I read an very exciting article here https://futurism.com/the-byte/something-strange-synchronizing-distant-galaxies. It looks like galaxies in our universe are synchronising, that is they are rotating in the same rate, kinda moving together despite their large separation. Scientists are puzzled about it and don’t know why it’s happening.
Many things have puzzled us, the lightning, now we all know it’s just bunch of electrons, before we thought God’s were playing marbles in sky. We thought all clock’s tick at the same rate, but our assumption seems not to agree with the way universe is behaving, we now know time is not the same everywhere thanks to relativity https://en.wikipedia.org/wiki/Time_dilation. Similarly there are many stuff we still don’t know about this place we are in. If we are lucky, our humanity in some form will survive for billions of years and find the answers to almost all questions.
Regarding galaxies synchronisation, take metronomes synchronisation. You put a bunch of them on an oscillating platform, they exchange energy between them and synchronise as shown here
In a similar way I think two galaxies that synchronise together are doing so either due to random coincidence or exchange of information. The information could be energy or some weird stuff we haven’t found out. Possibly our universe wobbles, say you start walking, then our universe wobbles to synch with you. Say two star’s crash, our universe wobbles. That is every action in this universe transfer’s energy to a base that’s omnipresent, and this base transfers it’s energy to everything. Something like that could enable galaxies to sync.
Possibly our universe would have wobbled very harmoniously, that is all parameters in it would have expanded and collapsed at the same time, and our big bang is nothing but a small luminescence created by it, just like we have sonoluminescence.