scott wrote:
>> 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.

That would be a lower bound on the non-virtual photons, yes.  Of course, 
there are heptazeptazillions of photons deep inside each star being created 
and destroyed. It takes about a million years for a photon created in the 
sun to actually get to the surface. Count those?

>> 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 :-)

I'm not sure that "typically" means what I'm talking about. I'm talking 
about photons that by definition don't exist long enough to be measured. Do 
you want to count them? There are, by the math, potentially infinite numbers 
of them, which is what makes doing the actual math of QED difficult.

-- 
   Darren New, San Diego CA, USA (PST)
   There's no CD like OCD, there's no CD I knoooow!

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