As I wrote, perhaps not explicitly enough, cosmic inflation cannot have anything to do with having perfectly 0 movement in the late epochs of the universe. We

As I wrote, perhaps not explicitly enough, cosmic inflation cannot have anything to do with having perfectly 0 movement in the late epochs of the universe. We can do away with inflation entirely and have a consistent accelerating expansion of a vacuum universe universe. Cosmic inflation "only" helps explain some aspects of the observed uniformities in the distribution of matter that we can currently observe. There are other ways to add matter back to a vacuum acclerating-expanding universe that do not require a very-early-times and very brief period of inflation. Physical cosmologists need more data to properly decide among the various feasible alternatives. Cosmic inflation == turned off much sooner than 10^-30 seconds after it started. (That's a million million million million millionth of a second. A verrry short time.) Metric expansion == demonstrably ongoing, and accelerating, until at least a couple of million years ago (and in no more than a couple million years future astrophysicists will be able to demonstrate that it was still ongoing as I typed this). The strength of the metric expansion is increasing slowly for billions of years. The strength of cosmic inflation has been practically (or even exactly) zero since before there were even electrons and photons. The metric expansion in the past few million years has much less than 10^-25 of the strength of cosmic inflation. Finally, most physically-motivated variations on the simplest model of cosmic inflation gives the inflationary mechanism features that the expansion mechanism lacks, and cannot be hidden by equating expansion with super-weak inflation. "Expansion" and "inflation" are not synonymous. If you're genuinely interested, Alan Guth's 1998 book (while not representing the state of the art in physical cosmology) is probably more readable than what you'll get on hackernews. Guth is one of the originators of cosmic inflation, and his lively book explains how and why he got there. It also has useful appendices discussing aspects of relativity related to what you've written above. ISBN 9780201328400. It is a good "pop sci" book written by an actual scientist working and teaching in the field at the time. Konstantinos Dimopoulos's 2019 (1st ed.) introductory textbook is another good option; it is likely to become a standard textbook for second-entry undergraduates and advanced undergraduates. ISBN 9780367611040. Dimopoulos is a reader in particle cosmology at Lancaster University, in England. Most other (recent) textbooks at the top of my head are less focused on the issues you have "Cunninghammed" in this thread, or are clearly intended for graduate students. I don't understand your third and fourth paragraphs, sorry.