We don't need to look hard. If interstellar travel is possible and someone in our Galaxy have developed it in the past, the whole Solar System including Earth should be already colonized.
We don't need to look hard. If interstellar travel is possible and someone in our Galaxy have developed it in the past, the whole Solar System including Earth should be already colonized.
There are many other answers to why it isn’t outside of “they should have done this but haven’t and therefore cannot exist”.