How many particles could be crammed into the universe?

[Atomised]

I came across the following claim:

Observable Universe Volume
~ 4.077 × 10^32 cubic light-years
Whole Finite Universe, Poincaré dodecahedral best guess
~ 1.17 × 10^33 to 2.34 × 10^33 cubic light-years

Assuming this to be correct (or improve on it), what is the smallest known particle and how many could be fitted into the universe?

This is one of the most ludicrous hypothetical questions imaginable but I think I heard a discussion of something among these lines somewhere.

The real fascination for me is how such dangerous to contemplate numbers can be jotted down on a text message. Surely this is a reflection on the phenomenal power of mathematics. Anyway, back to that number...

If it all gets too odd with quarks perhaps it could be estimated for carbon atoms.

 

[Ripley]

Do you know roughly how many atoms are in a grain of sand? Thinking about that means I'm therefore too lazy to even begin to attempt this.