Two observers o and o' observe two events a and b. the observers have a constant relative speed of 0.8c. in units such that the speed of light is 1, observer o obtained the following coordinates: event a: x 3,y 3, z 3,1 3 event b: x 5,y 3, 1,15 a) find the length of the space-time interval between these two events, as measured by b) are a and b causally connected? if so why? what is the time difference between a and b as observed in o"?