How did you, a prisoner on death row, become an important weapon of the country? Yecheng Gao Weiming

"Light?"

"We were stunned for a while and didn't understand what the teacher meant."

"What light? Bright light or bright light? Or is it the light that the sun shines on the teacher's face? Or is it the light that hides the ugly faces of those people when they beat Teacher Dai?"

"Teacher Dai has continued."

"In 1899, there was a great scientist named Tesla. He said that everything in the world is light!"

"Tesla is a very powerful person. He is a very famous physicist, mechanical expert, and electrical engineer. He invented the alternating current system, the radio system, the power stations we use now, radios, and radars, all related to He couldn't get away from it, and he spent almost his entire life studying light."

"Haha, I unknowingly started talking about distance again, let's continue talking about light!"

"What is light? It is the sunlight, moonlight, and light emitted by light bulbs that our eyes can see."

"But the light we can see only occupies a very small part of the large family of light. Most of the light is invisible to our naked eyes."

"For example, radar signals, electromagnetic waves, radio broadcasts, and high-frequency rays in the universe are also a type of light."

"Light has no size, and we can't describe its size. It doesn't have a prescribed size like a car, nor does it have strengths and weaknesses like sound. It exists in the world and in the universe so ethereally. , exists around us.”

"Its transmission moves very fast, so people invented a word to call the distance it can reach in one second, which is... the speed of light!"

"How fast is light?"

"It reached a speed of 300,000 kilometers per second, the fastest speed known to mankind."

"It's like I'm sitting in the classroom of the orphanage now. If I had the speed of light, I would appear on the moon in 1.28 seconds..."

"When we heard this, we all opened our mouths. The speed of light must be too fast."

"How far is the moon from the earth? Teacher Dai told us that it is at least 380,000 kilometers. If we have the speed of light, we can reach the moon in the next second?"

"Teacher Dai ignored our surprise, coughed twice and continued."

"Haha, is it fast? But no matter how fast it is, it is still too small for the entire universe!"

"The universe we observe is nothing more than what we saw before."

"For example, the sun is about 8 million kilometers away from the earth. Even if light wants to reach the earth, it will take 20 minutes and seconds. In other words..."

"Teacher Dai pointed to the sun outside the window."

"The sun we see now is only the scene 8 minutes and 20 seconds ago. If it suddenly exploded or disappeared, it would take 8 minutes and 20 seconds for us to know the news."

"Let's start thinking again. If you could instantly appear in the universe ten light years away, you might be able to see what our earth looked like ten years ago."

"What if the instant appeared a hundred light years ago, a thousand light years ago, or two thousand light years ago?"

"Perhaps we can see the scene when King Qin Yingzheng ascended the throne in 221 BC!"

"boom……"

"Hearing this, the six or seven of us kids widened their eyes again and tried hard to digest this knowledge."

"It's no wonder we can't understand it, because being able to see what history looks like, and even the scene of Qin Shihuang's ascension to the throne, sounds exciting."

"But we also know that it is impossible. We cannot appear two thousand light years away in an instant and see the earth two thousand years ago. That is too far, too far away."

"But we know a lot about light, and even about the vastness of the universe."

"There was another burst of violent coughing. The classroom was quiet. No one dared to speak and interrupt. Qin Wenjing, who always likes to ask questions, remained silent. Because everyone knows that the teacher does not have much time."

"Teacher Dai started teaching again."

"Cough cough cough... Haha, I've gone too far without realizing it, kids! We won't talk about the speed of light today, we will just talk about our human's understanding of light and how far humans have studied it now."

"First, people discovered that light is invisible! Yes, including visible light, we cannot observe it, because all the objects you see are just a refraction reaction of light. It refracts objects into our eyes , let the brain form a perception of it and understand what it looks like.”

"Is it difficult to understand? It's like in the dark, our eyes become useless and we can't see anything."

"So without light, our eyes have no function. As for what light itself looks like, I'm afraid no one in this world can answer it."

"Later, people thought, what does light look like?"

"If it is a substance, what form does it take?"

"It is definitely not a liquid or a gas. Does it exist in this world in a solid state?"

"If it is a solid state, it must be very small, so small that we cannot observe it with the naked eye. In the scientific world, especially in the physical world, we call it --- [light particles]."

"Yes! Light is a kind of particle, a light particle! The person who proposed this discovery is called Isaac Newton."

"Everyone should know Isaac Newton very well. The teacher told you the story of the apple hitting him on the head, and also told you Newton's three laws."

"Newton, around 1666, discovered that light may be a particle. To prove this, he even stuck a steel needle into his own eye socket to determine whether his eyes could detect the existence of light particles."

"This completely unreliable experiment naturally failed. His vision was greatly damaged, but the experiment was not a complete failure."

"Newton discovered that light has colors, and he could see the colors in the halo."

"For example, rainbows are not the colors emitted by gases and liquids themselves, but the colors displayed by light through refraction."

"Every object we see has no color itself, but the light gives it its splendor."

"Later, Newton used a triangular lens and discovered that light has the functions of refraction and reflection, which further proved that it is a particle and has the basic property of direct radiation."

"Can……"

"A hundred years later, other scientists came up with different ideas."

"They believe that light also has diffraction, interference and polarization phenomena. Light is not a particle, but may be a wave!"

"The people who raised this doubt were Eagle Country scientist Thomas Young and French scientist Fresnel. They used a simple experiment to prove to people that light is actually a wave."

"This experiment is the famous Young's double-slit interference experiment."

"The experiment is very simple, but the teacher cannot reproduce it for you. If you are interested, you can try it privately."

"It is composed of a light source, a piece of cardboard with two slits, and a background board that receives the light source."

"When the light source passes through the two slits of cardboard, the light is cast into irregular stripes on the background board."

“This discovery shocked the world!”

"Why? Because Isaac Newton's light particle theory has dominated physics for more than a hundred years! No one can accept that light is actually a wave? An existence similar to sound waves and water waves!"

"Because it has the phenomena of diffraction, interference and polarization, it also has wave crests and troughs. Where the crests and troughs intersect, there is a strong oscillation!"

"As a result, the understanding that light is a particle was completely overturned, and the understanding that light is a wave became popular."

"But a few decades later, in 1905, German scientists Hertz and Einstein jointly proposed the photoelectric effect. People's understanding was once again subverted."

"As for what the photoelectric effect is, the teacher will not tell you more. Anyway, through a series of experiments, it proves that light is still a particle."

"Someone asked Einstein, how do you explain the double-slit interference experiment? Why does it show a wave state passing through two slits?"

"Even though Einstein was the most powerful physicist of his time, he couldn't answer this question."

"He could only smile bitterly and shake his head, saying that everything still needs to be studied. If the research yields results, perhaps our entire human cognition will be overturned, and the progress of the entire civilization will take a huge leap forward!"