Albert Einstein

“ Since light can also propagate through empty space, one had to imagine a strange substance, an ether, that mediated the propagation of light waves. Since light also propagates in material objects, one had to assume that this ether was also present in material objects, and was chiefly responsible for the propagation of light in material objects. The existence of the ether seemed beyond doubt. In the first volume of Chwolson's excellent physics textbook, he states in the introduction to ether, "The hypothesis of this one agent's existence is extraordinarily close to certainty." ”

“ The relativity principle states that all natural laws that hold in a reference frame moving uniformly relative to the ether are identical with those that hold in , a reference frame at rest relative to the ether. If that is so, we can just as well imagine the ether is at rest relative to , not . It is completely unnatural to distinguish the two reference frames and by introducing an ether that is at rest in one. A satisfying theory can only be reached if we dispense with the ether hypothesis. ”

“ If the above is really true then, because of the independence of the secondary cathode rays' speed on the primary cathode rays' intensity, we must assume that an electron impinging on P1 will either cause no electrons to be produced at P2, or else a secondary emission of an electron whose speed is of the same order as that of the initial electron impinging on P1. In other words, the elementary process of radiation seems to occur in such a way that it does not scatter the energy of the primary electron in a spherical wave propagating in every direction, as the oscillation theory demands. ”

“ If many such singularities are separated by a distance small with respect to the dimensions of the field of one singular point, their fields will be superimposed, and will form in their totality an oscillating field that is only slightly different from the oscillating field in our present electromagnetic theory of light. ”

“ For the elementary quantum of electricity, Rutherford and Geiger obtained the mean value , Regener , while Planck, using his radiation theory, determined the intermediate value from the constants of the radiation formula.
Planck's theory leads to the following conjecture. If it is really true that a radiative resonator can only assume energy values that are multiples of , the obvious assumption is that the emission and absorption of light occurs only in these energy quantities. ”

“ This experiment demonstrated that matter does not completely carry along its ether but, in general, the ether is moving relative to matter. Now the Earth is a material object, which moves in different directions over the course of a year relative to the solar system. The ether in our laboratories was assumed to not participate in the Earth's motion completely, just as the ether did not participate in the water's motion completely in Fizeau's experiment. ”

“ A radiation of definite composition occupies the interior of a cavity of temperature , and is independent of the cavity's material composition. The cavity contains an energy density for frequencies between and . Finding as a function of and poses a problem. If an electric resonator of eigenfrequency and negligible damping occupies the cavity, the time average of the resonator's energy as a function of can be calculated from the electromagnetic theory of radiation. ”

“ Nevertheless, with respect to this question, I believe that we stand at the beginning of a development of the greatest importance that cannot yet be surveyed. The statements that follow are largely my personal opinion, or the results of considerations that have not yet been checked enough by others. ”

“ We consider a free object at rest that emits the same amount of radiative energy in two opposing directions. In doing so, it remains at rest. Let the object's energy prior to emission be denoted , and its energy after emission and let be the energy of the emitted radiation. By the energy principle, we have
Now consider the object and the same emitted radiation from a reference frame moving with velocity relative to the object. Relativity theory gives us the means of calculating the energy emitted in the new reference frame. ”