Abstract

Einstein's principle of relativity is an important fundamental of relativity. It can also be said that relativity is based on the assumption of the principle of relativity. This assumption can be represented by a diagram of "relativity of time interval", as shown in Fig.  a . According to the theory of relativity, a flash emits from the light source in the moving car and returns to the light source after being reflected by the mirror on the roof. The person in the train thinks that the flash returns to the light source along a vertical line, and the person off the train thinks that the flash returns to the light source along the AMB  curve. The time taken in the two routes is inconsistent. In fact, it is a preconception. Einstein believes that the flash will undoubtedly return to the light source, which is a matter of course and need not be discussed. Therefore, he did not think more and immediately carried out the next research on the time taken inside and outside the train. Here's where the problem arose. Is there an experimental evidence? If the flash does return to the light source, then the next analysis carried out by Einstein is correct and impeccable. However, if the flash does not return to the light source, then Einstein's next analysis and the whole theory of relativity make no sense.

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