# Relativity events

1. Sep 17, 2010

### seto6

1. The problem statement, all variables and given/known data

2. Relevant equations
no equations needed b/c its a conceptual question.

3. The attempt at a solution
my attempts..

A) the earliest it can occur and can only be connected by speed of light there t2= 1200/3*108=4*10-6..

B) yes it can because event(E0) occurred 1micro sec before event E1, there E0 could trigger event E1

I'm partly sure I'm correct but i need someone to verify..

2. Sep 17, 2010

### vela

Staff Emeritus
Your reasoning and answer to part A is correct, but it's not consistent with your answer to B. Can you see why? It's not enough that one event occur before another for them to be causally related.

3. Sep 17, 2010

### seto6

what you say is true, but im not sure how to explain if it is or not.. any other hits you can throw at me?

4. Sep 17, 2010

### vela

Staff Emeritus
Think "light cone."

5. Sep 17, 2010

### seto6

light cone ummm.... heard of it but not sure could you expand on it.. is it like with out the past there is no present ...something like that?

6. Sep 17, 2010

### seto6

really having a hard time with this :/

7. Sep 18, 2010

### timon

if event 0 happened (-4000m, -1μs) away from event 1, how fast must information between these events have traveled for event 0 to cause event 1? Is this possible?

8. Sep 18, 2010

### seto6

well if its -4000m away and the fastest it can get to event 1 is like....-4000m/3*108 m/s=-1.33...*10-5= so... event 0 occurred at t=-1μs and the information would take -1.33...*10-5 sec to get to event 1.. so event one would see as if it occurred at -1μs + -1.33...*10-5=-12.3μs..

edit: not getting the concept somewhere....

9. Sep 18, 2010

### seto6

A) if we do -4000/-1μs= 4*10^9 m/s.. which does not make any sence....

B) im confused on the part now....(-4000m,-1μs).... they refer to the part at the instance explosion took place.so.. doing part A would not make any sence ..

10. Sep 18, 2010

### timon

Your calculation in part A) is correct.

For A to cause B some kind of information must be send from A to B.

A-------->------------------------B

Like you calculated, if the information has 1μs to traverse 4000m, it has to move at 4*10^9 m/s.
Which is faster then light. Is it possible for information to move this quickly? If not, what does that mean for the causal relation between A and B?