Answer to Question #97813 in Mechanics | Relativity for AbdulRehman

Question

Suppose that you and your friend are inertial observers (that is, that both
reference frames are inertial). Suppose that two events, A and B, are
simultaneous in your own reference frame. Draw two spacetime diagrams
in your reference frame. Include your friend’s worldline in both. For the
first, arrange the relative velocity of you and your friend so that event A
occurs before event B in your friend’s reference frame. For the second,
arrange it so that event B occurs first in your friend’s frame. In both
cases, include one of your friend’s lines of simultaneity on the diagram.

Answer 1

Below is the combined spacetime diagram. In the blue frame of reference (moving to the left) event A occurs before event B, because its line of simultaneity crosses time axis below B. In the red frame of reference event B occurs first in the friend’s frame of reference mowing to the right, because B is below A (follow its line of simultaneity). However, both events, A and B, are simultaneous in your own (black) reference frame.