Into Unscientific

"Primordial gravitational waves?"

This time.

After hearing this concept proposed by Yang Zhenning, Huang Kun's face was no longer as confused as before.

Instead.

It is a hint of enlightenment.

Gravitational waves.

These three words should actually be understood in two parts, namely "gravity" and "wave".

So why does gravity have waves?

The answer is obviously not because gravity is female, but because space and time have a structure - the movement of matter that we usually observe all occurs in space and time.

In a sense, it can be understood that matter is the actor, and time and space are the stage on which these actors perform.

For ordinary waves, such as water waves, sound waves, and electromagnetic waves, the actors are moving and the stage is stationary.

Gravitational waves, on the other hand, are the movement of the stage itself.

In Newtonian Mechanics at Mavericks.

Time and space are an ordinary stage, because time is a uniform passage and space is a uniform duration.

No matter how much matter there is or how it moves, it has no impact on this stage, so there can be no fluctuations, which is the absolute space-time concept mentioned before.

But in Lao Ai’s Theory of Relativity, the nature of the stage is very special.

In the general theory of relativity, Lao Ai’s way of describing gravity has become much more complicated than Maverick’s inverse square law, and it has become a big detour:

Mass causes space-time to curve, and objects moving in curved space-time appear to be affected by gravity.

It's like there is a flat piece of paper in front of you, its curvature is zero.

On this piece of paper, the sum of the interior angles of a triangle is equal to 180 degrees, the circumference of a circle is equal to 2π times the radius, and so on. The theorems of Euclidean geometry (that is, the plane geometry you learned in junior high school) are all true.

If this piece of paper is deformed, for example, into a sphere with a curvature greater than zero, many theorems of Euclidean geometry will not hold true here.

For example, the sum of the interior angles of a triangle is greater than 180 degrees - you can even make a spherical triangle with three interior angles all right angles. The sum of its interior angles is as high as 270 degrees. The circumference of the circle is less than 2π times the radius, etc.

If you turn this piece of paper into a saddle shape with a curvature less than zero, you will also find many violations of Euclidean geometry, but in the opposite direction.

For example, the sum of the interior angles of a triangle is less than 180 degrees, and the circumference of a circle is greater than 2π times the radius.

When the curved object is extended from a piece of paper, which is a two-dimensional surface, to the space-time of the theory of relativity, which is a four-dimensional geometric structure, we will understand what "space-time curvature" means, that is, every point in space-time can have a or Positive or negative or zero curvature.

General relativity gives the relationship between mass and the curvature of nearby space-time. The greater the mass, the greater the curvature of the surrounding space-time.

When an object moves under the influence of gravity without any other force, no matter whether space-time is curved or flat, it will only move along the path with the shortest distance, that is, the "geode".

If space and time are flat, the geodesic is a straight line. At this time, there is no gravity, and what it does is uniform linear motion.

If spacetime is curved, geodesics become curves.

At this time, to other observers, the object seems to be moving under the influence of gravity - for example, the earth's orbit around the sun is the geodesic of the earth's curved space-time around the sun.

If you still can't understand, let's give a simple example.

The sun is like an ear. As soon as he sits on the sofa, a big pit will be created. Then when other people sit on the sofa, they will be involuntarily sunk into this big pit.

In general relativity.

Space-time in different places can have different curvatures, so space-time has a structure.

Now that there is a structure, it can naturally fluctuate.

So according to general relativity.

Gravitational waves should be an extremely common phenomenon. The accelerated motion of any object that is not spherically symmetrical will produce gravitational waves.

This concept is extremely well-known in theoretical physics, so Huang Kun was able to keep up with Yang Zhenning's ideas this time.

Then his eyes moved slightly and asked Yang Zhenning:

"Lao Yang, isn't that right? Why can we say that we have found gravitons when we detect gravitational waves?"

"Although theoretically gravitational waves should have wave-particle duality, it seems reasonable if we use metric fields to explain them from the perspective of relativity, right?"

"In other words, there should be no absolute supporting evidence relationship between the two, otherwise Einstein would not be able to support the existence of gravitational waves."

Wave-particle duality.

When this concept was first proposed, it was only used for photons, but later with the development of the theory, it has been extended to all elementary particles.

Therefore, from the perspective of waves, a wave in the microscopic realm should also have corresponding particles.

but

Gravitational waves are somewhat special.

Mentioned earlier.

The theory of relativity is currently the most perfect theory to describe gravity. It only believes that there is a gravitational field in the universe but not gravitons. The transmission of gravitational waves relies on the metric field.

In other words, gravitational waves are tensor waves. When the wave passes through a certain area, it causes space to contract and expand in the vertical direction.

This explanation can also explain gravitational waves, and it can form a good closed-loop ecosystem in itself.

To explain it with examples from later generations.

General relativity is equivalent to Apple's iOS system, and the standard particle model is equivalent to the Android camp.

Even if ios does not need to interact with Android, it can still live well, and it can even be said to be the overlord in many situations.

The Android camp, which represents standard particles, has an advantage over all users - that is, the standard particle model has a greater impact on the development of science and technology than Guangxiang. The two are currently in a very anxious struggle.

Gravitational waves are equivalent to a very important software. iOS can support it and Android can also support it.

Of course.

It's different with gravitons.

This thing is equivalent to the law of sudden death. As long as it is proven or falsified, both the general phase and the standard particle model must be inferior.

"."

Looking at Huang Kun who was a little confused, Yang Zhenning quickly shook his head:

"Old Huang, think about it again."

"I'm not talking about ordinary gravitational waves, but primordial gravitational waves."

"Primordial gravitational waves?"

Huang Kun adjusted his glasses subconsciously:

"What is that?"

Yang Zhenning thought for a while, made a gesture with his hands in front of him, and explained:

"Old Huang, you should know that the so-called gravitational waves, as the name suggests, are fluctuations in the gravitational field, or disturbances in the metric of the gravitational field."

"This kind of disturbance is complicated due to the interference or influence of various circumstances, just like the steamed buns you love to eat. From the initial wheat to the finished buns, there are many steps involved - such as threshing, wiping, Fermentation and so on.”

"The same is true for gravitational waves. Conventional gravitational waves are caused by various scenarios, and the internal information is also very complicated. As you said before, it can be analyzed by the standard model, but it can also be interpreted by the broad phase."

"But what if we could find a gravitational wave that spans a very long time span? For example, as far back as the early universe?"

Huang Kun was stunned for a moment.

Yang Zhenning then continued to explain:

"In the very early universe, the energy scale was very high and the quantum effects of gravity could not be ignored, so the gravitational field would have quantum perturbations like other matter fields."

"That is to say, the gravity at that time was in a quantum state - of course, since gravitational waves are classical effects and not quantum effects, this quantum perturbation of the gravitational field cannot be regarded as gravitational waves, it can only be regarded as gravitational waves' seed'."

"Later, this seed grew and expanded with the inflation of the universe, and its wavelength was stretched to a scale far larger than the horizon of the universe at that time. It was canonized and became a gravitational wave that filled the entire universe."

"And these first batch of gravitational waves born are primordial gravitational waves."

"Once we can capture the primordial gravitational waves, we can infer the physical information of the very early universe, including the possible existence of gravitons."

After Yang Zhenning finished speaking, he subconsciously looked at Li Zhengdao.

When Li Zhengdao stated the quantum system equations, he knew that his old enemy also thought of primordial gravitational waves.

As everyone knows.

Starting from the cosmological perturbation theory, the equation for the perturbation h of the gravitational field metric tensor can be derived:

d/dτ=ag00c2dt2+ag0jdx0dxj+h+k^2h+gijdxidxj

where a is the scale factor of the universe, k is the perturbed momentum mode, and ≡d/dτ is the derivative with respect to conformal time.

Then by redefining it, it can be transformed into a variable frequency oscillator equation:

ααhμν+aμνh+a′(λμhλν+λνhλμ)+bημναβhαβ+b′ημνααh=kTμν

That's right.

The smart classmates must have figured it out.

It is not difficult to see from this equation that if the universe is expanding, that is, a1/τ, then the equation will have the following solution:

(13a)ααh+2αβhαβ=kT

It can be seen that the imaginary part of the solution is proportional to the scale of the universe a. In exchange for the originally defined perturbation h, due to the energy density of the perturbation h, the imaginary part ρ|imaginary part|2/a2, and the total energy Eρa3.

It can be seen that the total amount of gravitational waves will increase rapidly with the rapid increase of the universe scale a during inflation. This is how the original gravitational waves are generated.

Perhaps hoping that Huang Kun could better understand his thoughts, Yang Zhenning quickly explained:

“The physical information of the very early universe mainly refers to the specific physical mechanism of cosmic inflation. The original gravitational waves formed by different mechanisms are different. Therefore, we can judge how the inflation of the very early universe was by observing the characteristics of the original gravitational waves. occurring."

"Specifically, the original gravitational wave has a parameter called the tensor-to-scalar ratio r, which is the ratio of the intensity of the original tensor perturbation to the original scalar perturbation."

"Usually different inflationary mechanisms predict different tension-to-standard ratios r. As long as we detect the original gravitational waves in the future and obtain the specific values ​​of the tension-to-standard ratio r and another parameter spectral index ns, we can judge what the universe is in. What physical mechanism drives inflation to occur?"

“Once the physical mechanism of the early universe is understood, the problem of gravitons will naturally be solved.”

Huang Kun nodded thoughtfully.

I see

The inflation theory of the universe has always been a very cutting-edge and hot topic, but this thing is also a type of theory that is highly convincing but lacks evidence for a long time.

If we follow the situation mentioned by Yang Zhenning and combine it with part of the meta-hadron model, an iterative logical inference will appear:

During the Big Bang, primordial gravitational waves were produced almost earlier than any other form of energy. They existed as early as when the electroweak interaction merged and matter and radiation were not yet separated.

Therefore, the primordial gravitational wave is undoubtedly the most experienced and knowledgeable character in the universe. Those early experiences have been carefully recorded by the primordial gravitational wave.

During the first tens of thousands of years of the "cosmic dark period," which was impermeable to light, the appearance of the entire universe changed dramatically several times.

When the "dark period" ends, the first ray of light can calmly shine into the distance, and the original gravitational wave will be the earliest witness.

At the same time, the original gravitational wave itself is enough to prove the authenticity of the graviton force - no matter whether gravitons exist or not, as long as the original gravitational wave can be captured, everything can reach the final conclusion.

Think of this.

Huang Kun realized something again, frowned and asked Yang Zhenning:

"Lao Yang, according to you, the accuracy requirements for equipment to detect primary gravitational waves should be very high, right?"

Yang Zhenning nodded calmly:

"That is inevitable. At least based on the current situation in our country, even the accuracy of the equipment across the sea is several orders of magnitude behind that requirement."

"However, no matter how high the accuracy is, it is at least within the scope of human power. At least it is not as desperate as the Planck scale."

Hear this.

Li Zhengdao on the side also nodded slightly.

The Planck length is 1.6×10^-33 centimeters. The Planck scale means that the units may not be the same, but the energy levels of each other are the same.

There are two types of equipment accuracy in this era. One is applied physics. That is, the level that can be achieved by producing parts. This level is about 10 minus six meters.

There is also measurement accuracy, which can be understood as induction accuracy, which is about ten minus nine meters.

No matter which one of the above two, there is a huge gap between it and the Planck scale.

The detection accuracy of original gravitational waves is relatively small. After all, Yang Zhenning and others have already tinkered with the corresponding framework.

Then Yang Zhenning looked at Li Zhengdao again and called out his name for the first time today:

"Lao Li, which one are you going to choose?"

Li Zhengdao was slightly startled, but he soon understood what Yang Zhenning meant - was he asking whether he should choose dark matter or primordial gravitational waves for the bet.

The difficulty of dark matter is relatively low. After all, its difficulty mainly lies in locking the corresponding energy level.

Although this energy level is also difficult to reach with current technology, Li Zhengdao estimates that even the China he knows should be able to reach this level within 20 years.

As for primordial gravitational waves, it may take a longer time.

Not to mention 20 years, or even 40 years of doubling in 20 years, may not be enough to solve this problem.

"."

Then Li Zhengdao was silent for about a minute before giving his answer:

"I want both in this project. As for the result that determines who wins, let's choose primordial gravitational waves."

Yang Zhenning glanced at him and asked:

"Are you sure? If it is primordial gravitational waves, then we will probably have to fight for a lifetime."

Li Zhengdao looked at him calmly for a few seconds:

"Then let's fight for the rest of our lives. We can settle our grudges by the time you and I are about to be buried, and leave the rest to future generations to judge."

Note:

I have made an itinerary. When I feel better at the end of January, I will probably go to the capital and visit Mr. Yang. However, I have just made an itinerary, so I can’t talk about some of my ideas now. I’ll see about it then.