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At the beginning of the principles of Natural philosophy of Mathematics, Newton put forward a hypothetical experiment, which is the famous "Newton bucket".

Many smart people are trapped by the wonderful idea of this experiment, and before you know it, Newton achieves his goal and makes you believe what he said: there is an "absolutely immobile space" in the universe.

The experiment of "Newton bucket", which can be practiced by everyone in Newton, is so simple that everyone can try it with their own hands.

The experiment is like this: hang a bucket with half water by a rope, hold it still, let go after rubbing the rope with twist, the bucket begins to rotate, the twist knot of the rope is gradually loosened, the bucket continues to rotate, and the rope twists in the opposite direction. As the bucket turns more and more slowly, until a moment stops, the bucket turns back and forth.

The phenomenon of the experimental diagram is so simple, but it contains a very profound truth. The experiment involved great mathematicians, physicists and philosophers Leibniz, Mach and Einstein. Today, more than 400 years later, people are still studying it.

How did Newton achieve his goal? In order to demonstrate that the "absolutely immovable space" is "absolute", two special moments can be chosen: one is when the bucket begins to rotate, relative to the bucket and the surrounding objects, such as houses, trees and even distant stars, the water is still and the water surface is flat. Another moment is when the bucket turns until the rope is completely loosened, and the bucket continues to spin the rope and twists the twist in the opposite direction. When the bucket finally stands still, the bucket is still, the water in the bucket is still, the water rotates fastest, and the surface of the water is sunken downwards. The water moves relative to the bucket and the surrounding objects.

Newton drew two conclusions: when the ① is motionless relative to the external object, the water surface is flat, on the contrary, when it moves relative to the external object, the water surface is sunken, and whether the water surface is flat or sunken is related to whether the water moves relative to the surrounding objects.

Whether the water surface of ② is flat or sunken has nothing to do with the movement of water relative to the bucket.

When you accept Newton's two conclusions, Newton plays another trick.

He envisions taking away all the objects outside the bucket and making the bucket spin in an "empty" universe, with no object to refer to. How can you tell whether the water is moving or still? Newton believes that there is a "way" to judge whether the water surface is "flat" or "concave". If the water surface is flat, the water is still; if the water surface is sunken, the water is moving and there is no need for the surrounding reference. By the time you accept Newton's conclusion, his goal will have been achieved.

It seemed easy for Newton to achieve his goal, because the "flat" and "concave" of the water surface were "absolute", and there was no need to determine whether the water was moving or not. This shows that there must be an "absolutely immovable space", which has nothing to do with "something" and "nothing". As long as the water does not rotate relative to this "absolute space", the water surface is flat, on the contrary, if the water rotates relative to the "absolute space", the water surface will be sunken. Newton leads you by the nose with his bucket, so that you have to follow his train of thought and accept his conclusion. The experiment was flawless and lasted for more than 30 years after it was proposed, and no one can refute it. In this way, "absolute space" has become an important foundation of Newtonian mechanics and even classical physics.

Most of the philosophical people in the questioned "Newton bucket" are people who like to use their brains and dare to get to the bottom of the matter, and philosophers can no longer sit still. The first to question was the British philosopher George Berkeley.

In 1721, he discovered the flaw in the Newton bucket experiment. He believes that the "depression" of the water surface is the result of the rotation of "water relative to the surrounding fixed galaxies," or "water relative to all the fixed objects around," implying that if everything around is completely removed, this is not the case with the experiment.

George Berkeley in 1883, the German philosopher Ernst Mach also questioned, he wrote: "Newton's bucket looks simple, as if water is subjected to centrifugal force, has nothing to do with whether the bucket moves or not." But this centrifugal force is actually the result of the interaction between the earth and all the stars around it. No one can answer with certainty what the experiment would be like if the bucket wall were made very thick. "

Ma Heming pointed out that the reason why the water is sunken is that the water is "dragged" by the surrounding stars, which is similar to a "gravitational effect." once there are no stars around, this gravity does not exist, at this time, whether the water turns or not, the water surface will be flat. Of course, Mach's statement is also questionable. It is impossible to take everything out of the bucket, including all the stars, so people are not sure whether Newton or Mach is right. However, Mach's previous argument fully shows that Newton's conclusion can neither be proved nor falsified, so the "Newton bucket" experiment can not simply prove the existence of "absolute space".

Ernst Mahmach's ingenuity lies in that he negates Newton's "hypothesis" of "nothing", and his explanation of Newton's bucket phenomenon does not depend on the existence of "absolute space". More importantly, he endows the "surrounding starry sky" with dynamic properties, which can exert a dynamic effect on any object that accelerates motion, which is the source of the "inertia" of the object.

In daily life, Mach's phenomenon that "the surrounding starry sky exerts power on rotating objects" can often be seen, such as merry-go-round, centrifugal dryers, raindrops flying from rotating umbrellas, flying gyroscopes and even tornadoes. These centrifugal phenomena are all the result of "gravitation exerted by the surrounding starry sky", and even the Coriolis force on Earth comes from this.

Tornado image source pexels "the gravitation of the surrounding starry sky to objects" is shown not only in rotation, but also in all accelerated movements, such as starting, accelerating, turning, decelerating or even stopping suddenly. The greater the mass of the object, the stronger the "gravity" given by the surrounding starry sky, thus deducing that the "inertia" of the object is not its own nature. As a result, Mach revealed the source of the consistency between "inertial mass" and "gravitational mass".

Einstein was inspired by Mach. He very much agreed with Mach's refutation of the "Newton barrel" experiment. Mach's thought inspired him to think about the new gravity and the inertia of matter. He not only incorporated Mach's idea into the principle of general relativistic equivalence, but also believed that Mach's idea could be used to accurately verify the principle of equivalence in the earth environment.

Up to now, the modern version of "Newton bucket" has been put forward for more than 300 years, and the modern version of "Newton bucket" has reappeared in scientific experiments with a new look.

The modern version of the "Newton bucket" experiment was conducted by British physicist Everett, funded by the National Aeronautics and Space Administration (NASA) and jointly carried out by the Stanford University research team.

There are two experimental projects, called "geodesic drift experiment" and "inertial frame of reference drag" experiment. In both experiments, the "Newton bucket" is replaced by a rotating "gyroscope", while the "flat" and "concave" of the water surface are replaced by the "axis direction" of the gyroscope.

In order to improve the accuracy and prevent the interference of stray objects on the ground, the gyroscope is placed on a satellite operating in a synchronous orbit at an altitude of 642 kilometers above the ground, and the gyroscope is placed under the condition of superconductivity and rotates relative to the starry background. According to the comparison between the observed data of the gyroscope and the theoretical calculation data, Mach's prediction and general relativity theory are verified.

Everett completed Newton's hypothetical experiments, but far from being as simple as "Newton barrel". It combines aerospace technology, superconducting technology, telemetry and remote sensing technology, automation technology and computing technology. in the 45 years from 1963 to 2008, it cost a total of 750 million US dollars, making it the longest experimental project supported by NASA. This is an extremely arduous and tedious work. In as long as 45 years, after the efforts of two generations, the modern version of the Newton barrel experiment finally completed the data collection on August 14, 2005.

Since then, after more than 5 years of data analysis and calculation, the experimental results were sent in 2011. The experiment confirmed Mach's original prediction: "once there is no external interference, the axis of the gyroscope will always point to a certain direction of the starry background."

For as long as 45 years, using a lot of manpower and material resources, just to prove Mach's prediction?

In fact, it is not, it proves a truth: the correctness of physical laws does not need the existence of absolute space. In addition, when there is a massive object nearby, the gyro axis observed in the experiment shows a small deviation, and this deviation just supports Einstein's theory of general relativity, which is by no means possible in ordinary experiments.

More than three hundred years ago, Newton put forward the hypothetical experiment of "Newton bucket", which was intended to demonstrate the existence of "absolute space", but what he did not expect was that "one stone stirs up thousands of waves".

Picture source: "Scientific Calendar" Tsinghua University Press his hypothesis triggered a lasting debate in the field of physics and even mathematics and philosophy, the result of which freed people from the shackles of "absolute space" and triggered the formation of Einstein's new theory of gravitation. Newton Bucket not only did not support Newton's hypothesis, but provided future generations with an experimental means to test general relativity. There is a lot of mystery in the "Newton bucket" that everyone can play, and this "bucket" plays an important role!

Source: 365th days in the History of Science, slightly edited by: Wei Fengwen Wu Yi Editor: Zhang Runxin this article comes from the official account of Wechat: original Reading (ID:tupydread), author: Wei Fengwen Wu Yi, Editor: Zhang Runxin

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