4-2. This problem is to give you some practice putting everything together. Once again, we and our friends, Alice and Bob, are inertial observers who all meet at a single event. At this event, our clock, Alice's clock, and Bob's clock all read zero and a firecracker explodes. Alice moves to our right at c/2 and Bob moves to our left at c/2.
Draw a single spacetime diagram in our reference frame showing all of the following:
(a) Alice, Bob, and the outgoing light from the explosion. (b) The curve representing all events that are a proper time of one second to the future of the explosion. Also draw in the curves representing the events that are: i) one second of proper time to the past of the explosion, ii) one light-second of proper distance to the left of the explosion, and iii) one light-second of proper distance to the right of the explosion. (c) The events A, U, and B where Alice's clock reads one second, where our clock reads one second, and where Bob's clock reads one second.
(d) Finally, suppose that we (but not Alice or Bob) are holding the middle of a stick that is two light-seconds long (and which is at rest relative to us). Draw in the worldlines of both ends of that stick. Also mark the events X and Y occupied by the ends of that stick on the line t = 0.