> if Einstein's cosmological constant is positive, every atomic / sub-atomic particle will eventually be in its own “observable universe”
This is not correct. Gravitationally bound systems will remain bound in a universe with a positive cosmological constant. A "Big Rip" scenario, where gravitationally bound systems get ripped apart and eventually every elementary particle is beyond the cosmological horizon of every other, requires "phantom energy", i.e., a density of dark energy that increases with time.
This is not correct. Gravitationally bound systems will remain bound in a universe with a positive cosmological constant. A "Big Rip" scenario, where gravitationally bound systems get ripped apart and eventually every elementary particle is beyond the cosmological horizon of every other, requires "phantom energy", i.e., a density of dark energy that increases with time.