I have a full-time hero system

Chapter 401 Yuan Xiao's Theory of Relativity ([-])

Assuming that the speed of light is constant, what will the entire physical world look like.

When this question was raised, apart from the students whispering to each other, the physicists present also frowned.

This assumption violates Newtonian mechanics' view of absolute space and stationary reference system.

Let's see how Yuan Xiao justifies himself.

Yuan Xiao is very satisfied, he has noticed that the system's proud index is constantly increasing.

In order to respect the original discoverer, Yuan Xiao decided to call the theory Einstein's theory of relativity.

"Now we have a hypothesis that we think is correct," Yuan Xiao played the PPT, "that is, the propagation of light does not require a medium, and the speed is constant.

Under this premise, we will soon find that the speed of light seen by the observer is the same no matter what state of motion the observer is in.

In this way, there will be disagreements about the simultaneity of events in the two locations. "

This passage was a bit mind-boggling. Yuan Xiao knew that most people couldn't understand it, so he showed the picture and began to give examples.

For example, a spaceship is flying in a straight line at a very high speed.

People inside the spaceship, do the following experiments.

First, install a photon detector at the same height of the head and tail of the spacecraft.

Once a photon arrives, the detector will immediately light up to remind.

Next, place a photon emitter right between the two detectors.

Then operate the photon emitters to send photons to the head and tail of the spaceship at the same time.

As a result, people inside the spacecraft must see both detectors light up at the same time.

Because the photon takes the same time to reach the head and the tail.

This result can also be established with the explanation of Newtonian mechanics.

Because the state of uniform linear motion is equivalent to the state of rest.

Therefore, although the spaceship is flying at a very high speed, for the people inside the spaceship, it is no different from standing still.

The photons must arrive at the nose and tail of the spacecraft at the same time.

But for the subsequent derivation, the theory of relativity is different.

Newtonian mechanics holds that time and space are absolute, and what changes here is the speed of light.

Therefore, for people outside the spacecraft, what they see is that the detectors at the head and tail of the spacecraft light up at the same time.

For example, this spaceship is flying in a straight line at a high speed and at a constant speed relative to the Bruya planet.

Then on the planet Bruya, someone observing the spaceship is stationary relative to the spaceship.

This is because after the photon emitter emits a photon in the middle position, the bow of the ship is constantly moving away from the photon, while the stern of the ship is constantly approaching the photon.

But the speed of light changes.

The speed of light toward the bow becomes the speed of light plus the speed of the spaceship, and the speed of light toward the stern becomes the speed of light minus the speed of the spaceship.

This change in the speed of light cancels out the speed of the spaceship.

Because according to the analysis of Newtonian mechanics, what people outside the spaceship see is that the head and tail detectors light up at the same time.

In this way, no matter the people inside the spaceship or the people outside the spaceship, they have the same understanding in terms of time and space for the event that the detector lights up.

but!

Yuan Xiao raised his hand: "Now we assume that the speed of light remains constant, so what will happen?"

Froz seemed to understand something in an instant, and his face immediately turned pale.

The rest of the physicists also stared wide-eyed.

The students frowned.

Yuan Xiao first gave a conclusion: "It's very simple, according to the principle that the speed of light is constant, the speed of light is constant for people who are far away from the spaceship.

Then the distance for the photon to reach the head of the spacecraft becomes larger, and the distance for the photon to reach the tail becomes smaller.

So they will see that the detectors at the stern light up first and the detectors at the bow light up last.

I think everyone can understand this result after thinking about it for a while. "

With such an explanation, even the students nodded.

Imagine, it's a very simple thing to do.

Yuan Xiao's PPT presentation diagram clearly explained it.

However, this creates a problem.

The people inside the spaceship thought that the detectors at the head and tail were lit up at the same time.

People outside the spacecraft think that the tail lights up first, and the head detector lights up last.

Yuan Xiao looked back at the screen: "This is because the speed of light is constant, and the resulting simultaneity is relative.

In this way, the time when the detector lights up measured by people outside the spacecraft is different from that of people inside the spacecraft.

Therefore, the spatial location of the event also changes.

This is the most important core idea of ​​Einstein's theory of relativity.

When the speed of light is absolutely constant, time and space are no longer absolute but relative. "

As soon as these words came out, there was an uproar in the audience.

Impossible, how can time and space change relative to each other.

This is not reasonable.

In the more than 200 years of human history in the new era, countless scientific and technological theories have been unearthed. An important premise is the equivalence of time.

Time should be constant for anyone, anything, and any change.

The space is also the same, although there is space superposition technology such as the space capsule.

But it does not mean that the inherent space can be changed at will.

If time and space are relative, then the existence of human beings is also relative.

Froz realized such a conclusion early on, so his face was pale.

Time is also relative, that is to say, the time is different at different speeds in different places!

"The relativity of simultaneity described here is only the first step in reconciling the two theories," Yuan Xiao continued to explain, "When the speed of light is constant, an event measured in an inertial system, the moment of occurrence and the spatial location, and the other The inertial frame is different.

It's just that most of the movements we see in our daily life are far slower than the speed of light.

Therefore, we generally believe that under different inertial references, the time and spatial location of the two events are consistent.

This is Newton's law of mechanics, which solves the problem of macroscopic low-speed motion. "

Yuan Xiao finally made a conclusion: "That is to say, in order to keep the speed of light constant, the distance and time seen by observers in different motion states should be different.

Since speed is distance divided by time, to keep speed constant, distance and time must vary.

That's it for the first part of what we're going to talk about today.

Thank you all for listening. "

The get out of class bell rang.

No one moved in the audience.

Everyone was stunned. The theory proposed by Yuan Xiao broke the traditional thinking.

But if you think about it carefully and analyze it before and after, you can't get around such inferences.

Is what this guy is saying true?

Time and space are relative.

Over there, Yuan Xiao had already turned off the screen, picked up the handout and was about to leave.

Only then did everyone realize something, and all rushed forward.

Even an old man like Froz blushed: "Mr. Yuan, you not only have derivation of thinking, but also specific calculation formulas."

"Time and space, how do they change?"

"It's impossible, isn't everyone's time the same?"

"Teacher Yuan, please explain again..."

Proud index +25430, +56110, +17938...

The index skyrocketed, Yuan Xiao smiled.

(End of this chapter)