Saw this article on Giant Freakin Robot:
Scientists Say Interstellar Travel Could Be Possible Without Spaceships
https://www.giantfreakinrobot.com/sci/in...ships.html
And basically the premise is that humans would hop on a rogue planet as it travels through (or maybe near) the Solar System, colonizing it as it travels away, and then eventually hopping from it to a planet in another star system.
This would be a very forward-thinking strategy for spreading to the stars. But it also opens up a lot of questions.
For example, how would these rogue planet colonists survive? They'd need energy, not just for their personal needs but to grow food and sufficient plant-life to generate an oxygen-rich atmosphere.
Theoretically they could tap the planet itself for heat to generate electricity. But they might need to create an artificial sun (that orbits the rogue planet) to cast light on its surface. Short of using nuclear materials to generate a lot of light, I don't see how they could power an artificial sun (or how they could do it for very long).
Still, it's an interesting idea and maybe what would work would be to scale it down. Instead of jumping on to rogue planets humans could colonize rogue asteroids, assuming they pass through the Solar System. They could be hollowed out and converted to galaxy-roaming habitats. But they'd still need abundant supplies of air, water, and energy.