Is dt/ds always positive in General Relativity?

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deadringer
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Is it always true that dt/ds is always positive, where t is the coordinate time and s is the proper time? I suspect his is the case, but am not sure why.
 

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No, it's not true. dt^2-dx^2=ds^2. You can reverse coordinate time freely t->-t. After all, it's just a coordinate.
 

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