we go any further, it's important to get a clear idea of what time reversal symmetry really means. At the simplest level, we may think of the laws of physics as equations involving a time variable , and say that they are symmetric under time reversal if given any solution, and making the substitution , we obtain another solution.

http://math.ucr.edu/home/baez/time/time.html

 

What does t (and - t) stand for in physics ?

 

only time ?

You may also mean an affine parameter, which may play the role of "Newtonian" time or simply parametrise a curve or family of objects. Depends on the context.

well, What does - t stand for in physics ?

-t , travel back in time ?

t =0 is "now", t > 0 "future" t < 0 "past".

Fascinating.