Questions about the singularity

[Jim92672]

How much do we know about the singularity?
It's properties, size, weight?
I understand it contained all the matter in the universe but do we know how much matter that amounts to in numerical terms?
I understand it was incredibly unstable so how could it exist in the first place?

 

[Chronos]

The mass of the observable universe can be roughly derived from its density and size [both of which have been measured with reasonably good accuracy]. It works out to around 3E+55 grams. The catch is that only applies to the observable universe, which may only be an insignificant fraction of the 'total' universe. Under the 'universe from nothing' hypotheses both the mass and size of the universe increased exponentially immediately following the big event.

 

[Drakkith]

How much do we know about the singularity?
It's properties, size, weight?
I understand it contained all the matter in the universe but do we know how much matter that amounts to in numerical terms?
I understand it was incredibly unstable so how could it exist in the first place?

There is no guarantee that a singularity ever actually existed. The standard model for cosmology breaks down past a certain point in the past. This is where the singularity comes from. It is unknown what the exact state the universe was in past that point in time. Perhaps it was a real singularity, or maybe the universe was only compressed to a certain density before "rebounding" and avoiding any singularity, or any of an uncountable number of possibilities. We only use the term "Singularity" because it means that beyond this point we cannot predict what happens using current models.