Corpuscular theory of light
The corpuscular theory (also emission theory or ballistic theory of light ) is a particularly Isaac Newton attributed to physical theory, according to which the light from small particles or corpuscles ( corpuscles ) exists. The corpuscular theory was replaced by the wave theory of light in the 19th century, however, the light from the photon theory of Albert Einstein (1905 ) can be partially attributed also corpuscular properties.
Since the original emission theory is compatible with the principle of relativity and thus with the Michelson - Morley experiment, such models were at the beginning of the 20th century again discussed and considered as an alternative to the theory of relativity into account. However, in theory, the light emission rate of the speed of the light source would depend on what has been clearly demonstrated that a number of other experiments. Likewise, never a fully worked- theory has been presented. Consequently, the emission theory no longer be considered.
17th to 19th century
There are in the history of science many different emission theories. As the literature shows, a lot of emission theories have emerged in the last few centuries and been forgotten. Emission theorists, for example, Sir Isaac Newton (1643-1727), Pierre Simon de Laplace (1749-1827), Jean -Baptiste Biot (1774-1862), Sir David Brewster ( 1781-1868 ).
The theory is that the light of tiny particles, or corpuscles there that are ejected straight from luminous bodies with great speed, the speed of light depends on the speed of the light source. This theory could both rectilinear propagation, as explain the reflection of light. Also, various colors can be explained by assuming different size of the light particles. Diffraction, refraction at interfaces or partial reflection, however, cause difficulties. The refraction has been clearly explained: In a greater distance from the interfacial light particles are surrounded on all sides by ( other ) identical particles and therefore fly in a straight line. " Dense " at the interface of two different transparent materials are the " light particles " differently strongly attracted and therefore abruptly change the direction of flight. This was associated with the assumption that the light in the " optically dense " medium flies faster. Only much later, after 1820, it was shown that the speed of light in the " optically dense " media is smaller than for example in vacuum ( Snell's Law). Thus, although the reasons for this is " optically dense " false, this term is still used today.
Some researchers recruited from the corpuscular nature of light further conclusions: Newton suggested already in 1704 a possible deflection of light rays by gravity to, but without calculating the distraction. John Michell (1783 ) and independently of him, Pierre- Simon Laplace (1796 ) concluded that such massive stars are to imagine that even light could not escape them, that is, they designed an early form of a black hole. Finally, (1801, published 1804) calculated Johann Georg von Soldner the indicated deflection of light by Newton, where he " was given the value of 0.84, which is only in the context of the Newtonian theory of gravitation, however, is incorrect. To determine the correct value of the following from the general theory of relativity space curvature must be taken into account, whereby the Newtonian value doubled, as Albert Einstein calculated. This prediction has been experimentally confirmed many times.
In the question of whether the Christiaan Huygens ( 1690) reasoned, based on the etheric wave theory of light, or the corpuscular theory was right, won for the time being Newton. In the 19th century Newton's model was, however, primarily through the works of Thomas Young ( 1800), Augustin Jean Fresnel (1816 ), and James Clerk Maxwell ( 1865) overcome and the wave theory seemed to be proved. This was followed on the one hand from the fact that refraction and diffraction effects, such as ( especially in the form of the Poisson spot ) could be explained by the much simpler wave theory as needed in the framework of the corpuscular repeatedly auxiliary hypotheses are introduced. Similarly, the consistency in the speed of light of different light rays spoke for the wave model. The key, however, was the above mentioned prediction of the corpuscular theory, according to which light in denser media would have to be faster than in less dense. 1850 Jean Bernard Léon Foucault was first determined by means of the rotating mirror method, the speed of light in the media, and found that it was greater in air than in water, which corresponded to the predictions of wave theory. This was seen as a definitive refutation of the corpuscular theory.
Since the photon theory of Einstein ( 1905), the light can be partially attributed also corpuscular properties but possess photons according to the theory of relativity no rest mass, but only energy and momentum. In the context of quantum mechanics is also spoken by the wave -particle duality.
20th century
Emission theories are usually based on the assumption that the light propagates constant exclusively in relation to the light source with the speed of light. In contrast to the ( stationary ) aether theory that light propagates constant with respect to the aether, and in contrast to the special relativity theory (SRT ), according to which light propagates constant in all inertial frames. Consequently, as in the original Newtonian corpuscular that the speed of light is dependent on the speed of the light source. The change of the inertial system is performed by the Galilean transformation, whereby the classical principle of relativity is satisfied. That is, in contrast to the ether theory, the relative movement of the source and the receiver for the Doppler effect, as well as aberration is solely responsible for the emission theory. Similar considerations were occasionally transferred to electromagnetic waves, not only particles, but which were incorporated different ideas about the source function of the speed of light.
Since an emission theory as opposed to the ether theory does not violate the classical principle of relativity and thus with the unsuccessful aether drift experiments ( such as the Michelson - Morley experiment ) is tolerated, it was drawn in the early 20th century as an alternative to Lorentz between electrodynamics and the SRT again considered. This was particularly so in order to avoid the associated with the constancy of the speed of light in all inertial systems to radically change the understanding of space and time. Albert Einstein himself retired before 1905 an emission theory into consideration, but he rejected it even before 1905, as he saw it as incompatible with the lessons learned electrodynamics.
As the light propagates in the most emission models constant with respect to the original light source, there were different ideas about what is ever to be regarded as light source and whether mirror may be counted to do so. From this developed various kinematic variations of emission theories:
- Light propagates only constant relative to the original light source, irrespective of whether it is subsequently reflected by a mirror. That is, the center of the spherical wave is always moving at the same speed as the original light source. This model was proposed by Walter Ritz in 1908, and was considered the most advanced emission theory.
- Everyone's body is to be regarded as a new light source. That is, a mirror, which is struck by a light beam and this reflected acts as a new light source, relative to which the light is now propagating constant speed of light. Thus, light spreads as a spherical wave whose center moves at the speed of the most recent body from which the light is finally reflected. This model was proposed by Richard C. Tolman 1910 ( which Tolman even Einstein's theory of relativity preferred ).
- Light which is reflected by a mirror propagates from now on with the speed of the mirror image of the original source. ( This theory was proposed by Stewart 1911).
- A modification of the scoring - Tolman theory was introduced by Fox ( 1965). This argued that the absorbance (that is, absorption, scattering, and emission of light within a medium traversed ) must be considered. In the air, Extinktionslänge visible light would be only 0.2 cm. After this distance the speed of light would not be constant for the source, but constant to the medium (the said Fox even Einstein's theory of relativity preferred ).
None of these models, however, was completely worked through, so they were never considered by the experts as a serious alternative to the SRT into consideration. In particular, its fundamental prediction, namely the dependence of the speed of light from the source velocity, experimentally many times refuted ( see next section ).
Experiments
The fundamental kinematic statement or experimental prediction of most emission theories, namely the dependence of the speed of light from the source velocity, was mentioned in the professional world in some older articles until the 1960s in connection with tests of special relativity or tests of constant light.
Both emission theory and SRT agree that no ether wind or no influence of a preferred reference frame exists. This means that if the source and receiver in the same inertial rest, both models predict a null result, and are compatible for example with the negative result of the Michelson -Morley experiment.
Differences arise when source and receiver are moving relative to each other. While here according SRT the speed of light is constant in all inertial systems, resulting in the emission theory with a source velocity of ± v is a velocity of light c ± v. In experiments, the following scheme is commonly used:
Where c is the speed of light, v is the source speed, and c ' is the resultant speed; k indicates the extent of source dependence. When k = 0 the speed of light is independent of the source velocity (as in the SRT or the stationary ether ), whereas at k = 1 is completely dependent on her. Values between 0 and 1 are also possible, and represent a limited source dependency. Since it was shown in the context of the current measurement accuracy that k ~ 0, the emission theories are considered to be experimentally refuted, while the SRT is thus confirmed.
Michelson - Morley experiment
In the rest frame of the interferometer and the light source, the light rays propagate with constant speed in all directions. With an arm length of D ( where D = ct ), there are the times in longitudinal and transverse direction of each t = D / c and thus for the round trip of
In contrast, in an inertial system in which the arrangement moves with v, receives the light, the speed of the light source as in a basement according to the Galilean transformation added. The speed of light in the longitudinal direction is c v and the distance to be D vt When you return to the light beam moves with cv and the distance to be covered is D -vt. This results in a term of:
In the transverse direction is determined by the Pythagorean Theorem: a) if D is the path in the y- direction and vt in the x- direction, a path from b) where c is the velocity component in the y- direction and v in the x direction, a speed of light. This results in a term of
The running time T is thus equal in all inertial systems, that is, the light beams propagate in all systems constant relative to the light source. Emission theories are therefore compatible with the use of a stationary light source to the negative result of this experiment. On the other hand, as Tolman pointed out, would result in the model of Ritz when using sunlight or starlight a positive result.
Refutations
Astronomic
The different speeds at which the light would sent depending on the position of double stars in orbit would distort according to the emission theory the received on Earth image of the orbits. That is, the stars seem to behave as if they were no longer subject to Kepler 's laws. However, this is not the case, as Daniel Frost Comstock (1910 ) and especially Willem de Sitter (1913 ) proposed, was being achieved. This objection, however, does not affect the Extinktionsmodell Fox (ie, absorption, scattering, and emission of light by interstellar dust, which is at rest relative to the earth practically ), whereby the light rays take relative to the earth again the speed of light. However crusher (1977 ) examined the radiation emitted by X-ray double stars that barely interacts with interstellar dust. This is the extinction is not large enough to distort the results significantly. Also here were no distortion, and thus no dependence on the source velocity can be determined, which corresponds to.
Hans Thirring had in 1924 indicated that "if an atom to the sun during the emission act undergoes a change of the velocity component in the vision direction by a thermal collision, then the light emitted from him wave of about 3 m total length on the way to Earth, first to shrink the length zero, then to some extent on strike and eventually pulled to the rear end first, to a total length of 500 km apart, arrive at the observer on earth, which receives the radiation as a radio wave from a few centimeters wavelength. The ballistic hypothesis is therefore refuted in its consistent version alone by the fact that the solar radiation has a visible spectrum with sharp spectral lines. "
Terrestrial
Sadeh (1963 ) used a method of flight measurement to measure differences in speed in the opposite direction of the propagating gamma rays resulting from positron annihilation. Another experiment was of Alväger et al. (1963) carried out the comparison, the flight time of gamma rays, which are emitted from stationary and moving sources. In both experiments, no source could be easily detected.
Filippas and Fox ( 1964), however, were of the opinion that Sadeh (1963) and Alväger (1963 ), the extinction effects not sufficiently considered. Therefore, they conducted an experiment with gamma rays from the decay of π0 mesons, which was particularly aimed at the prevention of Exinktionseffekten. Again, no source could be dependence observed.
Alväger et al. (1964 ) is now carried out further tests with π0 mesons, which decay at a rate of 99.9 % the speed of light in gamma rays. The measurement of the flight time showed that the photons continue moving at the speed of light, at. The analysis of the media that have been traversed in this experiment of the photon, revealed that the absorbance is not sufficient to distort the result appreciably.
Meanwhile, measurements of neutrino speed were made, with decaying mesons are used together with the speed of light as the source. Since neutrinos interact only weakly electro, extinction does not matter. There were maximum limits in terrestrial experiment.
Interferometry
Emission theories contradict the Sagnac effect. This effect is due to the fact that the path of a beam becomes longer due to the rotation of an interferometer, and the other shorter. This is only possible if the speed of light is independent of the speed of the source. Also plays absorbance does not matter since the Sagnac effect occurring in a vacuum.
Albert Abraham Michelson (1913) and Quirino Majorana (1918 /9) performed experiments with moving sources and mirrors and could show that in the air there is no source dependence. Beckmann and Mandics (1965), carried out similar experiments in a high vacuum, a source dependency could be excluded with k less than 0.09. Although extinction could not completely, but be excluded with high probability.
Babcock et al. (1964 ) placed rotating glass plates between the mirrors of a static interferometer. When the speed of the glass sheets would add to the speed of light, it would result in a measurable shift in the interference fringes. However, the result was negative because the experiment was carried out in vacuum, absorbance also plays no role. Only the original theory of Ritz, after which the glass plates are not to be regarded as a new light source is compatible with the result. But there is in the Ritz 's theory no absorbance, which it is contrary to all other experiments, to be agreed only by extinction with the emission theory.
Other refutations
The Maxwellian electrodynamics and the SRT based on the independence of the speed of light from the source, and their predictions have been confirmed experimentally with high precision all. For example, emission theories are based on the Galilean transformation and thus on a reference system independent, absolute time. However, by the proof of time dilation, such as at the Ives - Stilwell experiments or the time dilation of moving particles, this concept could be excluded, and the Lorentz transformation can be confirmed. Similarly, the related Galilean velocity addition and the Newtonian momentum relationship is refuted by tests of the relativistic energy - momentum relation, according to which mass -prone particles can not be accelerated to the speed of light and beyond.
There was as yet no emission theory developed that could explain all these experimental results at least as good, which is a prerequisite, so that it can ever be considered a realistic alternative. In addition, the Maxwellian electrodynamics was developed to quantum electrodynamics, which ever is considered the most accurate theory confirmed - here the speed of light is independent of the source velocity.