry about what that more fundamental particle is for now."

"Let's first classify these existing hadrons in a more detailed way." (An idea proposed by Li Qiwei)

So, how should we classify them?
Gell-Mann was indeed a genius; he classified hadrons according to their quantum numbers based on the principle of quantum number conservation.

He drew a diagram that was very similar to the Chinese Bagua diagram.

He placed those hadrons at various nodes of the Bagua diagram according to a certain rule of quantum numbers.

As mentioned earlier, particles decay and become new particles.

Therefore, the connection between the nodes of the Bagua diagram is a decay behavior.

In this way, the path from one particle to another becomes immediately clear.

But then another problem arose.

The Bagua diagram has only eight nodes, but the newly discovered ones have nine types of mesons and nine types of baryons.

Nine is one more than eight, which seems to be a glimmer of hope for the great path.

When nine particles were forcibly placed into the Bagua diagram, the diagram became asymmetrical, revealing a small tail.

At this point, the physicists' faith began to play a role again.

"The universe must be simple and symmetrical!"

Gell-Mann was struck by inspiration and wrote in a single stroke:
"There must be a new type of particle here!"

"With it added, the Bagua diagram becomes a hadron decafold, which is still symmetrical."

Gell-Mann called this new particle the "Ω particle," which is a type of baryon.

Soon, in 1964, physicists discovered the omega particle through the collision of K-mesons with protons.

Gell-Mann's victory cemented his legendary status!
This achievement was also the main reason he won the Nobel Prize.

But the story doesn't end here.

Does the hadron have any internal structure?

At this point, Gell-Mann was the absolute authority in the field of hadrons.

His classification method makes the chaotic particles very orderly, like viewing text on the palm of your hand.

Gell-Mann launched another attack.

His idea was simple: first, assume the existence of a fundamental particle that can combine to form any known hadron.

What combination of factors will it rely on?
I'm sure you, being so clever, have already guessed it.

That's right, it's still quantum numbers.

Gell-Mann resorted to his old trick, "forcing it together" using quantum numbers.

He conceived of three fundamental particles: the up quark (u), the down quark (d), and the strange quark (s).

In addition, there are their respective anti-versions, namely anti-up quark, anti-down quark, and anti-strange quark.

As mentioned earlier, the secret of particle decay can be explained by adding and subtracting quantum numbers in the Bagua diagram.

And now these six quarks also have their own quantum numbers.

Gell-Mann thought:
"If I can combine the quantum numbers of all known hadrons using the quantum numbers of the six quarks, wouldn't that prove that quarks are more fundamental particles?"

Just do it!

It actually worked!

Gell-Mann's quark model could indeed be combined to form all the hadrons known at the time.

Two quarks can form a meson; for example, the π+ meson is composed of an up quark and an anti-down quark.

Three quarks can make up a baryon; for example, a proton is made up of two up quarks and one down quark.

It can be seen that the impressive quark and quark model is actually just a product of quantum numbers.

It's not what everyone imagines: that a brilliant mind racked his brains to derive it through various complex, profound, and unfathomable theories.

It seems like I could do it too.

In 1964, Gell-Mann formally published his quark theory.

Clearly, most physicists at the time did not accept this theory.

"Can this piece of work out of thin air?"

"Even a big shot shouldn't play like this."

And most importantly, the idea that quarks carry fractional electric charge is a bit ridiculous.

An electron's charge is a single unit of elementary charge, which has withstood countless tests.

The electron is a universally recognized fundamental particle and cannot be further divided. (In Gell-Mann's theory, the electron is also indivisible.)

So, what's the deal with fractional charge?

But Gell-Mann was a super big shot after all, and no matter how outrageous his theories were, people would still study them.

After all, the Ω particles that others had previously put together were eventually found.

Perhaps the same applies to quarks.

As a result, many people began searching for quarks, the "more fundamental particles".

What is the result?

It was both found and not found.

Because researchers discovered that when electrons bombard protons, they do indeed strike some internal structure of the proton.

This indicates that the proton is not a fundamental particle; there is something inside it.

However, whether it is the quark predicted by Gell-Mann is uncertain, because quarks are too small to be detected.

Therefore, the conclusion is that quarks may exist.

Gell-Mann has been deified once again!
At this point, some people became anxious:

"Author, why haven't you mentioned the Standard Model yet?"

Not urgent.

Between 1964 and 1974, Gell-Mann's quark theory gained increasing attention.

Because all the newly discovered hadron phenomena can be explained by the three types of quarks and their antiquarks.

It seems that the three quarks are the fundamental particles.

However, at this very moment, a prominent Chinese figure stepped in!

"The three quarks aren't symmetrical either!"

(End of this chapter)