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Spacetime diagrams.

  1. Jul 11, 2007 #1
    I have some very basic doubts on spacetime diagrams.
    Please refer the figure attached.
    Here in this spacetime figure an event E is shown as observed from K and K'.
    K' moves with v with respect to K.
    The axis CT is tilted angle alpha following vt, so that any event that occurs at x' = 0 in K' would occur at x = vt in K.
    For frame K, to find space coordinate of the event, draw a perpendicular to x-axis.

    But to find time coordinate draw a perpendicular to CT. why??
    I dont get this and moreover the length of perpendicular gives x'??
    Please explain

    Abhishek Jain

    Attached Files:

  2. jcsd
  3. Jul 11, 2007 #2


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    On a Minkowski-spacetime diagram, you should be drawing Minkowski-perpendiculars... not Euclidean-perpendiculars. Minkowski-perpendiculars to radii are tangents to hyperbolae, just as Euclidean-perpendiculars to radii are tangents to circles.
  4. Jul 12, 2007 #3


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  5. Jul 12, 2007 #4
    space-time diagrams

    I only mention that different space-time diagrams we find in the literature define i the same way the space-time diagrams of the involved events. As I learned from a teacher of mine: There is no advantage without disadvantage. See please for instance a book by Shadowitz devoted to the subject.
  6. Jul 12, 2007 #5
    I agree that the problem seems to be with this particular diagram. Can you construct a Minkowski diagram in the usual way, with a 45-degree diagonal representing a light path? Then a moving reference frame is drawn with x' and ct' axes at equal angles from the diagonal and on opposite sides of it. Just as lines of constant t are parallel to x, lines of constant t' are parallel to x' (and not perpendicular to each other). Likewise, constant x' lines are parallel to t'.

    I know this is elementary, but it's worth going through the exercise to see if it clears up your doubts.
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