Part 1 (1/2)
”Ether and the Theory of Relativity”
by Albert Einstein
University of Leyden, May 05, 1920
HOW does it coside of the idea of ponderable matter, which is derived by abstraction from everyday life, the physicists set the idea of the existence of another kind of ht in those phenoiven rise to the theory of action at a distance, and in the properties of light which have led to the undulatory theory Let us devote a little while to the consideration of these two subjects
Outside of physics we know nothing of action at a distance When we try to connect cause and effect in the experiences which natural objects afford us, it seems at first as if there were no otherthe co or inducing combustion by means of a flame, etc
It is true that even in everyday experience weight, which is in a sense action at a distance, plays a very iht of bodiesnot linked to any cause which is variable in time or place, we do not in everyday life speculate as to the cause of gravity, and therefore do not become conscious of its character as action at a distance It was Newton's theory of gravitation that first assigned a cause for gravity by interpreting it as action at a distance, proceeding froreatest stride ever made in the effort towards the causal nexus of natural phenomena
And yet this theory evoked a lively sense of disco Newton's contemporaries, because it see from the rest of experience, that there can be reciprocal action only through contact, and not through immediate action at a distance
It is only with reluctance that e endures a dualism of this kind Hoas unity to be presented in his co to look upon contact forces as being themselves distant forces which admittedly are observable only at a very small distance -- and this was the road which Newton's followers, ere entirely under the spell of his doctrine,that the Newtonian action at a distance is only apparently immediate action at a distance, but in truth is conveyed by aspace, whether by movements or by elastic deformation of this medium Thus the endeavour toward a unified view of the nature of forces leads to the hypothesis of an ether This hypothesis, to be sure, did not at first bring with it any advance in the theory of gravitation or in physics generally, so that it became customary to treat Newton's law of force as an axiom not further reducible But the ether hypothesis was bound always to play some part in physical science, even if at first only a latent part
When in the first half of the nineteenth century the far-reaching similarity was revealed which subsists between the properties of light and those of elastic waves in ponderable bodies, the ether hypothesis found fresh support It appeared beyond question that light must be interpreted as a vibratory process in an elastic, inertup universal space It also seeht is capable of polarisation that this medium, the ether, must be of the nature of a solid body, because transverse waves are not possible in a fluid, but only in a solid Thus the physicists were bound to arrive at the theory of the ”quasi-rigid” luminiferous ether, the parts of which can carry out no movements relatively to one another except the sht-waves
This theory -- also called the theory of the stationary lu support in an experiment which is also of fundamental importance in the special theory of relativity, the experied to infer that the luminiferous ether does not take part in the movements of bodies The phenoid ether
The develop the path opened up by Maxwell and Lorentz gave the develop the ether quite a peculiar and unexpected turn For Maxwell himself the ether indeed still had properties which were purely h of a much ible solid bodies But neither Maxwell nor his followers succeeded in elaborating a ht furnish a satisfactory mechanical interpretation of Maxwell 's laws of the electro-netic field The laere clear and simple, the mechanical interpretations clumsy and contradictory Almost imperceptibly the theoretical physicists adapted themselves to a situation which, frora They were particularly influenced by the electro-dynaations of Heinrich Hertz For whereas they previously had required of a conclusive theory that it should content itself with the funda densities, velocities, deforradually accustonetic force as fundamental concepts side by side with those ofa mechanical interpretation for theradually abandoned But this change led to a funda-run was insupportable
A way of escape was now sought in the reverse direction, by reducing the principles of mechanics to those of electricity, and this especially as confidence in the strict validity of the equations of Newton's mechanics was shaken by the experiments with beta-rays and rapid kathode rays
This dualism still confronts us in unextenuated form in the theory of Hertz, where matter appears not only as the bearer of velocities, kinetic energy, and netic fields Since such fields also occur in vacuo -- ie in free ether -- the ether also appears as bearer of electrouishable in its functions from ordinary matter Within matter it takes part in the motion of matter and in empty space it has everywhere a velocity; so that the ether has a definitely assigned velocity throughout the whole of space
There is no fundamental difference between Hertz's ether and ponderable matter (which in part subsists in the ether)
The Hertz theory suffered not only fro to matter and ether, on the one hand mechanical states, and on the other hand electrical states, which do not stand in any conceivable relation to each other; it was also at variance with the result of Fizeau 's iht influids, and with other established experis when H A Lorentz entered upon the scene He brought theory into harmony with experience by means of a wonderful simplification of theoretical principles He achieved this, the most important advance in the theory of electricity since Maxwell, by taking fronetic qualities As in empty space, so too in the interior of material bodies, the ether, and not matter viewed atonetic fields According to Lorentz the ele out netic activity is entirely confined to the carrying of electric charges Thus Lorentz succeeded in reducing all electros to Maxwell's equations for free space
As to the mechanical nature of the Lorentzian ether, it may be said of it, in a somewhat playful spirit, that immobility is the only mechanical property of which it has not been deprived by H A Lorentz It e in the conception of the ether which the special theory of relativity brought about, consisted in taking away from the ether its last mechanical quality, namely, its immobility How this is to be understood will forthwith be expounded
The space-time theory and the kinematics of the special theory of relativity were netic field This theory therefore satisfies the conditions of the special theory of relativity, but when viewed from the latter it acquires a novel aspect For if K be a system of co-ordinates relatively to which the Lorentzian ether is at rest, the Maxwell-Lorentz equations are valid permanently with reference to KBut by the special theory of relativity the sa also hold in relation to any new syste in uniform translation relatively to KNow couish the K system above all K' systems, which are physically equivalent to it in all respects, by assu that the ether is at rest relatively to the K system?