Sorry, I was imprecise with my language and also got confused. You are correct, Erebons are not MACHOS.
It just spurred a thought from the Penrose thing, where he states, essentially, that he thinks Dark Matter are these Erebons, but the mass density of them is, I believe, so high, they should really effectively
also be black holes. Bosons can have mass and I don't see why they can't form or be part of black hole entities (Black holes will happily absorb photons for example). But he hand-waves the issues away saying, 'they are particles, and I want them to remain as particles, so there's probably a Quantum mechanical reason they don't collapse into miniature black holes'.
Regarding your question about mass in the universe. I believe you can calculate it from measuring the curvature of space (it's almost zero and you can get this info from the Cosmic Microwave Background Radiation data), Now General Relativity says that mass curves space. And therefore there is a certain amount of mass implied by the observation, which can be calculated.
You can then estimate the average mass & energy-mass equivalent density of all the particles we can see (it works out at about one proton for every four cubic metres of space) - apparently 4.9% of the total implied above. (At least that's what Wikipedia thinks.)
And observations of the accelerating expansion of the universe, the Dark Energy, will give you an average energy-mass equivalent density. Which actually turns out to be much smaller than the average density of normal/dark matter within and around galaxies...but this is applied to
all space, whereas these high densities of normal and dark matter are confined to galaxies, so when it is all added up by using estimates of the total size of the universe, it is the dominant component with about ~68% of the Universe.
Hence, I guess, the remaining ~27% is Dark Matter, purely by fixing the other two!
Regarding trying to see if there's more normal matter and if it will go above 4.9%.
Yes, you're probably correct. There is matter in the dark voids between galaxies, and this can be estimated by observations of distant galaxies and quasars - via observing absorption lines in their spectra. Perhaps a little paradoxically, given the voids are so dark and empty looking, I've read that only 10% of the ordinary matter of the universe is actually in galaxies. The rest has a very lonely and boring existence in this (mostly!) dark inter-galactic space*. But, by god, there is such a lot of this inter-galactic space compared to the rest! So it adds up.
Finally regarding Penrose's model. From my listening, I believe he is saying that this expansion, or Lambda term, is eternal.
With this 'compression of the top end' he describes this as a mathematical trick. He's not saying the universe actually compresses...but that it's properties are such, when all mass disappears, that one can describe it using some 'hyperbolic' transformation. He points out that this similar property can be used to describe the situation at the very start of the big bang.
So my reading of that was - when all mass disappears and there's just some photons in this empty vast universe, scale and time 'become irrelevant' and the end of the old Eon becomes the seed for the next Eon and it's big bang because all of the conditions and hyperbolic properties are then correct.
I've probably got a lot wrong up there, but I'll leave it there for the mo'
-----------------------------------------------------------------------------
* Okay, filaments and halos around and between galaxies seem to be a lot more fun and have much more gas and dust, but there's a small volume of the total size of the universe!
