Video spoilers history, starting with the blitzkrieg on Poland

A new sky picture appeared amidst a melodious melody.

The picture shows the mysterious universe.

In the pitch-black universe, the famous Gargantua from "Interstellar" slowly appeared.

A supermassive black hole radiates brilliant light in the center of the image.

Awesome and intoxicating.

The video also slowly tells the story:
【do you know? 】

There is a famous saying in astrophysics:

【Destiny lies within the light cone.】

【Outside the light cone is nothingness.】

【Why do we say "Destiny lies within the light cone"? 】

【Imagine such a scene. 】

[You light a candle in the dark, and in an instant, soft light spreads around in the form of expanding bubbles.]

[According to Einstein's theory of relativity, the speed of any object with mass cannot exceed the speed of light.]

[This means that you can never escape the range of the "bubble" formed by this beam of light.]

【If we regard the current state as a cross section of two-dimensional space. 】

【At this moment, the bubble is expanding. 】

[It's like circles that keep getting bigger.]

【When we stack these circles layer by layer along the time dimension. 】

[A unique cone-shaped structure was created.]

This is the light cone.

[As a crucial structure in Einstein's theory of relativity, the light cone silently dominates the most fundamental cause and effect relationship in the universe. ]

【We assume. 】

【In the depths of the unreachable universe. 】

[A supernova explosion occurred extremely far away from the Earth.]

[Until the light cone from its explosion reaches Earth, this stunning astronomical event will have no effect on us.]

[We also have no information about the explosion. ]

[Only when the light cone crosses the long time and space and finally reaches the earth. ]

【We can witness this gorgeous and heroic explosion scene. 】

[This is a vivid manifestation of the law of causality in classical physics.]

[That is to say, on the grand stage of the universe.]

[When one event triggers another, the speed of light becomes an invisible but strict limitation. ]

[Any transmission of cause and effect must follow this law of speed. ]

Outside the sky.

Warring States Period.

Zhuang Zhou sat cross-legged, looking up at the constantly twisting light cones and black holes in the sky, with a hint of trance in his eyes.

"Inside the cone of light is destiny, outside the cone of light is nothingness..."

"Light cone is cause and effect?"

"Interesting, interesting. This is more like the great way between heaven and earth. Everything has its own limits, even light is no exception."

“I don’t understand the cause and effect of this light cone, but it seems that it is not just astronomical science of later generations.”

"And it's also about philosophy?"

"After all, a black hole devours everything, not even light can escape, which is very similar to the formlessness of the Tao."

Zhuangzi continued to watch carefully, determined to understand it completely.

And the sky continues.

So, what is the difference between time and space? 】

[Within the scope of space, we seem to have unlimited freedom, able to move in any direction at will, without any specific constraints. ]

【However, the time is completely different. 】

【The continuous light cone is like an invisible and powerful hand. 】

[It forces us to move forward along a one-way track from the past to the future. ]

【And there will never be any turning back. 】

[In the theoretical system of relativity, time is defined as the direction pointed by the light cone. ]

【Space is the collection of all other directions that are perpendicular to time.】

[In those regions of the universe where there is no gravitational interference. ]

[The structure of time and space presents a straight shape.]

[They interweave to form a symmetrical rectilinear grid.]

[The directions of all light cones also remain uniformly consistent. ]

[But when the force of gravity intervenes, everything changes quietly. ]

【Take the earth as an example, when an apple falls downward under the influence of the earth's gravity. 】

[The influence of gravity is not limited to the apple itself.]

[Even the direction of the object's light cone is not immune. ]

【Around massive planets. 】

【The direction of the light cone will bend. 】

[This also means that time will bend towards the center of the planet.]

【The reason why apples fall toward the ground. 】

【It is because its future direction is pulled by gravity. 】

【Then he pointed to the Earth.】

[Mass, a seemingly ordinary but powerful factor in the universe, distorts the geometry of space and time.]

【It makes time and space no longer absolute. 】

【It becomes relative. 】

[This is the core of Einstein's general theory of relativity.]

[Also, the more massive an object is, the more significant the curvature of spacetime it causes.]

[When mass reaches an extreme state, such as the existence of an object with infinite gravity. ]

【The curvature of space-time will tend to infinity. 】

【At this point, all light cones will be completely downward. 】

If we light a candle in such an area, you will be surprised to find that all the light cones will quickly fall into the center of this object.

[This mysterious and powerful object is the black hole we are familiar with. ]

[Black holes are celestial bodies with extremely strong gravitational force in the universe. ]

[Its powerful space-time curvature will ruthlessly pull all surrounding objects towards the center. ]

[We can try to imagine a black hole as a two-dimensional slice. ]

[In space and time, it is like a cylinder.]

[And the boundary of this cylinder is the famous event horizon. ]

[In the area outside the event horizon, some light can still escape with its own energy. ]

【However, once you enter the event horizon. 】

【All light will be ruthlessly bound. 】

【No more escape.】

[Inside a black hole, the light cone makes the path of any object's movement inevitably downward.]

【Time seems to have lost its original meaning.】

[In order to gain a deeper understanding of the unique physical properties of black holes, we have to mention the famous Hawking black hole life and death paradox. ]

【Suppose there are two astronauts, Alice and Bob. 】

【They carried out missions together in the vast space. 】

[Unintentionally, the two gradually approached a mysterious black hole. ]

【Suddenly an accident occurred and Alice's booster lost control. 】

[She was instantly captured by the black hole's powerful gravitational force and flew towards the black hole involuntarily.]

【For Bob, who is far away from the gravitational influence of the black hole. 】

[The gravity in the space-time around him is extremely weak and can be almost ignored.]

[In his perception, time is like a straight line that extends smoothly from the past to the future.]

【Everything seems so calm and orderly. 】

[Therefore, the black hole he saw and Alice who was flying towards the black hole seemed to be in a static state, and time seemed to have frozen at this moment.]

【As for Alice, who is flying towards the black hole at high speed. 】

【The situation is completely different.】

[As Alice gets closer to the event horizon, the distortion of time and space she feels becomes more intense.]

[When she finally reaches the event horizon.]

[Time and space seemed to have undergone a fantastic transformation, tilting 45 degrees.]

【From Alice's perspective, time is no longer the familiar straight line from the past to the future. 】

【Instead, it becomes a diagonal line that rises at a 45-degree angle. 】

【The shape resembles the surface of a light cone. 】

[This also explains why any object, once it passes through the event horizon, is like being trapped in an inescapable cage and can never escape. ]

[When Alice crosses the event horizon, the concepts of time and space seem to be reversed compared to the outside world.]

【The normal time direction now points downward. 】

[But this direction is used to describe the direction of space before traveling. ]

[At this moment, the event horizon of a black hole is no longer just a simple concept of spatial location. ]

【It becomes a moment in Alice's past.】

【It's fleeting.】

【And yet eternal. 】

[And the center of the black hole is no longer an ordinary point in the geometric sense, but has evolved into the entire world that Alice will face in the future. ]

[To put it another way, a black hole is like a light cone that is firmly fixed by the curvature of space-time. ]

【If we try to straighten the distorted space-time, let the direction of time flow in an orderly manner from left to right. 】

【Then we can see clearly. 】

[The event horizon of a black hole appears as a light cone in this model.]

[This also clearly shows that once any object passes through the event horizon, it can only fall involuntarily towards the center of the black hole.]

[Because in this unique space-time structure, the center of the black hole is the future direction of all events. ]

[If we further compress the entire image, we can see it intuitively. ]

[The outside and inside of a black hole form two completely different regions. ]

[Once you cross the event horizon, everything outside becomes the past that you can never go back to. ]

[Falling towards the center has become the inevitable fate for all travelers. 】

The video ends here.

Netizens are also discussing it enthusiastically.

《Light cone? Huang Renxun: I'm familiar with this.》

"Wow! So you also play Bengtie?"

"I finally understood half of it at the beginning, but then I couldn't understand it as I went on."

《It’s actually very easy to understand, because time is not absolute, but relative.》

"In another reference frame, if he observes you traveling faster than the speed of light, it means time is reversed, which will lead to a causal paradox."

"In short, the transmission of information cannot exceed the speed of light, right?"

"What can be used to send information faster than the speed of light?"

"Perhaps the universe was destroyed the moment it was born, but due to the light cone, we cannot perceive it."

"Crossing the black hole, the universe ends in an instant in your eyes."

"The hypothesis is interesting, but do you mean I can survive if I approach the speed of light?"

"It's not that you can live, it's that the light you reflect back is very slow, so it looks like a frozen frame in the eyes of a third party."

"After watching it, there was only endless emptiness, so I ordered a takeaway."

……

It's not just netizens who are discussing this.

The ancients also found it very interesting.

Eastern Han Dynasty.

Astronomer Zhang Heng gazed at the sky and was also deeply attracted.

"Light cone...cause and effect..." Zhang Heng whispered to himself.

"The speed of light is limited. The changes in the stars and the trajectories of comets are all subject to this constraint."

"So when the ancients said 'the sky is round and the earth is square', they actually mistook the light cone for a dome?"

"If gravity can distort space-time, then when the earth shakes, will it also disturb the light cone?"

"Unfortunately, there is no way to actually measure it, otherwise we would be able to deduce the law."

And in the Ming Dynasty.

While Xu Guangqi was looking at the sky, he was also carefully hand-drawing conic sections.

"The light cone is the conic curve of space-time."

"When the tangent plane is 45 degrees to the generatrix, it is a parabola - is this the silhouette of the light cone?"

"Let this room be the event horizon, and the candlelight be the escape limit. If a person is inside the room, he or she cannot cross the limit even a step."

It can be said that Xu Guangqi has put a lot of effort into imagining and exploring the light cone.

But even if we deduce according to the contents of the sky curtain.

Xu Guangqi was still seriously stuck.

I can only sigh: "The distance between the Cowherd and the Weaver Girl may not be 'a river', but two arcs in the light cone that never intersect." (End of this chapter)