particle horizon
the maximum distance from which light from particles could have traveled to the observer during the age of the universe
en-US/ˈpɑɹtɪkəl hɚˈaɪzən/
en-GB/ˈpɑːtɪkəl həˈɹaɪzn/
the maximum distance from which light from particles could have traveled to the observer during the age of the universe