# The nature of causality in special relativity (not faster than light travel)

I am having trouble understanding how special relativity reconciles the concept of causality. In one frame of reference event A may be followed by event B, but in another frame of reference event B may occur before event A. In the first frame of reference an observer may claim that event A causes event B, but of course the second frame of reference will disagree. I am sure i am making a simple mistake here...

Furthermore, how does special relativity deal with the concept of a big bang singularity? I am aware that general relativity is the domain of acceleration (thus inflation), but is it not possible for there to be a preferred frame of reference with respect to some big bang singularity qualifier? (I am aware that this is vague, but the fact that the universe was once a singularity troubles me with respect to the "no frame of reference preferred" result of special relativity).

PAllen
When the order of two events is frame dependent, that implies they cannot be be causally connected. The fallacy of you statement is saying A caused B, or the reverse.

A little more: such frame dependent order of events only occurs for events with spacelike separation, which means that neither can cause the other - they are said to be causally independent.

As for the big bang, I am guessing you are picturing the big bang as occurring in some 'place' in a pre-existing space. This is not correct. Space itself expanded from the big bang. However, there is a sense that the big bang provides a preferred frame. Not in the sense of 'you must use it', nor in the sense that the laws of physics are simpler; but in the sense that you can locally detect your motion relative to the cosmic background radiation. If you see it as isotropic, you are a 'comoving' observer, moving with the expanding space without any extra motion.

When the order of two events is frame dependent, that implies they cannot be be causally connected. The fallacy of you statement is saying A caused B, or the reverse.

A little more: such frame dependent order of events only occurs for events with spacelike separation, which means that neither can cause the other - they are said to be causally independent.

As for the big bang, I am guessing you are picturing the big bang as occurring in some 'place' in a pre-existing space. This is not correct. Space itself expanded from the big bang. However, there is a sense that the big bang provides a preferred frame. Not in the sense of 'you must use it', nor in the sense that the laws of physics are simpler; but in the sense that you can locally detect your motion relative to the cosmic background radiation. If you see it as isotropic, you are a 'comoving' observer, moving with the expanding space without any extra motion.

Thanks, i realise my mistake now! That was quite silly.