1900: A physics genius wandering around Europe

Chapter 589 Quantum Mechanics Completed! Questions Continuously! Experiment Upgraded! Introducing Observers! Shocking the Audience!

In the conference room.

Everyone's face was filled with shock and confusion.

The incredible single-electron double-slit interference experiment was presented vividly before our eyes, subverting our three views.

Professor Bruce's explanation left them stunned.

For a moment, most people didn't react.

In their eyes, Professor Bruce was no longer domineering, but rather mysterious.

"That man is like the Creator playing with the world!"

“How many incredible things are there in the field of physics?”

Looking at everyone's expressions, Li Qiwei felt deeply moved.

At this point, all the classical content of quantum mechanics appears.

These contents are the parts that ordinary people can understand as long as they study them carefully.

Re-examining quantum mechanics from a higher perspective will give us new insights.

The two core theories of quantum mechanics are Schrödinger's wave mechanics and Heisenberg's matrix mechanics.

Matrix mechanics studies quantum completely from the perspective of classical mechanics. It describes the particle nature of quantum objects and does not include any wave properties.

Particle nature is materiality, which is manifested in mechanical quantities such as momentum and the ability to produce material phenomena such as collisions and trajectories.

Microscopic particles such as electrons and protons can interact with other matter by colliding with other matter, just like real matter.

And the momentum and position of the particle also satisfy the uncertainty principle.

The connotation of wave mechanics is richer.

Before today, the physics community has always regarded wave mechanics as describing the wave nature of quantum objects, which is in contradiction with matrix mechanics.

But in fact, this statement is not rigorous.

The core of wave mechanics is the Schrödinger equation.

The core of the Schrödinger equation is the wave function ψ.

According to current understanding, the quantum state described by the wave function ψ changes over time.

The state here includes quantum position (spatial distribution), momentum and other mechanical quantities. Obviously, these are concepts that only particles in classical physics have.

Therefore, the Schrödinger equation actually assumes that quantum has the properties of particles.

It’s just that the properties of particles are not as definite as in classical mechanics.

For example, using the thinking of classical mechanics to describe an electron, we can say that at this moment the electron is at point A and its momentum is 1.

But in quantum mechanics, [the electron is at A] is not certain, but a probability. (Similarly, the momentum of the electron is also a probability, which leads to the uncertainty principle.)
The specific value of this probability is equal to the square of the absolute value of the wave function ψ |ψ|, which is the probability explanation.

In addition, the probability distribution of quantum states behaves like a wave, so it is called a probability wave.

The most amazing thing is that this imaginary probability wave can interfere, diffract, and experience other phenomena just like real mechanical waves and electromagnetic waves.

However, you may ask a question:
“Since the state of a quantum, such as the position of an electron, is uncertain, its specific location in space is probabilistic.”

"Then why can we determine the position of electrons when doing various collision experiments in reality?"

"For example, when an electron hits a display, it is fixed in that position."

“What happened in this process from uncertainty to certainty?”

At this time, the principle of complementarity comes into play.

According to the principle of complementarity, neither wave nor particle properties can describe the full picture of a quantum object alone.

The wave-particle duality of matter is a whole.

If you want to know the properties of a single quantum, you must measure it.

But each measurement can only obtain one aspect of the property.

Using wave methods, we can measure the properties of waves; using particle methods, we can measure the properties of particles.

But in any case, it is impossible to measure both the wave and particle properties of quantum at the same time.

Therefore, before measurement, the quantum can be considered to be in a superposition state of wave and particle.

Once measured, the superposition state will become a certain eigenstate, which is the collapse of the wave function.

With these theories, let’s look at the position of electrons.

Before measurement, the position of the electron is in a superposition state.

So it can appear in any position.

For example, the probability of appearing at A is 0.3, the probability of appearing at B is 0.2, and the probability of appearing at C is 0.1.

Once it is measured, for example, by using a photon to hit an electron, the measurement is completed based on the state of the photon after feedback.

At this time, the electron will instantly change from the position superposition state, undergo wave function collapse, and be in a certain position eigenstate.

The specific location where it appears has nothing to do with the size of the probability value. It can be in A, C, or even D.

but!

Here comes the point!

Although there is no regular pattern to where an electron appears after it collapses.

But when a large number of electrons undergo wave function collapse one after another under the same conditions, the situation changes.

For example, at this moment there are 10 billion electrons, and the wave function of their positions collapses one after another.

If we count the locations where they appear, we will find that:
There are 3 million electrons appearing at A, 2 million at B, and 1 million at C.

The position distribution of a large number of electrons is consistent with the calculation of the wave function!

This is the principle of why interference fringes appear in the single-electron double-slit experiment.

At this moment, many bigwigs present were still digesting it.

With their IQ, Li Qiwei didn't need to explain in too much detail.

The reason why the big guys found it difficult to accept it at first was that they were not familiar with the principle of complementarity.

Once you figure it out, there's nothing magical about this experiment.

Currently, the premise is to recognize the content of Bruce's interpretation.

If someone were like Einstein and Schrödinger and refused to admit it, it would be really hard to understand.

At this time, Li Qiwei saw that Bohr, Heisenberg and Pauli actually had smiles on their faces.

He smiled and asked:

"Bohr, it seems you understand this experiment."

Bohr smiled and said:

"Yes, Professor."

"If we accept the principle of complementarity, then this experiment is easy to understand."

Bohr's words caused a burst of exclamations!
If someone who doesn't understand heard it, they would definitely think Bohr was bragging.

But those present were all big names in physics, and they were aware of Bohr's talent.

Heisenberg even boasted:
"Professor Bruce, Lee's double-slit interference experiment will definitely become the most beautiful experiment in the history of physics!"

Wow!
Heisenberg became so shameless that he actually called it Lee's double-slit experiment.

This flattery is almost to the sky.

Even Li Qiwei couldn't help but smile.

"Ruzi can be taught."

"If Thomas Young can name it, why can't I, Bruce Lee?"

The strange thing is that no one felt anything was wrong.

Given the importance of this experiment and Professor Bruce's current status, Lee's double-slit experiment is truly worthy of its name.

Even if there really is a selection event, at least they will vote for this experiment.

Just as everyone was discussing and communicating with each other, trying to thoroughly understand the principles behind the experiment.

Einstein, who was silent for a while, suddenly spoke.

"Bruce, I have a question."

Wow!
Everyone was shocked when they heard this!
"Did Professor Einstein discover something?"

Many people immediately went into the "meat-eating" mode. Far from looking down on Professor Einstein, they felt fortunate that he was participating today.

Otherwise, where can we see such wonderful academic discussions!
On this occasion today, even failure in the discussion is an honor!
Because not everyone is qualified to challenge Professor Bruce!

Li Qiwei smiled slightly and said:

"Einstein, go ahead."

Einstein said to the crowd:

"Before asking any questions, I would like to ask Professor Bruce to do a small experiment."

After that, he looked at Li Qiwei again and said with a smile:

"Bruce, please close the left slit and leave only the right slit open, and do the single electron experiment again."

"It won't take long."

Everyone didn't know why.

"What does this mean, Professor Einstein?"

"What's so good about this experiment?"

However, Li Qiwei just smiled lightly. He probably knew what Lao Ai wanted to ask.

He restarted the instrument as Einstein requested.

There is no suspense this time.

When only one slit is open, the electrons no longer diffract, but pass through the slit like particles.

Therefore, the interference fringes on the display disappear, leaving only a bright stripe.

At this time, Einstein asked:
"When there are two slits, interference fringes appear. When one slit is closed, the interference fringes disappear. Why is that?"

"The distance between the two slits is very small, only a few tens of nanometers."

"But for the size of an electron, this distance is like a million miles."

"So how does the electron know that the other slit is closed so that it doesn't interfere with itself?"

Huh?
Everyone was stunned.

This question is quite interesting.

Opening and closing the slit is a human process, so how do the electrons know about it?

Could it be that it has consciousness?

Otherwise, how would it know when to intervene and when not to?

Li Qiwei said:
"This question just proves the correctness of the principle of complementarity!"

"Because the double slit itself is actually a measurement method, and it is a wave measurement method."

"So, at this moment, the electrons exhibit wave properties, which allows them to pass through the two slits at the same time and cause interference."

"Until it encounters the display screen and collapses into particles."

"We need to note that even after the electron collapses into a particle, it still has the wave-particle duality and can return to the superposition state."

"If you remove the display at this point, the electrons will continue to propagate in this superposition state."

"Now, change the double slit into a single slit, so the electron can only pass through one slit."

"And a slit can actually be seen as a particle-based measurement method."

"At this point, the electrons become definite particles after passing through the slits, so interference no longer occurs, and there are no interference fringes on the display."

"So when we try to get information about the path that the electron took, we are measuring the particle nature of the electron."

"Path information and interference fringes are two complementary quantities, and only one of them can be seen in the same experiment."

"So, the electron does not have consciousness, but the measurement affects the state of the electron!"

"And this is exactly what the principle of complementarity is all about!"

Wow!
Everyone suddenly realized!

With the double-slit experiment in mind, it is now much easier to understand.

Einstein was silent.

He found Bruce's logic impeccable.

Everything is so perfect!
It’s just that this perfection is built on the incredible basis that objective facts cannot exist independently.

At this time, Schrödinger suddenly asked:

"Professor, why can a display screen be considered a means of measurement?"

Everyone was stunned again.

That’s also a good question.

Just because you are Professor Bruce, it doesn’t mean that what you say is true.

Ridgeway explained:

"The so-called measurement actually refers to the interaction."

"We should have a consensus that in quantum mechanics, there is no such thing as measuring an object without having any effect."

"In the macroscopic world, measuring the speed of a car has no real impact on the car itself."

"But for microscopic particles like electrons, if you want to measure them, you have to hit them with a photon or another electron of the same size."

"By analyzing the state of the photons after the collision, we can know the state of the electron to be measured."

"But the collision process itself will inevitably have an impact on the electrons."

"And the effect is that the electron collapses into particles."

Everyone nodded silently, feeling awe-inspiring.

Then, de Broglie asked another question:
"Professor, I can't imagine what the process of wave function collapse is like?"

Li Qiwei said:
"The electron's wave function itself does not represent any physical meaning."

"The collapse here is not a process, but more like a state change. It happens instantly and has no time significance."

"Just like when an electron is in a superposition state of wave and particle, we cannot imagine what that state is."

"You can think of them like the axioms in relativity that the speed of light is constant, which cannot be further elaborated."

At this time, Li Qiwei suddenly said something meaningful:
“Perhaps the purpose of science is not to explain the nature of nature; but what kind of description science can make about nature.”

Wow!
Everyone was shocked!

This is not Professor Bruce's style before.

If science cannot reveal the nature of things, what is the use of science?
Everyone felt deeply:

"It seems that the magic of quantum mechanics has not only affected us, but also Professor Bruce."

"His realm has become even more ethereal."

Li Qiwei did not pursue this issue any further.

Even in later generations, there is still no explanation for the collapse of wave function.

It is an unimaginable objective process.

No one asked any more questions now, but Li Qiwei's speech was far from over.

Next, he will continue to conduct an experiment that will be talked about by countless people in later generations.

Most people's misunderstanding of quantum mechanics and the double-slit experiment is due to this experiment.

Things like "physics no longer exists", "human consciousness can affect reality", etc.

That is the "observer effect double-slit interference experiment"!
Under the gaze of everyone, Li Qiwei continued:
"In fact, based on the single-electron double-slit experiment, I have also prepared an upgraded experiment."

“It further proves the correctness of the principle of complementarity.”

“That means bringing in observers!”

"If I put an electron detector at the double slit, I can see how the electrons actually pass through the double slit."

"So what do you think will happen?"

boom!
The whole audience was shocked!

Everyone found it incredible!

Is this really possible?
(End of this chapter)