Risa

I'll help out. Here you go: https://www.askamathematician.com/2012/07/q-how-does-instantaneous-communication-violate-causality/

I love it when sci-fi teaches us about real stuff. The problem is that when you mix instant and classical (non-instant) communication channels, you get situations where information time-travels, and the receiver gets information from the future. This breaks causality (present based on future events), and so nature rightfully abhors it.

The closest we've come to instant communication is the use of entangled particles, but we can't make practical use of the phenomenon. Touch one such particle, and it's pair instantly changes to the opposite state. The catch is that you can't know when to observe the particle, nor can you know what the original state was, via the same mechanism. So you still need to use normal photons moving at slow-ass light-speed to communicate that meta-information, thereby undoing any attempt to exploit it.