The mass and density increases

Yes, it convinces me, although for the observer who always looks from within his frame of reference, there is always the present. Only a comparison of the information contained in different systems (calculating the dividing distance) would give an idea of what is the past and what is the future for a given observer. I only have a problem with how for someone from a distant system there can already be an observable future that has not happened in the observed system yet …?

Interesting ways to explain. I feel it and understand it a little differently each time. It is a phenomenon that will still satisfy and force you to ask more questions.