The Bitcoin Universe is the totality of all the paths that Bitcoin actually follows... whether through wallets, or exchanges, merchants, or even just paper wallets.  The first thought would be that bitcoin is pretty much the size of the space humans inhabit.  There are science stations on Antarctica, but I don't know if there are any bitcoin wallets there.

Funny thing is that you can inhabit a pretty good portion of this universe all by yourself.  If you participate in different income income opportunities, and bitcoin chat rooms, etc., you rapidly find yourself posted in different stations throughout the known universe... and all from your computer.

You kind of have to... because if you keep your bitcoin all in one place, it will probably get stolen.  If you want to keep most of your bitcoin, you have to spread it... (I believe the term is decentralize it)... to the very ends of the bitcoin universe.

It is pretty easy to have your own global financial network in bitcoin, and the best part is... your whole universe need have no more value than five or ten cents.  

When I was a kid, I read Jule's Verne's around the world in 80 days.  I never dreampt that by the time i grew up, you could be in all of those place at the same time, and that a single bitcoin could travel that circuit... faster than... well almost as fast as the blinking of an electron.

If you inhabit most of the bitcoin universe, and the universe itself is vastly large, then how do reconcile the difference is size between the space you inhabit, and the space the universe inhabits.  It is a question of density.  There are different people spread as thinly as you... throughout the same space.  

Just as the Bitcoin of each person exists in the same spaces as that of each other Bitcoin person, electrons in matter exist in the same space around protons.  Maybe not exactly the same space... but close enough that we will never know the difference.  If human beings can independently occupy the whole universe thusly, and simultaneously... certainly other sentient species may have awareness existing in the same space as ours without our knowing... Well maybe not the exact same space, but close enough that nobody who could perceive both could tell their locations apart.  A being that can percieve in two dimensions is called bidimensional.

I remember a particular Star Trek episode where the Enterprise was cruising through space, and then suddenly it became subject to a being much larger than the enterprise.  I don't remember the episode too well, but I seem to remember a huge eyeball staring through the front port window.  That part might not be Star Trek... it might be Twilight Zone, but you get my point.  That alien was big... and he made the human space vessel look very small.   The human toilets inside that space vessel were event smaller.  I don't know what happens with those space toilet when you fall into a temporary state of having no gravity.

Then the though occurred to me... that as occupant of the Bitcoin Universe... I am not so much like the feeble Star Trek Bipeds... as the huge alien, that gets to hold the enterprise between two fingers and stare through the front port window with my supersize eye.  If I was an alien I would not do that though.  Even though I was much bigger, and could generally wallop the enterprize, I would not want to give it an opportunity to shoot me with a tiny war grade lazer.  Tiny or not... a lazer gun is a lazer gun.  It is not a toy.

So how big is the Bitcoin Universe?  Infinitely large and infintessimally small, depending on how you look at it.  The point is that you are looking at it.  An occupant of the well known universe, and the bitcoin world, you are... as they say... bidimensional.