In 1881, Michelson carried out a famous experiment, with the help of which he hoped to discover the motion of the Earth relative to the ether (the ethereal wind). In 1887, Michelson repeated his experience together with Morley on a more advanced instrument. The Michelson-Morley installation is shown in fig. 150.1. The brick base supported an annular cast-iron trough filled with mercury. A wooden float floated on the mercury, shaped like the lower half of a donut cut lengthwise. A massive square stone slab was installed on this float. Such a device made it possible to smoothly rotate the plate around the vertical axis of the device. A Michelson interferometer was mounted on the plate (see Fig. 123.1), modified so that both beams, before returning to the translucent plate, several times passed back and forth along the path coinciding with the diagonal of the plate. The diagram of the beam path is shown in fig. 150.2. The designations in this figure correspond to the designations in fig. 123.1.
The experiment was based on the following considerations. Let's assume that the arm of the interferometer (Fig. 150.3) coincides with the direction of the Earth's motion relative to the ether. Then the time required for the beam to travel to the mirror and back will be different from the time required for beam 2 to travel the path.
As a result, even if the lengths of both arms are equal, beams 1 and 2 will acquire some path difference. If the device is rotated by 90°, the arms will change places and the path difference will change sign. This should lead to a shift in the interference pattern, the magnitude of which, as shown by Michelson's calculations, could well be detected.
To calculate the expected shift of the interference pattern, let's find the times of passage of the corresponding paths by beams 1 and 2. Let the Earth's velocity relative to the ether be equal to .
If the ether is not entrained by the Earth and the speed of light relative to the ether is equal to c (the refractive index of air is practically equal to unity), then the speed of light relative to the device will be equal to c - v for the direction and c + v for the direction. Therefore, the time for beam 2 is given by
(the speed of the Earth's orbit is 30 km/s, so
Before proceeding to the calculation of time, consider the following example from mechanics. Suppose that a boat, which develops speed c relative to water, needs to cross a river flowing at speed v in a direction exactly perpendicular to its banks (Figure 150.4). In order for the boat to move in a given direction, its speed c relative to the water must be directed as shown in the figure. Therefore, the speed of the boat relative to the coast will be equal to The same will be (as Michelson assumed) the speed of beam 1 relative to the device.
Therefore, the time for beam 1 is
Substituting the values (150.1) and (150.2) for into the expression, we obtain the difference between the paths of rays 1 and 2:
When the instrument is rotated by 90°, the path difference will change sign. Consequently, the number of fringes by which the interference pattern will shift will be
The arm length I (taking into account multiple reflections) was 11 m. The wavelength of light in the Michelson and Morley experiment was 0.59 μm. Substituting these values into formula (150.3) gives bands.
The device made it possible to detect a shift of the order of 0.01 fringes. However, no shift in the interference pattern was found. To rule out the possibility that at the time of measurements the horizon plane would be perpendicular to the Earth's orbital velocity vector, the experiment was repeated at different times of the day. Subsequently, the experiment was carried out many times at different times of the year (for a year the Earth's orbital velocity vector rotates in space by 360°) and invariably gave negative results. The ethereal wind could not be detected. The world ether remained elusive.
Several attempts have been made to explain the negative result of Michelson's experiment without abandoning the hypothesis of a world ether. However, all these attempts were unsuccessful. An exhaustive, consistent explanation of all experimental facts, including the results of Michelson's experiment, was given by Einstein in 1905. Einstein came to the conclusion that the world ether, i.e., a special medium that could serve as an absolute reference frame, does not exist. In accordance with this, Einstein extended the mechanical principle of relativity to all physical phenomena without exception. Further, Einstein postulated, in accordance with experimental data, that the speed of light in vacuum is the same in all inertial frames of reference and does not depend on the motion of light sources and receivers.
The principle of relativity and the principle of the constancy of the speed of light form the basis of the special theory of relativity created by Einstein (see Chapter VIII of the 1st volume).
Before getting into the details of the Michelson interferometer, let's look at it from above and try to understand what the underestimation of the effect of light aberration leads to.
On the left in fig. 1 shows the full path of light rays, on the right in the same figure a simplified diagram is drawn, adopted by modern science. In the right figure, we see the square base of the device, on which is fixed a light source, a system of mirrors that repeatedly reflect a beam of light, and an optical device (Michelson called it a “telescope”) for observing an interference pattern. A system of mirrors is needed to increase the optical path of interfering rays, which is directly related to the phase difference. Of fundamental importance, however, mirrors do not have: there may be more or less of them.
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Rice. one. The path of light rays in the Michelson interferometer. In the right figure, beam 1 from light source 0 propagates in the direction of the Earth's motion; beam 2 is beam 1 reflected from mirror C. Beam 3, reflected from mirror A, becomes beam 4. As Michelson noted, the optical path taken by beams 1-2 is not equal to the optical path taken by beams 3-4. Consequently, having met at point B, they will give interference fringes, the distances between which are proportional to the difference in the path of rays 1-2 and rays 3-4. In this traditional scheme, which is reproduced in all textbooks that talk about the Michelson-Morley experiment, the angle of aberration is actually the angle α. The effect of aberration is compared with the effect of "drift" of a light beam in one direction or another, depending on the movement of the source or receiver. Unfortunately, when choosing the sign of beam 3 deflection, a mistake was made: on the diagram, beam 3 deviates to the right, in reality it should deviate to the left (beam 3").
In school textbooks, aberration is explained through oblique jets of water that rain leaves on the side windows of a moving car. These jets form an acute angle with the direction of the vehicle's motion vector. In fact, imagine that you are sitting inside a car that is moving down the road. Raindrops on the side windows of the car interior draw oblique lines, as a triangle of speeds is formed: a horizontal leg v 1 - vehicle speed; vertical leg v 2 - the speed of the drop from top to bottom. Then the hypotenuse of this triangle is the vector sum of these two velocities. This is the effect of aberration.
According to this phenomenon, astronomers, when observing the stars, slightly turn their telescopes in the direction of the Earth's movement. Otherwise, the section of the wave front that entered the telescope lens will not reach its eyepiece. Moreover, the magnitude of the aberration depends on the location of the star in the night sky. The stars that are directly above our heads describe a regular circle with an angular radius of aberration deviation α \u003d 20.45 during the year. Stars located at some angular distance from the zenith describe an ellipse. Stars on the horizon, i.e. in the plane of the ecliptic (Earth's orbit), they oscillate along a straight line with the same angular deviation ±α.
Rice. 2. The essence of the light aberration effect. The star, the direction to which lies at a right angle to the plane of the Earth's orbit, turns out to be displaced in the direction of the Earth's motion by an angle α = 20.45 ". Therefore, the telescope tube must be inclined at an angle α to the vertical direction. The aberration effect is explained by the fact that the light entering the telescope lens at a point A, must reach the eyepiece to the point V so that it can be seen by an observer on the ground. The angle of inclination α is determined vector sum of two speeds- the speed of light c and the speed of the Earth in orbit v, so that the speed of light inside the telescope tube ( c") on the segment AC is determined by the Pythagorean formula, i.e. on the classical formula for adding velocities - (c² – v²) ½ (These explanations are taken from an article I wrote earlier The main argument against the theory of relativity).
In the first part of this work, it was repeatedly emphasized that the correct understanding of the Michelson-Morley experiment comes from considering the wave nature of light - and this is true. However, it must also be remembered that the phenomenon of aberration can also be observed on the example of point objects. It must not be forgotten that J. Bradley, the discoverer of aberration, according to Newton's optical theory, represented light in the form of corpuscles.
So, in the examples with a telescope or a car, the moving one is receiver. We repeat, if the rays from a star or a raindrop fall vertically downward, then due to the motion of the receiver, an acute angle α is formed, which will be deposited from the normal to the side in the direction of the receiver. Well, what happens if it moves a source? Imagine that a fountain is installed in the back of a car, the jet of which is directed vertically upwards. When the car is moving, this jet will naturally deviate back. Therefore, the angle of aberration α, when the light source moves, must be postponed from the normal to opposite side from the source velocity vector.
Thus, in fig. 1 beam 3 from light source 0 will not go towards point A, but towards point D. Michelson was wrong. In his head was a picture of a river with two boats moving along and across the current. It was for this picture that he calculated the time of the rays in the device and obtained the phase difference. But this does not exhaust the shortcomings of his drawing and, consequently, his calculations.
Outwardly, the Michelson diagram of the path of rays in the interferometer, taken from the work (see the figure on the right), resembles a drawing from geometric optics, when all angles of reflection are equal to the angles of incidence. But in the presence of aberration, this law is violated. A beam of light falling on a translucent mirror at an angle of 45° will be reflected not at the same angle, but at a different angle: 45° + α. Therefore, in the case fast travel source, receiver and system of mirrors, it is no longer possible to use the laws geometric optics, valid only for stationary case.
In a moving system, the concept of "optical path" is modified. In this case, it is necessary to take into account the effect of aberration and the Doppler effect, which are not taken into account in the optics of stationary light sources and receiving sensors. The traditional ray path scheme in an interferometer is not suitable for calculating the phase difference, which is responsible for the interference pattern. It was taken directly from Michelson's example of boats being swept away by the current of a river. With rays of light, the situation is completely different. They propagate in a stationary ethereal medium, while the source and receivers of light vibrations move.
Before delving into the details of the interferometer and the design of the experiment, let's take a look at what happened the day before. To this end, we will quote an excerpt from an article by Michelson and Morley, written on the results of an experiment in 1887.
“According to Fresnel,” the authors write, “in the wave theory, the ether, firstly, is assumed to be at rest, with the exception of the interior of transparent media, in which, secondly, it is considered to be moving at a speed less than the speed of the medium in relation to ( n² – 1)/ n², where n- refractive index. These two hypotheses provide a complete and satisfactory explanation for aberration. The second hypothesis, despite its seeming improbability, must be considered fully proven, firstly, by Fizeau's remarkable experiment and, secondly, by our own research. Experimental verification of the first hypothesis is the goal of this work.
If the Earth were a transparent body, then, taking into account the experiments just mentioned, it would probably be possible to assume that the intermolecular ether is at rest in space, despite the movement of the Earth in orbit; but we have no right to extend the conclusions from these experiments to opaque bodies. However, there can hardly be any doubt that the ether can and does pass through metals. Lorenz cites the tube of a mercury manometer as an illustration. When the tube is tilted, the ether in the space above the mercury will certainly be pushed out from there, since it is not compressible. But again, we have no right to suppose that it comes out quite freely, and if there were any resistance, however slight, we could not, of course, believe that an opaque body, such as the Earth as a whole, provides free passage of ether through all this mass. But, as Lorenz aptly remarks, “be that as it may, in my opinion, in this matter, also important, it is better not to allow yourself to be guided by considerations based on the plausibility or simplicity of this or that hypothesis, but to turn to experience in order to learn to recognize the state of rest or movement in which the ether is on the surface of the Earth.
In April 1881, a method was proposed and tested to solve this problem.
When deriving the formula for the measured quantity, then the influence of the Earth's movement through the ether on the path of the beam perpendicular to this movement was overlooked. The discussion of this omission and the entire experiment is the subject of a very deep analysis by G. A. Lorentz, who found out that this effect should by no means be neglected. As a consequence, in reality the quantity to be measured is only half the quantity supposed, and since the latter was already scarcely beyond the error of the experiment, the conclusions drawn from the results of the experiment could well be doubted. However, since the main part of the theory is not subject to doubt, it was decided to repeat the experiment with such changes that would give confidence that the theoretical result is large enough not to be hidden by experimental errors.
“Even Fresnel, in the letter cited above, in which the concept of the drag coefficient was introduced, showed that the acceptance of the value k = (n² – 1)/ n² makes it possible to explain the lack of influence of the Earth's motion on some optical phenomena, even if we recognize the immobility of the ether, i.e. explicitly refuse to extend the principle of relativity to electrodynamics. In what follows, the question of the entrainment coefficient becomes the central point of the theory. Recognizing Fresnel's initial premises (different ether density in different bodies with the same elasticity) as insufficiently substantiated, subsequent researchers tried to give a dynamic interpretation of the drag effect based on other models.
Stokes noted that the Fresnel coefficient can be obtained if we assume that all the ether moves inside the body, and the ether entering the Earth or another body in front is immediately compressed, and the ether leaving behind the body is discharged.
From this it becomes clear that Michelson and Morley actually tested precisely this idea of Stokes, which was also preferred by Lorentz. According to the Fresnel model, the ether does not cause any wind: physical bodies create inhomogeneity in the density of the ether, which move around the Sun with the orbital speed of the Earth, but the ether itself is at rest. Frankfurt and Frenk correctly noted that if we accept this, it means "explicitly refusing to extend the principle of relativity to electrodynamics." Meanwhile, by the time this acute problem was discussed, the total principle of relativity had already been proclaimed by Mach. Those who agreed with him automatically switched to the positions of Stokes and Lorentz, who adhered to by no means a new concept.
According to the old ideas, the Earth, when moving around the Sun, should be blown by the ethereal medium, just as a flying ball is blown by air. No matter how discharged the ether is, as a result of friction, the Earth and other planets will sooner or later have to fall on the Sun. However, astronomers did not notice any slowdown in their movement: each subsequent year is exactly equal to the previous one. The matter was aggravated by the fact that physicists found that light is an oscillation of an electric and magnetic field directed perpendicular to the propagation beam. It was found that such transverse fluctuations are possible only in absolutely solid body. So the planets and all other bodies move in a solid body? Absurd!
At the time of Michelson, there were no objects that could serve as a model for this kind of movement. Today, knowledge about the world has expanded significantly. When studying the physics of semiconductors, mechanisms were discovered that make it possible to simulate the situation described above. For example, at low temperatures in germanium, the so-called excitons. These quasiparticles move in the semiconductor without transferring the semiconductor substance.
Thus, energy excitations are formed in a solid body, which are similar to hydrogen atoms and are described by the corresponding characteristics: the Bohr radius of the orbit, momentum, mass, etc. Under certain conditions, one can obtain biexcitons- analogue of helium, triexcitons- analogue of lithium. Physicists discovered exciton liquid, which is going to drops; droplets can be evaporated. Shortly speaking, solid state physics dealing with mechanics supersubstances, which is built on top of ordinary matter.
However, even at the time of Michelson, many constructively thinking physicists believed that the atoms and molecules of ordinary matter were formed by vortices or some more complex excitations of the ethereal medium. For example, J.J. Thomson tried to model the electron and the atom using vortices and Faraday tubes (see below). Matter and ether , electricity and matter, and also useful to read). Physicists like him understood perfectly well that no "ethereal wind" could be registered. The earth and everything on it (including the Michelson interferometer) flies in open space, just like a wave glides over the surface of the ocean.
It is hard to say why the Michelson-Morley experiment made such a strong impression on relativists. After all, even Mascar, after a large series of experiments in 1869 - 1874. concluded: "The phenomena of light reflection, diffraction, double refraction and rotation of the plane of polarization are equally unable to reveal the translational motion of the Earth when we use the light of the Sun or an earthly source." The question is, why should one expect something extraordinary from the interference pattern that was obtained in the Michelson setup? Frankfurt and Frank recall that in addition to the aforementioned Miller, who obtained a positive result, similar experiments were carried out by Rayleigh (1902) and Bres (1905), who confirmed Michelson's already negative result. It is clear that the discrepancy in the interpretation of experiments, the degree of misunderstanding and distrust of empirical results largely depend on the worldview positions of the physicist.
We can talk about the differences in the epistemological approach of the formalist-phenomenalists and the rationalist-constructivists for a long time. But now it is important to understand that the worldview of Lorenz gravitated towards the former, and J. J. Thomson towards the latter. In his electron theory, Lorentz, unlike J. J. Thomson, represented the electron as a mathematical point and did not puzzle over its internal structure. He also believed that the atoms of matter exist by themselves, and the ethereal medium - by itself. His thinking is permeated with abstract symbolism, and little space was given to visual representations. Behind long mathematical calculations, the physics of the phenomenon was lost.
The experiment of Hippolyte Louis Fizeau (1819 - 1896), carried out in 1851 and repeated by Michelson in 1886, concerned the determination of the speed of light in a moving medium. The simplified scheme of the experiment is as shown in Fig. 16 taken from the book.
Fig. sixteen. light from source L, dividing into two beams, passes through a pipe through which water flows at a speed u. Due to the difference in the path of the rays at the point A interference fringes appear, which can be shifted if the direction of speed is changed u. In theory, the resulting speed should be found according to the elementary formula for adding two speeds: V = c" ± u, where c" = c/n- the speed of light in a medium with a refractive index n. However, the experiment showed that this formula is not suitable for calculating V.
Recall that if the speed of light in vacuum is denoted by c, then in a medium with a refractive index n it will decrease: c" = c/n. In air, as well as in vacuum, it is equal to c" = c\u003d 300,000 km / s, since for air the refractive index n close to unity; for water n= 1.33 and c"= 225,000 km/s, and for diamond n= 2.42 and c"= 124,000 km/s. It turns out that the denser the medium, the lower the speed of light (the density of diamond is 3.5 times higher than water). In acoustics, in general, an inverse relationship is observed. If sound propagates in air at a speed of 331 m/s, then in water - 1482 m/s, and in steel 6000 m/s. However, the dependence of the acoustic wave velocity on the density of the medium is not so unambiguous and depends on structure of matter(see table 3 Introduction to acoustics).
Fizeau showed that when the water medium begins to move, the speed of light in it is found by the "relativistic" formula for adding two speeds:
where u= 7 m/s, at which turbulent eddies are not formed. In one section of the pipe, the speed of water movement u matches the speed c" and then it appears in the formula, it does not match in another section, and then "-" is put.
But there was no question of any "relativistic" interpretation of the last formula in the middle of the 19th century. The interpretation yielded to its approximate value, behind which a more complex dependence of the resulting velocity was hidden. V on the wavelength of light radiation. The expression in brackets is called entrainment coefficient, which was deduced and explained by Augustin Jean Fresnel (1788 - 1827) as early as 1818, after an experiment carried out by Dominique François Jean Arago (1786 -1853).
Arago experimented with a moving glass prism, while measuring the angle of aberration. He expected that the two velocity vectors familiar to us would be added and subtracted in the usual way: V = c" ± u. Then, in accordance with the logic of the experiment, the angle of aberration should have changed. However, with an accuracy of one arc second, the value α = 20.45 ", found by J. Bradley, did not change.
The purpose of the experiment could be formulated differently and solve the inverse problem: how will the refractive index of a prism located on the Earth moving at a speed of 30 km / s change if light from a fixed star is passed through the prism. Then the negative conclusion from this formulation of the problem looks like this: the refractive index of the prism does not change.
Fresnel accepted that light waves carry longitudinal character, like acoustic waves ( transverse the nature of light waves was established by him in 1821). The speed of sound in a particular substance, as we already know ( Introduction to acoustics) depends on the density of the material. An excess of density arises as a result of various excitations of the medium, for example, air and water vortices. If acoustic waves are passed through a moving at a speed u vortex, then their sound velocity inside the vortex will react to excess density in accordance with the "relativistic" formula. It seems that all the air contained in it is spinning in a whirlwind and is transported along with the whirlwind. If so, then the resulting speed would be determined by the "classical" formula for adding speeds, but this did not happen. At a high formal-theoretical level, Fresnel managed to draw a parallel between optical and acoustic phenomena. He showed that only the excess of ether density in material bodies is subjected to entrainment in comparison with the ether density in outer space.
Fresnel's wave theory, which explains a whole range of optical problems, including diffraction and polarization, reigned serenely during his lifetime and then for nearly two decades after his death. french school opticians, primarily in the person of Arago, Fresnel, Foucault and Fizeau, clearly dominated the world. The British, the eternal rivals of the French, looked with envy at the successes of their opponents, not only in the scientific field, but also in the cultural, political and military.
Fresnel derived coefficient partial entrainment, operating with two characteristics of the ether, which determine the speed of light. It is his elasticity, which remained unchanged for moving media, and its variable density. The Englishman George Gabriel Stokes (1891-1903) first proposed the idea in the mid-1840s complete entrainment of the ether by moving objects such as, for example, our planet. At the same time, he relied on the third mechanical characteristic of the ether - viscosity. In 1849, he published his fundamental work "On the Theory of Internal Friction in Moving Fluids and on the Equilibrium and Motion of Elastic Solids", in which he obtained the famous differential equation for describing motion viscous liquids.
Stokes believed that the whole Earth carries the ether not only inside its volume, but also far beyond its surface. How high the layer of ether carried by the planet extends is unknown. Miller, trying to measure the speed of the ethereal wind, tried to rise as high as possible together with the interferometer: perhaps the wind was blowing high in the mountains or at the altitude of the airship. The Fizeau experiment of 1851 was good precisely because it convincingly proved the inconsistency of Stokes's theory and the validity of Fresnel's theory.
In 1868, the well-known Englishman, James Clerk Maxwell (1831-1879), himself did an experiment similar to Fizeau's. However, as a result of experimentation, he was forced to recognize the victory for Fresnel's theory. Since Fizeau's experiment concerned a first-order effect in β, Maxwell suggested that the effect in β² might make itself felt in the future, when physicists learn how to measure such small quantities.
A subsequent experiment by the Englishman George Biddel Airy (1801–1892) in 1871, measuring stellar aberration when viewed through a telescope filled with water, also confirmed Fresnel's point. Finally, the experiment of 1886, carried out by Michelson and Morley, according to the scheme close to the experimental setup of Fizeau in 1851, once again proved the correctness of the theory of partial drag of the ether. Here is how Michelson spoke of it at the 1927 anniversary conference:
“In 1880, I thought about the possibility of measuring optically the speed v the motion of the earth in the solar system. Early attempts to detect first-order effects were based on the idea of a system moving through a stationary ether. First order effects are proportional v/c, where c is the speed of light. Based on the concept of the beloved old ether (which is now abandoned, although I personally still stick to it), one possibility was expected, namely that the aberration of light should be different for telescopes filled with air or water. However, experiments have shown, contrary to existing theory, that such a difference does not exist.
Fresnel's theory was the first to explain this result. Fresnel suggested that the substance captures the ether, in part (entrainment of the ether), giving it speed v, so v" = kv. He determined k- Fresnel coefficient through the refractive index n: k = (n² – 1)/ n². This coefficient is easily obtained from the negative result of the following experiment.
Two light beams are passed along the same path (0,1,2,3,4,5) in opposite directions and create an interference pattern. I is a pipe filled with water. If now the whole system is moving at a speed v through the ether, when moving the pipe from position I to position II, a shift of interference fringes should be expected. No shift was observed. From this experiment, taking into account the partial drag of the ether, the Fresnel coefficient can be determined k. It can also be very simply and directly derived from Lorentz transformations.
The result obtained by Fresnel was recognized by all researchers as universal. Maxwell pointed out that if the expected first-order effect is not found, then perhaps there may be second-order effects proportional to v²/ c². Then at v= 30 km/s for the orbital motion of the Earth v/c= 10 –4 we have v²/ c² \u003d 10 -8. This value, according to Maxwell, is too small to measure.
It seemed to me, however, that by using light waves one could devise an appropriate device for measuring such a second-order effect. I came up with a device that included mirrors moving at a speed v through the ether. In this device, two beams of light propagate. The first goes back and forth parallel to the vector v, the second passes at right angles to the velocity vector v. In accordance with classical theory changes in the light path caused by speed v, must be different for the longitudinal and transverse beam. This should produce a perceptible shift in the interference fringes. …
When the device is moving at a speed v through the ether there should be the same effect in the light as with boat movement, floating up and down the river, as well as back and forth across the stream. The time required to cover the distance forward and backward will be different for both cases. This is easy to see from the following consideration. Whatever the speed of the current of the river, the boat will always have to return to the place from which it started, if only it is moving across the stream rivers. If the boat is moving along the stream, then it may no longer reach the place where it started when it swims against the current.
I tried to conduct an experiment in the Helmholtz laboratory in Berlin, but the vibrations of the city highways did not allow to stabilize the position of the interference fringes. The equipment was transferred to the laboratory in Potsdam. I forgot the director's name (I think it was Vogel), but I remember with pleasure that he immediately showed interest in my experiment. And although he had never seen me before, he placed the entire laboratory, along with its staff, at my disposal. In Potsdam, I got a zero result. The accuracy was not very good because the optical path length was about 1 m. However, it is interesting to note that the result was quite good.
When I returned to America, I had the good fortune to enter into collaboration with Professor Morley in Cleveland. The same principle was applied in the device as in the device used in Berlin. True, the length of the light path was increased by introducing a number of reflections instead of a single passage of the beam. In fact, the length of the path was 10 - 11 m, which, due to the orbital motion of the Earth through the ether, should have given a shift in half the band. However, the expected shift could not be found. The fringe shift has been determined to be less than 1/20 or even 1/40 of that predicted by theory. This result can be interpreted in such a way that the Earth captures the ether almost completely, so that the relative velocity of the ether and the Earth on its surface is zero or very small.
This assumption, however, is highly doubtful because it contradicts another important theoretical condition. Lorentz offered another explanation ( Lorentz contraction), which he deduced in the final form as a result of the known Lorentz transformations. They are the essence of the whole theory of relativity» .
In this fragment, Michelson reflected the main milestones in the formation special relativity. As we can see, the incorrectness of the experiment on the detection of the ethereal wind follows from two false assumptions. First of all, the author of the experiment incorrectly believed that the material of the world environment and the material from which the Earth is "made" are different. That is why an ethereal wind must be observed on the surface of the planet when it revolves around the Sun. The second error stemmed from the false analogy between the movement of boats on a river and the path of rays in an interferometer, which was discussed at the end of the previous subsection.
The theory of Augustin Jean Fresnel (1788 - 1827), created after the successful interpretation of Arago's 1810 experiment to measure the speed of light in a moving lens, using the concept partial entrainment of ether explained the immutability of the interference pattern in Fizeau's experiment as well. In the same way, it was necessary to find a specific reason for the invariance of the interference pattern in the Michelson-Morley experiment. Lorentz, who worked closely with Michelson, proposed a reduction in the linear dimensions of physical bodies in the direction of the vector v, which, as it seemed to him, followed from the transformations he found. However, these redundant transformations had physical meaning, especially in the interpretation of Einstein's version of the theory of relativity.
The true reason for the negative result lies elsewhere, and its meaning is as follows. If the wave source is on the same moving platform as the receiver, then due to compensation the wavelength, frequency and period of oscillation will remain the same as with a stationary platform. You can rotate this platform at any angle with respect to its displacement vector - all the same, the interference pattern will remain unchanged, since the compensation mechanism will work in this case too. This argument has already been mentioned, but it is so important that its unnecessary reminder does not hurt, especially for relativists.
Movement of the Earth around the Sun and through the ether. 
Scheme of the experimental setup 
Experimental setup illustration Michelson's experiments- a class of physical experiments investigating the dependence of the speed of light propagation on the direction. At present (2011), the accuracy of the experiments makes it possible to find relative deviations of the isotropy of the speed of light in units of 10−16, but no deviations have been found at this level. Michelson's experiments are the empirical basis of the principle of invariance of the speed of light, which is included in the general theory of relativity (GR) and the special theory of relativity (SRT).
Theory
Compute the total time t 1 (\displaystyle t_(1)) using the sum of the times of the two paths:
T 1 = L 1 c + v + L 1 c − v = (\displaystyle t_(1)=(\frac (L_(1))(c+v))+(\frac (L_(1))(cv ))=) 2 c L 1 c 2 − v 2 = 2 L 1 c 1 1 − v 2 c 2 ≈ 2 L 1 c (1 + v 2 c 2) (\displaystyle (\frac (2cL_(1)) (c^(2)-v^(2)))=(\frac (2L_(1))(c))(\frac (1)(1-(\frac (v^(2))(c^ (2)))))\approx (\frac (2L_(1))(c))\left(1+(\frac (v^(2))(c^(2)))\right))
The approximation is due to the fact that (v 2 / c 2) 1 (\displaystyle (v^(2)/c^(2))) when the speed v (\displaystyle v) is taken, which is the same as the ground.
Ether speed c = ∥ v + v 1 ∥ (\displaystyle c=\|\mathbf (v) +\mathbf (v_(1)) \|) , and v 1 = ∥ v 1 ∥ (\displaystyle v_(1) =\|\mathbf (v_(1)) \|) - wave speed in the direction of the mirror.
C = ∥ v + v 1 ∥ = v 2 + v 1 2 (\displaystyle c=\|\mathbf (v) +\mathbf (v_(1)) \|=(\sqrt (v^(2)+v_ (1)^(2)))) ; it follows that: v 1 = c 2 − v 2 = c 1 − v 2 c 2 (\displaystyle v_(1)=(\sqrt (c^(2)-v^(2)))=(( c)(\sqrt (1-(\frac (v^(2))(c^(2)))))))
Taking symmetry into account, we can now compute:
T 2 = 2 L 2 c 1 1 − v 2 c 2 ≈ 2 L 2 c (1 + v 2 2 c 2) (\displaystyle t_(2)=(\frac (2L_(2))(c))( \frac (1)(\sqrt (1-(\frac (v^(2))(c^(2))))))\approx (\frac (2L_(2))(c))\left( 1+(\frac (v^(2))(2c^(2)))\right))
The phase difference is proportional to:
δ = c (t 2 − t 1) = 2 (L 2 1 − v 2 c 2 − L 1 1 − v 2 c 2) (\displaystyle \delta =c(t_(2)-t_(1))= 2\left(((\frac (L_(2))(\sqrt (1-(\frac (v^(2))(c^(2))))))-(\frac (L_(1) )(1-(\frac (v^(2))(c^(2))))))\right))
S = | δ + δ′ | (\displaystyle S=|\delta +\delta ^(")|) , where δ ′ (\displaystyle \delta ^(")) is proportional to the phase difference when rotated by π 2 (\displaystyle (\frac (\pi )( 2))) :
S = | 2 L 1 (1 1 − v 2 c 2 − 1 1 − v 2 c 2) + (\displaystyle S=|2L_(1)\left(((\frac (1)(\sqrt (1-(\frac (v^(2))(c^(2))))))-(\frac (1)(1-(\frac (v^(2))(c^(2))))))\ right)+) 2 L 2 (1 1 − v 2 c 2 − 1 1 − v 2 c 2) | ≈ (L 1 + L 2) v 2 c 2 (\displaystyle 2L_(2)\left(((\frac (1)(\sqrt (1-(\frac (v^(2))(c^(2 ))))))-(\frac (1)(1-(\frac (v^(2))(c^(2))))))\right)|\approx (L_(1)+L_ (2))(\frac (v^(2))(c^(2))))
It has been shown that the theory of the ether implies a difference that can be quantified and detected by appropriate means (Michelson-Morley interferometer).
Story
background
Main article: Ether (physics)The theory of light propagation as oscillations of a special medium - the luminiferous ether - appeared in the 17th century. In 1727, the English astronomer James Bradley explained the aberration of light with its help. It was assumed that the ether was motionless, but after Fizeau's experiments, an assumption arose that the ether was partially or completely entrained in the course of the movement of matter.
In 1864, James Maxwell set up an experiment to determine the speed of the Earth relative to the ether, but later found an error in his calculations and did not publish the results. Shortly before his death, in 1879, he wrote a letter to a friend on this subject, which was published posthumously in the journal Nature. In 1871-1872, Airy conducted a series of precise experiments with an astronomical light source, concluding from them that the orbital motion of the Earth completely entrains the ether.
Michelson's experiments
The aforementioned publication of Maxwell's letter interested the American physicist Albert Michelson. Around 1880, he invented an optical instrument of exceptional precision, which he called the interferometer. The purpose of the first experiment (1881) was to measure the dependence of the speed of light on the motion of the Earth relative to the ether. The result of the first experiment was negative - the displacements of the bands are out of phase with the theoretical ones, and the fluctuations of these displacements are only slightly less than the theoretical ones. The article about the results of the experiment drew criticism from the leading theoretical physicist Hendrik Lorentz, who pointed out that the theoretical accuracy of the experiment was overestimated.
Later, in 1887, Michelson, together with Morley, carried out a similar but much more accurate experiment, known as Michelson-Morley experiment and showing that the observed displacement is certainly less than 1/20 of the theoretical one, and probably less than 1/40. In the theory of unentrained ether, the displacement must be proportional to the square of the velocity, so the results are equivalent to the fact that the relative velocity of the Earth in the ether is less than 1/6 of its orbital velocity and certainly less than 1/4.
Under the influence of these results, George Fitzgerald and Lorentz put forward a hypothesis about the contraction of material bodies in the direction of motion in a motionless and unentrained ether (1889).
Miller's experiments
According to Professor Dayton K. Miller (Caesian School of Applied Sciences):
It can be assumed that the experiment only showed that the ether in a particular basement room is carried along with it in the longitudinal direction. We are therefore going to move the apparatus to a hill to see if the effect is found there.[ source unspecified 1066 days]
K. Miller and Professor Morley designed a more sensitive interferometer than that used in the first experiment, with an optical path length of 65.3 m, equivalent to about 130 million wavelengths. K. Miller expected to see a shift of 1.1 bands.
In the autumn of 1905, Morley and Miller conducted an experiment at the Euclidean Heights in Cleveland, about 90 meters above Lake Erie and about 265 meters above sea level. In 1905-1906. five series of observations were made, which gave a certain positive effect - about 1/10 of the expected drift.
In March 1921, the methodology and apparatus were somewhat changed and a result of 10 km/s "ether wind" was obtained. The results were carefully checked for possible elimination of errors associated with magnetostriction and thermal radiation. The direction of rotation of the apparatus had no effect on the result of the experiment.
Later studies of the results obtained by D. Miller showed that the fluctuations observed by him and interpreted as the presence of an "ethereal wind" are the result of statistical errors and neglect of temperature effects.
Kennedy's experiments
Dr. Roy Kennedy (California Institute of Technology), after publishing the results of the Morley-Miller experiment, modifies the experiment for the purpose of verification. The interferometer is placed in a sealed metal case filled with helium at a pressure of 1 atm. Using a device capable of distinguishing very small shifts in the interference pattern, it became possible to reduce the size of the arms to 4 m. Polarized light was used in order to eliminate as much as possible the scattering of light on the mirrors. The accuracy of the experiment corresponded to the shift of the bands by 2·10−3 of their width. On this apparatus, Miller's 10 km/s would give a shift corresponding to 8 x 10 −3 green wavelengths, four times the smallest detectable value. The experiment was carried out in the Norman Bridge laboratory, in a room with a constant temperature, at different times of the day. To test the dependence of the speed of the ethereal wind on the height of the terrain, experiments were also carried out at Mount Wilson, in the building of the observatory. The effect turned out not to exceed 1 km/s for the ethereal wind.
Now I would like to make a few remarks about Miller's experiment. I believe that there is a serious problem associated with the effect, which is periodic for a complete revolution of the apparatus, and was discounted by Miller, who emphasizes the significance of the half-cycle effect, i.e., repeating during a half-turn of the apparatus, and concerning the question of the ethereal wind. In many cases, the full cycle effect is much larger than the half cycle effect. According to Miller, the total period effect depends on the width of the bands and will be zero for indefinitely wide bands.
Although Miller claims that he was able to eliminate this effect to a large extent in his measurements in Cleveland, and this can be easily explained in experiment, I would like to understand the reasons for this more clearly. Speaking at the moment as a relativityist, I must say that such an effect does not exist at all. Indeed, the rotation of the apparatus as a whole, including the light source, does not give any shift from the point of view of the theory of relativity. There should be no effect when the Earth and craft are at rest. According to Einstein, the same lack of effect should be observed for the moving Earth. The total period effect is thus in conflict with the theory of relativity and is of great importance. If Miller then discovered systematic effects whose existence cannot be denied, it is also important to know the cause of the full period effect.
Experiments of Michelson and Gal
Scheme of the Michelson-Gal experiment In 1925, Michelson and Gael were laid on the ground at Clearing in Illinois. water pipes in the form of a rectangle. Pipe diameter 30 cm. Pipes AF and DE were directed exactly from west to east, EF, DA and CB - from north to south. The lengths DE and AF were 613 m; EF, DA and CB - 339.5 m. One common pump, operating for three hours, can pump out air to a pressure of 1 cmHg. To detect displacement, Michelson compares in the field of the telescope the interference fringes obtained by running around the large and small contours. One beam of light went clockwise, the other against. The shift of the bands caused by the rotation of the Earth was recorded by different people on different days with a complete rearrangement of the mirrors. A total of 269 measurements were made. Theoretically, assuming the ether to be immobile, one should expect a shift of the band by 0.236±0.002. Processing of the observational data gave a bias of 0.230±0.005, thus confirming the existence and magnitude of the Sagnac effect.
S. I. Vavilov in the article "Experimental Foundations of the Theory of Relativity" explains this effect as follows:
The rotational experiments of Sagnac and Michelson-Gal in the theory of relativity (special and general) are explained almost in the same way as the possibility of detecting rotational motion from the manifestations of centrifugal forces in mechanics. This is a natural consequence of the theory of relativity, adding nothing new.
Modern options
In 1958, at Columbia University (USA), an even more accurate experiment was carried out using counter-directional beams of two masers, which showed the invariance of the frequency from the Earth's movement with an accuracy of about 10−9%.
Even more accurate measurements in 1974 brought the sensitivity to 0.025 m/s. Modern versions of the Michelson experiment use optical and cryogenic [ clarify] microwave resonators and make it possible to detect the deviation of the speed of light if it were several units per 10−16.
/ New folder_2 / Determining the speed of light (2)
HISTORY OF DETERMINING THE SPEED OF LIGHT
The speed of light in free space (vacuum) is the speed of propagation of any electromagnetic waves, including light waves. It represents the limiting speed of propagation of any physical influences and is invariant in the transition from one frame of reference to another.
The speed of light in the medium depends on the refractive index of the medium n, which is different for different radiation frequencies: с’() = c/n(). This dependence leads to a difference between the group velocity and the phase velocity of light in a medium, if we are not talking about monochromatic light (for the speed of light in vacuum, these quantities are the same. Experimentally determining c ', always measure the group velocity of light.
For the first time, the speed of light was determined in 1676 by O. K. Römer by changing the time intervals between eclipses of Jupiter's satellites. In 1728, it was established by J. Bradley, based on his observations of the aberration of starlight. In 1849, A. I. L. Fizeau was the first to measure the speed of light by the time it took the light to travel a precisely known distance (base), since the refractive index of air differs very little from 1, ground-based measurements give a value very close to the speed.
In Fizeau's experiment, a beam of light from a light source S, reflected by a semitransparent mirror 3, was periodically interrupted by a rotating toothed disk 2, passed the base 4-1 (about 8 km) and, reflected from mirror 1, returned to the disk. Getting on the prong, the light did not reach the observer, but hitting the
the gap between the teeth could be observed through eyepiece 4. From the known disk rotation speeds, the time for the light to pass through the base was determined. Fizeau obtained the value c = 313300 km/s.
In 1862, J. B. L. Foucault realized the idea of D. Argo, expressed in 1838, by using a rapidly rotating mirror (512 revolutions per second) instead of a toothed disk. Reflecting from the mirror, the beam of light was directed to the base and, upon returning, fell again on the same mirror, which had time to turn at some small angle. With a base of only 20 m, Foucault found that the speed of light is 298,000 500 km/s. The schemes and basic ideas of the Fizeau and Foucault methods were repeatedly used in subsequent works on determining the speed of light.
Determination of the speed of light by the rotating mirror method (Foucault method): S – light source; R is a rapidly rotating mirror; C is a fixed concave mirror whose center coincides with the axis of rotation R (therefore, the light reflected by C always hits R back); M is a semitransparent mirror; L - lens; E - eyepiece; RC - accurately measured distance (base). The dotted line shows the position R, which has changed during the time the light travels the path RC and back, and the return path of the beam of rays through the lens L, which collects the reflected beam at the point S', and not at the point S, as it would be with a fixed mirror R. The speed of light is set by measuring the displacement SS'.
The value c = 299796 4 km/s obtained by A. Michelson in 1926 was then the most accurate and was included in the international tables of physical quantities.
Measurement of the speed of light in the 19th century played a big role in physics, further confirming the wave theory of light. Foucault's comparison of the speed of light of the same frequency in air and water in 1850 showed that the speed in water is u = c/n(), in accordance with the prediction of wave theory. The connection of optics with the theory of electromagnetism was also established: the measured speed of light coincided with the speed of electromagnetic waves, calculated from the ratio of electromagnetic and electrostatic units of electric charge.
In modern measurements of the speed of light, a modernized Fizeau method is used with the replacement of a gear wheel with an interference or some other light modulator that completely interrupts or attenuates the light beam. The radiation receiver is a photocell or a photoelectric multiplier. The use of a laser as a light source, an ultrasonic modulator with a stabilized frequency and an increase in the accuracy of measuring the base length will reduce measurement errors and obtain the value c = 299792.5 0.15 km/s. In addition to direct measurements of the speed of light from the time of passage of a known base, indirect methods are widely used, which give greater accuracy.
The most accurate measurement of the quantity c is extremely important not only in general theoretical terms and for determining the values of other physical quantities, but also for practical purposes. To them, in particular. This includes the determination of distances in the time of passage of radio or light signals in radar, optical location, light ranging, etc.
Michelson and the speed of light
It is not very often that a man in his seventies has to return to the work he did in his youth to try to refine the results of already very accurate and reliable research, because everyone believes that no one else can do it better than him. Such an enviable opportunity presented itself to Michelson.
In 1923, George Ellery Hal, director of the Mount Wilson Observatory, invited Michelson to come to Pasadena and make a new determination of the speed of light. Michelson accepted his offer with enthusiasm. He had long been waiting for an opportunity to clarify the results of his famous measurement of 1882. He quickly packed up and left for California, where he set up his headquarters at the foot of Mount Wilson.
The preparation of the experiment was carried out with great care. A site was chosen for two installations. One of them was placed on the top of Mount Wilson, already familiar to him, and the other on the top of Mount San Antonio, known by the nickname "Old Baldness", at an altitude of 5800 m above sea level and at a distance of 35 km from Mount Wilson. The United States Coast and Geodetic Survey was tasked with accurately measuring the distance between two reflective planes—a rotating prismatic mirror at Mount Wilson and a fixed mirror at San Antonio. The possible error in measuring the distance was one seven millionth, or a fraction of a centimeter per 35 km. A rotating prism of nickel-plated steel, with eight mirror surfaces polished to an accuracy of one part in a million, was made for the experiment by the Sperry Gyroscope Company of Brooklyn, whose president, engineer-inventor Elmer A. Sperry, was a friend of Michelson. In addition, several more glass and steel prisms were made. The octagonal high-speed rotor made up to 528 revolutions per second. It was set in motion by an air jet, and its speed, as in previous experiments, was regulated by an electric tuning fork. (A tuning fork is not only used by musicians to determine the pitch. It can be used to very accurately determine short equal periods of time. You can create an instrument with the right frequency, which, under the influence of an electric current, will vibrate like an electric bell.)
Sperry also suggested to his friend an improved high-arc searchlight he had built shortly before for military purposes. Preston R. Bassett, the engineer who led the searchlight and later became president of the company, developed a special arc lamp mechanism for this experiment and took it himself to California in the summer of 1924. Fred Pearson came from Chicago to participate in the experiment.
A new measurement of the speed of light
Michelson, like a captain on the bridge of a ship, enthusiastically led the preparations for the operation, delving into every detail. Every possible precaution has been taken to eliminate or minimize errors. The learned world watched the preparations with interest. Finally, everything was ready, and the light from the arc lamp was directed to a mirror on San Antonio and reflected on a rotating prism on Mount Wilson (Fig. 12). The measurements were carried out every clear night from ten o'clock in the evening to midnight, and each series of observations lasted several weeks. Measurements were received daily at Michelson's headquarters in Pasadena.
Rice. 12. Improvements made by Michelson to his installation. The principle remained the same (the main change was to increase the path of the light beam).
From 1924 to the beginning of 1927, five independent series of observations were made. The average result was 299,798 km per second.
But Michelson was still not entirely satisfied. He hoped that by increasing the length of the path of the light beam and transferring the experiment to another locality, he would be able to obtain an even more accurate definition. In his report on the experiment on Mount San Antonio, he wrote: "The success of measurements at a distance of 22 miles, most of which were carried out in not the most favorable conditions (fog and smoke from forest fires), indicates the feasibility of conducting an experiment at a much greater distance."
For this experience, he chose Mount San Jacinto, located 130 km from Mount Wilson. He even did a preliminary test. But the light from the arc lamp on the way back was so severely attenuated by smoke and fog that the idea had to be abandoned.
Michelson returned to Chicago and traveled to Washington in November 1928 for an anniversary scientific conference at the National Bureau of Standards. It was convened by the Optical Society of America in honor of the fiftieth anniversary of the publication of Michelson's first work (1878) on the speed of light and in recognition of his great contributions to the field of optics. This conference was unofficially called the "Michelson Conference", and Michelson himself, of course, was an honored guest at it.
Final try
V next year Michelson, who was seventy-seven at the time, suffered a severe cerebral hemorrhage. He retired from the university, painted a lot and walked, trying to restore his failing health. That was not easy. However, he did not stop dreaming about returning to the study of the speed of light; he hoped that, having gained strength, he would make another determination. He is back where he started over fifty years ago. He cherished the idea of getting rid of interference in the form of fog, smoke, and even the most transparent atmosphere. He wanted to set up the experiment in such a way that the beam passed through the void, if possible, through an almost absolute vacuum.
And then Michelson again received an invitation to Pasadena. “Hal said that Mount Wilson and Caltech were at my disposal,” he said. “The temptation was too great. I went." He was provided with all the necessary tools and equipment. The Rockefeller Foundation provided $30,000 for the experiment, the Carnegie Corporation $27,500, and the University of Chicago $10,000.
The location for the epic experience was the Irvine Ranch near Santa Ana, Southern California. The United States Coast and Geodetic Survey was again tasked with measuring the distance. Giant pipes were rolled from sheets of corrugated steel. They consisted of 18-meter sections with a diameter of about a meter, riveted together. The result was a pipe with a length of more than 1.5 km. She cost 50 thousand dollars. It could be entered through four hatches - two at the ends and two in the main section of the pipe. The Sperry Gyroscope Company again produced rotating steel mirrors - with 8, 16 and 32 facets. In addition, a 32-sided mirror was made from first-class optical glass.
The pipe was soldered and the air was pumped out of it with special pumps for several days and nights in a row until the pressure in the pipe dropped to 0.5 mm Hg. Art. (normal pressure is 760 mm Hg). An arc lamp served as the light source. Repeatedly reflected, the light had to travel a path of about 16 km. For the first time in history, the measurement of the speed of light was carried out in almost absolute vacuum.
Meanwhile, Michelson's health left much to be desired. He was never able to recover enough to take measurements with his own hands. They were handled by Francis G. Pease and Fred Pearson; they also brought together the results. During 1930 and early 1931, hundreds of observations were made. Michelson supervised the work, lying in bed. Alone, he would never have coped with every now and then arising problems requiring immediate resolution. Every time something went wrong in the equipment, you had to let air into the pipe so that you could get in and fix the damage. And then you had to wait forty-eight hours for the pumps to pump air out again. Heat waves distorted the light image, so most of the work had to be done at night, when it got cool.
In early 1931, when the work was still far from complete, and Michelson seemed to be recovering from the effects of illness, a scientific conference was held in Pasadena, which was attended by Einstein and many prominent scientists from different countries. On January 15, a banquet was to be held in honor of Dr. Einstein and his wife. Michelson, of course, was also invited. He felt well enough then and was very glad to be present at this solemn meeting, which took place in the newly built magnificent building of Athenium.
Einstein gave a short speech. Next to him sat the greatest scientists - Michelson, Milliken, Hal and others. “I am glad to be in the company of those,” Einstein began, “who for many years have been my faithful comrades in my work.” Then, turning to Michelson, he continued: “You, dear Dr. Michelson, began your research when I was still a boy. You opened new paths for physicists and paved the way for the theory of relativity with your wonderful experiments. You exposed the fallacy of the ethereal theory of light and stimulated the ideas of Lorentz and Fitzgerald, from which the special theory of relativity developed. Without your work, this theory would still be just an interesting conjecture; it has received its first real confirmation in your experiments.”
Michelson was deeply moved. It was the highest praise. He stood up to thank for such a generous assessment of his merits. Michelson rarely gave speeches, and when he did, he always spoke briefly and to the point. And this time he did not change himself. He thanked Einstein on his own behalf and on behalf of his late collaborator Edward Morley, who died eight years ago. Michelson never forgot to pay tribute to his employees and assistants.
This was Michelson's last public appearance. He tried to return to work, but on March 1 he was unable to get out of bed. Gradual paralysis set in and he began to weaken rapidly. Meanwhile, more and more new data was coming in from Santa Ana. Gathering the last of his strength, Michelson slowly but clearly dictated to Piz the introduction to the article, which was supposed to sum up the final results of the experiments. This paper should have been sent to the Astrophysical Journal for publication.
Michelson's condition continued to deteriorate, but he refused to admit that he was seriously ill. “My health is getting better,” he wrote optimistically forty-eight hours before he collapsed into unconsciousness. Near him were his wife, one of the daughters and two nurses. Pease and Pearson joined them. At twelve fifty-five minutes on May 9, 1931, Michelson died quietly without regaining consciousness.
The pastor of the local Unionist-Liberal church served a very modest and short service in his house. At the request of Michelson's widow, the news of his death did not appear in print until after the funeral. The funeral was attended by Michelson's wife, Edna, their three daughters - Madeleine, Dorothy and Beatrice - and several other relatives and closest friends. Millikan, Hal and Hubble carried the coffin to the hearse. The body, according to Michelson's wishes, was cremated and the ashes scattered to the wind.
Scientists all over the world celebrated his services to science. Einstein learned of Michelson's death in England, where he was a lecturer at Oxford. "Dr. Michelson was one of the greatest artists in the world of scientific experiment," he said.
Three of Michelson's closest associates at the University of Chicago, Forest R. Moulton, Henry J. Gale, and Harvey B. Lemon, who had known him for a quarter of a century, wrote in an obituary:
“His life was a magnificent example of determination, not subject to the vicissitudes of fate. It seemed that even the forces of love, hatred, jealousy, envy, vanity hardly touched him. Absorbed by scientific research, he was generally rather indifferent to people in general, but nevertheless he had devoted friends, whose friendship he carefully kept ... The main content and purpose of his life were scientific pursuits, aesthetic pleasure derived from work. .. Hurry, fuss was alien to him. It did not throw him into a fever at the thought that a decisive moment had come for science or for all mankind. He did not tremble, standing on the threshold of a great discovery...
He was soft and calm and devoid of any affectation, like the sea on a sunny day - serene, boundless, immeasurable ... Such a character can be felt, but not analyzed. Michelson did not reveal his soul to anyone, but everyone understood that in the depths of it, much was hidden that was inaccessible to the eyes. Very few people knew him intimately."
After Michelson's death, work on measuring the speed of light in a vacuum tube more than 1.5 km long continued for almost two more years. In 1933, during the Long Beach earthquake, the installation was destroyed, but by this time all observations had already been completed. A total of 2885 determinations were made. The average speed of light in vacuum turned out to be 299,774 km per second. This figure was 24 km less than the figure found during experiments on the tops of two mountains. The International Geophysical and Geodetic Union and the International Radio Science Union have adopted a value for the speed of light of 299,792.5 km per second*. This figure lies within the experimental error of Michelson's determination.
The title of the article reporting Michelson's latest experience echoed the title of his first work, published more than half a century earlier, when he was still Lieutenant Michelson. It was called "On the method of measuring the speed of light." The last work, entitled "Measurement of the speed of light in a partial vacuum", was the completion of Michelson's great contribution to science.
Continuation of the search
There is no last word or final decision in scientific research. If Michelson were to visit the world's major scientific laboratories today, he would find that researchers are still wrestling with the same problems that he and other scientists of his time were trying to solve. Scientific ideas that seemed to be firmly established are constantly subverted, replaced, expanded or supplemented. This is what happened with Newton's laws, modified by Einstein. And what about the speed of light - this constant, which Michelson, it would seem, caught once and for all? There are also doubts about her. Scientists have approached it again and again with new instruments and new methods. In 1939, two groups of researchers, one at Harvard University and the other in Germany, using the so-called electronic light shutter (Kerr cell), obtained slightly different results: 299,798 km/s in the USA and 299,799 km/s in Germany. Two years later, National Bureau of Standards scientists came up with a figure of 299,795 km/s. In 1951, Captain Carl E. Aslakson of the US Coast and Geodetic Survey obtained a value of 299,805 km/s while testing a radar system. Three years later, a group of English scientists repeated his result.
It has been suggested that the speed of light is still not a constant. Some scientists claim that it has changed, pointing to the difference in the results of measurements taken before the Second World War and after it with an interval of ten years. It is approximately 16 km per second. Texas Tech College Professor J.H. Rush believes that "this should not be taken too lightly and explained by the inevitable technical errors." Rush believes that "New dimensions may lead to a new discovery." And the search continues*.
And what about the issue of ether? In 1899, Michelson touched on this issue in his Lowell Lectures. “Suppose,” he said, “that the contraction of the ether corresponds to an electric charge, the displacement of the ether to an electric current, the ether vortices to atoms; if we continue these assumptions, we will come to a conclusion that may be one of the greatest generalizations modern science, - that all the phenomena of the physical Universe are only different expressions of the diverse types of motion of one all-penetrating substance - the ether. It seems to me that the day is not far off when the lines of many seemingly distant areas of thought will finally converge on one common plane. Then the nature of the atom, and the nature of the chemical bond of atoms, and the interaction between them, and the continuous ether, declaring itself through light and electricity, and the structure of the molecule, and the explanation of cohesion, elasticity and attraction - all this will find its place in a single and consistent system. scientific knowledge".
More than sixty years have passed since then, but Michelson's prophecy has still not come true. Light and other types of electromagnetic radiation still do not need any conductive medium. The idea of aether is finally abandoned, in large part due to the genius of Michelson.
MICHELSON EXPERIENCE is:
MICHELSON'S EXPERIENCE MICHELSON'S EXPERIENCEput by Amer. physicist A. A. Michelson in 1881 to measure the effect of the Earth's motion on the speed of light. In physics con. 19th century it was assumed that light propagates in a certain swarm of universal world medium - ether. At the same time, a number of phenomena (the aberration of light, the Fizeau experiment) led to the conclusion that the ether is immobile or is partially carried away by bodies during their movement. According to the fixed ether hypothesis, it is possible to observe the “ethereal wind” when the Earth moves through the ether, and the speed of light relative to the Earth should depend on the direction of the light beam relative to the direction of its movement in the ether. M. o. was carried out using a Michelson interferometer with equal arms, one - along the motion of the Earth, the other - perpendicular to it. If the ether is stationary, then when the device is rotated by 90 °, the difference in the path of the rays should change sign and interfere. the picture is to shift. However, the mixing of interference the picture was not found, i.e. M. o. gave a negative result. In 1885-87 the experiments of Michelson and Amer. physicist E. W. Morley confirmed with great accuracy. result of the original M. o. In 1964 Amer. physics in modification. the form was repeated by M. o., using two identical helium-neon lasers as light sources, which have a very high degree of monochromaticity and space. coherence, and with even greater accuracy received negative. result. In the classic physics is denied. the result of M. o. could not be understood and agreed with other phenomena of the electrodynamics of moving media. In the theory of relativity, the constancy of the speed of light for all inertial frames of reference is taken as a postulate, confirmed by a large set of experiments.
Physical Encyclopedic Dictionary. - M.: Soviet Encyclopedia. Editor-in-Chief A. M. Prokhorov. 1983.
MICHELSON EXPERIENCE
An experiment first set up by A. Michelson in 1881 to measure the influence of the Earth's motion on the speed of light. Negative The result was one of the experimental facts that formed the basis relativity theory.
In physics con. 19th century it was assumed that light propagates in a certain swarm of universal world medium - broadcast. At the same time, a number of phenomena ( aberration of light, Fizeau experience) led to the conclusion that the ether is immobile or partially entrained by bodies as they move. According to the fixed ether hypothesis, one can observe the "ethereal wind" when the Earth moves through the ether, and the speed of light relative to the Earth should depend on the direction of the light beam relative to the direction of its movement in the ether.
M. o. was carried out with the help Michelson interferometer with equal shoulders; one arm was directed along the motion of the Earth, the other - perpendicular to it. When the entire device is rotated by 90 °, the difference in the path of the rays should change sign, as a result of which the interference should shift. painting. The calculation shows what the displacement is, expressed in fractions of the interference width. stripes, equal to , where Z is the length of the interferometer arm, is the wavelength of the applied light (yellow line Na), With- the speed of light in the air, v is the Earth's orbital speed. Since the value for the orbital motion of the Earth is about 10-4, then the expected displacement is very small and in the first M. o. was only 0.04. Nevertheless, already on the basis of this experience, Michelson came to the conclusion that the fixed ether hypothesis was incorrect.
In the future, M.o. was repeated many times. In the experiments of Michelson and E. W. Morley (1885-87), the interferometer was mounted on a massive plate floating in mercury (for smooth rotation). optical the path length was brought up to 11 m with the help of multiple reflections from the mirrors. result of M. o. In 1958 at Columbia University (USA) the absence of a fixed ether was once again demonstrated. Beams of radiation from two identical quantum microwave generators (masers) were directed v opposite sides - along the motion of the Earth and against the motion - and their frequencies were compared. With great accuracy (~ 10-9%), it was found that the frequencies remain the same, while the "ethereal wind" would lead to the appearance of a difference in these frequencies by a value that is almost 500 times greater than the measurement accuracy.
In the classic physics is denied. result of M. o. could not be understood and agreed with other phenomena electrodynamics of moving media. In the theory of relativity, the constancy of the speed of light for all inertial reference systems accepted as a postulate, confirmed by a large set of experiments.
Lit.: Vavilov S. I., Experimental Foundations of the Theory of Relativity, Sobr. soch., vol. 4, M., 1956; Einstein collection, 1980 - 1981, M., 1985. E. TO. Tarasov.
Physical encyclopedia. In 5 volumes. - M.: Soviet Encyclopedia. Editor-in-Chief A. M. Prokhorov. 1988.
Michelson, Albert Abraham
Date of birth: Place of birth: Date of death: Place of death: Country: Scientific field: Place of work: Academic title: Alma mater: Supervisor: Awards and prizes: Signature:| Albert Abraham Michelson | |
| Albert Abraham Michelson | |
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Strelno, Prussia |
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Pasadena, California, USA |
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USA |
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physicist, astronomer |
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Case Western Reserve University |
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Corresponding Member of the Academy of Sciences of the USSR |
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United States Naval Academy |
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Hermann Helmholtz |
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Rumfoord Prize (1888) |
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| Albert Abraham Michelson at Wikimedia Commons | |
Albert Abraham Michelson(English) Albert Abraham Michelson; December 19, 1852, Strelno, Prussia - May 9, 1931, Pasadena, USA) - American physicist, known for the invention of the Michelson interferometer named after him and for precision measurements of the speed of light. In 1907, he received the Nobel Prize in Physics "for the creation of precise optical instruments and the spectroscopic and metrological studies carried out with their help."
Biography
Albert Abraham Michelson Born one of six children in a Jewish family, in the Polish part of the Prussian kingdom. His father, Samuil Mikhelson, was engaged in trade; mother - Rosalia Mikhelzon (nee Prilubskaya), was the daughter of Abram Prilubsky from Inowroclaw .. When the boy was two years old (1855), his parents emigrated to New York (USA), where their surname began to be pronounced as "Mikelson". From there, the family moved to the west of the country, first living in the mining settlements of Murphys (in California) and in Virginia City (Nevada), where his father developed a successful dried fruit business. During his school years, Albert Michelson lived in San Francisco, in the family of his aunt, Henrietta Levy (mother of the writer Harriet Lane Levy, cousin scientist).
In 1869, Michelson began training at the United States Naval Academy in Annapolis. In 1873 he completed his studies. From the very beginning of his studies, Michelson was very interested in science and in particular the problem of measuring the speed of light. After continuing, for two years, training in Europe, he retires from military service. In 1883 he became professor of physics at the Cleveland School of Applied Sciences and focused on developing an improved interferometer.
After 1889 he worked as a professor at Clark University in Worcester. In 1892 he became professor and head of the physics department of the newly founded University of Chicago. In 1907, Michelson becomes the first American to win the Nobel Prize in Physics. In the same year, Michelson also received the Copley medal for outstanding achievements in experimental physics.
speed of light
First measurements
Already in 1877, when he was an officer in the US Navy, Michelson began to improve the method of measuring the speed of light using a rotating mirror proposed by Leon Foucault. Michelson's idea was to use better optics and longer range. In 1878, he made the first measurements on a rather makeshift apparatus. This work attracted the attention of Simon Newcomb, director of the Nautical Almanac Office, who also planned to do similar experiments. Michelson published his result of 299,910 ± 50 km/s in 1879. After that, he moved to Washington (USA) to help with Simon Newcomb's experiments. Thus began a friendship and collaboration between the two scientists.
Newcomb obtained in his experiments, which were better funded, the value of the speed of light 299 860 ± 30 km / s, which coincided within the limits of measurement errors with Michelson's value. Michelson further improved his method; he published in 1883 the value of 299,853±60 km/s.
Mount Wilson and the time before 1926
In 1906, E. B. Rosa and N. E. Dorsey measured the speed of light using a new, electrical method. In their experiments, they obtained a value of 299,781±10 km/s.
After 1920, Michelson proceeded to the "final" measurement of the speed of light at the Mount Wilson Observatory, and the measurement was based on a distance of 22 miles - to Lookout Mountain, located on the south side of Mount San Antonio.
In 1922, the US Coast and Geodetic Commission began a careful measurement of this distance using the newly invented invar tapes, which lasted two years. In 1924, when the length was measured with an accuracy of 10−6, they started measuring the speed of light, which also lasted two years and gave the value of the speed of light 299,796±4 km/s.
This famous experiment is also known for its problems. For example, a big problem was Forest fires, the smoke from which led to clouding of the mirrors. It is also entirely possible that geodetic measurements made with such great accuracy were erroneous due to the base shift that occurred during the June 29, 1925 Santa Barbara earthquake, which had a magnitude of 6.3 on the Richter scale.
Michelson, Pease and Pearson in 1932
After 1927, many measurements of the speed of light appeared using new, electro-optical methods, which gave significantly lower values for the speed of light than Michelson's optical method determined in 1926.
Michelson continued to search for a measurement method that would exclude the influence of atmospheric disturbances. In 1930, he began, together with Francis Pease and Fred Pearson, to measure the speed of light in vacuum tubes 1.6 km long. Michelson died after the 36th of a total of 233 measurements taken. The experiment was hindered mainly by geological instabilities and condensation in the pipes. In the end, the experiments gave a value of 299 774 ± 11 km/s, which coincided with the results of electro-optical methods.
Interferometry
In 1881 Michelson held physical experience(Michelson's experiment) on his interferometer in order to measure the dependence of the speed of light on the movement of the Earth. The result of the experiment was negative - the speed of light did not depend in any way on the speed of the Earth and on the direction of the measured speed.
In 1887, Michelson, with E. W. Morley, conducted an experiment known as the Michelson-Morley experiment. In this experiment, the speed of the Earth's movement relative to the ether was determined. Contrary to expectation, the experiment (as well as its later and more precise modifications carried out to the present day) did not reveal the motion of the Earth relative to the ether. Einstein, in his first paper on the theory of relativity, mentions "failed attempts to detect the motion of the Earth relative to the 'light-bearing medium'" and, on this basis, builds a new universal kinematics (not only for electromagnetic phenomena). Michelson's experience became the basis and the first experimental confirmation of the theory of relativity.
In 1920, Michelson conducted an experiment to measure the angular size of stars. To do this, he used an interferometer with a shoulder length of 6 m. The light from the interferometer was sent using mirrors to the input of a 254-cm telescope. In this case, a system of bands was observed in the telescope. As the arms of the interferometer were lengthened, the fringes disappeared. From the distance between the mirrors of the interferometer, it was possible to determine the angular size of the star, and with a known distance to the star, also its diameter. Michelson thus determined the diameter of the star Betelgeuse.
Memory
In 1970, the International Astronomical Union named a crater on reverse side Moon. The Albert Michelson Medal awarded by the Franklin Institute is named in his honor.
Bibliography
- A. A. Michelson, "Research in Optics", URSS Publishing House, Moscow, 2004. ISBN 5-354-00945-6
- Albert A. Michelson, MA, US Navy "The Relative Motion of the Earth and the Luminous Aether" (1881). (The relative motion of the Earth and the Luminiferous ether. Albert A. Michelson, Master, U.S.Navy) // The American Journal of Science. 1881. III series. Vol XXII, No. 128. P. 120-129. Translation from English. L. S. Knyazeva.
- Albert A. Michelson, Edward W. Morley "On the relative motion of the Earth and the luminiferous ether" (1887) (The relative motion of the Earth and the Luminiferous ether. Albert A. Michelson, Master, USNavy) // The American Journal of Science. 1881. III series. Vol XXII, No. 128. P. 120-129. Translation from English. L. S. Knyaeeva.
- A. A. Michelson. “Effect of the rotation of the Earth on the speed of light. Part I "(1925) (The effect of the earth's rotation on the velocity of light. Part. 1. A.A. Michelson) // The Astrophys. J. April 1925. Vol. LXI. No. 5. P. 137-139. Translation from English. L. S. Knyaeeva.
- A. A. Michelson, Henry G. Gehl, Contributed by Fred Pearson. “Effect of the rotation of the Earth on the speed of light. Part II". (1925) (The effect of the earth's rotation on the velocity of light. Part II. A.A. Michelson, Henry G. Gale. Assisted by Fred Pearson) // The Astrophysical J. April 1925. Vol LXI. No. 5. P. 140-145. Translation from English. L. S. Knyazeva.
- Conference on the Michelson-Morley experiment. Held at the Mount Wilson Observatory, Pasadena, California, February 4 and 5 , 1927) //The Astrophysical Journal. December 1928. Vol. LXVIII, no. 5. P. 341-402. Translation from English. V. A. Atsyukovsky and L. S. Knyazeva.
- A. A. Michelson, F. G. Peace, and F. Pearson. "Repetition of the Michelson-Morley experiment" (1929) (Repetition of the Michelson-Morley experiment. By F.F.Micheson, F.G.Pease and F.Pearson) // Optical Society of America. Journal of the Optical Society of America and Review of Scientific Instumcnts. March 1929. Vol 18, No 3. P. 181-182. Translation from English. V. A. Atsyukovsky.
Hypothesis of the world ether. Michelson and Morley experiments
K.Maxwell found the correct equations of electrodynamics, relying on the idea of the ether, which eventually became obsolete. All waves known at that time could propagate only in various media, therefore, not only Maxwell, but all physicists believed that an electromagnetic wave is an elastic oscillation of some lightest, all-penetrating medium. This medium was called the world ether. Since the electromagnetic wave is a transverse wave, it was necessary to assume that the ether is solid.
The well-known experimenter A. Michelson (see Michelson interferometer) decided to try to experimentally register the fact of the existence of the ether and measure the speed of the Earth passing through the ether. For this purpose, he used his interferometer. Let's remember how it works. A parallel beam of light falls on a translucent plastic P oriented at an angle 450
to the bundle. Some of the light travels on and some is reflected. The reflected light falls on the mirror Z1 and, returning, passes a translucent plate to the screen E. The beam that has passed through the plate is incident on another mirror during the first pass. Z2 and, returning, is reflected from the translucent plate onto the screen. The superposition of two beams that have traveled different paths gives an interference pattern. A small difference in the angle between the mirrors from 900
leads to the fact that the interference pattern is a system of interference fringes.
The interferometer was aligned along the estimated speed of the Earth relative to the ether. If, for simplicity, we assume that the lengths of the arms of the interferometer are equal, then the light propagating along and across the motion of the Earth will take different times to reach the screen. If we now turn the interferometer to 900 , then the delay times of the beams will change places and the interference pattern will shift. The shift can be used to determine the delay time and, accordingly, the speed of the Earth relative to the motionless ether.
Task 3. Suppose the Earth moves relative to the ether with a speed v. Calculate the expected shift of the interference pattern (in units of the distance between the intensity maxima) at a wavelength of light l, after turning the interferometer by 900 with the interferometer arm length L.
An experiment carried out together with Morley showed that there is no shift in the interference pattern when the interferometer is rotated by 900 not visible. Hence it was necessary to conclude: either the ether is completely carried away by the Earth and the relative motion of the Earth and the ether is absent, or the ether does not exist, and the process of light propagation is not the propagation of an elastic wave. Michelson concluded that the ether is completely carried away by the Earth.
2.2 Experimental contradictions to the hypothesis
ether hobbies
The assumption about the complete entrainment of the ether by the Earth contradicted other experimental facts. Thus, the English astronomer J. Bradley discovered that the most distant stars make an apparent annual movement in a circle or in an ellipse. This phenomenon is called aberration of starlight. It turned out that the angular diameter of the trajectories of almost all stars is the same and equal to 40,5 arc seconds. An elementary explanation of aberration becomes simple and understandable if we draw an analogy between the propagation of light and the fall of raindrops. When there is no wind, a stationary observer sees that the drops fall vertically. However, if you sit in a moving car, you can see the oblique fall of drops. The rain is falling from above and in front.
Task 4. Let the rate of fall of raindrops relative to the Earth be c, the speed of the car is v. What is the angle at which the droplets fall from the car? Using the result obtained and data on the apparent angular diameter of the trajectories of stars, determine the speed of light. The orbital speed of the Earth is 30 km/s.
If the ether were completely carried away by the Earth, then there would be no aberration.
Conclusion
So, from Michelson's experiments and from phenomena similar to the aberration of stellar light, it should be concluded that the speed of light in any frame of reference is the same and is equal to c.[The most accurate measurements so far give the value c=(2.997925 ± 0.000003)×108m/s.]
Let us assume that a light signal from the Earth is received on a spacecraft departing at great speed from the Earth. When measuring the speed of its propagation, a value will be found c regardless of ship speed: c– v =c!Or another example. At the present time, it is reliably established that galaxies far from the solar system are receding. The universe is expanding. The escape velocity is greater the farther away the galaxy is. Very distant galaxies run away at speeds close to the speed of light. However, the light coming from these galaxies has a speed c. This fact, as well as electrodynamic experiments, speaks of the need to abandon the Galilean transformations of coordinates and velocity, the rule for adding velocities.
The experience of A. Michelson and the special theory of relativity
As already mentioned in the section on the microworld, the new physics was born at the turn of the 19th and 20th centuries, since classical science could not explain the results of a number of experiments carried out in the 19th century. From the desire to explain X-rays and radioactivity, quantum mechanics and nuclear physics arose. A. Einstein's theory of relativity grew out of an attempt to explain the results of the experience of an American physicist and engineer Albert Michelson(1852 - 1931) to determine the speed of light relative to the motionless ether, the existence of which was suggested by J. Maxwell. The results of Michelson's experiment, for which he received the Nobel Prize, were unexpected: it turned out that 1) the speed of light does not depend on the speed of its source; 2) that it is a world constant and is constant in all inertial frames of reference; 3) that it cannot be exceeded. i.e. the speed of light is maximum speed signal transmission. As a result, the results obtained by A. Michelson showed that ether does not exist.
These results were the first of the "whales" on which the special theory of relativity. The second "whale" was the principle of relativity of G. Galileo, which A. Einstein reformulated as follows: all inertial frames of reference are equivalent to each other with respect to setting any physical experiments in them, and none of them (with respect to which the ether would be motionless) has advantages over others.
A. Einstein was the greatest theorist, and when working on the theory of relativity, he used the method of a thought experiment called "A. Einstein's ship." The essence of this experiment is as follows. A ship is sailing along the shore, inside which a mouse is running in the direction of the ship. The speed of the mouse relative to the coast is the sum of its own speed relative to the ship and the speed of the ship relative to the coast. If we assume that the speed of the ship approaches the speed of light (theoretically, this is possible), then the speed of the mouse relative to the shore will exceed the speed of light, which contradicts the result of A. Michelson's experiment.
To resolve the contradiction that arose, A. Einstein had to change the paradigm: through logical reasoning and mathematical calculations, he came to the conclusion that at high speeds commensurate with the speed of light (and these are the speeds of MEGA WORLD , whose objects are stars, galaxies and the Universe), Newton's paradigm about the absoluteness and independence of space and time does not work. From this it followed that at high speeds space and time turn out to be interconnected, and time becomes the fourth coordinate, i.e. space under these conditions has at least four dimensions.
Three consequences followed from this:
1) at high speeds, commensurate with the speed of light,
the distance is shortened, the segment is shortened and at a speed
light (if it turned out to be achievable), shrinks to a point;
2) at high speeds, time slows down; Einstein’s example is widely known, which he called the “twin paradox”: two twin boys were born on Earth on the same day, one went on a long space flight, the other spent his whole life on Earth. When the astronaut returns home, he will still be young (at the enormous speeds of space flight, time will flow more slowly than on Earth), and his brother will turn out to be a very old man.
3) the mass of the body does not depend on the speed of the body. Hence it follows that
no body with a mass other than zero can be accelerated to
the speed of light, because this would require infinite energy.
Further, A. Einstein found a connection between mass and energy: the mass of a body is a measure of the energy contained in it. This is how the famous formula Å= mc2 appeared, where E is the particle's rest energy, m is its rest mass, c is the speed of light.
Experimental confirmation of the special theory of relativity came from the microcosm. It turned out that in experiments with elementary particles, which are accelerated to very high speeds in special accelerators, for good agreement between the experimental and calculated data, the effect of mass increase, the so-called relativistic corrections to mass, should be taken into account (the English word "relativ" means "relative"). Time dilation has already been experimentally recorded at space flight speeds (in space, clocks are a little behind). All of the above indicates that the special theory of relativity describes not only the mega-world, but also the micro-world. In the macrocosm, however, the velocities are too low and the masses are too large to experimentally observe relativistic effects.
So, the special theory of relativity says that at high speeds (in the mega-world and the micro-world) the interrelation of space and time is manifested, i.e. realized at least four-dimensional space-time. In the macrocosm, the speeds are so small that the relationship between space and time cannot be experimentally fixed.
What was the Michelson experiment?
Sapphire
It is difficult to imagine absolute emptiness - a complete vacuum containing nothing. Human consciousness seeks to fill it with at least something material, and for many centuries of human history it was believed that the world space is filled with ether. The idea was that interstellar space is filled with some kind of invisible and intangible subtle substance. When Maxwell's system of equations was obtained, predicting that light propagates in space with a finite speed, even the author of this theory himself believed that electromagnetic waves propagate in a medium, just as acoustic waves propagate in air, and sea waves propagate in water. In the first half of the 19th century, scientists even carefully worked out the theoretical model of the ether and the mechanics of the propagation of light, including all kinds of levers and axes, supposedly contributing to the propagation of oscillatory light waves in the ether.
In 1887, two American physicists - Albert Michelson and Henry Morley - decided to jointly conduct an experiment designed to once and for all prove to skeptics that the luminiferous ether really exists, fills the Universe and serves as a medium in which light and other electromagnetic waves propagate. Michelson had unquestioned authority as a designer of optical instruments, and Morley was famous as a tireless and infallible experimental physicist. The experience they invented is easier to describe than to carry out practically.
Michelson and Morley used an interferometer - an optical measuring device in which a beam of light is split in two by a translucent mirror (a glass plate is silvered on one side just enough to partially transmit light rays entering it, and partially reflect them; a similar technology is used today in SLR cameras) . As a result, the beam splits and the two resulting coherent beams diverge at right angles to each other, after which they are reflected from two reflecting mirrors equidistant from the translucent mirror and return to the translucent mirror, the resulting beam of light from which allows you to observe the interference pattern and reveal the slightest desynchronization of the two beams (delay of one beam relative to the other; see Interference).
The Michelson-Morley experiment was fundamentally aimed at confirming (or disproving) the existence of the world ether by revealing the "ethereal wind" (or the fact of its absence). Indeed, moving in orbit around the Sun, the Earth moves relative to the hypothetical ether for half a year in one direction, and for the next six months in another. Consequently, for half a year the "ethereal wind" should blow over the Earth and, as a result, shift the readings of the interferometer in one direction, and for half a year - in the other. So, observing their installation for a year, Michelson and Morley did not find any shifts in the interference pattern: complete ethereal calm! (Modern experiments of this kind, carried out with the highest possible accuracy, including experiments with laser interferometers, gave similar results.) So: the ethereal wind, and, therefore, the ether does not exist.
In the absence of the ethereal wind and the ether as such, an unresolvable conflict between Newton's classical mechanics (implying some absolute frame of reference) and Maxwell's equations (according to which the speed of light has a limit value independent of the choice of frame of reference) became obvious, which resulted in to the advent of the theory of relativity. The Michelson-Morley experiment finally showed that there is no "absolute frame of reference" in nature. And, no matter how much Einstein subsequently claimed that he did not pay any attention to the results of experimental studies when developing the theory of relativity, it is hardly necessary to doubt that the results of the Michelson-Morley experiments contributed to the rapid acceptance of such a radical theory by the scientific community seriously.
Michelson's experiment is a physical experiment set up by Michelson in 1881 to measure the dependence of the speed of light on the motion of the Earth relative to the ether. The ether was then understood as a medium similar to volumetrically distributed matter, in which light propagates like sound vibrations. The result of the experiment was negative - the speed of light did not depend in any way on the speed of the Earth and on the direction of the measured speed. Later, in 1887, Michelson, together with Morley, conducted a similar but more accurate experiment, known as the Michelson-Morley experiment, which showed the same result. In 1958, an even more accurate experiment was conducted at Columbia University (USA) using the counter-directional beams of two masers, which showed the invariance of the frequency from the Earth's movement with an accuracy of about 10−9% (the sensitivity to the Earth's velocity relative to the ether was 30 m/s) . Even more precise measurements in 1974 brought the sensitivity to 0.025 m/s. Modern versions of the Michelson experiment use optical and cryogenic microwave cavities and make it possible to detect a deviation from the anisotropy of the speed of light if it were several units per 10−16.
Michelson's experience is the empirical basis of the principle of invariance of the speed of light, which is included in the general theory of relativity (GR) and the special theory of relativity (SRT).
Bernard Jeff
5. Michelson-Morley experiment
The Case School of Applied Science, which opened its doors to students in 1881 and later became the Case Institute of Technology, was housed in a house that had previously belonged to Case on Rockville Street, not far from Cleveland's central square. The first thing Michelson had to do upon taking up his duties was to equip a laboratory in an outbuilding on the school grounds.
Adjacent to Case's property was Western Reserve University, which was transferred to Cleveland in the summer of 1882 from Hudson, Ohio. Across the street, a hundred meters from Michelson's laboratory, was Adelbert Hall, one of the university buildings where chemistry professor Edward W. Morley worked.
Michelson and Morley soon became acquainted and became close on the basis of common scientific interests. Together they traveled to scientific conferences in Baltimore, Montreal and other cities, and the better they got to know each other, the more their mutual sympathy and respect grew stronger.
Outwardly, these two scientists seemed very different. Morley was more than fifteen years older than Michelson and descended from English settlers who left the British Isles at the beginning of the 17th century. His father was a Congregationalist minister, and he himself graduated from the seminary in Andover (Massachusetts) in 1864 and was preparing to take holy orders. His career is an example of how a hobby turns into a life's work. Not having received a suitable spiritual department, he took up chemistry, which until then he had only done amateurly. In 1868, Western Reserve University offered him a professorship in chemistry and natural philosophy. Morley was very religious and from time to time delivered sermons in the surrounding churches. Moreover, he agreed to accept a professorship at the Western Reserve only on the condition that he be allowed to preach regularly in the university chapel.
As for Michelson, he was very far from religion. His father was an atheist, and religion did not occupy any place in the life of their family. Thus, he did not join the ancient faith of his forefathers and was an unbeliever all his life. He entrusted the upbringing of children in the spirit of religion to his wife. Admiring the wonders of nature, he nevertheless refused to attribute them to some creator. One starry night, showing and naming the constellations in the sky to his children, he said: “You can forget the names of the constellations, but I consider people who do not bow to the wonders of nature unworthy of respect.” He once wrote: “What can compare in beauty with the magnificent correspondence between the means of nature and its ends, and with that invariable rule of regularity that governs the most seemingly disorderly and complex of its manifestations?” However, he did not recognize the idea of God.
Michelson was good-looking, slender, and always immaculately dressed. Morley dressed, to put it mildly, casually and would have completely corresponded to the stereotypical idea of an absent-minded professor, if not for the liveliness of his movements, energy and talkativeness. He wore shoulder-length hair and a huge red mustache that stuck out almost to his ears. He was married but childless.
However, Michelson and Morley had much in common. Both loved music. Michelson played the violin well, and Morley was an excellent organist. Both were distinguished by ingenuity in terms of precise measuring instruments and extraordinary thoroughness in their work. Morley, like Michelson, did not miss a single detail and, just like him, when he took up the study of any scientific problem, he did not retreat until he brought the matter to the end.
Prior to meeting Michelson, Morley, while checking reports of varying percentages of oxygen in different air samples, undertook a study of the relative weight of oxygen and hydrogen in pure water. This research took almost twenty years. He conducted thousands of experiments, many at his own expense. He analyzed countless samples of distilled water by electrolysis and synthesized water by the method of an electric spark by combining given amounts of two elements. As a result of many years of research, he determined the weight of these elements to the fifth decimal place. A liter of oxygen weighs 1.42900 g, and hydrogen 0.89873 g, with a possible error of one three hundred thousandth. These values were universally accepted as standard, as was Morley's ratio of hydrogen to oxygen of 1.0076 to 16. Morley's experiments were classic and won him worldwide recognition.
Influence of the motion of the medium on the speed of light
Lord Kelvin and Lord Rayleigh asked Michelson to test the influence of the motion of the medium on the speed of light. Michelson decided to take water as a moving medium and shared his idea with Morley. He offered him his laboratory for work. It was located in a large basement room, and the conditions in it were ideal for the experience conceived by Michelson. Morley was not a physicist, but he was quick-witted, resourceful, and passionate about the problem. In 1860, while still a student, he worked at one time in the field of astronomy. Michelson told him about the task before them and about the device that he was thinking of using. Morley was ready to get to work immediately. However, in September 1885, when work on the experiment was still in its infancy, Michelson appeared in the laboratory in the morning in a completely miserable state. He told Morley that he was suffering from nervous exhaustion and needed a long rest. He said he needed to leave Cleveland for at least a year. Wouldn't Morley agree to complete the device on his own, conduct experiments and publish the results? He handed over to Morley a certain amount he had received for experiments, and added another 100 dollars of his own. Morley then received a letter from Michelson from New York. They corresponded regularly about the experiment. Four months later, Michelson unexpectedly arrived in Cleveland and offered to continue working together. His health improved significantly and he was able to complete the experiment. In 1886, in the American Journal of Science, signed by both of them, the work The Influence of the Motion of a Medium on the Speed of Light appeared. Michelson and Morley found that the movement of water has an effect on the speed of light, but not in the way that one would expect from the aether theory. Their experience confirmed the results of research done by Fizeau in 1851. Two educational institutions at once - Western Reserve University and Stevens Institute of Technology awarded Michelson a Ph.D. This was Michelson's first degree, since in his time the Naval Academy did not yet have the right to award the title of Bachelor of Science.
Now, with improved apparatus and enriched experience, Michelson was able to return to the experiment with the ether, which he had been postponing for so long. Morley also had to take part in this work. They were full of the most optimistic hopes, and Morley wrote to his father on April 17, 1887: “Michelson and I have begun a new experiment, which should show whether the speed of propagation of light is the same in all directions. I have no doubt that we will get the final answer." Of course, Morley somewhat simplistically defined the purpose of the experiment. Michelson and Morley were about to make a determined attempt to "catch" the elusive ether. In the case of a positive result, science will receive not only the speed of the Earth in orbit relative to the ether, but also the speed of its rotation around its axis, and, perhaps, even a method for determining the speed of movement in space of the entire solar system. This would be the first attempt, by means of a local optical phenomenon, to determine the absolute motion of the Earth in space, which was identified with the ether.
Michelson-Morley instrument
The device they designed turned out to be a very massive structure. It consisted of a stone slab approximately 150 square centimeters in area and about 30 cm thick. On the slab were placed four mirrors made of an alloy of copper, tin and arsenic, as well as all other equipment, including an Argand burner. To ensure a strictly horizontal position of the stone slab and to avoid errors due to vibration, friction and tension, the slab was floated in mercury purified by Morley. Mercury was poured into an annular cast-iron vessel with a wall thickness of about 1.5 cm; a donut-shaped wooden stand floated on top of the mercury, and a stone slab was already installed on it. The axial rod ensured the concentricity of the wooden float and the cast iron vessel. The gap between the vessel wall and the outer rim of the float was less than 1.5 cm (Fig. 9).
Rice. 9. Michelson-Morley installation.
A large and very heavy stone slab rested on a wooden float placed in liquid mercury. The vessel with mercury had the shape of a donut. Floating in the liquid, the stone slab and wooden stand remained strictly horizontal.
The cast-iron vessel rested on a support, which was a low, sloping brick octagon, inside of which cement was poured. The foundation of the interferometer went deep into the ground, to the bedrock, since the topsoil was not stable enough. On the circumference of the vessel, at the same distance from one another, sixteen marks were made. The wooden case protected the optical part of the device (a mirror at each corner of the plate) from air currents and sudden changes in temperature.
The resistance to the motion of a heavy apparatus was reduced to a minimum, and by applying a slight force around its circumference, it was possible to give it a slow, smooth and continuous rotation. One full rotation was completed in about 6 minutes. The observer walked around the apparatus, moving simultaneously with the rotating stone slab, and periodically stopped, looking through a small telescope to check if the interference fringes had shifted. Such a shift would mean a change in the speed of light in that direction (Fig. 10).
Rice. 10. Interferometer in the Michelson-Morley setup.
The principle of its operation is the same as that of the device shown in Fig. eight.
It took several months to adjust this unique device. In the end, Michelson achieved that he registered the slightest shift in the interference fringes. Morley and Michelson alternately walked around the instrument and looked through the telescope.
They assumed that there should be two days during the year when the maximum bias effect (if such an effect exists at all) will be observed. On one day the Earth will move in the exact opposite direction to that in which it moved on that other day.
They made observations daily at twelve o'clock in the afternoon and at six o'clock in the evening in sixteen different directions. Straining their eyes, they peered into the interference fringes, trying to determine their displacement.
The experiments were completed in July 1887. When all the results were brought together and analyzed, all the calculations were made and repeatedly verified, the researchers found themselves in the face of a stubborn fact that destroyed the whole harmonious theory. Against all expectations, no displacement of the order required by the fixed ether hypothesis was found. It was like a death sentence for the idea of a motionless ethereal ocean. Michelson was quite sympathetic to the theory of the fixed ether and hoped that experiment would make it possible to discover it. How else could electromagnetic oscillations, including light waves, propagate? Again, the result of a finely conceived and brilliantly executed experiment led Michelson to complete bewilderment.
"The Greatest of All Negative Results"
Michelson and Morley sent their report to the American Journal of Science. It was entitled: "On the relative motion of the Earth and the luminiferous ether." In the same year it was also published in the English Philosophical Magazine. Michelson's conclusion became known to scientists all over the world. In whatever direction the observer moved, there was no perceptible difference in the speed of light. In other words, you had to admit the incredible: no matter how fast you run after the light, it is impossible to catch up with it. He will still run away from you at a speed of 300,000 km per second. Such a conclusion was contrary to all human experience. An airplane flying at a speed of 600 km per hour with a tailwind blowing at a speed of 50 km per hour makes, relative to some fixed point, 650 km per hour. If it flies against the wind, its speed will decrease to 550 km per hour. Since the Earth moves around the Sun at a speed of about 30 km per second, the speed of a light beam traveling in the same direction as the Earth should be more speed beam traveling in the opposite direction. However, Michelson's experience refuted this assumption.
The English physicist and philosopher John D. Bernal called Michelson and Morley's discovery "the greatest of all negative results in the history of science." However, Michelson was not completely discouraged by the results of his experience. Although they ruled out the existence of a fixed ether, there remained one more possibility that “the Earth drags the ether with it, giving it almost the same speed with which it moves itself, so that the speed of the ether with respect to the surface of the Earth is zero or very small.”
Ten years after the publication of this historic report, Michelson experimentally tested “the second hypothesis by sending two beams of light along the perimeter of a vertically placed rectangle, the sides of which were equal to 15 and 60 m. The results did not confirm this hypothesis.
Michelson was not convinced that the "failure" of his experiment finally settled the issue. “Since the result of the experiment was negative, the problem is still waiting to be resolved,” he publicly stated. And to console himself, he brought a rather unexpected argument: “In my opinion, the experiment was not in vain, since the search for a solution to this problem led to the invention of the interferometer. I think that everyone recognizes that the invention of the interferometer fully compensates for the negative result of this experiment.
Many years later, speaking to a scientific audience at Mount Wilson Observatory, Michelson gave a very different assessment of the relative importance of the experiment with the ether and the invention of the interferometer. He acknowledged that his assertion of greater value for the instrument ran counter to "some important theoretical considerations" that shook the scientific world. As it turned out over the past years, Michelson, without knowing it, prepared the material from which one of the greatest scientific theories of all time was built in Europe. This is one of the rare cases where the original discovery was made in America and later used in Europe. It almost always happened the other way around.
The idea of the experiment is to compare the light passing through two paths, one of which coincides with the direction of motion of the body in the ether, and the other is perpendicular to it.
Plate B is translucent. On it, the beam is divided into two coherent perpendicular beams going to mirrors D and C. Two coherent beams meet in the interferometer, having passed different paths from the separation point.
If these paths are covered by them in the same time, then they will come to the meeting point in one phase and reinforce each other. If for a different time, then at the meeting point the phase difference and oscillations will change. Observing the interference, one can draw a conclusion about the phase difference of the coherent waves that came into the interferometer, and from here calculate the delay time of one wave relative to the other. This was done by Michelson and Morley. It was one of the most remarkable experiments of the 19th century. Simple in essence, this experience led to a revolution in science.
Let the device move in the direction of the shoulder BC with a speed v relative to the ether. The speed of light relative to the ether c. The total time during which the path to mirror C and back will be traversed will be equal to:
To mirror D path BDB /
Here v is the speed of the Earth in its orbit around the Sun (~30 km/s). Therefore, if the device is on the ground, then . Given the smallness of this term, the expressions can be expanded into series:
We get:
The difference in the path of the rays is equal to:
Now let's rotate the device by 90° so that the arm BD coincides with the direction of movement, and the arm BC is directed perpendicularly. For the path difference we get:
The total change in the difference in the path of rays in time when the device is rotated is:
In the experiment, the device slowly rotated, since the true movement of the device relative to the ether was unknown. Thus, when the device is rotated through 360°, each of the arms coincides twice with the direction of motion and twice becomes perpendicular to the direction of motion. If the difference in the path of the rays changes when the device is rotated, then the position of the interference fringes in the field of view should also change. Let us estimate the magnitude of the shift.
Relative to the shift of the interference fringes is:
the distance between the bands, and this can be easily observed and measured.
But experimentally, no effect was found. The absolute speed of the Earth proved impossible to detect.
It turned out that the speed of light in all directions is the same and there is no ethereal wind. The longitudinal and transverse components of the velocity are always equal to each other. With the advent of lasers, the accuracy of experiments has been significantly improved.
Experiments have shown that the speed of light does not add up to either the speed of the source or the speed of the receiver.
The constancy of the speed of light is in deep contradiction with the usual ideas of experiments and with the formulas for adding speeds based on Galilean transformations. At speeds much lower than the speed of light, deviations are not observed, since they are very small. The incorrectness of the formula for adding velocities manifests itself when the velocities are sufficiently large. Deviations were first discovered in 1860 in Fizeau's experiments.
