Stars in the Milky Way form a pancake-like disc 120,000 light-years across. In ~80 years our fastest space ships will hurl along around 900,000 kilometres per h

Stars in the Milky Way form a pancake-like disc 120,000 light-years across. In ~80 years our fastest space ships will hurl along around 900,000 kilometres per hour, assuming they can leave orbit. ;-) That makes 144 million years to travel across the galaxy. Now space-faring peoples probably won't have evolved near the disc's edge. So let's say it takes about 100 million years to fan out and colonize most of the galaxy's habitable planets. Our one data point on technologically advanced life indicates 4.5 billion years for it to find a foothold after the dawn of a new solar system. Depending on the values you put into an E.T. calculator[1], there are between 4 and ~200 advanced alien civilizations loitering about. We know of many Sun-like stars that are ten billion years old in the Milky Way, twice as ancient as our star. One hundred million years barely registers on either a 5.5 or a 10 billion year scale. That scale affords aliens an enormous amount of time to have sown their seeds. Hence Fermi's Paradox and hence why a Kessler Cascade setback would be a footnote's footnote on these timescales. In short, a Kessler Cascade is important to avoid, but doesn't resolve Fermi's Paradox (it isn't a Great Filter). [1]: https://www.omnicalculator.com/physics/alien-civilization https://www.omnicalculator.com/physics/alien-civilization P.S. I describe a novel solution for Fermi's Paradox in my hard sci-fi book. Am looking for beta readers; see my profile for contact details.