1900: A physics genius wandering around Europe

Chapter 308 The ultimate romance of human wisdom: time and space bend because of you!
Through rational thinking and in-depth analysis, Li Qiwei boldly hypothesized two basic principles.

First, the inertial field and the gravitational field are locally equivalent.

Second, all physical laws have the same form in any reference frame.

Based on these two principles, we can conclude that non-inertial system = inertial system + gravitational field.

Therefore, the non-inertial system problem that the special theory of relativity is helpless to solve can be decomposed into the inertial system problem.

The inertial system is very simple, and Newton's laws have been studied perfectly.

All that remains is to concentrate on studying gravity.

Let’s begin the thought experiment.

We said before that suppose there is a spaceship moving at an acceleration of g.

If there is a person K holding a basketball, when he lets go of the basketball, it will fall to the ground of the spacecraft like a free fall.

Moreover, the trajectory, speed, etc. are exactly the same as on Earth.

Because at this time the spacecraft feels like the earth.

He couldn't tell whether the basketball was being pulled by gravity or by the inertia of the spacecraft.

Okay, here comes the point!
Now let us take our thoughts a step further.

What if K was holding a flashlight instead of a basketball?

Now the spacecraft continues to move upward with acceleration g.

At this time, K turned on the flashlight horizontally, and light was generated instantly, moving horizontally toward the wall directly opposite to K.

So, imagine what someone standing on Earth would see at this moment?

Very simple.

The spacecraft is moving with uniform acceleration g, while the speed of light is constant.

Therefore, the distance traveled by light in the horizontal direction and the vertical direction is different.

Therefore, people on Earth will see the light moving in the opposite direction of the spacecraft's acceleration.

It looks like the light is "hanging" downwards.

That is, the light becomes curved instead of being straight and horizontal.

It looks like a parabola.

You can imagine this scene in your mind.

Suppose in a rectangular coordinate system, a small ball is thrown at the origin.

If the distance traveled by the Y axis per unit time is greater than that of the X axis.

So if they are connected together, it will be a parabola.

This is what happens to light in an accelerating spacecraft.

This is serious.

You know, the inertial field and the gravitational field are equivalent.

At this time, the spacecraft is actually equivalent to the earth.

Then similarly, light is bent inside the spacecraft, which means that light is also bent on Earth.

It is all due to the effect of acceleration g that causes light to no longer travel in a straight line, but instead travel in a curved manner.

This step is critical. Think about it carefully and try to figure it out.

Why don't we see light bending on Earth?

Because the mass of the Earth is so small, the degree of bending of light is very small.

Now we have our first bizarre yet reasonable conclusion: gravity bends light.

If an average person were to reason this way, they would probably be overjoyed.

Wow, that’s awesome.

Light actually bends.

What a significant achievement this is.

But the real Einstein was not satisfied with this conclusion and continued to think deeply about it.

What does it mean that gravity bends light?

At this moment, he suddenly thought of the Leaning Tower of Pisa experiment.

Of course, it is not quite the same as the real experiment, he went a step further.

Einstein was thinking about two completely different objects, like a basketball and a chicken.

If they are placed in a vacuum, then under the influence of gravity, their falling speed, trajectory, etc. are exactly the same.

This has nothing to do with the physical and chemical properties of basketballs and chickens.

If we make a bold assumption that the basketball and the chicken reach the speed of light, then they will follow the path of light, just like light.

Light bends, and so do they.

Einstein had a flash of inspiration. He felt that this phenomenon was as if gravity did not exist.

Whether it's light, basketball, or chicken, they all seem to be moving along a predetermined path.

What does that mean?

Just like now there is a smooth track with a bumpy shape.

Then no matter what you put in, they will take the same route.

It can only be the shape of the track itself.

Because the route has been fixed, it is in this shape.

No matter what material or speed, it cannot affect the orbit.

At this point, Einstein discovered a shocking secret: gravity does not exist, and it is space-time itself that changes the trajectory of objects.

So he boldly guessed: the essence of gravity is the curvature of space-time!
boom!
After reasoning to this point, Li Qiwei felt as if thunder was exploding in his mind.

It felt like a hot current in my chest was rushing straight to the top of my head!

The heat flow exploded, forming a domineering figure.

The figure stood on the earth, with his back to all living beings and facing the vast universe.

He uttered a note softly: "Power!"

The sound exploded into space, reaching the edge of the universe.

To the ears of all living beings in the universe, it sounds like the sound of a huge bell, so powerful and domineering.

Li Qiwei took a deep breath and slowly withdrew the vision.

He deduced step by step from Newton's laws and finally discovered the relationship between gravity and the curvature of space-time.

Is there anything more exciting and crazy than this?

He had never done such a thing in his previous life because there was no such special environment.

And now, even if he turned a deaf ear to what was happening outside, he already knew about the outside world's expectations of him through Delia.

He is now the center of physics, and the entire trend of the era falls on his shoulders.

At this moment, his brain seemed to have evolved, gradually approaching true genius.

Li Qiwei's breathing and heartbeat quickened, and the tip of his pen was trembling.

The mysteries of the universe seemed to materialize at this moment.

Held in his hand, it bent and entangled like a strange and magnificent light.

Li Qiwei took another deep breath and slowly calmed down, but things were not over yet.

Next, he had to find a way to prove the shocking idea that space-time was curved.

The same old rules: it’s still a thought experiment, so don’t do it if you can avoid it.

This is the famous disk experiment.

Now, please close your eyes.

Imagine a huge disk in the dark, vast and lonely space.

At this time, there are two people standing on the disk, namely X and Y.

X stands at the center of the disk, and Y stands at the edge of the disk.

Now, the huge disk begins to rotate clockwise, and the centripetal acceleration it produces is exactly equal to the gravitational acceleration of the earth.

(Note: Although the speed of the disk's rotation remains constant, it is still a variable speed motion because the direction of motion is changing all the time.)
(The direction of acceleration in circular motion is always toward the center of the circle.)
Same with spaceships then.

At this moment, Y, who is standing on the edge of the disk, moves with the disk, so he will be subject to an inertial centrifugal force, the magnitude of which is equal to the gravitational force he experiences on the surface of the earth.

Therefore, Y will feel as if he is still standing on the earth, which is very comfortable.

But X felt uncomfortable.

Because he is at the center of the disk.

The disk exerted no inertial force on him, nor any gravity.

So X will be in a state of weightlessness, which is equivalent to him standing at the center of the earth.

This disk is a device equivalent to the earth's gravitational field.

According to the special theory of relativity, Y is accelerating relative to X at this time.

(Don't ask the other way around, why X isn't accelerating relative to Y. The explanation is in the previous section.)
So time Y is slower than time X. (Slow Clock Effect)

Because the acceleration of the disk is equivalent to gravity.

So we can assume that it is gravity that causes Y's time to slow down.

If the center X starts to gradually approach Y at this time, then its time will gradually slow down due to acceleration.

As X moves further, the inertial acceleration he experiences increases, and time goes slower.

This is equivalent to the fact that the greater the gravitational force on X, the slower time goes.

Li Qiwei calculated for a while.

The process of time slowing down is a curve.

Therefore, he could conclude that gravity can cause time to bend.

Okay, now let’s look at the space.

First, let X return to the center of the disk.

Next, let X and Y measure the circumference of the disk simultaneously.

At this moment, the size of the disk measured by X is the same as the size measured by an observer on Earth.

Because both X and the observer on Earth are stationary relative to the disk.

However, the size measured by Y is different from that of X because of the contraction effect of the special theory of relativity.

The Y measurement has a larger circumference.

Because Y is shrinking in the eyes of X and the observer on Earth, the ruler in his hand also becomes shorter.

So for the same disk, he needs to use his ruler to measure the circumference several times to complete the measurement.

(Note that the circumference of the disk, as seen from X's perspective, has also shrunk at the same time.)
(But the ruler in X's hand has not shrunk, so the circumference he measured is still smaller than that measured by Y.)
Next, Y uses the circumference he measured to calculate the disk's pi and finds that the result is greater than π.

Li Qiwei accurately obtained this result through complex mathematical calculations.

It is logical that he can draw a conclusion from this disk experiment:
That is, the space where the disk is located is curved, and pi is no longer π.

Because on a two-dimensional plane, the circumference of a circle is fixed at π.

Now that the value of pi has changed, it is enough to show that the circle is no longer in a flat space.

Therefore, the huge disk in space is not in flat space either.

Gravity curves space.

At this point, Ridgwell had demonstrated, simply through a clever and sophisticated thought experiment, that gravity causes space-time to curve.

In other words, where there is gravity, space-time is not flat.

At this point, he perfectly proved that gravity is just an illusion and does not exist.

Gravity is just a result of the curvature of space-time, a geometric effect.

Essentially, it is because of the curved space-time that objects have tracks on which to move, thus creating the illusion of force.

Wow!
When Li Qiwei wrote this, he let out a heavy breath.

The core theory of the earth-shaking and shocking general relativity was completed in his hands.

No one could understand how he felt at the moment.

Excitement, passion, trembling, nervousness, confusion, all kinds of emotions intertwined together.

Even with the calm temperament he had developed over the past decade, he couldn't help but be moved.

That's general relativity!
It is the pinnacle of intellectual achievement in the millions of years of human history.

It allows the human mind to transcend the limitations of the flesh and embrace the entire universe.

No great language can over-praise it.

The so-called emperors and generals are probably not even qualified to carry shoes in the face of this theory.

And now, Li Qiwei has created this unparalleled theory from scratch.

His heart was pounding and his mouth was dry due to excitement, so he picked up the tea beside him and drank it in one gulp.

The finest tea made from tea leaves worth a fortune is just a thirst quencher at this moment.

Every word on the paper in front of him is more valuable than all the tea in the world combined.

Li Qiwei shouted: "Delia, add tea."

squeak!
Delia, who was outside the office, came in upon hearing the noise, teapot in hand.

She closed the door and turned around to see Li Qiwei. Suddenly, she let out an "Ah" and covered her mouth.

Li Qiwei was a little confused. There was no scratch on his face, so what happened to the other party?

However, at this moment, in Delia's eyes, the temperament emanating from Li Qiwei made her fall in love with him.

What kind of charm is that?

There was an irresistible attraction to her.

It's like all the best qualities of men in the world are concentrated in one person.

Delia had been at King's College London for several years, but she had never met a man like Li Qiwei at this moment.

Sexy, invincible, mysterious, making all women dare only watch from afar and not touch her.

Delia's mouth was dry and her whole body was hot. She felt like she could no longer control herself.

Li Qiwei's figure seemed infinitely tall, even the sky couldn't hold him down.

The aura of wisdom emanating from his body almost made Delia suffocate.

This is the remaining aura of Li Qiwei after he had just broken through to the level of heaven and became a saint through physics.

After discovering the great truth of the universe, Li Qiwei's temperament has completely changed.

For a woman like Delia who studies science, it is no less than the strongest drug in the world.

She stammered and trembled, "Professor Bubrus, you. You. Are."

Li Qiwei smiled and said, "What's wrong, Delia, come over and add more tea."

"Was my voice too loud just now?"

Delia woke up with a start, and the feeling gradually disappeared.

"No, no, I just seemed to have seen something incredible."

"Professor Bruce, are you okay?"

Li Qiwei looked at the silly foreign girl and smiled, "I'm fine. I just had a major breakthrough in theory, so I drank a few more sips of excitement."

"Please fill it up for me."

Delia quickly said "oh" and quickly walked to Li Qiwei's side. While adding tea, she asked excitedly:

"Wow, Professor Bruce, are you finally completing your theory of general relativity?"

Li Qiwei smiled faintly, "It's still a little short, but it's almost there."

Delia smiled sweetly, and her chest trembled violently again, causing Li Qiwei's eyelids to twitch when he stole a glance at her.

After Delia finished adding tea, she quietly left. She didn't dare to disturb Professor Bruce from continuing his thinking.

When she walked to the door, she suddenly felt something strange in her lower body. Her cheeks turned red with shame and she ran away with her face covered.

However, our upright gentleman, Young Master Li, did not see this scene.

At this moment, after replenishing his energy with tea, he regained his spirit and focused on his paper again.

It is now known that the essence of gravity is the curvature of space-time.

So the next natural step is to study how space-time is curved.

A classic quote from later generations: Matter tells space-time how to bend, and space-time tells matter how to move.

So what exactly is this “how”?
(End of this chapter)