One thing to keep in mind is that the US population is levelling off (as, indeed, it is in the world). The highest estimate I've seen for the eventual human poulation is 9 billion. (Actually, Al Gore, in "Earth in the Balance", claims 14 billion, but no one -- not even the most doom-and-gloom population expert -- has any idea where the heck he got the extra five billion.) So if everyone on Earth tried to live in the US, and no comments from the peanut gallery, that would be, at most, ten digits if numbers are recycled.

So anyway, what will happen is that the number of people in the US will be constant, or more likely grow slowly thanks to immigration. The number of SSNs will increase linearly with time, not exponentially. There is plenty of time for the SSA to worry about this. Although, from my experience with government contracting in particular and the bureaucratic mind in general, I don't expect them to do anything about it until things reach a crisis.

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tbone1
As God is my witness, I thought turkeys could fly.