The expanding Universe and Galactic collisions

Coming in rather late here... No, it doesn't, not least because we don't have a 'linear perspective of how the universe works' - I'm not actually sure what you mean by this. Our primary model of how the Universe works is General Relativity, and it is highly non-linear - famously so... But it does - as others have already said, you can't play hardball with soft terms... 'big bang' is a generic term, and you need to refer to specific General Relativity space-time solutions. You could say that the acceleration doesn't fit with Friedmann-Roberston-Walker (FRW) cosmology, that that we grew up on, and you'd be right. But it is a good fit with Friedmann-Lemaitre-Robertson-Walker (FLRW) space-time... both exhibit 'big bangs', so where's the problem?There is a big mystery as to what is causing the acceleration - not because we cannot think of anything that can do this - but simply that we don't have enough evidence yet to pin down which of several possibilities it could be... many of us are not in the slightest bit surprised by the acceleration and in fact spent plenty of time in the past wondering why there was none! We have been studying such theories for decades... this is nothing new. And all of them incorporate the major features of the 'big bang' when they come to describing our Universe - good job, as the evidence for the post-singularity comsology of the big bang is rather good