Bob is moving to the right (positive x direction) in his spaceship at a velocity v, and Alice is observing him. Each has their own lattice of clocks and measuring systems, which can be represented in two spacetime diagrams, one for Bob’s frame of reference and one for Alice’s. True or false: Bob’s world line is the line of same location given by xB = 0, whether it’s drawn on Alice’s spacetime diagram or Bob’s spacetime diagram.

6.Question 6Consider a spacetime diagram for Alice’s frame of reference (so Alice is positioned at x = 0) where x is in units of light years and t is in units of years. At t = 0 Alice plans to have a party. Consider the spacetime points listed below. If Bob was located at the point, and he had a spaceship that could travel at any speed up to the speed of light, would he be able to get to the party in time? (Mark all that are possible for him to get to the party in time.)1 pointx = 23, t = -17x = 3, t = 9x = 0, t = -3x = 17, t = -23

9.Question 9In the twin paradox example done in lecture, just after Alice leaves the star on her return trip (and she's back up to her cruising speed of 0.6c), she observes Bob's clock back where he is located. (In other words, she has a photo taken of his clock and her corresponding clock at that location, her clock being part of her lattice of clocks.) Compared to her clock, does she observe Bob's clock to be behind, ahead, or the same time as hers?1 pointBob's clock is behind her clock.Bob's clock is ahead of her clock.Bob's clock has the same time as her clock.

Question 3Consider the twin paradox example done in lecture: On Alice's outbound trip to the star, Bob observes Alice's clocks running slower than his clocks. What does Alice observe regarding Bob's clocks?

1.Question 1On a spacetime diagram with time in years and x in light years, what is the slope of a world line of a faster-than-light object that is moving to the right (positive x direction)?1 pointThe slope is greater than 1 (greater than 45 degrees)The slope is less than 1 (less than 45 degrees)The slope equals 1 (45 degrees)

7.Question 7In the twin paradox example done in lecture, it seems that Alice's and Bob's situations should be parallel or symmetric to each other. That is, Bob observes Alice travel to the star and back, but from Alice's frame of reference, it is Bob that travels away (in the opposite direction) and returns. Why aren't their situations symmetrical?1 pointActually, there is no difference between their two situations--it's why it is called a paradox. Bob undergoes acceleration, but in the opposite direction to Alice, thus causing the asymmetry which leads to the time difference.Only Alice undergoes acceleration (and deceleration), leading to a change in her frame of reference.