After a simple certificate-issuing ceremony, Michelson said to Li Yu: "According to tradition, we have to conduct a physics discussion with new members." Li Yu said: "No problem, please invite the president." Michelson thought for a while and said : "Why don't you just use the field of optics, which I am good at. You must know that the current physics community has not been able to give an explanation for the constant speed of light. Even Lord Kelvin, the British physics guru, called it a dark cloud." Michelson This question is so pertinent, after all, this dark cloud was brought about by his Michelson-Morley experiment.
Li Yu said: "It is indeed an incredible dark cloud, because the speed of light cannot be explained by classical mechanical theory." Michelson said: "This is the problem. Many people can faintly feel that there seems to be something hidden behind it. What a mystery of nature, so many people try to explain or prove it theoretically." Li Yu said: "I think the speed of light cannot be explained or proven at all, because it is the most basic physical quantity, just like Bohr. Zemann constant, etc." Michelson said: "But according to Mr. Maxwell's equations, the speed of light can be derived." The derivation Michelson said is to use Maxwell's equations to calculate the speed of light.
The process involves some relatively advanced mathematical content, but overall it is not particularly difficult. Students from the physics department can complete it without having to specialize in mathematics.
After all, the physics major of later generations cannot do without important mathematical tools. In short, after a series of substitutions such as tensors and curls, a very simple expression for the speed of light can be obtained: c=1\/eμ.
In short, the final speed of light can be determined by only two constants, namely the vacuum dielectric constant e and the vacuum magnetic permeability μ.
Since the last two are constants, the speed of light is naturally also a constant. Maxwell is only 0.1 millimeters away from special relativity.
But on the eve of the birth of special relativity, Maxwell failed to figure out why the speed of light became a constant. This was a super difficult problem.
But in fact, modern people understand that in a strict sense, we cannot say that Maxwell's equations have derived the speed of light or proved the principle of invariance of the speed of light. The above derivation only gives the relationship between the speed of light and electrical conductivity and magnetic permeability.
So Li Yu said: "Mr. President, as an excellent physicist, you must know that many of the most basic physical principles cannot be proven since ancient times."
"Can't prove it?" Michelson originally wanted to refute, but after all, he had been immersed in the measurement of the speed of light for too many years and knew that there was nothing wrong. Maybe he couldn't prove that it was really the answer.
Li Yu continued: "In Mr. Conan Doyle's "The Adventures of Sherlock Holmes", Sherlock Holmes said this to Watson, when you eliminate all impossible situations, the rest, no matter how unbelievable, is It's a fact." Those who have watched related movies or TV series must be very impressed. This sentence is very cool to say in English.
Michelson said: "I have read this excellent set of reasoning, and your quote makes sense. If, as you said, it cannot be proven that the speed of light remains unchanged, then wouldn't it become an axiom or a postulate?" Li Yu said solemnly. : "That's right!" Michelson took a breath. The revolutionary fifth postulate in the history of mathematics was right in front of him, and he had to express his great shock.
The so-called postulates are basic principles that do not require proof. Euclid used five postulates to deduce the huge Euclidean geometry, which is known as classical geometry. The five postulates seem to be very basic: a straight line can be drawn from any point to any other point, and a finite line segment can continue. Extension 3. A circle can be drawn with any point as the center and at any distance. 4. All right angles are equal to each other. 5. A straight line intersects two other straight lines in the same plane. If the sum of the two interior angles on a certain side is less than the sum of the two right angles, then These two straight lines intersect on this side after being infinitely extended.
The problem lies in the fifth postulate. Because it is obviously too long compared to the first four. Even Euclid himself was dissatisfied with it and wanted to prove it, but in vain.
——Don’t think that mathematicians are just looking for something to do. The establishment of mathematics has always been the most rigorous, and there is no room for sloppiness.
Later, mathematics became axiomatized, and a long proof process was even conducted for 1+1=2. Note that it is
"Later", that is, at least at the end of 1903, no proof has been given.
This matter is more complicated. To put it simply, Russell and his teacher Whitehead began to write "Principles of Mathematics" seven years later, in order to solve various paradoxes and then use logic to explain the axioms.
At first they took a big detour and proved that 1+1=2 took 379 pages! This book seems to be a heavenly book.
Of course, there is no need to read it, because they make too many detours and the language is too long-winded. Many people have complained about it, and the emergence of Gödel's incompleteness theorem has basically declared the failure of Russell's theory.
But people have always made exploratory attempts. In fact, people in later generations can use Peano's axiom system and prove that 1+1=2 in two pages.
Coming back to the fifth postulate, it actually not only deeply affected the world of mathematics, but also had a profound impact on the world of physics, especially the birth of the theory of relativity, so it has to be said.
Because the fifth postulate directly led to the birth of non-Euclidean geometry. The Russian mathematician Lobachevsky and the German Riemann respectively completed their own non-Euclidean geometry deductions.
The two are not exactly the same, but the processes are both revolutionary events in the history of mathematics. In short, once the basic axioms or postulates are wrong, the entire mathematical edifice must be revised, and then a more magnificent edifice will be born.
The world of mathematics has already undergone such a massive change. As a precursor, mathematics has completed the revolution, and disciplines such as physics can use mathematical tools to carry out revolutions.
Because the theory of relativity is based on Riemannian geometry, that is, on non-Euclidean geometry. Later, people became familiar with it
Theories such as "gravity causes space-time to curve" are inseparable from Riemannian geometry. In addition, gravity seems to be the easiest to understand, but it is a super bottomless pit.
Even Einstein stumbled over this in his later years, which directly led to the so-called
A "grand unified theory" is impossible to complete. Because Einstein went in the wrong direction, gravity is actually the hardest and should be included last.
But no wonder Einstein, because at that time people did not know the strong and weak forces among the four major forces.
The relationship is a bit complicated and will be discussed later. Anyway, now Michelson instantly understood the meaning of Li Yu's words: "You mean, the constant speed of light should be used as an axiom for a huge deduction?" Li Yu nodded: "The expression of the speed of light is derived relative to Maxwell's equations Of the two constants used in electrical conductivity and magnetic permeability, the speed of light in vacuum is a more basic physical quantity. Of course, the greatness of Maxwell's equations cannot be denied. It suggests to us in a simple way that the speed of light may be constant. ." Li Yu was a little conservative, because it was later proved that Maxwell's equations are also applicable to the relativistic system.
That's why it is said that Maxwell almost touched the threshold of special relativity. He was really right in front of the door.
Michelson is different from conventional physicists. He himself is a firm supporter of the constant speed of light.
Who told him to spend his whole life measuring the speed of light? No one knows better than him that no matter how the experiment is done, the speed of light remains unchanged.
What we are talking about here is the speed of light in a vacuum, because it is well known that the speed of light slows down in water. The reason is simple: the propagation of light itself does not require a medium, but the medium will slow down the speed of light.
Michelson pondered for a while and said: "I have read your books, and your papers are all about rigorous mathematics and profound physical explanations. Today, you say that the speed of light cannot be deduced mathematically, which makes me feel a chill in my heart." He believed in Li Yu's ability, but Li Yu's words today contained too much information.
Li Yu said: "There is nothing surprising. There are many principles in physics that are not derived through derivation, but are obtained through experiments. Since the experiments are not wrong, it means that the mysteries of nature are like this. Just like apples fall from trees. Falling." Michelson was a little stunned: "I understand what you mean. The apple falling from the tree inspired Newton to discover the magnificent three laws of mechanics; and people did not want to prove why the apple fell from the tree. The same holds true for the constant speed of light today, no need to prove it.”
"It is indeed the president! That's the truth," Li Yu said. There are probably very few people in the world who can accept this point of view calmly. He then said,
"So even if you ask me why the speed of light is constant, I can only regretfully answer three words, 'I don't know'." Michelson smiled and said: "You are very honest." Li Yu spread his hands: "I can only To answer this, after all, the fact that the speed of light remains unchanged is a test result, not a theoretical derivation." At least before Li Yu traveled through time, humans really didn't know why the speed of light remained unchanged.
To put it more bluntly, it is an artificial rule because the experiment is like this. If one day experiments show that the speed of light can change, it is estimated that more than half of the entire physical world will collapse by then.
Because this kind of subversion is like an apple falling from the earth and suddenly flying into the sky. At that time, the entire physical theory will have to be rebuilt.
Physics is just like that. Once you have experiments and then explain the phenomena, you cannot doubt that there are errors in nature.
But this kind of thing should be impossible, at least not in the current universe. , Michelson said: "I feel more and more that it is a wise choice for you to join the Physics Society. We met briefly at the White House dinner last time, and today we have an in-depth discussion. I am so impressed by your mathematical knowledge." Li Yu said with a smile: "It's so overwhelming." Since the release of his Star Wars series, Li Yu has found that many people like to say something
"Chinese proverb", but the idiom is really not good. Michelson said: "I will compile the conversation today and publish it in the conference paper tomorrow." - Kitty Hawk, North Carolina, USA.
Many people's initial impression of North Carolina should come from Jordan. Jordan came out of the University of North Carolina team and is now the owner of the Charlotte Hornets in North Carolina.
The cold wind at this time was already quite biting. When Li Yu appeared on the empty beach with a few people, the Laite brothers saw them at a glance.
Because there were very few people present today, except for Li Yu and his party, only five people were watching at the scene. Brother Laite ran over excitedly: "Mr. Li Yu, why are you here?" Li Yu smiled and said, "I told you, I want to see you fly into the sky with my engine." Brother Wilbur Laite Said: "I never thought that as the world's top scientist, you would be optimistic about our flight test." Li Yu basically told them the story of Wanhu.
His younger brother Orwell Wright said: "It turns out that the Chinese had such a dream hundreds of years ago. I always thought that it was Mr. Leonardo da Vinci who originally had the idea of flying." Leonardo da Vinci was also an all-rounder. The manuscript does include designs for an ornithopter, and even helicopters and parachutes.
It feels like a time traveler. Newton has a famous saying: "If I have seen further than others, it is because I stand on the shoulders of giants." Although this sentence was originally directed at Hooke, it does make sense.
The same applies to the Wright brothers. In fact, in the decades before the Wright brothers, many people had done a lot of work and achieved many results in aircraft structure, lift and drag research, stability and control, gliding flight, etc.
Without them as pioneers, the Wright brothers would not have been able to succeed. The Laite brothers happily took Li Yu to visit their plane today.
"Aviator 1". This aircraft doesn't look too small, with a wingspan of more than 12 meters, which is about 14 to 15 meters for a modern fighter jet.
However, the take-off weight is only a pitiful 360kg. For comparison, the take-off weight of the J-15 or F18 is more than 30 tons.
If it is a civil airliner such as a Boeing 737 or something, it will be even higher, directly exceeding 50 tons. The elder brother Wilbur Wright looked at the weather and said: "It's time to start." The younger brother Orwell Wright took out a coin, and the two guessed the coin and finally decided that the younger brother Orwell would drive first.
Orwell climbed onto the lower wing of the plane, holding the wooden joystick in his hand, and said to Wilbur: "Brother, start it!" Yes, this plane cannot be started by one person, it requires force. Erber revved the engine under the plane and pushed it into taxi.
This... is actually a bit inappropriate. Li Yu felt it necessary to introduce his electronic ignition system to them.
Using a joystick to start a car is already ungentlemanly, but starting an airplane with a joystick is really awesome. Hand-operated tractors call you an expert!
But overall, after so many wind tunnel tests, the aircraft's attitude control is pretty good.
After the speed increased, Wilbur let go of his hand, and Flyer 1 flew out tremblingly. Fortunately, the thrust-to-weight ratio of this aircraft is only 0.03, otherwise it would be impossible to push the aircraft manually.
Flyer 1 flew for only 12 seconds and landed 36 meters away. Then I switched to my brother as the driver and flew 59 seconds and 260 meters.
The data sounds inferior to later generations of wingsuit flight, but as the first powered flight for humans, it is significant enough.
The two brothers were having fun and wanted to continue the test flight, but a strong wind blew over the plane and caused serious damage, so they had to stop the flight test.
