If both points are moving through space (and they would be), it would probably be very fast relative motion in an arbitrary non-shared direction. Wouldn't that

If both points are moving through space (and they would be), it would probably be very fast relative motion in an arbitrary non-shared direction. Wouldn't that also change the dynamics of local time for both parties in the communication? Instant communications doesn't mean much when the time flow isn't the same for both parties. It could create a paradox where an entire conversation has happened for one party before it even began for the other. Once I considered that, I considered all such communications moot. I don't know how far one has to go before time dilation would be that extreme, but stars are really far apart from each other. The information might be instant, but the concept of "instant" to each party locally won't be in sync anymore. Even between our Sun and its closest stellar neighbour I don't think it would be possible to sync because of that constantly changing dilation. If we can manage it, we'd have a delay like we do with everything else, but it would be a whole lot shorter. And that is entirely connected to how fast and how far (dilated in time) you are moving.