**Authors:** Espen Gaarder Haug

This paper discusses the similarities between Einstein’s length contraction and the FitzGerald, Lorentz, and Larmor length contraction. The FitzGerald, Lorentz, and Larmor length contraction was originally derived for only the case of a frame moving relative to the ether frame, and not for two moving frames. When extending the FitzGerald, Lorentz, and Larmor length transformation to any two frames, we will clearly see that it is different than the Einstein length contraction. Under the FitzGerald, Lorentz, and Larmor length transformation we get both length contraction and length expansion, and non-reciprocality, while under Einstein’s special relativity theory we have only length contraction and reciprocality. However, we show that there is a mathematical and logical link between the two methods of measuring length. This paper shows that the Einstein length contraction can be derived from assuming an anisotropic one-way speed of light. Further, we show that that the reciprocality for length contraction under special relativity is an apparent reciprocality due to Einstein-Poincar ́e synchronization. The Einstein length contraction is real in the sense that the predictions are correct when measured with Einstein-Poincar ́e synchronized clocks. Still we will claim that there likely is a deeper and more fundamental reality that is better described with the extended FitzGerald, Lorentz, and Larmor framework, which, in the special case of using Einstein-Poincar ́e synchonized clocks gives Einstein’s length contraction. The extended FitzGerald, Lorentz, and Larmor length contraction is also about length expansion, and it is not recipro- cal between frames. Still, when using Einstein synchronized clocks the length contraction is apparently reciprocal. An enduring, open question concerns whether or not it is possible to measure the one-way speed of light without relying on Einstein-Poincar ́e synchronization or slow clock transportation synchronization, and if the one-way speed of light then is anisotropic or isotropic. Several experiments performed and published claim to have found an anisotropic one-way speed of light. These experiments have been ignored or ridiculed, but in our view they should be repeated and investigated further.

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[v1] 2017-01-05 08:58:59

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