Length contraction is used to explain Michelson–Morley experiment. A Michelson interferometer is formed by 2 perpendicular arms. The journey of light along the vertical arm gives the time dilation law. The journey of light along the horizontal arm gives the length contraction law. The derivation scheme of the length contraction law is:
1. The time of the journey along the horizontal arm is computed using a method that does not give directly the correct time.
2. Length contraction was invented to adjust the computed time.
3. The Michelson–Morley experiment dictates the ratio of length contraction.
But the variation of distance due to time dilation is more appropriate to explain this experiment. We expose a method that gives directly the correct time called Time Dilation Approach which does not need the length contraction assumption and the experimental result. So, these 2 conditions are not necessary for explaining the Michelson–Morley experiment.
Special Relativity cannot work with acceleration because length contraction creates contradiction. But in real world objects accelerate all time, which call for a theory to explain the acceleration of high speed objects.
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PDF: From Michelson–Morley experiment to length contraction https://pengkuanonphysics.blogspot.com/2019/08/from-michelsonmorley-experiment-to.html