A physicist arranges to trigger two flashbulbs simultaneously: a blue flash located at the origin of her reference frame and a red flash at a distance x = 100 km in her reference frame. A second physicist, moving a speed v = 0.5c in the direction of increasing x also observes the two flashes. The origins of the two reference frames coincide at t = t′ = 0, i.e. x = x′ = 0 at t = t′ = 0. (a) What time interval between the two flashes will the second observer measure? (b) Which flash does the second observer see happen first?

A physicist arranges to trigger two flashbulbs simultaneously: a blue flash located at the origin of her reference frame and a red flash at a distance x = 100 km in her reference frame. A second physicist, moving a speed v = 0.5c in the direction of increasing x also observes the two flashes. The origins of the two reference frames coincide at t = t′ = 0, i.e. x = x′ = 0 at t = t′ = 0. (a) What time interval between the two flashes will the second observer measure? (b) Which flash does the second observer see happen first?