2.1 quadrillion. That will the number of outstanding Satoshis (the smallest BTC denomination at 1/100,000,000th) in the Bitcoin economy by 2140.
I for one, have to completely agree with the respected economists who claim this this figure is obviously too small to ever be able to facilitate any semblance of actual trade.
If Bitcoin were to become popular, we would obviously encounter the problem of people hoarding the crypto-currency. This would decrease the flow and availability of Bitcoin to a dangerous level.
Just imagine if 99% of the Bitcoins in circulation were held by savers, leaving only a paltry 21 trillion Satoshi to service the actual functioning economy.
With time, maybe 99.999999999% of all Bitcoins would just be held. Nobody would ever spend them and they would just get more and more valuable. People would actually get richer without doing anything. This would simply be morally wrong, and we would have to put a stop to it.
And if Bitcoin continued to be popular even still, we would eventually only be left with a single Satoshi to service the whole economy. Just one! Bitcoiners say that this Satoshi could be broken into smaller increments if need be, but I would call that cheating. You can't just create something from nothing.
For the good of humanity, we must put a stop to Bitcoin in its present form. To this end, I propose that we increase the total number of eventual Bitcoin to 21,000,000,000,000,000,000,000,000,000,000,000 (21 undecillion). By my calculations, this should be just about right.
Bitcoin enthusiasts, while well meaning, really just aren't that good with math.