As far as I understand, given that there is such a thing called entanglement, we know that there are non-local interactions. The line that this is usually followed with is "since no information travelled faster than light , locality isn't violated". I have a few interrelated questions about this. As far as I know in GR, we demand that all real particles travel through spacetime with tangent vectors which are non-positive. No mention of information, it's a constraint on allowed tangent vectors of particles. We have another assumed condition on "causality" which takes explicitly that two regions in spacetime which can be connected by timeliness or null curves are said to be in causal contact with each other. This also makes no reference to information, but does seem to have a notion that causal interactions do not propagate faster than light. What distinguishes causal interactions from non causal ones? A final question, what is information, and why would it be the measure of what can and cannot travel faster than light?