It has always seemed arrogant to think that aliens exist anywhere within our galaxy. Look at how many galaxies are out there. Now realize that the universe extends far beyond our Hubble sphere. We can’t hope to colonize even a fraction of 1% of our galaxy, even with wildly futuristic technology. There is one option, though: Become our own aliens. If we set up colonies separated by time and distance, we will culturall…
Von Neumann probes could probably colonize a good chunk of the Milky Way given a few hundred thousand years.
Life on Earth consists of Von Neumann machines. That's exactly what life is. Yet our life has not converted the entire mass of Earth into itself, and there's still plenty of places where you can't easily find signs of life. And our life has had billions of years. The assumption that Von Neumanns will very cleanly and exponentially increase in number until they are all over the galaxy is too ideal.