Into Unscientific Chapter 717

 After getting a positive reply from Xu Yun.

Yang Zhenning subconsciously drew an [O]-shaped circle on the math paper in front of him, his eyes flickering inexplicably:

 “Black hole?”

 Mentioned earlier.

At the end of the 1940s of this century, people successfully quantized various material fields in flat space and time.

So they naturally tried to quantize the material field in curved space-time and quantize the gravitational field itself.

Even when establishing a self-consistent quantum gravity theory encounters huge difficulties and resistance, it still does not prevent people from establishing quantum field theory in curved space-time.

 The space-time at that time was still classical, and the material field was quantized.

However, unlike classical physics, which can be verified by finding an open space, the concept of "field" is easy to calculate, but it is a bit difficult to verify it in phenomena - at least this is true for the technological level in the 1960s.

 And black holes are undoubtedly a powerful place to test the quantum field theory of curved space-time.

Black holes were actually proposed very early, which may have subverted many people's perceptions:

The concept of black holes was first coined in 1783.

 That's right.

  Not 1983, nor 1883, but 1783.

This year in China was the forty-eighth year of Qianlong. Emperor Qianlong completed his fourth eastward tour of Shengjing and squandered a lot of money.

 At the same time, on the fifth day after Qianlong arrived in Jilin.

John Mitchell, then professor of geology and chaplain at the University of Cambridge, speculated on the influence of the sun's gravity on the light it radiates in a lecture to the Royal Society.

Roemer, who was earlier than him, determined that the speed of light is limited by observing the eclipse time of Jupiter in the 17th century. Therefore, Michel believed that photons from the sun would slow down due to the gravity of the sun when they leave the sun.

His speculation states that if the diameter of the Sun were 500 times larger and the density was the same, its mass would be 10^8 solar masses, and gravity would prevent light from escaping from the Sun.

 Then in 1915, Einstein formulated the general theory of relativity and obtained a coordinated theory of how gravity affects light.

  1916.

 The Schwarzschild solution based on Einstein's field equations was published.

  1939.

Oppenheimer proved that if the mass of a dead star is greater than a certain limit, it will be unable to resist its own gravity and form a black hole of infinite density, which is the famous Oppenheimer limit.

 At this point, the understanding of black holes in mathematics and physics has been deduced to a range that is not to say perfect, but at least relatively mature.

 Theoretically speaking.

By observing the gravitational effects around black holes, scientists can verify the predictions of relativity—such as the bending of light and the distortion of space-time.

In addition, by observing black hole accretion disks and jets, the physical world can study the behavior of high-energy matter in extreme gravitational fields, which is almost the cornerstone of plasma and radio waves.

Of course.

The above sentence is from the perspective of future generations. At this time, the understanding and exploration of black holes are still very simple.

At present, the name of black hole has not been completely determined. In addition to black hole, it also has other names such as black star and dark star.

Then Yang Zhenning's pen tip clicked inside the circle he drew, and said to Xu Yun:

“Xiao Xu, I hear what you mean. Do you think there is new physics hidden in black holes?”

 Different from the previous broad concept of the universe, Chen Ning Yang is still relatively clear about the value of black hole research—still relatively speaking.

Xu Yunze nodded quickly:

“Mr. Yang, I think this sentence should be an affirmative sentence.”

Yang Zhenning's expression remained unchanged and he asked:

“What about the evidence? You should know that almost all current derivation of black holes is just mathematical conjecture.”

“If we take it to the extreme, we are not even sure whether black holes exist or not.”

“The existence of the black hole itself is like this, let alone the physical state inside it.”

“I personally have reservations about this project unless you can give me evidence of new physics within it.”

Xu Yun tapped his fingers on the table a few times:

 “Theoretical evidence? Or actual phenomena?”

Yang Zhenning's tone remains calm:

"Of course the former is enough. If you can come up with the latter, I will really suspect that you are an alien donkey turned spirit."

There are few signs of black holes in the physics community today. If you want Xu Yun to provide evidence of the phenomenon, it is obviously a bit difficult.

 Especially in Yang Zhenning's opinion.

Even if it is just theoretical evidence, Xu Yun may not be able to produce much.

After all, this is different from the methadron model. No matter how transcendent this era is, the methadron model is still a framework built on the experimental reports of accelerators.

Black holes are not a thing that can be understood nowadays. It is not difficult to come up with some results of average value just by relying on mathematical and logical deductions, but it is almost impossible to achieve subversive results.

However, what surprised Yang Zhenning was that after a moment, Xu Yun's voice came faintly from the opposite side:

“Mr. Yang, to be honest with you, I can really produce this evidence.”

Yang Zhenning was suddenly startled and said subconsciously:

 “What evidence?”

Xu Yun was silent for a while:

“For example, there is entropy in the black hole system.”

 Entropy?

Since the phone signal is not very good these days, Yang Zhenning did not realize what Xu Yun was referring to when he heard the word.

 But immediately afterwards.

Yang Zhenning suddenly stood up from his seat, and his shocked voice was so loud that even Lu Guangda outside could sense it:

 “What did you say? Black holes have entropy??!”

Xu Yun nodded firmly, and then added some weight to his words:

“Accurately, the entropy of a black hole is proportional to the surface area of ​​the black hole.”

 More than ten seconds later.

Yang Zhenning, who recovered from the shock, wanted to calm down, but found that his cheeks were trembling slightly:

be honest.

If Xu Yun hadn't previously shown a strong foundation in physics, and if Rabbit officials endorsed this call, Yang Zhenning would have almost flipped the table.

Black holes have entropy?

How can this be?

 Entropy.

  This is a concept of thermodynamics, but in the development of history, various factors have created a very rich connotation and entered the field of vision of many disciplines.

This concept is very complicated to explain in terms of definition, involving Shannon, Clausius, Boltzmann, etc., and also includes thermal entropy, information entropy, chemical entropy, etc.

 But in fact it can also be explained very popularly:

 Simply put, entropy represents the degree of disorder of matter.

 Those students who have bedrooms should all know this.    While maintaining a human life, your bedroom will become more and more messy if you don't tidy it up.

 At first, the clothes may become messy, then books, intellectual disabilities, pens, data cables, and express boxes begin to appear in various places, and eventually it becomes a doghouse.

 The definition of chaos in the house here is entropy. The higher the degree of chaos, the higher the entropy, which is the so-called entropy increase.

Entropy reduction means that in a closed system, the entropy value of the system decreases over time - this is impossible under normal circumstances, unless you manually intervene to organize your bedroom, otherwise the house itself will Unable to clean itself.

 Concise and clear.JPG.

The concept of entropy increase also holds true from the perspective of the universe. The physics community recognizes that the entropy of the universe has been increasing because the planets are constantly changing:

 Some planets collide with each other and break into small pieces, some planets end their lifespan and become red giants, etc.

but

Many scholars have different views on black holes:

 They believe that there is no entropy in black holes.

Because according to the example of cleaning the house above, no matter how complex the thing is, its "state" will become simpler after it is swallowed by a black hole. In theory, this is a case of entropy reduction.

However, entropy reduction is not allowed in independent systems, so black holes can only be in a state of "nothing"—no life, no light, and no entropy.

  This is the so-called unitarity principle.

 What I didn't expect was that the result was

Xu Yun not only said that black holes have entropy, but also said that the entropy of black holes is proportional to its surface area?

To know.

The surface area of ​​a black hole is constantly increasing. If the black hole entropy is proportional to the surface area, doesn't it mean that the black hole system is in a state of increasing entropy?

Think of this.

Yang Zhenning couldn't help but take a deep breath again, resisting the urge to refute the heresy, and asked Xu Yun:

“Xiao Xu, what you say is unfounded, where is your evidence?”

 Xu Yun raised his head and looked at the time on the wall. Unknowingly, his chat with Yang Zhenning had lasted for an hour:

“Mr. Yang, first of all we have to make it clear that to parameterize a black hole, theoretically only three quantities are needed.”

“That's mass M, charge Q and angular momentum J. Is this okay?”

Yang Zhenning nodded:

"Um."

 Mentioned earlier.

Einstein's field equations have the earliest and most famous special solution, called the Schwarzschild solution.

 The object described by this solution is a black hole, and the visual distance limit of the black hole is the so-called Schwarzschild radius. Therefore, some black holes are also called Schwarzschild black holes.

 Schwarzschild black hole is a stationary spherically symmetric black hole with only one parameter, mass M, and is also the simplest black hole in the model.

Then based on the Schwarzschild black hole, physicists deduced the rotating black hole, which is the Kerr-Newman black hole.

 It is a generalization of the Kerr black hole with Q=0, and is also the most common type of black hole in the entire universe.

According to the Kerr-Newman line elements, only mass M, charge Q and angular momentum J are needed to describe a black hole.

Xu Yun then listened attentively to what was happening on the other side of the phone. Soon, a "click" sound came from the other end of the phone.

This is the sound of Chen Ning Yang putting the pen on the table, which means that Chen Ning Yang has written the calculation.

So Xu Yun quickly said:

“On this basis, Robert Jerassi proposed a thought experiment that refuted the generalized second law.”

“That is, slowly move an object to the event horizon of the black hole and throw it into the black hole.”

“At this time, it can be found that the entropy of the black hole does not increase, but the entropy of the material decreases, so the general entropy decreases in this process.”

Yang Zhenning nodded. This is a very famous thought experiment.

Xu Yun then took a deep breath and continued:

“But in fact, since the object has thickness, for the sake of convenience, let's assume that a ball is used for the experiment.”

“For a spherical object, because it has a finite radius R, it is actually impossible for us to lower it to the black hole event horizon before throwing it in—it ends at R (the intrinsic distance) above the event horizon.”

“At this time, the entropy of the black hole will increase, and the entropy of the material will disappear, thus ensuring the establishment of the general second law.”

Yang Zhenning suddenly raised his eyes, this was quite a novel angle.

 Then without waiting for Yang Zhenning to think carefully, Xu Yun spoke again:

 “Then Mr. Yang, if this process is not a ball and a black hole, but”

 “What if two black holes merge at the same time?”

 “Black hole merger?”

Yang Zhenning subconsciously looked at the [O] representing a black hole that he originally drew on the paper. His eyes were lost in focus for a moment, and then his breath froze, and he quickly picked up a pen and started writing.

“Generally stable black holes satisfy dM=κ8πGdΩdJ+ΦdQ”

“If we assume that a black hole merges with a black hole, then it can be seen from the ball example that dA/dt≥0, and angular momentum is introduced at the same time”

Hearing Yang Zhenning talking to himself while calculating, Xu Yun couldn't help but feel a little emotion on his face.

Black hole.

 This is a very special topic in the history of physics.

 Its particularity lies not only in its phenomenal nature but also in its time span.

 Mentioned above.

The concept was proposed as early as 1783, when wheat was still a fertilized egg.

But it was not until the second decade of the 19th century that the physics community gained some mathematical understanding of it.

 However, this is only the beginning.

 According to historical development.

Starting from 1920, the physics community's research on black holes will stagnate for a full fifty years, and a key breakthrough will not occur until around 1970.

This breakthrough is the black hole area law proposed by Hawking, and the Bekenstein limit proposed by Jacob Bekenstein based on Hawking's law, which is the Bekenstein-Hawking entropy.

Bekenstein limit is very complicated to explain, but it can be summed up in just one sentence:

For a sphere with radius r, the total energy (including the energy corresponding to the rest mass) is E, then the entropy of this sphere is at most 2πkcEr.

From this perspective, the sentence "human imagination is endless" is actually wrong.

 The human brain weighs approximately 1.5kg, has a volume of 1260cm^3, and if viewed as a sphere, the radius is 6.7cm.

 Based on the size and mass of the average human brain, a person can only have a maximum of 10^42 thoughts.

Even if people's consciousness is uploaded and becomes a flowing thought in a huge computer, this limit will still exist.

 A computer or "brain" the size of the earth can only have 10^75 thoughts at most.

A 256-bit key may allow the computer to calculate two minutes faster, while a 512-bit key may require nearly 10 years to the power of 72. Therefore, in some novels, it is impossible for a certain character to deduce ancient and modern plots with just one thought. Yes, in fact, even a password lock may not be cracked, ahem.

At the same time, there is also the Brammerman limit that limits this. The fastest computing speed that can be achieved by 1kg of matter in 1 second is 1.36*10^50 bits. Even so, it still does not ruin fantasy novels.

all in all.

Bekenstein limit proves that black holes have black hole entropy, which is proportional to the event horizon area of ​​the black hole.

Although this process is a purely mathematical derivation, the gravitational wave event GW150914 observed by LIGO in 2015 proved the correctness of this derivation.

 At the same time, it is very touching.

The Bekenstein limit is a concept that you can see in online novels such as "Into the Native Donkey" in later generations, but in this era, it is completely mysterious and extremely knowledge.

Even a big shot like Yang Zhenning was unheard of before.

 (End of this chapter)

Chapter end