Any method of sending information that has to account for the freaky rules of Einstein's relativity, where the order of events can be subjective and nothing can outrace light. It's not about FTL; it's about dealing with the mind-bending fact that due to time dilation and the relativity of simultaneity, "now" for you isn't "now" for someone moving at a different speed. This makes syncing up conversations across interstellar distances or near light-speed ships a total headache.
*Example: You're on a generation ship cruising at 90% light speed to Alpha Centauri. You send a video message back to Earth. For you, the trip takes a few years. But due to time dilation, decades pass on Earth before they receive it. Their reply takes decades to catch up to your moving ship. You might be dead by the time you get a response. The entire conversation is less a chat and more like sending cosmic voicemails into a time-warped void. GPS satellites already do baby versions of this, correcting their clocks for relativistic effects so your "Turn left" command isn't based on a skewed time signal.* It's relativistic communication.
by Abzugal January 24, 2026
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