Causality moves at c, so if we have probes moving away from each other at nearly 2c, that suggests extinction risk could be permanently reduced to zero.
This isn’t right. Near-speed-of-light movement in opposite directions doesn’t add up to above speed of light relative movement. e.g., Two probes each moving away from a common starting point at 0.7c have a speed relative to each other of about 0.94c, not 1.4c, so they stay in each other’s lightcone.
(That’s standard special relativity. I asked o3 how that changes with cosmic expansion and it claims that, given our current understanding of cosmic expansion, they will leave each other’s lightcone after about 20 billion years.)
Right, so even with near-c von Neumann probes in all directions, vacuum collapse or some other galactic x-risk moving at c would only allow civilization to survive as a thin spherical shell of space on a perpetually migrating wave front around the extinction zone that would quickly eat up the center of the colonized volume.
Such a civilization could still contain many planets and stars if they can get a decent head start before a galactic x-risk occurs + travel at near c without getting slowed down much by having to make stops to produce and accelerate more von Neumann probes. Yeah, that’s a lot of if’s.
20 billion ly estimate seems accurate, so cosmic expansion only protects against galactic x-risks on very long timescales. And without very robust governance it’s doubtful we might not get to that point.
This isn’t right. Near-speed-of-light movement in opposite directions doesn’t add up to above speed of light relative movement. e.g., Two probes each moving away from a common starting point at 0.7c have a speed relative to each other of about 0.94c, not 1.4c, so they stay in each other’s lightcone.
(That’s standard special relativity. I asked o3 how that changes with cosmic expansion and it claims that, given our current understanding of cosmic expansion, they will leave each other’s lightcone after about 20 billion years.)
Right, so even with near-c von Neumann probes in all directions, vacuum collapse or some other galactic x-risk moving at c would only allow civilization to survive as a thin spherical shell of space on a perpetually migrating wave front around the extinction zone that would quickly eat up the center of the colonized volume.
Such a civilization could still contain many planets and stars if they can get a decent head start before a galactic x-risk occurs + travel at near c without getting slowed down much by having to make stops to produce and accelerate more von Neumann probes. Yeah, that’s a lot of if’s.
20 billion ly estimate seems accurate, so cosmic expansion only protects against galactic x-risks on very long timescales. And without very robust governance it’s doubtful we might not get to that point.