Why is the universe the mass it is?

[Astro Pen]

An apparently innocuous question that is bugging me. Big bang, i.e. the universe, has an exact mass.
Neither infinite nor zero but exactly yay kilograms (of mass/energy) big.
Why that precise size? and what are the implications of that in terms of the universe making original 'resource' (for lack of a better word)?

 

[Foxbat]

My completely uninformed view.....Mass and energy being interchangable, I'd guess that it would be changing regularly. I think the actul mass calculation is probably more a tool for studying the behaviour of the universe (is it contracting, expanding or doing some kind of interstellar Hokey Cokey)

 

[Ori Vandewalle]

There's a certain perspective by which the total mass and energy of the universe is 0, if you factor in what amounts to the negative potential energy of gravity.

Beyond that, in cosmological calculations we don't weigh the universe so much as measure its density. The true physical size of the universe is unknown (perhaps infinite), although you can restrict yourself to the observable universe. Currently, to one or two decimal places (not all that precise compared to some other measurements), the density of the universe appears to be exactly that which is required for it to be flat and open (1 in certain units).