8. In a gedanken experiment (▼ Figure 26.17), two events that cannot be related by cause and effect occur in the same inertial reference frame O: (1) strobe light A, at the origin of the x-axis, flashes; (2) strobe light B, located at x = +600 m, flashes 1.00 μs later.

B’s flash cannot be caused by A’s flash. (The fastest signal, light, would travel only 300 m between the event locations in the time between the two events.)

(a) Use qualitative arguments to show that there exists another inertial reference frame, traveling at a speed less than

c, in which these two events would be observed to occur simultaneously.

(b) What is the direction of the velocity of the reference frame in part

(a)? (Note: This question shows that relativity does not have to preserve the time order of events if they are not related by cause and effect. Since one event cannot cause the other, no physical principles are violated if they are seen in reverse order.)