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Minkowski Terminology

  1. Oct 19, 2006 #1
    Hey friends,

    When using phrases such as time-like and space-like, is it proper form to use the phrase light-like? Or is there a more professional expression?
  2. jcsd
  3. Oct 19, 2006 #2


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    "Space" and "time" are dimensions so it makes sense to talk about "space-like" and "time-like" regions of Minkowski space. Light is not a dimension and so there is no such thing as a "light-like" region. You may be thinking of a "light-path", the path light would follow, which is the boundary between "space-like" and "time-like" regions.
  4. Oct 19, 2006 #3
    What if I said:

    The set of events between event A and event B is timelike.
    The set of events between event A and event C is spacelike.
    The set of events between event A and event D is a light-path.

    Is that the way "it" is said?
  5. Oct 19, 2006 #4
    You can find this expressions in older books , like Tolman's when it comes to describing the metric being >0, <0 and exactly 0.
  6. Oct 19, 2006 #5


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    Timelike, Spacelike, and Lightlike (or Null) are still in common use.
    They are used to describe the nature of the causal relation between a pair of events in spacetime. (Example: Event A is lightlike-related to Event B.) They are also used to describe the sign of the Minkowski square-norm of a 4-vector. A lightlike (or null) vector has square-norm equal to zero, without the vector itself necessarily being the zero vector.
  7. Oct 19, 2006 #6


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    I would personally suggest space-like, time-like, and null. As in "space-like geodesics, time-like geodesics, null geodesics". If you were talking about intervals, it would be space-like intervals, time-like intervals, and null intervals. (I haven't seen "null interval" actually used much, so "light-like" interval might be just as good.)
  8. Oct 19, 2006 #7
    Yeah I always heard it as null.
  9. Oct 20, 2006 #8

    Meir Achuz

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    I think "light-like" is OK to describe an interval on the light cone.
    It is no better or worse that T-L or S-L, and consistent with their usage.
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