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"There's also the possibility that the existence of one civilization in a cosmic neighborhood tends to preclude the emergence of other civilizations in that sam

"There's also the possibility that the existence of one civilization in a cosmic neighborhood tends to preclude the emergence of other civilizations in that same neighborhood" Interesting. That's a point I haven't heard before. Or perhaps it's my lucky 10,000 day. :-) Although our path through the galaxy is somewhat unique. Stars don't really move in unison in the greater timescales, but more like slip past each other. Assuming Sol was born as a binary star, its sibling could be other side of the galaxy by now. Another thought is that if WE do expand to the stars, how long until our distant ancestors aren't really the same civilization anymore, but something completely alien to each other? Evolution could take some rather unexpected steps in the long run.

DavidSJ 5y ago
The concept of "cosmic neighborhood" is deliberately left a bit vague in my description, but it definitely doesn't mean the stars that were near the sun when the sun was born. Rather, it refers to those stars which are within reach of us, now, in a timescale that is short relative to the typical interval between births of civilizations that distance apart. That could be anything from a corner of a galaxy to a galactic supercluster, depending on the speed with which civilizations can expand and the frequency with which new ones arise in the universe. Note that if civilizations expand at sufficiently close to the speed of light, then there is only a tiny window of time between when their light arrives and when their colony ships do. So under this model, it is quite unlikely that a new civilization waking up for the first time would look around and see anyone. Most likely, either the light from those other civilizations hasn't yet gotten here, in which case we see nothing, or their colony ships have already gotten here, in which case we wouldn't be born in the first place.

DavidSJ 5y ago

The concept of "cosmic neighborhood" is deliberately left a bit vague in my description, but it definitely doesn't mean the stars that were near the sun when the sun was born. Rather, it refers to those stars which are within reach of us, now, in a timescale that is short relative to the typical interval between births of civilizations that distance apart. That could be anything from a corner of a galaxy to a galactic supercluster, depending on the speed with which civilizations can expand and the frequency with which new ones arise in the universe. Note that if civilizations expand at sufficiently close to the speed of light, then there is only a tiny window of time between when their light arrives and when their colony ships do. So under this model, it is quite unlikely that a new civilization waking up for the first time would look around and see anyone. Most likely, either the light from those other civilizations hasn't yet gotten here, in which case we see nothing, or their colony ships have already gotten here, in which case we wouldn't be born in the first place.