 Constant light speed 
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Some abreviations used in the text:
3D = ThreeDimensional, (width, depth, heigth), space.
4D = FourDimensional, (width, depth, heigth, time), spacetime.
LET = Lorentz Ether Theory
SR = Einstein Special Relativity
LT = Lorentz Transformations
No 'constant light speed' in 3D ether world.
Only 'constant light speed' in Block Universe.

Some abreviations used in the text:
3D = ThreeDimensional, (width, depth, heigth), space.
4D = FourDimensional, (width, depth, heigth, time), spacetime.
LET = Lorentz Ether Theory
SR = Einstein Special Relativity
LT = Lorentz Transformations
No 'constant light speed' in 3D ether world.
Only 'constant light speed' in Block Universe.

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Say you have a Red and Green 'observer'; Mr Green and Mr Red. Their relative speed is 0,5c. A light beam sets off when Mr Green and Mr Red pass each other. Speed of light = 1 space unit / 1 time unit. I.o.w. for an observer to measure speed of light his proper time units should be equal to his measuring units. (The sketches represent Minkowski diagram's space and time units.) By setting both clocks at 00 when they pass each other, then the coordinates (primed and unprimed) are nothing else than the proper wristwatch time indication and proper measuring stick space (distance) measurements. This simplifies things a lot. Ether Box 1: When Mr Green and Mr Red pass each other Mr Green's clock shows time 00 units. Clock or wristwatch time indication is part of the content of an event and the content of an event is observer independent, absolute. Mr Green's green immobile measuring rod measures 50 units distance to the tree. Mr Red (moving through the ether) has the same type of measuring rod in his hands, but because the rod is contracted (due to the ether) his red rod only measures 43,3 (say 43) units. Of course for Mr Red his red rod is still 50 units long, but due to the ether push the units are all smaller (shorter) relative to the ether, as indicated on sketch 1. Ether Box 2: The lightbeam has arrived at the tree. Mr Green measures light speed: 50 units distance over 50 time units. Mr Red is at the flagpole when the lightbeam arrives at the tree. What is the physically real time indication on the traveler's wristwatch when he is at the flagpole (event R)? (With real physical I mean: the clock and time indication (hands pointing to a number on Mr Red's wristwatch) at the flagpole is an absolute event. Mr Red's wristwatch indication, at the flagpole: 43.3 (say 43) Why? Time dilation due to relative speed 0.5c, means gamma= 1,1547 (time dilation and lenght contraction factor). Or: t' = 43.3 (say 43). In the ether the red time slowed down: physically real red clock time indication 43 compared with the simultaneous physically real green clock time indication 50. How can Mr Red, in the ether context, measure light being at 43 distance in order to measure light speed? You will often read this type of anwser: "The time slows down and the ruler of the moving observer is contracted just enough to make the measurement work." Ever checked that? I did. It doesn't make sense. Mr Red measures light speed in/with/relative to his reference frame (being the contracted measuring rod) moving in the ether. Relative to his reference frame, being his contracted rod, the light has traveled 29 length units in 43 time units. In the ether Mr Red with wristwatch time indication 43 marks off distance 29 on his contracted measuring rod. Mr Red does not measure constant light speed! To solve this problem Lorentz came up with his 'Lorentz Transformations' (LT). Let's check what the LT tell us. (Taylor & Wheeler) In units where c=1 (Time as meter units of light travel time. Equal space and time units means speed of light.) x' = [1/√(1V^2)] (xVt) t' = [1/√(1V^2)] (tVx) V is the relative velocity. Say v= 0,5c , then the relative velocity is V= 0,5 Green (unprimed) coordinates of event A: (50,50) x' = [1/√(1.25)](50.5(50)) = 28.8 (say 29) t' = [1/√(1.25)](50.5(50)) = 28.8 (say 29). Lorentz called this 'local time'. Red (primed) coordinates of event A: (29,29) After LT the green coordinates (50,50) are 'transformed' into red coordinates (29,29). After 29 time units (event Q) Mr Red is 29 spatial units separated from event A (lightbeam at the tree). Let's see what the ether tells us for wristwatch time 29:  <==
In the ether (there are only green ether worlds in the ether theory), when his wristwatch shows 29, his contracted measuring stick will mark off the light beam at 16.7, not 29 as required to measure constant speed of light ! In the ether theory there is no 'physical and experimental evidence' of the mathematical LT result (29,29). Because in the ether no constant light speed is measured.  <==
What is the real physical meaning of the primed coordinates of the LT? Mr Red's primed coordinates (29,29) tell us that Mr Red with wristwatch 29 is at 29 units distance from event A. This makes physically sense only if event 'red clock 29' and event A are physically simultaneous, i.o.w. part of a 3D world existence. That 3D world is not Mr Green's 3D world! In SR Mr Red and his measuring rod are not contracted at all. In Red's 3D space world the 3D landscape (including Mr Green and his measuring rod), is contracted! Mr Green's world is not an ether world (in which lengths contract dynamically in an absolute way due to the ether). There is no ether world at all. Mr Green's 3D world is 'only' a collection of simultaneous events. Mr Red's 3D world is also 'only' a collection of (other) simultaneous events. The different reference frames measure different sections through the 4D spacetime block. The frames are different 3D space/worlds of simultaneous events through 4D spacetime existence. Einstein: << From a "happening" in threedimensional space, physics becomes, as it were, an "existence" in the fourdimensional "world". >> Albert Einstein. "Relativity: The Special and the General Theory." 1916. Appendix II Minkowski's FourDimensional Space ("World") (supplementary to section 17  last section of part 1  Minkowski's FourDimensional Space). << Since there exists in this four dimensional structure [spacetime] no longer any sections which represent "now" objectively, the concepts of happening and becoming are indeed not completely suspended, but yet complicated. It appears therefore more natural to think of physical reality as a four dimensional existence, instead of, as hitherto, the evolution of a three dimensional existence. >> Albert Einstein, "Relativity", 1952. Lorentz invented the Transformations to achieve constant light speed, not because in the ether model constant light speed is measured, but because constant light speed is measured, period. The results of the LT do not make sense in/with an ether, because the fictitious simultaneity of events the moving observer has to use to achieve constant speed of light has no physical meaning. It was Einstein who solved that problem with his Special Relativity: all the LT data are physically real 3D space/world sections though 4D spacetime existence! No ether necessary. Ockam's razor. Lorentz admited his failure. Lorentz knew that the primed coordinates (moving coordinates) didn't make sense in his ether context, and finally admitted: (my bold) << The chief cause of my failure was my clinging to the idea that the variable t only can be considered as the true time and that my local time t' must be regarded as no more than an auxiliary mathematical quantity. In Einstein's theory, on the contrary, t' plays the same part as t; if we want to describe phenomena in terms of x'; y'; z'; t' we must work with these variables exactly as we could do with x; y; z; t. >> Lorentz, H.A (1916), The theory of electrons, Leipzig & Berlin: B.G. Teubner The ether fanatic reading this will still persist and say: "Crackpot! The mathematical result of the LT are identical in ether theory and SR..." They will tell you that the moving observer measures with a mathematical fictitious frame leading to fictitious relativity of simultaneity, leading to fictitious constant speed of light measurement. But why should an observer in the ether use such a fictitious frame if constant speed of light is not an issue in the ether, because in the ether different observers do not measure constant speed of light? Why do some people fanatically want to measure speed of light in the ether? If the ether world would be our correct representation of the world we all live in, then nobody would ever come up with the problem of measuring constant speed of light! Because the different results for time and space for the different observers (moving relative to each other) a so small and unnoticable in our everyday life, people, including scientists, erroneously came up with something like an ether and/of absolute 3D space. But Einstein/Minkowski showed us there is no scientific reason for doing this. They showed us how the LT give constant speed of light because of different 3D space/world cuts through 4D existence. No ether necessary. Ockam's razor rules.  <==
Here I show you Mr Red's 3D world when his wristwatch clock ticks 43. At event R the light is 43 space units separated from him. Hence at the flagpole Mr Red measures constant light speed: 43 space units in 43 time units. In reality when the traveler arrived at the flagpole (event R) with his wristwatch showing 43 the lightbeam is already at the wall! That's the physically true meaning of Einstein's Relativity of Simultaneity.  <==
In ether theory, with only the green ether world existing at event R, the light can never already be at the wall (event B) because for Mr Green the light is only at the wall in a not yet existing future (green) 3D ether space/world! Therefore constant speed of light calculations in the ether context give only fictitious (wrong) results. Instead of accepting that the future event (lightbeam at wall) already exists, which for Mr Green for whatever reason seems totally unacceptable (f.ex. because free will becomes only an illusion) the ether fanatic will be forced to consider simultaneity only a pure fictitious mathematical 'coordinate' concept, not a real physical one. (With 'physical' I do not mean 'absolute' simultaneity, but the physically real existence of the events part of a reference frame at a certain instant of time.)  <==
Here is a Loedel diagram of the same light speed exercise. (In a Loedel diagram the space and time units on all axes have equal lenghts.)  Length contraction. <==
In ether theory the length contraction had a dynamic origin. In SR a kinematic spatiotemporal origin. < Einstein was the first who completely removed the adhoc character from the contraction hypothesis, by demonstrating that this contraction was no dynamical effect in the aether, but rather a kinematic effect due to the change in the notions of space, time and simultaneity brought about by special relativity. > (wikipedia) In Mr Red's physically real 3D world the shorter green measuring stick is made of different events out of the past, present and future of the (immobile) green stick life (i.o.w. a cut or part of the green stick's 4D spacetime existence). In Mr Green's physically real 3D world the shorter red measuring stick is made of different events out of the past, present and future of the (immobile) red stick life (i.o.w. a cut or part of the red stick's 4D spacetime existence). In your world a relative to you 'moving' object (train, or f.ex. measuring stick) is made of events out of past, present and future events of the life of that object. The shorter train is a 3D section through the 4D existence of the train). In order to have a shorter moving train in your 3D world, the past, present and future of that train have all to coexist! The different 3D 'cuts' through 4D Block Spacetime select events out of billions of preexisting 'measuring stick' events in 4D spacetime. 4D 'Block' Spacetime is made of billions of events, all eternally present and located at a specific location. The different time and space coordinates of the LT do not measure time and space distances in 3D ether space, but time and space distances in 4D 'Block' spacetime 'existence'. <==
Here is a Loedel diagram of a red and green masuring sticks (or trains if you prefer), both of equal proper (own 3D space) length, but shortened ('contracted') in different worlds because of spatiotemporal Relativity of Simultaneity. The physically real reciprocity of contraction is only possible if 4D Block Spacetime Universe is a physically real existing entity. This insight gave me the answer to my original curiosity what really happened in SR's reciprocal length contraction (see Start page). Note on 'appearance'. Many authors writing about SR use very ambiguous wording. Sometimes on purpose because they do not know whether the 'Relativity of Simultaneity', the time dilation, space contraction and/or LT coordinates have a physical meaning or only a mathematical one, rather like an optical illusion, with no physical significance in a real 'observer independent' reality. Even I battle to find the correct words and phrasing to be sure the reader will understand what I mean. And I know I often do not succeed. English not being my first language complicates things. When I read that a moving train appears shorter, I doubt that the author understands what SR is all about. If one says that a tree appears shorter you automatically know the tree is not shorter, but only appears shorter due to for example an optical illusion. Which of course has nothing to do with SR. In popular books you often read that a stationary train is x meters long, but the moving train appears shorter. It should read: the stationary train is xmeters long, but the moving train is shorter. In SR it would be meaningless to state that the stationary train 'appears' x meters long. Hence there is no reason to write that the moving train appears shorter. The shorter train is no optical illusion. The moving train in your 3D world is physically shorter in your physically real 3D world than for the train passengers in their physically real 3D worlds. The reciprocal time dilation and length contraction are no optical illusion, nor only different abstract mathematical data measuring one and the same real 3D object. The reciprocal dilation and length contraction is a result of crosscutting 3D worlds through 4D spacetime existence (Block Universe). The reason why most people refuse to accept this is because, as long as you do not understand the physical implications of SR's Relativity of Simultaneity, you can not understand how the train can be really shorter for an observer in the landschape, and the landscape be really shorter for the observer in the train. At first sight it sounds indeed very contradictory, therefore you might think it can only make sense because of an (optical) illusion or mathematical trick. But it sounds only contradictory if you are unable or unwilling to grasp the essence of SR: 4D Spacetime existence (Block Universe)! _________________________________ Here I elaborate on the translation problem.  
