It's usually the explorers who do the detection and contact, while the lesser civilization simply acknowledges their presence. I don't think physics is a roadb

It's usually the explorers who do the detection and contact, while the lesser civilization simply acknowledges their presence. I don't think physics is a roadblock for space exploration at this point. We just need to figure out asteroid mining and building in space, after that we can send robots driven by AI to other systems, at low speeds. Once they reach other systems they would refuel, build more robots and carry on. It's a massive engineering challange, but it's quite predictable within a few thousand years (if we don't destroy ourselves by then).