From: ram@zedat.fu-berlin.de   
      
   Luigi Fortunati  writes:   
   >The time coordinate is part of the geodesic.   
      
     When I wrote my last post, I thought of a geodesic as being   
     a mere subset of space-time, i.e., a set of events like a   
     line is a set of points, and a mere line has no direction.   
      
     But you may be right that it can be seen as having more   
     structure. Maybe it depends on the details of how a specific   
     textbook defines it. For the book "Gravitation" by Misner   
     et al. it's a "curve". I can't find a formal definition for   
     "curve" in "Gravitation", but it seems to be a continuous   
     mapping from the real numbers into space-time. So it has a   
     natural positive direction.   
      
   [[Mod. note -- You're right, in relativity a curve is a continuous   
   mapping from the real numbers (or a closed interval of real numbers)   
   into spacetime.   
   -- jt]]   
      
   --- SoupGate-Win32 v1.05   
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