We observe from a far distant star the red shifted spectrum. This is explained by the expansion of the galaxy and the expanding room between us and this star. So the photons coming from there have a red-shifted and hence lesser engery. What has happend to the energy of the photon? Where's it gone to?
Would the star then appear to be a different color to "someone" its own solar system than it does us? Does OUR star thus appear to be moving TOWARD them since it's "our" color vs what "they" would consider to be the correct color for a star our size?
Doesn’t this require the photon to be emitted differently depending on where it ends up, as it would experience different amounts of redshift depending on the length of flight?
That’s some serious retro-causality if a photon from 13B ly hits us instead of Andromeda.
Forget about the expansion of the universe; you could ask the exact same question for an observer moving away from a source and detecting a different frequency (hence energy) of the light emitted due to "normal" Doppler effect in a non-expanding universe. Energy (on its own) is not an invariant in (special/general) relativity. You have the same situation for measurements of lengths (i.e. Lorentz contraction). Energy is one coordinate of a four-vector whose "length" is the true invariant.
This is similar to a situation where you draw a set of perpendicular axis on a plane and use them to give coordinates (x, y) to a point. You then rotate the set of axis, keeping the point fix. Your question about the energy amounts to asking "what happens to the x-coordinate of that point?".
The energy of a photon doesn't go anywhere, it just seems to us to be lower. The observed energy of a photon depends of the relative motion. If you move at the same velocity as the observed object, the redshift disappears and the energy of photon is there.
Those calories are known to dissipate via motion, light, and heat.
By contrast, the energy lost to expansion is simply lost, not emitted by the traveling photon through some mechanism. There is no conservation of energy in such a system, so it’s completely unlike the case of burning calories.
Why does it have to make any more sense than the original question? I didn't mean anything by it, it was flippant. And all the same, I have a hard time understanding what could otherwise be meant by the GP question. I heard that question in high school physics. It doesn't have an answer today (nor did it in 1998 when I took high school physics) that I'm aware of (which admittedly doesn't mean much). But, it especially doesn't have an answer today (or, in 2013, since that's when the OP article was written) if our notion of what happens to red-shifted photons and their energy depends on the expansion of the universe.
Maybe you'd like to postulate a theory to the original question with your own energy expenditure instead of deriding me for mine?
If you think there's something wrong with his question, this is the kind of place where you formulate that in a clear way, instead of dismissing it flippantly.
The question is why the red shift happens, and the proposed answer is that the photons were actually emitted with less energy.
It's not a nonsense question. You shouldn't treat it like one. And your weird sarcastic question is just off-topic, not nonsense, so it's very confusing as a counter to begin with.
Well, in my defense, I never intended it as a counter. Like I explained, I was being flippant. I responded with nonsense to something that I originally perceived as being nonsense. I can accept that I was wrong. And, absolutely, in retrospect, at the very least, it was all in bad taste.
> The question is why the red shift happens, and the proposed answer is that the photons were actually emitted with less energy.
I didn't get that from TFA or the GP question at all. What are you basing that on? What am I missing? A more careful reading?
