"How?" Wei Gong sat opposite Cui Xiaoxiao and looked at her with a smug face.

As soon as he came back from Dream Square, he told Cui Xiaoxiao everything that happened today, and until this moment, there was still a faint excitement in his heart.

It is better to be happy alone than to be happy in all, and of course another person needs to share what you are happy about.

Cui Xiaoxiao didn't look up at him, just looked at her immortal cultivation manual intently.

said that he didn't care about what happened to Wei Gong in Dream Square, but he knew better than anyone else.

At that time, Du Zheyi admired Wei Gong so much that he threw himself to the ground, and sincerely invited Wei Gong to teach at the Arithmetic Academy of the Heavenly Sword Kingdom.

However, you don't have to think about it to know that Wei Gong refused.

It's just that when Wei Gong left, in order to leave a memory for Du Zheyi, he proposed a so-called [New World Puzzle]-

Now that everyone already knows the circumference of the world ball, what is the mass of this fairy sword world?

"You're such a bad person." Cui Xiaoxiao closed the book, then raised her head and looked at him with wide eyes, "Why do you want to do this kind of thing?" ”

Wei Gong smiled, "I have to leave a thought for future generations, otherwise I will take all the credit, what will happen to the people in the future?" ”

"It's shameless."

Cui Xiaoxiao laughed after speaking.

You must know that after Eratostine calculated the diameter and circumference of the earth more than 200 years AD, it took more than 1,500 years for someone to solve this problem.

In the seventeenth century, human beings once thought that this was a puzzle that could never be solved, even Newton, the great god of physics who later discovered gravity, could not really calculate it in his lifetime, limited by the determination of the gravitational constant, until later Cavendish proposed a new measurement model when observing children playing with mirrors, so as to calculate the mass of the earth through the gravitational constant.

This new problem in the Wei Palace, for this world, I am afraid it is too advanced.

I don't know when someone like Newton will emerge who can discover gravity.

Cui Xiaoxiao picked up a royal snake fruit from the side and put it in her mouth and chewed it, her two little legs dangling on the chair, "Have you ever wondered why the planet we are on has a smaller radius than the original earth, but the various rotational periods are about the same, and the orbits of the moon and the sun outside are also similar?" ”

“…… This ......" Emiya was stunned for a moment, and really didn't think too much about this problem.

You must know that according to the original model of the rotation of the earth around the sun, the reason why the earth can maintain an elliptical orbit around the sun with a small eccentricity is mainly affected by the rotation of the earth and gravitational force.

A change in any parameter of mass or radius will trigger a series of changes.

In other words, if the radius of the planet is smaller than that of the Earth according to the existing calculations, then it is possible to cause a change in gravity with the same mass, first the gravitational force will increase, and then the Earth's rotation speed will become faster, and the time of day will be shortened.

Then, in order to counteract the corresponding gravitational attraction of the Earth and the Moon, the Moon will be closer to the Earth, the Moon will be larger, and the Moon will rotate at a faster speed around the Earth, and the Earth will inevitably be closer to the Sun, so as to offset the centripetal force demand generated by the faster rotation speed.

Once closer to the Sun, the planet will inevitably suffer more severe radiation, and the temperature changes will be more drastic, and the extremes of both temperatures will be much greater than they are now.

It is also possible to suffer from more intense gamma-ray storms emitted by sunspots.

In other words, in any case, according to conventional theory, the planet is simply not what it is now.

And judging from Emiya's understanding of the mineral density of this world, the density of this planet will only be greater than that of Earth, not smaller.

Thinking about this, Emiya couldn't figure it out anymore.

How can a planet with a large density and a small radius maintain a rotation and revolution period similar to that of the Earth?

Cui Xiaoxiao also had a trace of doubt in her eyes, she and Wei Gong almost thought of the same thing.

Emiya thought for a moment and said seriously, "If one variable changes, it will indeed trigger a series of reactions, but if all the environment changes, wouldn't it naturally make sense?" For example, if the moon and the sun have a small density and a large radius, then it is possible to form the same cosmic environment, isn't it? ”

Cui Xiaoxiao shook her head, "According to the razor principle, we should explain more things with the fewest variables possible, rather than complicating it. ”

She frowned, impatiently placed the Immortal Cultivation Handbook on the table, and then climbed down from the high chair.

She paced back and forth a few steps, looked up at the big moon in the sky from the window, and let out a sigh.

"Unless......" she stopped talking, and finally came up with an idea that even she couldn't believe—

"The planet is hollow."

……

In order to verify Cui Xiaoxiao's guess, Wei Gong specially measured it.

For those who are already standing on Cavendis's shoulders, the process of calculating the mass of the Earth is very simple, first measuring the gravitational acceleration based on the height and time of the object's fall, and then using the equation to calculate:

M=gRR/G, you can get the mass of the planet.

The calculated result surprised both Wei Gong and Cui Xiaoxiao, because this mass size is 5.964×10^24kg, while the mass of the original earth is 5.965×10^24kg.

That is, the mass of this planet is a little smaller than that of the original Earth.

So it is very likely to be the same as Cui Xiaoxiao said, it is hollow.

If so, what would the center of the earth look like?

Emiya's mouth opened wide in surprise, completely unbelievable.

……

However, when there is not enough technology to probe the center of the earth, the puzzle has to be put aside.

According to his idea, it is also time to take some new orders to expand the new products in addition to the Wing Qin Sword.

When Emiya routinely logged in to the source of the sword, he was still interested in a new order from Kira.

"Water spider infestation?"

Emiya had never heard of such a thing.

In addition to novelty, there is also a very important reason why employers are willing to spend a lot of money.

"Didn't you get some special deworming experts to take a look?"

"I looked for it, but it didn't work, and what was even more terrifying was that there seemed to be more and more of them. We are also desperate to ask you, because you are the greatest swordsmith of the day, and there is no problem that you cannot solve. ”

"Insect repellent sword?"

Emiya smiled bitterly, he really didn't think he would forge such a thing.

In this case, I had to go on a trip, and if I didn't conduct an on-site investigation, it would be impossible to figure out the root cause of the problem.

……