Wouldn't it only take 13 billion years if you'd started at the big bang and a photon that had the wavelength of the then observable universe (since space stretched under it)?
I also have to ask how that jives with it being a quantized change: either the photon emits or it doesn't (since a photon exists with that energy or it doesn't) -- or there's some probability distribution that we'll detect the photon (which might change over time) -- but how can it be half emitted 46 billion years in the process?
In the end, either it provides a kick at its energy level to another property (eg, electron momentum) in one quantum jump.
Hmm. In an expanding universe, what's happening to the Planck length? Is it staying constant? Expanding at the rate of expansion of the universe? Doing something else?
I also have to ask how that jives with it being a quantized change: either the photon emits or it doesn't (since a photon exists with that energy or it doesn't) -- or there's some probability distribution that we'll detect the photon (which might change over time) -- but how can it be half emitted 46 billion years in the process?
In the end, either it provides a kick at its energy level to another property (eg, electron momentum) in one quantum jump.