Through what medium does EM propagate in empty space?

[turbo]

For those that have not read Einstein's Leyden address:

According to this theory the metrical qualities of the continuum of space-time differ in the environment of different points of space-time, and are partly conditioned by the matter existing outside of the territory under consideration. This space-time variability of the reciprocal relations of the standards of space and time, or, perhaps, the recognition of the fact that empty space in its physical relation is neither homogeneous nor isotropic compelling us to describe its state by ten functions (the gravitation potentials gmn), has, I think, finally disposed of the view that space is physically empty. But therewith the conception of the ether has again acquired an intelligible content, although this content differs widely from that of the ether of the mechanical undulatory theory of light. The ether of the general theory of relativity is a medium which is itself devoid of all mechanical and kinematical qualities, but helps to determine mechanical (and electromagnetic) events.

What is fundamentally new in the ether of the general 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 the matter and the state of the ether in neighbouring places, which are amenable to law in the form of differential equations; whereas the state of the Lorentzian ether in the absence of electromagnetic fields is conditioned by nothing outside itself, and is everywhere the same. The ether of the general theory of relativity is transmuted conceptually into the ether of Lorentz if we substitute constants for the functions of space which describe the former, disregarding the causes which condition its state. Thus we may also say, I think, that the ether of the general theory of relativity is the outcome of the Lorentzian ether, through 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 the metrical relations in the space-time continuum, e.g. the configurative possibilities of solid bodies as well as the gravitational fields; but we do not know whether it has an essential share in the structure of the electrical elementary particles constituting matter. Nor do we know whether it is only in the proximity of ponderable masses that its structure differs essentially from that of the Lorentzian ether; whether the geometry 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 from Euclidean relations, with spaces of cosmic order of magnitude, if there exists a positive mean density, no matter how small, of the matter in the universe. In this case the universe must of necessity be spatially unbounded and of finite magnitude, its magnitude being determined by the value of that mean density.

If we consider the gravitational field and the electromagnetic 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 metrical qualities, without which it cannot be imagined 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 may very well be imagined without an electromagnetic field; thus in contrast with the gravitational field, the electromagnetic field seems to be only secondarily linked to the ether, the formal nature of the electromagnetic field being as yet in no way determined by that of gravitational ether. From the present state of theory it looks as if the electromagnetic field, as opposed to the gravitational field, rests upon an entirely new formal motif, as though nature might 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 electromagnetic type.

Since according to our present conceptions the elementary particles of matter are also, in their essence, nothing else than condensations of the electromagnetic field, our present view of the universe presents two realities which are completely separated from each other conceptually, although connected causally, namely, gravitational ether and electromagnetic field, or -- as they might also be called -- space and matter.

Of course it would be a great advance if we could succeed in comprehending the gravitational field and the electromagnetic field together as one unified conformation.

Then for the first time the epoch of theoretical physics founded by Faraday and Maxwell would reach a satisfactory conclusion. The contrast between ether and matter would fade away, and, through the general theory of relativity, the whole of physics would become a complete system of thought, like geometry, kinematics, and the theory of gravitation.

Einstein did not kill off the ether with his theories of relativity, but he did constrain its nature and demonstrate the necessity of its existence as a REAL entity.

 

[samalkhaiat]

MOST physics students can formulate Maxwell equations with no reference to the SOLID-ELASTIC ether of the 19th century. Because she/he knows that Einstein's SR abolished the need for such concept. He/she can also solve Maxwell equations in empty space and find that such solution is nothing but EM-field propagating in vacuum with the finite speed C. Now he/she recall that their physics school teacher once told them that E & H are perpendicular to each other and the oscillation of one causes the other to oscillate and the whole thing propagate in the K-direction. However, they are mature students now, so their conclusion about Maxwell vacuum solution IS; "IT MEANS THAT THE EM-FIELD ITSELF ACQUIRES PHYSICALREALITY". i.e such object is as real as Newton's material particle. Except for ancient thinker, nobody questioned the motion of material particle in vacuum in the absence of forces.So your question,in my opinion, is reducible EITHER to the phylosofical question; "why motion is possible?" (I do not want to speculate), OR you are actually asking about the structure of spacetime itself, But this belongs to Quantum Gravity! not to Maxwell or Einstein theories.
It is no accident that the excellent book of Landau & Lif****z (The classical theory of fields) never mentioned the word ETHER.

regards

 

[turbo]

The *propagation* through a medium nevertheless plays an essential role, but indeed at a level lower at which we can assume that unification has occurred. We need something to communicate the phases for our subsets of the vacuum in order to achieve synchronization. This has to be a level lower since it communicates phase *between* the constituents of what we have called “the medium” until now.

This finally would then be what bestows the limit of c upon us. Physical
wave-packets can not move faster then c because the synchronization
mechanism falters beyond it.

Regards, Hans

Thank you, Hans for your detailed posting. I do not have time to address all your points right now and relate them to my model of space-time, but rest assured that I will try to address them.

Note: This thread has been moved again (likely to allow the SR/GR crowd to bash it for a while ) and I want to thank the person(s) who decided to move it. Hopefully, the Cosmology and Quantum folks who have contributed will follow and consider the comments of the SR/GR crowd. The fresh exposure will likely bring some interesting insights from another audience, and we (and I personally) could benefit from a whole lot more of that.

 

[Janus]

This thread has gone nowhere fast.