A true dyson sphere is likely not physically possible. But superstructures that do the same thing, namely dyson swarms or dyson bubbles, are not particularly ha

A true dyson sphere is likely not physically possible. But superstructures that do the same thing, namely dyson swarms or dyson bubbles, are not particularly hard. If we so desired, we could begin construction of such a megastructure right now. At our current industrial capacity it would take a long time, but hopefully our civilization has a lot of time and industrial capacity ahead of it. Further, such dyson structures begin providing useful results pretty much immediately - it really only makes sense for a civilization to keep building up more and energy collectors over time. Interstellar travel, beyond small probes to the very nearest stars, is immensely difficult. Either you need propulsion systems that can go incredibly fast like say riding the blast waves of a bunch of nuclear explosions or colliding antimatter that somehow you have; or you need to build things that can survive for extremely long periods (like substantially longer than our civilization has existed) in an extremely harsh environment with no resources for support. Either are hard challenges that require substantial work across many disciplines, and those who devote their lives to carrying out the work will not live* to reap the rewards. And even if a civilization were to put in all that effort, there simply isn't much reward to reap. Certainly if a civilization was sufficiently long lived and advanced they would eventually do this just to say they could, the same way we would climb Everest just because it's there, but there's no way anyone's setting up an interstellar empire before their system's dyson swarm is well under way. * It is likely that extreme life extension will eventually be developed in one form or another, which should both make decades or centuries long projects much more viable, as well as make longer voyage times more acceptable. But developing such extreme life extension technology is probably comparable in difficulty to the engineering issues of interstellar travel.