September 5, 2015
In 1916, A. Einstein published his book titled “Relativity: The Special and General Theory.” In this book, Einstein introduced his method for recognizing the simultaneity of two lightning strikes; this method involved two mirrors inclined at 90° to reflect the flash of the lightning strikes. Using this method, Einstein considered the perspectives of both an observer at rest on a railway embankment and an observer in a running train. He subsequently found that the former could recognize that the two lightning strikes were simultaneous, but the latter could not. This result is correct, but it holds true only as a hypothetical judgment that necessitates the phrase “if we use mirrors inclined at 90° in order to observe the simultaneity of the two lightning strikes.” Because, there exist other methods that can be used for the same purpose.