# Spacetime diagrams.

1. Jul 11, 2007

### jainabhs

Hi
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'??

Abhishek Jain

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2. Jul 11, 2007

### robphy

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.

3. Jul 12, 2007

### morrobay

Hello
I had some problems with that exact diagram, its from:
www.colvir.net/prof/richard.beauchamp/rel-an/rela.htm
I recall pervect stating there is alot of misinformation on relativity on the internet.

4. Jul 12, 2007

### bernhard.rothenstein

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.

5. Jul 12, 2007

### country boy

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.