The great scientific discovery caused by meticulous inquiry-the history of science
Discovering the nutation of the Earth's axis from the subtle changes in the position of stars
Since Heliocentrism was put forward by Copernicus, Kepler's law of planetary motion and Newton's law of universal gravitation have been established one after another, which makes the motion of planets more perfectly explained.
According to the heliocentric system, the annual parallax of stars should be observed. The so-called parallax means that the observer observes the same celestial body in two different positions in different directions. Annual parallax is produced by the annual motion of the earth around the sun. However, many people tried their best to find the annual parallax of stars, so that some people were skeptical about Copernicus' theory.
British astronomer J Bradley (1693-1762) is also trying to detect the annual parallax of stars. Starting from 172 1, he used a reflective telescope to measure the position of stars directly above his head.
1725 65438+In February, Bradley spent more than half a month tracking Y star in Tianlong Star, and found that its position would change and drew an ellipse.
Is the displacement ellipse of Y star a parallax ellipse? He continued to track for more than a year, and finally denied the conjecture of parallax ellipse: the movement direction of Y star does not coincide with the parallax movement direction; The position of the star should be the southernmost in June+February, 5438, but the observation result is the southernmost in March.
Bradley switched to a more practical telescope with quadrants and found that other stars had similar phenomena. Why is this? Bradley was confused.
1728, bradley found the answer.
Once, while sailing on the Thames, he noticed that when the ship turned, the weather vane on the ship turned with it. This is not that the wind direction has changed, but that the direction of the wind vane depends not only on the wind direction, but also on the sailing direction of the ship.
Bradley compared the direction of the wind vane with the phenomenon of star displacement, and found that they are similar, both of which reflect the velocity synthesis effect: comparing the navigation of the ship to the orbital motion of the earth, and comparing the wind direction to the real direction of the starlight emitted by the observed star. The direction of the weather vane is the speed direction of the ship speed and wind speed, and he immediately realized that the observed star displacement phenomenon is a synthetic effect of starlight propagation and the revolution of the earth!
Bradley discovered the aberration phenomenon, that is, the deviation between the apparent direction of the celestial body seen by the moving observer and the true direction of the celestial body seen by the stationary observer at the same time. The discovery of aberration confirms that the earth is indeed moving around the sun, and enables people to eliminate aberration displacement in actual observation and detect the real position of stars.
But things didn't end there.
Bradley found that the declination position of the star still changed slightly after the aberration was excluded from the observation results, and the declination position of the star near 0h and 12h was more obvious than that near 6h and 18h.
He further removed the influence of precession (the direction of the earth's axis is constantly changing in space, and its long-term movement is called precession), but there are still errors. He guessed that there might be some reason behind this mistake.
Bradley was greatly inspired by Newton's research on precession.
Newton pointed out that the gravity of the sun and the moon on the equatorial uplift of the earth will make the earth swing and rotate like a gyro, which is the reason for precession.
1732, bradley proposed that the position of the constant star fluctuates up and down because the gravitational force of the moon on the equatorial uplift of the earth causes the earth's rotation axis to swing.
Bradley made a painstaking exploration to test his hypothesis.
Because the orbital plane of the moon's revolution around the earth has a periodic change of 18.6 years, the force of the moon on the equatorial uplift of the earth should also change periodically, and the fluctuation of the position of the star is also observed in the same period.
He tracked the change of the star's position for a long time, and finally saw the star return to its original position after 18.6 years, which confirmed that under the force of the moon, the earth's rotation axis vibrates slightly in space with a period of 18.6 years, and the vibration amplitude is extremely small, only 10''!
In 1748, Bradley published his findings on the observation data analysis of several stars from 1727 to 1747, including the aberration, precession and periodic oscillation of the earth's rotation axis. He called this swing nutation, which means "nodding". Bradley won the copley Prize from the Royal Society for his new discovery.
Discovery of Nuclei from 1/8000 Small Probability Event
1898, the British physicist E. Rutherford (1871-1931) discovered alpha rays. Unlike beta rays, alpha rays are positively charged particles and ions of helium atoms, that is, helium atoms lacking two electrons. He proposed to Geiger and marsden, young German students studying in Britain, to carry out the scattering experiment of alpha rays.
1908 In May, Geiger and his colleagues found that "a small part of α particles bombarded the metal foil changed direction and even appeared on the same side of the incident plane again. One in every 8,000 incident particles will be reflected back. "
1/8000 may seem like a small probability event to others, but Rutherford said after hearing the news: "This is the most unimaginable event in my life. It is as incredible as shooting a 38.6438+0 cm shell at cigarette paper, but being hit by a reflected shell. "
His surprise is not unreasonable. At that time, many people accepted the atomic model of the famous British physicist J.J. Tang Musun: the atom is a fluid sphere filled with positive charges evenly, with negative charges scattered inside, and the whole atom is like "raisin bread". In this way, it is impossible for the positively charged sphere without any resistance and the negative electrons scattered in it to prevent the α particles from returning.
Rutherford tested in the experiment that Geiger really reflected alpha particles, and carefully measured the total number of reflected particles, confirming that under their experimental conditions, one out of every 8,000 alpha particles was reflected back.
19 1 1, Rutherford made a judgment. He pointed out that J.J. Tang Musun's atomic model and the scattering theory of charged particles can only explain the small angle scattering of α particles, but can't explain the large angle scattering. Large angle scattering can be obtained by multiple scattering, but the calculation results show that the probability of multiple scattering is very small, which is far from the observation that one of the above 8000 α particles reflects back.
After careful calculation and comparison, Rutherford found that only assuming that all positive charges are concentrated in a small area, when alpha particles pass through a single atom, large angle scattering may occur; In other words, the positive charge of an atom must be concentrated in a small nucleus at the center of the atom.
On the basis of this assumption, Rutherford obtained some laws of α scattering through calculation, which were quickly confirmed by a series of beautiful experiments by Geiger and marsden.
19 13 years, under the guidance of Rutherford, Geiger and marsden carefully carried out the scattering experiment of α particles, which confirmed the correctness of the scattering formula, thus supporting the atomic nucleation model.
Rutherford's atomic nucleation model is similar to "Saturn's atomic model" proposed by Japanese physicist Oka Kantaro in 1903: a positively charged sphere shrinks into a smaller entity at the center, just like Saturn, whose ring is equivalent to an electronic ring, and the linearity of an electronic ring is the linearity of an atom.
Rutherford's atomic nucleation model did not attract attention at first, and the stability of the nucleus puzzled many people: according to classical electrodynamics, the electric field force between positive and negative charges could not keep electrons outside the nucleus stably.
However, it was not long before Bohr, a disciple of Rutherford, boldly put forward the revolutionary hypothesis of the steady state and transition of extranuclear electrons, which satisfactorily explained the phenomenon of hydrogen spectrum. Most physicists accept the atomic nucleation model.
The discovery of nuclear structure is an epoch-making contribution in the history of physics, which announced the birth of nuclear physics and opened the door for people to explore the atomic structure in depth.
Investigate the error of11000 and establish the chaos theory.
One day in 196 1 year, edward norton lorenz, a professor of meteorology at the Massachusetts Institute of Technology in the United States (19 17-2008), made an experiment to simulate the weather forecast on a computer.
He chose a set of simplified equations to describe the meteorological conditions at that time, and then gave them to the computer for calculation to predict the future meteorological conditions.
One day, Lorenz wanted to check whether the calculation results were reliable. He is ingenious, and the last calculation does not start with the initial input data, but with the intermediate results.
An hour later, the calculation result is quite different from the original one, just like one calculation result predicts that one day in a few months will be sunny in Wan Li, and another predicts that there will be a storm on this day.
Lorenz was surprised. He checked the data carefully and found that the computer kept the accuracy of 6 figures for each data when calculating.
For example, 0.506 127, but the last three digits were omitted when printing, and it became 0.506. When I entered the intermediate result of the last calculation, I only entered the first three digits. He thinks this omission is reasonable-an error of one thousandth is nothing, but it leads to "disastrous" consequences, as the saying goes, "a tiny difference makes a thousand miles"!
Lorenz wants to find out why his "simulated weather" can tolerate such a small error.
After ruling out the possibility of computer and calculation program errors, he found that nonlinear equations were used to describe meteorology. Unlike linear equations, linear equations represented a gradual change process and would not be greatly affected by small errors caused by omitting numbers. However, the process represented by the nonlinear equation is unruly and irregular, and there is no room for any error. Even a little interference will cause great changes.
Lorenz is soberly aware that he once thought that slight temperature changes or breezes would not affect the weather. Now it seems that this is wrong. Any slight disturbance will bring amazing results to the evolution of weather system. He made a vivid metaphor: a butterfly flapping its wings in Brazil will cause a tornado in Texas. This is the famous "butterfly effect".
The "butterfly effect" seems to be disastrous for the weather forecast, but Lorenz feels the inherent charm of the chaotic motion of the atmosphere dominated by contingency and complexity. The "butterfly effect" provides a clue for Lorenz to describe random and aperiodic motion.
Lorenz described the motion of this system with three equations with three variables. If each group of three numbers printed by the computer is taken as the coordinates in the three-dimensional space and corresponds to a point in the phase space, then the changes of these numbers will draw a curve in the phase space, which is the "track" of the system's movement in the phase space, because the movement is aperiodic and these curves will not overlap.
The trajectory of Lorenz system always falls within a certain boundary, which will not extend indefinitely and will not repeat the original moving image. Repeatedly, a strange image similar to butterfly wings is formed. It is called Lorentz attractor, which is a symbol of early exploration of chaos. Attractor refers to the destination of the system.
Is there some regularity behind the chaos?
Based on the simple ecological equation xn+ 1 = μ xn (1-xn), Mei, a mathematical ecologist, found that period-doubling bifurcation is a typical channel for the system to move from order to chaos, that is, under certain conditions, the system will move from the fixed point to the oscillation of period 2, then to the oscillation of period 4, period 8 .. 2n, and when the period is infinite, it is equivalent to no period.
American scientist feigenbaum (1944-2019) further explored the phenomenon of period-doubling bifurcation. He pointed out that the bifurcation process is geometrically convergent, and the doubling period comes faster and faster at a constant speed. After a series of bifurcations, no matter what form a function goes to chaos, their period-doubling bifurcations all produce the same universal constant δ = 4. 16090.
The existence of δ shows that the regularity of geometric convergence is universally applicable, and nonlinear iterative systems with different structures have the same behavior and way to chaos and follow the same law. Feigenbaum's work has brought the study of chaos to a new stage.
The establishment of chaos theory shows that simple deterministic systems can produce complexity, while overly complex systems may obey simple laws.
The world and its laws are complex, but it only implies a simple formula. It is the infinite repetition of this formula that makes the world complicated, and the diversity of the world contains unity.
Strive to improve scientific literacy and find more "weak flashes"
There are many similar cases in the history of science.
When Kepler studied the orbit of the planet, he found that there was an 8-minute deviation between the position of Mercury calculated according to the precise circular orbit and the observed position. After further exploration, he proved that the orbit of Mercury is elliptical, and then established three laws of planetary motion.
Oster noticed that when the current passed through the platinum wire, it would slightly disturb the nearby magnetic needle. He continued his research and discovered the magnetic effect of current.
Rui used two different methods to produce nitrogen, and their density was only 0.0064 g/L. He got to the bottom of it and finally found the inert element argon.
Beveridge has a point. Scientists who have made outstanding contributions to the in-depth exploration of trivial things are really accomplished and have high scientific literacy:
They have high vigilance and keen insight, rich knowledge reserves in thought, perseverance, strong will and perseverance.
As people praised Bradley: "He has waited patiently for decades, how strong his will is and how amazing his perseverance is!" Such fine nutation amplitude measurement is inseparable from his rich observation experience, superb measurement technology and long-term systematic comparative study. According to the accurate calculation of modern astronomy, the nutation amplitude of the earth is only 0~9.2 10 ",which is like a few carats of diamonds buried in hundreds of tons of gravel. Only with insight and patient and meticulous comparison can we find that faint flash. "
We should learn from these scientists, strive to improve our scientific literacy and find more "that faint flash".
Chen Jingquan is a professor at the School of Humanities, Donghua University.
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