Im thinking about writing a science fiction novel with as little ‚fiction‘ as possible and playing in a really, really far future, maybe millions of years, partly because I did not find any story covering this (although duck AI said there are some stories about that, feel free to recommend!). I found one podcast about this thought experiment I have yet to listen to, but nothing else.
So for as little fiction as possible, I need to have a somewhat realistic way of travelling of course. But not only that, communication would take way too long if colonies in different solar systems are lightyears apart.
So I got inspired by the greatest of geniuses Mister Patrick Star („why don’t we just take bikini bottom, and move it somewhere else?“) Now my actual question: would it theoretically be possible to travel with the entire solarsystem? Somehow use the suns energy and bundle it in one direction (but still don’t have the colonised planets get no sunlight) so that we ‚fly‘ to the next solar system, and the distances between us and exoplanets become so small that travelling and communicating between them takes a reasonable time? How would that affect gravity? Would it be possible to calculate and prevent from destroying the gravitational balance of our system or the milkyway?
And further, also move on with the second solar system and start ‚collecting‘ systems? For me, that sounds like the only realistic way to 1. colonise other planets (and not evolve into too different species) and 2. maybe even encounter alien life, maybe if the milkyway and andromeda collide we also will find intelligence.
Yes, you can do this in theory. The very simplest form of the idea I know of isn't even technically that high tech, just very large in terms of manufacturing scale and also very slow (even by slower than light star travel standards).
You've probably heard of the concept of a solar sail, where a spacecraft with a very big, thin reflective foil sail is pushed by the sun. If you design the size and mass of such a spacecraft right, you can make it's outward acceleration when pointed directly away from the sun equal the inward acceleration due to gravity. Add some means to control the orientation of the sail to keep it pointing directly outwards, and it can be made to stay balanced, staying in one spot, not actually in orbit, just hovering.
Say we make a lot of these. We figure out how close to the sun we can hang them without them overheating, and we cover one side of the sun, almost completely, in these sail craft (the actual amount of material, though large, might not be that insane even, if the sails can be thin enough. Not compared to the mass of a star anyway). They don't have to be attached together into a rigid shell, just a big swarm of them whose net effect is to stop most of the light on one half of the sun and reflect it to the other side. We can leave gaps between along the orbital paths of any planets we want to still have light.
The swarm of sails will stay bound to the sun, and the combined sun-sails system now emits light but biased in one direction on average. This makes it basically a form of rocket. It'll be extremely slow to accelerate on account of the extreme mass of the sun compared to the light and such coming off, but in space even a small acceleration adds up over time.
This is called a shkadov thruster. There are other, more complicated but probably faster to accelerate ways you could hypothetically use the sun to move itself, but I'm less familiar with how they work. The wiki page on stellar engines might give you ideas.
This is probably not a great way to go colonize other planets though. The sheer scale of manufacturing capability needed to do this implies enough resources and energy to launch much faster spaceships, and even a spaceship with spinning habitation rings so big or numerous as to fit an entire self sufficient country inside would be much easier to move around than the sun. You could even use the sun to move the ship instead of moving the sun (for example, take that swarm of solar sails, cover the whole sun instead of just one half, and include solar panels to turn a lot of the sunlight into usable energy. Then run big lasers off the sunlight, and point them at another sail attached to the ship, so that it's like a solar sail but with way more light pushing on it than it would normally have).
You could send out probes to do this to other stars and bring them closer to home though, or even hypothetically send out a very long term mission where a probe that can build copies of itself goes to another galaxy and when it gets there, builds copies and sends them to nearby stars, which copy themselves again, until every star in that galaxy has the probes, and then the probes build the mirror swarms and direct all the stars in the new galaxy to fly towards your original one. It'll take them a very long time, millions of years at the very fastest and closest, to get to you, but "running out of materials to the point that you need to harvest entire other galaxies to satisfy your needs" is such a far off problem that that's probably not an issue.