Tuesday, March 28, 2017

special relativity - Why does the minus sign in the Minkowski metric mean that nothing can move backwards in time?


I just watched this video:


http://www.youtube.com/watch?v=GkCWywO93b8#t=27


and there Mr. Cox states that because of the minus sign in the Minkowski metric nothing can move backwards in time. It's the first time I hear this argument and does anyone know how to show this?



To be precise: I'm looking for an explicit computation that shows why the minus sign in the Minkowski metric means that we can't rotate into a frame where $t \rightarrow -t$




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