Is there any way to send instantaneous signals w/o breaking causality?

In Star Wars, they move FTL by accessing hyperspace which is a short-cut of sorts or like a wormhole that allows them to travel very fast without breaking causality as they are technically not in this dimension. FTL signals are also sent through this same dimension (called hyperwave transmissions) yet signals are far faster than FTL ships as they arrive near-instantaneously while even the fastest ships (like the Millennium Falcon) still take hours or days (depending on the system)

Now I just watched a Dr. Ben Miles video on YouTube and he said instantaneous messages would still break causality. I didn’t 100% understand this as instantaneous seemed like the perfect loop-hole for the times Star Wars characters communicate from across the galaxy. Is there any way that signals can be sent that don’t break causality? Miles also introduced me to the Hartman effect which states that the quantum tunneling time is not equal to the depth of a barrier. I wonder if this is part of my answer???

NOTE: I love and appreciate this community but I am not looking to be scolded for trying to use real science to explain fake science magic. I KNOW it’s silly but I like to have my head-canon for these things so I feel better with my suspension of disbelief.

Maximum7 said:

Miles also introduced me to the Hartman effect which states that the quantum tunneling time is not equal to the depth of a barrier. I wonder if this is part of my answer

I have not watched the video but Dr Ben Miles explanation (as reported) makes no sense. The evanescent states in a barrier do not propagate, so to assign a speed somehow is fallacious. End of discussion for me.

Instantaneous communication still breaks causality because the question is instantaneous according to which frame? What one frame of reference calls "instantaneous", other frames of reference call "barely faster than light" and still others call "backwards in time". You can abuse this to construct a paradoxical device that sends a signal if it doesn't receive one at a particular time, then have the signal go back in time so the device did receive a signal so it doesn't send one so it didn't receive one so it does send one so it did receive one so it doesn't send one... Google "tachyonic anti-telephone" for more detail - the Wikipedia page is pretty decent IIRC.

That's the end of the matter in a relativistic universe. The solution is to pick out one frame and promote its definition of instantaneous to be the one all FTL signals use. Some frames still regard this as backwards in time, but they cannot create paradoxes because their definition is not relevant to the FTL signal. That's no longer a relativistic universe because it violates the principle of relativity, which may or may not have consequences, but it resolves the causality problem.

A nice demonstration of principle for FTL, without actually being a usable FTL communicator, would be an ether clock. Or an ether windvane. (Would such devices be useful in themselves, outside the proof value?)

Maximum7 said:

In Star Wars, they move FTL

"...a great disturbance in 'The Force'...."