Could you explicitly explain that second question, regarding how we would experience a large scale extinction event from a different timeline?
I'm also curious about this assumption: "It's the assumption that in our world, a machine civilization is an almost certain end"
Let's say machine civilization is an intractable problem, NP complete, requires a million fold difficulty more than the travelling salesman problem - it might not be a good assumption. We are assuming therefore that the compute power will grow enough to solve the required problem. It's also a question too what a machine civilization would look like. Might it decide to just power itself off one day (or accidently?).
The Fermi paradox relies on some assumptions (I'm pulling these from wikipedia):
- Some of these civilizations may have developed interstellar travel, a step that humans are investigating.[12]
- Even at the slow pace of envisioned interstellar travel, the Milky Way galaxy could be completely traversed in a few million years.[13]
- Since many of the Sun-like stars are billions of years older than the Sun, the Earth should have already been visited by extraterrestrial civilizations, or at least their probes.[14]
These assumptions could readily not hold up. Perhaps interstellar travel is actually impossible. Or, it's not feasible. If it takes a million years to travel to the nearest star, let alone one that is inhabited - why do it? We would really have to assume a machine civilization at that point - which leads to another assumption that machines would care and/or be motivated enough to explore.
The last assumption, perhaps Earth was visited by a probe, but just 200 years ago. Even today, we don't detect nearly all asteroids, let alone something that might be relatively small. The assumption that we have not detected a visitation from another species is a pretty big assumption too.