The biggest science “fiction” in my sci-fi worldbuilding is that, in the ancient past, someone infused the galaxy with a particular quantum entanglement that allows ships to reach high relativistic speeds without either the increasing mass problems or as much danger from radiation and impacts.

This artificial field is generally referred to as “The Medium” and the technology used to connect to and take advantage of The Medium is called the “Lupole Drive”.

No civilization is old enough to remember who set up The Medium, but it is definitely artificial and also allows long distance communication.

It does NOT allow faster than light travel. It does allow ships with powerful computation ability — capable of dealing with the strange relativistic sensor distortions at those speeds — to get very close to light speed.

Communication via The Medium travels at light speed, and is not blocked by mass or dust.