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Does anyone have any ideas about this scenario? I'm having trouble comparing what happens at the different speeds. It has to do with simultaneity

Suppose Al is at rest standing in between two sets of railroad tracks. Bob goes by in one direction at a speed u, as measured by Al, and Carl goes by on the other tracks going in the opposite direction at the same speed. Al, Bob, and Carl all have meter sticks and whatever other instruments needed to compare their length.

Suppose that u = 1/1000 c (one thousandth of the speed of light). Approximately how fast is Bob going according to Carl?

Suppose that u = 9/10 c. What does Al say about Bob's and Carl's meter sticks? What does Bob say regarding Al's and Carl's meter sticks? How are these two different accounts compatible?

Suppose Einstein's theory of relativity is true. Now consider what happens if light moves with infinite speed rather than the speed c. In particular, explain what would then be true regarding the relativistic effects we have considered in class -- length contraction, time dilation, and the relativity of simultaneity.

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What are your thoughts so far? Can you elaborate on what exactly you're having trouble comparing? This sort of question where you just post your homework problem and ask for ideas is not appropriate for this site (i.e. we're not going to just answer the question for you), but if you can focus in on what exactly is giving you trouble, it could definitely be a good question. – David Zaslavsky♦ Feb 7 '12 at 2:41
my thoughts are that Bob is traveling at a speed 2u according to Carl. Al says Bob's and Carl's meter sticks are shorter than 1 meter. I'm not sure what Bob would say about Al's stick and Carl's stick. I am also unclear on what happens if light moved with infinite speed. Are my thoughts correct? – theDazzler Feb 7 '12 at 2:49
OK, that's a start. Three things to consider: (1) 2u is not correct for the speed, (2) why are you not sure what Bob would say about Al's and Carl's meter sticks? (3) try taking $c\to\infty$ in the formulas for length contraction and time dilation and see what you get. – David Zaslavsky♦ Feb 7 '12 at 2:58

closed as too localized by David Zaslavsky♦ Feb 7 '12 at 2:43

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