little fool's child bride

This time, no one said that Xiao Xiao was wrong. After all, everyone had heard about the horror of the epidemic. How could they dare to gossip about the person who invented the preventive method?So everyone began to discuss how to go to the Imperial College to meet this god-man side, and it would be good to get some talent.At this time, the storyteller saw that the timing was just right, so he smiled and said to everyone: "Xiao Xiao has published a book called "The Collection of Puzzles". I heard that as long as you can solve all the problems in any part of it, you can go to the Imperial College to meet him." Woolen cloth!"

There are mostly illiterate people in this teahouse, and they get discouraged when they hear "Difficult Problems".However, there are also curious storytellers who want to read a few passages to see if they can understand them.

"Then all guests listen carefully," the storyteller looked at the nervous crowd and raised his index finger, "The first question is, what is the speed of light?"

"The speed of light?" Everyone looked at each other, not even understanding what this question meant.Then someone frowned and asked, "What's the speed?"

Not only him, almost everyone has such doubts.The storyteller thought to himself that no one would be able to solve it again this time, but he still repeated the explanation countless times: "Speed ​​is the ratio of distance to time, and it is the learning content of the Imperial Academy of Computing."

"Then how could we know?" Someone said dejectedly, "If we can get into the Imperial College, why are we here?"

The rest of the people couldn't help but nodded, most of them didn't know a single word, let alone explain the problem of Guozijian.And what about some people who think they have some knowledge?Although they have read some books, they are really unfamiliar with arithmetic.Not to mention measuring the speed of light—

"How can light have speed?" Someone retorted strangely, "When the sun appears, the light will fall down at once. When will it take time?"

"But when I opened the cellar last year, I remembered that although the light is fast, it still takes a certain amount of time to shoot in," someone shook his head, "but how to calculate it? The distance is easy to measure, but the time—is it possible to use a sundial?"

"You're talking nonsense!" Someone raised a different opinion, "How can a sundial be able to measure it with a brush of light? I think you have to use an hourglass!"

Everyone expressed their opinions one after another, the storyteller was happy to rest, and everyone almost quarreled because of the speed of light.But soon someone gave up and asked the storyteller to come up with another question, they really couldn't figure out the math.So Mr. Storyteller flipped through the book and picked out another philosophical problem: "A ship that can sail at sea for hundreds of years can be attributed to the uninterrupted maintenance and replacement of parts. As long as a piece of wood rots, it will be destroyed. Substitute, and so on, until all the functional parts are not the original ones. The question is, is the resulting ship still the original ship, or is it a completely different ship? If not the original ship , so at what point is it no longer the original ship? By extension, if a new ship is rebuilt with old parts taken from the original ship, which of the two ships is the real original ship ?”

"This question is easy!" Someone immediately shouted loudly, "Of course it will be a different ship when all the replacements are completed!"

"Then when half of the parts were changed, it was still the original ship?" Another person raised the opposite point of view, "It shouldn't be the original ship when the first one was replaced."

"But a person eats different meals every day. Does this person become a new person just because what he eats today is different from yesterday?" Another person shook his head.

There is no doubt that this classic philosophical question "The Ship of Theseus" has aroused everyone's interest again, and opinions have begun to diverge.And the storyteller at the other end wrapped Xiao Xiao's "Difficult Problems" with a smile on his face and handed it to several guest officers who bought it, thinking about how much share he could get.It turned out that this was the sales plan that the bookstore gave Xiao Xiao as a gift, asking Mr. Storyteller to sell Xiao Xiao's "Difficult Problems" and give them a share of the money.

"Wangjiang Tower, Wangjiang Stream, Wangjiang Tower Downstairs, Jiangliu, Jianglou Eternal, River Flow Eternal," the scholar who bought the book couldn't wait to open it, "Hey, is this right? It's too difficult, too difficult It's..."

"The teacher's test is really too difficult," the supervisors on the other side also complained, "How can it be possible to measure the speed of light? When will we learn this?"

How is the speed of light calculated?

In fact, in human history, it was Galileo who conducted the earliest experiment to measure the speed of light in 1607.

Galileo's method is to have two people stand on two hills one mile apart, and each person holds a lamp. The first person lifts up the lamp first, and when the second person sees the first person's lamp, he immediately lifts it up. For your own lamp, the time interval between the first person holding up the lamp and the time he sees the second person's lamp is the time it takes for the light to travel two miles.But since the speed of light travels so fast, this method simply won't work.But Galileo's experiment opened the prelude to the study of the speed of light in human history.

1676年，丹麦天文学家罗麦第一次提出了有效的光速测量方法。他在观测木星的卫星的隐食周期时发现：在一年的不同时期，它们的周期有所不同；在地球处于太阳和木星之间时的周期与太阳处于地球和木星之间时的周期相差十四五天。他认为这种现象是由于光具有速度造成的，而且他还推断出光跨越地球轨道所需要的时间是22分钟。1676年9月，罗麦预言预计11月9日上午5点25分45秒发生的木卫食将推迟10分钟。巴黎天文台的科学家们怀着将信将疑的态度，观测并最终证实了罗麦的预言。

Rohmer's theory was not immediately accepted by the French Academy of Sciences, but it was endorsed by the famous scientist Huygens.Huygens calculated the speed of light for the first time based on the data he proposed and the radius of the earth: 214000 km/s.Although this value is far from the most accurate data measured so far, it inspired Huygens's research on the wave theory; more importantly, the error of this result does not lie in the error of the method, but comes from Luo Mai's understanding of light. The wrong guess of the time across the earth, the result obtained after various corrections by the modern method of Luo Mai is 298000 km/s, which is very close to the exact value measured by the modern laboratory.

In 1725, British astronomer Bradley discovered the "aberration" phenomenon of stars, which confirmed Rohmer's theory in an unexpected way.At the beginning, he could not explain this phenomenon. Until 1728, he was inspired by the relative relationship between the wind direction and the ship's course when he was on a boat, and realized that the propagation speed of light and the revolution of the earth together caused the phenomenon of "aberration of light". .He used the ratio of the speed of the earth's revolution to the speed of light to estimate that it takes 8 minutes and 13 seconds for the sun's light to reach the earth.This value is more accurate than that determined by the Rohmer method.Ledley's measured value proved Rohmer's statement about the finiteness of the speed of light.

The determination of the speed of light has become an important basis for the debate about the nature of light since the seventeenth century.However, due to the limitations of the experimental environment at that time, scientists could only measure the propagation speed of light in a vacuum with astronomical methods, and could not solve the problem of light being affected by the propagation medium, so the debate on this issue has always remained unresolved.

In the eighteenth century, the scientific world was dull, and the development of optics was almost at a standstill.After Bradley, after more than a century of gestation, it was not until the middle of the nineteenth century that new scientists and new methods emerged to measure the speed of light.

In 1849, Frenchman Fizeau designed an experimental device on the ground for the first time to measure the speed of light.The principle of his method is similar to that of Galileo.He placed a point light source at the focal point of the lens, placed a gear between the lens and the light source, and placed another lens and a plane mirror in sequence at the other side of the lens, and the plane mirror was located at the focus of the second lens.The light emitted by the point light source becomes parallel light after passing through the gear and the lens, and the parallel light converges at one point on the plane mirror after passing through the second lens, and returns on the original path after being reflected on the plane mirror.Since the gears have backlash and teeth, the observer can see the returning light when the light passes through the backlash, and is blocked when the light happens to hit the tooth.The time from the beginning to the return of the light disappearing for the first time is the time it takes for the light to go back and forth once. According to the rotation speed of the gear, this time is not difficult to find.Using this method, Fizeau measured the speed of light to be 315000 km/s.Since the gear has a certain width, it is difficult to accurately measure the speed of light with this method.

In 1850, French physicist Foucault improved Fizeau's method. He only used a lens, a rotating flat mirror and a concave mirror.Parallel light converges to the center of the concave mirror through the rotating plane mirror, and the time can also be obtained by using the rotation speed of the plane mirror.The speed of light measured by Foucault in this way is 298000 km/s.In addition, Foucault also measured the speed of light in water. By comparing it with the speed of light in air, he measured the refractive index of light entering water from air.After the theory of particles has been overthrown by the theory of waves, this experiment once again made a judgment on the theory of particles, and brought the final impact to the theory of particles of light.

In 1928, Kalolas and Mitestad first proposed to use the Kerr cell method to measure the speed of light. In 1951, Betsy Trande measured the speed of light with this method to be 299793 km/s.

Light waves are a small part of the electromagnetic spectrum, and contemporary humans have made sophisticated measurements of each of them. In 1950, Eisen proposed the cavity resonance method to measure the speed of light.The principle of this method is that when the microwave passes through the cavity, resonance occurs when its frequency is a certain value.According to the length of the cavity, the wavelength of the resonant cavity can be obtained. After converting the wavelength of the resonant cavity into the wavelength of light in vacuum, the speed of light can be calculated from the wavelength and frequency.

当代计算出的最精确的光速都是通过波长和频率求得的。1958年，弗鲁姆求出光速的精确值：299792。5±0。1千米/秒。1972年，埃文森测得了目前真空中光速的最佳数值：299792457。4±0。1米/秒。

The determination of the speed of light is of great significance in the course of optical research.Although it took more than 300 years from people trying to measure the speed of light to people measuring the more accurate speed of light, every bit of progress during this period has promoted the development of geometric optics and physical optics, especially in the debate between particle theory and wave theory In , the determination of the speed of light has provided a very important basis for this famous scientific debate.