They could not come to that conclusion as anything that expands away from you faster than the speed of light is functionally in a black hole. The cosmic background radiation gone, all other galaxies flying away: they would conclude they are in an eternal singular galaxy and never have a sense of a big bang.
Empiricism can only get you so far before you reach the limits of what can possibly be observed... which seems to be the lesson of quantum physics.
Not eternally no. There was a time when their galaxy was one of many. Before their ability to make observations I presume is what DixyCrat is saying.
I wish I had a better argument.
Yes they are.
The thing is, why would it matter? Sure they wouldn't be able to determine (using our methods) that the universe was once like we observe it today. So what? Why would that matter to them other than just curiosity of how it once was? Especially if it will never be liek that again?
By the way we are presuming them to be too much like us. They could have methods we wouldn't even be able to imagine.
So we are talking about hypotheticals that have little to no effect on your life and you have to wonder if this is akin to debating science fiction which would be a sort of mental masturbation. It doesn't accomplish anything other than make you feel good temporarily but you learn nothing useful for improving your life in this universe in the process so I think it to be a bit of a waste of time. But then time wasting seems to be a popular pastime among many people so I'm not judging just making an observation.
Science plays an important role in improving our lives and the scientific method bears repeating: First we make observations, then we come up with theories to explain those observations, then we test them.
We don't just imagine a hypothetical situation that doesn't exist and try to explain
that because it's a waste of time, even if it's pleasurable to do so.
Similarly, if that civilization observes that they are in a single galaxy in the entire universe, then that is the data they have to work with and they wouldn't need to know it wasn't always like that.