Can Event A Cause Event B in Relativity?

[seto6]

Homework Statement

Homework Equations

no equations needed b/c its a conceptual question.

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..

thanks in advance!

 

[vela]

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.

 

[seto6]

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

 

[vela]

Think "light cone."

 

[seto6]

light cone ummm... heard of it but not sure could you expand on it.. is it like without the past there is no present ...something like that?

 

[seto6]

really having a hard time with this :/

 

[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?

 

[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...

 

[seto6]

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

B) I am 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 sense ..

 

[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?