@Soothfast said'Dark matter' as I have understood it, is the 'missing mass' which allows the universe to function as it does; we can't see it but it must be there, or else we've got our sums wrong. It's purely theoretical and not all scientists think it exists.
Ah, so, as something of an aside, what are your thoughts on so-called "dark matter"?
(This is just a quick drive-by, since I haven't yet gathered up the gumption to create another long post.)
I think once we attempt to step away from reality into the realms of philosophical theory as to the nature of reality, we enter the realms of philosophical dark matter; something other than reality as we perceive it might exist, but we can't prove it, and actually it makes no difference. The universe and reality are as they are, regardless of their respective dark matter.
Whether I'm actually writing this and whether you are actually reading it is something which we can discuss until the philosophical cows come home, if indeed they really do, but in reality I'm writing it and you are reading it, and there isn't much, now, that either of us can do about that.
@Indonesia-Phil
A difference which makes no difference is no difference. A cause we cannot detect does not cause anything. It's sheer speculation at this point. Of course, acknowledging that our current 'theory of everything' does not explain everything is the first step towards correcting it, and that is bound to lead down some blind alleys (phlogiston ....).