Comment by tempestn

Thank you; this is a better explanation of what I was getting at in the GP comment. While it is theoretically possible that we could conclusively find BB(X) for any X, we don't know, nor can we prove, that we can (aside from the ones that have already been proven). Therefore I don't know that it makes sense to talk about it being a specific number, but rather the concept of a number (more like his "number of grains of sand in the Sahara" example, which he explicitly mentioned is not valid^.)

^Although his reasoning is that it is not valid because it is always changing, not specifically because it is unknown. Still, I assume that "Number of grains of sand in the Sahara at exactly midnight, Jan. 1 2050, on this atomic clock" would also be disallowed, even though it's possible we would somehow be able to know exactly what that number is in the future.