> The question doesn't make sense to ask. If you didn't look at the photon, 
> it might or might not have existed.

You can estimate the number of photons coming off a star though, can't you? 
Just multiply that figure by the estimated number of stars in the entire 
universe and that's a start for the lower bound.

> There's probably some statistical thing that'll tell you some expected 
> numbers, but it's not really the same question.

Well that's why I said "typically" rather than asking for an exact number 
:-)

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