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On the Scientific Method Learned from Albert Einstein in 2005--The World

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On the Scientific Method Learned from Albert Einstein in 2005--The World On the scientific method learned from Albert Einstein in 2005—the World Year of Physics Y. H. Yuan∗ (Dated: November 22, 2005) We review the physics at the end of the nineteenth century and summarize the process of the establishment of Special Relativity by Albert Einstein in brief. Following in the giant’s footsteps, we outline the scientific method which helps to do research. We give some examples in illustration of this method. We discuss the origin of quantum physics and string theory in its early years of development. Discoveries of the neutrino and the correct model of solar system are also presented. I. HISTORICAL REVIEW AND A METHOD ics tells us that wave propagation needs a medium to DEDUCED support it. For example, sound waves have to travel in the air medium. For the propagation of electromagnetic The year 2005 was declared the World Year of Physics wave, physicists presumed an ether medium which was which is an international celebration of physics. It marks entirely frictionless, pervaded all space, and was devoid the hundredth anniversary of the pioneering contribu- of any interaction with matter. Although many ingenious tions of Albert Einstein, the greatest man in the twenti- physics papers during 1885-1905 were dedicated to ver- eth century as chosen by Time magazine. ifying it, the ether refused to reveal its presence to the In 1905, one hundred year ago, a Swiss patent em- pursuers. ployee, Albert Einstein, published a paper entitled “On In 1881, a 28-year-old American physicist, Albert the Electrodynamics of Moving Bodies” [1] which de- Michelson, realised the possibility of an experimental test scribed what is now known as Special Relativity. It dras- for the existence of ether by measuring the motion of tically changed human fundamental concepts of motion, the earth through it. He performed the experiment in space and time. The year 1905 was the miraculous year Potsdam, Germany. Although he got negitive results in for Einstein. In the same year he also published three detecting the relative motion of the earth and ether, his other trailblazing papers. One [2] accounted for the pho- measurement is not so accurate as to give an important toelectric phenomena and made up a part of the founda- result. Six years later, Albert Michelson and Edward tion of quantum mechanics. He won the Nobel Prize in Morley in Cleveland, Ohio carried out a high-precision physics due to the ideas of this paper in 1921. The second experiment to demonstrate the existence of ether with an one [3] was about the explanation of Brownian motion interferometer, which is now called the Michelson inter- and helped to establish the reality of the molecular na- ferometer. This experiment is a high-precision repetition ture of matter and to present convincing evidence for the of Michelson’s experiment in Potsdam. In their experi- physical existence of the atom. The third one [4] gave the ment shown in FIG. 1, a beam of light from the source most famous and beautiful equation in special relativity, was directed at an angle of 45 degree at a half-silvered E = mc2, which has received various experimental verifi- mirror and was split into two beams 1 and 2 at point O cations and has had wide application in modern physics. by the mirror too. These beams 1 and 2 traveled at a These groundbreaking papers have shattered many cher- right angle to each other. The two beams were reflected ished scientific beliefs and greatly promoted the devel- by separate mirrors, then recombined and entered a tele- opment of modern physics. They won for Einstein the scope to form a fringe pattern. The fringe pattern would greatest physicist as Newton in all human history. Next, shift if there was an effect due to the relative motion of we will follow the process of the establishment of Special the earth and the ether when the apparatus was rotated. Relativity and summarize some useful skills in research. Therefore, by monitoring the changes in the fringe pat- One of the most famous puzzles at the end of the nine- tern, they could tell the relative motion of the earth and teenth century was the ether which was proposed as a the ether. Even with the high-precision apparatus, they medium to support the electromagnetic wave propaga- did not find any experimental evidence for the existence arXiv:physics/0510124v3 [physics.hist-ph] 22 Nov 2005 tion. Maxwell’s fundamental equations about the elec- of relative motion of the earth and ether. These results tromgnetic field were published in 1862. It leads to the indicated that either there is no ether or the earth is in electromagnetic wave equation in free space, the ether rest frame all the time during the experiment. 2 Since the earth is always altering its velocity when mov- ∇2 − 1 ∂ φ φ 2 2 = 0 (1.1) ing around the sun, the experimental result appeared to c ∂t show that there was no existence of ether. All the repe- where φ is any component of E~ or B~ . Classical mechan- titions of their experiment in the succeeding years were still unable to detect any relative motion of the earth and the ether. But ether died hard. Many physicists including ∗E-mail: [email protected] Michelson himself made great efforts to retain the ether 2 Mirror where we assume coordinate system Σ moves relative to another one Σ′ in the x-axes with uniform velocity v and γ = 1 [5]. Although he laid the foundation for 1− v2 Beam 1 c2 q Mirror the theory of relativity with his mathematical equations, Lorentz still tried to fit these remarkable equations into the ether hypothesis and save the ether from the contra- Light O 45˚ diction of the Michelson experiment. source All these efforts failed to explain the Michelson exper- Half-silvered Beam 2 iment while retaining the ether. It was genius Albert mirror Einstein who abandoned the ether entirely. He wrote in his celebrated paper on relativity in 1905[6]: “The introduction of a ‘light ether’ will prove to be 1 2 superfluous, inasmuch as in accordance with the concept to be developed here, no ‘space at absolute rest’ endowed with special properties will be introduced, nor will a ve- Telescope locity vector be assigned to a point of empty space at which electromagnetic processes are taking place.” Furthermore he developed the Special Relativity by conjucturing two postulations: FIG. 1: Diagram of Michelson-Morley experiment. A beam 1. The laws of nature are the same in all coordinate from a source was split into beams 1 and 2 at point O by a half-silvered mirror. The two beams were reflected by sep- systems moving with uniform motion relative to one an- arate mirrors and then entered a telescope to form a fringe other. pattern. 2. The speed of light is independent of the motion of its source. Of which, the first one is a natural generalization for yet explain the Michelson experiment. He attributed the all kinds of physical experience since it is reasonable to negative results to the earth dragging some of the ether expect that the laws of nature are the same with respect along with its motion. As a consequence the ether was to different inertial frames of reference. Whereas the sec- motionless with respect to the earth near its surface. ond one just represents a simple experimental fact. In George FitzGerald put forward another possible expla- Michelson’s experiment, the speed of light was found to nation in 1892 following the Lorentz-FitzGerald contrac- be constant with respect to the earth. Put in other words, tion equation, as we now know, the speed of light is the same for observers in different in- ertial frames of reference since an observer on the earth at two different times may be regarded as an observer v2 in two different inertial frames of reference. It is only a L = L0 1 − (1.2) r c2 small jump to the postulate of Einstein’s Special Relativ- ity that the speed of light is independent of the motion where L0 is called the proper length of an object which of its source. is measured in the rest frame of the object. To a mov- From the above condensed outline of the establishment ing observer of velocity v, any length along the direction of special relativity, we learn that when proposing an of motion undergoes a length contraction by a factor of idea or theory with which we may account for some un- − v2 explained phenomena, they should be based upon the 1 c2 . He proposed that the experimental appara- tusq would shorten in the direction parallel to the motion given facts of experiment or phenomena. Sometimes, the through the ether. This shrinkage would compensate the ideas may contradict well-known theories which are not light paths and prevent a displacement of the fringes due experimentally proved, such as the ether. If the prob- to the relative motion of the earth and the ether. lem is subtle and complicated, especially in physics, we Hendrik Lorentz discovered the well-known Lorentz should make incisive analyses, see through the general transformation in 1904 under which the electromagnetic appearance and grasp the underlying nature. The above theory expressed by the celebrated Maxwell equations method is of practical use in research which could be seen were in form invariant in all inertial frames. from the following four examples. ′ v t = γ(t − x) (1.3) II. FOUR EXAMPLES c2 ′ x = γ(x − vt) (1.4) ′ A good example in illustration of the method is the y = y (1.5) origin of quantum physics which now plays an important ′ z = z (1.6) role in various scientific areas.
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