1 hour ago, michel123456 said:

There is no cosmological principle in archaeology, AFAIK

There is (the same one that basically applies in all science but also in the study of history, linguistics, literature, art, ...)

For example: https://en.wikipedia.org/wiki/Uniformitarianism

 

Just to be clear, because Michel has mentioned it a few times...
In the far, far future the CMB will not just 'disappear', it will get weaker ( much less than 2.7 deg K ) and be 'buried in the noise', and, as a result, be much harder, if not impossible, to detect.
But an advanced civilization will have various noise-cancelling techniques available to them ( just as we do )

6 minutes ago, MigL said:

But an advanced civilization will have various noise-cancelling techniques available to them ( just as we do )

That depends on distance rather than technology, but even if we can determine one photon from another, how do we fit them together?

9 hours ago, michel123456 said:

 

2. Good question: he would live in a universe without the BB.  He would not get any information about the BB. He may suspect that his galaxy has been created woof just like that by some kind of magic, or that his galaxy was always there & will remain forever. Anyway he would have no clue about the BB & thus should base his physics on some other Theory. So that is a problem to me.

 

At this point, all you have still, is argument from incredulity.

Why is this a "problem"?