World Science Scholars
3.1 The Speed of Light
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Jamie Coleshill
I do have one point I would like to make towards this part and the following Office Hours (section 3.2). In both Brian Greene quickly brush over the concept of the Ether (or Aether) and how Einstein showed it wasn't required, this is a mistake most people make when discussing this topic. Below is a list of quotes on the topic from Einstein's May 5th 1920 address at the University of Leidon entitled "Ether and Relativity", you can find the full transcript here https://mathshistory.st-andrews.ac.uk/Extras/Einstein_ether/ and appear in the order in which he states them. One quote found below which I would ask those to ponder is Einstein's belief that all of Space is made up of the Gravitational Ether. "More careful reflection teaches us however, that the special theory of relativity does not compel us to deny ether. We may assume the existence of an ether; only we must give up ascribing a definite state of motion to it" "The special theory of relativity forbids us to assume the ether to consist of particles observable through time, but the hypothesis of ether in itself is not in conflict with the special theory of relativity. Only we must be on our guard against ascribing a state of motion to the ether." "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 the mechanical behaviour of a corporeal system hovering freely in empty space depends not only on relative positions (distances) and relative velocities, but also on its state of rotation, which physically may be taken as a characteristic not appertaining to the system in itself. In order to be able to look upon the rotation of the system, at least formally, as something real, Newton objectivises space." "Mach's idea finds its full development in the ether of the general 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-time, and are partly conditioned by the matter existing outside of the territory under consideration." "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." "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." "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." "Recapitulating, we may say that according to the general theory of relativity space is endowed with 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 time (measuring-rods and clocks), nor therefore any space-time intervals in the physical sense. But this ether may not be thought of as endowed with the quality characteristic of ponderable media, as consisting of parts which may be tracked through time. The idea of motion may not be applied to it."
Roelof Vuurboom
Thanks for posting this link. Indeed, Einstein very much states that an ethereal concept is required however we cannot ascribe any concept of motion to it. The concept of motion has no meaning in space - or in an ether concept - as I already conjectured in my previous reply. Motion is an object based construct.
Roelof Vuurboom
Its not the ether Einstein is objecting against. Its the "stationariness" of the ether.We cannot ascribe either motion or stationariness to the ether.
Tony Lee
Is the speed of light a constant or is it that we always measure it as a constant since any velocity we have as we measure it would affect the clock we are holding to measure it and thus change the V=d/t equation so that the answer is always the same?
Luke Gurbin
Dark matter and dark energy may allow us to see light travel in a medium. This slows the light.
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