&gt; <i>may be tens of thousands of years - absolutely not enough to have overlaps between tech civilizations to listen&#x2F;watch radio&#x2F;TV of each other</i><p>From what we know, that is a reasonable assumption.<p>&gt; <i>Space expansion is different machinery and not subject to &quot;c&quot; limit (that limit is only valid against static space)</i><p>The expansion of the universe and rapidly-increasing distance to far galaxies is not a good example, but yes, the &quot;limit&quot; of c is only applicable to static space. And you are right in the sense that the Hubble flow is an example of objects changing their relative positions without momentum being the primary component.<p>As I like to frame it: in day-to-day life we are used to define &quot;travel&quot; as accelerating matter to a certain velocity until we reach a destination point. However, acceleration is not the goal of travel: being at the destination point itself is the goal. For example, travel through an artificially shortened corridor of spacetime would still be a valid form of FTL even though acceleration itself never reached relativistically relevant levels.