Volume 4: Spacetime Singularity Chapter 20 The Curve of the Universe
"The earth is a drop of blue water, with a tiny flame living in the middle."
As Fang Cheng's pace became faster and faster, the earth slowly changed from a circle to a flat surface, the arc on the horizon gradually straightened, and the motionless clouds and the sun became clearer and clearer.
As they got closer and closer to the ground, the straight dividing line under their feet began to bend, slowly bending towards both sides with the place where they were standing as the apex to form a circle with a very small curvature. However, since there were no obstructions around, the arc could be seen very clearly.
Unlike Fang Cheng, Ning Yu'an is not nearsighted at all, although her eyesight is still slightly worse than her father's, so she can see very clearly that the space around her is slowly changing from flat to curved with her footsteps.
“Is this space changing?”
Ning Yu'an looked around, and as soon as she blurted out this sentence, she realized that she had probably said a very sci-fi sentence.
"It should be. If my understanding is correct, we are now moving away from the straight side of the three-dimensional interface and entering the curved part of the interface."
"Curved three-dimensional space... I always thought this kind of thing was just made up in science fiction..."
Like most humans, Ning Yu'an could not understand why space could be curved, nor could he imagine it.
"Well... In fact, not only is this artificially created space curved, but the universe we were in before was originally curved."
"Ah, I remember now, you told me about the theory of relativity before."
When she listened to Fang Cheng talking about physics, it usually went in one ear and out the other, but the word "relativity" was so famous that it naturally caught her attention.
Ning Yu'an still remembers the scene of their conversation.
It was the end of the summer vacation during her freshman year. Everyone had become very lazy at this moment, and she had no strength in her body. She basically lay on the sofa, turned on the TV and played with her phone every day.
Theoretically, the summer vacation after freshman year is the last one in which you can really have fun. There will be various internships and scientific research tasks that will fill up the vacation, so it’s actually okay to relax a little.
One day in early autumn, Fang Cheng knocked on her door as usual and came in. At this time, she was only wearing a sleeveless tank top and denim hot pants that were not longer than her knees. She was resting her head on the armrest of the sofa and pressing the screen of her mobile phone.
As soon as Fang Cheng entered the room, he saw her lying on the sofa. He was stunned for a moment, and after four or five seconds he managed to say:
"...I brought a few apples. My dad said they were distributed by the department. I'll peel them and we can eat them together."
"Oh, the fruit knife is in the basket under the coffee table."
After saying this, she hesitated for a moment as to whether to pull her clothes up to her chest , but in the end she didn't, feeling that doing so would make the atmosphere awkward.
"Do you bring fruit when you visit someone's home? It feels like visiting a patient."
"Um...what else should I bring?"
“…”
Ning Yu'an stopped pressing the phone and thought for a while. It seemed that there was really nothing to bring.
"…It's almost autumn now, aren't you cold wearing so little?"
"It's fine. I usually cover myself with a blanket or something, but I didn't today."
Fang Cheng peeled the apple skin. He was very careful when doing it. The thickness and coarseness of the peeled skin were basically consistent, and there was no break in the middle.
He couldn't explain why he did this, maybe to focus attention on Apple.
Fang Cheng pinched the two ends of the apple and used a knife to cut a circular cross-section on the spherical shape. He then put the cut bowl-shaped flesh into a small plate on the coffee table and handed the plate to Ning Yu'an.
"Why do I feel like I'm your servant?"
He said this while gnawing at the remaining flesh around the core, wondering in his mind why he started to serve her so skillfully, so naturally that he didn't even react.
Am I a service-oriented person? It seems not.
Ning Yu'an sat up , put his cell phone aside, took the plate, and naturally put his feet on the coffee table, facing Fang Cheng on the other side.
"You were the one who wanted to be the role. I didn't ask you to do anything, but you just started it on your own."
She bent slightly when she took the apple, and Fang Cheng's body leaned back.
"I say...why don't you put on a coat?"
"Well...that's fine." Ning Yu'an took off a very thin knitted hooded sweatshirt from the sofa and put it on in two seconds.
"When does your school start?"
"It's almost there, but it should be later than you guys. However, many people have already returned to school now, so it's still pretty exciting... but definitely not as exciting as you guys."
"It's hard to say. There are hard-working people everywhere..."
There is no more topic.
Fang Cheng slowly raised his gaze from the coffee table, his eyes scanning the feet on the coffee table, the calves swaying naturally from side to side, the slightly fleshy belly, and then the curves wrapped in the sweatshirt.
His sight moved upwards again. Ning Yu'an was eating fruit and browsing her phone, not looking at him.
“You know the curve of the universe?”
"What? Say it again. I didn't hear you clearly."
"What I mean is... according to the principles of relativity, the universe itself is curved, not a flat three-dimensional space."
"Oh! I've heard of this before, something like 'The Universe in a Nutshell'..."
"Um... Actually, that's a translation error. The original text is 'The Universe in a Nutshell'. 'in a Nutshell' is a slang term, meaning to talk about it briefly... The correct translation should be 'A Brief Discussion of the Universe' or 'The Universe in a Nutshell' or something like that..."
"Wow, is that so? I didn't know that."
"What I want to say is that the universe we live in is actually curved. Gravity causes the curvature of space to change. This is the main content of the general theory of relativity... Einstein summarized this principle with an equation..."
"I've heard of Einstein's equation. Is it E=mc^2..."
"It's another Einstein equation, written as Rab minus one-half Rgab..."
Fang Cheng took a look around and saw no paper or pen. His intuition told him that there was no need to write down the formula.
"Because of this curvature, the orbit of the planet is not a circle on a plane, but is always precessing, such as the orbit of the sun..."
"Ah, does the sun have an orbit of its own?"
Fang Cheng could tell that this was not just a perfunctory response; she was indeed beginning to be interested.
"That's right. Our entire solar system has been orbiting the center of the Milky Way. If we take the center of the Milky Way as a reference, our Earth is flying through the universe at an average speed of 828,000 kilometers per hour every moment following the sun..."
This is far more than traveling 80,000 miles a day while sitting on the ground.
