The problem with endless expansion is it requires stability over very long time scales. Sending a probe to another solar system is hardly enough. If you can send a ship say 100 light years from your home planet that’s 2,000+ repetitions of terraforming and colonizing a planet, building up an industrial base, then sending ships to every planet in reach. Under ideal conditions that might take 10,000 years assuming everything went well so you need 20 million years to colonize our galaxy. But, assuming everything goes well for 20 million years and colonization continues to be a priority seems unlikely.
It’s very possible to reach a wall where zero teraformable planets are within reach of your ships. For large civilizations that’s unlikely to totally block expansion, but it might make the path very convoluted thus increasing total time by a rather extreme factor.
It’s very possible to reach a wall where zero teraformable planets are within reach of your ships. For large civilizations that’s unlikely to totally block expansion, but it might make the path very convoluted thus increasing total time by a rather extreme factor.