Re: [Phys-l] The "why" questions

[John Denker <jsd@av8n.com>]

On 12/04/2010 10:55 AM, chuck britton wrote:
> but relativity tells us that two separate locations can't agree on 
> simultaneous events.
> nicht wahr?

No, that's not what relativity says.  Also simultaneity and causality
are two very different questions.

Relativity says that if if A is in the forward light-cone of B, all
observers will agree that this is so.  This is important if you think
B might be a cause of A.

The same holds in reverse if B is in the forward light-cond of A.

Alternatively, if A and B are spacelike separated, all observers will
agree that this is so.  This is sufficient to ensure that neither A
nor B can cause the other.

  Questions about simultaneity are amusing but not necessary for answering
  questions about causality.  Simultaneity is observer-dependent but not
  important to the physics.  The physics doesn't care which (if any) 
  observers are watching the action.

In summary:  The qualitative relationships that are relevant to causality 
are Lorentz-invariant.