Part 1 (2/2)

For the theoretician such an asy asymmetry in the system of experience, is intolerable If we assume the ether to be at rest relatively to K , but in motion relatively to K' , the physical equivalence of K and K' seeht incorrect, but nevertheless inacceptable

The next position which it was possible to take up in face of this state of things appeared to be the following The ether does not exist at all The electronetic fields are not states of a medium, and are not bound down to any bearer, but they are independent realities which are not reducible to anything else, exactly like the atoests itself the netic radiation, like ponderableto the special theory of relativity, both matter and radiation are but special for its isolation and appearing as a special fory

More careful reflection teaches us, however, that the special theory of relativity does not compel us to deny ether We ive up ascribing a definite state of motion to it, ie we must by abstraction take from it the last mechanical characteristic which Lorentz had still left it We shall see later that this point of view, the conceivability of which I shall at once endeavour tocoeneral theory of relativity

Think of waves on the surface of water

Here we can describe two entirely different things Either wethe boundary betater and air alters in the course of time; or else -- with the help of small floats, for instance -- we can observe how the position of the separate particles of water alters in the course of ti the motion of the particles of a fluid were a funda else whatever were observable than the shape of the space occupied by the water as it varies in tiround for the assumption that water consists of movable particles But all the same we could characterise it as a netic field For weof lines of force If ish to interpret these lines of force to ourselves as so material in the ordinary sense, we are tempted to interpret the dynamic processes as motions of these lines of force, such that each separate line of force is tracked through the course of ti the electro we must say this: -- There may be supposed to be extended physical objects to which the idea of ht of as consisting of particles which allow theh time In Minkowski 's idiom this is expressed as follows: -- Not every extended conforarded as composed of world-threads The special theory of relativity forbids us to assuh time, but the hypothesis of ether in itself is not in conflict with the special theory of relativity Only wea state of motion to the ether

Certainly, from the standpoint of the special theory of relativity, the ether hypothesis appears at first to be an enetic field there occur, in addition to the densities of the electric charge, only the intensities of the field The career of electronetic processes in vacuo appears to be completely determined by these equations, uninfluenced by other physical quantities The electronetic fields appear as ultimate, irreducible realities, and at first it seeeneous, isotropic ether-netic fields as states of this ument to be adduced in favour of the ether hypothesis To deny the ether is ultimately to assume that empty space has no physical qualities whatever The fundamental facts of mechanics do not harmonize with this view For thefreely in empty space depends not only on relative positions (distances) and relative velocities, but also on its state of rotation, which physicallyto the system in itself In order to be able to look upon the rotation of the syste real, Newton objectivises space

Since he classes his absolute space together with real things, for hi real Newton ht no less well have called his absolute space ”Ether”; what is essential is , which is not perceptible, must be looked upon as real, to enable acceleration or rotation to be looked upon as so to accept as real so to substitute in mechanics a mean acceleration with reference to the totality of the masses in the universe in place of an acceleration with reference to absolute space But inertial resistance opposed to relative acceleration of distant masses presupposes action at a distance; and as the modern physicist does not believe that he may accept this action at a distance, he comes back once more, if he follows Mach, to the ether, which has to serve as medium for the effects of inertia But this conception of the ether to which we are led by Mach's way of thinking differs essentially from the ether as conceived by Newton, by Fresnel, and by Lorentz Mach's ether not only conditions the behaviour of inert masses, but is also conditioned in its state by them

Mach's idea finds its full developeneral theory of relativity

According to this theory the metrical qualities of the continuum of space-time differ in the environment of different points of space-ti outside of the territory under consideration This space-time variability of the reciprocal relations of the standards of space and tinition of the fact that eeneous nor isotropic coravitation potentials gmn), has, I think, finally disposed of the view that space is physically eain acquired an intelligible content, although this content differs widely froht The ether of the general theory of relativity is a medium which is itself devoid of all mechanical and kinematical qualities, but helps to deternetic) events

What is fundaeneral theory of relativity as opposed to the ether of Lorentz consists in this, that the state of the former is at every place determined by connections with theplaces, which are amenable to law in the form of differential equations; whereas the state of the Lorentzian ether in the absence of electro outside itself, and is everywhere the saeneral theory of relativity is transmuted conceptually into the ether of Lorentz if we substitute constants for the functions of space which describe the for the causes which condition its state Thus we eneral theory of relativity is the outcoh relativation

As to the part which the new ether is to play in the physics of the future We are not yet clear We know that it determines thethe configurative possibilities of solid bodies as well as the gravitational fields; but we do not knohether it has an essential share in the structure of the electrical ele matter Nor do we knohether it is only in the proximity of ponderable masses that its structure differs essentially froeometry of spaces of cosmic extent is approximately Euclidean But we can assert by reason of the relativistic equations of gravitation that there must be a departure fronitude, if there exists a positive mean density, no matter how small, of the matter in the universe

In this case the universe nitude, itsdetermined by the value of that ravitational field and the electronetic field from the standpoint of the ether hypothesis, we find a remarkable difference between the two There can be no space nor any part of space without gravitational potentials; for these confer upon space its ined at all The existence of the gravitational field is inseparably bound up with the existence of space On the other hand a part of space netic field; thus in contrast with the gravitational field, the electronetic field seems to be only secondarily linked to the ether, the for as yet in no way deterravitational ether Fronetic field, as opposed to the gravitational field, rests upon an entirely new forht just as well have endowed the gravitational ether with fields of quite another type, for example, with fields of a scalar potential, instead of fields of the electro to our present conceptions the elementary particles ofelse than condensations of the electronetic field, our present view of the universe presents two realities which are coh connected causally, nanetic field, or -- as they ht also be called -- space and reat advance if we could succeed in conetic field together as one unified conformation

Then for the first time the epoch of theoretical physics founded by Faraday and Maxould reach a satisfactory conclusion The contrast between ether and eneral theory of relativity, the whole of physics would becoeoly ingenious attempt in this direction has been made by the mathematician H Weyl; but I do not believe that his theory will hold its ground in relation to reality

Further, in conteht not unconditionally to reject the possibility that the facts comprised in the quantum theory may set bounds to the field theory beyond which it cannot pass

Recapitulating, we eneral theory of relativity space is endoith physical qualities; in this sense, therefore, there exists an ether

According to the general theory of relativity space without ether is unthinkable; for in such space there not only would be no propagation of light, but also no possibility of existence for standards of space and ti-rods and clocks), nor therefore any space-time intervals in the physical sense But this ether ht of as endoith the quality characteristic of ponderable h time

The End