Do Civilizations Exist Beyond the 20,000 Light-Year Sphere?

[Holocene]

EDIT: Title should read "Would you agree with THIS notion".

Take for example, human civilization. If we say civilizations have existed for 10,000 years, we know that in principle it's possible for information regarding the existence of these civilizations to have propgated some 10,000 light years away. Now, would you agree that with respect to places of the universe outside this 20,000LY diameter sphere, we can state that not only can we not prove these civilizations exist, but in fact they DON'T exist with respect to space outside the sphere?

 

[Wallace]

I get the impression that you're trying to set a trap here! Whether or not your proposition is reasonable depends on how a number of terms you've used are defined (for instance 'exist'). If you define 'exist' by 'lies within the observers past light cone' then clearly your proposition is correct. If you define 'exist' as 'lying within the observers past OR future light cone' then it is false.

I'm sure you could define 'exist' in other ways and then the answer to your question would follow deterministically from that definition.