@nottelling - Yes, I understood the question you were asking about ambiguity in language, and Lergnom gave the right answer. I just thought it was interesting (to me at least) to mention some of the deeper related issues about space and time. Please feel free to ignore it if you aren’t interested.
I shouldn’t have put words in your mouth when I said you just wanted to know what humans on Earth would observe. But Einstein and others taught us that when we are confused it is good to focus on actual empirical facts like what an astronomer on Earth observes when they look through a telescope. By saying the answer is “100,000 years from now, astronomers on Earth expect to see the collision”, I hoped to give a useful, meaningful answer that was also scientifically rigorous.
Never said that “past” or “future” were meaningless - in fact, I think I said the opposite. What I said was scientifically meaningless was saying that event A occurs at an earlier time than event B.
Some events are in my past, other events are in my future, and some are neither. That’s what Einstein figured out. The collision event, when/if it occurs, happens to be in the “neither” category relative to us. And that’s what makes the distinction between past/future/neither, and earlier/later time relevant in this case.
One thing that may interest you - one of the original reasons why they invented the theory of inflation was that scientists are careful about this distinction that I’ve been talking about. (See this article https://en.wikipedia.org/wiki/Inflation_%28cosmology%29#Horizon_problem, especially about causal contact).
Scientists have the expertise to know when they can meaningfully talk about the “past” and “future”. There’s an enormous scientific context that they bring to bear when they use everyday words in a technical sense. When they observed the microwave background they were definitely making an observation of our past.
I’m almost sure we can not rule anything out for the reasons I’ve been talking about. The event simply hasn’t happened yet from our perspective, so there’s no way we can make any inferences from the event since it hasn’t happened yet. That’s why I’ve been harping on making sure that the phrase “3.4999 billion years ago” doesn’t create its own set of confusions.
If the collision triggered a “new inflation”, then in 100,000 years we would see the collision and then the galaxies would “wink out” because they would “recede faster than the speed of light” from us. Then we’d all be dead in the very next instant as the boundary of the new bubble universe hits us. But we wouldn’t see any evidence until then since the inflation itself would move through our “normal” spacetime at the speed of light. Honestly, I’m not 100% sure about the inflation stuff since I’m certainly not an expert, but this is my understanding. I’m sure about normal non-inflation effects.