# Homework Help: Special Relativity, Light cones in Minkowski Diagrams

1. Sep 27, 2009

### king vitamin

1. The problem statement, all variables and given/known data

Show that a point Q outside the "light cone" can occur either before or after a point P inside the light cone (eg: at the origin), depending upon the frame of reference. Show that a point R inside the light cone is always in the future or in the past with respect to P, irrespective of frame S'.

2. Relevant equations
this is just diagrams

3. The attempt at a solution
I know this isn't a difficult problem, but I'm having trouble conceptualizing it because I've never even seen light cones displaced from the origin, let alone in other frames of reference. How does a light cone transform between reference frames? I can't picture it because the x' and ct' axes are no longer orthogonal when drawn over S, so I'm not sure how to represent things.

2. Sep 28, 2009

### tiny-tim

Hi king vitamin!

Forget the shape of the cone …

the question is just asking you to prove that x2 > c2t2, then in some frames t' > 0 but in others t' < 0 (while if x2 < c2t2, then in all frames, t' has the same sign).