"What, Mr. Huygens's calculation of the speed of light is wrong?"
Hearing Xu Yun's words.
Faraday was stunned.
As we all know.
The unit of the speed of light is very large, so it is very normal, and even inevitable, to have errors.
Don't mention anything else.
Just compare the results calculated by Huygens and Mavericks.
One is 212,000 kilometers per second, and the other is 210,000 kilometers per second, which is a full 2,000 kilometers different.
But the error that Xu Yun said deserves to be corrected is obviously not this kind of error in nearby figures.
The error he refers to is undoubtedly a concept at the level of ‘magnitude’, which is at least 20%.
But
How is this possible?
To know.
It is different from exploring the nature of light.
Because the speed of light is so fast, on the scale of daily life, people simply cannot realize that it takes time for light to travel from point A to point B.
Therefore, in the ancient world, no matter in the East or West, ancestors basically had no concept of the speed of light.
This common-sense concept lasted until the 17th century, when Galileo Galileo questioned it and designed an experiment.
The experiment designed by Galileo went like this:
Two people each held a lantern and stood on two hills respectively. Each person covered the lantern in his hand with a baffle.
Next.
One person takes off the baffle in his hand.
When people on the hilltop on the opposite side saw the light, they immediately took off the baffles in their hands.
The first person records the time from when he takes off the baffle to when he sees the lantern in the other person's hand. This is the time it takes for the light to travel back and forth between the two mountains.
Divide the distance between two mountains by time to get the speed of light.
There is no doubt that this experiment ultimately failed.
Because assuming the distance between two hills is one kilometer, it only takes 0.0000067 seconds for light to travel back and forth between the two hills.
Human reaction time is generally in the range of a few tenths of a second, which is 30,000 times the time it takes for light to travel back and forth across the mountains.
So no matter how Galileo measured it, what he measured was just the reaction time of these two people.
So Galileo finally gave up the idea of measuring the speed of light. Humanity's first attempt to calculate the speed of light ended in failure.
However, Galileo is not the only genius of mankind. Twenty years after Galileo's death, someone came up with a method to measure the speed of light.
This man also has a Roman in his name, called Romer, and he is a Danish astronomer.
When Romer was observing the universe in the early years, he noticed that Jupiter has a satellite called "Io", which is also Io.
at that age.
The development of astronomy has made it possible to calculate the period of this satellite's orbit around Jupiter and to calculate the precise time at which it can be observed from Earth.
Romer was keenly aware that the distance between the Earth and Jupiter was constantly changing throughout the year.
Therefore, the time it takes for the light from Io to travel to the Earth is also different.
The difference in time that people observe on the earth is exactly the difference in the time it takes for light to travel through different distances.
Later, after a long period of observation, Romer discovered a situation:
When the Earth and Jupiter are closest, Io appears 11 minutes earlier than average.
When the Earth and Jupiter are farthest apart, Io appears 11 minutes later than average.
11+11=22.
In other words.
This 22-minute difference is the time it takes for light to travel between the maximum and minimum distances between the Earth and Jupiter, and can be used to calculate the speed of light.
The vastness of the universe provides humans with a large enough scale to calculate this number.
then.
Romer published this conjecture and corresponding observational data in 1676.
However, Romer himself did not personally calculate a specific value. It was Huygens mentioned above who finally completed the calculation, and the speed of light was 212,000 kilometers per second.
Mavericks mentioned similar values in its "Optics", but did not say how it was obtained. Later, it was generally believed that it was most likely based on Romer's data.
Of course.
Based on the urine properties of Mavericks in the official history, even if it is referenced, it will not be acknowledged.
all in all.
Guaranteed by the calculation results of Mavericks and Huygens, the concept that the speed of light is 212,000 kilometers per second has always been regarded as truth in the scientific community.
Although there were examples like Bradley who took a different approach and calculated the speed of light by using the star's optical aberration method to be about more than 300,000.
However, because the calculation method involves revolution, there are too many logical loopholes, so it has never been accepted by the mainstream.
So when he heard Xu Yun's words of "correct the mistake", Faraday subconsciously wanted to open his mouth to refute.
But before he could say anything, another thought came to his mind:
The data in Xu Yun's hands is most likely the result of Feiyu's calculations.
That's a fat fish
The two emotions collided fiercely in his mind, making Lafayette's face look a little uncertain.
after awhile.
He looked deeply at Xu Yun, left the shed silently, and chose to be a waiter
The winter sky gets dark very quickly.
Less than half an hour after Faraday left, the sky began to get dark.
After a while.
William Whewell sent bread and milk.
Around the entire blocked road, students gradually gathered to watch the excitement.
after an hour.
Darkness has completely fallen.
Da da da
A student federation cadre walked quickly into the shed, and the cowhide boots made a clear contact sound with the soles.
I saw him whispering a few words to his colleagues, and then said to Xu Yun:
"Classmate Luo Feng, the time and equipment are almost gone. Please come with me."
Xu Yun nodded and followed him out of the shed and came to an open space.
At this time, except for the middle area, this open space was already densely surrounded by many people:
Among them are Wheat and Aveline. One of them is the second tuition-reduced student of Trinity College, known as the "Second Maverick", and the other is simply the only direct descendant of the Aisku family. It is possible to appear here for practical purposes.
It's normal.
There is also Angus Roman,
Frederick Agar Ellis, who regarded Thomson as a love rival,
Future composers Max Christian Friedrich Bruch and others.
These people are elected student representatives who witness the entire process on behalf of the student body.
The rest were the leaders and professors including Prince Albert, William Whewell, Faraday, Stokes and others were all present.
In the center where they gathered were some equipment that had been prepared.
The set of equipment Xu Yun requested is actually very simple. There are four modules distributed in four different areas:
The first is the console where Xu Yun is.
There is a table, a flashlight fixed on the table, a silver-plated lens, and a telescope.
The second area is directly to his left, about 20 meters in the nine o'clock direction.
There stood an imaging board.
The third area is at 10:30 on the left front.
There is a rotating mirror that is constantly rotating, and the line connected to the imaging plate is exactly perpendicular to the line connecting the operating table and the imaging plate.
The rotating mirror, imaging plate, and operating table just form an "L" shape.
As for the last module, it is five kilometers away, where a concave mirror is placed and guarded by several teaching assistants from Trinity College.
The line between the concave mirror and the rotating mirror is perpendicular to the line connecting the rotating mirror and the imaging plate, that is, a vertical line is drawn across the top of the left side of the 'L'.
See here.
Some smart students must have guessed it.
That's right.
What Xu Yun plans to use this time is the rotating mirror photometry method invented by Foucault!
Mentioned above.
The speed of light values calculated by Mavericks and Huygens were regarded as authoritative for a long time.
This situation lasted until 1849.
At that time, a scientist named Armand Fizeau was inspired by Arago and came up with a sophisticated experiment, thereby breaking this 'authority':
He designed a gear and placed it between the light source and the mirror.
When the gear is stationary, the light emitted from the light source passes through the gap in the gear.
After being reflected by the mirror, it will pass through the same gap and be observed by the observer.
When the gear starts to rotate and reaches a certain speed, when the light returns, the original tooth gap has just turned.
The light will hit the gear and cannot be observed.
If you continue to increase the speed of the gear, the light will be reflected back again through the next tooth gap.
The entire process does not need to consider the speed of human visual reaction. You only need to know the number of teeth of the gear, the rotation speed and the distance between the observer and the mirror to calculate the speed of light.
However, due to the influence of the process, this method still has some problems.
After all, the gear is used to block the light, resulting in an error of about 5% in the final measured speed of light.
So later Foucault was the one who came up with Foucault's Pendulum. He thought about it and changed the gear into a rotating mirror.
At the same time, some optimizations were carried out in the process, locking the accuracy to 289,000 kilometers.
During the Michelson period, he changed to an eight-way mirror, which improved the accuracy again.
Xu Yun once discovered it when he was checking information in the library.
Due to the changes in the world line in the copy, Arago, who inspired Armand Fizeau, did not propose the idea of photometry. After graduating from college, he plunged into the embrace of the wave theory.
Naturally.
Armand Fizeau had not completed his gear photometry experiment a year ago.
There is no gear metering yet, let alone Foucault:
Foucault completed rotating mirror photometry about a year and a half later than Fizeau, and Foucault was inspired by Fizeau's paper.
So when he was in the library, Xu Yun had already made preparations, preparing to use the measurement of the speed of light as an entry point.
I just didn't expect that this opportunity would come so quickly.
Of course.
Some students may ask:
its not right.
Isn't Michelson's accuracy higher? Why not use an octagonal mirror?
The reason is very simple. In the final analysis, it can be summed up in two words:
site.
Although the steps for Fizeau photometry seem very simple, the distances on the schematic diagram seem to be very short.
In fact, because the speed of light was so fast that the gears could not block the light, Fizeau's experiment failed at first.
He could only continue to extend the experimental distance and number of teeth, and increase the speed of the gear, hoping to block the reflected light.
Illustrations of Fizeau photometry can be found on the Internet in later generations. It seems that the distance is very short, but in actual operation the light path reached 8633 meters.
As for the eight-sided mirror?
Excuse me.
22 miles, two more can go to London.
So after thinking about it for a while.
Xu Yun finally chose the rotating mirror photometry method invented by Foucault.
In fact, the shortest light path of the rotating mirror photometry method can be reduced to about 20 meters, but in order to make the experiment more exciting, Xu Yun chose five kilometers, a value that Cambridge University could spare.
Doing experiments in a 20-meter venue and demonstrating in a five-kilometer venue will attract completely different audiences.
Anyway, the optical path and the rotational speed of the rotating mirror are positively correlated. As the optical path becomes longer, the rotational speed can be adjusted accordingly.
When Xu Yun came to the edge of the field.
Faraday was standing beside the console with Stokes, frowning and silent.
Their expressions showed obvious doubts, but there was also a hint of understanding, as if they were about to touch some boundaries.
Seeing this, Xu Yun stepped forward and greeted several elders in turn:
"Your Majesty Albert, Dean Whewell, Mr. Faraday, Professor Stoker, good evening."
"Um?"
Upon noticing Xu Yun's appearance, Faraday immediately pulled Xu Yun to his side as if a reader had seen an update from the author:
"Classmate Luo Feng, what is your idea for this set of equipment? Please tell me in detail!"
See this situation.
Even before Xu Yun made any expression, William Whewell, whose face was always tense, could not help but feel slightly relieved.
Although William Whewell invented the word ‘scientist’, his main focus was still in the field of philosophy.
Although his knowledge in physics is not completely unknown, it is relatively poor.
Therefore, although he participated in the entire preparation process of this equipment, he still had no idea.
But judging from what Faraday said
This set of equipment prepared by Xu Yun seems to have some validity?
Xu Yun's wrist was a little painful from being pulled by Faraday, but he was too embarrassed to let him go, so he had to ponder for a moment and said to Faraday:
"Mr. Faraday, this equipment is a light speed measurement system designed by Fat Fish's ancestors. It's called rotating mirror photometry."
Then he pointed to the rotating mirror diagonally opposite and explained:
"First, start lighting at the light source, and adjust the position of the rotating mirror so that it can direct the light from the light source directly to the center of the concave mirror five kilometers away."
"This way, this section of light will first reach the concave mirror and then return to the rotating mirror."
"The retroreflected light is refracted by the rotating mirror and hits the imaging plate around us."
"We only need to gradually adjust the rotational speed of the rotating mirror and then adjust the position of the light spot."
"When the light spot moves to the optimal position, we can collect data and start calculating the speed of light."
Farah blinked as he listened, and by the end, his blinking frequency was as fast as a vibrator.
After a while.
He ignored Prince Albert beside him, walked to the operating table as if no one else was around, picked up a pen and paper and drew a schematic diagram.
"Light source s semi-silvered mirror M1"
"Lens L rotating mirror M2"
"M2 reflects to the concave reflector M3"
Then he paused his pen tip, looked at Xu Yun, and asked:
"Where is the center of curvature of the M3 mirror?"
Xu Yun pointed at the rotating mirror and replied without hesitation:
"On the O-axis of the mirror, the 3/4 position."
Faraday said nothing, and started calculating again:
"That's right about the O axis, symmetrical reflection will occur."
"The image of the light source generated by the s′ point moves to the left"
Seeing this, Stokes and several other professors on the side couldn't help but walked over to Faraday and discussed the schematic diagram.
The elders present are not to mention the best in the world right now, at least they are generally in the first echelon in the field of physics, and their abilities naturally need no elaboration.
They did not expect that the experimental steps were a matter of inspiration and had little to do with theoretical knowledge.
Now that Xu Yun has announced the entire operation process, with their abilities, they can quickly analyze the specific principles.
"So the angle that the reflected light turns is the approximate angle of the optical path?"
"No no no, it should be twice that"
"Does a concave mirror need to be calculated using Gaussian curvature, or does it just need to be able to form a direct beam?"
"Ah, yes, yes!"
A few seconds passed.
Stokes suddenly frowned and asked a question:
"The general idea is fine, but do we need to consider the conditions for complete destruction?"
Faraday paused again with the pen in his hand, remained silent for a few seconds, and wrote a formula:
4lw/+1/4)2π/n.
After I finished writing, I drew a line under the formula:
"What are the conditions like?"
The professors looked at the formula written by Faraday and started a new round of discussion:
"It seems okay, but what is the range of n?"
"Would it be better to directly compare the angle with the angular velocity?"
"Good idea, but in this case, the light path will have to be 2l+2d."
"Why use 2l+2d? What we are talking about is obviously the light path in the reflection stage? It should be 2d+l!"
"Are you stupid? Shouldn't you consider the reflection angle of m3?"
"Xiao Chi Lao, are you crazy about farming? Are you thinking about a poor M3?"
Just as the professors were arguing, a weak voice suddenly sounded from the side:
"Professors, is there a possibility that we only need to consider the rotation speed?"
After hearing this, the scene suddenly fell silent.
The next second.
Everyone, including Faraday, looked at the speaker.
I saw Xu Yun raising his hands weakly at this time, looking at them with a smile that was more honest than wheat.
Only then did everyone remember that they had been discussing for a long time and had actually forgotten Xu Yun, the designer.
Faraday thought for a moment, then waved to him and motioned for him to come forward. His tone was obviously much gentler than before:
"Classmate Luo Feng, what do you mean?"
Xu Yun walked to him obediently, glanced at Lao Fa's handsome face, and explained:
"Professor Faraday, although the optical path has three stages and two values, it is very troublesome to calculate."
"But don't forget that the rotational speed of the rotating mirror is easy to measure, and the positive correlation can be calculated using the variable method."
"So actually, we only need to measure the difference in gear speed between two consecutive times when the reflection is completely extinguished. The worst we can do is adjust it a few more times."
After Xu Yun finished speaking, he hesitated for a moment and picked up the pen on the table. Seeing that Lao Fa didn't stop him, he wrote another formula:
2lw/+1/2)2π/n.
Compared with the old formula, two values have been corrected.
Xu Yun then explained:
"Θ represents the relative angle between the gear position aligned by the observer and the gear position aligned by the candle. n is an arbitrary number. This is the boundary condition for total annihilation."
"After simplification, it is 2l△w/."
""
As Xu Yun finished speaking, the scene fell into an eerie silence.
after awhile.
The old professor who proposed 2l+2d suddenly slapped his head and said to the other person next to him who was arguing with him not long ago:
"Oh, Professor Vertonghen, I heard that a live maggot cheese shop has recently opened in London. The fly larvae in it taste great. If you have a chance, let's go and try it?"
"That's great. My wife also bought a very sexy swimsuit recently. Come to my house to look at it together on the weekend?"
"Very good, very good!"
Looking at the two professors chatting awkwardly, Xu Yun's lips twitched slightly:
""
But then again.
He had heard of the live maggot cheese that the old professor was talking about. It was a strange cheese from Italy called Casumazu.
It is said that when maggots are touched, they will jump around in your mouth, like popping candy.
Ahem
Then Lao Fa calculated Xu Yun's formula again, put down his pen, and sighed with emotion.
Although the person who proposed the entire experimental idea was Fei Yu, it seemed that Xu Yun was just a porter.
But Xu Yun's ability to keep up with the discussion ideas between himself and other professors is enough to prove that his knowledge reserve is not that limited.
After the idea verification is completed, the rest is the practical part.
With permission from Prince Albert.
Xu Yun walked to the fixed light source, the flashlight, and pressed the switch.
Swish
A ray of light comes from the flashlight.
Then, under the focus of a lens coated with a little mercury, it turned into an extremely thin thread of light.
The light filament hit the slowly rotating rotating mirror and immediately began to refract toward the concave mirror five kilometers away.
In the dark night.
This ray of light traveled straight along the blocked path, and in the eyes of everyone along the road, it hit the center of the concave mirror.
at the same time.
Laofa stood beside the imaging board, began to observe the situation on the imaging board, and proactively reported the situation:
"The light spot flickers on and off on the left side. What is the speed of the rotating mirror?"
Stokes, who was standing next to the rotating mirror, glanced at the dashboard and read out a number:
"60 rpm!"
Lao Fa looked at Xu Yun who was walking next to him and asked:
"Classmate Luo Feng, try increasing it to 300?"
Xu Yun nodded:
"good."
The speed increases quickly.
300 revolutions per minute, the period is 60/300=0.2 seconds.
=2π/T=10πrad/s.
From the perspective of later generations, this speed is obviously not enough. For a five-kilometer optical path, the speed must be at least 800 or above.
However, out of practical considerations, Xu Yun decided to let Lao Fa and the others slowly explore on their own.
ten minutes later.
Laofa looked at the light spot at the center of the imaging plate, vaguely realized something in his heart, and a flush appeared on his face.
at the same time.
Stokes walked up to him holding a table with a large amount of data and said respectfully:
"Mr. Faraday, the data has been calculated. All the professors agree that the final calculation step should be completed by you."
Now, no one, including Prince Albert, has any objection to Stokes's words.
As the soul who single-handedly opened the door to the second industrial revolution, there is indeed no one more suitable than Lao Fa to complete this final step.
Lao Fa saw that he took a deep breath, took the form, and started doing calculations on the spot.
Although there were crowds of onlookers standing around the operating table, no one dared to make the slightest sound. It was as quiet as the Busan Library in 2022.
Only the rustling sound of the pen touching the parchment could be faintly heard.
ten minutes later.
Lao Fa put down his pen and sighed with a complicated expression.
There was a long silence, and finally no words were spoken.
Prince Albert on the side stepped forward, picked up the parchment and took a look:
"The speed of light is 298,372 kilometers per second?"
Lao Fa nodded slowly but firmly, took off his glasses with trembling fingers, and pinched the bridge of his nose, feeling complicated.
The principle of the rotating mirror photometry method is very simple. Compared with the measurement method through Io, it is obviously intuitive and countless times more accurate.
The reason why scientists previously recognized the figure of 212,000 kilometers per second was because of the double guarantee of Huygens and Mavericks.
Secondly, the scientific community cannot find any way to measure light other than the starry sky.
In everyone's subconscious mind, if you want to measure the speed of light, the scale space beyond the earth is the only option.
The result was unexpected
Xu Yun just used a few mirrors and easily calculated the speed of light on the earth?
"Mr. Fat Fish, it's so scary."
And just when Lao Fa was surprised, an inappropriate voice suddenly sounded in the open space:
"Isn't that right? Mr. Luo Feng, didn't you say you could produce evidence to refute the wave theory? Is there any direct relationship between measuring the speed of light and the wave theory?"
Lao Fa and Xu Yun looked subconsciously.
as expected.
The person who spoke out was none other than Angus Roman.
Looking at Angus Roman who was a little angry.
Xu Yun suddenly smiled brightly, revealing a row of white teeth:
"Yes, so measuring the speed of light is just an appetizer, and the meal is at the end."
Note:
It’s my birthday today. Although I’m past the age to eat birthday cake, can I ask for a monthly pass?
It’s really my birthday, I’m not just looking for an excuse for the monthly ticket. I only remembered it when I saw a bunch of harassment intercepted text messages reminding me of happy birthday.
